625478012B e.
>n
Technology Transfer
Sludge Treatment
and Disposal
Sludge Disposal
This document has not been
submitted to NTIS, therefore it
should be retained. S
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EPA-625/4-78-012
October 1978
Sludge Treatment and Disposal
Sludge Disposal
Volume 2
Environmental Research Information Center
Cincinnati, Ohio 45268
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NOTICE
The mention of trade names or commercial products in this publication is for illustration
purposes, and does not constitute endorsement or recommendation for use by the U.S.
Environmental Protection Agency.
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Contents
Page
Volume 1
Introduction vii
Chapter 1. Lime Stabilization of Wastewater Treatment Plant
Sludges 1
Chapter 2. Anaerobic Digestion and Design of Municipal Wastewater
Sludges 35
Chapter 3. Aerobic Digestion and Design of Municipal Wastewater
Sludges 57
Chapter 4. Thermal Treatment for Sludge Conditioning 69
Chapter 5. Thickening of Sludge 79
Chapter 6. Review of Developments in Dewatering Wastewater
Sludges 101
Volume 2
Chapter 7. Incineration-Pyrolysis of Wastewater Treatment Plant
Sludges 1
Chapter 8. Sewage Sludge Composting 35
Chapter 9. Principles and Design Criteria for Sewage Sludge Applica-
tion on Land 57
Chapter 10. Sludge Landfilling 113
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Chapter 7
Incineration-Pyrolysis of Wastewater
Treatment Plant Sludges
Sludge disposal is a major consideration in the planning
and design of new wastewater treatment plants and in
the expansion and upgrading of existing facilities. Along
with the increasing sophistication of wastewater treat-
ment comes more sludge and greater disposal problems.
Many wastewater treatment facilities have shown that
satisfactory treatment and disposal of sludge can be the
most complex and costly operation in a municipal waste-
water treatment system. A sludge disposal system which
reduces the volume of material to be handled and dis-
posed and saves or recovers needed energy and re-
sources is very desirable. If this system is cost-effective,
the selection of a sludge disposal system is facilitated
for particular communities.
Sewage sludge incineration has been practiced since
the early part of the century. This method of sludge
disposal was an adaptation of various industrial combus-
tion processes developed during the latter part of the
nineteenth century. Availability of cheap energy, limited
capability of sludge dewatering equipment, and minimal
or nonexistent air pollution requirements all led to the
selection of incineration as a practical and inexpensive
method of sludge disposal. However, increasing concern
for air quality and experience with sludges from more
advanced treatment processes, which are more difficult
to dewater and, thus, require more energy to evaporate
the excess water, considerably dampened the enthusiasm
for incineration. These problems, coupled with rising en-
ergy costs, increasing quantities of sludge, and limited
resources, have led to the development of improved
sludge dewatering methods and more efficient incinera-
tion equipment and systems.
This chapter describes various sewage sludge incinera-
tion systems in the United States and some of the new
and promising combustion systems proposed for various
facilities. Currently, there are many sludge incineration
systems being tried or in use, such as the rotary kiln.
However, this paper is limited to the consideration of the
following four furnace systems: multiple-hearth, fluid bed,
single-hearth cyclonic, and electric. The new combustion
systems reviewed are pyrolysis in multiple-hearth fur-
naces and alternate fuel sources, such as solid waste or
coal in conventional combustion processes. While there
are many other systems being tested and demonstrated,
this paper is limited to the systems which are considered
proven technologies. Heat recovery methods used to
recover the energy spent in the combustion of sewage
sludge are also discussed. Two design examples for
combustion of sewage sludge are presented to illustrate
the basic methodology of furnace selection and design.
PRINCIPLES OF COMBUSTION
Combustion is the rapid chemical combination of oxy-
gen with the volatile elements of the fuel. The combusti-
ble elements that characterize any fuel are carbon, hy-
drogen, and, in some cases, sulfur. Quantities of sulfur
contained in sewage sludge are so low that combustion
of sulfur does not significantly contribute to the overall
combustion process and thus is not considered in this
paper.
Combustion reactions are exothermic and release large
amounts of energy as heat. The ideal combustion reac-
tions for carbon and hydrogen are:
14,100 Btu/lb of C
= 2H2O + 61,100 Btu/lb of H2
Air is usually the source of oxygen for combustion, al-
though pure oxygen feed systems have been used in
some cases.
The objective of an incineration system is to release
heat from a fuel and completely destroy all the volatile
elements, while minimizing combustion imperfections and
heat losses. Sewage sludge is difficult to combust com-
pletely because it is not homogeneous and it contains
high levels of inert material and water.
Complete combustion is a result of the proper combi-
nation of the combustible elements of the fuel with oxy-
gen. This requires a temperature high enough for ignition
of the constituents, good turbulence for contact and
mixing, and sufficient time for complete reaction. Since
only an ideal system can meet all of these requirements,
excess air, greater than the stoichiometric combustion
requirement, is provided to assure sufficient oxygen
when complete combustion is desired. In typical sewage
sludge incinerators, excess air quantities vary upward
from 30 percent and may exceed 150 percent, depend-
ing upon the type of furnace used and the method of
operation. This excess air leaves the system at the stack
exhaust temperature, and the heat used to raise ambient
air to stack temperature is a severe heat loss from the
system. Thus, it is desirable to keep the excess air at a
minimum to reduce stack heat losses.
-------
Pyrolysis is defined as: gasification and/or liquification
of the combustible elements by heat in the total absence
of oxygen. Partial pyrolysis, or more correctly, starved-
air combustion, can be defined as: gasification of the
combustible elements by heat in the presence of con-
trolled amounts of oxygen. Partial pyrolysis uses less
than the stoichiometric combustion air requirements. The
ash from a pyrolysis reaction contains combustible mate-
rial and some fixed carbon which was not volatilized
during combustion. The gas, also called fuel gas, from
the pyrolysis reactor consists of various combustible gas-
es, such as carbon monoxide, methane, ethylene, and
some higher hydrocarbons, and appreciable quantities of
carbon dioxide and water vapor. Small quantities of hy-
drogen, oxygen, and nitrogen are sometimes present.
The yield and composition of the pyrolysis products are
dependent upon several variables; the interrelationships
of these are so complex that predicting final product
characteristics is a difficult task and is determined em-
pirically.
ENERGY RECOVERY
Energy conservation is a great concern of industries
and municipalities. Costs are rising for both fossil fuel
and electric power. This cost consideration, coupled with
increasing air quality requirements, has led to the devel-
opment of new, more efficient incineration processes,
alternate fuel sources, and new ways to recover energy
and limit energy losses.
Combustion energy losses are generally due to radia-
tion, leakage, ash and stack loss, with the greatest heat
loss being stack loss. Much of the stack loss can be
recovered by heat recovery systems. Heat recovery sys-
tems can be applied to any hot gases, but system eco-
nomics must be reviewed to determine their feasibility in
the particular application. The San Francisco Bay Area
Air Pollution Control District (SFBAAPCD) requires fur-
nace exhaust temperatures high enough to prevent
carryover of unburned hydrocarbons. This requirement is
satisfied by maintaining a temperature of 1400°F for
one-half second. This high exhaust gas temperature re-
quirement is becoming more common throughout the
country. Some form of waste heat recovery should be
considered for all projects with similar constraints.
There are three basic transfer methods used to recov-
er heat from stack exhaust: gas-to-water, gas-to-air, and
gas-to-organic fluid. Gas-to-water systems produce steam
and are the most commonly used heat recovery systems.
Steam has a tremendous heat energy per unit weight.
Gas-to-air systems generally use recuperators or air
heaters to preheat incoming combustion air. Research is
underway on gas-to-air waste heat recovery where heat-
ed air is used for power generation. Gas-to-organic fluid
systems have the advantage of high temperature with
low pressures resulting in low installation and operation
costs and are used in industrial plant processes. Use of
this type of system has increased markedly over the
past several years. Fluids used for this system include
mineral oil and ethylene glycol. This technology has not
been used in wastewater treatment facilities because of
the low number of heat-demanding or shedding process-
es as compared to industry.
Minimizing the other heat losses, radiation, ash and
leakage, should be economically evaluated. Proper insu-
lation is important for personal comfort and safety and
minimizing radiation losses. When safety concerns have
been alleviated, the amount of additional insulation is an
economic consideration. Leakage must be minimized for
safety reasons and is usually not a major loss in a well-
constructed furnace. Heat lost to the ash can be due to
temperature and/or unburned combustibles. Unburned
material can be reduced by process control or by using
the ash as a filter aid and returning it to the furnace.
The temperature of the ash can be used to preheat
boiler makeup water or to satisfy other low volume heat
demands.
Selection of a system that will recover the maximum
available heat with the highest transfer efficiency and
lowest cost is a challenging engineering problem. The
selection requires a complete system review. Typical sys-
tem components and processes reviewed include: the
furnace, the gas collection and removal equipment, com-
bustion air supply, combustion products (gas and ash),
waste heat boiler, refractories, insulation, baffles, supple-
mental air and water systems, boiler feedwater, boiler
feedwater treatment, boiler blowdown, boiler trim, steam
separation, foundations, supports, breeching, exhaust gas
scrubbers, etc.
A complex waste heat recovery boiler system is shown
on figure 7-1. A typical sewage sludge furnace heat
recovery system would only require the evaporation sec-
tion of the boiler with some feedwater conditioning. To
properly design any heat recovery system, consideration
of the following parameters is required:
• Chemical nature, temperature, and corrosiveness of
the exhaust gases.
• Quantity, specific gravity, size and nature of the fly
ash.
• Available draft.
• Type of exhaust gas system (pressure or vacuum).
• Space available.
• Requirements for supplemental firing for: start-up,
preheating, emergency use, stabilizing furnace con-
ditions or other uses.
• Present and future steam demands.
• Type of demand (continuous or intermittent).
• Equipment redundancy requirements.
• Other special requirements of the individual pro-
cess.
The waste heat boiler alone requires a review of: ma-
terials of construction; type of design, fired or unfired;
type of tubes, bare or fin; type of circulation, natural- or
forced-air; number of passes, superheater requirements,
economizer requirements, ash removal and disposal sys-
tem, steam pressure and temperature, degree of feedwa-
ter treatment, methods of feedwater treatment, chemical
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SUPERHEATER
EVAPORATOR
ECONOMIZER
CHEMICAL FEED
' (NATURAL CIRCULATION
BOILER)
AIR HEATER
(RECUPERATOR)
AMBIENT AIR
EXHAUST
GASES TO
SCRUBBER,
THEN STACK
HEATED
COMBUSTION
AIR TO
CHEMICAL FEED
RAW MAKEUP
WATER
BOILER
FEEDWATER
PUMPS
BOILER WATER TREATMENT
Figure 7-1.—Complex waste heat boiler flowsheet.
additives, etc. Other important concerns of a system
include operation and maintenance costs and operator
experience and expertise. A small intermittent facility
cannot support the capital and operation costs of a
complex boiler system, and operators would be difficult
to hire. However, a large plant may find that a very
efficient heat recovery system saves sufficient fuel and
power costs to justify a system as shown on figure 7-1.
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Each sludge incineration facility demands a thorough
analysis of energy recovery to determine if recovery is
practical and, if so, what type of system is most feasi-
ble.
Three brief case histories of heat recovery installations
are presented below:
Erie, Pa., Wastewater Treatment Plant
Boiler start-up date: August 1974.
Boiler ratings:
design—165 lb/in.2(11.6 kgf/cm2) saturated steam
(700 boiler hp).
actual—15 lb/in.2(1.1 kgf/cm2) saturated steam.
Furnace data: Two multiple-hearth furnaces, 22 ft, 3
in. (6.78 m) in diameter, 11 hearth, no afterburner,
one boiler for each furnace.
Boiler operation: Unfired, continuous operation with
furnace.
Backup steam generators: none.
Steam uses: Plant heating and cooling.
Boiler data: Two pass—bare and fin tube; 500 to
700° F inlet, 200° F outlet; evaporator portion only
with natural water circulation; three rotating soot
blowers.
Treatment: Feedwater—Modul chemicals, deaerator,
manual, blowdown (10 sec per hr); condensate,
none (95 percent recovery of condensate); steam,
none.
O. & M. data: Dedicated engineer and water tender
each shift (local ordinance requirement); no forced
downtime, systems are alternated every 6 months for
furnace repairs; major cost is chemical treatment.
Green Bay Metropolitan Sewage District Treatment Plant
Boiler start-up date: September 1977.
Boiler rating: 100 lb/in.2g (7.03 kgf/cm2) saturated
steam, 36,000 Ib/hr (16,330 kg/hr).
Furnace data: Two multiple-hearth furnaces, 22 ft, 3
in. in diameter, 7 hearth, separate afterburner, one
waste heat recovery boiler shared by furnaces.
Boiler operation: Unfired, continuous operation.
Backup steam generators: Two package 31 million
Btu/hr (9,080,000 W) fired hot water boilers.
Steam uses (in preferential order): Augment plant heat-
ing, heat treatment, boiler deaerator heating, preheat
for nitric acid solvent, caustic soda tank car heater.
Boiler data: One pass, bare tube; design, 1600°F in-
let, 475° F outlet; actual, 1200°F inlet, 400° F outlet;
evaporator portion only with natural water circulation
no soot blowers or ash removal system.
Treatment: Feedwater, dual bed demineralizer, deaera-
tor, hydrazine, chelates, continuous blowdown; con-
densate, none (95 percent + recovery of condensate);
steam, none.
O. & M. data: No dedicated boiler operator; no down-
time since startup; only costs to date are chemicals.
Central Contra Costa Sanitary District Water Reclamation
Plant
Boiler start-up date: Expected, June 1978.
Boiler ratings: 170 lb/in.2g (12.0 kgf/cm2) saturated
steam, 35,000 Ib/hr (15,880 kg/hr).
Furnace data: Two multiple-hearth furnaces, 22 ft 3 in.
(6.78 m) in diameter, 11 hearth, No. 1 hearth used
as 1400°F afterburner, 1 waste heat recovery boiler
per furnace.
Boiler operation: Unfired, continuous operation with
furnace.
Backup steam generators: Two package 23,000 Ib/hr
(10,430 kg/hr), 170 lb/in.2g (12.0 kgf/cm2) saturated
steam fired water tube boilers.
Steam uses (in preferential order): (1) 2,750 hp (2054
kW) aeration blowers, (2) 81 hp (60 kW) boiler feed-
water pumps, plant heating and cooling, CO2 vapor-
izers.
Boiler data: One pass-bare tube; design, 1400° F inlet,
450° F outlet; evaporator portion only with natural
water circulation; three rotating soot blowers.
Treatment: Feedwater, water softener deaerator, sodi-
um phosphate, sodium sulfite, automatic blowdown
by conductivity; condensate, none (95 percent recov-
ery of condensate expected); steam, filming amines.
0. & M. data: Since system not yet operational, actual
O & M data are not available.
There are several heat recovery installations in opera-
tion or in start-up, such as:
Louisville Metropolitan Sanitation District, Ky.: Three 22
ft 3 in. (6.78 m) diameter x an 8-hearth multiple-
hearth furnace, each hearth with 28,000-lb/hr
(12,700 kg/hr), 125 lb/in.2g (8.8 kgf/cm2) saturated
steam heat recovery boiler. The steam is used for a
sludge heat treatment system and for building heat-
ing.
West Berlin, Germany: Three 14 ft 0 in. (4.27 m) diame-
ter fluid-bed furnaces, each with a 3,600-lb/hr
(1,630 kg/hr), 360 lb/in.2g (25.3 kgf/cm2) saturated
steam heat recovery boiler. The steam is used for
building heating and process equipment.
Tokyo, Japan: Two 11 ft 0 in. (3.35 m) fluid-bed furn-
aces, each with a 3.4-million Btu/hr (996,000 W)
heat recovery boiler. Heat is used for process re-
quirements.
Toronto, Ontario: Two 28 ft 0 in. (8.53 m) fluid-bed
furnaces, each with a 26,100-lb/hr (11,800 kg/hr),
260 lb/in.2g (18.3 kgf/cm2) saturated steam heat
recovery boiler. The steam is used for process re-
quirements and building heating.
Leeds Sewage Works, Great Britain: Single-hearth cy-
clonic furnace with a 12-million Btu/hr (3,516,000 W)
heat recovery boiler.
Upper Stour Authority, Great Britain: Single-hearth cy-
clonic furnace with a 6-million Btu/hr (1,758,000 W)
heat recovery boiler.
SLUDGE INCINERATION
Transportation of sewage sludge to its final disposal
point demands maximum volume reduction and the high-
est solids content possible for efficient operation. Treat-
ment methods used to achieve these goals include:
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sludge thickening followed by dewatering with vacuum
filters, filter presses, or centrifuges; sludge thickening
followed by anaerobic digestion and dewatering; chemi-
cal stabilization followed by dewatering, etc. Incineration
could be used with any of these processes for ultimate
volume reduction. The cost of an incineration system has
been prohibitive at many locations because of inexpen-
sive, readily available disposal alternatives, such as
sludge lagoons, ocean disposal or land disposal with
short-haul distances. Increasing restrictions on the dis-
posal of sewage sludge and decreasing availability of
suitable land have increased the importance of sludge
volume reduction to the point where incineration is now
a viable consideration in many wastewater treatment
plants. Public health concerns regarding polychlorinated
biphenoles (RGBs) and pathogenic bacteria, both of
which are destroyed during combustion, also increases
the use of incineration.
Although the heat value of sludge is fairly high (5,000
to 10,000 Btu/lb dry solids) (11,600 J/g to 23,200 J/g),
the water content of most sludges requires the addition
of auxiliary fuel to maintain combustion in the furnace.
Fuel cost is a major operational cost of incineration. The
reduction of this cost can be achieved by raising the
solids content of the sludge, thereby increasing the net
heat value, or by lowering the amount of inert material
in the sludge prior to incineration.
Many processes which reduce the moisture content of
the sludge increase the amount of inert material in the
sludge. Anaerobic digestion decreases the volatile con-
tent and increases the inert content of the sludge. This
results in a lower sludge heat value but produces a
digester gas which is commonly used in the treatment
plant. Sludge from physical-chemical treatment processes
has a high content of inert material but tends to dewa-
ter better than sludge from biological processes. Autoge-
nous or self-sustained combustion is possible with some
sludge feeds but is dependent on the net heat content
of the sludge. When incineration is considered as the
final sludge processing step, the benefits and penalties
of the conditioning steps on the fuel consumption of the
furnace must be evaluated. These pretreatment steps
include the addition of lime, ferric salts, or ash to the
sludge to improve the operation of the dewatering equip-
ment. These materials reduce the heat content of the
sludge and, thus, represent an increase in the amount of
inert material which has to be heated during incineration.
Sludge incineration can be considered to occur in four
steps:
1. Temperature of the sludge is raised to 212° F.
2. Water is evaporated from the sludge.
3. Water vapor temperature and air temperature are
increased.
4. Temperature of the sludge is raised to the ignition
point of the volatiles.
The heat evolved by the incineration of sludge can be
utilized in many ways: heating and drying of the incom-
ing sludge, production of steam for space heating, pow-
ering mechanical equipment, or generating electricity.
Because of the relatively high temperature of the com-
bustion gases, approximately 1300 to 1700°F, and the
excess air injected into the furnace, a large amount of
the heat evolved is used to raise the temperature of the
incoming mixture of combustion air and fuel.
For successful incineration, proper mixing of the com-
bustion gases, the fuel mixture and the volatile solids in
the sludge are important. There are two types of fur-
naces generally used for sludge incineration in the Unit-
ed States—the multiple-hearth and the fluid-bed. The
single-rotary hearth cyclonic furnace has several installa-
tions in Great Britain, Europe, and Japan and is also
available in the United States. The electric furnace is a
relatively new development, but there are a number of
installations in the United States at small sewage treat-
ment plants. All four furnaces provide adequate mixing
of sludge with the combustion gases and a residence
time which insures complete combustion. There are other
types of furnaces available for sludge incineration, but
they are not discussed herein.
Three hypothetical plants have been used to compare
the different furnaces; the general design criteria are
given in table 7-1. The solids content of the sludge
as fed to the incinerator is assumed to be either 20 or
40 percent, depending upon the alternative. A general
flow sheet of the hypothetical plants is given on figure
7-2. When these data are further developed in later
tables, it should be noted that the volatile solids for the
40 percent solids cake has been reduced in most cases
Table 7-1.—Hypothetical wastewater treatment plant design data
Alternate
IA
IB
IIA
MB
IIIA
IIIB
Flow, Mgal/d
Total solids, Ib/day dry basis
Volatile solids, percent of dry solids
Furnace operation, hr/week
Furnace loading rate, Ib/hr dry basis
Solids content of furnace feed, percent solids by weight
Furnace loading rate. Ib/hr wet basis
5
10,320
77
40
1 810
20
9.030
5
10320
77
40
1 810
40
4.515
15
31 000
77
80
2 710
20
13.560
15
31 000
77
80
2710
40
6.780
50
1 03 000
77
168
4 300
20
21 .460
50
1 03 000
77
168
4300
40
10.730
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BAR GRIT PRIMARY
SCREENS REMOVAL SEDIMENTATION
AERATION
(CARBONACEOUS
OXIDATION)
SECONDARY CHLORINE
SEDIMENTATION CONTACT
RAW SEWAGE /
T
SCREENINGS
TO LANDFILL
LU
1-
cc
CENTRATE OR F
GRIT TO
LANDFILL
\
CL2
1
PRIMARY MIXED f FINAL
EFFLUENT , , LIQUOR
J
LU
0
Q
_J
£ RETURN ACTIVATED SLUDGE
-------
COOLING AIR DISCHARGE
SLUDGE INLET
FLUE GASES OUT
RABBLE ARM
AT EACH HEARTH
SHAFT COOLING
AIR RETURN
GAS FLOW
ASH DISCHARGE
SOLIDS FLOW
SHAFT COOLING AIR FAN.J
Figure 7-3.—Cross section of a multiple hearth furnace.
sludge is fed at the periphery of the top hearth and is
raked toward the center where it drops to the hearth
below. On the second hearth, the sludge is raked out-
ward to holes at the periphery of the bed where the
sludge drops to the next hearth. The alternating drop
hole locations on each hearth and the counter-current
flow or rising exhaust gases and descending sludge pro-
vide good contact between the hot combustion gases
and the sludge feed to insure complete combustion.
The central shaft is normally of cast iron and has an
inner tube called the cold air tube. Each of the rabble
arms is connected to the cold air tube and has a return
tube which returns the heated cooling air to the annular
space between the cold air tube and the shell of the
central shaft which serves as an exhaust passageway for
the cooling air. Cooling air is fed to the cold air tube by
the cooling air fan. The heated cooling air is usually
taken from the top of the central shaft and reinjected
into the lowest hearth as preheated combustion air.
Cooling air vented to the atmosphere represents a heat
loss of roughly the same magnitude as radiation.
The MHF can be divided into four zones during incin-
eration. The first zone, which consists of the upper
hearths, is the drying zone where most of the water is
evaporated; the second zone, generally consisting of the
central hearths, is the combustion zone, where tempera-
tures reach 1400 to 1700°F; the third zone is the fixed
carbon burning zone, which oxidizes the carbon to car-
bon dioxide; and the fourth zone is the cooling zone,
which includes the lowest hearths. In this zone, the ash
is cooled by rejecting heat to the incoming combustion
air. The sequence of these zones is always the same,
but the number of hearths in each zone is dependent on
the quality of the feed, the design of the furnace, and
the operational conditions.
When the thermal quality of the sludge feed is insuffi-
cient to sustain autogenous combustion, burners supply
the additional heat by operating either continuously or
intermittently on all or selected hearths. Generally, off-
gas temperatures of 600°F, or lower, indicate incomplete
combustion and a need for supplemental fuel. Off-gas
temperatures from 800 to 1600°F indicate complete
combustion. When autogenous, the off-gas temperatures
are usually maintained below 1400°F by eliminating pre-
heating of the combustion air and by adding excess air.
Excess air requirements for the MHF are generally 75 to
100 percent of stoichiometric requirements when sludge
is the furnace feed material. Excess air is also used for
ash cooling.
A flow sheet for the MHF is given on figure 7-4.
Energy and mass balances for the MHF for the treat-
ment plant alternatives are given in tables 7-2 and 7-3
for use with figure 7-4.
Multiple-hearth furnace manufacturers use different
loading rates based upon varied experience in incinera-
tion. This variation results in a range of recommended
furnace sizes, although the cost range is not significant.
These costs, however, do not represent a bid condition.
For areas where air pollution requirements are similar
to those for the San Francisco Bay Area, the MHF
would require an afterburner, fired with supplemental
fuel. This requirement would increase fuel consumption,
equipment size, and capital and operating costs from
those shown in tables 7-2 and 7-3.
The MHF can operate successfully over a large range
of operating modes and feeds. Operating problems have
included failure of rabble arms and teeth and failure of
hearth refractories. The problems with the rabble arm
and teeth have generally been solved by using different
construction materials. The refractory problem is usually
caused by improper operation and is a disadvantage
which must be considered when evaluating an MHF. An
MHF generally requires at least 24 hours to cool off to
ambient temperature or be brought back to operating
temperature from ambient temperature. During intermit-
tent operation, supplemental fuel is usually fired to main-
tain the temperature of the furnace during the hours
when it is not being used so that the long heating time
for the furnace can be reduced. When the furnace is
heated or cooled too quickly, the refractories can be
damaged. Multiple-hearth furnaces should not be oper-
ated at temperatures above 1800° F; thus, with high-en-
ergy fuels, there may be operational problems due to
high temperature in the combustion zone.
Fluid-Bed Furnace
The fluid-bed furnace (FBF) is a vertically oriented,
cylindrically shaped, refractory-lined, steel shell which
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GAS EXHAUST
SHAFT COOLING AIR NOT RETURNED
SHAFT COOLING
SLUDGE
AIR RETURN
FEED
PRECOOLER-
AND VENTURI
MULTIPLE
HEARTH
FURNACE
SHAFT
VENTURI WATER
CONNECTED POWER
ASH
COOLING AIR
Figure 7-4.—Flowsheet for sludge incineration in a multiple-hearth
furnace.
contains the bed and fluidizing air diffusers. The FBF is
normally available in sizes from 9 ft (2.74 m) to 25 ft
(7.62 m) in diameter. However, there is one industrial
unit operating with a diameter of 53 ft (16.15 m). A
cross section of the fluid-bed furnace is shown on figure
7-5. The sand bed is approximately 2.5 ft (0.76 m) thick
and sits on a refractory-lined grid. This grid contains
truyeres through which air is injected into the bed at a
pressure of 3 to 5 lb/in.2g (0.21 to 0.35 kgf/cm2) to
fluidize the bed. Bed expansion is approximately 80 to
100 percent. Temperature of the bed is controlled be-
tween 1400 and 1500°F by auxiliary burners located
either above or below the sand bed and in some instal-
lations by a water spray or heat removal system above
the bed which reduces the furnace temperature when it
is too high. Ash is carried out the top of the furnace
and is removed by air pollution control devices, usually
wet venturi scrubbers. Sand, which is carried out with
the ash, must be replaced. Sand loss is approximately 5
percent of the bed volume every 300 hrs of operation.
Furnace feed is introduced either above or directly into
the bed, depending on the type of feed. Generally, sew-
age sludge is fed directly into the bed.
Excess air requirements for the FBF vary from 20 to
40 percent. This reduces supplemental fuel requirements
and reduces heat losses from heating and exhausting
excess air as compared to a multiple-hearth furnace.
The mixing action caused by the air flowing through the
bed and the injection of sludge directly into the bed
ensures complete contact between the sludge solids and
the combustion gases.
There are two basic configurations for the FBF. In the
-------
Table 7-2.—Material and heat balance for sludge incineration in a multiple-hearth furnace; manufacturer Aa
Stream
Alternate
IA IB IIA MB IMA NIB
5 Mgal/d 5 Mgal/d 15 Mgal/d 15 Mgal/d 50 Mgal/d 50 Mgal/d
20 percent 40 percent 20 percent 40 percent 20 percent 40 percent
solids solids solids solids solids solids
Furnace design
Diameter (ft-m.) 18-9 14-3 22-3 16-9 22-3 18-9
Number of hearths 7 6 7 6 10 7
Hearth loading rate (Ib wet solids/sq ft/hr) 7.3 9.3 7.4 9.5 8.4 103
Sludge feed
Ib dry solids/hr 1,806 2,133 2,713 3,200 4,293 5,064
Heat value (MM Btu/hr) 13.91 13.93 20.89 20.90 33.06 33.07
Volatile content (percent dry solids) 77 65 77 65 77 65
Supplemental fuel
No. 2 fuel oil (Ib/hr) 143 — 205 — 312 —
Heat value (MM Btu/hr) 2.64 — 3.79 — 5.77 —
Combustion air
Volume at 60° F (Ib/hr) 22,060 27,531 32,959 41,544 51,945 66,740
Shaft cooling air
Volume (Ib/hr) 19,273 9,178 24,321 13,766 34,416 19,273
Shaft cooling air return
Volume at 325° F (Ib/hr) 16,560 — 20,880 — 29,520 —
Heat value (MM Btu/hr) 1.26 — 1.59 — 2.25 —
Shaft cooling air not recovered
Heat loss (MM Btu/hr) 0.22 0.71 0.28 1.06 0.40 1.48
Ash
Volume at 500° F (Ib/hr) 415 740 624 1,110 987 1,757
Heat value (MM Btu/hr) 0.04 0.07 0.06 0.10 0.09 0.15
Radiation
Heat loss (MM Btu/hr) 0.32 0.21 0.41 0.26 0.53 0.33
Furnace exhaust
Volume (Ib/hr) b30,817 C32,123 b46,102 C48,434 b72,735 C77,643
Heat value (MM Btu/hr) 15.96 12.94 23.93 19.48 37.81 31.11
Boiler exhaust
Heat value at 500°F (MM Btu/hr) 13.26 9.64 19.73 12.28 31.11 1961
Recoverable heat
100 percent efficiency (MM Btu/hr) 2.70 3.30 4.20 7.20 6.70 11.50
Precooler and Venturi water feed
Flow at 70°F (gal/min) 90 86 135 130 215 209
Scrubber water feed
Flow at 70° F (gal/min) 182 174 273 260 429 418
Scrubber drain
Flow (gal/min) 296 264 428 398 676 638
Temperature (F) 98 98 98 98 98 98
Gas exhaust
Volume (Ib/hr) 26,667 38,938 44,278 58,646 61,116 91,393
Temperature (F) 142 170 139 168 138 166
Heat value (MM Btu/hr) 9.44 6.00 14.01 6.80 22.09 10.82
Connected power
Horsepower 238 93 305 178 305 238
Installed cost (MM dollars) 2.0 1.6 2.2 2.0 2.4 2.0
aAII data supplied by the manufacturer.
bAt 800° F.
cAt 1,000°F.
-------
Table 7-3.—Material and heat balance for sludge incineration in a multiple-hearth furnace; manufacturer Ba
Stream
Alternate
IA IB MA IIB IMA 1MB
5 Mgal/d 5 Mgal/d 15 Mgal/d 15 Mgal/d 50 Mgal/d 50 Mgal/d
20 percent 40 percent 20 percent 40 percent 20 percent 40 percent
solids solids solids solids solids solids
Furnace design
Diameter (ft-in.) 22-3 16-9 22-3 18-9 22-3 18-9
Number of hearths 5 5 7 5 10 7
Hearth loading rate (Ib wet solids/sq ft/hr) 6.9 6.4 7.4 7.6 8.4 8.7
Sludge feed
Ib dry solids/hr 1,806 1,806 2,712 2,712 4,292 4,292
Heat value (MM Btu/hr) 13.91 13.91 20.88 20.88 33.05 33.05
Volatile content (percent dry solids) 77 77 77 77 77 77
Supplemental fuel
No. 2 fuel oil (Ib/hr) 119 — 175 — 271 —
Heat value (MM Btu/hr) 2.32 — 3.39 — 5.23 —
Combustion air
Volume at 70° F (Ib/hr) 21,400 20,688 32,050 32,039 50,592 51,273
Shaft cooling air
Volume (Ib/hr) 11,970 10,710 17,100 11,970 23,940 17,100
Shaft cooling air return
Volume at 350° F (Ib/hr) 11,970 — 17,000 — 23,940 —
Heat value (MM Btu/hr) 0.75 — 1.07 — 1.50 —
Shaft cooling air not returned
Heat loss (MM Btu/hr) — 0.67 — 0.75 — 1.07
Ash
Volume at 600" F (Ib/hr) 415 415 623 623 987 987
Heat value (MM Btu/hr) 0.05 0.05 0.08 0.08 0.13 0.13
Radiation
Heat loss (MM Btu/hr) 0.29 0.20 0.36 0.23 0.47 0.30
Furnace exhaust
Volume (Ib/hr) b30,134 C24,788 "45,162 C38,196 b71,336 C61,017
Heat value (MM Btu/hr) 15.89 12.99 23.83 19.82 37.68 31.55
Boiler exhaust
Heat value at 500° F (MM Btu/hr) 12.99 7.00 19.49 10.63 30.82 16.89
Recoverable heat
100 percent efficiency (MM Btu/hr) 2.90 5.99 4.34 9.19 6.86 14.66
Precooler and Venturi water feed
Flow at 70° F (gal/min) 117 92 167 133 253 203
Scrubber water feed
Flow at 70° F (gal/min) 228 228 342 205 540 327
Scrubber drain
Flow (gal/min) 350 331 530 346 828 540
Temperature (F) 132 116 133 116 134 116
Gas exhaust
Volume (Ib/hr) 23,015 22,285 34,473 46,466 54,418 72,297
Temperature (F) 110 169 110 156 110 155
Heat value (MM Btu/hr) 1.82 2.43 2.72 3.48 4.29 5.44
Connected power
Horsepower 250 150 250 200 350 200
Installed cost (MM dollars) 1.6 1.2 1.8 1.4 2.0 1.5
aAII data supplied by the manufacturer.
bAt 800° F.
°At 1,000°F.
10
-------
SIGHT GLASS
EXHAUST *
Figure 7-5.—Cross section of a fluidized bed furnace.
first system, the fluidizing air passes through a heat
exchanger or recuperator prior to injection into the com-
bustion chamber. This arrangement is known as a hot
windbox. In the second system, the fluidizing air is in-
jected directly into the furnace and is known as a cold
windbox. The first arrangement increases the thermal
efficiency of the system by utilizing the high temperature
of the exhaust gases to heat the incoming combustion
air.
A general flow sheet for the FBF is given on figure
7-6. Energy and material balances for the fluid-bed fur-
nace for the treatment plant alternatives are given in
table 7-4 for use with figure 7-6.
The FBF has a slightly lower capital cost than the
MHF. Start-up fuel requirements are low, and no fuel is
required for start-up following an overnight shutdown.
The fluid-bed furnace has a minimum of mechanical
components and is relatively simple to operate. The sane
bed acts as a large heat reservoir which minimizes the
amount of fuel required to reheat the system following
shutdown. This makes the FBF very attractive for inter-
mittent operation. Since normal operation of the FBF
results in exhaust temperatures in excess of 1400°F,
there is no requirement for an afterburner using supple-
mental fuel to comply with air emissions regulations in
some areas as may be required with the MHF.
The main problems with the FBF have been with the
feed system and temperature control with high-energy
feeds. Screw feeds and pump feeds have jammed be-
FURNACE EXHAUST
GAS EXHAUST
Figure 7-6.—Flowsheet for sludge incineration in a fluid bed furnace.
11
-------
Table 7-4.—Material and heat balance for sludge incineration in a fluid bed furnace; Dorr-Oliver, Inc.3
Alternate
Stream IA
5 Mgal/d
20 percent
solids
IB
5 Mgal/d
40 percent
solids
IIA
15 Mgal/d
20 percent
solids
MB
15 Mgal/d
40 percent
solids
IMA
50 Mgal/d
20 percent
solids
- NIB
50 Mgal/d
40 percent
solids
Furnace design
Inside diameter (ft)
Loading rate (Ib wet solids/sq ft/hr)
Sludge feed
Ib dry solids/hr
Heat value (MM Btu/hr)
Volatile solids (percent dry solids)
Supplemental fuelb
Volume (Ib/hr)
Heat value (MM Btu/hr)
Combustion air
Volume (Ib/hr)
Heat value (MM Btu/hr)
Ash
Volume (Ib dry solids/hr)
Heat value (MM Btu/hr)
Water flow (gal/min)
Radiation
Heat loss (MM Btu/hr)
Recoverable heat
100 percent efficiency (MM Btu/hr)
Recuperator
Venturi water
Recycle water (gal/min)
Makeup water at 70° F (gal/min)
Scrubber water feed
Flow at 70°F (gal/min)
Scrubber drain
Flow at 130°F (gal/min)
Gas exhaust
Volume (ACFM)
Temperature (F)
Connected power
Horsepower
Installed cost (MM dollars)
14
56.9
1,810
13.93
77
151
2.80
19,353
4.4
416
0.12
20
0.42
=5.0
Yes
83
10
365
391
5,042
120
218
1.1
12
47.0
2,132
13.93
65
—
—
16,250
—
746
0.14
32
0.29
d8.9
No
68
12
345
359
3,972
120
162
1.0
18
53.3
2,710
20.87
77
224
4.14
28,976
6.7
623
0.18
30
0.63
C7.5
Yes
124
15
548
582
7,524
120
320
1.4
14
47.0
3,192
20.87
65
—
—
23,576
—
1,117
0.26
43
0.44
d13.4
No
102
19
565
600
5,949
120
234
1.1
22
56.5
4,300
33.10
77
353
6.52
45,978
10.6
959
0.29
40
1.00
°12.0
Yes
197
24
868
924
12,007
120
425
1.6
18
45.0
5,065
33.10
65
—
—
38,620
—
1,772
0.42
70
0.71
d18.1
No
161
30
824
900
9,459
120
350
1.5
aAII data provided by Dorr-Oliver, Inc.
bAfterburner not necessary to meet SFBAAPCD regulations.
cAt 1,400°F.
dAt 1,650°F.
cause of overdrying the sludge when it is injected di-
rectly into the bed. When spray nozzles have been used,
thermocouples have occasionally burned out. These
problems have generally been solved by using different
materials. There have been some problems with preheat-
ers and with scaling of the sand on the venturi scrub-
ber. In some installations, there have been serious ero-
sion problems in the scrubber due to the excessive
carryover of bed material and the resulting sandblasting
effect. The fluid-bed incinerator can be operated at
2200°F and is suitable for high energy sludges when
appropriately designed. Since there is a minimum of air
always required for bed fluidizing, energy savings in
turndown (feed reduction) are minor.
Cyclonic Furnace
The cyclonic furnace, sometimes called a single-rotary
hearth furnace, is a vertically oriented, cylindrically
shaped, refractory-lined, steel shell normally with a
domed cover. There is one rotating hearth and a fixed
plow which moves the combustible material from the
12
-------
CYCLONIC ACTION
ROTATING HEARTH
ASH DISCHARGE IN
CENTER OF FURNACE
Figure 7-7.—Cross section of a cyclonic furnace.
outer edge of the hearth to the center. The furnaces are
available with hearths to 30 ft (9.14 m) in diameter but
larger sizes can be built. The sludge is fed by a screw
feeder which deposits the sludge near the periphery of
the rotating hearth. A sectional view of the furnace is
given on figure 7-7.
This furnace design differs from the multiple-hearth
and fluid-bed designs in that it does not allow the com-
bustion air to pass upward through the feed material.
Combustion air and auxiliary fuel, if required, are inject-
ed tangentially into the combustion chamber above the
rotating hearth, creating a swirling action which mixes
the gases and allows adequate contact between the
oxygen and the furnace feed. The gases from the com-
bustion process spiral upward to the outlet. The furnace
exhaust temperature is approximately 1500°F and can
be used for heat recovery, preheat of inlet air, or wast-
ed. The ash is circulated to the middle of the hearth,
where it drops through the hearth to a quench tank for
final disposal. The rotating hearth is sealed at the edges
by a water bath.
A general flow sheet for the furnace is given on figure
7-8. Energy and material balances for the cyclonic fur-
nace are given in table 7-5 for use with figure 7-8.
The low capital cost of this furnace and the low fuel
requirements make it a competitive alternative furnace
GAS EXHAUST
Figure 7-8.—Flowsheet for sludge incineration in a cyclone furnace.
13
-------
Table 7-5.—Material and heat balance for sludge incineration in a cyclonic furnace; AFB Engineers and
Contractors, Inc.3
Alternate
Stream
IA
5 Mgal/d
20 percent
solids
IB
5 Mgal/d
40 percent
solids
HA
15 Mgal/d
20 percent
solids
MB
15 Mgal/d
40 percent
solids
IMA
50 Magl/d
20 percent
solids
1MB*
50 Mgal/d
40 percent
solids
Furnace design
Diameter (ft-in) 19-6 13-9 24-0 17-0 30-3 21-6
Hearth loading rate (Ib wet solids/sq ft/hr) 30.4 30.9 30.1 30.1 29.9 29.7
Sludge feed
Ib dry solids/hr 1,806 1,806 2,712 2,712 4,292 4,292
Heat value (MM Btu/hr) 14.27 14.27 2143 21.43 33.91 33.91
Volatile solids (percent dry solids) 77 77 77 77 77 77
Supplemental fuelb
Volume (Ib/hr) 132 — 184 — 546 —
Heat value (MM Btu/hr) 2.48 — 3.46 — 10.28 —
Primary air
Volume (Ib/hr) 19,665 19,665 29,519 29,519 46,694 46,694
Temperature (F) 1,100 60 1,100 60 1,100 60
Burner air
Volume at 60° F (Ib/hr) 2,280 — 3,178 — 9,430 —
Ash
Volume at 260° F (Ib/hr) 415 415 624 624 987 987
Heat value (MM Btu/hr) 0.19 0.19 0.29 0.29 0.46 0.46
Radiation
Heat loss (MM Btu/hr) 0.90 0.60 1.17 0.80 2.0 1.00
Waste heat boiler No Yes No Yes No Yes
Recuperator Yes No Yes No Yes No
Furnace exhaust
Volume (Ib/hr) 30,692 23,765 45,817 35,675 77,143 57,424
Temperature (F) 1,420 1,411 1,420 1,421 1,420 1,420
Heat value (MM Btu/hr) 19.90 13.48 29.75 20.34 50.10 32.38
Boiler/recuperator exhaust
Temperature (F) 960 500 960 500 960 500
Heat value (MM Btu/hr) 15.66 6.87 23.43 10.32 39.45 16.51
Recoverable heat—boiler
100 percent efficiency (MM Btu/hr) — 6.61 — 10.02 — 15.87
Precooler water feed
Flow at 60° F (gal/min) 12 5 19 7 30 15
Scrubber water feed
Flow at 60° F (gal/min) 292 197 437 296 699 507
Scrubber drain
Flow (gal/mm) 319 207 477 311 763 535
Temperature (F) 120 110 120 110 120 110
Gas exhaust
Volume (Ib/hr) 23,468 21,209 34,969 31,838 62,225 49,002
Temperature (F) 120 110 120 110 120 110
Heat value (MM Btu/hr) 1.79 1.62 2.67 2.43 4.75 3.74
Connected power
Horsepower 175 125 260 190 460 290
Installed cost (MM dollars) 1.3 1.0 1.6 1.1 CN/A 1.5
aAII data provided by AFB Engineers/Contractors sole U.S. distributors of the Lucas Cyclonic Furnace.
bAfterburners not necessary to meet SFBAAPCD regulations.
cNot available.
14
-------
for sludge incineration. However, there are presently no
units operating on a sludge feed in the United States. A
pilot unit was run for approximately 2 years at the San
Leandro, Calif., wastewater treatment plant, but the unit
has been dismantled.
The rotary-hearth furnace has a relatively low capital
cost and is mechanically simple with only one rotating
hearth; however, the feed system is very similar to the
feed system of the fluid-bed furnace, which has had
problems as previously described. Because of the high
exhaust temperatures, no afterburner or supplemental
heater would be required with the cyclonic furnace to
comply with air emissions regulations in the San Francis-
co Bay Area. Additional heat could be recovered in a
waste heat boiler with the exhaust gas from the recuper-
ator because of the temperature of this gas.
Electric Furnace
The electric, or infrared, furnace (EF) is a horizontally
oriented, rectangular, ceramic fiber blanket-lined, steel
shell containing a moving horizontal woven-wire belt and
electric radiant heating elements. Electric furnaces are
available in a range of sizes from 4 ft (1.22 m) wide by
20 ft (6.1 m) long to 9.5 ft (2.9 m) wide by 96 ft (29.26
m) long; larger sizes are currently under development. A
typical cross section is shown on figure 7-9. Sludge is
fed into the furnace through a feed hopper which drops
the sludge onto the conveyer belt. The sludge is leveled
by means of an internal roller to a layer approximately 1
in. (2.54 cm) thick, spanning the width of the belt. This
layer of sludge moves under the heating elements, which
provide supplementary energy, if required, to effect the
incineration process. Ash is discharged from the end of
the belt to the ash handling system. Combustion air flow
is countercurrent to the sludge flow, with most of the
combustion air being introduced into the ash discharge
end of the unit. There is normally no rabbling or plowing
of the sludge as it is conveyed through the furnace.
The EF can be divided into three general zones: the
feed zone, the drying and combustion zone, and the ash
discharge zone. The feed and discharge zone are each
8 ft (2.44 m) long. The length of the drying and com-
bustion zone varies with each design. A flow sheet for
the electric furnace is shown on figure 7-10. Energy
and mass balances for the treatment plant alternatives
are given in table 7-6 for use with figure 7-10. In
addition to the alternative cases I, II, and III, similar
information for a 1-mgd treatment plant application has
been included as the EF is suited to relatively small
wastewater treatment plants.
The hearth loading rate of the EF, in the larger sizes,
is slightly greater than that of a multiple-hearth furnace.
The supplemental energy (or fuel) requirements of the
EF is much less than the requirements of the MHF, FBF,
or the cyclonic furnace. This is due to the low excess
combustion air requirements of 20 percent and the ab-
sence of cooling or fluidizing air requirements. However,
the energy source is electric rather than the fossil fuel
used by the other systems, and since electricity is gen-
erally a more expensive energy source, the advantage is
reduced somewhat, depending upon the cost differential
of the alternate fuels.
The capital cost combined with a relatively low energy
demand make this an attractive furnace, especially for
small treatment systems. By using ceramic fiber blanket
insulation, instead of solid refractories, the electric fur-
nace may be shut down and heated up without refrac-
tory problems, which can occur in the other furnaces
previously discussed. This makes the EF suitable for
intermittent operation. However, each restart requires
auxiliary energy since there is no heat sink such as the
sand bed in the FBF. There are presently no units in-
stalled with a capacity over 1,200 pounds per hour. The
first electric furnace was put into operation in Richard-
son, Tex., in 1975, so there are only 2 years of perfor-
mance data available.
The electric furnace appears to be a feasible alterna-
BELT
DRIVE
SLUDGE FEED
RADIANT
INFRARED
HEATING
ELEMENTS (TYP)
WOVEN WIRE
CONTINUOUS BELT
EXHAUST
COMBUSTION
o o o o o oooooooo oo o
Figure 7-9.—Cross section of an electric furnace.
15
-------
GAS EXHAUST
COMBUSTION
AIR
FURNACE
EXHAUST
HEAT
RECOVERY
BOILER
BOILER
EXHAUST
RECUPERATOR
RECOVERABLE
HEAT
SLUDGE
FEED
SUPPLEMENTAL
ENERGY
ELECTRIC FURNACE
COMBUSTION
VENTURI
SCRUBBER
SCRUBBER
WATER
DRAIN
AIR
CONNECTED POWER
1 I
RADIATION ASH
Figure 7-10.—Flowsheet for sludge incineration in an electric furnace.
tive for both small and large systems due to inherent
simplicity, cost and energy demand, but this furnace
requires considerably more floor space than other fur-
naces which are vertically oriented. Connected horse-
power, whether for heating or motive power, may create
a significant electric utility demand charge in some
areas, regardless if the energy is used or not. Due to
the gas flow being countercurrent to the sludge flow,
the electric furnace may require an afterburner to com-
ply with the prohibitory regulations of the SFBAAPCD.
This requirement would increase the supplemental energy
requirement, the amount of equipment, and capital and
operating costs from those shown in table 7-6. Air emis-
sion control equipment would tend to be smaller to allow
for the low excess air requirements than other furnaces
of similar feed capacity.
SLUDGE PYROLYSIS
Due to the rising fuel costs and the inherent heating
value of sludge fed to incinerators, partial pyrolysis, or
more correctly, starved-air combustion (SAC), has been
investigated and demonstrated in multiple-hearth furnaces
to be a means of combusting sludge without large
amounts of supplementary fuel. Based upon current
data, SAC of sludges with a solids content of over 25
percent is possible without the addition of fossil fuel
while maintaining an afterburner temperature over
16
-------
Table 7-6.—Material and heat balance for sludge incineration in an electric infrared furnace; Shirco, Inc.3
Alternate
Stream
IA IB MA MB IIIA 1MB
5 Mgal/d 5 Mgal/d 15 Mgal/d 15 Mgal/d 50 Mgal/d 50 Mgal/d
20 percent 40 percent 20 percent 40 percent 20 percent 40 percent
solids solids solids solids solids solids
Furnace design
Number of units 2 1 2 1 3 2 1
Overall width (ft) 8.5 8.5 95 9.5 9.5 8.5 6
Overall length (ft) 72 72 88 88 96 88 32
Belt area per furnace (sq ft) 382.6 3826 560.5 560.5 616.8 4795 94.5
Loading rate (Ib wet solids/sq ft/hr)b 11.8 13.9 12.1 14.3 11.6 13.2 11.3
Sludge feed
Ib dry solids/hr 1,806 2,133 2,713 3,200 4,293 5,064 427
Heat value (MM Btu/hr) 13.91 1391 20.89 20.89 3306 33.06 279
Volatile content (percent dry solids) 77 65 77 65 77 65 65
Water (Ib/hr) 7,224 3,200 10,582 4,800 17,172 7,596 641
Heat value (MM Btu/hr) 0.28 0.12 0.41 0.18 0.65 029 002
Supplemental power
Electric infrared (kW) 280.8 — 402.5 — 643.8 — —
Heat value (MM Btu/hr) °0.96 — C1.37 — C1.88 — —
Combustion air
Volume at 60° F (Ib/hr) 17,736 24,786 26,676 37,184 42,161 58,844 4,962
Heat value (MM Btu/hr) 0.26 0.36 0.38 0.54 0.61 0.85 0.07
Ash
Volume at 500° F (Ib/hr) 415 747 624 1,120 987 1,772 149
Heat value (MM Btu/hr) 0.10 0.18 0.16 0.28 0.24 0.44 0.04
Radiation
Heat loss (MM Btu/hr) 0.36 018 0.47 0.24 077 043 0.07
Furnace exhaust
Volume (Ib/hr) d26,351 e29,372 d39,616 e44,064 d62,628 e69,732 e5,880
Heat value (MM Btu/hr) 14.95 14.03 2242 2109 34.54 33.34 270
Boiler exhaust
Heat value at 500°F (MM Btu/hr) 13.00 8.53 19.49 1279 3133 2023 171
Recoverable heat
100 percent efficiency (MM Btu/hr) 1.95 5.50 293 8.30 321 13.11 099
Scrubber water feed
Flow at 70° F (gal/min) 397 201 584 314 1,049 498 201
Scrubber drain
Flow (gal/min) 390 196 606 306 1,081 485 196
Temperature (F) 120 120 120 120 120 120 150
Gas exhaust
Volume (Ib/hr) 29,538 35,811 39,616 53,838 54,744 85,186
Temperature (F) 120 120 120 120 120 120
Heat value (MM Btu/hr) 1.98 277 2.96 4.18 4.71 6.57
Total connected power
Horsepower (22 25 '30 40 f50 60 7
Total installed cost (MM dollars) 1.0 0.7 1.3 0.9 1.5 12 03
aAII data supplied by Shirco, Inc.
bUseable area of belt.
cAutogenous with combustion air preheated to 500 °F.
dAt 750 °F.
"At 1,200°F.
'Does not include supplemental power requirements for infrared heaters
17
-------
1400°F; however, nominal solids level for autogenous
SAC is a function of the net heating value of the
sludge. Starved-air combustion reduces sludge to an ash
containing up to 30 percent combustibles and up to 20
percent fixed carbon, depending upon the method of
operation of the MHF. The gas produced from the de-
struction of sludge has a heat value of up to 90 Btu/-
standard dry cubic foot (sdcf) and is suitable for many
applications. Starved-air combustion is more thermally
efficient than incineration because of the small amount
of air, 25 to 50 percent of the theoretical air required
for combustion, that must be heated to combustion tem-
perature. This prevents wasting energy to heat excess
air in the furnace and reduces the size and, hence, the
capital cost of the gas-handling facilities. Fluid-bed, cy-
clonic, and electric furnaces could also be operated as
SAC reactors although to date, none of these furnaces
have been operated in this manner with a pure sludge
feed. An FBF has been used to make charcoal, a SAC
operation, and research is underway to pyrolyze wood
waste with the FBF.
Development and Application
Autogenous pyrolysis (SAC) of sludge was successfully
demonstrated in a full-size project with an MHF at a
wastewater treatment plant at Concord, Calif., near San
Francisco, operated by The Central Contra Costa Sani-
tary District. The project was funded by the Environmen-
tal Protection Agency, the State of California, and the
Central Contra Costa Sanitary District. Sludge from the
plant had a heating value of 9,000 Btu/lb (20,900 J/s)
volatile solids, a volatile solids content of 75 percent,
and was centrifuged to a solids content of 24 percent.
The SAC reactor was a converted six-hearth, 18-ft, 9-in.
(5.71 m) diameter MHF. The centrifuged sludge was py-
rolyzed without any auxiliary fuel, either in the furnace
or the afterburner, while maintaining an afterburner tem-
perature of 1400° F. The fuel gas had a heating value of
90 Btu/sdcf. Other significant results of this two-month
test program included:
• Pyrolysis was found to be easier to control than
incineration.
• Hearth temperature was used to control the fur-
nace, using air addition as the manipulated variable.
• In SAC, air addition to the furnace should be auto-
matically controlled.
• Particulate production on a solids-fed basis was
about 50 percent lower using SAC than incinera-
tion.
• Although the controlled variable in SAC was tem-
perature, the degree of pyrolysis, as measured by
the amount of feed heating value remaining uncom-
busted in the fuel gas, is actually controlled by the
fraction of the theoretical air required for combus-
tion that is added to the reactor.
• During the corrosion tests, the most resistant alloys
for SAC were type HK stainless steel and Inconel
690 for high temperature conditions and Hastelloy
C-276 and Inconel 625 for low temperature condi-
tions.
Additional details of the test work and application for
the Central Contra Costa Sanitary Dictrict can be found
in references 3, 9, 10, 11, 38, and 44.
Two furnace manufacturers, BSP Division of Envirotech
Corp., and Nichols Engineering & Research Corp., a
subsidiary of Neptune International, are actively involved
in ongoing research and development of SAC systems.
Because of this research, there are refinements and up-
dating of design parameters regularly; therefore, the data
presented here are approximate only. A typical flow
sheet for a MHF operated as a SAC reactor is shown
on figure 7-11. Energy and material balances for the
SAC systems are shown in table 7-7 for the wastewater
alternatives previously described.
Advantages and Disadvantages
With all of the test work, much of which is still under-
way, SAC in a MHF was found to have many significant
advantages as compared to incineration or other com-
bustion process. These advantages include:
• Easier and more positive control of the combustion
process.
• More stable operation with little response to chang-
es in feed.
• Greater solids feed capacity due to higher hearth
loading rates.
• All equipment used is currently being manufactured
and has a long performance history.
• Reduced particulates and other air emissions.
• Significant reduction in fuel usage including after-
burning at 1400°F.
• Autogenous SAC can occur at lower sludge solids
content than incineration.
• Slightly lower operating costs.
• Most existing MHFs can easily be retrofitted to op-
erate in a SAC mode.
These advantages are clearly shown in table 7-8 where
MHF for incineration and SAC are compared.
As expected, with many advantages there are signifi-
cant disadvantages, such as:
• Need for afterburner may limit use in existing instal-
lations with space problems.
• More instrumentation is required.
• Must be very careful of bypass stack exhaust since
furnace exhaust is high in hydrocarbons and may
be combustible in air. This may result in bypassing
only after afterburning with appropriate emergency
controls.
• Corrosivity of furnace exhaust gases.
• Combustibles in ash may create ultimate disposal
problems.
Although there are several disadvantages, it is apparent
that they are outweighted by the advantages, particularly
in this era of high energy costs. With sound engineering
18
-------
GAS EXHAUST
SHAFT COOLING AIR NOT RETURNED
SHAFT COOLING
AIR RETURNED
SLUDGE
TO FURNACE
FEED
AFTERBURNER
COMBUSTION AIR
FURNACE
-SHAFT COOLING AIR
RETURNED TO AFTERBURNER
AFTERBURNER
PRECOOLER-
ANDVENTURI
MULTIPLE
HEARTH
STARVED
AIR REACTOR
SHAFT
COOLING AIR
Figure 7-11.—Flowsheet for starved-air combustion of sludge in a multi-
ple-hearth furnace.
practices and a thorough system analysis, all of the
disadvantages can be resolved.
Conversion of Existing Systems
One of the significant advantages of SAC is that most
existing MHF systems can be converted to operate as
SAC reactors. This retrofitting involves relatively few
changes, and the costs and benefits are site specific.
One definite incentive for conversion is that the existing
system may be able to handle projected waste loads
without the addition of more incinerators. This incentive
is demonstrated in a design example presented later in
this paper. Assuming an increase in solids loading of
19
-------
Table 7-7.—Material and heat balance for starved-air combustion of sludge in a multiple-hearth furnace3
Manufacturer
Stream
Alternate (all 40 percent solids feed)
IB MB IIIB IB MB 1MB
5 Mgal/d 15 Mgal/d 50 Mgal/d 5 Mgal/d 15 Mgal/d 15 Mgal/d
Furnace design
Diameter (ft-in.) 12-9 14-3 16-9 16-9 18-9 22-3
Number of hearths 6 7 8 5 5 5
Hearth loading rate (Ib wet solids/sq ft/hr) 12.1 12.0 11.4 7.6 9.0 9.6
Sludge feed
Ib dry solids/hr 2,132 3,200 5,064 2,132 3,200 5,064
Heat value (MM Btu/hr) 7.35 10.73 16.90 13.91 20.88 33.05
Volatile solids (percent dry solids) 65 65 65 65 65 65
Supplemental fuel — — — — — —
Combustion air
Volume (Ib/hr) — b780 b1,500 13,210 19,473 32,107
Temperature (F) — 60 60 70 70 70
Shaft cooling air
Volume (Ib/hr) 9,178 10,095 15,602 10,710 12,206 12,206
Shaft cooling air return
Volume at 350° F (Ib/hr) 6,480 8,640 13,380 — — —
Shaft cooling air to stack
Volume at 325° F (Ib/hr) — — — 10,710 12,206 12,206
Shaft cooling air to afterburner
Volume at 350° F (Ib/hr) 2,698 1,455 2,222 — — —
Ash
Volume (Ib/hr) 787 1,181 1,869 740 1,112 1,760
Temperature (F) 500 500 500 900 900 900
Heat value (MM Btu/hr) 0.23 0.34 0.54 0.10 0.14 0.23
Radiation
Heat loss (MM Btu/hr) 0.44 0.62 0.94 0.14 0.15 0.21
Furnace exhaust
Volume at 800°F (Ib/hr) 11,010 16,250 25,658 CN/A CN/A CN/A
Heat value (MM Btu/hr) 6.82 10.16 16.05
Afterburner combustion air
Volume at 60° F (Ib/hr) d4,382 d8,805 d14,098 °N/A CN/A CN/A
Afterburner exhaust
Volume (Ib/hr) 17,638 26,537 42,041 17,799 26,360 43,008
Temperature (F) 1,495 1,495 1,495 1,600 1,600 1,600
Heat value (MM Btu/hr) 12.76 19.18 30.04 13.91 19.75 31.78
Boiler exhaust
Heat value at 500° F (MM Btu/hr) 6.76 9.18 13.04 6.62 9.89 15.80
Recoverable heat
100 percent efficiency (MM Btu/hr) 6.0 10.0 17.0 7.29 9.86 15.98
Precooler and Venturi water feed
Flow at 70°F (gal/min) 51 77 121 72 102 155
Scrubber water feed
Flow at 70° F (gal/min) 102 153 243 123 183 293
Scrubber drain
Flow (gal/min) 160 240 380 203 295 465
Temperature (F) 98 98 98 120 125 126
See footnotes at end of table.
20
-------
Table 7-7.—Material and heat balance for starved-air combustion of sludge in a multiple-hearth
furnace—Continued
Manufacturer
Stream
Alternate (all 40 percent solids feed)
Gas exhaust
Volume (Ib/hr)
Temperature (F)
Heat value (MM Btu/hr)
Connected power
Horsepower
Installed cost (MM dollars)
IB
5 Mgal/d
14280
120
462
78
1 4
MB
15 Mgal/d
21 480
120
596
123
1 6
IIIB
50 Mgal/d
34080
120
794
218
23
IB
5 Mgal/d
25063
160
1 79
100
1 3
IIB
15 Mgal/d
33 137
173
2 40
150
1 5
IIIB
15 Mgal/d
46 837
155
3 47
200
1 s
aAII data supplied by the manufacturers.
bln addition to shaft cooling air returned to furnace.
cNot available.
dln addition to shaft cooling air returned to afterburner.
Table 7-8.—Comparison of multiple-hearth furnaces used for incineration and
starved-air combustion of sludge3
Alternate IB
Manufacturer A
Incineration
SAC
Manufacturer B
Incineration
SAC
Alternate IIB
Manufacturer A
Incineration
SAC
Manufacturer B
Incineration
SAC
Alternate IIIB
Manufacturer A
Incineration
SAC
Manufacturer B
Incineration
SAC
Furnace size
(ft-in. x hearths) (I
14 3X6
12 9X6
16—9X5
16-9x5
16-9x6
14_3X7
18-9X5
18-9x5
18-9X7
1 6-9 X 8
18-9x7
22 3X5
Hearth loading rate
b wet solids/sq ft/hi
9 3
12 1
6 4
7 6
9 5
12 0
7 6
9 0
103
11 4
87
96
Maximum
. heat recovery
; (MM Btu/hr)
i ^n
R on
K QQ
7 ?Q
7 20
10 00
91Q
Q flfi
11 50
17 00
14 fifi
15 Qfl
Installed cost
(MM dollars)
1 C
1 A.
1 9
1 ^
9 n
1 R
1 A
1 ^
9 n
9 *3
1 ^
1 ft
aData extracted from tables 7-2, 7-3, and 7-7.
21
-------
approximately 30 percent, the basic changes necessary
are:
Change
Addition of an afterburner (if ex-
isting system has an afterburn-
er, size may have to be in-
creased. If furnace is large
enough, top hearth may be
used as an afterburner; how-
ever, refractories must be ex-
amined).
Addition of combustion air flow
control and temperature con-
trollers.
Possible replacement of combus-
tion air fan.
Modification of induced draft
fan—may be only speed
change or damper position.
Review and modify venturi and
wet scrubber.
Add additional emission control
equipment.
Reason
Required to burn combustible fuel
gas prior to exhaust.
Review furnace system and re-
placement of remote instrumen-
tation.
General "tightening up" of fur-
nace system.
Required to control SAC process.
May be required to provide nec-
essary pressure for proper con-
trol of air to furnace and to
reduce air flow rate.
Required since total system, in-
cluding afterburner, uses less
than 50 percent excess air.
Required to maintain high per-
formance with lower air flows.
Also may need precooler sec-
tion if boiler is not in process
tram.
Required, depending upon local
air emission control regulations
regarding applicability of new
source performance standards.
Converted SAC system will re-
duce emissions as compared to
present incinerator.
Good practice for any major
process revision.
SAC process depends upon good
air control, therefore, peak and
poke holes must be modified
along with several other pene-
trations into the furnace.
With these modifications and others deemed necessary
during the review of the system, the retrofitted SAC
system is suitable for operation.
COCOMBUSTION OF SLUDGE AND OTHER
MATERIALS
Wastewater treatment plant sludges have a high water
content which results in a fairly low net heat value.
Sludges produced by advanced wastewater treatment
processes contain a lower percentage of volatile solids
than less sophisticated treatment processes which also
results in a fairly low net heating value. The heat con-
tent of volatile solids in sewage sludge is approximately
10,000 Btu/lb (23,200 J/s). Depending upon the percent
of volatile solids in the sludge and the heat content of
the volatile solids, autogenous incineration of wastewater
treatment sludges is only possible with a sludge solids
content of 30 to 35 percent or greater. Since gravity or
flotation thickening can only produce a sludge of about
5 to 10 percent solids, some type of dewatering process
must be used to raise the sludge solids content or auxil-
iary fuel will be required for combustion. With fossil fuel
costs increasing rapidly and availability being curtailed,
any combustion system that requires a constant feed of
power, either fossil fuel or electricity, will in most cases
be uneconomical. If sludge is combined with other com-
bustible materials, in a cocombustion scheme, a furnace
feed can be created that has both a low water content
and a heat value high enough to sustain autogenous
combustion.
There are a variety of materials that can be combined
with sewage sludge to create a furnace feed with a
higher heat value than sludge. Some materials are: mu-
nicipal solid waste, coal, wood wastes (sawdust), textile
wastes, bagasse, and farm wastes, such as corn stalks,
rice husks, etc. Virtually any material that can be burned
can be combined with sludge. An advantage of cocom-
bustion is that many times a waste material, municipal or
industrial, can be disposed while providing an autoge-
nous sludge feed thereby effecting a solution to two
disposal problems.
In recent studies, the addition of pulverized coal to
liquid sludge showed that coal addition improves filtra-
tion efficiency and results in a much higher solids con-
tent and heat value in the filter cake than if the coal is
added directly to the sludge cake. Addition of the coal
to the sludge results in a furnace feed that has a higher
solids content and heat value than sludge alone. This
reduces or eliminates the demand for supplemental fuel.
This approach is a solution to the problem of maintain-
ing a high volatile solids content with a low moisture
content; however, coal is not a refuse material, and the
utilization of coal to improve filtration and increase the
fuel value of the furnace feed is a substitution of one
fossil fuel for another, not a replacement of fossil fuel
with a material of little current value. On the other hand,
coal is considered to be an available fuel as compared
with other fossil fuels, and this approach could be ap-
propriate in some parts of the country.
Two plants, Rochester, N.Y., and Vancouver, Wash.,
are experimenting with sawdust as a filter aid prior to
combustion. The results to date have been very good
but detailed data are not yet available.
There are currently many sludge and solid waste co-
combustion systems, including incineration and pyrolysis,
that are being operated, tested, or demonstrated in full-
scale plants. Codisposal technology is continually being
revised and updated because of this ongoing work.
However, the systems described herein have been oper-
ated at full-scale, have been thoroughly reviewed and,
although not necessarily fully developed, have sufficient
background to be implemented wherever the particular
system proves cost-effective.
Coincineration Methods (Sludge and Mu-
nicipal Refuse)
Coincineration of sewage sludge with raw municipal
refuse has historically not been successful in convention-
al solid waste incinerators. Incomplete combustion of the
22
-------
sludge indicated that failures were due to inadequate
contact of the sludge and refuse, high sludge water
content and inadequate detention time in the furnace.
Generally, it appeared that existing solid waste incinera-
tors were not easily adaptable to sludge incineration,
and that mixing of the sludge and refuse prior to incin-
eration was not feasible because of the variation in size,
density and composition of the materials commonly
found in municipal wastes; however, several systems are
currently in operation which have been specifically de-
signed to incinerate solid waste with sewage sludge, and
these are described herein.
Fluid Bed
Municipal solid waste and sewage sludge have been
coincinerated in a fluid-bed furnace in Franklin, Ohio,
since 1971, which began as an EPA-supported resource
recovery demonstration project. A wet pulper removes
ferrous metal and heavy solids from 150 tons (136 Mg)
per day of shredded refuse. Fiber is recovered from the
pulper effluent by selective screening and elutriation, and
all unrecovered residuals are conveyed to a barrel thick-
ener. Sludge from a 2.5-Mgal/d secondary treatment
plant is added to the thickened residuals, and the com-
bined stream is dewatered in a cone press to solids
content of 45 percent before injection into the furnace.
The furnace feed is blown into the bed about 1 ft over
the truyeres. There is a buildup in bed volume with this
coincineration scheme, and a small amount of bed mate-
rial must be removed periodically from the furnace. The
preparation steps reduce the amount of noncombustible
material in the furnace feed to between 3 and 6 per-
cent. Feed size is 1/2 in. (1.27 cm) or less. A detailed
review of this system is presented in reference 2.
In a normal dry shredding and separation operation,
the feed stock would not be as uniform as it is at
Franklin, Ohio. If the feed to the fluid-bed furnace is not
uniform in both size and density, material will tend to sift
downward through the bed. This material must be re-
moved quickly or it could upset the air flow through the
bed. Systems are in operation which can continuously
remove settled noncombustible material from the bed.
Waterwall Combustion
Three waterwall combustion units in Europe are pres-
ently incinerating solid waste and sewage sludge. At
Dieppe, France, 54 tons (49 Mg) of solid waste and 21
tons (19 Mg) of dried sludge are incinerated daily. Di-
gested sludge with a solids content of 4 percent is
pumped from the wastewater treatment plant and dried
with 350° F process steam in two thin film evaporators
to a solids content of 55 percent. The vapors generated
are returned to the furnace. The dried sludge is con-
veyed to the charging chutes of the furnace and is
mixed with the solid waste from the receiving pit. A
small plant at Brive, France, is similar to Dieppe except
raw sludge is used rather than digested sludge.
A waterwall combustion unit at the Krefeld plant near
Dusseldorf, Germany, processes 600 tons (544 Mg) of
solid waste and 45 tons (41 Mg) of dried sewage solids
daily. The facility generates electricity for the wastewater
treatment plant, the incineration facility, and exports hot
water for use in the community. Raw sludge with a
solids content of 5 percent is pumped from the waste-
water treatment plant to the disposal facility. The sludge
is centrifuged to a solids content of 25 percent and
then flash-dried with 1500°F flue gases in a vertical
shaft flash drying chamber. The powdered sludge is then
suspension-fired by injection into the furnace immediately
above the top of the flame. The facility has been in
operation for 2 years.
Incineration With Flue Gas Drying
Two plants in the United States use the flue gases
generated in a solid waste refractory lined incinerator to
dry the sewage sludge prior to combustion with solid
waste. In Ansonia, Connecticut, sludge with 4 percent
solids is dried in a disk type cocurrent spray dryer with
1200°F incinerator flue gases. Dried sludge and vapors
are injected into the incinerator for suspension burning.
The plant capacity is 200 tons (181 Mg) per day of
solid waste. Presently the sludge is not being incinerated
but is being used as a soil conditioner. Holyoke, Mass.,
utilizes a similar incinerator and averages 50 tons (45
Mg) per day throughput; however, the sludge is dewater-
ed to 28 percent solids prior to drying in a rotary drier
using hot flue gases. Dried sludge and vapors are also
suspension fired.
Incineration With Furnace Drying
Recently at Norwalk, Conn., a process was tested in
which a stoker-fired incinerator was used to coincinerate
sludge and solid waste. In this project the sludge cake,
with a solids content of 5 percent, was sprayed onto
the front wall of the charging chute to form a thin
sludge layer on top of the refuse. The sludge layer dries
and burns during the 30 minutes residence time in the
incinerator. This process has been incorporated into the
design of a plant at Glen Cove, N.Y., which will burn a
mixture of 12.5 percent sludge (at 20 percent solids)
and 87.5 percent refuse. The plant is designed to pro-
duce 2.2 megawatts of power, sufficient to meet the
demands of the sewage treatment plant and the inciner-
ation facility. The Glen Cove facility is currently in con-
struction and should be completed in three years.
Multiple-Hearth
Several plants in England and Europe have been prac-
ticing coincineration in multiple-hearth furnaces for sever-
al years; however, serious problems such as severe ero-
sion of the hearths, poor temperature control, refractory
failures, and air pollution have accompanied these proj-
ects. All of these problems appear to be a direct result
of poor preprocessing of solid waste prior to addition
into the furnace. Poor preprocessing causes extreme
variations in feed heat value which in turn causes wide
23
-------
and uncontrollable temperature variations in the furnaces
and results in refractory failures and air emission prob-
lems. Also, metals are usually not removed; therefore,
hard objects are dragged across each hearth, causing
erosion problems.
These problems were resolved in test work conducted
at the Central Contra Costa Sanitary District operated
wastewater treatment plant at Concord, Calif. All refuse
was shredded, air classified and screened prior to use.
This test work, when the furnace was operated in an
incineration mode, showed none of the problems en-
countered in England or Europe except that temperature
control was still difficult. This was corrected by operat-
ing the furnace in a pyrolysis (starved-air combustion)
mode, described further under copyrolysis. Based upon
European experience and the test work in Concord,
coincineration of raw solid waste and sludge in a multi-
ple-hearth furnace does not appear to be a viable proc-
ess.
Copyrolysis Methods (Sludge and Munici-
pal Refuse)
Partial pyrolysis and true pyrolysis have been applied
by several furnace manufacturers to the combustion of
solid waste, but there are only three partial pyrolysis
systems (more correctly, starved-air combustion) that
have been operated on sewage sludge and solid waste.
Only one system, using the multiple-hearth furnace, used
a sludge furnace with solid waste as the fuel source.
The other systems are solid waste combustion systems
modified to permit the addition of wet sludge. This basic
difference allows the multiple-hearth furnace to operate
on 100 percent sludge to 100 percent refuse, while the
other systems must have a refuse-to-sludge wet ratio of
at least 2:1. The key to any pyrolysis process is to add
less air than is required for complete combustion in the
reactor. The combustible gas produced in the reactor is
fired in an afterburner, providing an efficient two-stage
combustion process.
Multiple Hearth
Copyrolysis of sludge with processed municipal solid
waste in an MHF was first successfully performed in a
small-scale test in November 1974. Recognizing scale-up
problems, a full-scale prototype test was implemented as
described under "Sludge Pyrolysis" and further herein. A
flow diagram of the test system is given on figure 7-12.
The test MHF pyrolyzed a combination of sewage sludge
TO
ATMOSPHERE
LIVE BOTTOM
TRUCK
SLUDGE
FROM
PLANT
PLANT EFFLUENT
FROM LAGOON
NATURAL GAS
COMBUSTION
AIR FAN
Figure 7-12.—Central Contra Costa test project flow diagram.
24
-------
and refuse-derived fuel (RDF) in several ratios from pure
sludge to pure RDF.
Municipal refuse was shredded, air classified and
screened to produce a refuse-derived fuel. The RDF had
a heating value of 7,500 Btu (17,400 J/g) per pound of
dry solids and a moisture content of 25 percent. A
combined feed rate of up to 10,000 pounds (4,540 kg)
per hour was applied to the 6-hearth, 18 ft 9 in. (5.71
m) diameter MHF. Because of the addition of RDF, the
heat value of the feed was greatly increased as com-
pared to sludge alone. This resulted in a fuel gas heat
value averaging 136 Btu/sdcf (5066 kJ/m3) and after-
burner temperatures up to 2500° F. The furnace was
controlled by regulating the addition of air to maintain
hearth temperature. This approach proved to be a sta-
ble, dependable control system.
Significant results of the test, in addition to that noted
under "Sludge Pyrolysis," include:
• RDF should be fed to a midfurnace hearth and
sludge to the top or second hearth to maximize
energy conversion.
• The ash handling system must be capable of han-
dling small amounts of metal.
• Autogenous combustion of a 16 percent solids
sludge cake could be accomplished with an RDF-
to-sludge wet ratio of 1:2.
This type of system is being reviewed for several
Table 7-9.—Material and heat balance for copyrolysis of municipal refuse and sludge in a multiple-hearth
furnace3
Alternate
Stream
IA
5 Mgal/d
20 percent
solids
IB
5 Mgal/d
40 percent
solids
IIA
15 Mgal/d
20 percent
solids
MB
15 Mgal/d
40 percent
solids
IMA
50 Mgal/d
20 percent
solids
1MB
50 Mgal/d
40 percent
solids
Furnace design
Diameter (ft-in.)
Number of hearths
Hearth loading rate (Ib wet solids/sq ft/hr)
Sludge feed
Ib dry solids/hr
Percent of total furnace feed
Volatile content (percent)
RDF feed
Ib dry solids/hr
Percent of total furnace feed
Volatile content (percent)
Percent moisture
Combined feed rate
Total Ib wet solids/hr
Heat value (MM Btu/hr)
Total furnace inlet air (Ib/hr)
Ash
Volume (Ib/hr)
Heat value (MM Btu/hr)
Afterburner inlet air
Volume (Ib/hr)
Afterburner exhaust
Volume (Ib/hr)
Heat value (MM Btu/hr)
Radiation
Heat loss (MM Btu/hr)
Recoverable heat
100 percent efficiency (MM Btu/hr)
Connected power
Horsepower
Installed cost (MM dollars)
22-3
6
11.4
1,806
50
77
7,224
50
84
20
18,060
20.28
12,753
1,749
0.50
34,123
63,186
62.45
1.62
33
555
2.8
16-9
7
10.8
1,806
50
65
4,267
50
84
20
10,664
11.12
7,320
1,589
0.46
25,867
42,260
40.80
1.12
29
343
2.2
25-9
6
11.8
2,713
50
77
10,850
50
84
20
27,126
30.71
19,316
2,627
0.76
51,049
94,861
92.39
2.33
60
725
3.0
18-9
8
11.3
2,713
50
65
6,400
50
84
20
16,000
16.38
10,782
2,384
0.69
39,065
63,461
61.29
1.61
37
418
2.4
25-9
9
12.5
4,293
50
77
17,172
50
84
20
42,930
47.29
29,747
4,158
1.20
81,838
150,355
146.05
3.57
100
725
3.5
22-3
8
12.1
4,293
50
65
10,128
50
84
20
25,320
25.53
16,806
3,772
1 09
112,888
151,240
97.68
2.45
60
555
3.0
aAII data supplied by the Eimco BSP Division of Envirotech Corp.
25
-------
plants with implementation expected for the Central Con-
tra Costa Sanitary District and the city of Memphis.
Energy and mass balances for copyrolysis of sewage
sludge and RDF in an MHF are given in table 7-9 for
the selected treatment plant alternative. The addition of
RDF to sludge could provide for more efficient heat
recovery, due to higher afterburner temperatures. This in
turn could permit combustion of wet sludges without
supplemental fuel.
Vertical Packed Bed
There are two vertical packed bed solid waste partial
pyrolysis systems currently operating in the United
States: Andco-Torrax and PUROX.
The Andco-Torrax system is a vertical furnace in
which unprocessed municipal solid waste is charged into
the system from the top. This ram of refuse provides a
combustion seal. The refuse is burned at the bottom of
the ram at 3000° F by the addition of small quantities of
hot air heated by the afterburner exhaust. The combusti-
ble off-gases are afterburned at 2000° F and scrubbed
by electrostatic precipitators. Wet sludge has been add-
ed to an existing 75-ton-per-day (68 Mg) system but no
detailed test data are presently available.
PUROX, a Union Carbide process, is a vertical fur-
nace pyrolyzing a processed refuse. Processing includes
shredding and ferrous metal separation. The PUROX
process uses pure oxygen rather than air. The refuse is
combusted at 3000° F, and fuel gas very low in nitrogen
with a heat value of 385 Btu/sdcf (14,340 kJ/m3) is
produced. The slag produced at the high combustion
temperature is primarily silica and is inert. A test pyro-
lyzing processed refuse and sludge was sponsored by
EPA and successfully run on the test unit at South
Charleston, W. Va., for 2 months. Daily average wet test
feed rates were 90 tons (82 Mg). The test report has
been submitted to EPA for review but has not yet been
published. Significant test results include:
• A refuse to sludge ratio of 4.26:1 was pyrolyzed.
Lower ratios were not tested due to the limited
availability of sludge.
• Pure oxygen feed rate was approximately 0.2 ton
(0.2 Mg) of oxygen per ton (0.9 Mg) of feed.
• Fuel gas production and quality, and slag produc-
tion and quality do not differ radically from refuse
pyrolysis.
• Heavy metals in the sludge were found to be
trapped in the slag and not discharged via the
exhaust gases.
Institutional Constraints
Coincineration and copyrolysis of sewage sludge with
municipal solid waste is a viable, cost-effective, and so-
cially beneficial approach to the solids handling problem.
Not only are both solid waste streams disposed in an
environmentally acceptable manner, but benefits can be
accrued by utilizing the waste heat or combustible ex-
haust gases for energy conservation. Although the tech-
nical feasibility of copyrolysis and coincineration of
sludge and solid waste has been demonstrated, there
remain a number of institutional constraints that may
have to be resolved prior to implementation of a codis-
posal project.
In many localities in the country, wastewater treatment
and solid waste disposal are controlled by different gov-
ernmental agencies. Many communities have contracts
with private firms for refuse handling and disposal which
release ownership of the refuse to the contractor. Some
of the contracts are long-term, lasting 15 to 20 years.
Although there have been legal opinions that these
agreements can be modified for the benefit of the pub-
lic, these opinions have not been tested in court. In
recent waste disposal contract negotiations, local gov-
ernments have retained the ownership of the refuse with
the private firm acting strictly as a collector and hauler.
Retaining ownership of the waste material would simplify
resource recovery operations.
Consolidation of the governmental agencies which are
responsible for solid and liquid waste disposal would
also simplify disposal operations; however, with more
emphasis on codisposal techniques by both federal and
state agencies, serious institutional problems may be re-
solved by governmental interaction with local agencies.
Jurisdictional disputes could prove to be more of an
impediment than technical difficulties of the codisposal
process.
Funding
Funding of codisposal projects is a very complex issue
because several federal, state, and local agencies are
involved and there are many departments within these
agencies which can also fund projects. To further com-
plicate the total project funding picture, the ownership o1
the nonsewerage facilities (municipal solid waste, indus-
trial wastes, etc.) can be either public or private. Be-
cause of this, EPA has developed a memorandum, PRM
#77-4, entitled "Cost Allocation for Multiple Purpose
Projects."
While this memorandum has been used in recent proj-
ects to determine fundable costs, some projects cannot
be distributed equitably by this method due to a compli-
cated cost distribution formula, impact of operation and
maintenance costs, and the basic philosophy differences
between a single-purpose and a multiple-purpose project.
For instance, if solid waste is used to combust sludge
when no solid waste problem exists, is there a solid
waste savings as defined by the memorandum? This
memorandum is not a regulation or a guideline but sim-
ply one method which may be used.
A few states have instituted guaranteed loan programs
for bonding solid waste projects and some financial con-
sultants are beginning to specialize in solid waste
project funding. Also, several solid waste equipment
manufacturers have designed, built and operated large
resource recovery solid waste projects to produce RDF
and recover metals.
The method and type of funding for these cocombus-
26
-------
tion projects appears very open but obtaining the funds
demands considerable time and effort.
AIR POLLUTION CONSIDERATIONS
In any combustion system, air emissions are a major
concern and may be the most difficult and costly regula-
tions to satisfy. On the federal level, EPA has establish-
ed standards of performance for municipal incinerators
(solid waste) and sewage sludge incinerators. In cocom-
bustion schemes involving municipal solid waste and
sewage sludge, both standards will probably apply with
each being prorated on a Btu feed basis. In January
1978, EPA published proposed emission standards of
performance for new, modified or reconstructed electric
utility steam generating units that burn fossil fuel or a
combination of fossil fuels and other fuels, e.g., solid
wastes. These guidelines offer some indication of air
pollution requirements in cocombustion schemes.
Generally, new sludge furnaces will have to comply
with the following federal standards:
• National Ambient Air Quality Standards.
• National Emission Standards for Hazardous Air Pol-
lutants, subparts A and E.
• Standards of Performance for New Stationary
Sources, subparts A, O and probably E if cocom-
bustion is proposed.
• New Source Review Rule
• Regulations Pertaining to Prevention of Significant
Deterioration of Air Quality.
A basic problem in evaluating any emission is predict-
ing the effect on the overall air basin. Projecting emis-
sion and the resulting air quality is, at best, an imperfect
science. Air basins in which critical air quality levels are
consistently exceeded have been studied in depth and
have been the object of mathematical modeling. The
results of these efforts have been mixed.
National Ambient Air Quality Standards
(NAAQS)
Federal air quality regulations are derived from the
Clean Air Act Amendments of 1970, the Energy Supply
and Environmental Coordination Act of 1974, and most
recently, the Clean Air Act Amendments of 1977. The
NAAQS are designed to protect public health and wel-
fare and are established at threshold levels below which
no adverse effects would occur. Air pollutants are di-
vided into two groups: primary pollutants and secondary
pollutants. Primary pollutants are those emitted directly
from sources, while secondary pollutants are formed by
chemical and photochemical reactions in the atmosphere.
Primary pollutants include carbon monoxide (CO), hydro-
carbons (organic gases), oxides of nitrogen (NOJ, sulfur
dioxide (SO2), and total suspended particulates (TSP).
Photochemical oxidants and nitrogen dioxide (NO2) are
the principal secondary pollutants. Nitrogen dioxide is
the visible brown-yellow haze. The formation of secon-
dary pollutants is dependent upon the availability of sun-
light as much as the emission of primary pollutants that
are converted to secondary pollutants. Health effects of
contaminants are summarized in table 7-10. Federal pri-
mary standards are to be achieved in 1977 and secon-
dary standards in a reasonable period of time, whereas
state standards are considered goals without a specified
time for compliance.
The 1970 Amendments to the Clean Air Act require
the States to develop implementation plans to meet the
Federal standards by 1975 or 1977, depending on the
severity of the State's air quality problems. The 1977
Amendments have delayed attainment deadlines and
have detailed some appropriate control measures. For
"nonattainment areas," those which have not yet at-
tained NAAQS, states must have an approved implemen-
tation plan revision by July 1, 1979, which provides for
attainment by December 31, 1982. If a State cannot
obtain primary standards for carbon monoxide or photo-
chemical oxidants, it must submit a second plant revision
by December 31, 1982, which provides for attainment by
December 31, 1987. For areas which are cleaner than
NAAQS, implementation plans must include a program to
prevent significant deterioration of air quality. EPA guide-
lines require the implementation plans to provide for
emission controls, transportation controls, source moni-
toring, ambient air quality monitoring, and a procedure
for review and approval of new sources of air pollution
prior to construction. EPA has the authority to approve
or disapprove these plans and to promulgate an accept-
able plan if the submitted plan is disapproved. EPA,
state air resources boards, and local air pollution control
districts also have the authority to restrict issuance of
permits for construction of stationary sources if emis-
sions from that source would cause the violation of any
air quality standard. In both nonattainment and nondeg-
radation areas, major stationary sources may be con-
structed only by permit and must at least meet new
source performance standards.
National Emission Standards for
Hazardous Air Pollutants (NESHAPS)
Subpart A of NESHAPS comprises general provisions
covering definitions, applications, reporting and waivers.
Subpart E deals with mercury and applies to all opera-
tions that burn or dry sewage sludge. The NESHAPS
standard (Federal Register, vol. 40, No. 199, Tuesday,
October 14, 1975) is currently 3,200 grams or 7 pounds
of mercury per 24-hr period. Beryllium is also controlled,
and several other air contaminants such as lead and
PCB are currently under study for possible inclusion into
NESHAPS.
Standards of Performance for New Sta-
tionary Sources (NSPS)
Subpart A of NSPS involves general provisions cover-
ing definitions, performance tests, authority, monitoring
requirements, etc. Subpart A is applicable to all incinera-
tors with a charging rate greater than 50 tons (45 Mg)
27
-------
Table 7-10.—Health effects of air pollutions
Pollutant levels
Air quality
level
TSP
(24-hour),
ng/m3
SO2
(24-hour),
ng/m3
CO
(8-hour),
mg/m3
03
(1-hour),
iug/m3
NO2
(1-hour),
jug/m3
Health
effect General health effects
descriptor
Cautionary statements
Significant harm.
1,000
2,620
57.5
1,200
3,750 Hazardous
Emergency.
875
2,100
40.0
1,000
3,000 Hazardous
Warning.
625
1,600
34.0
800
2,260
Very
unhealthful
Alert...
375
800
17.0
a400
1,130 Unhealthful
Premature death of ill
and elderly. Healthy
people will experi-
ence adverse symp-
toms that affect their
normal activity.
Premature onset of
certain diseases in
addition to signifi-
cant aggravation of
symptoms and de-
creased exercise tol-
erance in healthy
persons.
Significant aggravation
of symptoms and
decreased exercise
tolerance in persons
with heart or lung
disease, with wide-
spread symptoms in
the healthy popula-
tion.
Mild aggravation of
symptoms in suscep-
tible persons, with ir-
ritation symptoms in
the healthy popula-
tion.
All persons should re-
main indoors, keep-
ing windows and
doors closed. All
persons should mini-
mize physical exer-
tion and avoid traf-
fic.
Elderly and persons
with existing dis-
eases should stay
indoors and avoid
physical exertion.
General population
should avoid outdoor
activity.
Elderly and persons
with existing heart
or lung disease
should stay indoors
and reduce physical
activity.
Persons with existing
heart or respiratory
ailments should re-
duce physical exer-
tion and outdoor ac-
tivity.
NAAQS
50 percent of NAAQS . .
260
C75
0
365
C80
0
10.0
5.0
0
160
80
0
b
b
b
Moderate
Good
a400 fig/m3 was used instead of the O3 Alert Level of 200 fig/m3 (see text).
bNo index values reported at concentration levels below those specified by "Alert Level" criteria.
°Annual primary NAAQS.
Source: EPA, Environmental News, August 23, 1976.
per day with municipal refuse comprising more than 50
percent of the charge. Subpart E requires that particu-
lates discharged be no greater than 0.08 grain/sdcf
(0.18 g/m3), corrected to 12 percent carbon dioxide.
Subpart O is applicable to incinerators that burn munici-
pal sewage sludge and requires that particulates dis-
charged cannot be in excess of 1.30 pounds (0.65
kg/Mg) per ton of dry sludge feed and that the gas
discharged shall not have more than 20 percent opacity.
New Source Review Standards (NSR)
This regulation, 40 CFR 52.18, requires a preconstruc-
tion review of all stationary sources to determine if the
source will meet all applicable emission requirements of
the State Implementation Plans.
The reviewing authority is usually a state agency
which can apply more strict emission standards than the
EPA regulations. In areas where the NAAQS is being
28
-------
violated, emission trade-offs, or offsets, in the air basin
may be required prior to acceptance of the new source.
Prevention of Significant Deterioration
(PSD)
Federal Regulation, 40 CFR 52.21, limits increases in
particulate and sulfur dioxide concentrations above base
levels measured in designated areas. Data on total emis-
sions for the entire air basin are required to evaluate
incremental increases in specific emissions due to opera-
tion of any new furnaces.
SYSTEM DESIGN
Determining the feasibility of a solids disposal system
entails the review of many components of the system.
Each acceptable solids disposal system must meet all
environmental constraints while being an economical and
feasible system. In evaluating the effectiveness of a fur-
nace system, important considerations are:
Sludge quantity and quality.
Installed cost of the equipment.
Method and cost of housing the system.
Local air pollution requirements.
Methods of funding.
Supplemental fuel costs including start-up fuel,
standby fuel, fuel availability, etc.
Pretreatment options.
Operation and maintenance costs.
Ash disposal options and costs.
Equipment redundancy requirements.
Type of operation, continuous or intermittent.
Emergency methods of sludge handling.
Institutional constraints.
Many other detailed design considerations must be
analyzed as set forth previously in this paper. Heat re-
covery must be analyzed in any combustion process.
There are no strict guidelines to the review of a furnace
system, but experience and review of existing systems
with a consultation of various equipment manufacturers
provide an excellent foundation.
DESIGN EXAMPLES
Two design examples are presented to demonstrate
some of the principles introduced in this paper. The first
example involves the selection of an incineration system
to replace the existing sludge handling system at a small
wastewater treatment plant. The second example consid-
ers retrofitting an existing multiple-hearth furnace in a
large municipal wastewater treatment plant to meet
changing values of plant capacity, air emissions, fuel
cost and fuel availability.
Design Example 1: New Sludge Incinera-
tion System
The first design example involves a small treatment
facility with a sludge handling system that must be re-
vised to minimize increasing disposal costs.
Problem Statement
A municipal wastewater treatment plant with an aver-
age daily flow of 5 Mgal/d (0.22 m3/s) must modify its
present solids handling and disposal method. The plant
uses a conventional activated sludge process with anaer-
obic digestion of combined primary sludge, waste acti-
vated sludge, and scum. The digested sludge is vacuum
filtered and is hauled to the local landfill which is sched-
uled to close shortly. The new disposal location must
limit the water discharged to the site and is several
miles from the treatment plant. These conditions result in
extremely high disposal costs. Onsite disposal options
are limited because the area surrounding the plant has
been heavily developed by meat packing and rendering
operations. These industries discharge significant am-
ounts of animal greases and oils to the treatment plant
and are concerned about finding an economical solution
to the sludge disposal problem because of the large
industrial sewer service charges. Most of the industrial
wastes discharged to the plant are removed in the pri-
mary tanks and result in a combined scum and sludge
with an extremely high heating value. The basic plant
data are shown in table 7-11.
Approach
The city hired a consultant to evaluate several dispos-
al methods including land disposal, composting, heat
treatment, combustion and continuation of the present
operation. A cost-effective solution was identified to be
combustion due to the high energy content of the
sludge and the limited available land for sludge disposal.
Digestion would be eliminated so that the full heat value
of the sludge could be utilized in combustion eliminating
all supplemental fuel requirements. The existing digesters
would be converted to sludge thickening/storage units
Table 7-11.—Design Example 1: wastewater treatment
plant operating data
Parameter
Value
Plant flow, Mgal/d 5
Sludge to disposal, Ib/day dry basis 10,320
Solids heat value, Btu/lb dry basis 11,000
Volatile solids to digester, percent of dry solids 77
Sludge solids content, percent solids by weight 20
Vacuum filter operation, hr/week 40
29
-------
Table 7-13.—Design Example 1: heat and material
balances for a fluid bed furnace
Stream, unit
Value
with the existing vacuum filters remaining to provide an
incinerator feed solids content of approximately 20 per-
cent.
Presently, the vacuum filter operates 6 to 8 hours a
day, 5 days a week. Due to the limited plant area, there
is no room for filter cake holding facilities and the fur-
nace will therefore be designed to operate in conjunc- Furnace design
tion with the vacuum filters. A review of the various inside diameter, ft-in 15.0
furnace systems indicated that because of the high heat- Loading rate, it> wet soiids/sq ft/hr'"^^^]]]\]".'.'.'.'. 51^2
ing value of the sludge, the intermittent operation re- Sludge feed
quirement and the space limitations, a fluid bed furnace ib dry soiids/hr 1,810
would be the most cost- and energy-effective furnace Heat value, MMBtu/hr 19.91
solution. Volatile solids, percent dry solids 77
Supplemental fuel 0
Preliminary Design C°SmobI 22,950
The data in table 7-12 were given to experienced Heat value, MMBtu/hr 5.40
fluid bed furnace manufacturers for analysis including As,h, tj u
heat and material balances. Table 7-13 was provided by ™umeb/d* ~'f.^ "!
the manufacturers and shows all sizing criteria as well wSr *ow gaT/mm °>o
as requirements for peripheral equipment. For intance, Radiation
416 dry Ib (188.7 kg) per hour of ash must be disposed Head loss, MMBtu/hr 1.27
for each hour of furnace operation. The amount of ash Recoverable heat
storage, ash truck size, and frequency of runs to the 100 percent efficiency, MMBtu/hr ae.o
landfill can be calculated from this number based upon Recuperator Yes
site specific constraints including the method of ash de- venturi water
watering. Also, the amount of scrubber water recycled to Recycle water, gai/min 94
the plant is shown so the extra load to the liquid waste 0 Makeup water at 70°F' 9al/min 5
stream can be determined. S™bb^watrcfeec^
As is evident herein, the detailed design of the com- scSSef i dS, "
plete system actually starts with the data provided by Flow at 130°F, gai/mm 410
the furnace manufacturer. Air emissions must be studied Gas exhaust
and submitted to the local, state and federal authorities volume, ACFM 6,162
to obtain a permit to construct. Contracts for ash dis- Temperature, °F 120
posal should be developed to assure continued, depend- Connected power, np 240
able and economic disposal sites. Options for using startup fuel requirements
available excess heat should also be examined. Table weekday operation, 16-hour shutdown, MMBtu/hr o
7-13 shows 6.0 MMBtu per hour (1,758,000 W) are Monday morning °Peration' 64-hour shutdown, MMBtu/hr... "0.42
available for use; however, this is an intermittent heat
availability and intermittent demands are difficult to de- aAt 1,400°F.
termine. As an example, since the day shift staffing of bFuei required:
the plant is the largest, space heat and cooling loads 1 hour on Saturday.
would be larger during the day. To satisfy off-peak de- 1 nour on Sunday.
mands, heated and chilled water storage vessels may be 1/2 hour on Mondav morning.
economical rather than providing auxiliary fired boilers. Data suPP|ied bv Dorr-oiiver inc.
Table 7-12.—Design Example 1: sludge furnace design
criteria
Parameter
Value
Sludge feed
Solids content, percent by weight
Volatile solids content, percent of dry solids .
Heat value, Btu/lb of dry solids
Furnace operation, hr/week
Average solids loading rate, Ib/hr, dry basis....
20
77
11,000
40
1,810
Other design considerations to be investigated would
include but are not limited to:
• Scrubber and quench water quality, i.e., is secon-
dary effluent quality sufficient?
• Effect of scrubber return water on treatment plant
operation (quality, quantity and temperature).
Expected ash quality.
Ash dewatering methods.
Ash hauling methods: by city, by separate contract,
by other city departments.
Type of sludge conveyors.
Type and location of fans.
30
-------
Heat recovery methods.
Electrical distribution.
Control philosophy.
Sophistication of instrumentation and control.
Supplemental fuel availability and storage (for
start-up and problem periods).
Area clearance including access platforms.
Housing the furnace, i.e., is a building needed?
Structural requirements: seismic, wind, etc.
Noise levels and other OSHA requirements.
Heating, ventilating and cooling the area near the
furnace.
Spare parts.
Level and quality of staffing.
These points only relate to the installed system. Other
important considerations involve the interfacing of the
existing plant with the construction of the furnace. For
instance, it may be economically attractive to dispose of
the digested sludge at the plant in the furnaces prior to
converting the digesters to thickeners or there may be
site-specific scheduling problems. If the digested sludge
will be burned, this should be a part of the contract
documents in case minor additions are required. In any
case, all systems and details relating to the furnace
should be discussed with the furnace manufacturer and,
in some cases, made the responsibility of the furnace
manufacturer, e.g., the combustion air fans, the recuper-
ator (if used), the heat recovery boiler (if used), scrub-
bers, and some or all of the controls.
Design Example 2: Retrofit of an Existing
Multiple-Hearth Sludge Incinerator
This example involves retrofitting an existing sludge
incineration system to accommodate more stringent air
emission regulations and increasing quantities of sludge
due to area growth.
Problem Statement
A 20-Mgal/d (0.88 m3/s) domestic wastewater treat-
ment plant in the Midwest has been incinerating primary
and excess activated sludge in two multiple-hearth fur-
naces. All sludge is thickened prior to dewatering on
vacuum filters which provide a 25 percent solids feed
cake. Polymers are used in the vacuum filters. The ash
from the furnaces is sluiced to ash holding ponds and
the supernatant is recovered and returned to the plant
sewer. Stabilized ash is clammed at least once a year
and hauled to the local landfill.
Both multiple-hearth furnaces are used simultaneously
about 3 months of the year as the original design pro-
vided 100 percent redundancy and the plant is currently
overloaded for a portion of the year.
The growth in the present service area has been re-
duced in recent years to an E-O level, approximately 2
percent; however, the city is planning to annex several
more surrounding areas in the immediate future. Due to
the present overloaded conditions, anticipated growth,
and service area increases resulting in increased flows,
planning for a 10-Mgal/d (0.44 m3/s) expansion is cur-
rently underway which would provide for projected flows
through 1988. In addition, new air emission regulations
were recently promulgated limiting hydrocarbon, carbonyl
and carbon monoxide emissions to about half of the
current incinerator emissions. The city has been given
notice to correct this situation shortly or the local air
pollution control district (APCD) will begin levying fines.
The city has applied for and received a time extension
to review and correct this problem. The existing plant
data are shown in table 7-14.
Approach
The city had retained a consultant to prepare a facili-
ties plan/project report to obtain funding for the expan-
sion to 30 Mgal/d (1.31 m3/s) under the Clean Water
Grant Program. Due to the urgency of the experts air
emissions problem, the city had its consultant hire air
pollution experts to assist in the development of an in-
terim plan which would be consistent with the goals of
the expansion. The basic intent was that all interim emis-
sion control measures could be used in the expanded
facilities, therefore possibly affording grant funding for
the interim facilities.
Several methods for reducing critical emissions were
reviewed and after detailed design studies, including cost
estimates, afterburning at 1200°F for 1/2 second was
determined to be the most cost-effective solution which
could guarantee a continuous and dependable operation
while satisfying all regulations.
Since afterburning was proposed, it was also decided
to study starved air combustion (SAC) which could pos-
sibly increase the furnace capacity and/or reduce the
equipment to be added. Prior to reviewing SAC, it was
determined that each furnace would require an after-
burner and that a new furnace and afterburner would be
required for the plant expansion to 30 Mgal/d (1.31
m3/s).
Table 7-14.—Design Example 2: existing wastewater
treatment plant operating data
Parameter
Value
Treatment plant operating conditions
Design flow, Mgal/d 20
Total solids, Ib/day dry basis 40,800
Volatile solids, percent of dry solids 75
Furnace operating conditions
Operating hours/week 168
Loading rate, Ib/hr dry basis 1,700
Solids content of feed, percent dry weight 25
Loading rate, Ib/hr wet basis 6,800
31
-------
Table 7-15.—Design Example 2: heat and material balances for multiple-hearth furnaces
Exi^n9 Casel Case II Case
condition
Case IV
Type of operation
Furnace design
Number of furnaces
Diameter, ft-in
Number of hearths
Hearth loading rate, Ib wet solids/sq ft/hr
Afterburner
Sludge feed
Ib dry solids/hr ... .
Heat value, MMBtu/hr
Volatile solids, percent dry solids
Feed solids percent
Afterburner supplemental fuel, Ib/hr
Heat value, MMBtu/hr.. .
Temperature, °F
Furnace combustion air
Volume, Ib/hr ... . .
Shaft cooling air
Volume, Ib/hr
Shaft cooling air return to furnace
Volume at 350° F, Ib/hr
Shaft cooling air to stack
Volume at 350° F Ib/hr . . . . .
Heat value, MMBtu/hr
Shaft cooling air to afterburner
Volume at 350° F, Ib/hr
Ash
Volume, Ib/hr
Heat value, MMBtu/hr
Radiation
Heat loss, MMBtu/hr
Furnace exhaust
Volume at 800° F Ib/hr
Heat value, MMBtu/hr .
Afterburner combustion air
Volume at 60° F, Ib/hr
Afterburner exhaust
Volume, Ib/hr ....
Temperature, "F
Heat value, MMBtu/hr
Boiler exhaust
Heat value at 400° F, MMBtu/hr
Recoverable heat
100 percent efficiency, MMBtu/hr . . .
Precooler and Venturi water feed
Flow at 70 °F gal/min
Scrubber water feed
Flow at 70° F, gal/min
Scrubber drain
Flow gal/min
Gas exhaust
Volume, Ib/hr
Temperature °F
Heat value, MMBtu/hr
Combustion
2
16-9
7
70
None
1 700
12.75
75
25
0
60
17,833
15,939
13,548
2,391
0.35
0
425
0.04
0.29
24209
12.07
N A
N.A.
N A
N.A.
NA.
3.20
51
243
306
21,368
120
6.35
Modified
combustion
"3
16-9
7
70
External
1 700
1275
75
25
3.77
60
17,833
15,939
13,548
2,391
035
0
425
004
029
24209
1207
2555
26,764
1 200
15.84
9.51
6.33
51
243
306
20,759
120
7.53
SACa
b3
16-9
7
70
External
1 700
12.75
75
25
2.44
60
9,822
15,939
9,840
5,919
1 09
180
d478
014
0.29
16145
11 23
4296
19,366
1 200
14.05
8.78
5.27
45
282
338
15,480
120
4.11
SACa
b2
16-9
7
102
External
3473
26.05
75
35
0
60
12,507
15,939
12,480
0.0
00
3660
d975
0.28
0.29
21 454
14 87
11 534
32,987
1 430
24.24
13.92
10.32
65
456
536
26,220
120
8.52
SAC3
b2
16-9
C7
10.2
Internal
(top hearth)
2957
2218
75
35
0
60
9,867
15,939
9,867
0
0
6072
d866
025
029
17448
10.55
10989
28,437
1 200
21.64
458
6.13
65
456
532
27,837
120
2.64
N.A.—Not applicable.
aSAC—Starved air combustion.
bNumber of furnaces required in 1988, 30 Mgal/d for increased sludge quantities with one furnace on
standby.
°Note, top hearth is afterburner, therefore, not included in hearth loading calculations
Includes fixed carbon and volatile heat content.
32
-------
Preliminary Design
The data in table 7-14 was given to experienced mul-
tiple-hearth furnace manufacturers for analysis including
detailed heat and material balances for incineration fol-
lowed by external afterburning and starved air combus-
tion followed by external afterburning. Both cases used
the present sludge dewatering method, vacuum filters,
which provided a feed cake of 25 percent solids. Two
additional cases were studied using improved dewatering
equipment to give a feed cake solids of 35 percent.
These cases both used starved air combustion but one
had an external afterburner and the second used the
top hearth of the present furnace as the afterburner.
Capacities of the systems using the existing furnace(s)
were required.
Table 7-15 was provided by the manufacturers and
shows some very significant comparisons of incineration
versus SAC and the effect of improved dewatering. For
instance, converting the existing furnace to SAC with an
external afterburner would save 1.53 MMBtu/hr (448,000
W) as compared to adding an afterburner to the present
incinerators. This would result in an annual savings of
slightly over $30,000 which, in this case, would not justi-
fy the conversion, especially since the recoverable heat
from SAC would be less than incineration due to the
lower exhaust volumes.
A significant advantage is shown for case IV where
the top hearth of the existing furnace is used as an
afterburner resulting in large cost savings by not requir-
ing a separate afterburner. Also, by improving the dewa-
tering methods, the existing system would easily handle
the expected sludge loads through 1988, the design
year.
The fuel savings would result in an annual reduction
of plant operation expenses by almost $100,000 and the
energy generated would be sufficient to save another
$50,000 per year. These savings alone would justify cap-
ital expenditures of over $1,500,000. In addition there
would be a capital savings which would occur because
the addition of a third furnace would not be required.
After receiving detailed cost estimates, the city pro-
ceeded with the design of case IV. As noted in the
previous design example, the detailed design effort be-
gins with the data provided by the manufacturer. Details
for necessary furnace modifications for conversion to
SAC were noted earlier in the paper and other design
details are similar to those discussed in Design Example
1.
SUMMARY AND CONCLUSIONS
The ultimate disposal of wastewater treatment plant
sludges is a complex problem. New and emerging tech-
nologies in incineration, pyrolysis and starved air com-
bustion are providing solutions for the safe, clean, effi-
cient and inexpensive reduction of sewage sludge. Use
of alternate fuel sources in coincineration and copyroly-
sis can provide excess energy which can be converted
to steam for use within the treatment plant or for sale,
all while reducing overall plant operation and mainte-
nance costs.
Although many systems are still in the research and
development stage, systems similar to those tested by
the Central Contra Costa Sanitary District at Concord,
Calif., and by the city of Franklin, Ohio, can be imple-
mented using current technology and existing equipment.
ACKNOWLEDGMENTS
Credits
This paper was sponsored by the U.S. Environmental
Protection Agency under contract with the Office of
Technology Transfer, Cincinnati, Ohio. The data on py-
rolysis, coincineration, and copyrolysis represent several
projects funded by the U.S. Environmental Protection
Agency. Special thanks are extended to the following
manufacturers, listed in alphabetical order, for their as-
sistance: AFB Engineers/Contractors, exclusive U.S. li-
censees for the Lucas Cyclonic Furnace, Dorr-Oliver,
Inc., BSP Division of Envirotech Corp., Nichols Engineer-
ing & Research Corp., a subsidiary of Neptune Interna-
tional Corp., and Shirco, Inc.
BIBLIOGRAPHY
1. Niessen, W., Daly, A., Smith, E., and Gilardi, E. A Review of
Techniques for Incineration of Sewage Sludge With Solids Wastes.
EPA-600/2-76-288, U.S. Environmental Protection Agency, Cincin-
nati, Ohio, 1976.
2. "A Technical, Environmental, and Economic Evaluation of the Wet
Processing System for the Recovery and Disposal of Municipal
Solid Waste," Contract 68-01-2211, U.S. Environmental Protection
Agency, Office of Solid Waste Management, 1975.
3. Aberley, R. C., Sieger, R. B., Bracken, B. D., "Pyrolysis Gas Frorr
Solid Waste Will Provide Total Power Demand for a Major Waste-
water Reclamation Plant." Presented at the International Confer-
ence on Alternative Energy Sources, 1977.
4. Allen, Ken, Nichols Engineering & Research Corp., Personal Com-
munications, 1977
5. Allen, Terry, BSP Division of Envirotech, Personal Communications
1977.
6. Babcock and Wilcox, Steam, Its Generation and Use, 38th Edition
1975.
7. Booth, Phillip, Dorr-Oliver, Inc., Personal Communications, 1977.
8. Boyen, J. L, Practical Heat Recovery, John Wiley & Sons, 1975.
9 Bracken, B. D., Coe, J. R., Allen, T. D., "Full Scale Testing of
Energy Production from Solid Waste." Proceedings of the 1976
National Conference on Sludge Management, Disposal and Utiliza-
tion, 1976.
10. Bracken, B. D., Sieger, R. B, Coe, J. R., Allen, T. D., "Energy
from Solid Waste for Wastewater Treatment—A Demonstration
Project." Presented at the Annual Conference of the Water Pollu-
tion Control Federation, 1977.
11. Brown and Caldwell, "Central Contra Costa Sanitary District Solid
Waste Resource Recovery Full Scale Test Report," March 1977.
12. Cardinal, P J., Sebastian, F. P., "Operation, Control and Ambient
Air Quality Consideration in Modern Multiple Hearth Incinerators."
Proceedings of the 1972 National Incinerator Conference, 1976.
13. Combustion Fundamentals for Waste Incineration, American Societ)
of Mechanical Engineers, 1974
14. Corey, R. C., Principals and Practices of Incineration,
Wiley-lnterscience, 1969.
15. "Decision-Makers Guide in Solid Waste Management," SW-127,
U.S. Environmental Protection Agency, Office of Solid Waste Man-
agement Programs, 1976.
16. Dvirka, M., Bartilucci, N., "Co-Disposal of Sewage Sludge and
Municipal Refuse with Waste Heat Recovery." Presented at the
33
-------
Annual Meeting of the New York Water Pollution Control Associa- 31.
tion, 1977.
17. Dyer, James, Green Bay Metropolitan Sewage District Treatment
Plant, personal communication, May 1978. 32.
18. "Energy Conservation in Municipal Wastewater Treatment," Con-
tract 68-03-2186, Task 9, Culp/Wesner/Culp, U.S. Environmental
Protection Agency, Office of Water Program Operations, 1978. 33.
19. "Environmental Pollution Control Alternatives: Municipal Wastewa-
ter," EPA-625/5-76-012, U.S. Environmental Protection Agency, 34.
Office of Technology Transfer, 1976.
20. General Electric, Solid Waste Management Technology Assess- 35.
ment, 1975.
21. Glover, Charles, Erie Pennsylvania Wastewater Treatment Plant,
personal communications, May 1978. 36.
22. Hathaway, S. W., Olexsey, R. A., "Improving Incineration and
Vacuum Filtration with Pulverized Coal Addition," Journal of the 37.
Water Pollution Control Federation, December 1977.
23. Jacknow, Joel, "Environmental Aspects of Municipal Sludge Incin-
eration." Presented at the Fifth Conference on Acceptable Sludge 38.
Disposal Techniques, January 1978.
24. Jacknow, Joel, "Environmental Impacts from Sludge Incineration- 39.
Present State of the Art," WWEMA Sludge Furnace Technology
Committee, 1976.
25. Jones, J. L. "Municipal Refuse and Sludge Disposal Economics,"
Presented at the Fifth Conference on Acceptable Sludge Disposal 40.
Techniques, January 1978.
26. Jones, J. L., Bomberger, D. C., Lewis, F. M., and Jacknow, Joel.
"Municipal Sludge Disposal Economics," Environmental Science 41.
and Technology, vol. II, October 1977.
27. Jones, J. L., Bomberger, D. C., Lewis, F. M., "The Economics of
Energy Usage and Recovery in Sludge Disposal." Presented at
the Annual Conference of the Water Pollution Control Federation, 42
1976.
28. Kimbrough, W. C., Dye, L. E., "Pyrolysis of Sewage Sludge and
Refuse Combined." Presented at the First International Conference 4,
and Technical Exhibition on Conservation of Refuse to Energy,
Montreux, Switzerland, November 1975.
29. Lewis, F. Michael, "Sludge Pyrolysis for Energy Recovery and
Pollution Control." Proceedings of the 1975 National Conference
on Municipal Sludge Management and Disposal, 1975. 44-
30. McGinnis, F. K., Shirco, Inc., Personal Communications, November
1977.
Olexsey, R. A., "Pyrolysis of Sewage Sludge." Proceedings of the
1975 National Conference on Municipal Sludge Management and
Disposal, 1975.
Process Design Manual for Sludge Treatment and Disposal, EPA-
625/1-74-006, U.S. Environmental Protection Agency, Office of
Technology Transfer, 1974.
Roy, Guy, AFB Engineers/Contractors, Personal Communication,
1977.
Scharver, C. D., Union Carbide Corporation, Personal Communica-
tions, November 1977.
Shelton, R. D., "Stagewise Gasification in a Multiple Hearth Reac-
tor." Presented at the 175th Annual Meeting of the American
Chemical Society, Anaheim, 1978.
Shields, C. D., Boilers, Types, Characteristics, and Functions,
McGraw-Hill, 1961.
Sieger, R. B., Bracken, B. D., "Combined Processing of Wastewa-
ter and Solid Waste," AICHE Solids Symposium Series, October
1976.
Sieger, R. B., "Sludge Pyrolysis: How Big a Future?" Civil Engi-
neering - ASCE, May 1978.
Smith, E. M., Dely, A. R., "The Past, Present, and Future Pros-
pects of Burning Municipal Sewage Sludge Along with Mixed Mu-
nicipal Refuse." Proceedings of the 1975 National Conference on
Municipal Sludge Management and Disposal, 1975.
Smith, J. E., "Inventory of Energy Use in Wastewater Sludge
Treatment and Disposal," Industrial Water Engineering, July/-
August 1977.
Srinivasaraghavan, R., Wilson, T. E., DeLisle, K. R., "Evaluation of
Pyrolysis as a Wastewater Sludge Disposal Alternative." Presented
at the Annual Conference of the Water Pollution Control Federa-
tion, 1976.
Sussman, David B., "More Disposal Operations Mixing Sewage
Sludge and Municipal Solid Wastes," Solid Wastes Management,
August 1977.
Von Dreusche, C. Negra, J. S. "Pyrolyser Design Alternatives and
Economic Factors for Pyrolysing Sewage Sludge in Multiple Heartt
Furnaces." Presented at the 175th Annual Meeting of the Ameri-
can Chemical Society, Anaheim, 1977.
Wright, I. J., Sieger, R B., "The Multiple Hearth Furnace—An
Efficient Pyrolyser for Solid Wastes." Presented at the Annual
Conference of the American Institute of Chemical Engineers, 1977
34
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Chapter 8
Sewage Sludge Composting
INTRODUCTION
Most of the early work on composting was concerned
with composting municipal refuse. The University of Cali-
fornia, Michigan State University and the U.S. Public
Health Service were among the first to conduct basic
studies on composting in the United States.1'2 Two feder-
ally supported, large-scale research and demonstration
projects were inititated in the United States at Johnson
City, Tenn., and Gainesville, Fla. The Johnson City
project investigated the open-windrow method of com-
posting, whereas Gainesville employed a high-rate me-
chanical digester. These large-scale studies confirmed
the technical feasibility of composting domestic municipal
refuse and the lack of economic viability.3 The paper by
Wiles3 also contains a brief historical review of solid
waste composting.
Sewage sludge composting is a relatively recent devel-
opment in the United States. The Eimco Corp. conduct-
ed a study in 1967 to 1969 for the U.S. Public Health
Service on composting primary sludge from the Salt
Lake City Sewage Treatment Plant.4 In a project support-
ed by EPA, the U.S. Department of Agriculture, Agricul-
tural Research Service (USDA) in cooperation with the
Maryland Environmental Service and the Blue Plains
Wastewater Treatment Plant began investigating sludge
composting in 1972.5 This project is located on the
grounds of the USDA Agricultural Research Center at
Beltsville, Md., and the studies have demonstrated new
techniques in sewage sludge composting.6'7 Sludge com-
posting studies and demonstration projects are also in
progress at Bangor, Maine;8 Durham, N.H.; and the Los
Angeles County Sanitation Districts, at Carson, Calif.
Composting of wastewater sludge differs significantly
from composting solid wastes. There are several advan-
tages of composting sewage sludge compared to solid
waste and the past poor publicity and problems associ-
ated with solid waste composting need not discourage
the use of composting as an alternative in the treatment
and reuse of wastewater sludge.
1. Composting solid wastes requires a complex materi-
als handling and separation process that is not
necessary in sludge composting.
2. Solid wastes vary widely in composition and as a
result the composting process is usually more diffi-
cult to operate than a sludge composting system.
3. Several past solid waste composting operations
were evaluated on the basis of their profit making
potential rather than as an alternative disposal
method.
4. The per capita quantity of solid waste is several
times the wastewater sludge quantity; therefore,
marketing or disposal of solid waste compost is a
more difficult task.
5. Sewage sludge compost is a more uniform product
because plastics, metals and other materials often
remain in solid waste compost.
Present day composting is defined as the aerobic
thermophilic decomposition of organic solid wastes to a
relatively stable humus like material.9 The basic compost-
ing mechanisms are similar for any organic material and
are described in more detail in several publications.10'11
Modern composting actually involves both mesophilic and
thermophilic temperatures, and, since it is a biological
process, is subject to the constraints of any biological
system. Decomposition is accomplished by various mi-
croorganisms including bacteria, actinomycetes and fungi.
The principal byproducts of this aerobic decomposition
are carbon dioxide, water and heat.
Proposed sludge regulations in California define sludge
composting as follows:
Compost means to process dewatered sludge in a manner that (a)
exposes all portions of the sludge to air and to a temperature at
least 60 degrees centigrade for at least 48 hours; (b) subsequently
reduces the water content of the sludge to 40 percent or less, by
weight; and (c) sufficiently decomposes the sludge so that it will not
produce excessive odor or reheat above 40 degrees centigrade in
the center of a pile that is one meter high, one meter wide, and
one meter long, in a test wherein the sludge is remoistened to a
water content of 55 percent, by weight and held for four days, after
having undergone steps (a) and (b) above.
Sludge compost is a natural organic product with high
humus content similar to peat. It has a slight musty
odor, is moist, dark in color, can be bagged; the texture
varies depending on the degree of screening. Compost
increases the water holding capacity of sandy soils, im-
proves the structure of heavy clay soils, and increases
the air content of the soils. The organic matter in com-
post improves the workability of the soil and makes it
easier for plant roots to penetrate. Compost contains
small amounts of nitrogen, phosphorus and potash;
therefore, its primary usefulness is as a soil amendment
and not as a fertilizer. The typical compositions of
sludge and compost produced at Beltsville, Md., and
Bangor, Maine, are shown in tables 8-1 a and 8-1 b.
35
-------
Table 8-1 a.—Average composition of sludge and com-
post, Beltsville, Md.a
Table 8-1 b.—Average composition of sludge and com-
post, Bangor, Maine
Digested
sludge
Screened
compost
Pile Aa
Pile Ba
Dewatered filter cake
Water 80 35
Total solids 20 65
Solid fraction
Organic matter 50 50
Nitrogen 2.5 0.9
Phosphoric acid 2.7 2.3
Potash 0.6 0.2
Sulfur 0.9 0.4
Calcium 2.9 2.6
Magnesium 1.0 0.3
Boron 23 ppm 27 ppm
Heavy metals
Zinc 2,000 ppm 1,000 ppm
Cadmium 19 ppm 9 ppm
Copper 600 ppm 250 ppm
Lead 540 ppm 320 ppm
Microorganisms, MPN/100 g
Total conforms 23,000,000,000 97,000
Fecal conforms 2,400,000,000 3,000
Salmonella 6,000 0
aPercent by weight except where noted.
COMPOSTING SYSTEMS
General Process Description
The composting process may be physically achieved in
basically three types of systems: (1) windrow, (2) aer-
ated static pile, and (3) mechanical units of various de-
signs which usually supply continuous mixing and posi-
tive aeration. The windrow and static pile methods have
been used almost exclusively for composting sewage
sludge in the United States.
The basic steps in both the windrow and static pile
composting systems are similar and are illustrated in the
process flow diagram in figure 8-1. Several mechanical
composting systems are described later in this paper.
The sequential steps in the windrow and static pile
methods are as follows:
1. Dewatered sludge is delivered to the site and usu-
ally mixed with a bulking agent. The purpose of the
bulking agent is to decrease the moisture content
of the mixture, increase porosity of the sludge and
assure aerobic conditions during composting. Vari-
ous bulking agents can be used including wood
chips, bark chips and rice hulls. Unscreened fin-
ished compost has also been used. Generally, one
part sludge is mixed with two to three parts bulking
agent.
Constituent
Total sulfide
Total phosphorus
Total chloride
Total nitrogen
Cadmium
Copper
Chromium
Mercury
Nickel
Lead
Zinc . . .
Iron
Arsenic
Manganese0
Potassium0.
Calcium0
Magnesium0
Sodium0
Sludge
mg/kg
121 8
3002 2
661 8
1 9 350 0
4 78
2777
286
93 12
226
4080
4530
75500
039
1107
1 0150
144290
2 1980
2349
Screened
compost"
mg/kg
05
1 010 7
6944
8 6200
067
839
170
1 46
25 2
118 1
153 7
4 173 0
026
779 7
1 9460
23 689 0
36020
6980
Sludge
mg/kg
192 7
2 052 6
718 2
10 7100
0 92
1673
334
1902
348
2742
2820
1 3 708 0
1 73
295 0
1 7250
1 2 986 0
4 5250
3739
oC 1661160
compostb
mg/kg
0 5
787 3
762 3
6850 0
0 58
32 2
10 0
0 97
19 2
64 2
983
3 041 0
0 20
616 0
1 683 0
1 8 1 63 0
30660
274 9
"The sludge used in pile A and that used in pile B came from
separate batches processed through the sewage treatment plant more
than 6 months apart.
bOne inch mesh screen.
Increases noted in manganese, potassium, calcium, magnesium, and
sodium are due to the bark in the compost.
2. Piles are constructed by placing the sludge-bulking
agent mixture in windrows or static piles.
3. Piles are aerated for 21 to 30 days by mechanically
turning (windrow method) or by forced aeration
(static pile method). Oxygen levels are maintained
in the range of 5 to 15 percent of gas volume to
assure aerobic conditions. Temperatures in all parts
of the pile should be maintained at 60° C or above
for at least 48 consecutive hours.
4. Piles are dismantled and the sludge-bulking agent
mixture moved to a curing area for an additional 30
days. Curing provides time for additional stabiliza-
tion and drying. The curing piles are not mechani-
cally aerated.
5. The sludge-bulking agent mixture (compost) is
screened to recover and reuse the bulking agent. It
may be possible to screen the mixture before cur-
ing if it has dried sufficiently to permit screening
and to prevent the development of anaerobic condi-
tions. About 70 to 75 percent of the wood and
bark bulking agents have been recovered in opera-
36
-------
SLUDGE
MAKEUP
BULKING
AGENT
MIXING
2-3 porti bulking ogtnt
to t port sludgt
<
COMPOSTING
cirattd pil«
21 day«
1
DRYING
RECYCLE
,
CURING / STORAGE
30 doyt
BULKING AGENT
PRODUCT COMPOST
60 X (Olldl
Figure 8-1.—Aerobic composting.
tions at Beltsville and Bangor. The finished compost
can then be used or stored.
Research at the University of California and other lo-
cations developed some fundamentals of composting and
these are summarized by Golueke.10'11
1. Obtaining thermophilic temperatures requires no in-
put of external energy when the composting mass
is sufficiently insulated and favorable environmental
conditions are maintained for the biological organ-
isms.
2. No inoculation with external microbial cultures is
necessary either before, during or after the com-
posting process.
3. The relations between environmental factors and the
course of the process are characteristic of any
biological process.
The net result of the composting process is the partial
stabilization of organic material. Sludge is not completely
stabilized or rendered inert by composting because this
would result in end products of carbon dioxide, water
and mineral ash. Obviously this is not possible nor desir-
able in a composting system. The desired degree of
stability is one in which the product will not give rise to
nuisances when stored even if moisture is added. It was
observed in studies at the University of California that
attainment of a satisfactory degree of stabilization was
always accompanied by a final decline in temperature:
once the temperature had declined to about 45 to 50° C
the material was sufficiently stabilized to permit indefinite
storage.
Composting is a dynamic process representing the
combined activity of a succession of mixed populations
of bacteria, actinomycetes and fungi associated with a
diverse succession of environments, one overlapping the
other and each emerging gradually as a result of contin-
ual changes in temperature and substrate. The principal
environmental factors important in composting are mois-
ture, temperature, pH, nutrient concentration and avail-
ability, and oxygen concentration.
Moisture
The minimum moisture content at which bacterial activ-
ity takes place is from 12 to 15 percent. The moisture
content of composting material should be maintained in
the range of 45 to 50 percent. Most sludge composting
experience has been with sludge solids concentrations of
10 to 35 percent.
A recent paper by Haug and Haug12 discusses the
engineering and thermodynamic principles of composting
systems and concludes in part that:
Probably the single most Important variable in determining the suc-
cessful composting of sludge is the solids content produced during
dewatering. Moisture and volatile solids control, and the energy
budget for the system are largely influenced by this parameter.
Implementation of any composting system should be coupled with
serious consideration for maximizing dewatered cake solids. This
conclusion is valid regardless of the type of composting system,
whether windrow, aerated pile, or mechanical.
Temperature
Modern composting processes are designed to operate
within the mesophilic and thermophilic ranges. The range
of optimum temperatures for the composting process as
a whole is quite broad, probably from about 35° C to
65° C. The temperature of a reasonably large composting
mass will gradually rise to within the thermophilic range
due to excess energy from microbial activity. This in-
crease will inevitably take place unless positive measures
are taken to dissipate the heat or improper composting
procedures are used.
Sludge composting should reach thermophilic tempera-
tures for a significant period of time for several reasons:
(1) the optimum temperature for some of the organisms
involved in the composting process is within the thermo-
philic range, (2) most pathogenic organisms and weed
seeds cannot survive long exposure to thermophilic
temperatures, and (3) a composting mass will reach
thermophilic temperatures unless definite countermeas-
ures are taken to dissipate heat.
pH
In practical operations little can be or needs to be
done to alter the pH in a composting mass.
37
-------
Nutrients
One of the more important nutrient requirements in
composting is the carbon-nitrogen balance or ratio (C/N
ratio). Part of the carbon is lost as CO2 and carbon is
present in the cellular material in greater concentration
than is nitrogen; therefore, the amount of carbon re-
quired is considerably greater than nitrogen. The opti-
mum C/N ratio for most wastes falls within the 20 to 25
parts carbon to 1 part nitrogen range.
The more the carbon-nitrogen balance deviates from
the optimum, especially in the upper range, the slower
the process proceeds. However, the actual upper limit
for an individual application depends upon the degree of
availability of the carbon. The principal deleterious effect
of too low a C/N ratio is the loss of nitrogen through
the production of ammonia and its subsequent volatiliza-
tion. Apparently, any excess nitrogen ends up as ammo-
nia. As far as the composting process itself is con-
cerned excess nitrogen is not detrimental. Nutrient
concentrations and balances in most sludges are ade-
quate and not limiting to the composting process.
Oxygen
Optimum oxygen levels in a composting mass are be-
lieved to be between about 5 and 15 percent. Some
method must be employed to achieve these levels in any
aerobic composting method. Since the composting proc-
ess is aerobic, low oxygen levels will slow down the
process and may precipitate anaerobic conditions in
some parts of the composting mass. Excessively high
oxygen concentrations increase aeration expense and
may reduce temperature.
Windrow Composting
The windrow process is conducted in uncovered areas
and relies on natural ventilation plus periodic turning to
maintain aerobic conditions. The sludge-bulking agent
mixture is spread in windrows with a triangular cross
section normally 6 to 15 feet (1.8 to 4.6 m) wide and 3
to 5 feet (0.9 to 1.5 m) high. An alternative method to
mixing the bulking agent and sludge before forming the
windrow is placing the bulking agent as a base for the
windrow. The sludge is then dumped on top of the
bulking agent and spread. A composting machine (similar
to a large rototiller) then mixes the sludge and bulking
agent and forms the mixture into a windrow. Several
turnings (about 8 to 10 times) are necessary to ade-
quately blend the two materials.
The windrow is normally turned at least once per day,
with a composting machine, for a three week period, or
longer depending on the weather and efficiency of com-
posting. During rainy periods, turning is suspended until
the windrow surface layers dry.
In the initial studies by the USDA at Beltsville, Md.,
digested sludge was successfully composted in win-
drows.5'7 Fifty tons (45 Mg) of wet sludge (23 percent
solids) were composted daily. The windrow process was
found to be unsatisfactory for composting undigested
primary and waste activated sludges because offensive
odors were produced. Also, survival of conforms and
salmonella was extensive, with indications of regrowth,
as material in the center of the compost windrows was
shifted to the exterior when the windrows were turned.
The unsatisfactory performance of the windrow process
for composting undigested sludges led USDA research-
ers Epstein, Willson and their coworkers to develop a
forced aeration, static pile method.67
The County Sanitation Districts of Los Angeles are
currently composting an anaerobically digested and cen-
trifuged primary sludge in the windrow process. Previ-
ously composted sludge is mixed with dewatered sludge
in a 1:3 ratio, formed into windrows and composted for
21 days or longer. Mixing, forming, and turning the win-
drows are accomplished with mobile equipment. Approxi-
mately 100 dry tons (91 Mg) per day of 35 percent
solids cake from solid bowl centrifuges were composted
during a five year period beginning in 1972. Finished
compost with a moisture content of approximately 40
percent is sold to Kellogg Supply Co. Kellogg hauls the
compost to its nearby plant for further processing and
packaging and pays for the compost on a royalty basis.
The composted sewage sludge is blended with other
ingredients to form various specialized soil conditioners.
The basic product is marketed under the trade name
Nitrohumus. Kellogg has developed several garden soil
conditioning and fertilizer products as well as offering
soil testing and analysis services. These products and
services are marketed within a radius of about 300 miles
(482 km) directly to large users, such as golf courses,
commercial nurseries, and stadiums, and through retail
outlets such as nurseries, garden stores and chain
stores.
Studies were conducted by the Los Angeles County
Sanitation Districts on the effects of windrow turning
frequency on temperature, moisture content, volative sol-
ids content and survival of microorganisms.13 Windrow
turning frequencies ranged from three turns per day to
one turn every three days. Turning was accomplished by
passage of a Cobey Rotoshredder lengthwise through
the windrows. Samples were collected from various
points in the piles and tested including analyses for
human parasitic worms, bacteria and virus. Conclusions
from these studies include the following:
1. Temperatures as high as 60 to 65° C were
achieved during compost cycles when rain did not
occur and when the composting apparatus was
consistently available throughout the cycle. It was
concluded that more frequent turning produced
temperatures above 60° C for longer periods of
time. Ambient temperature, rainfall, and composter
malfunctions caused temperatures in the interior of
the compost windrows to reach only 55 to 60 °C
during winter months.
2. Human parasitic ova were monitored and intact ova
of Ascaris lumbricoides, Trichuris trichiura, and
hookworm were isolated throughout the compost
38
-------
cycle. However, viability testing of these ova indi-
cated that viable parasites are consistently present
only through the first week and a half of compost-
ing. Viable Ascaris ova were isolated in only three
of the final compost samples collected during this
study. Six of 116 samples collected after more than
one and a half weeks of composting contained
embryonated Ascaris.
3. Total coliform and salmonella concentrations were
rapidly reduced within the first week and a half of
composting. Final compost coliform concentrations
of less than one MPN per gram were obtained
during warm weather composting in samples collect-
ed in the interior of compost windrows. Exterior
windrow samples were not below one MPN per
gram with consistency. Final compost salmonella
concentrations of <0.2 MPN per gram were ob-
tained in both interior and exterior samples collect-
ed from warm weather compost cycles. Regrowth
of salmonella during winter compost cycles was
observed, but it was not determined whether poor
winter performance was due mainly to climate or
failure of the composter.
4. Reduction of human pathogen concentrations to be-
low the level of detection was achieved with great-
er frequency than achievement of the coliform
standard of less than one MPN per gram dry
weight. Assays of virus, parasitic ova, and salmonel-
la yielded negative results in the vast majority of
final compost samples; whereas total coliform con-
centrations in final compost samples were not uni-
formly below one MPN per gram.
In early 1977 the Los Angeles County Sanitation Dis-
tricts installed second stage basket-type centrifuges that
treat the centrate from the first stage solid bowl centri-
fuges. This method of operation increased the total
sludge produced from about 100 dry tons (91 Mg) per
day to about 275 dry tons (249 Mg) per day and in-
creased the moisture content from an average of about
65 percent to about 80 percent. This increased moisture
content has created odor problems in the windrow com-
posting process while there had been no odor problem
with composting the drier sludge. The Sanitation Districts
and LA/OMA are investigating odor prevention proce-
dures and alternative methods of composting such as
forced aeration and the use of bulking agents other than
composted sludge.
Forced Aeration Static Pile Composting
In the forced aeration static pile process the pile re-
mains fixed, as opposed to the constant turning of the
windrow, and a forced ventilation system maintains aero-
bic conditions. The static pile system developed by
USDA for composting undigested sludge is illustrated in
figure 8-2. The forced aeration system is in routine op-
eration at Beltsville, Md., Bangor, Maine, and Durham,
N.H. A system is under design for Camden, N.J. and
pilot test work is in progress by LA/OMA at the Los
8-IO
SCREENED
COMPOST
DEODORIZING
PILE
BLOWER
SCREENED COMPOST
OR BULKING AGENT
UNSCREENED COMPOST
OR BULKING AGENT
CROSS SECTION
Figure 8-2.—Forced aeration static pile composting. Developed by the
U.S. Department of Agriculture, Beltsville, Md.
BULKING AGENT
AND SLUDGE
PERFORATED PIPE
39
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Angeles County Sanitiation Districts plant in Carson,
Calif.
Beltsville, Md.
Operations at Beltsville are described in several re-
ports and articles.5"7-14'15 This program is supported by
EPA and operated jointly by the Maryland Environmental
Service and USDA. Most of the Beltsville compost is
provided free of charge to public agencies and it must
be picked up at the site. As of January 1978 the Mary-
land State Department of Public Health will permit the
use of this compost by individuals; however, the demand
exceeds the supply and very little has been used by
individuals to date.
As previously described, digested sludge was success-
fully composted at Beltsville by the windrow process.
Static pile composting studies at Beltsville have been
conducted with: (1) combination of primary and second-
ary undigested sludges, (2) 75 percent undigested and
25 percent anaerobically digested sludge, and (3) anaer-
obically digested sludge. The results of these studies
were reported by Epstein et al.6 Data on pathogen re-
moval was reported by Surge et al.16 It was concluded
that:
1. Either digested or undigested sludge can be com-
posted in an aerated pile without releasing objec-
tionable odors.
2. Destruction of total coliforms, fecal conforms, sal-
monella and virus was much greater than windrow
composting. Survival of microorganisms in the lower
corner of the triangular shaped piles was believed
to be a result of the lack of insulation, or compost
depth, and resulting heat loss in this section.
Currently, 50 tons (45 Mg) per day, 5 days per week
are composted by the aerated static pile process at
Beltsville. Undigested sludge cake (approximately 23 per-
cent solids) from the Washington, D.C., Blue Plains
wastewater treatment plant is delivered to Beltsville in 10
wet ton (9 Mg) loads by conventional 3 axle dump
trucks. Two trucks are used and each truck makes 3
trips per day. Delivery generally begins early in the
morning and continues into early afternoon. Prior to the
sludge delivery, pads of bulking agent are prepared in
the mixing area. These pads are 9 to 10 feet (2.7 to 3.0
m) wide, 1 to 2 feet (0.3 to 0.6 m) deep and as long as
required for the bulking agent to sludge ratio mix for
one truck load of sludge.
The sludge trucks arrive on site, are weighed, and
then the sludge is dumped onto the bulking agent pad.
A front loader is used to spread the sludge evenly over
the top of the bulking agent. A Terex composter then
moves along one side of the sludge-bulking agent pad
and then along the other side, mixing the materials
toward the middle to form a partially mixed windrow of
triangular cross section. A Roto-Shredder then passes
through the windrow, turns around, and passes back
through the windrow. This operation mixes the sludge
and bulking agent to form a relatively homogeneous
blend. The Terex composter and Roto-Shredder are both
used because they are available at Beltsville. Satisfacto-
ry mixing can be accomplished using either machine
alone. Mixing can also be accomplished using only the
front loader, but is more time consuming to produce a
good mix.
Beltsville has been using the extended pile forced aer-
ation composting configuration. Material is added to the
pile each day and aeration pipes are spaced about ev-
ery 8 feet (2.4 m) on center. The composting pad for
each day's sludge-bulking agent mixture is prepared by
laying out the aeration piping on the asphalt composting
pad and covering this pipe with a 12-inch (0.3 m) layer
of wood chips using a front loader. The sludge-bulking
agent mixture is then placed on the wood chip base
using a front loader. The mixture is piled to a height of
about 8 feet (2.4 m). The top and ends of the pile are
then capped with an 18-inch (0.5 m) layer of unscreenec
compost or a 12-inch (0.3 m) layer of screened com-
post. At the end of each day's operation the side of the
pile (which will be added to the next day) is covered
with a thin layer of compost. A 1/3 horsepower (0.25
kW) blower rated at 335 cubic feet (9.49 m3) per minute
is connected to the piping. A 5 cubic yard (3.8 m3) pile
of screened compost is placed over the end of the
blower discharge piping for deodorizing the discharged
air. The blower pulls air through the composting pile and
discharges to the deodorizing pile. The blower is gener-
ally operated on an on-off cycle controlled by a timer.
Currently, blowers are operated 8 minutes on and 12
minutes off in 20 minute cycles.
Generally, compost is removed from the opposite end
of the extended pile each day, or every other day, after
21 days of composting. This part of the pile is disman-
tled using a front loader and is moved to the curing
pile. The aeration pipe is a light weight plastic consid-
ered expendable and therefore, is moved with the com-
post. The compost stays in the curing pile for at least
30 days, usually for a much longer period, awaiting
screening or off site use. The unscreened compost can
be stored for long periods depending on the needs of
the particular operation and the screening and compost
distribution operations.
Processing of the dewatered raw sludge cake and
formation of the compost pile must be carried out on a
regular basis consistent with raw sludge delivery. Raw
sludge is mixed with bulking agent (wood chips pur-
chased from local contractors and lumberyards) and
processed into a compost pile promptly as it is received
on site to avoid odors. Raw sludge is not stored on
site. Should site conditions or weather shut down opera-
tions (there are practically no instances of this occurring
at Beltsville) sludge would not be delivered but would be
either stored at the Blue Plains plant or diverted to
other disposal sites.
Screening is used to separate the wood chips from
the compost so that: (1) a portion of the chips can be
reused, (2) the final product has a finer particle size,
and (3) the carbon-nitrogen ratio of the finished compost
40
-------
is decreased. Most screening is performed with a 5/8
inch (1.59 cm) mesh rotary drum screen. The drum is 7
feet (2.1 m) in diameter and about 14 feet (4.3 m) long.
The tilt of the drum and the feed rate are adjustable.
Screening can be scheduled independent of other opera-
tions because of unscreened compost storage availabili-
ty. In practice, however, enough compost is screened to
meet: (1) any onsite need, (2) the demand from users,
and (3) to provide room in the unscreened storage area
for current production. Compost is screened at all times
when the temperature is above freezing and it is not
raining. Peak hourly capability of the drum screen with
fairly dry material is about 50 cubic yards (38.2 m3).
However, under actual conditions of startup, shutdown,
cleanup, and typical breakdowns, the input drum screen
capability is about 150 to 250 cubic yards (114.7 to
191.1 m5) per day. The screen is mounted on wheels
and can be moved with the front loader for cleanup.
Other site operations include regular cleanup of work
areas, receipt and storage of bulking agent, loading and
measurement of finished compost for users, and equip-
ment maintenance.
The staff at Beltsville consists of 8 people: 2 adminis-
trative and 6 operating. This number is more than actu-
ally needed for normal operations. The additional person-
nel are used for special operations and to support the
research demonstration program. The operating staff is
highly trained. Each member is qualified on each piece
of equipment and the staff is able to perform all preven-
tative maintenance and much of the repair work. Person-
nel and equipment are available for the composting op-
eration full time. A list of equipment is shown in table
8-2.
The approximate materials quantities used in the Belts-
ville operation are shown in table 8-3. These quantities
are based on: (1) annual undigested sludge cake (ap-
proximately 23 percent solids) input of 15,000 wet tons
(13,600 Mg), (2) ratio of 2.1:1 wood chip bulking agent
to sludge cake by volume (this is the ratio now being
Table 8-2.—Beltsville equipment
2 Terex rubber tired front loaders, 4.5 cu yd
2 dump trucks, 10 ton, 3 axle
2 flat bed trucks, 1.5 ton
2 pickups
2 rubber tired farm tractors, one with loader
1 rotary screen with power unit
1 Sweco screen, fixed (new)
1 mobile rotary screen, small (not used)
1 Terex composter
1 Imco Roto-Shreader
1 large conveyor with engine drive (not used)
1 Fixed Toledo truck scale
1 mobile office
1 storage building
1 lot small equipment and hand tools
Table 8-3.—Beltsville materials requirement for 15,000
wet ton annual sludge input
Limed raw sludge, wet tons 15,000
Solids, percent 23
cu yd 20,700
Density, Ib/cu yd 1,450
dry tons 3,450
Extended pile construction
Sludge, cu yd 20,700
Bulking agent
mixing w/sludge, cu yd 51,750
pile base, cu yd 8,100
Pile cover
screened compost, cu yd 12,000 (12 in. cover)
unscreened compost, cu yd 18,000 (18 in. cover)
Individual pile construction
Sludge, cu yd 20,700
Bulking agent
mixing w/sludge, cu yd 51,750
pile base, cu yd 17,000
Pile cover
screened compost, cu yd 24,000 (12 in. cover)
unscreened compost, cu yd 36,000 (18 in. cover)
used at Beltsville), and (3) 5/8 inch (1.59 cm) screening
of all compost for wood chip recovery and recycle of 70
percent (the wood chip loss/attrition rate at Beltsville is
currently about 20 to 25 percent).
Output or production quantities are shown for both a
12-inch (0.3 m) screened compost pile cover and an 18-
inch (0.5 m) unscreened pile cover in table 8-4. The
unscreened compost production is based on 15 percent
reduction in sludge volume during composting and cur-
ing. This example serves only to illustrate general con-
cepts because the materials loss through composting
and curing are estimated and have not been precisely
documented at existing operations.
Bangor, Maine
Composting began at Bangor in August 1975 and op-
erations are described in detail in two recent reports.8'14
The city of Bangor, Maine, has a permanent year-round
population of 38,900 residents of whom 32,000 are
served by the sewage treatment plant. The 32,000 resi-
dents provide a flow of about 3 Mgal/d (0.13 m3/s) to
the plant. Commercial and industrial establishments pro-
duce an additional 1 Mgal/d (0.04 m3/s) and 0.7
Mgal/d (0.03 m3/s) respectively, for a base flow of
about 4.7 Mgal/d (0.20 m3/s). Infiltration and storm wa-
ter runoff contribute an additional 2.3 Mgal/d (0.10
m3/s), making the average total flow about 7 Mgal/d
(0.31 m3/s).
This flow receives primary treatment consisting of pas-
sage through bar screens, settling in primary sedimenta-
tion tanks, and prechlorination. Sludge is pumped from
the primary sedimentation tanks through a hydrocyclone
41
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Table 8-4.—Approximate materials output, Beltsville type operation
Case3
Net
unscreened
compost
production,
cu yd
Net
screened
compost
production6
cu yd
Bulking agent, cu yd
Total
required
Recycled
Net used
(new make-up)b
Extended pile with:
Screened compost cover
Unscreened compost cover ...
Individual piles with:
Screened compost cover
Unscreened compost cover . . .
82260
87,660
101 070
111,355
39170
35,210
51 570
43,351
59,850
59,850
68750
68,750
43100
52,450
49500
68,000
16,750
7,400
19,250
750
Materials input shown in table 8-3.
bDoes not reflect actual Beltsville operations because only a portion of the Beltsville compost is
screened.
Assumptions
1. 15 percent reduction in sludge volume during composting and curing.
2. 10 percent of the bulking agent lost in composting and curing cycle.
3. 20 percent of the bulking agent lost in screening (passing through screen into finished
compost).
4. 15,000 wet ton annual sludge input.
for grit removal. The sludge flows by gravity to two
sludge thickeners and is then pumped to a conditioning
tank where lime and a polymer are added. The pH of
the conditioned sludge is 11 to 12 and is dewatered by
vacuum filtration.
The treatment plant currently produces about 3,000
cubic yards (2290 m3) or 2,500 tons (2270 Mg) per year
of vacuum filtered sludge with an average solids content
of 20 percent. The vacuum filters are operated about 70
times per year, producing 40 to 60 cubic yards (30.6 to
45.9 m3) of sludge each time.
Undigested raw lime conditioned sludge cake (approxi-
mately 25 percent solids) is delivered from the treatment
plant, in 5 to 7 cubic yard (3.9 to 5.4 m3) containers by
a single lift and carry type truck, to the composting site
located at the Bangor International Airport approximately
3 miles (4.8 km) from the treatment plant. Generally, the
raw sludge is dewatered, delivered, and composted once
a week; on occasions twice a week. Usually the dewa-
tering operation is started the day before so that all
available sludge containers are filled the morning com-
posting is to commence.-Sludge hauling to the site be-
gins early on the morning of composting. An operator
and 4 cubic yard (3.1 m3) front loader are at the site on
the day of composting. As the containers of sludge are
delivered to the site, they are dumped on a previously
prepared bed of bulking agent in the mixing area, mixed
with the front loader, and the compost pile is formed
over a previously prepared base. Generally, one com-
posting pile is constructed per week and typically con-
sists of approximately 40 to 60 cubic yards (30.6 to
45.9 m3) of raw digested sludge cake mixed in 1:3 ratio
with about 120 to 180 cubic yards (91.7 to 137.6 m3) of
bulking agent. Approximately 6 to 8 trips must be made
to the site to deliver the sludge cake. The mixing and
pile construction requires about 10 hours.
Bark is currently used as a bulking agent. Most com-
posting piles are mixed in a 3:1 ratio of bulking agent
to sludge cake. The bark consists of a wide range of
particle sizes from very fine to 18 inches (0.5 m) long.
When the bark moisture content is less than 50 percent
it is satisfactory for composting. Moisture is a problem
during rainy weather because the bark is stored outside.
During winter, there is little rain and the bark is quite
satisfactory.
The base for the compost pile is prepared using 7
feet (2.1 m) lengths of perforated schedule 40 steel pipe
jointed together by short pieces of plastic pipe. The city
found that the short lengths of steel pipe can be re-
moved from the pile without significant damage and
reused many times. Longer pipes were used previously,
but were easily bent when pulled from the pile. The city
has been experimenting with many different pile configu-
rations. Currently, no base material is used; the sludge-
bulking agent mixture is placed directly on the pad and
aeration pipes. The city has also satisfactorily used un-
screened compost as the bulking agent in a number of
piles. Unscreened compost has been used up to three
cycles as bulking agent with good results which has
dramatically reduced requirements for new bulking mate-
rial. The city plans further tests using unscreened com-
post as bulking agent.
The compost piles are constructed as high as the
front loader can reach and capped with 1 to 2 feet (0.3
to 0.6 m) of unscreened compost. The finished pile is 10
to 12 feet (3.0 to 3.7 m) high. The blower is then
42
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operated on an on-off cycle drawing air through the pile.
It was found that during cold weather all available
heat must be conserved to bring the piles up to temper-
ature. Reuse of unscreened compost provides a warm
bulking agent. The interiors of the bark storage piles are
also sources of warm materials for mixing. Generally, if
the sludge-bulking agent mixture can be maintained at
about 4°C the pile will perform much better than if the
mixture falls below 4°C. Recycle of warm exhaust air
from an older composting pile into the new pile is also
helpful for the first few days. The exhaust air from an
older composting pile is very wet and will cause high
moisture levels in the new pile receiving the air if used
for more than the first several days. The city has also
purchased a heater to provide initial heat to the piles.
The piles are composted at least 21 days. Tempera-
ture and oxygen levels are monitored every 2 to 5 days
during the composting cycle. The blower operating cycle
is adjusted according to the performance of the pile.
The aeration pipes, blowers, and moisture traps are
checked for freezing during cold weather because of the
large amount of moisture drawn through the aeration
piping.
At the end of the composting cycle the pile is disman-
tled, usually at the time another pile is constructed. The
material removed from the pile is either used as the
bulking agent for the new pile or is transferred to cur-
ing.
Raw sludge is not stored at the compost site, but is
stored at the plant. Generally, operations are scheduled
so that sludge is dewatered and a compost pile con-
structed once a week. The exact day of pile construc-
tion is varied depending on weather conditions. The city
has been able to compost nearly all of the sludge pro-
duction simply by selecting a good day each week for
compost pile construction.
A Lindig rotary drum screen is used to screen com-
post prior to distribution. The drum is presently fitted
with a 1-inch (2.54 cm) mesh screen. City personnel are
planning to construct a 5/8-inch (1.59 cm) screen as-
sembly so that either size material can be produced.
Tests performed at Bangor indicate that the screen is
capable of handling about 20 to 25 cubic yards (15.3 to
19.1 m3) (900 pounds per cubic yard (533 km/m3)) of
feed per hour under the best conditions. Compost is put
in the screen with a front loader. One loader operator
and a laborer are required during operation.
Currently, operations at Bangor are being performed
by treatment plant personnel under the direction of the
treatment plant superintendent. There are no full time
composting personnel because of the cyclical nature of
the operations. Approximately 11 hours per week are
required at the site, primarily for loader operation. In
addition, approximately 9 hours per week are required
for a truck driver to deliver sludge to the site. Sampling
and monitoring for temperature and oxygen content re-
quires 10 hours per week not including the pathogen
and heavy metals monitoring which is performed under
contract by the University of Maine. The supervision and
administration requirements are about 15 hours per
week. Annual equipment and labor requirements are
shown in table 8-5.
The equipment used for composting operations is
shown in table 8-6. This equipment is provided by the
city motor pool and is available for composting when
needed.
The approximate materials quantities based on 1976
sludge volume for the Bangor operation are shown in
table 8-7. These quantities are based on an annual
sludge input of 3,000 cubic yards (2290 m3) and a mix-
Table 8-5.—Estimated annual operations requirements,
Bangor, Maine3
Operation
Labor Equipmen
hours hours
Composting, labor
front loader
Sludge hauling, labor
truck
Monitoring, labor
pickup
Administration, labor
Screening (8,000 cu yd), labor.
screen
front loader
Maintenance, labor
572
468
520
780
1,040
100
468
468
520
520
520
aThis table is based on information provided by the city of Bangor
personnel.
Table 8-6.—Bangor equipment
1 case W24B rubber tired front loader, 4 cu yd
1 rubber tired front loader, 1.5 cu yd
1 truck, sludge container hauling
1 mobile screen, Lindig
Small tools as required
Miscellaneous vehicles as needed from motor pool
Table 8-7.—Bangor materials requirements
for 2,170 wet ton annual sludge input
Limed raw sludge, wet tons 2,170
solids, percent 23
cu yd 3,000
Density, Ib/cu yd 1,450
dry tons 500
Static pile construction
sludge, cu yd 3,000
bulking agent, cu yd 9,000
pile cover, cu yd 1,560
43
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Table 8-8.—Approximate materials output, Bangor type operation
New or recycled bulking agent
Unscreened compost from pile
Unscreened
compost
from
pile
Case3
used in pile construction
used as bulking agent for one cycle ....
used as bulking
agent
for two cycles...
Net
unscreened
compost
production,
cu yd
10,920
6,240
4,654
Net
screened
compost
production,
cu yd
4,160
3,198
2,785
Bulking agent, cu yd
Total
required
9,360
4,680
3,114
Recycled
6,760
3,042
1,868
Net used
(new make-up)
2,600
1,638
1,246
"Materials input shown in Table 8-7.
Assumptions
1. 15 percent reduction in sludge volume during composting and curing.
2. 10 percent of the bulking agent lost in each composting and curing cycle.
3. 20 percent of the bulking agent lost in screening (passing through screen into finished compost).
4. 2,170 wet ton annual sludge input.
Table 8-9.—Compost pile performance, Bangor, Maine, 1975-76
Pile
number
1A .
2B
3C
4A
5B
6C
7A ..
8B ....
9A
10B
11C
12A
13B
14C
15A
16B
17C
18A
Compost
period
8/19- 9/10
8/26- 9/15
9/2 - 9/25
9/10-10/2
9/23-10/10
10/2 -10/17
10/8 -10/31
10/15-10/31
11/7 -12/4
11/13-12/23
12/3 -12/23
12/10-12/23
1/13- 2/5
1/15- 2/5
2/12- 3/8
2/23- 3/12
3/1 - 3/29
3/9 - 3/30
Days to
peak
emperature
4
7
5
8
15
8
7
13
11
17
20
14
20
11
20
20
15
17
Days
above
55° C
8
14
21
17
g
12
18
10
18
0
1
3
15
10
7
9
17
10
Peak
temperature,
°C
67
83
65
67
72
76
76
67
62
50
61
60
66
58
60
74
71
70
Average
temperature,
°C
58
60
60
62
63
75
73
62
58
50
61
60
60
58
58
71
68
68
Average
ambient
temperature,
°C
15
15
16
15
11
10
7
7
3
-5
-11
-12
-5
-6
-2
-5
0
5
Average
02
(percent)
17
17
18
17
13
13
12
12
12
12
9
14
15
15
14
11
10
10
ture of 3 parts bulking agent to one part sludge. The
calculated materials production is shown in table 8-8 for
three assumed cases. These production outputs assume
a 15 percent reduction in sludge volume during com-
posting and curing and one inch screening of compost
before distribution. Recovery of bark is estimated at 70
percent by either screening and/or recycle of the un-
screened compost as bulking agent.
Performance data are summarized in table 8-9 for 18
piles which were composted during 1975-76. The mois-
44
ture content of the bulking agent varied widely from 40
to over 60 percent. Bulking agent used in piles 10B,
11C, and 12A was wet, very fine, and somewhat decom-
posed. Bulking agent of more uniform and larger size
would probably have produced more consistent results.
Durham, N.H.
The city operates a primary treatment plant and pro-
duces approximately 15 cubic yards per week of raw
-------
dewatered (15 percent solids) primary sludge. The plant
is to be expanded to secondary treatment and sufficient
land is not available for the projected requirements for
sludge spreading. As a result, the city set up a test
program for evaluating aerated static pile composting
and obtained a grant through the New Hampshire De-
partment of Public Health. The purpose of the test was
to determine: (1) whether proper composting could be
accomplished outdoors in a severe northern climate and
(2) composting costs.
Approximately 15 cubic yards (11.5 m3) per week of
raw primary sludge was composted on a temporary 1.75
acre (0.71 ha) site. Operations were conducted similar
to those at Beltsville except air was drawn from the
piles for 12 days and then blown into the piles for the
rest of the period. It was found that temperatures would
drop after 12 days if the air flow were not reversed.
Wood chips were used as a bulking agent. Sludge-bulk-
ing agent mixing was accomplished with a combination
of a front loader and motor grader.
The test operation was considered successful and the
treatment plant and composting operation will be up-
graded and expanded. This expansion will include a
mechanized aerated static pile composting operation
which will incorporate a number of materials handling
features. Much of the materials handling will be accom-
plished with fixed equipment as opposed to the mobile
equipment used previously. General operations will in-
clude the following:
1. Mechanized movement of sludge and bulking agent
and measuring of the components to a specified
ratio.
2. Mechanized mixing of sludge and bulking agent
with fixed equipment to obtain adequate and con-
sistent results independent of weather.
3. Mechanical movement of the mixture to the desig-
nated composting area and rapid construction of
the pile.
4. Mechanical screening of compost and direct place-
ment in curing bins (five months storage in year
2025).
5. A front loader will be used to form the piles, dis-
mantle the piles, load the compost into the screen,
transfer bulking agent from the storage bin to the
mixer feed hopper and transfer finished compost
from the curing bins to trucks.
The new Durham facility will be designed for produc-
ing approximately 10 cubic yards (7.6 m3) of compost
per day initially and 17 cubic yards (13.0 m3) by 2025.
The area required for composting is 15,000 square feet
(1394 m2), but with all appurtenant requirements such as
sludge processing building, storage areas, roadways, and
truck washing areas the total requirement is 3.5 acres
(1.4 ha). The total estimated construction cost for the
facility is $658,000 not including land and sludge dewa-
tering equipment.
It is anticipated that the dewatering and composting
facility will be staffed by 2 persons based on an 8 hour
shift. For 2 or 3 days a week, these people will operate
the facility with 5 hours a day for operations and the
other 3 hours for clean-up, start-up and shutdown. The
remaining days will be devoted to clean-up, maintenance
and compost screening and testing. The work force will
increase to an anticipated 6 persons in the year 2025
for the dewatering and composting operation.
LA/OMA
The LA/OMA project is supported by the city of Los
Angeles, Los Angeles County Sanitation Districts, Orange
County Sanitation Districts, State of California and the
Environmental Protection Agency. The LA/OMA staff, its
consultants and the member agencies are conducting
comprehensive management studies for the approximately
900 dry tons (816 Mg) per day of sludge produced in
the Los Angeles metropolitan area. Included in these
studies are pilot tests and demonstration projects for
various sludge treatment methods.
Forced aeration static pile composting is one process
currently being tested. The test systems include two
10x10x10 feet (3.1 x 3.1 x 3.1 m) insulated concrete
bins and several Beltsville type piles. Various bulking
agents and operating modes are being studied in the
concrete bins. Composted sludge, redwood chips and
rice hulls in various proportions are being tested in the
Beltsville type piles.
Mechanical Composting Systems
The early composting tests by Eimco were conducted
with a mechanical composting unit.4 The paper by Wiles3
briefly describes several types of mechanical composting
units in use throughout the world. Most of these units
compost refuse and none are in service composting
sewage sludge in the United States. The following sec-
tions briefly describe three mechanical systems that have
some experience in processing sludge and may be use-
ful in some applications in the United States. No attempt
has been made in this paper to describe all mechanical
systems available. The description of the following three
systems is intended to provide general information on
the types of available systems and does not imply that
other systems are inferior or that those systems de-
scribed herein are preferable to other systems.
Fairfield Digester System
The Fairfield Engineering Co.
Marion, Ohio
(614) 387-3327
The Fairfield Digester is a circular vessel. Aerator au-
gers are suspended from a bridge that travels around
the top of the digester wall. Integral units of the bridge
include: (1) drive machinery to rotate the bridge, (2)
machinery for the multiple aerator augers, and (3) a
conveyor which transports incoming material from an
overhead center hopper to the place where it enters the
digester near the wall. The material is aerated and
moved toward the center discharge by the action of the
45
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multiple augers. A conveyor at the bottom of the digest-
er removes digested material. Air is forced into the di-
gester by a motor driven blower and distributed through-
out the material by pipes.
Self-generated temperature of approximately 150 de-
grees Fahrenheit is produced and maintained by the
metabolism of the aerobic-thermophilic microorganisms
multiplying within the waste material. No starter inocu-
lants or external heat are used. The speed of the au-
gers, the rate of rotation of the carriage assembly and
the amount of air introduced into the digester are con-
trollable to obtain optimum temperature and correct re-
tention time of material in the digester. Sensors provide
the means for automatic control. They measure condi-
tions at a number of locations within the digester and
provide automatic adjustment of controls which maintain
desired operating conditions.
From May 27, 1969, through July 7, 1969, the Fairfield
Digester at Altoona, Pa., which normally is utilized com-
mercially for processing garbage collected from the city
of Altoona, was used to process 459 tons (416 Mg) of
vacuum filtered raw sludge cake (75 percent moisture)
from the primary clarifiers of the sewage treatment
plant.17 The volume of the sludge cake was reduced
approximately 65 percent during a seven-day processing
cycle.
The Fairfield Digester at Altoona is 38 feet (11.6 m) in
diameter and, with a depth of material of 6 feet (1.8 m),
has a capacity of 25 tons (23 Mg) per day organic
input containing 58 percent moisture and weighing 30
pounds per cubic foot (480 kg/m3). The digester is to-
tally enclosed with air pipes in the bottom which receive
forced air from the plenum chamber by means of motor
valves that are operated automatically from temperature
and oxygen probes located in the bottom of the digest-
er. The digester is of continuous flow type so that di-
gested material, having been retained in the digester ap-
proximately 7 days, is automatically discharged as new
material is introduced. The sludge cake with conditioner
is conveyed across the top of the digester and intro-
duced adjacent to the wall. Multiple augers, supported
from the enclosed top of the digester, aerates the mate-
rial up and down and at the same time moves the
material toward the center discharge port. The top deck
turns 360 degrees and the augers revolve at different
speeds.
The digester was emptied and the test was started by
mixing approximately 2 tons (1.8 Mg) of shredded paper
with 18.5 tons (17 Mg) of sewage sludge cake contain-
ing 75 percent moisture. A mechanical shredder was
utilized to properly size the sludge cake and more effec-
tively mix the paper with the sludge before the mixture
was conveyed to the digester. This same approximate
mixture of sewage sludge and paper was introduced into
the digester 5 days per week, until the material reached
a level of 4 feet (1.2 m) which automatically started to
discharge digested material. This digested material, con-
taining approximately 50 percent moisture, was then
dried, to approximately 10 percent moisture, in a rotary
dryer and recirculated back through the digester as a
conditioner for the sludge cake.
For mechanical reasons, the density of the material
within the Altoona digester must be kept below approxi-
mately 30 pounds per cubic foot (480 kg/m3), so, after
several days of using dried recirculated digester output
as the conditioning material, it was found necessary to
add a small amount of paper to the mixture. Thereafter,
each day until the test was terminated, 0.25 ton (0.23
Mg) of paper and 5.36 tons (4.86 Mg) of dried digester
output were mixed with 14.5 tons (13.2 Mg) of sludge
cake having 75 percent moisture.
The digester input material weighed an average of 25
pounds per cubic foot (400 kg/m3) and had pH of 5.6.
The material discharged from the digester weighed 30
pounds per cubic foot (480 kg/m3) and pH was 7.5.
During the tests, the sludge cake was reduced by ap-
proximately 80 percent in total weight, 33 percent in
solids weight, 98 percent in water weight, 50 percent in
organic matter weight, and 65 percent in volume.
Metro-Waste
Resource Conversion Systems, Inc.
9039 Katy Freeway
Houston, Tex. 77024
(713) 461-9228
Resource Conversion Systems, Inc., offers the patent-
ed Metro-Waste Aerobic Thermophilic Bio-Reactor and
associated equipment for application in the composting
of wastewater sludge. The Bio-Reactor consists of syste-
matized mixing, conveying, agitation, aeration and finish-
ing. The Bio-Reactor system is fully automated, has con-
tinuous process control and monitoring equipment, and is
enclosed for all weather operation. The process utilizes
a bulking agent to assist in the handling and aeration of
the dewatered residuals in the thermophilic aerobic Bio-
Reactor. The bulking agent and dewatered residuals are
blended together in a matrix mixer and then transferred
via conveyor into the aerated Bio-Reactor. The Bio-Re-
actor consists of a patented agitation and aeration sys-
tem. The stabilized residuals are then transferred via a
conveyor to a bulking agent recovery and recycle sys-
tem and then to an interim storage facility. Moisture
content of the residuals is reduced from 75 to 85 per-
cent to about 30 percent.
The company offers either a complete equipment sys-
tem or individual components for dewatering and aerobi-
cally composting municipal and industrial organic waste-
water residuals.
BAV System
Biowaste Management
175 East Shore Road
Great Neck, NY 11023
(516) 482-5944
There are over 30 of these systems operating on sew-
age sludge in Germany, France, and Japan. In these
46
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operations, sludge with a water content of about 98
percent, is concentrated by centrifuging or pressing to
achieve about 75 to 80 percent water. Initially, peat,
sawdust, chopped straw, brown coal, or some other
acceptable carbon carrier is mixed with the sludge. The
mixed material passes through the bioreactor from top
to bottom in about 2 weeks. Air is forced in at the base
of the bioreactor and passes through the material from
bottom to top. Samples and temperatures from different
levels are monitored continuously. The bioreactor at-
tempts to provide optimum conditions for micro-organ-
isms to multiply rapidly, and efficiently cause decomposi-
tion of the material into compost.
COMPOSTING COSTS
Sludge composting may be a viable alternative for
many locations but the basic processes are still in the
development and demonstration phase. Consequently, it
is not possible to prepare generalized cost estimates at
this time. Some cost considerations and estimates pre-
pared in several studies are presented.
The cost of sludge disposal by composting may be
considered in two components: (1) capital, operation and
maintenance costs of producing the compost, and (2)
cost of (or income from) disposal of the compost prod-
uct. A market study18'19 found several successful munici-
pal sludge composting operations where all of the end
product was sold or otherwise successfully used. The
study concluded that the current upper price limit for
bulk sludge compost is about $4 to $10 per ton ($4.41
to $11.02/Mg) and for packaged, bagged, sludge com-
post, about $60 per ton ($66.14/Mg). Bagging costs
could approach $30 per ton ($33.07/Mg). Sludge com-
post marketing operations that have been successful
have generally: (1) had favorable local publicity, (2) had
the product available for pickup (or made deliveries), (3)
offered guidelines for its use, or at least suggestions, (4)
offered the product at no or low cost, and (5) given the
product a trade name.
A study of the sludge disposal alternatives for the
New York-New Jersey metropolitan area developed a
cost of $40 to $45 per dry ton ($44.09 to $49.607Mg)
for composting large quantities of dewatered sludge
without any hauling or land costs included.20 A study by
USDA estimates total costs for composting in 10 and 50
dry ton (9 and 45 Mg) per day facilities to be $51 and
$36 per dry ton ($56.22 and $39.68/Mg), respectively.21
A report by Camp, Dresser and McKee estimated a cost
of $45 per dry ton including land, but excluding hauling,
to windrow compost 600 wet tons (544 Mg) per day of
sludge.22
Composting costs are documented for both Beltsville
and Bangor.14 The Beltsville costs must be considered
carefully because they include allowances for various
research activities and the equipment and site may be
capable of handling two to three times more sludge than
is presently processed. Various financial aspects of the
Beltsville operations are shown in table 8-10. The 1976
actual and projected 1977-78 costs were developed
Table 8-10.—Beltsville actual and projected costs
Projected
Oct. 1977-
Sept. 1978
Actual
1976
Estimated costs3
18,200 45,500
wet tons/yr6 wet tons/yr
Onsite operations
Telephone and travel
Utilities
Fuel and oil
Sludge hauling
Labor including fringes
Miscellaneous contract services
Wood chips
Supplies and materials
Equipment insurance
Total excluding offsite
Dry tons sludge per year (23 percent solids)
Annual cost, $/dry ton sludge solids
$1,300
2,211
10,500
132,000
125,750
27,540
144,000
22,250
4,000
469,551
3,450
$136
$3,971
426
13,036
120,000
152,919
C1 12,942
73,145
32,176
3,955
512,570
3,450
$149
$1,300
2,211
10,500
—
80,000
27,540
b1 44,000
22,250
4,000
291 ,801
4,200
$69
$1,300
3,000
25,000
—
125,750
37,000
"350,000
35,000
4,000
581 ,050
10,500
$55
aExcluding requirements of research work.
bAssume 50 percent of compost marketed unscreened and 70 percent recovery of bulking agent after
screening finished compost.
Includes screening performed by outside contract, screening now performed on site by MES personnel.
47
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from information on the total operation including re-
search, but do not include the amortization of equipment
or site costs. The onsite labor cost includes site supervi-
sion. Sludge hauling cost is for contract transport of
sludge cake from the Blue Plains Plant to the compost-
ing site and are site specific for the Beltsville operation.
Costs for bulking agent may not reflect actual usage
because chips are purchased when prices are favorable
and large quantities can be stockpiled. Screening in
1976 was performed by outside contract, however, all
screening is now performed using onsite labor.
The projected Beltsville costs for 1977-78 were modi-
fied to show two different sludge input rates and re-
search related costs were removed. Individual breakdown
of costs for various processes such as mixing, pile con-
struction, and screening are not available from Beltsville.
However, cost estimates were prepared for an operation
similar to Beltsvilie based on time and motion study at
Beltsville. This study estimated that total costs, including
capital amortization, are approximately $51 per dry ton
($56.227Mg) of sludge cake solids for an operation
processing 10 dry tons (9 Mg) of sludge solids per day.
Total capital costs for site improvement and equipment
were estimated at $376,000. Estimated costs for 50 dry
tons (45 Mg) of sludge solids per year were $36 per dry
ton ($39.68/Mg), including amortization of approximately
$1,500,000 of capital costs. Costs from actual operations
indicate that these estimated costs may be on the low
side.
The following costs are for operations at Bangor,
Maine, during 1975-76.
Costs to compost 525
dry tons per year
($/ton)
Capital amortization,
Operations
Bulking agent
Analysis
Total
6 percent, 5 years
3
43
37
8
86
The capital investment was very low because only
minor site work was required. Equipment is provided by
the City Motor Pool. Amortization of equipment is includ-
ed in the hourly equipment charge under "Operations."
Cost information is not available for 1976. An estimated
breakdown of labor and equipment by operation is
shown in table 8-5.
Preliminary estimates at Durham, N. H., indicate a cost
of about $107 per dry ton ($117.95/Mg) solids for 20
percent solids sludge5 for composting an estimated 200
to 250 dry tons (181 to 227 Mg) of sludge per year
excluding capital amortization.
The major cost items at existing composting opera-
tions are labor and bulking agent which can each be 30
to 45 percent of the total annual cost. Operation and
maintenance of the mobile equipment at Beltsville, ex-
cluding capital amortization, is 10 percent or less of the
total annual cost. Amortization of the purchase cost of
the equipment at Beltsville (approximately $400,000) over
6 years at 7 percent would be approximately $84,000
per year or about 13 to 23 percent of total annual costs
shown in table 8-10.
SOME EUROPEAN COMPOSTING
SYSTEMS
The major interest in composting in Europe is directed
toward the treatment of municipal solid waste. Much
attention has been paid to methods for reducing the size
of the waste and sorting out noncompostable materials.
Sludge is accepted in most systems as a source of
moisture and nitrogen to help reach a desirable C/N
ratio. Night soil and disposable plastic latrine containers,
both of which are essentially equivalent to raw sludge,
are also composted in some systems.
In Sweden a recent law offers subsidies to communi-
ties to compost solid waste, and the process is seen as
a good way to get rid of some of the increasing vol-
umes of sludge that are being generated as Sweden
approaches 100 percent secondary treatment of sewage.
In November 1977 a compost conference and trade
show in Jonkoping, Sweden, attracted 500 visitors, 300
of whom represented community officers. Six companies
described their composting systems, some of which are
currently under construction in Sweden. The Swedish
National Nature Protection Agency operates a compost-
ing research plant at Laxa which has been described.23
Current operation of the plant and experience with the
equipment was described in a paper in Swedish by Mr.
Hovsenius.
Although most of the descriptions were directed
toward the composting of solid waste, any of the sys-
tems can be used to compost sludge if it is mixed with
a suitable filler to allow air penetration. Bark, wood
chips from tree trimming and old compost have all been
used for this purpose. Any of the companies represented
at the meeting would be happy to design composting
equipment specifically for sludge. Many of the companies
in fact offer several combinations of equipment to suit
their customer's needs. Therefore, naming the manufac-
turer does not necessarily identify a particular process.
About half of the composting equipment described in
the trade show is for size reduction. Essentially any
chopping or grinding mill that can reduce solid waste to
less than 4 inch (100 mm) pieces can be used to pre-
pare material for composting. Chopped waste from which
metals, glass and plastics have been removed is an
effective filler for sludge composting, although in general
the emphasis has been reversed and sludge has been
considered as an adjuvant to the composting of solid
waste. Where chopped bark is used as a filler for
sludge composting, the high price of bark is cited as a
major disadvantage. Although Sweden is rich in forests,
bark commands a price equivalent to its fuel value in
heating oil. On the other side, the acceptability of com-
post made from solid waste is less than that made from
48
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sludge alone because obvious traces of glass, aluminum,
plastics and rubber remain from the solid waste.
In Europe, the emphasis seems to be turning from
ingenious mechanical reactors and solids handling de-
vices to systems for more efficient operation of classical
windrow composting. Gunnar Hovsenius reported that the
two mechanical reactors that have been studied at Laxa
are now out of operation because forced aeration in
windrows is more attractive. Even with the most ad-
vanced automatic composting reactor the product is re-
moved after the heating stage and stored in piles to
cure for periods of several weeks to months.
Composting Reactors
The original DANO company is bankrupt but licenses
to build DANO type drum reactors are offered by a
Swiss holding company, DANO Ltd., CH-Glarus. A DANO
composter is a long rotating drum that looks like a
cement or lime kiln. Typical dimensions are 11 ft (3.5 m)
diameter and 90 ft (28 m) long. The drum rotates at 0.6
to 2 rpm tumbling the contents against specially de-
signed baffles. Air is drawn through the drum counter-
current to the flow of composting material and dis-
charged to an odor trap. Unchopped solid waste and
sludge or water to provide moisture are charged to the
inlet of the drum. With a retention time of 48 hours the
temperature will reach approximately 140° F (60° C).
Moisture and the elevated temperature weaken paper
and packaging materials, and the tumbling action pro-
vides good disintegration of municipal wastes. The ele-
vated temperature also kills pathogenic microorganisms
and plant seeds.
Dano reactors are sometimes operated with as little as
24 hours' retention time. Although this is sufficient for
disintegration of solid waste, the contents do not reach
disinfecting temperatures, and some seeds may survive.
The output from a DANO reactor may be screened
through 3/4 inch (20 mm) holes with about 50 percent
recovery based on the initial charge of solid waste. Fur-
ther screening through 3/8 inch holes (10 mm) gives a
25-30 percent yield of fine compost. Wastes may be
chopped before charging to the reactor and sludge may
be composted with bark or chopped branches instead of
municipal garbage. Operating characteristics of a DANO
composter were quoted as follows:
Weight
Volume
Daily capacity
Municipal waste
Sewage sludge
Yield of finished compost.
Compressed rejects
Metric
tonnes
130
100
30
50
38
Tons
143
110
33
55
42
m3
630
600
30
70
46
Cubic
yards
824
785
40
92
60
Dano composters were quoted as costing from 15 to 30
million Swedish kroner equivalent to $4 to $8 million
depending on the peripheral equipment.
The "System Kneer" is offered in Sweden by BIAV,
S-11288 Stockholm. This is a squat silolike reactor up to
60 ft (18 m) in diameter and 45 ft (13.5 m) high. Raw
wastes are chopped, mixed and charged to the top of
the reactor and finished compost is withdrawn from the
bottom by a special helical screw. This helix rotates
axially conveying compost to a central discharge port
while at the same time it revolves around a central pivot
like the hand of a clock to bring waste from all sectors
of the reactor. Air is warmed by passage through a heat
exchanger and injected at the bottom. Warm moist air is
withdrawn from the top and passed through the heat
exchanger preheating the incoming air before being dis-
charged to an odor trap. Temperatures in the reactor
approach 176°F (80 °C) after 48 hours and compost
remains in the reactor for 8 to 14 days. The original
"System Kneer" was designed to compost sludge mixed
with bark, wood chips or an inert filler in the ratio of 1
part of sludge to 1-2 parts of filler. The first installation
to use chopped solid waste in Sweden ran into difficul-
ties when the waste set to a solid that blocked the
discharge screw. The screw has been redesigned but
remains a critical part of the system. A BIAV-Kneer re-
actor with a capacity of 30,000 ton per year was
quoted at about 5 million Swedish kroner or $1.25 mil-
lion.
The Carel-Fouche reactor tower installed at Laxa for
composting solid waste plus sludge is not now in opera-
tion. The tower measures 10x13 ft (3x4 m) in cross
section and is 40 ft (12 m) high. In this reactor, five
successive stages of composting are held, one below
another, on special "forks" with a forced updraft of air.
After one to three days' detention the forks are succes-
sively rotated starting at the bottom so that each layer
drops to the next lower fork and the finished compost is
removed on a conveyor for curing. A somewhat similar
reactor tower resembling a multiple hearth incinerator is
shown in literature distributed by Hazemag.
The INKA Compost Plant made by Johnson Construc-
tion Co. AB, S-17124 Solna, Sweden, that was installed
at Laxa has been dismantled and moved to Milan, Italy.
In this system an overhead traveling bridge rides on the
top of two walls about 8 ft (2.5 m) high and about the
same distance apart. Solid waste mixed with sludge is
piled between the walls and is agitated by means of twc
helical screws like post hole augers that introduce air
through hollow central shafts. This aeration proved to b«
insufficient so forced aeration was introduced through a
gravel bed under the compost. Experience with the INK/
reactor led directly to the forced aeration studies in
static windrows.
The SILODA System of ODA, Courbevoie, France, alsc
holds compost between walls in what they call a silo. A
special "Paddle Wheel" resembling the stern wheel of a
river steamboat rides on the walls, cuts and lifts the
compost and deposits it in the adjacent silo. Compost
remains in the silos for 8 to 14 days during which time
it is turned 4 to 5 times.
49
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Forced Aeration Composting in Static
Piles
There has been a marked swing away from mechani-
cally turned composting in reactors to forced aeration in
static piles. Major experimental work has been done by
Gunnar Hovsenius at Laxa. Voest-Alpine, A-4010 Linz,
Austria, has reported temperature profiles in forced aera-
tion compost bins. Ruthner, A-1121 Vienna, Austria,
treats wastes for a short time in a DANO type drum,
then charges the compost to bins with forced air suc-
tion.
The Laxa forced aeration system places compost on
paved slabs on which three inverted concrete "U"
beams are laid nearly 7 feet (2 m) apart and held above
the pavement by 3/8" (8 mm) rods. Chopped waste
blended with sludge is piled on top of the "U" beams in
flat topped windrows 7 to 10 ft high (2 to 3 m) and up
to 30 ft (9 m) broad. Blowers are attached to the con-
crete channel beams to provide either suction or forced
air to the piles. There are specific difficulties associated
with each of the modes of aeration but on the whole
Laxa has had most luck with forced air moving up
through the piles. It is possible that a combination of
suction and blowing at different stages of composting
will prove to be better than either mode alone.
In the winter months outside air temperatures at Laxa
drop to zero°F (-18°C). The incoming air is bone dry
but when it is blown through the pile, it becomes satu-
rated with moisture at the pile temperature, which may
exceed 160°F (71 °C). When this moist air comes in
contact with the cold outside air, most of the moisture
condenses soaking the outer layer. At the same time
compost near the air inlet channel is dried out. When air
is sucked through the pile in winter, the outside layers
are dried by the incoming cold air and composting activ-
ity in these layers stops. Moisture meanwhile condenses
on the cold floor and ducts and must be removed be-
fore the air reaches the blowers. Disposal of the con-
densate is a problem since it is highly polluted and
corrosive. Conceivably it could be sprayed on the piles
to help maintain the desired moisture level. With either
mode of operation moisture must be supplied to the pile
when parts of it get too dry.
The composting process is an efficient method for
drying sludge for the heat of biological oxidation. How-
ever, the initial moisture content must not be so high
that it interferes with aeration. The maximum moisture
level that can be tolerated depends on the structure of
the supporting filler, whether it be fresh wood chips,
bark, old compost or shredded solid waste. The most
important criterion is that there be open spaces for air
circulation throughout the pile to prevent the formation
of anaerobic zones. Too high a pile may crush the filler
and destroy air passages in the lower layers. The maxi-
mum proportion of sludge that can be tolerated must be
determined by experiment for each site. The moisture
content of the composting mixture is usually held below
60 percent and optimum values are usually quoted at 50
percent. If the sludge contains 80 percent moisture (20
percent solids) and the filler is dry then 53 parts of filler
must be added to each 100 parts of sludge to achieve
60 percent moisture in the final mixture. More commonly
the filler is moist and larger quantities are required. If
the percent moisture of sludge, filler and initial compost
mixture are S, F and C respectively, and M is the
weight of filler per unit weight of wet sludge then
C =
S + MF
M + 1
and
M =
S - C
C - F
On the dry side, when moisture levels drop below
about 40 percent, composting effectively stops. In one
study at Laxa composting action stopped after 40 days
of forced aeration when the reaction was only half com-
pleted. Additions of moisture restarted the reaction and
allowed it to go to completion.
The air supply must be sufficient to provide oxygen
and to dilute the CO2 produced. According to Hovsenius
the best control strategy is to keep the CO2 content of
the air leaving the pile between 3 and 6 percent by
volume. He uses an infrared CO2 meter for this purpose.
When the CO2 content exceeds 5 percent, the rate of
reaction begins to fall and composting essentially stops
when the CO2 level reaches 10 percent. During the peri-
od of maximum activity the air demand is 2 to 3 times
the volume of the pile per hour or about 1 to 1.5 cu ft
of air per minute for each cubic yard of compost. Lower
quantities of air must be used in later stages as the rate
of composting declines to avoid drying out the pile.
The progress of composting can be measured by the
CO2 produced. In the Laxa studies using shredded solid
waste and sludge the production of carbon dioxide lev-
eled out when about 40 percent of the carbon in the
waste had been converted to CO2. The practical control
remains temperature inside the pile which can be easily
and rapidly measured with probe thermometers. When
the temperature drops below 104° F (40° C), the pile can
be moved to storage for final curing.
Odor Traps
Odor control is necessary in all systems in which air
is passed through a composting mixture. Almost all of
the systems use some sort of a biological filter as an
odor trap. One DANO installation uses 16 inches (400
mm) asbestos cement pipes spaced 8 ft (2.25 m) apart.
The pipes are perforated and covered with 1-2 inch
(40-70 mm) gravel to a height of 16 inches (400 mm)
above the tops of the pipe. A layer of fresh compost
about 5 ft (1.5 m) high covers the gravel. There is
sufficient moisture and organic matter in the exhaust
gases to maintain an active deodorizing chemical micro-
bial flora even on old compost or soil, but the use of
fresh compost insures good deodorizing from the start.
Another deodorizing technique is to blow the foul air
directly into activated sludge or through a trickling filter
if the compost plant is situated on the grounds of a
50
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sewage treatment plant. In every case provision must be
made to remove condensed water and participate matter
that would corrode and clog blowers and air distribution
systems.
Curing and Handling
All reactor systems, including forced aeration in static
piles, provide separate areas for curing the fresh or
immature compost. Curing is usually done in bins or in
piles on paved storage areas. Storage areas may have
to be covered and drained to comply with local require-
ments. Curing usually requires several months of storage.
Most of the systems use mobile equipment especially
front end loaders to move and pile compost. A number
of elaborate conveyor systems have been built to handle
compost, but the large fixed investment and relatively
small fraction of the time that the equipment is actually
operated lead to very high unit costs. Mobile equipment
is more versatile and although it requires more labor, it
is apt to be cost effective for all but the very largest
installations.
The Cost of Composting
It is not possible to translate costs of composting to
U.S. equivalents without making corrections for the gen-
erally higher interest rates and lower labor costs in Eu-
rope. Costs of the order of $10 to $15 per ton ($11.02
to $16.53/Mg) of raw composting mixture were quoted
at the Jonkoping meeting. The sales value of compost
varies according to the market. A value of zero is real-
ized when a plant uses composting to stabilize wastes,
remove water from sludge and reduce the total volume
for land filling. At the other extreme is fine compost that
may be solid in bags for home garden use. Much of the
compost that has been produced so far has gone to
city parks and green areas and has not been sold on
the open market. Some compost is used in truck gar-
dens and there appears to be a good market for com-
post in the wine growing areas of central and southern
Europe. Markets for recovered iron scrap and paper are
quite undependable although profit from the sale of
these items is frequently entered in the net cost of
composting by promoters of equipment.
The yield of finished compost depends on the nature
of the raw materials and the amount that is removed by
screening. At Laxa with forced aeration one ton of
mixed waste yields 1,060 Ib (480 kg) of dry compost
containing only 240 Ib (109 kg) of organic matter. In the
DANO literature one ton of mixed waste is expected to
yield 770 Ib (349 kg) of screened compost passing a
3/4 inch (20 mm) mesh.
DESIGN EXAMPLE
Engineered composting systems applied to the stabili-
zation of sewage sludge are a relatively recent develop-
ment in the United States. There appears to be general
agreement among knowledgeable people in the field that
the forced aeration static pile method, as developed at
Beltsville, Md., could be used in many locations. One or
more mechanical type systems may prove to be useful ir
some applications. The greater space required for the
windrow system will restrict consideration of its use in
many locations.
Sludge composting at Beltsville, Bangor, and Durham
are all research and demonstration type operations.
Many of the criteria required to design a system are not
firmly established and there is certainly not a "typical"
design at the present time. The LA/OMA project in Cali-
fornia is currently conducting research in an effort to
determine more design and operating criteria.
Composting is largely a materials handling process anc
to date the systems operating on sludge in the United
States all utilize mobile equipment. Bulking agent and
labor costs are the largest components in total sludge
composting costs. There appear to be opportunities to
significantly reduce composting costs if (1) more efficient
methods of materials handling can be developed to re-
duce labor costs and space requirements, and (2) oper-
ating procedures can be developed to reduce, or elimi-
nate, the amount of bulking agent required.
This design example is a 4 Mgal/d standard activated
sludge plant and is based on a Beltsville type sludge
composting system utilizing existing technology and avail
able design criteria.
Sludge and Bulking Agent Characteristics
The following sludge quantities are used in the exam-
ple.
Pounds/million gallons
Sludge type
Percer
Total Volatile volatilt
solids solids Inerts solids
Primary 1,300 780 520 60
Waste activated 1.000 800 200 80
Total.
2,300 1,580 720
69
These sludge quantities were determined with the follow-
ing assumptions:
1. Raw wastewater suspended solids = 240 mg/l;
BOD = 200 mg/l.
2. Suspended solids removal = 65 percent in primary
treatment and 90 percent overall; BOD removal = 3C
percent in primary treatment and 90 percent overall
3. One-half pound activated sludge produced per
pound BOD removed.
It is further assumed that:
1. Primary sludge is 4 percent solids and is gravity
thickened to 8 percent solids.
2. Waste activated sludge is 1 percent solids and is
thickened to 4 percent solids.
3. Combined thickened primary and waste activated
sludge (5.5 percent solids) is dewatered to produce
20 percent solids sludge per composting.
51
-------
The weight and volume of sludge and bulking agent at
various points in the process must be known to deter-
mine the configuration of a composting facility. The ba-
sic design decisions include: (1) the bulking agent to
sludge ratio, and (2) the ratio of new to recycled bulk-
ing agent.
The materials flow system in this example of compost-
ing 2,300 pounds per million gallons (276 kg/1000 m3)
of 80 percent moisture undigested sludge is based on
the following assumptions:
1. New and used wood chips are added to the wet
sludge at the rate of 2.5 cubic yards (1.9 m3) of
chips per ton of wet sludge. This corresponds to a
volume ratio of bulking agent to sludge of about
2.25:1.
2. Three-fourths of the chips will be recovered by
screening and reused.
Information on the bulk density of sludge is surprising-
ly scarce in the literature. Tests conducted at Beltsville
for an engineering study of a large scale composting
facility provide some basic data on the bulk density of
sludge and wood chip bulking agents.24 The following
bulk densities are used in this example:
Bulk density
(pounds per cubic yard)
Dewatered sludge (20% solids).
New wood chips
Recycled wood chips
Screened compost
1,800
500
700
865
Design Criteria
The following criteria are used in this example for a 4
Mgal/d (0.18 m3/s) plant and are based on available
operating experience.
1. Sludge composting system is operated 5 days per
week, 8 hours per day.
2. Sludge to be composted
• 46,000 wet pounds (20,870 kg) per day (80
percent moisture).
• 26 cubic yards (19.9 m3) per day (wet) = 182
cubic yards (139.1 m3) per week.
3. Bulking agent required
• 60 cubic yards (45.9 m3) per day total.
• 15 cubic yards (11.5 m3) per day makeup (new
material) = 105 cubic yards per week.
4. The composting area is to be sized for 21 day
composting period.
5. The input volume of sludge and bulking agent to
the composting pad is 31,025 cubic yards (23,720
m3) per year or an average of about 120 cubic
yards (91.7 m3) per day based on a 5-day week.
6. Compost piles constructed in a triangular cross
section, 8 feet (2.4 m) high with 16 feet (4.9 m)
wide base. (Volume = 64 cubic feet per foot of pile
length.)
7. Individual compost pads will be sized to hold two
days sludge. Therefore, each pad will accommo-
date 240 cubic yards (183.5 m3) of sludge-bulking
agent mixture and will be 20 feet (61.0 m) wide
and 100 feet (30.5 m) long.
8. Provide 15 percent excess composting area; there-
fore, 12 composting pads, each 20x100 feet
(6.1 X30.5 m) are required.
9. Provide one blower for each composting pad. Size
blower for a minimum rate of 500 cubic feet per
hour per ton (15.6 m3/hr/Mg) of sludge solids.
Use blower rated at 200 cubic feet per minute
(5.7 rrrVmin).
10. Provide 10 cubic yards (7.6 m3) deodorizing pile
to serve 2 blowers.
11. Provide leachate and condensate collection system
for each pad with 50 gallons (0.19 m3) per day
capacity. Recycle leachate and condensate to
treatment plant or sewer.
12. Composting produces finished screened compost
with the following characteristics
• 40 percent moisture.
• volatile solids reduced 15 percent.
• 25 percent of bulking agent remains in com-
post.
• bulk density = 865 pounds per cubic yard (513
kg/m3) (32 pounds per cubic foot).
13. Provide covered and paved area for 60 days stor-
age (900 cubic yards (688 m3)) of new wood
chips. If bulking agent stored 8 feet (2.4 m) deep,
then area required is about 3,000 square feet (279
m2).
14. Finished screened compost production
• 31,250 pounds (14,170 kg) per day.
• 36 cubic yards (27.5 m3) per day (13,140 cubic
yards per year).
15. Composted moisture dried to 40 percent moisture
before screening. Provide six days drying with ma-
terial two feet deep; 10,000 square feet (929 m3)
area required.
16. Dried mixture is screened before transfer to
curing/storage area. Provide 60 days curing/
storage for screened compost; 6,000 square feet
(557 m2) area required.
17. Transfer screened wood chips to wood chip stor-
age area.
Discussion
A process and materials flow diagram for the design
example is shown in figure 8-3 and a conceptual layout
for the system is shown in figure 8-4.
The overall space required is about 102,000 ft2 (2.3
acres (0.93 ha)) which is about 0.5 acre per ton per
day (0.22 ha/Mg/day) of dry sludge solids (8,400 wet
tons (7620 Mg) per year) composted. Reducing or elimi-
nating the bulking agent would significantly reduce the
area required. Use of the extended pile configuration,
instead of so many individual pads, would reduce the
area required particularly in larger plants. By way of
comparison, the Bangor, Maine, site is 65,000 ft2 (1.5
52
-------
COMPOST
CURING/STORAGE
60 DAYS
CAPACITY
5 DAY PER WEEK OPERATION
CUBIC YARDS
PER DAY
36
21
63
96
16
40
133
I 17
50
77
Figure 8-3.—Process flow diagram. Composting sludge, 4 Mgal/d activat-
ed sludge plant.
acres (0.61 ha)) to compost 2,500 wet tons (2268 Mg)
of sludge per year.
Control of moisture is the key to a successful sludge
composting system. The sludge should be dewatered
and/or mixed with sufficient bulking agent to obtain a
moisture content of about 60 percent in the composting
piles. The composted mixture should then be dried to
about 40 percent moisture for efficient screening and
handling for distribution.
Oxygen requirements are not high and the blowers or
fans at all existing installations are operated intermittent-
ly. About 500 ft3/hr per ton (15.6 m3/Mg/hr) of dry
sludge solids provided by a centrifugal fan, operating at
5 inches (127 mm) water pressure drop, is recommend-
ed based on the experience at Beltsville, Md.15The Ban-
gor, Maine, system uses a 1/3-horsepower (0.25 kW)
blower, rated at 335 ft3/min (9.5 rrrVmin) at 4 inches
water pressure (102 mm), for each pile consisting of 50
cubic yards (38.2 m3) sludge and 150 cubic yards (114.7
m3) bulking agent.8 The blowers are operated intermit-
tently to maintain the oxygen level in the 5 to 15 per-
cent range and to obtain as uniform temperature as
possible.
The composting area should be paved. Probably the
most efficient design in a permanent facility is to use
fixed aeration and drainage systems. The aeration piping
and drainage system could be placed in trenches in the
composting pads and the blowers placed in permanent
protected structures and equipped with water traps and
controls.
Deodorizing piles should be replaced periodically. The
deodorizing piles are replaced every other month at
Bangor and the system has operated successfuly during
cool weather with no deodorizing piles.
After the compost piles are formed, they should be
covered with a layer of compost or wood chips for
insulation and to prevent the outer edges from excessive
drying and blowing dust. The insulating layer will also
retain a significant amount of moisture from rainfall.
Some of the operating facilities use a base layer of
bulking agent or unscreened compost to cover the aera-
tion piping. However, the piles are now constructed at
53
-------
.'BLOWER (TYP) 1 EA. PAD
/ .'DEODORIZING PILE (TYP) 3 EA SIDE
3*0'
O
0
0
o
o
o
-o
0
0
DRYING AREA
SO' » 100'
u
(9
<
cc
H
VI
•**.
0
z
K
3
U
"o
*
M
"«
N
<&
w
WOOD
CHIP
STORAGE
50' * 50'
MIXING
AREA
50'xSO'
\
DRYING AREA
30' X 100'
/
0
0
o
0
0
o
o
o
o
8
IO
'-COMPOSTING PADS
6 EA. SIDE (a) 20'» 100'-
Figure 8-4.—Static pile forced aeration composting system plan
(4 Mgal/d activated-sludge plant).
Bangor with no special base layer: the sludge-bulking
agent mixture is placed directly on the aeration piping.
The existing composting facilities operate in uncovered
areas, much of which are not paved. It may be desirable
to cover the mixing, chip storage, curing/storage and
drying areas; and cover and enclose the screening area.
Runoff from the site must be controlled and runoff
should be prevented from entering the composting pads.
REFERENCES
1. McGauhey. P. H., and Golueke, C. G., "Reclamation of Municipal
Refuse by Composting," Tech. Bull. No. 9, Sanitation Eng. Res.
Lab., University of California, Berkeley, June 1953.
2. Briedenbach, A. W., et al., "Composting of Municipal Solid Waste
in the United States," SW-474, U.S. EPA, Washington, D.C. 1971.
3. Wiles, C. C., "Composting of Refuse," Composting of Municipal
Residues and Sludges, Information Transfer, Inc., Rockville, Md.,
1978.
4. Satriana, M J., "Large Scale Composting," Noyes Data Corp.,
Park Ridge, N. J., pp. 76-100, 1974.
5. Epstein, E., and Willson, G. B., "Composting Sewage Sludge,"
Proc. National Conference on Municipal Sludge Management,
Pittsburgh, Pa., pp. 123-128, June 1974.
6. Epstein, E., et al., "A Forced Aeration System for Composting
Wastewater Sludge," Journal WPCF, pp. 688-694, April 1976.
7. Epstein, E., and Willson, G. B., "Composting Raw Sewage
Sludge," Proc. 1975 National Conference on Municipal Sludge
Management and Disposal, pp. 245-248, August 1975.
8. Mosher, D., and Anderson, R. K., "Composting Sewage Sludge by
High-Rate Suction Aeration Techniques," Interim Report, SW-614d,
U.S. EPA, 1977.
9. "Utilization of Municipal Wastewater Sludge," WPCF Manual of
Practice No. 1, 1971.
10. Golueke, C. G., "Composting, A Study of the Process and its
Principles," Rodale Press, Emmaus, Pa., 1973.
11. Golueke, C. G., "Biological Reclamation of Solid Wastes," Rodale
Press, Emmaus, Pa., 1977.
12. Haug, R. T., and Haug, L. A., "Sludge Composting, A Discussion
of Engineering Principles," Compost Science Journal of Waste
Recycling, pp. 6-11, November-December 1977.
13. "Pathogen Inactivation During Sludge Composting," Status Report,
Los Angeles County Sanitation Districts, August 1976.
14. Ettlich, W. F., and Lewis, A. E., "A Study of Forced Aeration
Composting of Wastewater Sludge," US EPA600/2-78-057,
Cincinnati, Ohio, November 1977.
15. Willson, G. B., et al., "A Manual for the Composting of Sewage
Sludge by the Beltsville Aerated Pile Method," draft EPA/USDA
publication, April 1977.
16. Burge, W. D., et al., "Pathogens in Sewage Sludge and Sludge
Compost," paper presented at the American Society of Agricultur-
al Engineers, Chicago, III., December 14-17, 1976.
17. "The Reduction of Organic Matter in Municipal Wastewater Under
Aerobic Condition in the Thermophilic Phase by the Fairfield Di-
gester System," Fairfield Engineering Co., Marion, Ohio (undated).
18. Ettlich, W. F., and Lewis, A. E., "User Acceptance of Wastewater
54
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Sludge Compost," EPA 600/2-77/096, NTIS PB-272 095/IWP, 56 22. "Draft Report, Alternative Sludge Disposal Systems for the District
pp., August 1977. of Columbia Water Pollution Plant at Blue Plains, District of Co-
19. Ettlich, W. F., and Lewis, A. E., "Is There A Sludge Market?" lumbia," Camp, Dresser & McKee, Inc., September 1975.
Water and Wastes Engineering, pp. 41-47, December 1976. 23. Hovsenius, G., "Composting and Use of Compost in Sweden,"
20. Kalinske, A. A., et al., "Study of Sludge Disposal Alternatives for Journal WPCF 47, pp. 741-7, 1975.
the New York-New Jersey Metropolitan Area," paper presented at 24. "Composting Site Evaluation and Preliminary Design Report for a
48th WPCF Conference, Miami Beach, Fla., October 1975. Montgomery County Composting Facility," vol. II, report for Wash-
21. Colacicco, D., et al., "Costs of Sludge Composting," USDA, Agri- ington Suburban Sanitary Commission by Toups and Loiederman,
cultural Research Service, ARS-NE-79, February 1977. August 1977.
55
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Chapter 9
Principles and Design Criteria for
Sewage Sludge Application on Land
INTRODUCTION
Land application of sludge involves spreading wastewater
solids on the soil surface or incorporating them into the
root zone. Deep trenching or burying of sludge is dis-
cussed under "Landfilling."
The utilization of both sewage sludge and animal
waste would require 1.3 percent of the cultivated land in
the U.S.1 Therefore, any concern about supply of land to
utilize fully the increasing quantities of sewage sludge
and animal waste being generated annually is not war-
ranted.
Two distinct rates of application can be considered
depending on the system objectives. If the objective is
to recycle nutrients or apply sludge at agricultural rates,
the nitrogen or heavy metal loadings will usually limit the
application rates. Monitoring of soils and crops can be
minimized when these rates are used. Higher loadings
can be used when (1) detailed monitoring of environ-
mental impacts is conducted, (2) uses such as reclama-
tion of strip-mined land or application to forests or sod
farms are considered, (3) nonfood chain crops are
grown on the site.
The process of planning a land application project
begins with collection of basic data on sludge, soils,
climate, and regulations and involves selection, design,
and operation of the site. Throughout the planning, sup-
port of local officials, farmers, and other key individuals
must be sustained.
This chapter will briefly describe how to proceed with
evaluating and implementing an agricultural sludge utiliza-
tion program for a community. Because of the complexi-
ty of the topic, only an overview of the various consid-
erations in implementing a sludge utilization program will
be provided. In addition, two illustrative case studies are
given as design examples. The material presented herein
deals with sludge application to (1) agricultural soil
growing crops consumed by humans or animals, and (2)
nonagricultural areas such as parks, golf courses, for-
ests, and median strips.
PRELIMINARY PLANNING
Obtain Local Support
Project implementation requires acceptance and ap-
proval by local officials, farmers, landowners, and other
affected parties. Securing and maintaining local support
is neither easy nor straightforward. Variations in local
political, social, and economic conditions make meaning-
ful generalizations difficult, but a few points are almost
always applicable.
Obtaining local support requires some type of public
involvement or participation program. These programs
should promote public awareness by presenting an ob-
jective discussion of land treatment technology. Techni-
cal information should be presented in an easily under-
standable manner to insure communication between the
public, engineer, planner, consultant, and other officials.
If sludge is to be accepted willingly by the local resi-
dents, they must be informed early of the project and
must be involved in its planning.
Public resistance can stem from concerns about the
adverse impacts of using sludge for agricultural purpos-
es. For example, there may be fear that a sludge may
contain concentrations of organic or inorganic substanc-
es that could be toxic to plants or accumulate in plants
to the detriment of animals or humans. Furthermore, in-
adequate treatment may produce a sludge that is a
potential source of noxious odors or diseases. Objec-
tions by rural residents to landspreading might be en-
countered if they perceive the situation to involve an
urban community imposing its waste disposal problem on
the rural community. A large city is more likely to be
seen as an outsider than a small city. Rural acceptance
will be more readily forthcoming if local autonomy is
assured and if the project has the apparent flexibility to
incorporate needed changes.
Establishment of a public participation program re-
quires answers to two basic questions:
1. Whose support should be obtained?
2. What methods of communication should be used?
Whose Support?
The initial task for obtaining public support is the se-
lection of a project team, whose members can offer
technical service and expertise.
Suggested personnel include:
1. Representatives of the city engineering or public
works department to direct the project, manage one
or more technicians or engineers from the city's
staff, and coordinate activities with other committee
members and outside consultants.
57
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2. The sewage treatment plant superintendent or con-
sultant knowledgeable in treatment plant operations.
3. Local soil conservation service agent, agricultural
extension service or forestry representatives to ad-
vise on site selection, management, soil and vegeta-
tion evaluation, and other matters.
The following individuals can be brought into the
project as the need arises:
1. Private citizens, chamber of commerce representa-
tive, or newspaper editors to gage public accept-
ability of proposed program and/or implement a
public education program to smooth the way for
acceptance and adoption of the utilization program
being formulated.
departments, agricultural extension services, private
consultants) knowledgeable about soils, plants,
chemistry, or sludge utilization problems and solu-
tions.
3. A state regulatory agency representative or private
engineering consultant conversant with detection,
monitoring, evaluation, and mitigation procedures.
4. Legal advisors to draw up contracts, evaluate laws
or regulations, or assist the city with implementa-
tion.
What Methods of Communication Should Be
Used?
There are a variety of communication methods avail-
2. Outside consultants (university agriculture or forestry able for a public participation program. The most corn-
Table 9-1.—Attitudes toward landspreading of sludge in five Ohio counties2
Mean responses
Those who
have spread
(17 percent)
Those who
haven't spread
but have heard
of spreading
(45 percent)
Those who
haven't spread
nor heard
of spreading
(38 percent)
How would you react to spreading on your land [by local city]? 2.50
1 = enthusiastically
2 = favorably
3 = cautiously
4 = unfavorable
5 = opposed
How would you react to [another] large city's proposal to spread on
your land? 2.85
1 = enthusiastically
2 = favorably
3 = cautiously
4 = unfavorably
5 = opposed
How would you feel about sludge being spread on neighbors' fields?... 1.75
1 = agreeable
2 = indifferent
3 = moderately opposed
4 = strongly opposed
How would neighbors react to sludge spread on your land? 1.87
1 = agreeable
2 = indifferent
3 = moderately opposed
4-strongly opposed
Would you allow your land to be used as a demonstration site? 1.63
1 = Yes, I would be most happy.
2 = Yes, if rates are safe.
3 = No, spreading is all right but I don't want a site.
4 = No, my neighbors would be opposed.
5 = No, I am opposed to sludge spreading.
3.05
a3.81
3.48
b4.06
2.00
2.71
2.48
°2.41
C3.12
a3.24
Responses are significantly different between groups at the 0.10 level.
"Responses are significantly different between groups at the 0.05 level.
cResponses are significantly different between groups at the 0.01 level.
58
-------
mon are structured procedures such as public hearings,
meetings, or workshops. Others are advertising or public
relations techniques, such as press releases, pamphlets
or brochures; and radio, television, or newspaper adver-
tisement.
More fundamental than the actual organization of the
participation program, are the basic attitudes of the
project's proponents. Public participation should be
viewed as an important and positive step in project
planning rather than a necessary evil, obstacle, or delay
tactic.
Because of the technical nature of the project, some
amount of education is necessary by the planner to
raise the public's level of expertise. The results of a
survey in five counties in Ohio (table 9-1) revealed that
landowners with prior experience in sludge spreading
had significantly more favorable attitudes toward landsp-
reading than those with no knowledge of spreading. This
difference applied in cases where a local city was
spreading on landowner's property and another larger
city was spreading on landowner's property. Judgments
of neighboring property owners followed similar patterns.
No group of respondents was completely opposed to a
demonstration project; however, those with less experi-
ence or less knowledge about sludge management were
significantly less inclined to support such a project.2 The
manner in which this education effort is handled by the
planner is an important factor in the success of the
public participation program. Patience and tact will usu-
ally win out over arrogance and hard-sell salesmanship.
Where resistance does arise, the situation may boil over
if opponents are regarded only as uninformed, irrational
or emotional.
In general, constructive public participation is occur-
ring when there is open, two-way communication be-
tween public and project proponents. In a successful
public participation program, all parties learn from each
other and emerge from the planning effort reasonably
satisfied with the final product.3
The most critical aspect of the entire sludge utilization
program is involving the farmers or foresters, who will
utilize the sludge, in the planning process. How this is
to be accomplished is highly dependent on the individual
communities involved; past experience with sludge appli-
cation systems; overall public acceptance of the con-
cept, and the extent to which related or tangential envi-
ronmental concerns are voiced in the community.
Generally, a low-key approach is most effective. The
various approaches can consist of one or more of the
following:
1. Check with the sewage treatment plant to see if
any local farmers have requested sludge in the
past.
2. Have the local soil conservation service, forest
service or agricultural extension service agent poll
various individuals in the area for expressions of
interest.
3. Describe the project in the local newspaper asking
interested parties to contact the extension agent.
4. Telephone or personally visit the identified parties
and solicit their participation.
Some of the salient points which need to be discuss-
ed with the landowners are:
1. How long are they willing to participate, i.e., a trial
period of one or more years; open-ended until one
or both parties decide to quit; or for a finite pre-
scribed period of time?
2. What crops are traditionally planted and what is the
prescribed crop rotation?
3. If the sludge were more amenable to a different
crop, would they be willing to plant that particular
crop?
4. Which fields would be included in the sludge
spreading program?
5. Under what conditions would the landowner accept
the sludge, what times of the year, and in what
quantities?
6. Is the landowner willing to pay a nominal fee for
the sludge, or is it necessary for the municipality to
pay the landowner for taking the material?
7. Is the landowner willing to engage in special proce-
dures, such as maintaining soil pH at 6.5 or great-
er?
Basic Data Collection
Any sludge utilization program must begin with basic
data on the sludge itself, laws and regulation, climate,
soil type, and land use. Data for specific alternative sites
are discussed in "Site Selection."
Sludge Characteristics
Characterization of sludge properties is a necessary
first step in the design of a land application system.
Important characteristics include:
1. Current and future sludge generation quantities—
cost estimates, land area requirements, site life, and
application rates are all based in part on sludge
production quantities.
2. Percent total and volatile solids—total solids con-
tent will influence the choice of transportation and
application method. Volatile solids content is an
important indicator of potential odor problems.
3. Nitrogen, phosphorus, and potassium—provides in-
formation on the fertilizer value of sludge. This in-
formation can be useful for determining optimum
application rates, and the need for supplemental
fertilization.
4. Heavy metals (principally cadmium, copper, nickel,
lead and zinc) and specific organic compounds—
provide information on limiting yearly or total appli-
cation quantities.
5. Pathogens, parasites and viruses (optional)—evalu-
ation of the above organisms is useful in assessing
the degree of sludge stabilization.
59
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Variability in Sludge Data
The physical and chemical properties of sludge are
functions of numerous factors, including composition of
the influent sewage, extent of industrial pretreatment,
extent of nonpoint pollution sources, and type of sewage
treatment. Because of these factors, sludge quantity and
composition are highly variable among treatment plants.
Furthermore, the daily fluctuations in sludge properties
within a treatment plant are often greater than those
found among plants.
The physical characteristics of sludge (quantity, per-
cent solids, specific gravity, etc.) depend principally on
the treatment processes used to generate the sludge.
For instance, tertiary wastewater treatment will increase
the quantity of sludge by almost an order of magnitude
over conventional methods. In addition, the chemical
composition of sludge is affected by handling methods.
Heat drying, for example, will decrease NH4+ levels, but
will leave absolute quantities of K+ or Na+ unchanged.
The effect of wet-air oxidation on sludge composition is
shown in table 9-2, while the differences among aerobi-
cally and anaerobically digested sludges and other
sludge types are shown in table 9-3.
The large variations in sludge metal content are illus-
trated in table 9-4. This variability may be a reflection
of the extent of metal-using industries served by the
treatment plant. However, not all cities exhibit such fluc-
tuations (i.e., certain suburban "bedroom" communities).4
Many cities may have instituted pretreatment measures
to reduce concentrations of heavy metals in sewage.
The effect of such pretreatment is shown by the exam-
ple in table 9-5. Heavy metal loads decreased in both
the wastewater and sludge after pretreatment.
The data shown in tables 9-2 through 9-5 are used
primarily for illustrative purposes. While useful for order-
of-magnitude estimates and preliminary planning, applica-
tion of the figures to any specific treatment plant for
design purposes is not warranted.
Data Sources
The wastewater treatment plant represents the best
source of sludge data. If data have not been collected,
a sampling procedure should be instituted as discussed
below. In addition, other agencies or individuals should
be located who have analyzed similar samples and who
can make their findings public. Possible sources are:
1. State Regulatory Agencies.
2. National Pollutant Discharge Elimination System
(NPDES) Report.
3. Local or state public health departments.
4. Local universities.
5. Environmental Protection Agency, Washington, D.C.,
or regional office.
Sampling and Analysis
The flow weighted average chemical composition of
sludge is desirable and requires continuous flow mea-
Table 9-2.—Effect of wet-air oxidation on the chemical
composition of sewage sludges5
Plant No. 1
Plant No. 2
Parameter
Before After Before Afte
percent3
Volatile solids
Soluble P
Particulate P
Soluble total N
Soluble organic N
Particulate total N
Particulate organic N
47.1
0.082
1 .074
1 .356
0.293
2.120
1.837
36.7
0.004
1.219
0.471
0.173
0.856
0.863
57.2
0.153
1.401
1.354
0.131
2.839
2.490
36.3
0.01
2.31
0.42
0.17
1.34
1.32
mg/kga
Total Cu
Total Zn
Total Ni
Total Cd
Total Pb
1 ,090
1 ,996
70
11.4
451
1,011
1,974
70
11.3
471
649
1,814
911
58.4
686
852
2,497
1,064
77
978
aPercent or mg/kg oven-dry solids basis.
Table 9-3.—Median concentrations of major constituents
in sewage sludge versus digestion method6
Type of sludge
Component
Anaerobic Aerobic Other3
All sludge
N
P
K .
Na
Ca
Mg
Fe
Al
Pb
Zn
Cu
Ni
Cd
Cr
4 2
30
03
0.7
4.9
0.5
1.2
0 5
540
1 ,890
1 ,000
85
16
1 350
Percen
4 8
27
04
0.8
3.0
0.4
1.0
04
mg/kg
300
1 ,800 1
970
31
16
260
t
1 8
1 0
0 2
0.1
3.4
0.4
0.1
0 1
620
,100
390
118
14
640
3 3
23
03
0.2
3.9
0.4
1.1
04
500
1,740
850
82
16
890
aLagooned, primary, tertiary.
60
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Table 9-4.—Chemical composition8 of sewage sludges6
Componen
Total N
NH4-N ....
NO3-N
P. . .
K
Ca
Ma
Fe
Mn
B
Hg
Cu
Zn
Ni
Pb .
Cd
Number
t Units of
samples
Percent0 191
103
45
189
192
193
189
165
mg/kgc 143
109
78
205
208
165
189
189
Range
01-176
01- 68
01- 05
01-143
01- 26
0 1-25 0
01-20
01-153
18- 7100
4- 760
05-10600
84-10400
101-27800
2- 3520
13-19700
3- 3410
Median
33
01
01
23
03
39
05
1 1
260
33
5
850
1 740
82
500
16
C
Mean
3.9
07
01
25
04
49
05
1 3
380
77
733
1,210
2790
320
1 360
110
Coefficient of
variability,
percentb
85
171
158
61
99
87
75
148
209
162
232
138
134
162
177
157
"Data are from numerous types of sludges (anaerobic, aerobic, activated, lagoon, etc.) in
seven states: Wisconsin, Michigan, New Hampshire, New Jersey, Illinois, Minnesota, Ohio.
bStandard deviation as a percentage of mean. Number of samples on which this is based
may not be the same as for other columns.
°Percent or mg/kg oven-dry solids basis.
Table 9-5.—Effect of pretreatment8 of plating shop
wastewater on sludge composition4
Element
Plating shop
wastewater,
mg/l
Digested sludge
mg/kg dry sludge
7/75 4/76 4-5/75 7/75 11/75 4/76
Zn
880
4.2
Cd.
Cu
Ni
Pb
Cr
296
17.2
1380
9.2
1 85
0034
0095
208
0.071
190
1 500
1 120
340
178
1,590
1 080
360
2590
90
1,440
460
310
1 030
50
1,370
410
305
aPretreatment began in July 1975.
surements in conjunction with periodic sampling for
chemical analyses. Even though this approach is pre-
ferred, it is difficult to implement, resulting in the tenden-
cy to collect grab samples.
For design purposes, the median concentration ob-
tained from analyses of several grab samples may prove
more useful than average chemical composition. The me-
dian, unlike the mean, tends to minimize data from sam-
ples exhibiting abnormally high or low concentrations
and may therefore prove more representative. The num-
ber of samples needed to estimate the median concen-
trations should be based on the residence time of the
sludge in the digester or process used. Seasonal varia-
tions of inputs to the plant should be considered when
establishing the time and frequency of sampling.
Other pertinent points of sludge sampling can be sum-
marized as follows:
1. Develop a sound sampling program. A minimum ef-
fort is 3 to 6 samples obtained over a one-year
period. The number of samples required can vary
from plant to plant and varies as a function of
desired accuracy and precision. The validity of re-
commendations for application rates is directly pro-
portional to the knowledge of sludge composition.
2. Sample the form of sludge being considered for
land application.
3. Consider the residence time of sludge in the treat-
ment plant when deciding the frequency of sam-
pling.
Samples must be preserved to prevent changes in com-
position between time of collection and analysis. Freez-
ing and low temperature storage (4°C) are recommend-
61
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ed for samples to be analyzed >7 and <7 days, re-
spectively, after collection.
To minimize nitrogen volatilization prior to analysis, all
N analyses should be performed at ambient moisture
levels. For liquid sludges «10 percent solids), subsam-
pling is facilitated by placing the sample in a blender to
disrupt solid particles. For sludges containing >10 per-
cent solids, dilution of the sludge sample with H2O and
then disruption in a blender may alleviate subsampling
problems. All other analyses (P, K and metals) can be
performed on samples dried at room temperature or in
an oven. After drying, the sludge should be ground to
<60 mesh to allow accurate subsampling. The percent
solids content of each sludge analyzed is obtained in
order to express all data on an oven-dry solids basis.
Climate
Precipitation, evapotranspiration, temperature, and wind
data can be used to determine (1) length of growing
season, (2) number of days when sludge cannot be
applied, and (3) storage requirements. For cases where
design application rates are governed by nitrogen uptake
rates, a limited growing season will require long periods
of storage or alternative methods of winter disposal.
Storage capacity considerations must also include per-
iods of inclement weather and frozen ground when
sludge cannot be applied.
The length of the growing season affects the amount
of time a site can be used for application. The length of
the growing season for perennial crops is generally the
period beginning when the maximum daily temperature
stays above the freezing point for an extended period of
days, and continues throughout the season despite later
freezes.7 This period is related to latitude and hours of
sunlight as well as to the net flow of energy or radiation
into and out of the soil.
Sufficient climatic data are generally available for most
locations from three publications of the National Oceanic
and Atmospheric Administration (NOAA—formerly the
U.S. Weather Bureau).
The Monthly Summary of Climatic Data provides basic
data, such as total precipitation, maximum and minimum
temperatures, and relative humidity, for each day of the
month for every weather station in a given area. Evapo-
ration data are also given where available.
The Climatic Summary of the United States provides
10-year summaries of data in the same given areas.
These data are convenient for use in most of the evalu-
ations, and includes:
1. Total precipitation for each month of the 10-year
period.
2. Total snowfall for each month of the period.
3. Mean number of days with precipitation exceeding
0.10 and 0.50 in. (0.25 and 1.3 cm) for each
month.
4. Mean temperature for each month of the period.
5. Mean daily maximum and minimum temperatures for
each month.
6. Mean number of days per month with temperature
less than or equal to 32° F (0°C), and greater than
or equal to 90° F (32.5° C).
Local Climatological Data, an annual summary with
comparative data, is published for a relatively small num-
ber of major weather stations. Among the most useful
data contained in the publication are the normals, me-
ans, and extremes which are based on all data for that
station, on record to date. To use such data, correlation
may be required with a station reasonably close to the
site.
Climatic data should be subjected to a frequency ana-
lysis to determine the expected worst conditions for a
given return period. Such analyses for rainfall for select-
ed cities appears in a recent EPA publication.8
Regulations
State and Local
Information on regulations governing sludge generation
and disposal can be obtained from the state wastewater
and/or solid waste regulatory authority in the state. The
state or local public health departments can also provide
information on local acceptability of sludge utilization as
well as detailed information on public health related as-
pects of sludge disposal. Other sources of regulatory
information include agricultural colleges, solid waste
management agency, or water-quality agency. State and
local regulations can often provide a variety of other
useful information.
Most states have not set policies regarding use of
sludge on land, but many states have recently issued
guidelines or are preparing to do so. Some of these are
regulatory documents, while others are information bulle-
tins.
Local control of land use can affect site selection for
sludge application. Small communities usually apply
sludge to farmers' land; thus, sludge use is apt to be
considered an agricultural practice. Big cities that buy or
lease land and apply sludge at rates higher than neces-
sary to fertilize a crop may face legal restraints. Zoning
ordinances may restrict landspreading by a city on land
outside its corporate limits.
Federal
On November 2, 1977, the U.S. Environmental Protec-
tion Agency (EPA) published a technical bulletin entitled
"Municipal Sludge Management: Environmental Factors."9
This technical bulletin is intended to assist the Agency's
Regional Administrators and their staffs in evaluating
grant applications for construction of publicly owned
sewage treatment works under section 203(a) of Public
Law 92-500. The bulletin, while not a regulatory docu-
ment, addresses factors important to the environmental
acceptability of particular sludge management options
and allows maximum flexibility to the regions. The docu-
ment emphasizes land application alternatives since no
62
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Agency guidelines have been issued. It does state, how-
ever, that priority should be given to application of
sludge on nonagricultural lands (e.g., parks, forests,
strip-mine reclamation, etc.).
The bulletin places primary reliance on the Food and
Drug Administration (FDA) and the U.S. Department of
Agriculture (USDA) to establish recommendations for ac-
ceptable tolerances for heavy metals and other contami-
nants in plants. Technical assistance needed to resolve
specific questions concerning sludge use is available
from these and other agencies. To obtain funds from the
construction grants program, a proposed project must
follow the guidelines set forth in the bulletin.
While the technical bulletin is not a regulatory docu-
ment, new solid waste legislation (the Resource Conser-
vation and Recovery Act of 1976 (PL 94-580, or
RCRA), may result in the regulation of some municipal
sludge. This law provides the Federal Government with
the authority to protect health and the environment and
facilitate resource recovery and conservation in the face
of the growing solid waste disposal problem.
The definitions of solid waste or solid waste manage-
ment stated in RCRA refer to sludge and sludge man-
agement. Furthermore, the definition of disposal, which
includes placing waste into or on any land, clearly en-
compasses both sludge landspreading and sludge dis-
posal in a landfill. The definition of hazardous waste also
leaves open the possibility that some sludges, like some
solid wastes, may be hazardous and may, therefore, be
covered under the hazardous waste control program of
Public Law 94-580 (subtitle C).
Sections dealing with residual sludge management are
summarized as follows:
1. Guidelines (section 1008)—The guidelines will likely
include descriptions of alternative sludge manage-
ment practices which will achieve acceptable envi-
ronmental performance levels.
2. Hazardous Wastes (subtitle C)—If some sludges are
defined as hazardous wastes, this subtitle will affect
sludge management.
3. Planning and Open Dumps (subtitle D)—Some cur-
rent sludge disposal practices may fall under the
definition of open dumps, and therefore, will be
regulated by this act.
SITE SELECTION
Site selection procedures normally begin after it has
been established, by rough estimate, that sufficient land
area is available for a sludge utilization program. Selec-
tion procedures normally include an areawide evaluation
of soils, geology, hydrology, topography, and land use.
In addition, potential site accessibility and proximity to
/ treatment plant are also considered. The following sec-
tions discuss the above factors as well as preliminary
screening, site identification, and site acquisition proce-
dures.
Preliminary Screening
To obtain an initial estimate of the area required for
land application, the total quantity of sludge must be
known or estimated. This number, when divided by an
assumed application rate, will provide an estimate of
total acreage needed. Initial values of 5 and 10 dry
tons/acre/yr (11.2 and 22.4 Mg/ha/yr) can be consid-
ered as estimates for forested and agricultural lands,
respectively. These numbers can be modified during lat-
ter stages of the design process, when other site specif-
ic factors have been demonstrated.
After estimation of total acreage required, potentially
available land areas within a radius of up to about 30
miles (48 km) of the treatment plant can be considered,
including croplands, forests, parks, golf courses, strip-
mined areas, and other arable lands. Local extension
agents and county planners can often aid in the selec-
tion process.
Not all land will be suitable for land application of
sludge. The use of soil survey maps can provide screen-
ing of potentially unsuitable areas, such as:
1. Steep areas having sharp relief and slopes greater
than 12 percent.
2. Land adjacent or close to urban/suburban develop-
ment.
3. Rocky, nonarable land (unless reclamation is being
considered).
In addition to these physical factors, local officials' expe-
rience with similar projects, such as locating a site for a
sanitary landfill for refuse disposal, may be useful. Cer-
tain areas may not be available because of historical
resistance to such projects. Such resistance may be
intensified if sludge hauling requires crossing political
boundaries. In other words, the aforementioned 30-mile
(48 km) radius circle should not fall within another city
or county.
This type of initial screening procedure takes only a
few days but could save months of potentially unneces-
sary work at a later time. If enough land appears to be
available, more detailed planning can get underway; oth-
erwise other sludge handling alternatives can be investi-
gated.
Site Identification
Once the preliminary screening has been accom-
plished, a more detailed study of potential sites can be
initiated. Land use, topography, and soil properties rep-
resent three factors useful for excluding undesirable ar-
eas and identifying best suited sites. Limiting criteria can
be set for each factor with the understanding that they
would be reexamined if excessive amounts of land were
excluded from consideration.
Land Use
Prevailing land use may exert a significant influence
on the acceptability of sludge spreading. Basic land
63
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uses such as agriculture, urban-suburban, commercial, or
industrial, along with size of holdings and type of farm-
ing should be considered. For example, small land hold-
ings in a community with a large nonfarm population
serve to restrict landspreading options. Areas devoted to
row crop production restrict the periods when sludge
can be applied to land. In contrast, sludge can be
spread on grasslands or forests throughout much of the
year. The methodology and management practices for
using sludge for forest production and disturbed land
reclamation are only now being developed, but it ap-
pears that the opportunity to use sludge beneficially in
these areas has been largely overlooked.
Land use considerations also involve identification of
areas with which land application of sludge may not be
compatible. Examples are housing or commercial devel-
opment, and areas of historical, archeological, or ecolog-
ical significance.
The local government's planning and/or zoning depart-
ment is the best source of general land use data. The
local Soil Conservation Service or Agricultural Extension
Service representative has knowledge of both the farms
and types of crops typically planted. The agent will, in
most cases, have a comprehensive, up-to-date county
soil survey with aerial photo maps showing the land
area, and describing the soil types, including physical
and mechanical properties of the soil, best land use,
and other pertinent farming information.
Often a real estate broker will have handy community
or areawide maps indicating the tract of land, present
owners, and property boundaries. The county recorder
or title insurance company is another useful source of
information on property ownership, size of tracts and
related information.
Detailed information on current cropping practices can
be obtained from the local Soil Conservation Service or
Agricultural Extension Service representative, or from
university or college departments of agronomy. These
people have extensive field experience and are quite
knowledgeable about many aspects of soils, cropping
practices, toxic, or deficient constituent levels, and farm
management. The agricultural colleges have done consid-
erable work on the impacts of sludge on plants and
soils. Related disciplines such as departments of horti-
culture, forestry, agronomy, soil science, or others can
be consulted as the need arises.
Topography
Topography asserts a major influence on surface and
subsurface water movement, soil erosion, and soil forma-
tion processes. Slope characteristics are important fac-
tors in determining the amount of runoff and erosion.
Erosion is a minimal problem on flat lands, but with
increasing slope the potential for erosion increases. The
degree, length, uniformity, and shape of the slope are all
important in determining the relative ease of establishing
suitable erosion-control practices.
The percent slope is usually more important than
length from the standpoint of erosion severity. The effect
of slope length on erosion varies considerably with the
type of soil. Generally, longer slopes have less runoff
than shorter ones, especially for permeable soils.
Regardless of slope, certain conservation practices
can be adopted which will minimize runoff from sludge-
treated soils. Such practices include reduced tillage sys-
tems, terraces, strip cropping, and retention of crop res
dues on the soil surface wherever possible.
Two general landscape drainage systems exist: the
open and the closed system.10 The open drainage syster
of most humid and subhumid areas permits the move-
ment of sediment and soluble material from a given site
to the watercourse. In contrast, the closed drainage sys
tern of some arid and semi-arid areas is a landscape
where essentially all products derived within the perime-
ter are trapped within the system and are not transmit-
ted to major streams or underground water supplies.
Excess water is ponded and then evaporates or perco-
lates through the soils. These systems contribute little tc
the pollution of the environments outside their perimeter.
A modified closed system can easily be developed on a
nearly level landscape by erection of small ridges acres;
the outlet of the drainage basin.
At any proposed site requiring major shaping, the
characteristics of the subsoil horizons should be carefull
evaluated to determine the types of chemical and physi-
cal characteristics which may be exposed or brought
closer to the surface during the shaping operation.
Soils on convex landscape positions or on steep
slopes usually are well drained, well oxidized, thinner,
and subject to erosion. Soils on concave landscape po-
sitions and on broad flats are often more poorly drainec
less well oxidized, and deeper. Water and sediment from
higher positions move to these low-lying landscape ar-
eas.
Therefore, a closed or modified closed drainage sys-
tem would be preferred with slopes less than 4 to 6
percent. Steeper gradients may be acceptable where
management application methods reduce erosion ha-
zards.
Slope data may also be obtained from U.S. Geologica
Survey topographic maps. In flat areas these maps are
plotted with one-foot contour intervals. The U.S. Soil
Conservation Service soil surveys also delineate soils by
slope.
Soils
The feasibility of sludge utilization is influenced by the
nature of the soils on which the sludge is applied. Wher
soil properties are known and properly considered,
sludge can be applied to land beneficially. Soils with a
wide range in physical, chemical, and biological charac-
teristics can be used successfully if the system is de-
signed to compensate for less-than-ideal properties.
Soils can be characterized by the following physical
properties:
1. Permeability.
2. Drainage.
64
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3. Runoff and flooding.
4. Available water capacity.
These soil characteristics are discussed in the follow-
ing paragraphs and are summarized in tables 9-6, 9-7,
and 9-8.
Permeability
Soil permeability influences the length of time wastes
remain in the soil and potential loading rates.11 The rate
at which soils will take in water is a function of the
size, shape, and number of their pores.
Drainage
Soil drainage is a measure of the length of time the
soil is naturally at or near saturation during the growing
season.12 This reflects both the ability of the soil to
remain aerobic and to support traffic.
Runoff and Flooding
It is important that the applied waste stay on the site.
Runoff is closely related to infiltration rate, soil slope,
and cover. In general soils that flood are considered to
have severe limitations for disposal of wastes. If the
Table 9-6.—Limitations of soils for application of biodegradable solids and liquids (nationwide, interim)
,13-15
Soil-limitation rating
Item affecting use
Slight
Moderate
Severe
Permeability of the most restricting 0.6-6.0 in./hr
layer above 60 in.a
Soil drainage class16 Well drained and moderately
well drained
Runoff16 Ponded, very slow, and slow
Flooding None
Available water capacity from 0-60 in.
or to a root-limiting layer
>8 in. (humid regions)
>3 in. (arid regions)
6-20 and 0.2-0.6 in./hr
Somewhat excessively
drained and somewhat
poorly drained
Medium
None for solids; only during
nongrowing season allow-
able for liquids
3-8 in. (humid regions)
Moderate class not used in
arid regions
>20 and <0.2 in./hr
Excessively drained, poorly
drained, and very poorly
drained
Rapid and very rapid
Flooded during growing sea-
son (liquids) or anytime
(solids)
<3 in. (humid regions)
<3 in. (arid regions)
aModerate and severe limitations do not apply for soils with permeability <0.6 in./hr: (1) for solid wastes unless the waste is plowed
or injected into the layers having this permeability or evapotranspiration is less than water added by precipitation and irrigation, and (2)
for liquid wastes if layers having that permeability are below the rooting depth and evapotranspiration exceeds water added by
precipitation and irrigation.
Table 9-7.—Soil limitations for sewage sludge to agricultural land at nitrogen fertilizer rates in Wisconsin17
Degree of soil limitation
Soils features affecting use
Slight
Moderate
Severe
Slope3
Depth to seasonal water table
Flooding and ponding
Depth to bedrock
Permeability of most restricting layer above 3 ft
Available water capacity
Less than 6 percent
More than 4 ft
None
More than 4 ft
0.6 to 2.0 in./hr
More than 6 in
6 to 12 percent
2 to 4 ft
None
2 to 4 ft
20 to 60 in./hr
02 to 0.6 in./hr
3 to 6 in.
More than 12 percent
Less than 2 ft
Occasional to frequent
Less than 2 ft
Less than 0.2 in/hr
More than 6 in./hr
Less than 3 in.
"Slope is an important factor in determining the runoff that is likely to occur. Most soils on 0 to 6 percent slopes will have very slow
or slow runoff; soils on 6 to 12 percent slopes generally have medium runoff; and soils on steeper slopes generally have rapid to very
rapid runoff.
65
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Table 9-8.—Soil suitability for sludge applications for agricultural production in New York State13
Item affecting use
Soil potential
Very good
Good
Moderate
Poor
Very poor
Drainage class and ap-
proximate depth in
inches to permanent or
fluctuating water table
Total water-holding capac-
ity [in. H2O/rooting
depth]
Slope (percent)
Rooting depth (in. to root
restricting horizon)
Trafficability (unified soil
group)
Permeability class (in./hr
in least permeable hori-
zon)
Well drained (>36)
>6
<3
>40
GW, GP, SW, SP,
GM, GC, SM, SC,
Pt (drained)
0.6-2.0
Moderately well Somewhat poorly
drained (18-36) drained (12-18)
4-6
3-8
30-40
3-4
8-15
20-30
CL with PI <15 ML, CL with PI
2.0-6.0
>6.0
Poorly drained Very poorly drained
2-3 <2
15-25
10-20
OH, OL, MH CH, R (undrained)
>25
0.6-0.06
<0.06
Erosion
Stoniness and rockiness . .
pH in B horizon
Texture
None to slightly
eroded
0
>70
si1
Slightly eroded
1
65-70
1, sicl
Moderately eroded
2
60-6.5
S1, C1
Severely eroded
3
5.5-6.0
sc1, c
Very severely eroded
4 and 5
<5.5
s, 1s (not irrigated)
soils flood only during the nongrowing season, however,
they are considered as having only moderate limitations
in some localities.
Very few soils are totally unsuitable for land applica-
tion of sludge. Some, however, are better than others.
The U.S. Soil Conservation Service (SCS) and several
states have developed tables which rate the suitability of
soils for receiving sewage sludge. Table 9-6 shows the
guidelines prepared by the SCS while tables 9-7 and 9-
8 are for Wisconsin and New York, respectively.
Tables such as these should be consulted to deter-
mine whether a potential site is suitable for land applica-
tion. However, additional onsite investigations should be
conducted for specific site selection and for system de-
sign.
The soil is rated by the single most severe character-
istic. The categories can be quite restrictive since one
poor characteristic forces a soil into the most limiting
category. Nevertheless, the method enables the planner
to quickly determine the best and worst soils. For exam-
ple, as a first approximation, all soils in the "severe"
rating of table 9-6 can be eliminated.
Geology
The movement of water into and through groundwater
aquifers is dependent on local and regional geology. For
sludge application systems requiring groundwater moni-
toring, a knowledge of subsurface conditions is essential
Bedrock characteristics can influence the direction anc
speed of groundwater movement and determine whether
a pollutant might be carried large distances with only
minimal biological or chemical renovation.
For example, limestone bedrock can be interlaced with
a complex pattern of relatively open fractures and solu-
tion channels. The fractures and channels can behave
like open pipelines. Any contaminant which enters such
an opening can travel substantial distances without any
significant reduction in concentrations. Under such con-
ditions, the discharge of the solution channel water into
a well or stream could result in pollution problems.
In evaluating the hydrogeologic conditions associated
with a specific site, the following factors should be con-
sidered:
1. Depth to the groundwater table.
2. Seasonal water table fluctuations.
3. Groundwater velocity.
4. Direction of travel.
5. Present and potential use of groundwater and sur-
face water bodies.
6. Existing surface and groundwater quality.
7. Interrelationship between ground and surface water
bodies.
8. Surface water body ecology.
9. Subsurface soil and rock characteristics which af-
fect groundwater movement patterns and quality.18
66
-------
Site Delineation and Evaluation
Following exclusion of unsuitable areas, specific sites
can be chosen. Since modes of transportation and trans-
portation distances are important to the economics of
sludge utilization, it is desirable to choose sites as close
as practical to the generating sewage treatment plant.
Using a regional map, concentric rings of incremental
radii can be drawn around the sewage treatment plant.
Candidate sites within each concentric ring can then be
identified. Sites within the inner ring have the highest
priority rating while sites more distant from the source
become progressively less attractive.
Each site can then be evaluated on the basis of soil
criteria presented in tables 9-6, 9-7, or 9-8. Factors
listed below should also be considered.
1. Proximity of disposal areas to homes, commercial
establishment, town center, etc.
2. Ready access from all-weather roads.
3. Prevailing wind direction for minimization of odor
complaints.
4. Distance to groundwater or nearest surface water
body.
5. Total farm acreage available on each farm.
6. Types of crops historically planted.
7. Prevailing soil types present with regard to their
suitability for sludge additions.
8. Field slopes and general site topography.
Ranking or scoring procedures and/or overlay tech-
niques can be used to help select the best sites. For
example, transparent map overlays can be prepared for
each criterion discussed above. Thus, the first map
might have areas with steep slopes shaded; the second
map would have urbanized and other excluded areas
shaded. Subsequent maps would have other restrictions
as shaded areas. Information from all maps would then
be combined to produce a composite map; the best
areas for land application would have the lightest shad-
ing or none at all.
Site Acquisition
Site acquisition represents the most critical step in the
implementation of a land application project. The points
discussed in "Preliminary Planning" are essential ground-
work for obtaining public support and acquiring the most
desirable sites.
A variety of contractural arrangements exist between
sludge producers and landowners. The most common
arrangements between municipalities and farmers in de-
scending order of frequency of occurrence are:
1. The city transports and spreads the sludge at no
expense to the farmer.
2. The city not only transports and spreads the
sludge, but pays the farmer a nominal sum of 50
cents to $2.00 per load. This is usually only for
sites which are close to the treatment plants or do
not generate a particularly desirable sludge.
3. The farmer pays a nominal fee of between $1 and
$2 per load. The city transports and spreads the
sludge. This is most common where there is a large
local demand for the sludge or the sludge is of
particularly good quality.
4. The city leases the site for a period of 1 to 5
years.
Less common arrangements are:
1. Outright purchase of the site. The advantage of this
is that the city has considerable control over both
the quantity and frequency of application, as well
as the crops grown on the site.
2. Contractual arrangement between the city and the
receiving farmers. The sludge is distributed on a
rotating basis to each of the participants. In at
least one system, payment of an initial sum of mon-
ey provides a commitment on the part of the farm-
er.
Written rather than oral contracts are preferred. With
written contracts there is less chance of ambiguity and
misunderstandings between parties. Despite the best in-
tentions of either party, oral contracts can often result in
different interpretations of the conditions of the agree-
ment (i.e., application rates, crops grown, etc.).
A survey of several Ohio communities revealed that
only 20 percent had written contracts.2 Most of those
contracts had one or more of the following points:
1. "Escape" clause for either party
2. Restriction to the type of crops grown on the dis-
posal site
3. Restrictions on application during growing season
and on application to wet soils
4. Restrictions on application rate
5. Placement of any liabilities due to odor, runoff, etc.
with the farmer.
The last provision would seem unfair to the farmer recip-
ient unless the analysis of the sludge is known by the
farmer. Making the farmer solely liable for the effects of
the sludge would be equitable only when the treatment
plant is able to provide a detailed analysis of the sludge
and is assured that the farmer has been informed of the
potential hazards of application.
PROCESS DESIGN
Process design involves the selection of suitable
crops, determination of sludge application rates, and
choice of application method. Although basic design
goals (maximization of crop yield and quality, and mini-
mization of environmental damage) remain constant re-
gardless of projected land use, design procedures differ
for application on agricultural, forested, reclaimed, or
parklands. Design procedures for agricultural lands are
based on principles developed from soil fertility research
in conjunction with results from sludge utilization studies.
In contrast, a minimal amount of information is available
concerning sludge application to forested, reclaimed, and
67
-------
Table 9-9.—Annual N, P, and K utilization by selected
crops3
Crop
Corn
Corn silage
Soybeans
Grain sorghum
Wheat
Oats
Barley
Alfalfa
Orchard grass
Brome grass
Tall fescue . . .
Bluegrass . .
Yield/acre
150
180
32
50
60
4
60
80
100
100
8
6
5
35
3
bu.
bu.
tons
bu.
bu.
tons
bu.
bu.
bu.
bu.
tons
tons
tons
tons
tons
N P K
(Ibs/acre)
185
240
200
"257
"336
250
125
186
150
150
"450
300
166
135
200
35
44
35
21
29
40
22
24
24
24
35
44
29
29
24
178
199
203
100
120
166
91
134
125
125
398
311
211
154
149
"Values reported are from reports by the Potash Institute of America
and are for the total above-ground portion of the plants. For the
purpose of estimating nutrient requirements for any particular crop
year, complete crop removal can be assumed.
bLegumes obtain N from symbiotic N2 fixation so fertilizer N is not
added.
other nonagricultural lands. Design procedures for agri-
cultural and nonagricultural lands are discussed sepa-
rately in this chapter.
Agricultural Lands
Type of Crop
It is usually advantageous to maintain or utilize the
normal cropping patterns found in the community.19'20
These patterns have evolved because of favorable soil,
climatic, and economic conditions and will probably
maintain certain advantages in the sludge application
system as well. One possible exception could occur if
the cropping pattern were restricted to a single crop. In
this case, additional crops could increase the opportunity
of applying sludge during a variety of seasons.
Row crops such as corn and soybeans probably offer
the least sludge application flexibility, but can be used
on sludge amended soils with few constraints. Corn has
an added advantage in that it accumulates little cadmi-
um. Forage crops can be superior to others in terms of
nutrient utilization during the growing season. Removal
of these grasses from the site maximizes nutrient reuse.
However, a continuous sod makes sludge applications
more difficult. Small grain crops use lower amounts of
nutrients as compared to row crops or forages, and are
subject to lodging. Vegetables, especially leafy and root
Table 9-10.—Removal of different elements from soils by crops21
Removal (Ibs/acre)
Cone (mg/kg)
Crop
Yield
per acre
N P K Ca Mg S Na Fe Mn Cu Zn
Corn grain 100 bu
Grain sorghum 80 bu
Soybeans 32 bu
Peanuts 2,500 Ibs
Cottonseed 1,800 Ibs
Wheat 60 bu
Rice 6,000 Ibs
Barley 75 bu
Sugarbeets 25
Corn silage 20
Alfalfa hay 7
Coastal bermuda hay 9.5
Reed canarygrass hay 7
Potatoes 30
Tomatoes 20
Lettuce 12.5
Carrots 20 t
Snap beans 5 t
Dry beans 1,800 Ibs
Loblolly pine annual growth
80
80
105
94
62
81
78
67
21
136
332
243
169
210
71
34
58
27
64
9
15
14
11
8
13
15
14
15
20
24
31
29
30
30
11
5
12
4
8
1
17
15
29
12
20
18
9
20
125
118
212
270
282
288
98
42
112
21
22
4
2
2
5
2
3
2
3
3
20
34
197
74
41
6
5
5
12
5
3
5
8
8
5
4
6
4
4
5
15
24
38
27
31
18
6
3
8
3
3
2
7
7
4
6
4
6
3
6
1
12
43
—
—
12
—
—
8
—
4
1
1
2
4
14
5
3
3
1
40
3
19
—
47
12
1
2
15
1
1
—
66
90
70
16
114
73
96
87
104
32
64
14
30
26
10
80
48
26
227 765
929 228
1,306 282
6 43
20 28
14 —
41 —
11 23
9 5
12 25
30 —
47 98
74 92
816 503 65
544 240 102
92 — —
55 — —
68
15
24 —
8 —
68
-------
vegetables, are not recommended on sludge amended
soils because they are heavy metal accumulators.
Nutrient Requirements
Fertilizer recommendations for crops are based on the
nutrients needed for the desired yield. The amounts of
N, P, and K required by the major agronomic crops are
shown in tables 9-9 and 9-10. Plant available nutrient
levels in the soil before planting will dictate the fertilizer
additions for a desired yield as illustrated in table 9-11.
Table 9-11.—Fertilizer P and K recommendations for
various yields of corn*
Available
nutrient
level
in soil
Yield level, Ib/acre
100-110 111-125 126-150 151-175 176-200
Ibs P/acre
Fertilizer P needed, Ibs/acre
0-10.
11-20.
21-30..
31-70.
Ibs K/acre
44
31
22
13
0
48
35
26
13
0
55
40
26
18
4
57
44
31
22
4
66
53
35
22
4
Fertilizer K needed, Ibs/acre
0-80
81-150
151-210
211-300
>300
83
58
42
25
0
100
75
50
25
0
125
100
58
33
0
149
116
75
50
0
166
133
100
66
0
The previous year's crops may exert an influence on the
nutrient recommendations for a crop at different yield
levels as shown in table 9-12. Figures 9-1 and 9-2
relate plant yield to nutrient concentrations. Recommen-
dations for sludge application stress utilization rates con-
sistent with nitrogen uptake by a crop.
Application Rate
Sludge application rates recommended for crop pro-
duction are calculated in the same manner as commer-
cial fertilizer application rates. At these rates, sludges
can be considered as strictly a low grade fertilizer.
Annual application rate recommendations for agricultur-
al soils are based on the nitrogen and cadmium con-
tents of a sludge and the crop being grown. The total
amount of sludge applied to soils is limited by the heavy
metal additions with zinc, copper, nickel, and cadmium
LIMITATION
o
tr
o
i-
z
O
LOW
ADEQUATE
HIGH
aPurdue University Plant and Soil Testing Laboratory Mimeo, 1974.
AMOUNT OF NUTRIENT SUPPLIED
Figure 9-1.—General relationship between any particular
nutrient or growth factor and plant growth.
Table 9-12.—Influence of previous crop of N fertilization rates for corn.3
Yield level (bu/acre)
Previous crop
100-110 111-125 126-150 151-175 176-200
Good legume (alfalfa, red clover, etc )
Average legume (legume-grass mixture or poor stand)....
Corn, soybeans small grains grass sod .
Continuous corn
40
60
100
120
70
100
120
140
Ibs N/acre
100
140
160
170
120
160
190
200
150
180
220
230
"Purdue University Plant and Soil Testing Laboratory Mimeo, 1974.
69
-------
QC
O
I
O
oc
(3
TOXICITY RANGE
SUFFICIENCY RANGE
*-
DEFICIENCY
RANGE
NONRESPONSE
LOW HIGH
CONCENTRATION OF A GIVEN NUTRIENT IN A PLANT
Figure 9-2.—Suggested terminology for the relationship
between yield and the concentration of a given nutrient
in a plant.
as the metals of primary concern.22'23 The approach can
be depicted as follows:
Annual rate
tons/acre
1
N required
by crop
1
Cd
2 Ibs/acre
Lower of
two amounts
Total amount
tons sludge/acre
Controlling metal
(Pb, Zn, Cu, Ni, Cd)
The plant available nitrogen from sludge is important in
determining application rate. From the composition of a
sludge, available nitrogen can be calculated:
Available N = NH4+ +NO3~ + 20 percent of organic N.
Data suggest that 15 to 20 percent of the organic nitro-
gen is converted to plant available forms the first year
and 3 to 10 percent of the remaining organic nitrogen is
released the second year (see table 9-13). Decreasing
amounts of organic nitrogen are subsequently released
each following year. Residual nitrogen from previous
years of sludge application can be calculated from the
amount of sludge added to soils. All inorganic nitrogen
is assumed available for plant uptake. The reason for
applying sludges at the nitrogen utilization rate of a crop
is to minimize groundwater contamination due to nitrate
leaching.
The amount of plant available N added to soils in
sludge is influenced by the application method used. If
sludges are applied and allowed to dry on the soil sur-
face, from 20 to 70 percent of the NH4-N applied can
be lost to the atmosphere as NH3. The exact proportion
of NH4-N lost through volatilization depends on soil,
sludge and climatic conditions and is, therefore, difficult
to predict. Based on laboratory24 and field25 studies, 50
percent volatilization losses of NH4-N are assumed for
surface applied sludges in the following design examples.
No NH3 volatilization losses are assumed for sludges
applied to soil by injection or incorporation methods. As
a result, the rate of sludge applied to satisfy the crop's
N requirement will be greater for surface than incorpora-
tion application procedures.
Annual loading rates for cadmium (Cd) on soils are
set at 2 Ib/acre-year (2 kg/ha-year) for food chain
crops;9 however, this value can be regarded as provi-
sional and may be revised based on ongoing and future
research.26 (Throughout this discussion, the units Ibs/acre
and kg/ha are used interchangeably because the uncer-
tainties involved in establishing fertilizer recommenda-
tions, interpreting soil test data and setting heavy metal
limits are greater than the 10 percent difference between
Ibs/acre and kg/ha. The actual conversion factor is 0.91
Ibs/acre = 1 kg/ha.) This annual limit for Cd is based on
Cd uptake by crops and the potential adverse effects on
human health.
The life of a disposal site is based on the cumulative
Table 9-13.—Release of residual N in soils treated with
sewage sludge22
Years after
sludge application
Organic N content of sludge, percent
2.0 2.5 3.0 3.5 4.0 4.5 5.0
Lb N released per ton sludge added3
1
2
3
1 0
... 09
09
1 2
1 2
1 1
1 4
1 4
1 3
1 7
1 6
1 5
1 9
1 8
1 7
2.2
2 1
2.0
?4
?1
? ?
a1.0 lb/ton = 0.5 Kg/metric ton.
70
-------
amounts of lead (Pb), copper (Cu), nickel (Ni), zinc (Zn)
and cadmium applied to the soil. These limits are de-
signed to allow growth and use of crops at any future
date. The limits for metal additions to soils are shown in
table 9-14.9 Phytotoxicity will be encountered for Zn, Cu
and Ni before the concentrations of these metals in
plants will adversely affect human or animal health.
Table 9-14.—Maximum amount of metal (Ib/acre) sug-
gested for agricultural soils treated with sewage sludge3
Soil cation exchange
capacity
(meq/100 g)b
Metal
<5 5 to 15 >15
Pb
Zn
Cu
Ni
Cd
Maxin
met
500
250
125
50
5
fium amount of
:al (lb/acre)c
1 ,000 2,000
500 1 ,000
250 500
100 200
10 20
"Developed by cooperative efforts of regional research projects NC-
118 and W-124 and ARS, USDA and cited in ref. 9.
bDetermined by the pH 7 ammonium acetate procedure.
°Lb/acre = 1.121 kg/ha.
Table 9-15.—Metal content of soils and crops3
Element
As
B
Cd
Cr
Co
Cu
Pb
Mn
Mo
Ni
Se
V
Zn
Cone.
Common
(mg/kg)
6
10
006
100
8
20
10
850
2
40
05
100
50
in soils
Range
(mg/kg)
0.1-40
2-100
001-7
5-3000
1-40
2-100
2-200
100-4,000
02-5
10-1 000
01-2
20-500
10-300
Cone, in
diagnostic
Normal
(mg/kg)
0.1-5
30-75
0.2-0.8
0.2-1.0
0.05-0.5
4-15
0.1-10
15-100
1-100
1
0.02-2.0
01-10
150200
plant
tissue
Toxic"
(mg/kg)
>75
>20
>50
50-100
>10
>200
Thus, the limits for Zn, Cu and Ni will prevent reduced
plant yields due to phytotoxicity. The principal problem
with Pb is the direct ingestion of soil particles by hu-
mans and animals. Essentially no plant uptake of Pb
occurs. The Cd limit, as described, is not related to
phytotoxicity but rather the accumulation of low concen-
trations of Cd in plants. Common metal levels in soils
and crops are shown in table 9-15. The major factor foi
applying sludges to agricultural crops is that soil pH be
maintained above 6.5, to minimize heavy metal uptake b}
plants.
The steps involved in calculating application rates can
be summarized as follows:
Step 1. Obtain N requirement for the crop grown (see
tables 9-9 to 9-12).
Step 2. Calculate tons of sludge needed to meet crop's
N requirement.
a. Available N in sludge
Percent organic N (N0) = (percent total N)
- (percent NH4-N) - (percent NO3-N
Incorporated application3
Lbs available N/ton = (percent NH4-Nx20)
+ (percent NO3-N X 20) + (percent N0x4
Surface application3
Lbs available N/ton = (percent NH4-NX10)
+ (percent NCyNx 20)+(percent N0X4
(Note: The factor for NH4-N is decreased by 50
percent to account for NH3 volatilization)
b. Residual sludge N in soil
If the soil has received sludge in the past 3 years,
calculate residual N from table 9-13.
c. Annual application rate
Tons sludge/acre
_crop N requirement - residual I
~ Ib available N/ton sludge
aThe conversion factor for NH4- and NO3-N is calculated from
Ibs N 2,000 Ibs
X-
"Adapted from ref. 27. '
bToxicities listed do not apply to certain accumulator plant species.
100 Ibs sludge ton
and for N0 (only 20 percent plant available)
Ibs N0
= 20
100 Ibs sludge
ton
71
-------
If sludge is surface applied, this rate is in-
creased due to N loss through NH3 volatilization
••x-r i ^ / h 2 lb Cd/acre
„) Tons sludge/acre* =
iii) The lower of the two amounts is applied.
Step 3. Calculate total amount of sludge allowable.0
a. Obtain maximum amounts of Pb, Zn, Cu, Ni, and
Cd allowed for CEC of the soil from table 9-14 in
Ibs/acre.
b. Calculate amount of sludge needed to exceed Pb,
Zn, Cu, Ni, and Cd limits, using sludge analysis
data.
Metal
Pb: Tons sludge/acre =
Zn: Tons sludge/acre =
Cu: Tons sludge/acre =
Ni: Tons sludge/acre =
Cd: Tons sludge/acre =
lb Pb/acre
ppm Pbx.002
lb Zn/acre
ppm Znx.002
lb Cu/acre
ppm Cu x .002
lb Ni/acre
ppm Nix.002
lb Cd/acre
ppm Cdx.002
Step 4. Calculate amount of P and K added in sludge.
Tons of sludge x percent P in sludge x 20 = lb of P added
Tons of sludge x percent K in sludge x 20 = lb of K added
Step 5. Calculate amount of P and K fertilizer needed.
d(lb P recommended for crop) - (lb P in sludge)
= lb P fertilizer needed.
d(lb K recommended for crop) - (lb K in sludge)
= lb K fertilizer needed.
Forested Lands
Forested sites offer special opportunities for the bene-
ficial use of sludge through improving soil fertility and
increasing plant growth.9 Yet, the potential of forest
lands as sites for utilizing sludge is often overlooked.28 In
contrast to many agricultural crops, forest products are
generally not consumed by humans and thus, there is no
reason to suspect forest products grown on sludge
treated areas as constituting a human health hazard.28
Furthermore, direct human contact in forests treated with
sludge is minimal because of the low population density.
However, not all features of forest land use are favor-
able. Public resistance may be encountered, accessibility
may be poor, resident species, including wildlife, may be
impacted, and special distribution systems may be nec-
essary to overcome rugged and sloping terrain.28
Stand Properties and Nutrient Relationships
The ability of a forest system to utilize the nutrients
applied in sewage sludge depends upon the maturity of
the species present. The principles of nutrient accumula-
tion in a forest stand are illustrated in figure 9-3. Nutri-
ent accumulation is greatest during the early stages of
growth. In a system approaching maturity, the majority of
nutrients accumulated in previous years are merely recy-
cled to maintain biomass. The time needed to achieve
maximum nutrient accumulation depends on the tree spe-
cies, but it is normally in terms of decades.
As with agronomic crops, the harvest of a forest stand
removes the nutrients accumulated during growth. How-
ever, the amounts removed on an annual basin are sig-
nificantly lower than for agronomic crops. The N and P
removals by corn and selected tree species are shown
in table 9-16. These data suggest that vegetative cover
on forest soils is less important than in agricultural sys-
tems. Therefore, the use of sludge in forests must rely
"The factor 0.002 is derived from:
1 lb 2.000 I
106lbsX ton
°Sludge metals should be expressed on a dry weight ppm (mg/kg)
basis. The lowest value from the five calculations is the maximum tons
of sludge per acre which can be applied.
dP and K recommendations based on soil tests for available P and
K.
UJ
o
I-
<
TIME (years)
Figure 9-3.—Annual and total accumulation of nutrients
for tree species.
72
-------
Table 9-16.—Nitrogen and phosphorus removal by corn
and selected tree species3
Table 9-17.—Response of tree species to effluent
irrigation28
Nutrient removal
Response class to effluent
Species
_ , ...
Cumulative
.
(Ibs/acre)
Corn
Annual harvest (16 yrs) 1,600 288
Annual harvest (30 yrs) 3,000 540
Loblolly pine, age 16 yrs
Whole tree (above ground) 227 27
Aspen, age 30 yrs
Whole tree (above ground) 170 25
Deciduous
Young
Medium to mature
Evergreen
Young
Medium to mature
Average
annual
Low
Intermediate
High
100
100
14.2
5.7
100
30-50
60
20-30
-yr)
18
18
1.7
0.8
Slash pine
Cherry Laural
Arizona cypress
Live oak
Holly
Hawthorne
Tulip poplar
Bald cypress
Saw-tooth oak
Red cedar
Laurel oak
Magnolia
Nuttall oak
Cherrybark oak
Loblolly pine
Cottonwood
Sycamore
Green ash
Black cherry
Sweet gum
Black locust
Red bud
Catalpa
Chinese elm
rates of nitrification (i.e., NH4+^>N(V->N(V) in forest
soils which are typically acid. Since NH4+ can be bound
by the exchange complex of soils, its downward move-
ment will be limited.
aAdapted from refs. 29 and 30
on soil processes in addition to plant uptake, to mini-
mize the potential for N03~ leaching into groundwater.
The utilization of sludge in the establishment of a
forest stand affords flexibility in choosing tree species
which exhibit rapid growth rates and assimilate apprecia-
ble quantities of nutrients. In addition to nutrient uptake
and growth considerations, the adaptability of a particu-
lar species to the climate (rainfall) and soil (pH, fertility,
drainage) conditions must be evaluated. For example,
pines favor acid soils whereas legumes (e.g., red bud,
black locust, red cedar) require a near neutral pH. Smith
and Evans28 categorized the response of tree species of
irrigation with municipal effluent (table 9-17). Similar re-
sults are anticipated when nutrients are applied in
sludge. However, effluent irrigation will add appreciable
quantities of water whereas a minimal amount will be
added in sludges. Additional data are needed prior to
recommending which species are most suited for sludge
application sites.
For established forests, processes other than nutrient
uptake by trees must be considered to prevent NO3~
leaching. Even though available N has been added in
excess of the N needed for tree growth, a minimal
amount of NO3~ leaching has been observed in field plot
studies (D. H. Urie, personal communication). At in-
creased rates of sludge amendments, NO3~ movement to
a 120-cm depth was encountered. Denitrification is the
likely mechanism for depressed NCV movement in forest-
ed systems. An additional consideration is the depressed
Application Rates
Because of the minimal data on annual uptake of N
by tree species, the approach adopted for calculating
slu.dge application rates on forested lands is essentially
the same as that used for slow rate wastewater irriga-
tion systems.31 The amount of sludge applied annually is
based on: 1) an allowable NO3"-N concentration in water
percolating through the soil profile; 2) a fixed percent-
age of the N applied is lost through denitrification and
3) N uptake by the forest stand occurs.
The annual N loading rate is calculated from
Ln = U
•D + 0.23 WnCn
where
U
D
W,
= plant available N applied (Ibs/acre -yr)
= plant N uptake (Ibs/acre -yr)
= denitrification constant as a fraction of Ln add-
ed (D = 0.2 Ln)
p = percolating water (in./yr)
p = percolate NCV-N concentration (mg/l)
The amount of percolating water can be either obtained
from data sources or calculated as follows:
where
l_s = sludge loading rate (in./yr)
Pr = precipitation (in./yr)
Wp = percolating water (in./yr)
ET = evapotranspiration (in./yr)
73
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The relationship between !_„ added and the percent
solids and volume of sludge is
n = 22.7 CSLSS
where
Ln = plant available N applied (Ibs/acre-yr)
Cs= percent of available N in sludge on a dry
weight basin (i.e., percent Cs= percent
N0 X 0.2+ percent ty)
Ls = volume of sludge applied (in./yr)
S = percent solids in liquid sludge
Since sludges often contain 1 percent plant available N,
the above equation indicates that a one inch application
of a 4 percent solids sludge would add ~90 IDS (40.3
kg) plant available N per acre. In many cases, the
amount of percolation will range from 5 to 10 times the
volume of water added in sludge when liquid sludges
are applied at a rate consistent with estimated plant
uptake and denitrification of N.
As shown previously for agricultural crops, the contri-
bution of residual N to the plant available N pool can
be subtracted from the amount of N that can be applied
each year. That is, Ln is corrected for residual N after
performing the above calculations.
It must be emphasized that the above approach for
calculating application rates for forest lands is based
upon criteria for wastewater irrigation. If N uptake data
are available for the species growing on a potential
sludge utilization area, the calculations discussed previ-
ously for agronomic crops could be applied to forested
lands and it would be the preferred method for obtaining
application rates.
In contrast to agricultural systems, annual Cd loadings
will not limit application rates because a nonfood chain
crop is being grown. Although data are not available to
substantiate the impact of cumulative metal additions in
forest ecosystems, it may be advisable to follow the
same criteria as used for agricultural lands (table 9-14).
The adoption of metal limits would not only minimize any
metal toxicities to trees but it would also allow growth
of other crops on the soils if the area were cleared at a
future date. In addition, the majority of forest soils are
acid which would promote increased metal solubility.
Based on limited data, it appears that the majority of
metals added to forest soils in a surface application of
sludge remain in the litter layer. To minimize the poten-
tial for metal movement, a soil pH near neutrality would
be preferred but is not required for sludge application
sites. In summary, the major differences between agricul-
tural and forest soils are that forest soils can receive
>2 Ibs Cd/acre/yr (2.2 kg/ha/yr) and can have a soil
pH <6.5.
Other Nonagricultural Uses
Stabilized sludge can also be used for the enhance-
ment of parklands and highway median strips and for
the reclamation of damaged or poor terrain. Since the
use of sludge on these lands generally involves the
growth of a crop (e.g., turf) or forest stand, design
procedures and management considerations are general!
similar to those previously considered.
FACILITIES DESIGN
Once the site has been chosen, the land application
project may proceed to the design phase. This chapter
covers detailed site investigations, preapplication treat-
ment of sludge, transportation of sludge, application
rates and methods, storage and types of crops.
Detailed Site Investigation
The site selection process described in "Site Selec-
tion" made use of available published sources of infor-
mation, such as soil surveys and topographic maps for
evaluating alternative sites. Onsite studies will also be
necessary for a detailed evaluation of the soil resource.
Soil mapping units of the published soil survey may in-
clude small areas of contrasting soils that could not be
shown at the scale of a published survey, but that may
influence the design and operation of the system or
render a site unsuitable.
The site study should involve evaluation of representa-
tive soils to which sludge is to be applied.
The basic information obtained from soil analysis is
useful for development of sludge application rates. The
analyses required are:
1. Available phosphorus (P) and potassium (K).
2. Soil pH and lime requirement.
3. Cation exchange capacity (CEC).-
4. Organic matter (only if plant available N is com-
puted from organic matter).
Other types of soil data that may be obtained but are
not essential to developing application rates include per-
meability, percolation, particle size distribution, bulk den-
sity, and conductivity. If soil analysis will be used to
assess the accumulation of metals in soils, either ex-
tractable or total zinc, copper, lead, cadmium and nickel
should be analyzed prior to initiation of sludge spread-
ing. Information for soil sampling techniques can be ob-
tained from SCS personnel or soil testing labs.
Preapplication Treatment
Preapplication treatment refers to sludge handling
processes within the wastewater treatment plant. The
basic objective of these processes is to prepare the
sludge for ultimate disposal. For an existing treatment
plant with its large capital investment, the composition of
the sludge and handling processes will probably dictate
or limit land utilization practices. The alternative is to
adapt sludge processing systems to a land application
system. This may include source pretreatment for control
of heavy metals. Furthermore, the physical form of the
74
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sludge will influence its transport mode from treatment
plant to application site.
Known waste-solids treatment processes usually are
designed for reducing sludge volume and stabilization of
solids. Several basic processes are used:
1. Conditioning.
2. Concentration or thickening.
3. Chemical or biological treatment (i.e., digestion, la-
goons).
4, Dewatering.
5. Heat treatment.
Stabilization
There are a variety of stabilization methods currently
in use. Their general effectiveness in attenuation of pa-
thogens and odors is summarized in table 9-18. Anaero-
bic and aerobic digestion are most frequently used with
heat and chemical treatment less prevalent. The recent
EPA Technical Bulletin9 suggests that stabilization meth-
ods other than anaerobic digestion may be equivalent to
anaerobic digestion in reducing odor potential and vola-
tile organics.
In the case of lime stabilization, absorption of CO2
from the air can result in a pH reduction, subsequent
regrowth of bacteria and the potential for odors. This
destabilization may occur at the application site, if sur-
face application methods are used. These problems are
minimized by incorporation of lime stabilized sludges.
Application of lime stabilized sludges will facilitate the
maintenance of soil pH.
Table 9-18.—Attenuation effect of well conducted proc-
esses for stabilizing wastewater treatment sludges.
Process
Lime treatment
Anaerobic digestion ...
Aerobic digestion
c Heavy chlorination . . .
Pasteurization (70 °C).
'Ionizing radiation . ...
/Heat treatment (195°C) ...
c Composting (60° C)
* Long-term lagooning of digested
sludge
Heat drying...
Pathogens
Good
Fair
Fair
Good
Excellent
Excellent
Excellent
Good
Good
Excellent
Putrefaction
potential
Fair
Good
Good
Fair
Poor
Poor
Poorb
Good
Goodc
Odor
Good3
Good
Good
Good
Poor
Fair
Poorb
Good
Good0
aMay only be temporary because of possible destabilization resulting
from pH reduction.
"Good for filter cake.
cAnaerobic conditions in the soil after sludge is applied could cause
odors.
Source: Reference 32.
Dewatering
Dewatering processes are used to reduce sludge vol-
ume and prepare the sludge for transport and disposal.
The moisture content of sludges dewatered by vacuum
filters and centrifuges is reduced to a range of 75 to 85
percent. At these concentrations the sludge can be car-
ried in dump trucks and applied to the land with manure
spreaders or incorporation equipment. The choice of de-
watering systems does not affect the actual land appli-
cation process, except for a consideration of the resul-
tant moisture contents and chemical aids used. Vacuum
filters often use lime for conditioning, and the resultant
increase in pH can be valuable for agricultural applica-
tion systems.
Transportation of Sludge
If sludge cannot be applied to a site immediately adja-
cent to the treatment plant, it must be hauled to another
area. The principal methods of transport are tank truck
and pipeline. Barge and rail have only limited applicabili-
ty and are not widely used. The method of transporta-
tion chosen and its costs depend on a number of fac-
tors: (1) the nature, consistency, and quantity of sludge
to be transported; (2) the distance to the site; (3) the
availability and proximity of the transit modes to both
the origin and destination; (4) the degree of flexibility
required in the transportation mode; and (5) the estimat-
ed useful life of the ultimate disposal facility.
To minimize the danger of spills, odors, and dissemi-
nation of pathogens to the air, liquid sludges should be
transported in closed vessels, such as tank trucks, cov-
ered or tank barges, or railroad tank cars. Stabilized,
dewatered sludges can be transferred in open vessels,
such as dump trucks or railroad gondolas, if they are
covered with a tarpaulin.
Truck
Tank truck transport is the most common method of
sludge haul. Flexibility and simplicity of operation are the
key reasons for its popularity. Either liquid or dewatered
sludge can be loaded into tank trucks or trailers directly
from the digesters or storage tanks and hauled over
most highways to any site or combination of sites. If
conditions permit the sludge can be applied directly,
eliminating the need for a distribution system at the site.
The tank trucks utilized for transporting liquid sewage
sludges range in carrying capacity from about 600 to
7,500 gal (2.27 to 28.39 m3). The smaller capacity trucks
(600-3,500 gal. or 2.27 to 13.25 m3) are usually straight
tank trucks, while the larger are tractor-trailer rigs. The
trucks, either gasoline or diesel fueled, seldom average
more than 3 or 4 miles (4.80 or 6.4 km) to the gallon. /
straight tank truck designed for hauling and spreading
sludge can be purchased either as a single unit built to
specifications, or the chassis, only, may be purchased
for later tank installation. Vehicles of this type can have
a "useful life" exceeding 10 years.
75
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A wide range of tank truck configurations is possible.
Some communities have converted water tanks and in-
stalled them on a truck chassis or even have carried
them in a conventional dump truck, thus allowing dual
use of the truck. A few communities have converted
gasoline trucks, and one has even baffled and enclosed
the box of a large dump truck in order to transport
liquid sewage sludge.
Most of the tank trucks utilize gravity filling and emp-
tying methods. Some trucks, however, are equipped with
gasoline motor driven pumps for loading and spreading.
The pumps can often supply the head of pressure re-
quired for short range spray irrigation. Keeping these
sludge pumps primed can be a problem and constitute
an additional energy requirement. As a general rule, tank
trucks also include in-cab sludge release controls.33
Capital investment in a trucking operation is small but
the operation may be expensive, especially for long
hauls because of labor costs. If daily sludge volumes are
small, one tank truck may be able to serve two or more
wastewater treatment plants.
Pipeline
Use of pipelines for sludge transport is limited to liquid
sludges. Applicability is further limited because the hy-
draulics of sludge flow vary with sludge characteristics.
In general, viscosity, velocity and temperature are the
principal factors influencing sludge flow. Viscosity, in
turn, is determined by the solids content of the sludge
and velocity is directly related to the flow rate and pipe
diameter.
Sludge flow in pipelines is not the same as for water
or other relatively uniform liquids. The usual engineering
flow equations are not applicable to sludge flow unless
the flow is turbulent. Design and operation of sludge
pipelines is complicated by the varying nature of the
sludge and the consequent unpredictable head losses.
A review of literature and practice gives the following
conclusions on sludge flow in pipelines:34
1. The head loss in the pipeline varies directly with
the viscosity of the sludge.
2. Increasing the velocity of sludge flow within the
laminar range decreases the apparent viscosity.
(Since sludges are a varying mixture of solids,
they do not exhibit a true viscosity of more uni-
form liquids.)
3. Increasing the velocity of sludge flow in the turbu-
lent range zone further decreases the apparent
viscosity of sludge until the true viscosity is ap-
proached as a limit.
4. Reducing the size of coarse sludge particles re-
duces the viscosity of the sludge.
5. Effective grit removal is necessary for economical
pumping of sludge in a pipeline.
6. The low velocities experienced in the laminar flow
zone when raw primary sludge is pumped often
result in deposition of grease on the inner periph-
ery of the pipe wall.
7. Flow velocities in a turbulent flow region tend to
prevent deposition of grease within the pipe.
8. Pumping anaerobically digested sludge results in
lower head loss as a result of friction than pump-
ing raw primary sludge of the same solids content
(dry basis) and flow condition.
9. Maintaining the operating velocity in the lower por-
tion of the turbulent flow zone results in maximum
economy for pumping sludge through a long pipe-
line.
10. Little or no grease deposition within the pipeline
has been observed over periods of many years
when low-solids-content activated sludge is
pumped.
11. Pipeline materials and linings influence pipeline
head losses as a result of differing friction flow
factors. Some pipeline materials and linings such
as glass lining, cement lining, and fiberglass-rein-
forced epoxy pipe resist the adherence of greases
more readily than other materials such as cast iron
and steel.
The critical factor in sludge piping is head loss. Head
loss (and energy requirement) is a function of pipe diam-
eter, pipe material (roughness) and velocity of flow. In
the laminar flow range, head losses can be prohibitively
high.35 Furthermore the low velocities could result in ac-
cumulation of grease and deposition of grit, further in-
creasing pipe roughness. To avoid these problems, a
turbulent flow velocity of at least 4 to 6 feet per second
(1.2 to 1.8 m/s) should be maintained.
Energy requirements are also inversely proportional to
the fifth power of the pipe diameter (Hazen-Williams for-
mula). Consequently, energy costs for sludge flow in
small pipelines at high velocities for long distances can
be very high.
For turbulent flow, head losses in sludge pipes need
to be adjusted upward from those computed based on
water. One reference suggests that the "C" factor in
the Hazen-Williams formula should be decreased as
moisture content decreases, as illustrated in figure 9-4.
An optimum solids content (in terms of economics of
pumping) appears to be about 5 percent for turbulent
flows in 10-inch (25.4 cm) diameter or smaller pipes.
Solids concentrations above 5 percent are believed to
result in flow regimes within the plastic flow range,
hence very difficult to produce a turbulent flow condi-
tion. In larger pipes, the optimum solids content may be
higher.37
Pipelines require a larger initial capital investment than
trucks, but operating costs are considerably lower than
labor-intensive trucking. Once the pipeline is constructed,
the route is fixed, restricting pipelines to long term appli-
cation sites. However, pipeline construction costs exhibit
economies of scale with respect to flow. Thus, for a
given distance, pipelines may be less expensive than
trucks for sludge transportation.
76
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p
z
LU
N
o
LU
O
LU
o
tr
LU
a.
100
90
80
70
60
50
40
30
I
I
100 98 96 94 92 90
MOISTURE CONTENT"M" IN PERCENT BY WEIGHT
Figure 9-4.—Variation in headless coefficients for turbu-
lent flow of raw sludge.36
Barge
Barge transport presents limitations for land applica-
tion, because other modes must be used to transfer the
sludge from the barge to the disposal site. Additional
capital investment for loading and unloading facilities
would therefore be required. Many different barge sizes
and types are available for transporting sludge. General-
ly, double-hulled vessels should be used to reduce the
possibility of spills in congested harbor areas. Barges
may be either towed or self-propelled but will usually
require pumped discharges.
Railroad
Rail transport is not a widely used alternative in the
United States. It provides the option of transporting
sludges of any consistency. Like pipeline and barge
transport, however, rail may require substantial fixed ca-
pital investment. In addition, availability of suitable cars
may be a problem. Using leased or shipper-owner cars
would be the best way to assure car availability.38
Summary Evaluation
Each mode is evaluated and rated in table 9-19 in
terms of reliability, staffing needed, and environmental
impact. Costs are considered in more detail in "Costs."
In determining which transportation mode will be select-
ed to convey sludge from the plant to the site, sludge
characteristics, elevation differences, distance, and
sludge volumes must be considered.
Application Methods
A variety of application methods is summarized in ta-
bles 9-20 to 9-22 and discussed below.
Liquid Sludge
Application of sludge in the liquid state is desirable
because of its simplicity. Dewatering processes are not
required and inexpensive liquid transfer systems can be
used. Four common liquid application systems are de-
scribed in the following paragraphs.
Tank Truck Spreading
A common method of liquid sludge application is di-
rect spreading by tank trucks (see figure 9-5), tractors
and farm tank wagons having capacities of 500 to 3,000
gal (1.9-11.4 m3). Sludge is spread from a manifold on
the rear of the truck or wagon as it is driven across the
field. Application rates can be controlled either by valv-
ing the manifold or by varying the speed of the truck.
One modification of the basic process is to mount a
spray apparatus on the truck so that a wider application
area can be covered by each pass. The spray system
can be refined so that larger tank trucks can operate
from a network of roads at the application site.
The principal advantages of a tank truck system are
low capital investment and ease of operation. The sys-
tem is also flexible in that a variety of application sites
can be served, such as pastures, golf courses, farmland,
and athletic fields.
Disadvantages include wet-weather problems and the
high operating cost of the sludge haul. Tank trucks are
not able to enter sites when the ground is soft. Conse- .
quently, storage or wet-weather handling alternatives
must be available. Special flotation tires used on the
trucks can partially control this problem.41 Repeated tank
truck traffic may also reduce crop yields. This is primari-
ly the result of damage to soil structure (higher bulk
density, reduced infiltration) from the trucks rather than
the sludge itself.42
77
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Table 9-19.—Evaluation of sludge transport modes
Transport mode alternatives
Rating criteria
Reliability and complexity3
Staffing skillsb.
Staff attention (time)0
Applicability flexibility1
Energy used6
Cost
Capital investment
Operation maintenance, labor...
Overall'
Truck-barge
pipe
2
3
4
3
7
High
High
Pipe-barge
pipe
2
3
3
3
3
High
Moderate
Barge-pipe
3
3
4
3
5
High
Moderate
Railroad
1
2
•\
2
2
Generally high9
Truck
1
•)
-3
•)
g
Fairly high
Pipeline
3
3
2
3
6
High
Low
a1 = most reliable, least complex; 3 = least reliable, most complex.
b1 = least skills; 3 = highest skills.
°Attention time increases with magnitude of number.
d1 =wide applicability (all types of sludges); 3 = limited applicability, relatively inflexible.
e1 = lowest; 8 = highest.
'Overall costs are a function of sludge quantities and properties (percent solids), distance transported, and need for special
storage, loading and unloading equipment.
9Rail costs would generally be in the form of freight charges; costs could be lower for large volumes of sludge.
Source: Adapted from ref. 39.
Table 9-20.—Surface application method and equipment for liquid sludges40
Method Characteristics Topographical and
seasonal suitability
Irrigation
Spray (sprinkler) Large orifice required on nozzle; large power and lower labor Can be used on sloping land; can be used year-
requirement; wide selection of commercial equipment available; round if the pipe is drained in winter; not suit-
sludge must be flushed from pipes when irrigation completed. able for application to some crops during
growing season; odor (aerosol) nuisance may
occur.
Ridge and furrow Land preparation needed; lower power requirements than spray. Between 0.5 and 1.5 percent slope depending on
percent solids; can be used between rows of
crops.
Overland Used on sloping ground with vegetation with no runoff permit- Can be applied from ridge roads.
ted; suitable for emergency operation; difficult to get uniform
aerial application.
Tank truck Capacity 500 to more than 2,000 gallons; larger volume trucks Tillable land; not usable with row crops or on
will require flotation tires; can use with temporary irrigation soft ground.
set-up; with pump discharge can spray from roadway onto
field.
Farm tank wagon Capacity 500 to 3,000 gallons; larger volume will require flota- Tillable land; not usable with row crops or on
tion tires; can use with temporary irrigation set-up; with pump soft ground.
discharge can spray from roadway onto field.
Spraying may be useful for application on agricultural and forest-
ed lands.
Wastewater sludge can be applied to the land by The advantages of spraying include reduced operating
either fixed or portable irrigation systems that have been labor, less land preparation, and a wide selection of
designed to handle solids without clogging. This method commercially available equipment. Operator attention is
78
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Table 9-21.—Subsurface application methods and equipment for liquid sludges'
.40
Method
Characteristics
Topographical and
seasonal suitability
Flexible irrigation hose with
plow furrow or disc cov-
er
Tank truck with plow furrow
cover
Farm tank wagon and trac-
tor
Plow furrow cover
Subsurface injection ...
Use with pipeline or tank truck with pressure discharge; hose connected to manifold
discharge on plow or disc.
500-gallon commercial equipment available; sludge discharged in furrow ahead of
plow mounted on rear of 4-wheel-drive truck.
Sludge discharged into furrow ahead of plow mounted on tank trailer—application of
170 to 225 wet tons/acre; or sludge spread in narrow band on ground surface
and immediately plowed under—application of 50 to 125 wet tons/acre.
Sludge discharged into channel opened by a tillable tool mounted on tank trailer;
application rate 25 to 50 tons/acre; vehicles should not traverse injected area for
several days.
Tillable land; not usable
on wet or frozen
ground.
Tillable land; not usable
on wet or frozen
ground.
Tillable land; not usable
on wet or frozen
ground.
Tillable land; not usable
on wet or frozen
ground.
Table 9-22.—Methods and equipment for application of
semisolid and solid sludges40
Method
Characteristics
Spreading.
Piles or windrows
Reslurry and handle as in
tables 9-20 and 9-21.
Truck-mounted or tractor-powered box
spreader (commercially available);
sludge spread evenly on ground; ap-
plication rate controlled by over-the-
ground speed; can be incorporated
by discing or plowing.
Normally hauled by dump truck; spread-
ing and leveling by bulldozer or grad-
er needed to give uniform application;
4 to 6 inch layer can be incorporated
by plowing.
Suitable for long hauls by rail transpor-
tation.
Incorporation
The principle of incorporation is to cut a furrow, deliv-
er sludge into the furrow, and cover the sludge, all in
one operation. Modifications include an injection system
in which the sludge is injected beneath the soil surface
(see figure 9-6), or use of a shallow disc. The advan-
tage of incorporation is the immediate mixture of sludge
and soil. Potential odor and vector problems from pond-
ing sludge are eliminated and surface runoff is con-
trolled. Incorporation procedures are favored because
less nitrogen is lost from the soil through ammonia vola-
tilization.
The principal disadvantages of incorporation are its
seasonal limitations and handling procedures. Application
can be made only prior to the growing season or on
noncultivated land, therefore, it may be difficult to se-
quence sites throughout the year. Further, equipment has
limitations for use on wet or frozen ground.
required to set portable sprinkler systems but fixed units
can be highly automated. Sprinklers can operate satis-
factorily on land too rough or wet for tank trucks or
injection equipment. The method can be used throughout
the growing season.
Disadvantages include power costs of high pressure
pumps, contact of sludge with all parts of the crop,
possible foliage damage to sensitive crops, and the po-
tential for aerosol pollution from entrained pathogens.
The sludge-crop contact problems will also limit the
types of crops that can be grown. For forested systems,
water under high pressure may physically damage trees
while, at low pressures, the dispersal of sludge may be
impaired by trees. Perforated pipe located above the
shrub layer may be most effective in forested systems.
Ridge and Furrow
Ridge and furrow sludge application is comparable to
that used in agricultural systems (see figure 9-7). Sludge
flows in furrows between row crops, simultaneously irri-
gating and fertilizing the soil. Furrow slope is the key
factor in the success of ridge and furrow application.
The effect of furrow slope on sludge application is sum-
marized in table 9-23 for a study in the Sacramento,
California, area.
Advantages of ridge and furrow irrigation include sim-
plicity, flexibility, and lower energy requirements than
irrigation. The disadvantages include the settling of sol-
ids at the heads of furrows and the need for a well-
prepared site, with proper gradients. Ponding of sludge
in the furrows, which can result in odor problems, is
also possible.
79
-------
Figure 9-5.—A flotation tire tank truck spray applying liquid sludge.
Figure 9-6.—Sludge incorporation into the soil.
80
-------
Figure 9-7.—A ridge and furrow system.
Table 9-23.—Furrow slope evaluation44
Slope3 Percent
(percent) solidsb
Observations0
0.1 3.1 Sludge ponded or flowed very slowly. On
slopes this flat slight variations in grade
cause ponding. Generally unsatisfactory.
.2 3.1 No ponding, sludge flowed slow. Minimum
grade for 3 percent solids. Would be too
flat for 5 percent solids.
.3 3.1 Sludge flowed evenly at a moderate rate. Ex-
cellent slope for 3 percent solids.
.4-.5 2.7 Sludge flowed evenly at a moderate rate. If
not covered when furrows was full all the
sludge would flow to the low end and pond.
Excellent slope for sludge with 5 percent
solids.
a0.1 percent equals 0.1 foot of fall per 100 feet of run.
"Percent solids expressed determined in a dry weight basis.
CAII observations are based on 12 in. deep furrows. Deeper furrows
would permit the use of flatter slopes.
Dewatered Sludge
Application of dewatered sludge is similar to applica-
tion of solid or semisolid fertilizers, lime, or animal ma-
nure. Spreading can be done with bulldozers, loaders,
graders, or box spreaders and then plowed or disced in.
Trench incorporation is also useful when reclaiming land
of marginal agricultural value.43
The principal advantage of using dewatered sludge is
that conventional equipment for application of fertilizer,
lime, etc., and for tillage can be used. Most farmers
already own tractors, discs, plows, or trucks, and would
not need to purchase special equipment. Another advan-
tage is that dewatered sludge usually may be applied at
higher rates than liquid sludge since concentration of
critical constituents (notably nitrogen) is reduced in the
dewatering process. The application process for dewa-
tered sludge is similar to liquid sludge and involves a
two-step operation—spreading followed by plowing or
discing.
Back-Up Systems
Site design should include contingency plans in case
of equipment breakdowns or inclement weather. Back-up
81
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equipment should always be available. Storage (see be-
low) can provide short-term protection against inability to
spread and an alternate disposal site or method should
be designated for long-term problems.
Storage
Storage facilities are required to hold sludge during
periods of inclement weather, equipment breakdown, fro-
zen or snow-covered ground, or when access would
damage the field or plants. Storage capacity can be
provided by digesters, tanks, lagoons, drying beds, or
stockpiles. Volume requirements will be dependent on
individual systems and climate. The minimum storage vol-
ume would consist of excess capacity in the digesters
while maximum storage volume would be that required
for an extended wet-weather or cold weather season.
Many sewage treatment plants which utilize land-
spreading do not have separate retention capacity for
containing the sludge prior to landspreading. Instead,
they utilize portions of the digester volume for storage.
Where possible, a secondary unheated digester may pro-
vide the required short-term storage capacity. In antici-
pation of periods when sludge cannot be applied to the
land, digester withdrawals proceed at an accelerated
rate to ensure the availability of retention volume until
the landspreading operation can be resumed. The fact
that digesters often serve as retention vessels can lead
to potential problems at the landspreading site if the
sludge withdrawn for landspreading is insufficiently stabi-
lized and contains high counts of pathogenic microor-
ganisms.
Some sewage treatment plants operate sludge lagoons
for either routine sludge dewatering or as holding reser-
voirs when landspreading practices are temporarily inter-
rupted due to adverse weather conditions and/or unan-
ticipated equipment failure. Other plant appurtenances
such as the sludge wells associated with decommis-
sioned or seasonally operated vacuum filter dewatering
equipment are often utilized to provide retention volume.
In rare cases, a cell of a secondary aerated system may
be utilized for the retention of liquid sludges prior to
transport to the landspreading site.
Extended use of vented sludge wells as holding reser-
voirs allows time for additional stabilization. However,
open retention vessels may create odors if the sludges
have not been sufficiently stabilized. Some plant opera-
tors have had difficulty in resuspending sludges which
have been retained in lagoons, wells, and secondary
unheated digesters due to long-term gravity separation
of the solid and liquid phases.45 Storage areas can also
provide for disinfection. However, some organisms can
survive extended storage so that disinfection is not com-
plete.46
MANAGEMENT AND MONITORING
Management
The design and management of each site will be
unique and require the coordinated efforts of the land
owner, the treatment plant operator, political officials,
and engineers. While no one management technique can
be recommended for all situations, there are a few gen-
eral principles that can always be followed:
1. Minimize the impact on soils, groundwaters, surface
waters, crops and air.
2. Control access to the site.
3. Schedule the operation.
4. Create favorable public impressions of the project.
Site Access Control
Although selected and designed to minimize environ-
mental hazards, it is wise to restrict site access to au-
thorized personnel. This is more important for sites dedi-
cated to sludge utilization than for privately owned farm-
land where lower rates of sludge application are used.
Access roads must be maintained in an all-weather
condition. As a minimum, gravel should be the minimum
surfacing.
Scheduling
Timing of sludge applications need to correspond to
farming operations and are influenced by crop, climate
and soil properties.
As mentioned in "Preliminary Planning," sludge cannot
be applied during periods of inclement weather and/or
when the ground is frozen or covered with snow. Soil
moisture is the key parameter affecting timing of sludge
applications. Applications to wet soils during or immedi-
ately following heavy rainfall could result in compaction
and reduced crop yields; muddy soils would also make
vehicle operation difficult. Application to frozen or snow-
covered ground may result in excessive runoff into adja-
cent streams. In addition, sludge applications must be
scheduled around the tillage, planting and harvesting
operations for the crops grown.
At very high application rates sludges can retard seed
germination and early plant growth. The retardation is
thought to be caused by a high concentration of soluble
salts and/or high ammonia contents. These problems
can be minimized by (1) reducing the application rate;
(2) applying the sludge 2 to 3 weeks before planting; (3)
mixing of the sludge in the tilled soil layer, or (4) irrigat-
ing prior to planting. In the humid regions of the United
States, the problem will be potentially less severe than
in the more arid nonirrigated regions.
Sludges can be applied to forage crops during the
season if applied prior to spring growth, after dormancy,
or immediately after cutting and before significant new
growth has begun.
Sewage sludge applied to the surface of poorly
drained soil and not immediately incorporated can be
transported in runoff waters and result in contaminated
surface waters. The potential danger of runoff increases
greatly on sloping land in regions of high rainfall and
can be severe if an intense rain occurs soon after liquid
sludge is spread on sloping land. Diversion or earthen
barriers may be necessary to contain runoff temporarily,
82
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and prevent sludge from reaching water courses. In ad-
dition, erosion control practices such as grassed water-
ways, terraces, and strip cropping are useful to de-
crease runoff from sludge amended soils. Regardless of
land use, runoff can be minimized by lowering sludge
application rates, using split applications, and by incor-
porating sludge rather than surface spreading.
Favorable Impressions
As discussed in "Preliminary Planning," knowledge of
landspreading operations was directly related to positive
attitude toward landspreading. A well-run operation
would help to sustain these attitudes.
The entire project should be professionally operated.
The staff should consist of personnel having working
knowledge of farming, wastewater treatment, and sludge
handling. Any complaints or questions from the public
should be dealt with promptly and courteously.
Presence of objectionable odors could result in an
unfavorable public impression of the concept. To mini-
mize odors, the following operational procedures can be
used:
1. Injection of unstable wastes.
2. Incorporation of all sludge as soon as possible af-
ter delivery to site.
3. Daily (or more frequently, if necessary) cleaning of
trucks, tanks, and other equipment.
Monitoring
Any sludge application site must have a monitoring
program for observing and evaluating systems perform-
ance. Sludge composition, groundwater quality, soil pro-
perties, and plant composition would be monitored in an
optimum sampling program.
Periodic Sludge Analyses
Sludge analysis confirms, on a regular basis, that the
waste is acceptable and provides a record of nutrient
and metal additions to soils. Sampling frequency de-
pends on sludge characteristics and sludge variability.47
For example, a treatment plant processing large amounts
of industrial wastes at irregular intervals may need con-
tinuous monitoring, whereas a system processing largely
domestic wastes may need only intermittent sludge moni-
toring.
Recommended analysis and suggested analytical meth-
ods are shown in table 9-24. Since the solids content
of sludges varies from batch to batch, all composition
data must be expressed on an oven-dry solids basis.
The following elements may be of concern in special
instances, but for most sewage sludges which are en-
countered these elements will not influence the rate of
application of sludge to land: selenium, cobalt, chromi-
um, arsenic, boron, iron, aluminum, mercury, silver, bari-
um, sulfur, calcium, magnesium, sodium, molybdenum,
inorganic carbon, and organic carbon. With the excep-
tion of boron, sulfur, and carbon, all analyses listed
Table 9-24.—Methods for sludge analysis:
,26
Parameter
Suggested method
Percent solids
Total N (nitrogen)....
NH4 + -N (ammonium).
NO3--N (nitrate)
Total P (phosphorus)..
Total K (potassium)
Copper (Cu), zinc (Zn), nick-
el (Ni), Lead (Pb), and
cadmium (Cd).
Stable organicsc
Drying at 105°C for 16 hrs.
Micro-Kjeldahl and S.D.a
Extraction with potassium chloride and
S.D.a
Extraction with potassium chloride and
S.D.a after reduction
Nitric acid-perchloric acid digestion
and colonmetry
Nitric acid-perchloric acid digestion
and flame photometry
Nitric acid-perchloric acid digestion
and atomic absorptionb
Variable
aS.D., steam distillation and titration of distillate with standard sulfu-
ric acid. Colorimetric procedures can be used for N species.
bBackground correction (e.g., deuterium or hydrogen lamp) may be
needed for cadmium and nickel.
°Optional and site specific.
above can be accomplished with atomic absorption
spectrophotometry. The elements arsenic, selenium, bo-
ron, chromium, and mercury are of greatest importance
in industrial wastes; however, some municipal sludges
may contain elevated levels if these metals of industrial
wastes are added to the sewage system.
Site Analyses
Monitoring requirements for sites are a function of the
sludge application rate. Sludges applied at a rate equal
to crop nutrient requirements can be considered as ferti-
lizers; therefore, no special monitoring is necessary. This
is usually the situation where sludge is given or sold to
a farmer and then applied by the farmer and/or treat-
ment plant on his land. Periodic soil testing should be
conducted, including soil pH. It is recommended, that
lime be added if soil pH decreases below 6.5.
When sludge is applied at rates exceeding recom-
mended plant nutrient requirements or heavy metal limits,
a special monitoring program will be required. This situa-
tion often occurs when sludge is applied to a municipal-
ly owned or leased site.
Soils
The initial monitoring of soils provides a reference
datum specifying original conditions as well as necessary
or tolerable sludge constituent additions which can be
made. Subsequent soil analyses document contaminant
buildups, efficacy of plant uptake and removals, even-
ness of sludge application and other environmental im-
pacts. Soil analysis also allows calculation of sludge
83
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loading rates and provides estimates of remaining site
life.
Irrespective of the constituent monitored, valid soil
sampling techniques are essential. Soil testing laborato-
ries describe procedures that can be used for obtaining
soil samples. The sampling design should take into ac-
count changes in soil type as the area is traversed as
well as within unit variability. Standardized analytical
procedures for sludge amended soils have not been es-
tablished but analytical procedures used for agricultural
or forested soils are generally satisfactory. Interference
problems may, however, negate the use of some analyti-
cal procedures.
The type of analysis is dependent on system objec-
tives, although it is generally agreed that heavy metal
and nitrate analysis should be performed for both agri-
cultural and nonagricultural systems. The vertical distribu-
tion of these parameters in the soil profile would provide
information on constituent mobility and potential for
groundwater contamination. Additional analyses (P, K,
pH, CEC, organic matter) would be required to provide
information for fertilizer recommendations and site man-
agement (e.g., liming to adjust pH).
The movement of nitrates into groundwater may re-
quire monitoring in some instances. If sludge applications
are applied in accord with the nitrogen requirement of
the crops grown, nitrate leaching will be minimized. One
approach to monitoring involves obtaining soil cores to a
depth of 3 to 5 feet (0.9 to 1.5 m) at the end of the
growing season and analyzing each 1 foot increment for
ammonium (NH4+) and nitrates (NO3~). Suction lysimeters
can also be used to obtain samples of the soil solution
at a 3 to 5 foot (0.9 to 1.5 m) depth but this procedure
has practical limitations.
Groundwater and Runoff
Most states have laws and regulations governing the
quality of surface and groundwater which must be con-
sidered when designing a monitoring program. Sludge
application to land is not the same as landfill, so regula-
tions for groundwater quality from landfills do not apply
to sludge applications.
Monitoring wells must be designed and located to
meet the specific geologic and hydrologic conditions at
each site. Furthermore, casing materials and drilling
needs should be chosen to minimize potential, construc-
tion-related contamination problems.
Consideration should be given to the following:
1. Geological soil and rock formations existing at the
specific site.
2. Depth to an impervious layer.
3. Direction of flow of groundwater and anticipated
rate of movement.
4. Depth of seasonal high water table and an indica-
tion of seasonal variations in groundwater depth
and direction of movement.
5. Nature, extent, and consequences of mounding of
groundwater which can be anticipated to occur
above the naturally occurring water table.
6. Location of nearby streams and swamps.
7. Potable and nonpotable water supply wells.
8. Other data as appropriate.16
If possible, existing background data should be obtained
from wells in the same aquifer both beyond and within
the anticipated area of influence of the land application
system. Wells with the longest history of data are prefer-
able. Monitoring of background wells should continue
after the system is in operation to provide a basis for
comparison.
In addition to background sampling, groundwater sam-
ples should be taken at perimeter points in each direc-
tion of groundwater movement from the site. In locating
the sampling wells, consideration must be given to the
position of the groundwater flow lines resulting from the
application. Perimeter wells should be located sufficiently
deep to intersect flow lines emanating from below the
application area but not so deep as to prolong response
times.
Water level measurements should be accurate to 0.01
feet or 1/8 inch (0.3 cm) and referenced to a perma-
nent reference point, preferably U.S. Geological Survey
datum. Measurements should be made under static water
level conditions prior to pumping for sample collection.
All monitoring wells should be securely capped and
locked when not in use to avoid contamination.
Again, sampling frequency is dependent on system
objectives, sampling variability and analytical costs. As a
general rule, samples should be collected monthly during
the first 2 years of operation. After the accumulation of
a minimum of 2 years of groundwater monitoring infor-
mation, modification of the sampling frequency may be
considered. The following sampling procedures should be
employed:
1. A measured amount of water equal to or greater
than three times the amount of water in the well
and/or gravel pack should be exhausted from the
well before taking a sample for analysis. In the
case of very low permeability soils, the well may
have to be exhausted and allowed to refill before a
sample is collected.
2. Pumping equipment should be thoroughly rinsed be-
fore use in each monitoring well.
3. Water pumped from each monitoring well should be
discharged to the ground surface away from the
wells to avoid recycling of flow in high permeability
soil areas.
4. Samples must be collected, stored, and transported
to the laboratory in a manner to avoid contamina-
tion or interference with subsequent analyses.
Water samples collected from sludge application sites
should be analyzed for the following:
1. Chloride.
2. Conductivity.
3. pH.
4. Total hardness.
5. Alkalinity.
6. Total nitrogen.
84
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7. Ammonia nitrogen.
8. Nitrate nitrogen.
9. Total phosphorus.
10. Methylene blue active substances.
11. Total organic carbon.
12. Heavy metals or toxic substances where appli-
cable.
Vegetation
Plant tissue composition is a sensitive and meaningful
indicator of impacts, provides useful information on plant
nutrient deficiencies and toxicities, and indicates poten-
tial health hazards in food-chain crops. However, the
validity and usefulness of a chemical analysis depends
on a realistic approach to the problem of obtaining a
reliable sample. To obtain reproducible data on plant
composition, the age and part of the plant sampled must
be specified because composition changes throughout
the growing season.
The basic principles underlying plant tissue sampling
are common to both forestry and agricultural species,
but specific methodologies are unique to both practices.
Forestry investigations in the Pacific Northwest recom-
mend the following foliar sampling procedures.48
1. Sample conifer foliage during the dormant season.
2. Sample deciduous leaves at maturity.
3. Sample both dominant and codominant trees.
4. Sample upper portion of the crown for foliage sam-
ples.
5. Sample current year foliage.
6. Do not sample foliage or twigs bearing cones.
A summary of sampling techniques for agricultural
crops is presented in table 9-25. Although the use of
vegetable crops is not recommended on soils treated
with sludge, diagnostic tissues for these crops are also
presented. From the standpoint of metal impact on the
human food chain, sampling the mature grain or forage
is the preferred method of monitoring. Plant analyses
can be performed using methods similar to those de-
scribed previously for sludge. The major emphasis is
placed on analysis of zinc, copper, nickel, cadmium, and
lead. In some cases, analysis of the diagnostic tissue
may allow prediction of the eventual metal concentration
in the grain; however, insufficient data is presently avail-
able for most crops to develop general predictive rela-
tionships. The U.S. FDA has not set limits for allowable
heavy metal concentrations in plant tissues consumed by
humans or animals.
COSTS
Generalized cost curves for land application of sludge,
including preapplication treatment and transport, are pre-
Table 9-25.—Suggested procedures for sampling diagnostic tissue of crops19
Crop
Stage of growth8
Plant part sampled
Number
plants/
sample
Corn Seedling All the above ground portion. 20-30
Prior to tasselling Entire leaf fully developed below whorl 15-25
From tasseling to silking Entire leaf at the ear node (or immediately above or 15-25
below).
Soybeans and other beans Seedling All the above ground portion. 20-30
Prior to or during early flowering Two or three fully developed leaves at top of plant. 20-30
Small grains Seedling All the above ground portion. 50-100
Prior to heading The 4 uppermost leaves. 50-100
Hay, pasture or forage grasses Prior to seed emergence The 4 uppermost leaf blades. 40-50
Alfalfa, clover and other legumes Prior to or at 1/10 bloom Mature leaf blades taken about 1/3 of the way 40-50
down the plant.
Sorghum-milo Prior to or at heading Second leaf from top of plant 15-25
Cotton Prior to or at 1st bloom, or at 1st Youngest fully mature leaves on main stem. 30-40
square
Potato Prior to or during early bloom 3d to 6th leaf from growing tip 20-30
Head crops (e.g., cabbage) Prior to heading 1st mature leaves from center of whorl. 10-20
Tomato Prior to or during early bloom stage 3d or 4th leaf from growth tip. 10-20
Beans Seedling All the above ground portion. 20-30
Prior to or during initial flowering 2 or 3 fully developed leaves at the top of plant. 20-30
Root crops Prior to root or bulb enlargement Center mature leaves. 20-30
Celery Mid-growth (12-15" tall) Petiole of youngest mature leaf. 15-30
Leaf crops Mid-growth (12-15" tall) Youngest mature leaf. 35-55
Peas Prior to or during initial flowering Leaves from 3d node down from top of plant. 30-60
Melons Prior to fruit set Mature leaves at base of plant on main stem. 20-30
'Seedling stage signifies plants less than 12 inches tall.
85
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sented. The curves should be used only for preliminary
work since actual costs vary considerably with local
conditions. Use of these curves for computing specific
project costs is not recommended.
Scope
Two sets of curves are presented: one set for sludge
transport and one set for application. Transportation
costs are presented as annual costs vs. distance to the
application site for treatment plant capacities of 4, 10,
40, and 80 Mgal/d (0.18, 0.44, 1.75, 3.50 nrvVs) for
each transport mode in "Facilities Design" (except rail-
road barge haul). Application costs are presented as
annual costs vs. treatment plant capacity for each meth-
od discussed in "Facilities Design." However, costs of
tank truck application are included in the costs of tank
truck haul.
Other site-specific cost items such as land (lease or
purchase), storage, field preparation (liming, grading,
etc.), and monitoring are not included. The costs do not
include revenues on crops harvested or credits for fertil-
izer not purchased.
Data Sources and Assumptions
Published reports49"51 •6i65 were the primary sources of
information on costs. Because of the differing bases for
cost computations, certain assumptions on sludge vol-
umes and unit costs were utilized to arrive at general-
ized cost curves. Additionally, all cost figures were up-
dated to 1978 levels with appropriate cost index (ENR
2700).
Sludge Volumes and Characteristics
The sludge was assumed to come from an activated
sludge treatment plant with anaerobic digestion. Two
types of sludge are considered: (1) a liquid sludge hav-
ing 4 percent solids and (2) a vacuum filter cake having
20 percent solids. In either case, a base figure of 1,300
Ib of dry solids per Mgal (15 g/m3) was used.
Transportation
Transportation costs were computed using the data
and procedures in reference 49. The cost curves in this
reference were for the year 1975 (ENR 2200) and were
based on the following values:
1. 8-hour working day
2. 2,500 gallon (9.5 m3) diesel tank truck
3. Fuel cost of $0.60 per gallon ($158.52 per m3)
4. Labor cost of $8.00 including fringe benefits
5. Overhead and administrative costs of 25 percent of
operation and maintenance costs
6. Amortization at 7 percent for 6 years for trucks
with a 15 percent salvage value
7. Amortization rate at 7 percent for 25 years for
truck loading and unloading facilities, pipelines, and
pumping stations.
Costs were taken from the curves and then updated to
mid-1978 (ENR 2700).
Truck
For truck haul, costs were computed for a 2,500 gal-
lon (9.5 m3), 3-axle tanker truck with loading and un-
loading facilities. For a 5,500 gallon (20.8 m3) semi unit,
annual costs would be reduced by factors ranging from
1.2 for 4 Mgal/d (0.18 m3/s) and 5 mile (8 km) one-way
distance to 2.1 for an 80 Mgal/d (3.5 m3/s) plant and
80 miles (129 km). For a 1,200 gallon (4.5 m3), 2 axle
truck, costs would increase by factors of 1.3 to 2.0 for
the aforementioned wastewater flows and distances.
For dewatered sludge, costs were computed for a 15
CY (11.5 m3), 3-axle dump truck with loading and un-
loading facilities and an 8-hour working day. For a 10
CY (7.6 m3), 2 axle truck the costs would be higher by
factors ranging from 1.3 for 80 Mgal/d (3.5 m3/s), 80
mile (3.5 m3/s) haul to 1.0 for 4 Mgal/d (0.18 m3/s), 5
mile (8 km) haul. For a 30 CY (22.9 m3) vehicle, costs
would be reduced by factors of 0.6 to 1.0 for the afore-
mentioned flows and distances.
For liquid sludge transport, loading and unloading fa-
cilities account for approximately 50 percent of the an-
nual costs at 4 Mgal/d (0.18 m3/s) flows and a 5-mile
(8 km) haul distance and less than 1.5 percent for 80
Mgal/d (3.5 m3/s) and 80 miles (129 km). For dewater-
ed sludge, loading and unloading facilities are about 60
percent of the total annual costs at 4 Mgal/d (0.18
m3/s) and 5 miles (8 km) and only 1 to 2 percent at 80
Mgal/d (3.5 m3/s) and 80 miles (129 km).
Pipeline
Hydraulic computations for pipelines were based on
the need to maintain a minimum velocity of 6 ft/sec (1.8
m/s). A level terrain was assumed, i.e., pumping energy
was required only to overcome head losses in the pipe.
A minimum diameter of 6 inches (15.2 cm) was used.
Costs include construction of the pipeline, pumping
stations, and appurtenances and operating costs such as
electricity (at 4^1 per kWh), labor, and materials. The
costs do not cover special conditions such as hard rock
excavation and highway or river crossings.
Rail and Barge
Because of their limited applicability, rail and barge
transport will not be estimated in this chapter. The lack
of information and the site-specific nature of these
nodes would make development of generalized cost
curves difficult. Further information can be found in re-
ferences 49, 38, 6.
Preapplication Treatment
Preapplication treatment was assumed to be the addi-
tion of a vacuum filter to an existing activated sludge
treatment plant with activated sludge thickening and an-
aerobic digestion of combined primary and secondary
sludges. Sources of cost data include references 6 and
86
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72a and actual plant operating records, updated to an
ENR Cost Index of 2700.
Spreading
There is little information available regarding land
spreading costs. This cost is highly site-specific, depend-
ing on extent of land preparation, application rate, and
type of equipment (i.e., new, used, or rebuilt).
In all methods, use of new equipment was assumed.
An application rate of 10 dry tons/acre-yr (22.4
Mg/ha/yr) was used to establish site acreages and
costs for spraying and ridge and furrow irrigation.51 For
other methods, published costs and estimates were
used"'48'50'52
Summary
The cost curves are presented for treatment plant
capacities of 4, 10, 40, and 80 Mgal/d (0.18, 0.44, 1.75
and 3.50 m3/s) in figures 9-8 through 9-11, respectively.
Figure 9-12 is a summary comparison of truck and pipe-
line unit costs for liquid sludge transport only. Costs for
spreading are shown in figure 9-13. Although these
costs curves are order-of-magnitude estimates only,
some tentative conclusions can be drawn.
1. For small treatment plants [<10 Mgal/d «0.44
m3/s)J and one-way haul distances of <5 to 10
miles (8-16 km), haul of liquid sludges by truck
appears to be the least expensive alternative.
2. As haul distances increase, addition of vacuum fil-
ters and hauling of dewatered sludge becomes less
expensive than hauling liquid sludge. However, the
savings will be partially offset by the additional cost
of applying dewatered sludge.
3. As distances to the site increase, pipelines become
economically competitive with trucking. The addi-
tional cost of terminal and application facilities tend
to offset the savings.
4. For application of liquid sludge, no single method
presents a clear economic advantage.
10,000 -
£1,000
o
o
z
<
100
80
PIPELINE,
TRUCK
(dewatered sludge w/vac. filt.)
I
5 10 50 100
ONE WAY DISTANCE TO SITE, MILES
Figure 9-8.—Annual costs of sludge transport for a 4
v Mgal/d treatment plant. Conditions: 15,600 gal/d liquid
sludge at 4 percent solids, or 15 CY/d dewatered
sludge at 20 percent solids.
10,000 -
o
o
i.ooo
100
PIPELINE,
I
I
TRUCK
(dewatered sludge
w/vac. filt.)
I
5 10 50 I
ONE WAY DISTANCE TO SITE, MILES
Figure 9-9.—Annual costs of sludge transport for a 10
Mgal/d treatment plant. Conditions: 38,000 gal/d liquid
sludge at 4 percent solids, or 38 CY/d dewatered
sludge at 20 percent solids.
87
-------
10,000
,
\
o
O 1,000
o
zr
z:
<
100
TRUCK
(liquid sludge)
TRUCK
(dewatered sludge
w/vac. filt.)
PIPELINE
I
I
5 10 50 100
ONE WAY DISTANCE TO SITE , MILES
Figure 9-10.—Annual costs of sludge transport for a 40
Mgal/d treatment plant. Conditions: 156,000 gal/d liquid
sludge at 4 percent solids, or 155 CY/d dewatered
sludge at 20 percent solids.
Figure 9-11.—Annual costs of sludge transport for a 80
Mgal/d treatment plant. Conditions: 312,000 gal/d liquid
sludge at 4 percent solids, or 310 CY/d dewatered
sludge at 20 percent solids.
DESIGN EXAMPLE A
A detailed example will be developed for a midwestern
city treating 4 Mgal/d (0.18 rrrVs) of wastewater. The
plant is assumed to produce 1,300 Ib of sewage sludge
per Mgal/d (13,490 kg/l/s), or 5,200 Ib (2,360 kg) dry
sludge/day.
Preliminary Planning
Sludge Composition
To illustrate the influence of sludge composition on
site design, two types of sludge will be considered: one
receiving predominately domestic sewage (sludge #1),
and the other receiving both domestic and industrial
wastes (sludge #2). The sludges have the following
properties:
Sludge #1 Sludge #2
Solids ..
Total N
NH4-N..
Total P.
Total K.
Pb
Zn
Cu . ...
Ni
Cd
4 percent
3 percent
1 percent
2 percent
0.5 percent
500 mg/kg
2,000 mg/kg
500 mg/kg
100 mg/kg
15 mg/kg
Climate
4 percent
3 percent
1 percent
2 percent
0.5 percent
5,000 mg/kc
10,000 mg/kc
1,000 mg/kc
200 mg/kc
300 mg/kc
Climatological data for the application area is shown
in table 9-26. Sludge application will be limited during
88
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100.0
10.0
1.0
O.I
Miles
80
Pipeline
I i i
I
10 50 100
1,000 gal/d LIQUID SLUDGE
200
400
300
§200
100
0
I
Ridge and Furrow
Portable Sprinkler
Irrigation (51)
Injection and tractor
drawn surface applic.
(6, 65, 27a)
Dewatered
spreading (37)
0 80 160 240 320
1,000 gal/d LIQUID SLUDGE
Figure 9-13.—Annual costs for application of sludge to
land.
Table 9-26.—Climatological data
Figure 9-12.—Summary costs comparisons for transport
of liquid sludge.
periods of high rainfall and high soil moisture conditions,
because of the potential for surface runoff and the in-
ability to use sludge application equipment. Sludge appli-
cation will also be limited during periods of extended
subfreezing temperatures due to frozen soils.
Regulations
For this site, permits are not required for sludge appli-
cation provided that:
1. Annual sludge applications do not exceed the nitro-
gen requirement for the crop grown or 2 Ibs
Cd/acre (2.2 kg/ha).
Mean number of days
Month
Precipitation > 0.1 in. < 32° F maximum
January
February
March
April
May
June
July
August
September ....
October .
November
December
Total
4
3
6
8
7
6
6
5
5
5
5
4
64
16
10
5
0
0
0
0
0
6
6
18
27
88
89
-------
2. Soil is maintained at pH 6.5 or above.
3. Monitoring is not needed annually other than rou-
tine soil testing to establish fertilizer recommenda-
tions and lime requirement.
4. Sewage treatment plant monitors chemical composi-
tion of sludge.
5. Records are maintained on the amount of sludge
applied to each area.
Preliminary Screening
As discussed previously, a 10 ton/acre/yr (22.4
Mg/ha/yr) rate of sewage sludge is a realistic first ap-
proximation for application to agricultural soils. The acre-
age required for the above city can be estimated as
follows:
Acreage needed =
2.6 tons sludge/day x 365 days/yr
10 tons/acre/yr (22.4 Mg/ha/yr)
=s100 acres (40 ha)
For a city with a 4 Mgal/d (0.18 m3/s) plant, about 100
acres (40 ha) are required for sludge utilization. After
contacting local extension staff, farmers, etc., the city
decided to develop a detailed plan for sludge utilization
on agricultural land, which is potentially available within
25 miles (40.2 km) of the treatment plant.
Site Selection
The potential sites for sludge application can be evalu-
ated using topographic maps, soil maps, etc. For the
example being considered, a soil map will be used. Fig-
ure 9-14(a) is a general soil map showing the area
available for sludge utilization. A detailed soil map of the
site area is shown in figure 9-14(b) and the map legend
is presented in table 9-27. Since the detailed soil map
is based on an aerial photo, farm buildings, houses, etc.,
are identifiable. The following areas can be eliminated as
potential sludge application sites.
1. Towns, subdivisions, schools, and other inhabited
dwellings.
2. Rivers and streams with appropriate buffer areas
(e.g., 250 ft or 76.2 m).
3. Wetlands and marshes.
The remaining areas can be identified according to soil
type (table 9-27). Information presented in the soil sur-
vey report includes: slope, drainage, depth to seasonal
water table, depth to bedrock texture, approximate CEC,
and a ranking according to suitability. The sites pre-
ferred are nearly level, well-drained, >6 ft (1.8 m)
above bedrock. The ranking in table 9-27 was based on
the use of soils without modification of slope or drain-
age. Soils with steeper slopes may be ranked higher if
terraces or other erosion control practices are used to
minimize runoff. Similarly, soils limited by poor drainage
may be used if a tile drainage system is installed. Fol-
lowing ranking of the soils, the acreage available for
sludge utilization can be estimated. Further evaluations
must be made during on-site visits.
Site Identification
The site, as shown in figure 9-14(a) and 9-14(b), was
chosen as the area best suited for land application
practices. This site was chosen primarily because it was
closest to the treatment plant, and had suitable soils.
The maximum distance from the plant to the selected
fields was estimated to be under 5 miles (8 km). Total
site area covered over 2,300 acres (930 ha), but only
about 100 acres (40 ha) will be needed for sludge appli-
cation. Most of the area is pastureland with some culti-
vated fields of corn and oats.
Many alternative sites were also suitable for sludge
application, but this area was selected due to its close
proximity to the treatment plant.
Site Acquisition
The land area in the site was owned by 10 individuals
A contractual agreement was drawn with the individuals
whereby sludges would be applied to certain fields at
rates commensurate with crop nitrogen requirements.
The treatment plant will transport and apply all sludge tc
the fields at times specified by the farmers.
Design
Soil Properties
Soils in the site area are generally silt loams, having z
CEC of 10 meq/100 g. Representative soil analysis is aj
follows:
CEC 10 meq/100 \
Water pH 6.0
Available P 15 Ib/acre
Available K 75 Ib/acre
Lime (to pH 6.5) 2.4 tons/acre
Crop Requirements
Crops grown in the area include corn, soybeans, oats,
wheat and pastureland. For this design example, one-hal
of the allocated land is cropped to orchardgrass pasture
requiring 300 Ib of available nitrogen/acre/yr (336
kg/ha/yr), and one-half is cropped with corn requiring
170 Ib available nitrogen/acre/yr (190 kg/ha/yr). Crop
fertilizer requirements were obtained from tables 9-9, 9-
11 and 9-12.
Fertilizer recommendations for the two crops are as
follows:
Yield
Corn 130 bu/acre
Orchardgrass 6 tons/acre 300
N P K
Ib/acre/yr
170 40 12
53 30
Phosphorous and potassium recommendations are based
on the soil test data shown above.
90
-------
MILES
LE8END
Deep, well-drained to poorly drained, medium textured
and moderately fine textured, nearly level soils that
formed in alluvium
Deep, somewhat poorly drained to well drained,
medium-textured, nearly level to steep soils that
formed in loess and the underlying outwash, in loess
and the underlying glacial till or m glacial till
Moderately deep and deep, well-drained, medium-
textured, gently sloping to steep soils that formed
in loess and the underlying sandstone and shale
residuum
Figure 9-14(a).—General soil map showing area selected for sludge utili-
zation.
Calculation of Annual Application Rate
Nitrogen Basis
The plant available nitrogen (Np) in the sludge is cal-
culated based on 100 percent availability of NH4-N and
20 percent availability of organic N during the year of
sludge application. The sludge does not contain detect-
able amounts of NO3-N, so only NH4-N and total N are
needed to calculate plant available nitrogen (Np). The
calculation of Np is as follows:
Lbs Np/ton sludge
= percent NH4-Nx 20 +percent organic-Nx4
= 1 x 20+ 2X4
= 28
This value of Np applies to both sludge #1 and #2,
91
-------
Sere 1 '5B4C
Figure 9-14(b).—Detailed soil survey map of potential site for sludge
application (areas not suited for use are shaded).
92
-------
Table 9-27.—Ranking of soil types for sludge application
Soil type
AvA
Ca
CnB2
CnC2
CnC3
CnD2. .
CnD3
Ee
FoA. . . .
FoB2 . . .
FxC3
Ge
Hh
La
MbA . . .
MbB2
Md
NqA
NgB2
NnA
RnF
Ro
Rp
RsB2
Sc
Sh
Sm
Sz
We
Wh
Depth to
percent Seasonal high ^^ ^^
wateMable (ft)
0-2
0.2
2-6
6-12
6-12
12-18
12-18
0-2
0-2
2-4
6-12
0-2
0-2
0-2
0-2
2-6
0-2
0-2
2-6
0-2
0-2
0-2
0-2
2-6
0-2
0-2
0-2
0-2
0-2
0-2
1-3 ;
>e :
>e ;
>e ;
>e ;
>e ;
>e ;
3-6 ;
>e ;
>e ;
>e ;
>e :
1-3 ;
>e ;
>e ;
>e ;
s-e :
>e ;
>e ;
>e :
>e ;
>e ;
>e :
3-6 ;
0-1 ;
1-3 ;
1-3 :
>e ;
0-1 ;
1-3 ;
>15 sil
>15 sil
>15 sil
>15 sil
>15 sil
>15 sil
>15 sil
>15 sil
>15 I
>15 I
>15 I
>15 I
>10 sil
>15 gsal
>15 I
>15 I
> 1 5 sicl
>15 I
>15 I
>15 I
>15 gl
>15 sicl
>15 sicl
>15 sil
>15 sicl
>15 sil
>15 I
>15 sal
>15 cl
>15 I
Drainage
classb
P
W
W
W
W
W
W
w
w
w
w
w
SP
w
w
w
MW
w
w
w
E
W
w
MW
VP
SP
SP
W
VP
SP
Approximate
CEC
10-15
10-15
10-15
10-15
10-15
10-15
10-15
10-15
10-15
10-15
10-15
10-15
10-15
<5
10-15
10-15
10-15
10-15
10-15
<5
10-15
10-15
10-15
5-10
10-15
Relative
ranking0
3
1
1
2
2
3
3
2
1
1
2
1
3
1
1
1
2
1
1
1
1
1
1
2
3
3
3
1
3
3
al, loam; gsal, gravelly sandy loam; sil, silt loam; sicl, silty clay loam; cl, clay loam; sal, sandy
loam; gl, gravelly loam.
bE, exclusively drained; W, well drained; MW, moderately well drained; SP, somewhat poorly
drained; P, poorly drained; VP, very poorly drained.
C1, 0-6 percent slope, >6 ft to water table and >15 to bedrock. 2, 6-12 percent slope or
3-6 ft to water table. 3, 12-18 percent slope or 0-3 ft to water table.
since their total and NH4 nitrogen contents are the same.
After obtaining Np, the annual sludge application rate
(tons/acre) is calculated by dividing Np into N required
by the crop. For corn,
tons/sludge/acre =
170
28
= 6.1
For orchardgrass, surface applications are used whereby
approximately 50 percent of the NH4-N applied will be
lost by NH3 volatilization. The available N content is then
decreased and Np is calculated from
Lbs Np/ton sludge
= percent NH4-N x 10 + percent organic N x 4
=1X10+2X4
= 18
(NOTE: The conversion factor for NH4-N has been
decreased by 50 percent)
93
-------
For orchardgrass, the annual application rate is:
tons sludge/acre=——
18
= 16.7
The above calculations apply to the first application of
sludge; however, the contribution of residual N to the
plant available N pool becomes important in the years
following initial sludge application. Based on the data in
table 9-13, additions of sludge containing 2 percent
organic N will release 1.0, 0.9, and 0.9 Ibs N/ton (0.5,
0.45, and 0.45 kg/Mg) sludge applied for the first, sec-
ond, and third years following sludge application. These
residual N values are subtracted from the crop N re-
quirements. The rate calculations for the corn and or-
chardgrass crops considered are summarized below:
Sludge #1
Corn (incorporated sludge)
Year Calculation
1.
2.
3.
170 - 0
28
170 - (6.1X1.0)
28
170 - (6.1X0.9) - (5.8X1.0)
28
4 170 - (6.1 X0.9) - (5.8X0.9) - (5.7X1.0)
28
170 - (5.8X0.9) - (5.7 X 0.9) - (5.5 X 1 .0)
O ........ ...... - „
28
Orchardgrass (surface application)
300 - 0
300 - (16.7X1.0)
18
300 - (16.7X0.9) - (15.7X1.0)
18
300 - (16.7X0.9) - (15.7X0.9) - (15X1.0)
18
300 - (15.7X0.9) - (15.0X0.9X14.1 X1.0)
18
Tons/acre
6.1
5.8
5.7
5.5
5.5
16.7
15.7
15.0
14.1
14.4
Cadmium Basis
In addition to considering the annual rate of N addi-
tion, the rate of Cd must be kept below 2 Ib/acre/yr
(2.24 kg/ha/yr). Currently it is felt that limiting Cd to 2
Ib/acre/yr (2.24 kg/ha/yr) will minimize the accumulation
of Cd in most crops, providing soil pH is maintained at
6.5 or above. The 2 Ib/acre/yr (2.24 kg/ha/yr) limit
should be considered tentative because ongoing and
future research may provide data for a more valid Cd
criteria. The rate of sludge application to limit
Cd to 2 Ib/acre/yr (2.24 kg/ha/yr) is calculated:
-r 2 lb Cd/acre/yr _. ,
Tons/acre/yr = '— = 66.7
15X0.002
Sludge #2
-r 2 lb Cd/acre/yr „ „
Tons/acre/yr = 30Q x Q QQ2 X = 3.3
A comparison of the rates based on N and Cd for
sludges #1 and #2 indicate that N application rates
can be used for sludge #1 but not for sludge #2.
Only 3.3 tons/acre/yr (7.40 Mg/ha/yr) of sludge #2
can be applied, requiring supplemental fertilizer additions
for optimum crop yield.
Total Amount of Sludge Applied
The total amount of sludge that can be applied for
the life of a site is based on the metal loadings as
calculated from the metal content of the sludge and the
data shown in table 9-14. The total sludge loadings are
calculated as follows for sludge #1.
Total metal Metal content
Metal
Pb
Zn
Cu
Ni
Cd
limit
(Ibs/acre)
1,000
500
250
100
10
of sludge
(ppm)
500
2,000
500
100
15
Calculation
1,000
500 x.002
500
2,000 X .002
250
500 X .002
100
100X.002
10
15X.002
Total amount c
sludge allowec
(tons/acre)
1,000
125
250
500
325
The above calculation indicates that Zn will control
total sludge applications for sludge #1 at 125 tons/acre
(280.3 Mg/ha) . Obviously, if pretreatment procedures
could be instituted to reduce Zn inputs to the treatment
system, the site life could be increased substantially.
Using 5.5 and 14.5 tons/acre (12.3 and 32.5 Mg/ha) for
corn and orchardgrass, respectively, the site life can be
calculated as follows:
Crop
Corn.
Orchardgrass.
Calculation
125 tons/acre
5.5 tons/acre/yr
125 tons/acre
Site lift
22.7
8.6 wr
14.5 tons/acre/yr
The total amount of sludge #2 that can be applied is
calculated similarly.
94
-------
Total metal Metal content
Metal
Pb
Zn
Cu
Ni
Cd
limit
(Ibs/acre)
1,000
500
250
100
10
of sludge
(ppm)
5,000
10,000
1,000
200
300
Calculation
1,000
5,000 X .002
500
10,000 X.002
250
1,000 X .002
100
200 X .002
10
300 X .002
Total amount of
sludge allowed
(tons/acre)
100
25
125
250
17
Based on the above calculation, total sludge additions
would be limited to 17 tons/acre (38.1 Mg/ha) for
sludge #2 due to the Cd concentration in the sludge.
At 3.3 tons/acre/yr (7.4 Mg/ha/yr), the site life would
be approximated to 5.2 years.
Phosphorous and Potassium Requirements
Fertilizer recommendations for these two elements will
vary according to the amount of sludge added to the
soil. Sludge application rates are presented in tables 9-
28 and 9-29, that include P and K additions and re-
quirements.
Land Area Required
Application rates for one-half of the land area cultivat-
ed in corn will require 5.5 tons/acre/yr (12.3 Mg/ha/yr),
whereas areas of orchardgrass will require 14.5
tons/acre/yr (32.5 Mg/ha/yr). Calculation of land area
required for sludge #1, after a four year period is as
follows:
Acres =
949 tons/yr
(5.5 +14.5)/2tons/acre/yr
= 94.9
The total amount of land required for sludge #2 is
calculated at 3.3 tons/acre/yr (7.4 Mg/ha/yr) (based on
Cd limits).
Acres =
949 tons/yr
3.3 tons/acre/yr
= 288
Table 9-28.—Application schedule for sludge #1
Year
Corn
1
2
3
4
to
22
Orchardgrass
1
2
3
4
5
6
7
8.
Sludge applied
(tons/acre)
Annual
6.1
5.9
5.7
5.5
5.5
16.7
15.8
15.0
142
143
144
144
144
Cumulative3
6.1
11.9
17.6
23.1
122.4
16.7
32.4
47.4
61.6
76.0
90.4
104.8
119.3
N
applied6
(Ibs/acre)
170
164
159
154
155
360
284
269
256
258
260
260
260
N
residual
(Ibs/acre)
0
6
11
16
15
0
16
31
44
42
40
40
40
P
applied
(Ibs/acre)
243
234
227
219
221
667
631
599
569
574
577
577
577
P
needed0
(Ibs/acre)
0
0
0
0
0
0
0
0
0
0
0
0
0
K
applied
(Ibs/acre)
61
59
57
55
55
167
158
150
142
143
144
144
144
K
neededd
(Ibs/acre)
64
66
68
70
70
133
142
150
158
157
156
156
156
"Total cumulative not to exceed 125 tons/acre (Zn unit).
bAmount of available N applied to meet crop N requirement.
cNo fertilizer P needed.
dFertilizer K needed to meet crop K requirement.
95
-------
Table 9-29.—Application schedule for sludge #2
Year
Corn
1
2
3
4
5
Orchardgrass
1
2
3
4 ...
5 ....
Sludge applied
(tons/acre)
Annual
3.3
3.3
3.3
3.3
3.3
3.3
3.3
3.3
3.3
3.3
Cumulative3
3.3
6.6
9.9
13.2
16.5
3.3
6.6
9.9
13.2
16.5
N
applied
(Ibs/acre)
92
92
92
92
92
92
92
92
92
92
N
residual
(Ibs/acre)
0
3
6
9
9
0
3
6
9
9
N
needed
(Ibs/acre)
78
75
72
69
69
208
205
202
199
199
P
applied
(Ibs/acre)
132
132
132
132
132
132
132
132
132
132
P
neededb
(Ibs/acre)
0
0
0
0
0
0
0
0
0
0
K
applied
(Ibs/acre)
33
33
33
33
33
33
33
33
33
33
K
needed0
(Ibs/acre)
92
92
92
92
92
257
257
257
257
257
aSludge #2 application is limited by Cd at 3.3 tons/acre/yr for 5 yrs.
bNo P fertilizer needed as P added in sludge exceeds crop requirement.
cFertilizer K needed to supply 125 and 300 Ibs K/acre for corn and orchardgrass, respectively.
Stabilization
A variety of stabilization techniques are available. For
the purpose of this example, it is assumed that sludge
undergoes anaerobic digestion. Characteristics for this
process, and other stabilization processes are presented
in table 9-18.
Dewatering
An additional consideration in the design of a system
is the relative advantages associated with dewatering
sludges. For example, a comparison can be made of
liquid versus dewatered sludge for transportation and
application costs, annual application rates and site life.
Dewatered sludge contains less NH4-N than liquid
sludge resulting in increased annual application rates. If
the rate is controlled by Cd, dewatering will decrease
the amount of plant available N added per year, neces-
sitating additional N fertilizer to optimize crop yields.
Annual application rates and site life for sludge #1
following dewatering are shown in table 9-30. Since the
site life depends on metal additions, the use of low
NH4-N sludges results in a reduced site life. However,
the larger annual rates result in less land needed per
year.
Transportation and Application
After deciding upon an area for sludge application, the
various alternatives for transportation and application
methods can be considered. Costs for transportation can
be estimated from the curves presented in "Costs." At a
Table 9-30.—Effect of NH4-N concentration in sludge on arwya
application rates for addition of 200 Ibs N/acre
Years of sludge application
Percent
NH4-N
in sludge3
0
0 25
05
0 75
0 90
(tons/ acre)
1
25.0
15.4
11.1
8.7
7.7
2
22.0
14.2
10.5
8.3
7.4
3
19.5
13.2
10.0
8.0
7.1
4
17.3
12.3
9.5
7.7
6.9
5
18.2
12.5
9.6
7.7
6.9
Site life'
(years)
6
10
13
16
18
3Sludge contains 2 percent organic N. Liquid sludge at 4 percent
solids contained 1 percent NH4-N. The NH4-N levels at 8 percent and
16 percent solids would be 0.5 and 0.25 percent NH4-N, respectively.
"Assumes total sludge addition is limited to 125 tons/acre, as for
sludge #1.
distance of 5 miles (8 km), figure 9-8 shows that truck
transport of liquid sludge is the least expensive alterna-
tive.
Using the criteria specified in "Costs," costs for a 5
mile (8 km) one-way truck haul from figure 9-8 would
be $86,000/yr. The cost would be $91 /dry ton
($100/Mg), or about $3.70/wet ($4.08/Mg) ton of
sludge. For a pipeline, the annual cost would be
$140,000 plus cost of application at the site.
96
-------
Many assumptions were used in calculating the curves
presented in "Costs." Many of these assumptions are
not applicable for any specific site (i.e., labor costs,
type and size of truck, loading facilities, etc.).
Costs for spreading sludge #2 would increase primar-
ily because more land is required, increasing application
costs. Dewatering would be advantageous only in reduc-
ing volume, since the same rates of solids must be
applied.
Storage
In the midwestern climate used for this example, stor-
age facilities will be needed during the winter months
because of frozen soils and wet soil conditions. If soil
freezing is not severe, sludge application could continue
if injection equipment is used during the winter. Based
on the data in table 9-26, the estimated number of days
when sludge could not be applied is approximately 100.
Assuming a 100 day storage requirement, the amount of
storage can be calculated:
tons storage = 100 days x 2.6 tons sludge/day
= 260 tons sludge
If the sludge is 5 percent solids, then storage would be
needed for 5,200 wet tons (4717 Mg) of approximately
1.2 X106 gallons (4,500 m3). A lagoon or other storage
facility of 100 ft x 100 ftx20 ft (30 mx30 mx6 m), or
200,000 cu ft (5,660 m3), would suffice.
Application Schedule
For a typical year, an application schedule can be
formulated for the crops considered.
Month
January
February...
March
April
May
June
July
August
September.
October
November..
December..
Corn Orchardgrass
NA NA
NA NA
SI S
SI S
C S
C S
C S
C S
C S
SI S
SI S
NA NA
NA, no application (e.g., frozen ground); S, surface application; SI,
surface or injection application; C, growing crop present.
The above table indicates the probable months of the
year that sludge can be applied on the crops. More
than 3 months of storage would be needed if inclement
climatic conditions were encountered during periods of
sludge application.
Split applications of sludge may be required for rates
of liquid sludge in excess of 5 dry tons/acre (11.2
Mg/ha). Split applications refer to adding small quanti-
ties of sludge at different times of the year to attain the
desired total rate. If the sludge contains 4 percent sol-
ids, the volume of sludge applied at a 5 ton/acre (11.2
Mg/ha) rate is —23,500 gallons (90 m3) or —0.9 acre-in
Realizing that surface runoff depends on soil properties
(e.g., infiltration rate) and slope, the likelihood of runoff
from relatively flat soils (less than 5 percent slope) is
increased when application rates approach 1 acre-in. of
liquid sludge. Obviously, subsurface application will mini-
mize runoff from all soils. An advantage of split applica-
tion is the increased efficiency of N utilization by the
crops grown.
Monitoring
The recommendations developed are based on mini-
mizing NO3-N movement into groundwater and Cd uptake
by plants. Therefore, the monitoring program would con-
sist of continuing soil analysis every 2 to 3 years for
plant available P and K and lime requirement. To pre-
clude excessive plant availability of metals, mainly Cd,
the soil must be maintained at pH >6.5.
Additional Cropping Patterns
To simplify the design example, only two crops were
considered. However, in many situations sludge will be
applied to more than two crops. It is suggested that
application rate calculations be made for all crops grown
when the detailed plan is developed. For Design Exam-
ple A, additional crops could be wheat, oats, barley and
soybeans. The results of these calculations are shown in
tables 9-31 and 9-32.
DESIGN EXAMPLE B
Preliminary Planning
This example will illustrate the procedure used for a
40 Mgal/d (1.75 rrrVs) treatment plant. The total amount
of sludge requiring utilization is 9,490 tons/year (8610
Mg/yr). The preliminary analysis based on a 10 ton/acre
(22.4 Mg/ha) application indicates that approximately
1,000 acres (405 ha) would be needed (or 10 times the
area for a 14 Mgal/d (0.6 m3/s) plant). Assuming that
initial inquiries suggest that land is available, the proce-
dures outlined for Design Example A would be followed.
An additional consideration for a 40 Mgal/d (1.75 m3/s)
plant would be the possibility of the city purchasing land
to increase their operational flexibility. The major advan-
tage in purchasing land is that the rate of sludge ap-
plied can add in excess of 2 Ib Cd/acre/year (2.2
kg/ha/yr) and in excess of the N required by the crop,
provided adequate monitoring procedures are used. The
major monitoring requirements are (1) all crops are ana-
lyzed for metals, mainly Cd, prior to consumption by
livestock or marketed and (2) ground and surface waters
are monitored to prevent off-site degradation of water
97
-------
Table 9-31.—Application rates for sludge #1 on soils cropped to oats or winter
wheat
N Residual P K K Annual Cumulative
Year required N added3 added fertilizer rate amount
(Ibs/acre) (Ibs/acre) (Ibs/acre) (Ibs/acre) (Ibs/acre) (tons/acre) (tons/acre)
Incorporated (0 percent NH3 lost)
to 39,
100
97
93
90
91
91
91
0
3
7
10
9
9
9
143
138
133
129
130
130
130
36
34
33
32
32
32
32
39
41
42
43
43
43
43
4
7
10
13
16
19
127
Surface applied (50 percent NH3 lost)
1
2
3
4
5
6
7 to
100
95
90
85
86
87
87
0
5
10
15
14
13
13
222
210
200
190
192
193
193
56
53
50
47
48
48
48
19
22
25
9fl
97
97
97
c
c
c
-M
1fi
01
OR
^1
1 9fi
aNo fertilizer P needed.
Table 9-32.—Application rates for sludge #1 on soils cropped to soybeans
Year
1
2
3. .
4
5
6 .
7 to 15
1
2
3..
4
5
6.'...
7 to 10
N
required
(Ibs/acre)
250
241
233
226
227
227
227
250
237
224
213
215
216
216
Residual
N
(Ibs/acre)
P
added3
(Ibs/acre)
K
added
(Ibs/acre)
K
fertilizer
(Ibs/acre)
Incorporated (0 percent NH3 lost)
0 357 89 11
9 345 86 14
17 333 83 17
24 323 81 19
23 324 81 19
23 325 81 19
23 325 81 19
Surface applied (50 percent NH3 lost)
0 556 139 0
13 526 131 0
26 499 125 0
37 474 118 0
35 478 120 0
34 481 120 0
34 481 120 0
Annual
rate
(tons/acre)
9
9
8
8
8
8
8
14
13
12
12
12
12
12
Cumulative
amount
(tons/acre)
9
18
26
34
42
50
122
14
27
39
51
63
75
123
aNo fertilizer P needed.
98
-------
quality from movement of pathogens, N, P, metals, etc.
Thus, neither annual Cd nor total metal limits are appli-
cable to soils dedicated to sludge disposal.
To minimize problems from NO3 leaching into ground-
water, the annual rate of sludge application is related to
N use by the crop grown. The annual N application can
be increased above the fertilizer recommendation for
dedicated sites subject to monitoring. For this example,
the amount of N applied will be 1.5 times the fertilizer
recommendation.
Design
Application Rates
The crops chosen are corn and orchardgrass as in
Design Example A. The application rate average, fertiliz-
er needs, etc., would be the same as those presented
earlier in Design Example A.
Corn was selected because it excludes Cd from the
grain to a greater extent than other crops (e.g., soy-
beans). Corn and orchardgrass also have the ability to
remove relatively large amounts of N during the growing
season.
Surface application of sludge will be used to minimize
the land required. Only N is considered in calculating
the surface application rate. For sludge #1 and #2:
creased to utilize all city-owned land most economically.
If all 550 acres (223 ha) were cropped to orchardgrass,
11,440 tons (10,380 Mg) could be utilized each year of
120 percent of the sludge produced.
Application Methods
Potential application methods for each crop include:
Crop Application method
Corn Surface—prior to planting and post harvest
Ridge and furrow irrigation—during growing season
Orchardgrass Surface—post-harvest
As discussed in Design Example A, split applications will
be needed for a sludge with 4 percent solids to attain
the desired application rates. The volume of liquid
sludge applied will be 3.0 and 4.4 acre-in./year for the
corn and orchardgrass areas, respectively.
The months available for application are given below:
Month Com Orchardgrass
Crop
Corn
Orchardgrass..
N
needed
170
250
N
added
255
375
Application rate,
tons/acre
14.2
20.8
Acres
needed
668
456
Note: N added = 1.5 xN needed.
Approximately 460 acres (186 ha) would be required for
utilization of all sludge from a 40 Mgal/d (1.75 m3/s)
plant (9,490 tons/year or 8,609 Mg) if orchardgrass, or
a similar cover crop were used, whereas 670 acres (271
ha) would be needed if corn were grown. Both the
forage and corn crop could be harvested and marketed
as long as metal analyses indicate that the crops do not
contain excessive concentrations of Cd or other meth-
ods. Guidance from FDA will be needed to assess ac-
ceptable levels of metals in grains and forages.
The quantity of land purchased by the city would de-
pend on the acreage of private farmland available pres-
ently and in the future. The city purchased 550 acres
(223 ha) similar to figure 9-14a and 9-14b and utilized
it as follows:
Crop
Corn
Orchardgrass.
Application rate,
tons/acre
14.2
20.8
Acres
350
200
Sludge applied,
tons
4,790
4,160
9,130
Using this distribution approximately 360 tons (326 Mg)
would be applied to privately owned cropland. If the
availability of private cropland decreases, the corn acre-
age can be decreased and the forage acreage in-
January
February
March
April
May
June
July
August R
September R &
October H
November S
NA
NA
S
S
S
R &
R &
&
December.
NA
NA
NA
S
S
S
S-H
g-H
S
S-H
S-H
S
NA
NA, No application; S, surface; R & F, ridge and furrow irrigation;
H, harvest crop.
The orchardgrass can be harvested 3-4 times per year
while corn is harvested in October or November. Man-
agement is needed to insure that sludge applications are
timed appropriately to allow relatively dry soil conditions
during harvest operations. For sludges containing persist-
ent organics (i.e., PCB's) at concentrations >10 mg/kg,
surface application to forages is not recommended.
Site Use
The site life for a dedicated system is difficult to
predict based on present knowledge. However, the crite-
ria for privately owned farmland are conservative to al-
low growth of any crop after sludge application ceases.
It is likely that the total amount of metals applied to
dedicated sites can be greater than those shown in
table 9-14. The most essential factor in minimizing
movement and plant uptake of metals is maintaining soil
pH at 6.5 or above.
Transportation and Application
The sludge transportation system adopted will depend
on local conditions such as availability of rail lines, etc.
99
-------
The data in figure 9-10 indicate that a pipeline is eco-
nomically feasible for a 40 Mgal/d (1.75 rrvVs) plant with
transportation distances of less than 25 miles (40 km).
The estimated costs/year for a site 10 miles (16 km)
from the plant are:
Pipeline Truck
Transportation $27,000 $980,000
Surface application (80 percent of volume) 110,000 (Included)
Ridge and furrow (20 percent of volume) 50,000 (included)
Total 187,000
980,000
Unit costs are $19.70/dry ton ($21.71/Mg) or $0.80/wet
ton ($0.88/Mg) for sludge applied to the dedicated site
via a pipeline and ridge and furrow irrigation plus sur-
face application. For truck transport and surface applica-
tion, costs are $103.30 and $4.13 per dry and wet ton
($113.86 and $4.55/Mg), respectively.
Monitoring
Strict monitoring procedures are needed on dedicated
sludge disposal sites. The monitoring procedures dis-
cussed in the Process Design Manual for Land Treat-
ment of Municipal Wastewater31 are also applicable to
sludge sites.
1. Groundwater—locate wells to sample on-site, perime-
ter and background. Proper location and depth of
wells is essential to obtain reliable data on changes
in groundwater quality.
a. Quarterly analyses—Total N, NO3~, total P, soluble
P, Pb, Zn, Cu, Ni, Cd, coliforms.
b. Optional analyses—BOD, COD, pH, total dissolved
solids, alkalinity, SAR.
2. Soils—annual analyses of soil samples are recom-
mended to monitor accumulation of metals and
changes in soil pH. Soils are sampled at 0-6 inches,
6-12 inches and 12-24 inches, or within homogene-
ous horizons.
a. Required analyses—pH, lime requirement, plant
available P and K, and extractable or total Pb, Zn,
Cu, Ni and Cd.
b. Optional analyses—CEC, organic C, total N, total
P, base saturation, organics.
3. Plants—metal analyses are required on all grain or
forages utilized by livestock or marketed. The metals
of main concern are Pb, Ni and Cd. Optional analy-
ses would include total N, P, K, Cu and Zn. Nitrate
analysis is suggested for crops consumed by live-
stock.
DESIGN EXAMPLE C
This example will illustrate the application of sludges
on forest land. The sludge composition, climate and soil
characteristics are the same as in Design Example A.
The data required are
Sludge:
Solids
Organic N
NH4+-N
Climate:
Rainfall
Deciduous trees:
Annual N uptake
Evapotranspi ration
Percolate NO3~-N
4 percent
2 percent (dry weight basis)
1 percent (dry weight basis)
40 in (101.6 cm).
50 Ibs/acreage (56.0 kg/ha)
(table 9-16)
17 in./yr (43.2 cm/yr) (table
5-36 in ref. 31)
10 mg/l
The available N content of the sludge is calculated as in
Design Example A:
Percent Cs = percent organic N x 0.2 + percent NH4+-N
= 2 percent x 0.2 +1 percent
= 1.4
The available N content is next converted to a volume
basis and related to N applied,
= 22.7
where
Ln - plant available N applied (Ibs/acre • yr)
I., = volume of sludge applied (in./yr)
S = percent solids in liquid sludge
(Conversion factors assume 1 ft3 of sludge = 62.4 Ibs
or 1 in /acre = 2.26 X105 Ibs.)
For a sludge containing 4 percent solids,
U = 22.7(1 .4)U(4)
= 127.1 U
or
= 0.0079 Ln
The climatic data and ET are used to calculate the
volume of percolate
^W- ET
where
Pr = precipitation (in./yr)
Wp = percolate volume (in./yr)
ET = evapotranspi ration (in./yr)
For the data used,
100
-------
or
- 17
Wp = L8 + 23
Substituting Lgfrom above,
Wp = 0.0079 Ln + 23
This information is then used in the following equation to
calculate plant available N that can be applied.
+ 0.23
where
U =N uptake by plants (Ibs/yr)
D = denitrification factor (0.2 LJ
Cp = percolate NO3-N concentration (10 mg/l)
Substituting the previous values into the above equation
yields
.2 Ln + 0.23(0.0079 Ln + 23)10
.2 U + 0.018 Ln + 52.9
Solving for Ln,
- 0.2 U~ 0.018 Ln = 102.9
0.78 U, = 102.9
Thus, 132 Ib (59.9 kg) of plant available N could be
applied to the deciduous tree stand considered. It
should be emphasized that these calculations assume
that 50 Ib (22.7 kg) of N are utilized by the trees and
that 20 percent of available N applied is lost through
denitrification.
The volume of liquid sludge applied can be calculated
from,
Ln = 22.7 (
132 = 22.7(1.4)^(4)
L$ = 22.7(1.4X4)
= 1.04 in.
This rate is equivalent to 118 wet tons/acre (264
Mg/ha) of 4,7 tons/acre (10.5 Mg/ha).
This example shows the relatively small influence of
water applied with the sludge on the total volume of
percolate. For dewatered and liquid sludges containing
>5 percent solids, the volume of sludge applied can be
ignored in the calculation of Wp.
The contribution of residual N to L,, can be used if
sludge has been applied previously to the site. For a
sludge with 2 percent organic N, approximately 1 Ib
N/ton will be released the second year and 0.9 Ib
N/ton in the third and fourth years after application.
Thus, the rates of sludge applied would be:
Year
N applied Residual N
1.
2.
3.
4.
132
127
123
119
0 .
4.7
8.8
12.8
Sludge applied,
tons/acre
4.7
4.6
4.4
4.3
As shown for Design Example A, the amounts P, K, and
metals can be calculated once the sludge application
rate is known.
It should be re-emphasized that the use of the above
design criteria is based on wastewater irrigation consid-
erations but it, hopefully, will simulate the responses
occurring when forest lands are treated with sludge. A
more conservative estimate can be made by assuming
that no N uptake by plants occurs, relying upon denitrifi-
cation to reduce the NO3-N concentration to 10 mg/l in
the percolate. For this case, the rate of sludge applica-
tion would be approximately 2.4 tons/acre (5.4 Mg/ha).
Appendix A: ENVIRONMENTAL IMPACTS
Soils
General Properties
Soil is a complex mixture of inorganic and organic
compounds. The inorganic fraction may consist of clay
minerals, other silicate minerals, oxides, and carbonates.
The organic fraction usually contains humic and nonhum-
ic substances. The proportions and properties of inor-
ganic and organic components in soils are a function of
time, climate, topography, vegetation and parent material.
In a well-aggregated soil, soil particles and pore space
each constitute 50 percent of the volume. Optimum con-
ditions for plant growth exist when water and air each
occupy 50 percent of the pore space. With respect to
the solid phase, the texture of a soil is defined by the
relative proportion of particles found in the sand
(>50ju), silt (2-50/x) and clay «2]n) size fractions.
Through use of a texture triangle, a soil containing a
certain percentage of sand, silt and clay is assigned a
name, such as sandy loam, silt loam, silty clay loam,
etc. In this context, the term clay is used to define a
size fraction, which may contain inorganic compounds in
addition to clay minerals.
Clay minerals, one of the more important inorganic
fractions of a soil, are composed of layered sheets of
tetrahedrally, or octahedrally coordinated cations. The
sheets of Si tetrahedra and Al octahedra are present in
a 1:1 or 2:1 configuration. Kaolinite is a typical 1:1 clay
mineral while montmorillonite and vermiculite are 2:1
clays. When aluminum or iron ( + 3) is substituted for
silicon ( + 4) and magnesium or iron ( + 2) for aluminum
101
-------
( + 3), a permanent, net negative charge results on the
surface of the clay mineral. This negative charge is sat-
isfied by surface retention of a cation such as H"1", K+,
Ca2+, Mg2+, AI3+, etc. The magnitude of the negative
charge is measured by determining the cation exchange
capacity (CEC), which is commonly expressed in
meq/100 g. The CEC arising from isomorphous substitu-
tion is not pH dependent. However, clay minerals pos-
sess some pH dependent CEC, about 10 percent, arising
from the dissociation of hydroxyl groups (-OH) present
at the edges of broken clay crystals. The ability of clay
minerals to attract and retain cations is a very important
characteristic in soils. Soil cation exchange capacity will
be discussed later in detail. In addition to CEC, addition-
al properties of clays include a high surface area, the
capacity to sorb metals and organics, and the ability to
swell or shrink depending on water content.
Other silicate minerals are less important than the
clays, primarily because of their minimal CEC and low
surface area. Included in this category are minerals such
as quartz, feldspars, micas, and amphiboles.
The predominant oxide minerals are compounds of Fe,
Al, and Mn. A significant part of the Fe and Al oxides in
soils may be present as amorphous rather than crystal-
line compounds, depending on soil pH, organic matter
and other properties. Amorphous compounds possess a
higher surface area and greater chemical reactivity than
their crystalline counterparts. Recent research indicates
that Fe and Al hydrous oxides can sorb Zn2+, Cd2+,
and probably other trace metals. It has been well estab-
lished that Fe and Al compounds in soil are important
sites for P fixation. In addition, Fe and Al oxides may
interact with clay minerals resulting in the general trend
observed for a direct relationship between clay, Fe and
Al content of soils. The solubility of Fe3+ and AI3+ in
soils is depressed with increasing pH. Since Fe and Mn
can undergo oxidation-reduction reactions, the forms and
subsequent solubility of Fe and Mn are controlled by soil
aeration.
Carbonates influence the pH and buffering capacity of
a soil. Leaching of soils causes the carbonates to dis-
solve and leach downward. This results in an acidic
environment and additional CaCO3 may have to be ap-
plied to promote crop growth, or, in the case of sludge
application, to maintain a pH above 6.5.
Organic matter is the other major component of soils
(i.e., humus). There are two major categories of soil
organic matter: the humic and nonhumic substances.
Nonhumic substances are the intact or partially degrad-
ed compounds from plants, animals, or microbial resi-
dues. In general, these substances account for less than
25 percent of soil organic matter. With time, the majority
of these compounds decompose and a portion of the
degradation products becomes incorporated into humic
substances.
Humic substances are a complex, high molecular
group of organic compounds that result from chemical
and enzymatic reactions of degradation products from
plant, animal and microbial residues. Humic substances
are subdivided into the following categories: fulvic acid
(acid and alkali soluble), humic acid (acid insoluble, al-
kali soluble), and humin (acid and alkali insoluble). Al-
though quantitative differences exist in chemical compo-
sition, all three fractions are characterized by possessing
a non-polar (aromatic rings) core with attached polar
functional groups. The non-polar nature of humics ac-
counts for the strong affinity of soil organic matter for
added organic compounds such as herbicides, pesti-
cides, etc. Functional groups found in soil organic mat-
ter include carboxyl (-COOH), phenolic and alcoholic
hydroxyl (-OH), amino (-NH2) and sulfhydryl (-SH)
groups. All of these functional groups exhibit acid-base
character and thus, soil organic matter is involved in the
buffering of soil pH. Furthermore, the ionization of func-
tional groups results in soil organic matter possessing a
net negative charge or CEC. Soil pH strongly influences
the CEC of soil organic matter with increasing pH result-
ing in increasing CEC. Metals may also interact with
functional groups through chelation and ion exchange
mechanisms.
Clay minerals and organic matter constitute virtually all
soil CEC. The humic fraction of soil organic matter nor-
mally ranges between 200-300 meq/100 g, whereas the
CEC of clay minerals varies according to the mineral
type, between 5-120 meq/100 g. Therefore, the relative-
ly small fraction of organic matter present in a soil may
exert a large influence on total CEC. Even though a
wide range is encountered for the CEC of individual clay
mineral types and soil organic matter, statistical analysis
of CEC, clay and organic matter data for soils have
resulted in development of an equation to predict CEC
from clay and organic matter content.17
Nitrogen Transformations
A simplified schematic of the N cycle is shown in
figure 9-A-1. Both organic and inorganic nitrogen are
added to soils by sludge addition. While the inorganic
nitrogen (NH4+ and NO3~) is readily available for plant
uptake, only 15 to 25 percent of the organic nitrogen is
converted to available forms the first year after applica-
tion.54 The availability then decreases each consecutive
year following application.
Ammonium-N is a major N species added to soils in
sludge applications. It may be held on the clay surface
as an exchangeable cation. In soils containing mica-
ceous minerals, NH4+ may penetrate between the mineral
plates causing collapse of the mineral and NH4+ fixation.
This form of NH4 is relatively inert and will not partici-
pate to a great extent in further chemical or microbial
reactions. Of most significance, especially when consid-
ering surface application of sludges, is NH3 volatilization.
In excess of 50 percent of the NH4-N is commonly vola-
tilized during air-drying of sewage sludges.24 The extent
of NH3 volatilization after surface application of sludge
will depend on the following factors: (1) soil pH; (2) soil
CEC; (3) climate (temperature, relative humidity); and (4)
soil conditions (water content, rate of infiltration). Labo-
102
-------
SLUDGE N
LEACHING
EXCHANGE NH4+
CLAY-FIXED NH4 +
NO3~ IN GROUND WATER
DENITRIFICATION
N2 IN ATMOSPHERE
Figure 9-A-1.—Nitrogen cycle in soil.
ratory experiments indicate that the extent of NH3 volatil-
ization is related inversely to CEC and directly to pH.
Volatilization of NH3 can be reduced to <5 percent of
applied NH4-N by incorporation of sludge into the soil.
Unfortunately, quantitative data are not available con-
cerning the magnitude of NH3 volatilization under field
conditions. At present, recommendations based on N
application rates assume that 50 percent of the plant
available N is lost via NH3 volatilization when sludge is
surface applied.
After addition to soil, essentially all ammonium will be
converted to nitrate (NO3~). This process, called nitrifica-
tion, involves two steps. First, NH4 + is oxidized to NO-r
by the bacterium Nitrosomonas, followed by oxidation of
NO2~to NO3~by Nitrobacter. In neutral soils, essentially
all NH4+ added will be converted to NO3~ within 2 to 4
weeks after application. Depressed nitrification rates may
occur in sludge amended soils at N application rates
approaching 1,000 Ibs/acres (1120 kg/ha), amounts in
excess of those recommended for most soils. In contrast
to NH4+ which is held as an exchangeable cation, NO3~
remains as a soluble anion in the soil solution.
The formation of NO3~ is significant because NO3~ can
be lost from the soil through leaching. In humid regions,
N applied to soils in excess of crop requirements may
leach and result in NO3~ contamination of groundwater.
Systems developed for land treatment of wastewater are
based on the premise that a growing crop will reduce
the NO3~ concentration in the soil solution to levels ac-
ceptable for drinking water. Thus, the annual amount of
N applied to soils in sludge is based on the N required
by the crop grown.
.In addition to leaching, NO3~ may be lost from soils
through denitrification. Denitrification occurs when facul-
tative anaerobic bacteria utilize NO3~ as a terminal elec-
tron acceptor in place of O2 under anaerobic conditions
(i.e., saturated or excessive water contents). In an "aer-
obic" soil, it is also possible that denitrification can be
occurring because the center of soil aggregates may be
water-saturated and anaerobic. The end-product of deni-
trification is generally N2, which diffuses into the atmo-
sphere. Denitrification may be a significant mechanism
for N loss in soils treated with liquid sludge because of
localized increases in soil H2O content. Thus, NH4+ may
be oxidized to NO3~ in an aerobic zone followed by
diffusion of NO3" into anaerobic microsites where denitri-
fication occurs.
The adverse effects of overfertilization of soils with
103
-------
sewage sludge are twofold. First, use of excess N caus-
es luxury consumption of NO3" by many plants and re-
sults in potential animal health problems when high NO3~
feedstuffs are consumed and second, NO3"can be
leached from the soil profile and enter groundwaters.
The latter problem is the most significant from a long-
term standpoint.
The two areas of concern involving high concentra-
tions of NO3" in waters are direct health effects and
eutrophication. Nitrate-nitrogen may present a health
hazard. Winton et al.33 described the circumstances
which may induce methemoglobinemia or cyanosis in
infants. The main controlling factor in this disease is the
daily nitrate intake, and hence, the nitrate concentration
of drinking water plays an important role. Drinking water
standards in the United States mention nitrate concentra-
tions of 45 mg NO3~/1, as maximally permissible levels.
Also livestock may suffer from a number of symptoms
caused by too high nitrate-nitrogen levels in the drinking
water like methemoglobinemia, vitamin A deficiency, re-
productive difficulties and abortions, and loss of milk
production. Increased concentrations of N in water may
also cause eutrophication (i.e., nutrient enrichment) of
surface water. Eutrophication results in rapid growth of
the nuisance aquatic plants. The most commonly known
features of eutrophication are phytoplankton blooms. The
exact factors responsible for eutrophication are still in-
sufficiently understood, however, P-concentrations below
0.01 mg/l and N concentrations below 0.2-0.3 mg/l
appear to minimize algal blooms in surface waters.
Phosphorus Interactions
The behavior of phosphorus in soils is controlled by
chemical rather than biological reactions. The interac-
tions of the phosphorus cycle are illustrated in figure 9-
A-2. The majority of phosphorus in sludges is present in
inorganic compounds, about 70 to 90 percent of total
phosphorus. Therefore, even though mineralization of the
organic phosphorus occurs during decomposition, inor-
ganic reactions of phosphorus are of greater importance
in sludge application.
The P immediately available for plants is present in
the soil solution. As plants deplete the soil solution, the
equilibria with sorbed P and P minerals are shifted re-
sulting in replenishment of the soluble P pool. The quan-
tity of soluble P in soil is referred to as an "intensity"
factor whereas the total amount of P present that may
enter the soil solution is a "capacity factor." Thus, the
concentration of soluble P in soils may not be related to
the ability of a soil to supply P to crops throughout the
entire growing season. Soils possess the ability to "fix"
P through sorption and/or precipitation reactions. As a
result, the concentration of P in the soil solution is
generally <0.1 mg/l, resulting in minimal leaching losses
of P. In fact, land treatment of wastewaters is based on
retention of P as wastewater percolates through a soil
profile. Because phosphorus accumulates in the soil sur-
face, phosphorus toxicity may occur following repeated
Figure 9-A-2.—Phosphorus cycle in soil.
sludge amendments. In most instances, other parameters
(e.g., heavy metals) will limit total sludge loadings to a
level where P toxicity to crops will not be a problem.
Serious problems in crop production due to excess
phosphorus are rare. It has occasionally been inferred
that excess P in the soil impairs plant growth via indi-
rect action. For example, Zn-deficiency symptoms can be
traced to P inhibition at the root surface when rather
soluble phosphates are present. However, sludge appli-
cations add both P and Zn to minimize any potential
P-Zn interactions.
Reactions of Metals in Soil
The majority of sludges add appreciable amounts of
trace metals to soils. The metal content of soils and
plants is quite variable depending on the soil type and
plant species. Trace elements such as B, Co, Cu, Mn,
Mo, Se and Zn are essential for plant growth; however,
if excessive concentrations are applied to soil, metal
toxicities may develop and crop yields will decrease.
Often times, the interpretation of a metal toxicity to
plants is not straightforward because of interactions be-
tween nutrients (e.g., P induced Zn deficiency). Non-es-
sential metals (e.g., Cd, Ni, Pb) may be toxic to plants
and decrease yields. Of greater concern is the enrich-
ment of food and fiber with metals potentially harmful to
humans and animals. Because As, Pb and Hg are not
taken up from soils by most plants, the element of
greatest concern is Cd. In general, the rationale of
sludge application guidelines is to minimize (1) de-
creased crop yields caused by metal additions to soil;
and (2) increased concentrations of non-essential metals
104
-------
(e.g., Cd) in the plant part consumed by man or ani-
mals. The fate of sludge metals in soils and plants has
been reviewed recently.47
The chemistry of metals in soils is quite complex and
incompletely understood. The fate of metals added to
soils in sewage sludge is depicted in figure 9-A-3. Me-
tals available to plants and susceptible to leaching are
present in the soil solution as the free metal ion (M2+),
complexes (MOH+, MCI + , etc.) and chelates (M-Fulvic
acid, etc.). As plant uptake or leaching occurs, the soil
solution re-equilibrates with the solid phase, resulting in
a relatively constant concentration in the soil solution.
The equilibrium concentration will be controlled by soil
properties such as pH, Eh, and solution composition. In
general, the solubility and plant availability of metals
decreases with increasing pH.
Metals in the soil solution are continuously interacting
with metals present as precipitates (carbonates, hydrox-
ides, etc.), bound with soil organic matter, sorbed by
clay minerals and retained by hydrous oxides. Further-
more, the properties of clay minerals in soil are influ-
enced to a great extent by interaction with organic mat-
ter and hydrous oxides. In general, the organic matter
present in clay-organic matter complexes is more resis-
tant to decomposition than "free" organic matter result-
ing in the common trend for the clay and organic matter
contents of soils to increase proportionately. The pres-
ence of acidic functional groups in soil organic matter is
CLAY MINERALS
Fe2°3'AI2°3.
MnO2
SOLUBLE
LEACHING
Figure 9-A-3.—Reactions of metals in soil (M2+ repre-
sents Cu, Zn, Ni, Cd, Pb, etc.).
responsible for metal retention through both exchange
and chelation mechanisms. Considerable evidence is ac-
cumulating concerning the importance of metal retention
by Fe and Al hydrous oxides. As shown in figure 9-A-3,
hydrous oxides may also be sorbed onto clay minerals
but they still retain the ability to sorb metals. The Fe
and Al hydrous oxide content of soils also tends to
increase with increasing clay content.
As a result of these interactions between clay, hydrous
oxides, and organic matter, CEC has been used as an
index of the metal retention capacity of a soil. This does
not imply that metals added to soils are retained through
an ion exchange mechanism. Metals present in soil as
an exchangeable cation are readily available for plant
uptake but it has been demonstrated in numerous stud-
ies that only a small fraction of metals added to soil are
present as an exchangeable ion. The above use of CEC
for recommending metal loadings is still open to ques-
tion.
Plants can selectively accumulate certain of these ele-
ments while omitting other elements present in soil solu-
tion. Often the interpretation of metal toxicity to plants is
complicated because of interactions between certain nu-
trients (i.e., P induced Zn-deficiency). However, in gener-
al, elements that can accumulate in plant tissues causing
reduced yields of crops or that pose health hazards to
man are the most important.56 Elements such as As, Co,
Hg, Mo, Pb, Se, and V may have some effect on crop
yield or health, but at present do not appear to be
limiting factors. One of the most serious elements con-
cerning health factors is cadmium,57 but other elements
such as nickel, copper, and zinc may cause serious
crop damage. These elements are discussed below.
Cadmium is currently the element of greatest concern
as a food chain hazard to humans. Acute toxicity to
humans has been reported from consuming acidic foods
prepared or served in cadmium-plated containers. The
more general alleged hazard to humans, however, is one
of chronic toxicity, expressed only after long exposure.
An annual loading rate for cadmium on soils has been
set at 2 Ib/acre-yr (2.24 kg/ha/yr). This value is based
on research by Keeney et al.,17 where additions of 2
Ib/acre (2.24 kg/ha) did not significantly increase the
concentration of cadmium in corn grain (table 9-A-1).
Higher additions of cadmium to the soil did show accu-
mulations of this metal in the plant tissue. A recent
analysis by Pahren et al.57 recommended using 0.9 Ib
Cd/acre/yr (1.0 kg/ha/yr) as a maximum value for
swiss chard. This plant is a heavy metal accumulator
and was used as an "indicator" for maximum uptake by
a crop. This report suggests that crops previously as-
sumed "not suited" for growth on sludge-amended soils,
such as swiss chard and other leafy vegetables, may be
used with some constraints on the cadmium in severe
sludge and would pose no more a hazard to the nation-
al diet than foods naturally high in cadmium such as
shellfish. This presumes that foods enter a marketing
system where products from many parts of the country
are mixed during distribution to retail grocery outlets.
105
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Table 9-A-1.—Cadmium uptake by crops from applica-
tion of sewage sludge
Year of
Rate of sludge application, tons/acreb
(Cd cone, in crop (mg/kg))
Appli-
cation
1971
1972
1973
Harvest
1972
1972
1973
1973
1973
1974
1973
1974
Crop3
Rye
Corn
Corn
Rye
Corn
Corn
Sorghum-
Sudan
Corn
0
0.10
0.09
0.06
0.23
0.08
0.07
0.53
0.07
2
0.25
0.09
0.05
0.25
0.06
0.07
0.50
0.07
4
0.30
0.13
0.05
0.35
0.07
0.07
0.75
007
8
0.25
0.08
0.08
0.45
0.07
0.07
0.75
0.07
16
0.30
0.11
0.05
0.40
0.02
0.07
0.85
0.07
32
0.30
0.09
0.05
0.50
0.05
0.19
0.95
0.12
aRefers to rye and sorghum-sudan forage and corn grain
bApplication of 0, 2, 4, 8, 16 and 32 tons/acre added 0, 0.28,
0.56, 1.12, 2.24 and 448 Its Cd/acre, respectively.
Zinc constitutes an essential element for animals and
plants. However, zinc toxicity in plants has also been
reported, though only at relatively high concentrations.
Zinc toxicity is usually caused by interactions with other
essential elements like phosphorus and iron.
Phytotoxic levels of Zn are at about 400 ppm and up,
and toxicity in animals starts when the Zn content of the
diet exceeds roughly 1,000 ppm. Most plants are severe-
ly injured at such high Zn levels.58 Therefore, lower toxic-
ity levels of plants as compared to animals serve as
protection against Zn accumulation in the food chain.
One of the major factors controlling Zn availability is the
pH. For the same Zn addition level the yield reduction
and the zinc contents of swiss chard leaves were found
to be much higher at pH 5.3 than at pH 6.4.59
Except for certain accumulator species, plants are ex-
cellent biological barriers for heavy metals.60 That is not-
ably true for nickel, copper, and lead. An exception to
the plant barrier rule is the potential for toxicity to rumi-
nants consuming forages with a low ratio of molybdenum
to copper.61 Molybdenum accumulation in soils from
sludge application and subsequent increases in forage
molybdenum content is a potential hazard to grazing
ruminants, especially where soils are neutral or alkaline.
With lead, nickel, and copper, the root provides the
barrier since uptake and, especially, translocation are
low. Baumhardt and Welch have shown a significant but
small increase of lead in corn stover from lead acetate
applications to soil (3,200 kg/ha) although the corn
grain content was only 0.4 mg/kg of lead and not af-
fected by application rate.62 No evidence of phytotoxicity
was observed. Numerous other studies have shown mini-
mal plant uptake of lead from soils amended with sew-
age sludge.36
Nickel and copper have the added protective mecha-
nism of phototoxicity at low plant concentrations. Copper
and nickel concentrations of 30 and 25 mg/kg, respec-
tively, are believed to be phytotoxic.73 Thus, not only is
uptake and translocation of these elements low but the
plant dies or fails to grow long before it can accumulate
a metal content toxic to a mammalian consumer.
At present, there is considerable disagreement among
researchers concerning the impact of annual versus total
metal loadings. Data exist to show that only the first
addition exerts a significant impact on cadmium in plant
tissues. The current approach used by EPA in the tech-
nical bulletin is used herein.23
The life of an agricultural disposal site is based on
the total amounts of lead, copper, nickel, zinc, and cad-
mium applied to the soil.58 These limits are designed to
allow growth, and use of crops at any future date and
stipulates soil pH >6.5. Metal toxicities and/or contami-
nation of the crops may occur due to increasing metal
availability if soils are not maintained at pH >6.5. Sug-
gested metal limits are shown in table 9-14. The total
metal additions shown in table 9-14 are the best avail-
able estimates. However, these values are not "the last
word," and will be revised based on research data that_
is being collected. Furthermore, the establishment of
standards for metals in crops by FDA will allow one to
establish the appropriate metal limits for agricultural
soils. The rationale of sludge application guidelines is to
minimize (1) decreased crop yields caused by metal ad-
ditions to soil; and (2) increased concentrations of non-
essential metals in the plant parts consumed by man or
animals.
Pathogens
Although the general health of the United States is
relatively good, the wastes from people infected with
disease organisms are also introduced into a sewage
system. Most of the organisms are subsequently found in
sewage sludges.
A large variety of disease organisms is present in
sewage sludges. These include protozoa, parasitic
worms, pathogenic bacteria, and viruses. The numbers
and kinds of pathogenic organisms present in sludges
are quite variable, depending primarily on the health of
the community. However, there are usually sufficient
pathogenic organisms present in raw sludges to warrant
public health concerns.
Only a few of the hundreds of disease organisms have
high enough survival rates in soil and water to warrant
concern. The organisms of most concern are: Ascaris
lumbricoides, Entamoeba histolytica, other parasites, Sal-
monella typhi, other Salmonella species, Shigella sp., Vi-
brio cholera, certain other bacteria, and some viruses. A
brief description of each is presented below.
106
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Parasites and Protozoa
Relatively little is known about the possibility of para-
sitic disease transmission via sludge amended soils. Par-
asitic ova and cysts generally are quite resistant to
sludge digestion, disinfectants, and adverse environmen-
tal conditions. Many, in fact, require a period of free
living existence in the soil to develop infectiousness for
man. While often thought of as "tropical diseases" many
of these pathogens are of cosmopolitan distributions and
commonplace within the United States.
The intestinal protozoan parasite, Entamoeba histolyti-
ca, causes amoebic dysentery and produces cysts that
are voided in the feces of infected individuals. However,
cysts are apparently unable to survive anaerobic diges-
tion, even at low temperatures, and are destroyed within
3 days on vegetable surfaces.66 Under optimum condi-
tions of temperature and moisture they survive 6-8 days
in soils.67
The intestinal nematodes (roundworms) and cestodes
(tapeworms) are probably of greater public health signifi-
cance than the protozoan agents in terms of sludge
disposal.
Among the intestinal parasites, Ascaris lumbricoides, a
roundworm or nematode, is most frequently mentioned
as a potential problem in human health. The eggs or
ova of this pest are excreted in the feces of infested
individuals and have been shown to survive sewage
treatment, including anaerobic digestion. The ova are
quite resistant to destruction and may persist in soil for
several years. The ova must be ingested in order to
parasitize.68
Since a portion of animal wastes reach municipal
sludges, parasites of animal origin are also of concern.
Two zoonotic roundworms, Toxacara canis and T. cati,
are nearly universal in our pet population and have a
life cycle in their normal host identical to Ascaris in
man. When ingested by a child these worms are unable
to complete their normal developmental cycle and con-
tinue to wander through the tissues for prolonged per-
iods before eventually succumbing. This results in a
chronic and usually mild disease (visceral larva migrans)
lasting up to a year. Occasionally, more serious manifes-
tations are seen, and the larvae are particularly danger-
ous if they enter the eye since blindness may result.57
The parasites considered potential problems in sludge
management are outlined in table 9-A-2.
Bacteria
Bacteria are apparently the most fragile of the three
groups of pathogens. The survival of bacteria in soil is
Table 9-A-2.—Parasites of concern for possible transmission via sludge amended soils1
.57
Organism
Disease
Reservoir(s)
Range(s)
Protozoa
Balantidium coli
Entamoeba histolytica
Giardia lamblia
Toxoplasma gondii
Nematodes (Roundworms)
Ascaris lumbricoides
Ancylostoma duodenalea
Necator americanus3
Ancylostoma braziliense (cat hookworm).
Ancylostoma caninum (dog hookworm)
Enterobius vermicularis (pinworm)
Stronglyoides stercoralis (threadworm)3
Toxocara cati (cat roundworm)
Toxocara canis (dog roundworm)
Trichuris trichiura (whipworm)
Cestodes (Tapeworms)
Taenia saginata (beef tapeworm)
Taenia solium (pork tapeworm)
Hymenolepis nana (dwarf tapeworm)
Echinococcus granulosus (dog tapeworm)
Echinococcus multilocularis
Balantidiasis
Amebiasis
Giardiasis
Toxoplasmosis
Ascariasis
Hookworm
Hookworm
Cutaneous Larva Migrans
Cutaneous Larva Migrans
Enterobiasis
Strongyloidiasis
Visceral Larva Migrans
Visceral Larva Migrans
Trichuriasis
Taeniasis
Taeniasis
Taeniasis
Hydatid Disease
Aleveolar Hydatid Disease
Man, swine Worldwide
Man Worldwide*1
Man, animals Worldwide
Cat, mammals, birds Worldwide
Man, swine
Man
Man
Cat
Dog
Man
Man, dog
Canivores
Canivores
Man
Man
Man
Man, rat
Dog
Dog, canivores
Worldwide—Southeastern USAb
Tropical—Southern USAC
Tropical—Southern USAC
Southeastern USA
Southeastern USA
Worldwide"
Tropical—Southern USAb
Probably worldwide
Sporadic in USA
Worldwide"
Worldwide—USA
Rare in USA
Worldwide"
Far North-Alaska
Rare in USA
aMan infested via skin contact.
"Has been identified in domestic sludges.
cReported in foreign sludges only to date.
107
-------
reduced by sunlight, drying, and other factors when
sludge is applied to land. Contamination of plants can
occur by direct contact and rain splashes, but survival
for an infective dose is usually short (a few weeks).
Bacteria can survive longer when protected from sunlight
or desiccation.
Typhoid and paratyphoid fevers are caused by Salmo-
nella typhi and S. paratyphi, respectively. These fevers
usually result from consumption of contaminated drinking
waters. However, food may be contaminated either di-
rectly or by a carrier individual, or indirectly by contami-
nated waters used for irrigation of fresh vegetables. For-
tunately, the incidence of this disease in the United
States is very low.69
The incidence of salmonellosis, other than typhoid fev-
er, is much greater. This disease, caused by a number
of species of Salmonella, is characterized by diarrhea,
abdominal pain, and vomiting. Its predominant cause is
due to S. typhimurium. Many cases of salmonellosis are
not reported because the symptoms may be very short
lived, or very mild, but the incidence is believed to be
about 2 million cases per year.40
Shigellosis, also known as bacillary dysentery, is
caused primarily by S. sonnei and S. flexneri. This is an
intestinal disease of man, and can spread rapidly from
person to person under improper sanitary conditions.
This organism is mainly transmitted via the water route
and does not survive long in the hostile environment of
the soil.
Cholera is caused by Vibrio cholera. The incidence of
waterborne outbreaks of cholera outside the United
States is numerous. However, there has been virtually no
reported cases of cholera in the United States for many
years.55 Therefore, the likelihood of cholera from sludges
in the United States is minimal.
Another class of bacterial diseases generally found
only in injured or weak individuals, include enteric infec-
tions with strains of Escherichia coll, Pseudomonas aeru-
ginosa, and Klebsiella sp. These pathogens can occur in
human wastes and are at least potential hazards in
sludges.55
Viruses
Viruses may persist in soils and on vegetation for
several weeks or months. If exposed to sunlight or de-
siccation, viruses will eventually be inactivated. Most en-
terovirus infections occur early in life and are mild when
evident. The majority of such infections usually are en-
tirely subclinical. For man, the virus of greatest potential
concern appears to be Hepatitis A. This is a serious
disease which has an appreciable potential for long-term
liver damage.
The other viruses found in wastes would include mem-
bers of the Coxsakie, Echo, Adeno, and Reovirus
groups. These produce a variety of diseases including
aseptic meningitis, myocarditis, respiratory involvement
and gastrointestinal upset.
A considerable amount of research has been conduct-
ed recently on viral survival and movement through soils
from sewage wastewaters and sludges. It is generally
believed that chlorination is more effective in eliminating
bacteria than viruses,71 but anaerobic digestion does in-
activate many viral particles.72 Even though viral particles
are adsorbed by soil particles, it is believed they are still
viable and may cause infection.
Controlling Vector Spread of Pathogens
The presence of pathogenic organisms is partially re-
sponsible for discouraging sludge applications on soils
where vegetables are grown. Since most pathogens of
concern do not survive for extended time periods in
soils, vegetables can be grown in sludge amended soils
as long as a rest period is provided. The application of
raw, undigested sludge to the soil surface is not recom-
mended not only because of potential contamination of
crops but also because of odor and other aesthetic
problems. However, raw sludges are amenable to sub-
surface (injection) application without undue environmen-
tal concerns. Obviously, vegetables, especially root
crops, should not be grown in such cases. Caution is
advisable when sprinkler irrigation is used for sludge
application. The major concerns are surface contamina-
tion of crops and potential spread of pathogens through
formation of aerosols and subsequent drift to adjacent
areas. Sprinkler irrigation of sludges requires more man-
agement to minimize potential problems than other appli-
cation systems.
In summary, although questions arise concerning the
impact of pathogens in land disposal systems, the lack
of problems encountered by the numerous ongoing proj-
ects using land application of sludges suggests that pa-
thogens are a potential problem only and that vector
spread has been minimal.
Organics
The concentration of organics, such as chlorinated
hydrocarbon pesticides and polychlorinated biphenyls
(PCB's), can be elevated above background levels «10
ppm) in sewage sludges from cities receiving wastes
from industrial discharges of these organic compounds.
The potential impact of organic compounds on land ap-
plication practices has been discussed recently by Pan-
ren et al.57 and Jelinek and Broude.65 Very little research
has been conducted on the uptake of organics by crops
growing on sludge treated soils so the following discus-
sion emphasizes data obtained from related experiments.
Pesticide and PCB levels in sludges are indicated in
table 9-A-3.
In general, a minimal amount of pesticides is sorbed
by plants and translocated to aerial pacts. For example,
the foliage of corn contains <3 percent of the Dieldrin
applied to soil while the concentration in the roots was
appreciably greater. Nearly all pesticides are relatively
non-polar molecules which are strongly bound by soil
organic matter and are, undoubtedly, likewise bound to
108
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Table 9-A-3.-
sludges3
-Pesticide and PCB content of dry
Compound
Range (mg/kg)
Minimum Maximum
Number of
sludges examined
Aldrinb.
Dieldrind
Chlordaneb
DDT+DDDb
PCB's6
NDC
<003
30
0 1
ND3
162
22
322
1 1
3520
5
21
7
7
83
aFrom Pahren et al.57
bExamined in 1971.
cNondetectable.
dExamined in 1971, 1972, 1973.
"Examined in 1971, 1972, 1973, 1975.
the surface of plant roots. Thus, the concentration of
pesticides in root tissue may not result from typical up-
take mechanisms where the molecule must permeate the
membranes of root cells.
The uptake of RGB's has been evaluated using carrots
as the test crop.74 Soils treated with Aroclor 1254 at 100
mg/kg produced carrots containing from 2-30 mg
PCB/kg, depending upon the examined component of
the PCB mixture. More significantly, 97 percent of the
PCB residue was found in carrot root peelings, which
.constituted only 14 percent of the carrot weight. These
results suggest thai PCB's are not actually taken up by
carrots but rather they are physically adsorbed on the
surface of carrot roots. Furthermore, carrots have been
used in several studies as "scavengers" for organochlo-
rine pesticides in soils. Additional evidence supporting
the inability of plants to accumulate organics was ob-
tained by Jacobs et al.,75 who grew orchardgrass and
carrots in soils treated with 10 and 100 mg/kg of poly-
brominated biphenyls (PBB's). At these rates of PBB
addition, the amount of uptake was essentially nonde-
tectable (20-40 jug/kg) in carrots and nondetectable in
orchardgrass. It should be emphasized that the rates
used in these studies far exceeds those expected from
sludge application. In general, plants possess the ability
to exclude the majority of organics added to soils, re-
sulting in minimal impact on the quality of forages and
grains. Furthermore, even though PCB's and related
compounds resist microbial degradation, they are slowly
decomposed after incorporation in soils.
A potential problem arising from organics in sludge is
direct ingestion by animals grazing on forages treated
with a surface application of sludge. Most organics are
concentrated in tissues (fats) and fluids (milk). Even
though a rain will remove the majority of sludge adher-
ing to forages after a surface application of sludge, a
sufficient amount of sludge may remain resulting in di-
rect ingestion of organics by cattle. For this reason,
Pahren et al.57 suggested that sludges surface applied to
grazed forages contain <10 mg/kg of PCB's. This prob-
lem can be eliminated for sludges containing >10
mg/kg PCB by incorporation of the sludge prior to
planting forages.
An estimate of the potential impact can be made by
assuming that sludge will be applied to 5 tons/acre to
satisfy the N needs of a crop. The FDA tolerance limit
for PCB's in infant foods is 0.2 mg/kg. If we use this as
the maximum concentration in soils (i.e., soil could be
consumed as food), a concentration of 40 mg/kg of
PCB's would be allowable in sludge.
Appendix B: SOIL TESTING
Soil testing is utilized extensively in agriculture, and to
a limited extent in forestry to assess the ability of a soil
to supply N, P, K and trace elements to plants.22 In
addition, plants vary in their ability to tolerate acid con-
ditions so soil pH and lime requirement are routinely
determined. Because a reliable soil test for plant avail-
able N does not exist, P and K are the principal plant
nutrients determined in soils. The approach used in soil
testing is to determine the amount of P or K extracted
from soil with a specific reagent. Knowing the relation-
ship between crop yield and nutrient concentration in
the soil, it is possible to recommend the amount of
fertilizer required to attain a specific yield. With increas-
ing levels of a nutrient in soil, both yield and concentra-
tion of the element in plant tissue increases. Crop yield
will plateau and, for some elements (e.g., metals), de-
crease when increasing amounts of an element are add-
ed to soil. Although yields do change at high (subtoxic)
rates of nutrient addition, the concentration in plant tis-
sues may continually increase. The concentration of ele-
ments in plant tissues can be used, in most cases, to
assess both deficiencies and toxicities.
Development of soil testing procedures involves evalu-
ating a range of extractants and soils in greenhouse
and/or field experiments with a particular crop. The ex-
tractant showing the best correlation with plant yields
and/or composition is used as a soil test. Walsh and
Beaton87 present additional information about the ap-
proaches used in soil and plant testing.
Regional variations in soil properties have led to the
development of P soil tests for different parts of the
U.S. For the sake of brevity, soil tests for P will be
subdivided on the basis of calcareous and acid soils.
The following extractants are commonly used to evaluate
available P in soils:
Calcareous soils
Acid soils
— 0.5 M NaHCO3
— 0.025 N HC1 +0.03 N NH4F
(Bray P,) .
— 0.05 N HC1 +0.025 N H,SO,
109
-------
The similarities of K reactions in acid and calcareous
soils result in the majority of states using 1 N NH4 ace-
tate (pH 7) as an extractant for plant available K. Rec-
ommendations for fertilizer P and K applications tend to
vary from region to region because yield potentials de-
pend on soil, crop and climatic factors.
Soil tests are also used to assess the availability of
Ca, Mg, S, B, and trace elements. Plant available Ca
and Mg are extracted with 1 N NH4 acetate, S with
water or Ca(H2PO4)2> and Zn, Cu, Mn and Fe with num-
erous salts, acids or chelating agents. A procedure used
in many of the western states employs DTPA (diethylen-
etriaminepentacetic acid) buffered at pH 7.3 as an ex-
tractant for plant available Fe, Zn, Cu and Mn.76For
sludge amended soils, the major concern is accumulation
of excessive metals rather than detecting deficiencies.
Nevertheless, the DTPA procedure may also serve as a
technique for evaluating plant available metals in soils
treated with sludges over a period of years.
A soil property routinely determined in soil testing and
one that is essential for soils receiving sludge is the
determination of soil pH and lime requirement. Soil acidi-
ty results from the presence of free H+ and exchange-
able H+ and AI3+ . Acidity is generated when exchange-
able AI3+ is displaced by another cation:
X Al3
3K +
3H2O
3XK + + AI(OH)3 + 3H:8 4
where X represents an exchange site on a clay mineral
or soil organic matter. In addition, the dissociation con-
stants for soil organic matter cover a broad range for a
given functional group resulting in a large buffering ca-
pacity. Hence, measurement of soil pH in H2O followed
by a simple calculation of the amount of CaCO3 needed
to reach a desired pH is not valid in soils. Current
Table 9-B-1.—Amount of lime (CaCO3) required to ad-
just mineral soils to pH 6.577
Soil pH determined
in SMP buffer
70
6.8
66
64 .
62
60
5 8
56
5 4
52 . ....
50 . ..
4 8
Lime required for
soil pH 6.5a
(tons/acre)
0
1.0
2.4
... . 3.9
5.3
6.7
8 1
96
11.1
.. . . 12.5
14.0
15.5
aApplies to mineral soils only.
methods for obtaining lime requirements are based on
measuring pH in water (or a dilute salt solution) and in
a buffer solution to estimate the buffering capacity of a
soil. The extent of pH depression of the buffer caused
by adding soil is proportional to the amount of lime
needed. The SMP buffer is used by many laboratories
and contains p-nitrophenol, K2 CrO4, CaCI2, Ca acetate,
triethanolamine and H2O (pH 7.5). The buffer method is
described in detail by McLean.77 The relationship be-
tween soil + buffer pH and lime requirement is shown
in table 9-B-1. Soil pH must be maintained at 6.5 or
above in soils treated with sludge so determination of
lime requirement is essential. For more detail, the Soil
Science Society of America has available a standard
soils analysis text.78
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Crop Production. Bioscience. 21(12):561-564. June 15, 1971.
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C. Loehr (ed). Ann Arbor, Mich. Ann Arbor Science Publishers,
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3. Connor, P. M. Citizen Inputs to Public Works Projects. Engineering
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Relationships During Land Utilization of Sewage Sludge in the
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Their Potential Use as Fertilizers. Journal of Environmental Quality.
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7. Blaney, H. F., and W. D. Griddle. Determining Consumptive Use
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in the United States.—A Five Year Review. American Journal of
Epidemiology. 92:13-24. 1970.
10. Hall, G. F., L. P. Wilding, and A. E. Erickson. Site Selection
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Management. 1977. 89-
73. Leeper, G. W. Reactions of Heavy Metals with Soils with Special
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(Araclor 1254) from Soil by Carrots Under Field Conditions. Bull.
Environ. Contamin. Toxicol. 11:523-528. 1974.
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Biphenyls (PBB's) in Soils: Persistence and Plant Uptake. J. Agric.
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Emissions for Organic Wastes. In: Soils for Management of Organ-
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112
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Chapter 10
Sludge Landfilling
INTRODUCTION
Sludge landfilling can be generally defined as the bury-
ing of sludge; i.e., the application of sludge to the land
and subsequent interment by applying a layer of cover
soil atop the sludge. To be defined as a landfill, the
sludge must be covered by a soil depth greater than
that of the plow zone. Therefore, subsurface injection of
sludge is a landspreading, not a landfilling operation.
This chapter provides general guidance and a source
of information to be used in the design of a landfill
receiving municipal wastewater treatment plant sludge.
Major alternative sludge landfilling methods are identified
and described. Guidance is given on the selection of a
landfilling method which is best suited for a given com-
bination of sludge characteristics and site conditions.
The design of a sludge landfill is described. Typical
costs are presented. A case study and a design exam-
ple are included.
LANDFILLING METHODS
Suitability of Sludge for Landfilling
In determining the suitability of sludge for landfilling, a
determination should be made of the sludge sources and
treatment. Analyses should also be performed on the
sludge to determine relevant characteristics. This infor-
mation is needed in order that a full assessment can be
made of its suitability for landfilling. Not all wastewater
treatment sludges are suitable for landfilling, due to
pathogen, odor, or operational problems. An assessment
of the suitability of various sludge types has been in-
cluded as table 10-1.
As shown, only dewatered sludges (having solids con-
tents greater than or equal to 15 percent) are suitable
for disposal in sludge-only landfills. Sludges having solids
contents less than 15 percent usually will not support
cover material. Obviously, the addition of soil to a low-
solids sludge may act as a bulking agent and produce a
sludge suitable for disposal at sludge-only landfills. How-
ever, soil bulking operations are generally not cost-effec-
tive on sludges with solids less than 15 percent. Further
dewatering should be performed at the treatment plant if
sludge-only landfilling is the disposal option selected.
Low-solids sludge (having solids contents as low as 3
percent) are suitable for codisposal landfilling. However,
sludge moisture should not exceed the absorptive capac-
ity of refuse at a codisposal landfill. Accordingly, low-
solids sludge should be received at such sites only if it
constitutes a small percentage of the total waste land-
filled.
Generally, only stabilized sludges are recommended for
landfilling and some degree of stabilization should occur
if landfilling is the selected disposal option. However,
since stabilization is not required in all States, suggested
procedures for landfilling such sludges are described.
The following section describes handling and operating
practices for typical sludges. Sludge ash as well as
other wastewater treatment plant solids such as screen-
ings, grit, and skimmings require special handling and
operating practices.
Sludge Landfilling Methods
The several alternative methods and sub-methods for
sludge landfilling include:
1. Sludge-only trench: narrow trench; wide trench.
2. Sludge-only area fill: area fill mound; area fill layer;
diked containment.
3. Codisposal: sludge/refuse mixture; sludge/soil mix-
ture.
In this section, each method will be defined and sub-
sequently described in terms of sludge and site condi-
tions specific to that method. In addition, design criteria
are identified for each method. The criteria suggested
for each method are based on experiences at numerous
sludge landfills which embrace a broad range of sludge
and site conditions. These criteria should be valid for
the vast majority of sludge landfill applications. However,
design criteria should be qualified as being "typical" or
"recommended." Variations are employed and may be
appropriate in some cases. For example, the range of
sludge solids contents recommended for each method in
this section may vary somewhat depending on the
sludge source, treatment, and characteristics. Specifical-
ly, a sludge treated with polymers is more slippery and
less stable; consequently it will require a higher solids
content to be landfilled in the same manner as a sludge
not treated with polymers. Nevertheless, the criteria sug-
gested by this section can serve as a starting point. It
is recommended that pilot-scale testing be performed to
ensure that an operation based on the criteria will func-
tion properly for a given sludge and site.
Sludge-Only Trench
For sludge-only trenches, subsurface excavation is re-
quired so that sludge can be placed entirely below the
113
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Table 10-1.—Suitability of sludges for landfilling
Process Feed
Thickening
Gravity Primary
WAS
Primary and WAS
Digested primary
Digested primary and WAS
Flotation Primary and WAS
WAS with chemicals
WAS without chemicals NS
Treatment
Aerobic digestion . Primary thickened
Primary and WAS, thickened
Anaerobic digestion .... Primary, thickened
Primary and WAS, thickened
Incineration Primary dewatered
Primary and WAS, dewatered
Wet oxidation . Primary or primary and WAS
Meat . . Any thickened
Lime stabilization.. . Primary thickened
Primary and WAS, thickened
Dewatering
Drying beds Any digested
Any, lime stabilization
Vacuum filter Primary lime conditioned
Digested, lime conditioned
Pressure filtration Digested, lime conditioned
Centrifugation Digested
Digested, lime conditioned
Heat drying Digested
Sludge-only
landfilling
Suitability
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
S
S
NS
NS
NS
NS
S
S
S
S
S
S
S
S
Reason
P.OD.OP
P.OD.OP
P.OD.OP
OP
OP
P.OD.OP
OP
P.OD.OP
OP
OP
OP
OP
OD.OP
OD.OP
OP
OP
Codisposal
landfilling
Suitability
NS
NS
NS
MS
MS
NS
NS
NS
MS
MS
MS
MS
S
S
MS
MS
MS
MS
S
S
S
S
S
S
S
S
Reason
P.OD.OP
P.OD.OP
P.OD.OP
OP
OP
P.OD.OP
P.OD.OP
P.OD.OP
OP
OP
OP
OP
OD.OP
OD.OP
OP
OP
WAS = Waste activated sludge.
NS = Not suitable.
MS = Marginally suitable.
S = Suitable.
P = Pathogen problems,
OD =Odor problems.
OP = Operational problems.
original ground surface. Trench applications require that
groundwater and bedrock be sufficiently deep so as to
allow excavation and still maintain sufficient buffer soils
between the bottom of sludge deposits and the top of
groundwater or bedrock.
In trench applications, soil is used only for cover and
is not used as a sludge bulking agent. The sludge is
usually dumped directly into the trench from haul vehi-
cles. On-site equipment is normally used only for trench
excavation and cover application; it is not normally used
to haul, push, layer, mound, or otherwise come into
contact with the sludge.
Although in some cases cover application may be less
frequent, cover is normally applied over sludge the same
day that it is received. Because of the frequency of
cover, odor control is optimized; therefore, trench is
more appropriate for unstabilized or low-stabilized sludg-
es than other landfilling methods. The soil excavated
during trench construction provides quantities which are
almost always sufficient for cover applications. Accord-
ingly, soil importation is seldom required in trench appli-
cations.
Two sub-methods have been identified under trench
applications. These include (1) narrow trench and (2)
114
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wide trench. Narrow trenches as® defined as having
widths less than 10 ft (3.0 m); wide trenches are defined
as having widths greater than 10 ft (3.0 m). The depth
and length of both narrow and wide trenches are vari-
able and dependent upon a number of factors. Trench
depth is a function of (1) depth to groundwater and
bedrock, (2) sidewall stability, and (3) equipment limita-
tions. Trench length is virtually unlimited, but inevitably
dependent upon property boundaries and other site con-
ditions. In addition, trench length may be limited by the
need to discontinue the trench for a short distance or
place a dike within the trench to contain a low-solids
sludge and prevent it from flowing throughout the
trench.
Narrow Trench
As stated previously, a narrow trench has a width of
less than 10 ft (3.0 m). Sludge is usually disposed in a
single application and a single layer of cover soil is
applied atop this sludge. Narrow trenches are usually
excavated by equipment based on solid ground adjacent
to the trench and equipment does not enter the excava-
tion. Accordingly, backhoes, excavators, and trenching
machines are particularly useful in narrow trench opera-
tions. Excavated material is usually immediately applied
as cover over an adjacent sludge-filled trench. However,
occasionally, it is stockpiled alongside the trench from
which it was excavated for subsequent application as
cover over the trench. Cover material is then applied by
equipment also based on solid ground outside of the
trench. Relevant sludge and site conditions as well as
design criteria are presented in the following tabulation.
Sludge solids content
Sludge characteristics
Hydrogeology
Ground slopes
Sludge and Site Conditions
15-20 percent for 2-3 ft (0.6-0.9 m)
widths
20-28 percent for 3-10 ft (0.9-3.0 m)
widths
unstabilized or stabilized
deep groundwater and bedrock
<20 percent
Trench width
Bulking required
Cover soil required
Cover soil thickness
Imported soil required
Sludge application rate
Equipment
Design Criteria
2-10 ft (0.6-3.0 m)
no
yes
3-4 ft (0.9-1.2 m)
no
1,200-5,600 yd3/acre (2,300-10,600
m3/ha)
backhoe with loader, excavator, trenching
machine
The main advantage of a narrow trench is its ability to
handle sludge with a relatively low solids content. As
shown, a 2 to 3 ft (0.6 to 0.9 m) width is required for
sludge with a solids content between 15 and 20 percent.
Normally, soil applied as cover over sludge of such low
solids would sink to the bottom of the sludge. However,
because of the narrowness of the trench, the soil cover
bridges over the sludge, receiving support from solid
ground on either side of the trench. In this operation
cover is usually applied in a 2 to 3 ft (0.6 to 0.9 m)
thickness.
A 3 to 10 ft (0.9 to 3.0 m) width is more appropriate
for sludge with solids contents from 20 to 28 percent.
At this width, the bridging effect of the cover soil is
non-existent. However, the solids content is high enough
to support cover. In this operation, cover is usually ap-
plied in a 3 to 4 ft (0.9 to 1.2 m) thickness and
dropped from a minimum height to minimize the amount
of soil that sinks into sludge deposits.
The main disadvantage of narrow trench operations is
that it is relatively land-intensive. As shown above, typi-
cal sludge application rates in actual fill areas (including
inter-trench areas) range from 1,200 to 5,600 yd3/acre
(2,300 to 10,600 mVha). Generally, application rates for
narrow trenches are less than for other methods. Anoth-
er drawback with narrow trench operations is that liners
are impractical to install.
Wide Trench
As stated previously, a wide trench has a width of
greater than 10 ft (3.0 m). Wide trenches are usually
excavated by equipment operating inside the trench. Ac-
cordingly, track loaders, draglines, scrapers, and track
dozers are particularly useful in wide trench operations.
Excavated material is usually stockpiled on solid ground
adjacent to the trench from which it was excavated for
subsequent application as cover over that trench. How-
ever, occasionally it is immediately applied as cover over
an adjacent sludge-filled trench. Relevant sludge and site
conditions as well as design criteria are presented in the
following tabulation.
Sludge solids content
Sludge characteristics
Hydrogeology
Ground slopes
Trench width
Bulking required
Cover soil required
Cover soil thickness
Imported soil required
Sludge application
Equipment
Sludge and Site Conditions
20-28 percent for land-based equipment
>28 percent for sludge-based equipment
unstabilized or stabilized
deep groundwater and bedrock
<10 percent
Design Criteria
>10 ft (3.0 m)
no
yes
3-4 ft (0.9-1.2 m) for land-based equip-
ment
4-5 ft (1.2-1.5 m) for sludge-based equip-
ment
no
3,200-14,500 yd3/acre (6,000-27,400
m3/ha)
track loader, dragline, scraper, track doz-
er
As shown, cover material may be applied to wide
trenches in either of two different ways. If its solids
115
-------
content is from 20 to 28 percent, the sludge in the
trench is incapable of supporting equipment. Therefore,
cover should be applied in a 3 to 4 ft (0.9 to 1.2 m)
thickness by equipment based on solid undisturbed
ground adjacent to the trench. In this way, a wide
trench may be only slightly more than 10 ft (3.0 m) wide
(if a front-end loader is used to apply cover) or up to
50 ft (15 m) wide (if a dragline is used to apply cover).
Alternatively, if its solids content is 28 percent or more
covered sludge in the trench is capable of supporting
equipment. Therefore, cover should be applied by equip-
ment which proceeds out over the sludge pushing a 4
to 5 ft (1.2 to 1.5 m) thickness of cover before it. Track
dozers are the most useful piece of equipment in this
application.
As for narrow trenches, wide trenches should be ori-
ented parallel to one another to minimize inter-trench
areas. Distances between trenches should be only large
enough so as to provide sidewall stability as well as
adequate space for soil stockpiles, operating equipment,
and haul vehicles.
One advantage of a wide trench is that it is less land-
intensive than narrow trenches. Typical sludge applica-
tion rates range from 3,200 to 14,500 yd3/acre (6,000 to
27,400 m3/ha). Another advantage of a wide trench is
that liners can be installed to contain sludge moisture
and protect the groundwater. Therefore, excavation may
proceed closer to bedrock or groundwater in wide
trenches with liners than in narrow trenches without such
protection.
One disadvantage of a wide trench is a need for a
higher solids sludge, with solids contents at 20 percent
and above. It should be noted that sludges with a solids
content of 32 percent or more will not spread out even-
ly in a trench when dumped from atop the trench side-
wall. If wide trenches are used for such high solids
sludge, haul vehicles should enter the trench and dump
the sludge directly onto the trench floor. Another disad-
vantage of a wide trench is its need for flatter terrain
than that used for narrow trenches. For wide trench
applications with sludge up to 32 percent solids, sludge
is dumped from above and spreads out evenly within the
trench. Accordingly, the trench floor should be nearly
level, and this can be more easily effected when located
in low relief areas.
Sludge-Only Area Fill
For sludge-only area fills, sludge is usually placed
above the original ground surface. Because excavation
is not required and sludge is not placed below the sur-
face, area fill applications are particularly useful in areas
with shallow groundwater or bedrock. The solids content
of sludge as received is not necessarily limited. How-
ever, because the sidewall containment (available in a
trench) is lacking and equipment must be supported
atop the sludge in most area fills, sludge stability and
bearing capacity must be relatively good. To achieve
these qualities, soil is usually mixed with the sludge as a
bulking agent. Since excavation is not usually performed
in the landfilling area, and since shallow groundwater or
bedrock may prevail, large quantities of soil required
usually must be imported from off-site or hauled from
other locations on-site.
Because filling proceeds above the ground surface,
liners can be more readily installed at area fill .opera-
tions than at trench operations. Of course, because of
the likely proximity of groundwater or bedrock to the
ground surface, the installation of a liner will often be
required at area fills. With or without liners, surface
runoff of moisture from the sludge and contaminated
rainwater should be expected in greater quantities at
area fills, and appropriate surface drainage control facili-
ties should be considered.
In area fills, the landfilling area usually consists of
several consecutive lifts or applications of sludge/soil
mixture and cover soil. As for any landfill, cover should
be applied atop all sludge applications. However, this
cover often is applied as necessary to provide stability
for additional lifts. Because some time may lapse be-
tween consecutive sludge applications, daily cover is
usually not provided and stabilized sludges are better
suited for area filling than are unstabilized sludges.
Three sub-methods have been identified under area fill
applications. These include (1) area fill mound, (2) area
fill layer, and (3) diked containment. Each of these three
sub-methods are described subsequently.
Area Fill Mound
In area fill mound applications, it is recommended that
the solids content of sludge received at the site be no
lower than 20 percent. Sludge is mixed with a soil bulk-
ing agent to produce a mixture which is more stable
and has greater bearing capacity. As shown below, ap-
propriate bulking ratios may vary between 0.5 and 2
parts soil for each part of sludge. The exact ratio em-
ployed will depend on the solids content of the sludge
as received and the need for mound stability and bear-
ing capacity (as dictated by the number of lifts and
equipment weight).
The sludge/soil mixing process is usually performed at
one location and the mixture hauled to the filling area.
At the filling area, the sludge/soil mixture is stacked into
mounds approximately 6 ft (1.8 m) high. Cover material
is then applied atop these mounds in a minimum 1 ft
(0.3 m) thick application. This cover thickness is usually
increased to 3 ft (0.9 m) if additional mounds are ap-
plied atop the first lift. Relevant sludge and site condi-
tions as well as design criteria are presented in the
following tabulation.
Sludge solids content
Sludge characteristics
Hydrogeology
Ground slopes
Sludge and Site Conditions
>20 percent
stabilized
shallow groundwater or bedrock possible
suitable for steep terrain as long as an
area is prepared for mounding
116
-------
Bulking required
Bulking agent
Bulking ratio
Cover soil required
Cover soil thickness
Imported soil required
Sludge application
Equipment
Design Criteria
yes
soil
0.5-2 soil:1 sludge
yes
3 ft (0.9 m) of interim
1 ft (0.3 m) of final
yes
3,000-14,000 yd3/acre (5,700-34,600
m3/ha)
track loader, backhoe with loader, track
dozer
Because equipment may pass atop the sludge in per-
forming mixing, mounding, and covering operations, light-
weight equipment with swamp pad tracks is generally
recommended for area fill mound operations. However,
heavier wheel equipment may be more appropriate in
transporting bulking material to and from soil stockpiles.
An advantage of the area fill mound operation is its
good land utilization. Sludge application rates are rela-
tively high at 3,000 to 14,000 yd3/acre (5,700 to 26,400
m3/ha). A disadvantage is the constant need to push
and stack slumping mounds. For this reason, area fill
mounds often have higher manpower and equipment re-
quirements. Some slumping is inevitable and occurs par-
ticularly in high rainfall areas due to moisture additions
to the sludge. Slumping can sometimes be minimized by
providing earthen containment of mounds where possible.
For example, area fill mound operations are usually con-
ducted on level ground to prevent mounds from flowing
downhill. However, if a steeply sloping site is selected, a
level mounding area could be prepared into the slope
and a sidewall created for containment of mounds on
one side.
Area Fill Layer
In area fill layer applications, sludge received at the
site may be as low as 15 percent solids. Sludge is
mixed with a soil bulking agent to produce a mixture
which is more stable and has greater bearing capacity.
Typical bulking ratios range from 0.25 to 1 part soil for
each part sludge. As for area fill mounds, the ratio will
depend on the solids content of the sludge as received
and the need for layer stability and bearing capacity (as
dictated by the number of layers and the equipment
weight).
This mixing process may occur either at a separate
sludge dumping and mixing area or in the filling area.
After mixing the sludge with soil, the mixture is spread
evenly in layers from 0.5 to 3 ft (0.15 to 0.9 m) thick.
This layering usually continues for a number of applica-
tions. Interim cover between consecutive layers may be
applied in 0.5 to 1 ft (0.15 to 0.3 m) thick applications.
Final cover should be at least 1 ft (0.3 m) thick. Rele-
vant sludge and site conditions as well as design criteria
are presented in the following tabulation.
Sludge solids content
Sludge characteristics
Hydrogeology
Ground slopes
Bulking required
Bulking agent
Bulking ratio
Cover soil required
Cover soil thickness
Imported soil required
Sludge application
Equipment
Sludge and Site Conditions
>15 percent
stabilized
shallow groundwater or bedrock possible
suitable for medium slopes but level
ground preferred
Design Criteria
yes
soil
0.25-1 soil:1 sludge
yes
0.5-1 ft (0.15-0.3 m) of interim
1 ft (0.3 m) of final
yes
2,000-9,000 yd3/acre (3,800-17,000
m3/ha)
track dozer, grader, track loader
As for mounding operations, equipment will also pass
atop sludge in performing mixing, layering, and covering
functions. Accordingly, lightweight equipment with swamp
pad tracks is generally recommended for area fill layer
operations. However, heavier wheel equipment may be
appropriate for hauling soil. Slopes in layering areas
should be relatively flat to prevent the sludge from flow-
ing downhill. However, if the sludge solids content is
high and/or sufficient bulking soil is used, this effect
can be prevented and layering performed on mildly slop-
ing terrain.
An advantage of an area fill layer operation is that
completed fill areas are relatively stable. As a result, the
maintenance required is not as extensive as for area fill
mounds. Accordingly, manpower and equipment require-
ments are less. A disadvantage is poor land utilization
with application rates from 2,000 to 9,000 yd3/acre
(3,780 to 17,000 m3/ha).
Diked Containment
In diked containment applications, sludge is placed
entirely above the original ground surface. Dikes are
constructed on level ground around all four sides of a
containment area. Alternatively, the containment area
may be placed at the toe of a hill so that the steep
slope can be utilized as containment on one or two
sides. Dikes would then be constructed around the re-
maining sides.
Access is provided to the top of the dikes so that
haul vehicles can dump sludge directly into the contain-
ment. Interim cover may be applied at certain points
during the filling, and final cover should be applied when
filling is discontinued. Relevant sludge and site condi-
tions as well as design criteria are presented in the
following tabulation.
Sludge solids content
Sludge characteristics
Hydrogeology
Ground slopes
Sludge and Site Conditions
20-28 percent for land-based equipment
>28 percent for sludge-based equipment
unstabilized or stabilized
shallow groundwater or bedrock possible
suitable for steep terrain as long as a
level area is prepared inside dikes
117
-------
Bulking required
Bulking agent
Bulking ratio
Cover soil required
Cover soil thickness
Imported soil required
Sludge application
Equipment
Design Criteria
no, but sometimes used
soil
0.25-1 soil:1 sludge
yes
1-2 ft (0.3-0.6 m) of interim with land-
based equipment
2-3 ft (0.6-0.9 m) of interim with sludge-
based equipment
3-4 ft (0.9-1.2 m) of final with land-based
equipment
4-5 ft (1.2-1.5 m) of final with sludge-
based equipment
yes
4,800-15,000 yd3/acre (9,100-28,400
m3/ha)
dragline, track dozer, scraper
As shown, the solids content of sludge received at
diked containments should be a minimum of 20 percent.
For sludges with solids contents between 20 and 28
percent, cover material should be applied by equipment
based on solid ground atop the dikes. For this situation,
a dragline is the best equipment for cover application
due to its long reach. Thicknesses should be 1 to 2 ft
(0.3 to 0.6 m) for interim cover and 3 to 4 ft (0.9 to 1.2
m) for final cover.
For sludges with solids contents of 28 percent and
above, cover material should be applied by equipment
which pushes and spreads cover soil into place as it
proceeds out over the sludge. For this situation, a track
dozer is the best equipment for cover application. Thick-
nesses should be 2 to 3 ft (0.6 to 0.9 m) for interim
cover and 4 to 5 ft (1.2 to 1.5 m) for final cover.
Usually diked containment operations are conducted
without the addition of soil bulking agents. The above
numbers reflect usual conditions. Occasionally, however,
soil bulking is added. Under these circumstances, soil
may be added to increase the solids content and allow
the operations described above.
An advantage of this method is that individual diked
containments are relatively large with typical dimensions
of 50 to 100 ft (15 to 30 m) wide, 100 to 200 ft (30 to
60 ft) long, and 10 to 30 ft (3 to 9 m) deep. According-
ly, efficient land use is realized with sludge loading rates
varying between 4,800 and 15,000 yd3/acre (9,100 to
28,400 rrrVha). A disadvantage of diked containment is
that the depth of the fill in conjunction with the weight
of interim and final cover places a significant surcharge
on the sludge. As a result, much of the sludge moisture
is squeezed into surrounding dikes and into the floor of
the containment. Accordingly, liners and other leachate
controls may be especially appropriate with diked con-
tainments to collect leachate emissions.
Codisposal
A codisposal operation is defined as the receipt of
sludge at a refuse landfill. Two sub-methods have been
identified under codisposal operations. These include (1)
sludge/refuse mixture and (2) sludge/soil mixture.
118
Sludge/Refuse Mixture
In a sludge/refuse mixture operation, sludge is depos-
ited at the working face of the landfill and applied atop
refuse. The sludge and refuse are then mixed as thor-
oughly as possible. This mixture is then spread, com-
pacted, and covered in the usual manner at a refuse
landfill. Relevant sludge and site conditions as well as
design criteria are presented in the following tabulation.
Sludge and Site Conditions
Sludge solids content >3 percent
unstabilized or stabilized
deep or shallow groundwater or bedrock
<30 percent
Sludge characteristics
Hydrogeology
Ground slopes
Bulking required
Bulking agent
Bulking ratio
Cover soil required
Cover soil thickness
Imported soil required
Sludge application
Equipment
Design Criteria
yes
refuse
4-7 tons refuse:1 wet ton sludge
yes
0.5-1 ft (0.15-0.3 m) of interim
2 ft (0.6 m) of final
no
500-4,200 yd3/acre (900-7,900 m3/ha)
track dozer, track loader
As shown, sludge with solids contents as low as 3
percent may be received in such operations. Usually,
such sludge is spray applied from a tank truck to a
layer of refuse at the working face. The bulking ratio for
a 3 percent solids sludge should be at least 7 tons of
refuse to 1 wet ton of sludge (7 Mg of refuse to 1 wet
Mg of sludge). Usually, only sludges with solids contents
of 20 percent or more are mixed with refuse in such
operations. Fewer operational and environmental prob-
lems may be expected than when a 3 percent solids
sludge is received. Also, less bulking agent is required
and ratios as low as 4 tons of refuse to 1 wet ton of
sludge (4 Mg of refuse to 1 Mg of sludge) are success-
fully practiced.
Also as shown, sludge application rates for
sludge/refuse mixtures compare favorably with other
methods, despite the fact that sludge is not the only
waste being disposed on the land. Application rates gen
erally range from 500 to 4,200 yd3 of sludge per acre
(900 to 7,900 m3 of sludge per ha).
Sludge/Soil Mixture
In a sludge/soil mixture operation, sludge is mixed
with soil and applied as interim or final cover over com-
pleted areas of the refuse landfill. This is not strictly a
sludge landfilling method since the sludge is not buried.
However, it is a viable option for disposal of sludge at
refuse landfills which has been performed and should be
used in many cases. Relevant sludge and site conditions
as well as design criteria are presented in the following
tabulation.
Sludge and Site Conditions
Sludge solids content
Sludge characteristics
Hydrogeology
Ground slopes
>20 percent
stabilized
deep or shallow groundwater or bedrock
<5 percent
-------
Bulking required
Bulking agent
Bulking ratio
Cover soil required
Imported soil required
Sludge application
Equipment
Design Criteria
yes
soil
1 soil:1 sludge
no
no
1,600 yd3/acre (3,000 m3/ha)
tractor with disc
One advantage of employing the sludge/soil mixture
operation is that it removes sludge from the working
face of the landfill where it may cause operational prob-
lems. Other advantages are that the mixture can be
used to promote vegetation over completed fill areas; a
savings in fertilizer can be realized; and siltation and
erosion problems can be minimized.
One disadvantage of employing the sludge/soil mixture
is that it generally has greater manpower and equipment
requirements than would be incurred by landfilling the
same sludge quantity at the working face. Another dis-
advantage is that since the sludge is not completely
buried, odors may be more severe than for
sludge/refuse mixtures. For this reason, only well stabi-
lized sludges are recommended for use in sludge/soil
mixture operations.
Sludge-Only or Codisposal
For a variety of reasons, consideration should be giv-
en to using codisposal methods for sludge disposal in
lieu of sludge-only methods. The advantages of using an
existing refuse landfill instead of a new sludge-only land-
fill include:
1. Shorter time delay: Processing of permits to dis-
pose sludge at an existing refuse landfill will proba-
bly be quicker than processing permits for a new
sludge-only site. Also, since most or all of the site
preparation required for sludge disposal is in place,
delays for construction may not occur.
2. Less environmental impact: The environmental im-
pact (odors, traffic, aesthetics, water) of one codis-
posal site will probably be less than the combined
impacts from two separate sites.
3. Less public opposition: The public is less likely to
resist an expansion in the operations of one site
than it is to resist the operation of a new site.
4. Less cost: Due to economies of scale, the cost of
one codisposal site will probably be less than the
combined costs of two separate sites.
Obviously, there are several disadvantages for refuse
landfill operators to consider when contemplating the
receipt of sludge. These include:
1. Odors may increase somewhat depending upon the
degree to which the sludge is stabilized.
2. Leachate may be generated sooner (if not already
existing) or leachate quantities may increase (if al-
ready existing).
3. Operational problems may develop including equip-
ment slipping or becoming stuck in sludge, or
sludge being tracked around the site by equipment
and haul vehicles.
Several other items should be considered by a refuse
landfill before receiving sludge. These include:
1. Pertinent regulatory authorities should be consulted
to ascertain whether sludge receipt is permissible.
2. Leachate collection and treatment systems may
have to be enlarged (if existing) or installed (if not
existing) to handle any increased leachate quanti-
ties.
3. Leachate treatment systems may have to be up-
graded to handle any change in leachate quality.
4. A sufficient volume of refuse should be delivered to
the site so that sufficient absorption of sludge mois-
ture can occur.
5. Ideally, delivery of sludge and refuse should occur
simultaneously. If not, storage capacity must be
provided for either sludge or refuse so that the
sludge can be mixed with refuse when landfilled.
6. Controlled dumping of refuse should occur to maxi-
mize its absorptive capacity with sludge. Such con-
trol may not be attainable when the public is al-
lowed access to the working face.
Conclusion
The major sludge landfilling methods have been identi-
fied and described. Sludge and site conditions as well
as design criteria have been presented for each method.
Tables 10-2 and 10-3 are compilations of the condi-
tions and criteria presented previously for each landfilling
method. They are provided to give guidance during the
investigation of alternative sites and landfilling methods.
It is important to note that there is no one best method
for a given sludge or site. Rather, these considerations
and criteria merely suggest sites and amenable landfilling
methods that can simplify and improve the design and
operational procedures required for an environmentally
safe and cost-effective sludge landfill.
DESIGN
The sludge landfill design directs and guides the con-
struction and on-going operation of the landfill. A design
should ensure (1) compliance with pertinent regulatory
requirements, (2) adequate protection of the environment,
and (3) cost-efficient utilization of site manpower, equip-
ment, storage volume, and soil. A design package (con-
sisting of all design documents) should be prepared to
provide a record of the landfill design. These may con-
sist of drawings, specifications, and reports.
Regulations and Permits
Many regulatory and approving agencies require per-
mits before a sludge landfill can be constructed or oper-
ated. The sludge landfill design is generally an integral
part of the application for such permits. Accordingly, all
pertinent agencies should be contacted early in the de-
sign phase to (1) identify regulations impacting on the
119
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Table 10-2.—Sludge and site conditions
Narrow
Wide tr
Area fill
Method
trench...
ench
I mound
Sludge
solids
content
(percent)
15-28
>20
>20
Sludge
characteristics
Unstabilized or stabi-
lized
Unstabilized or stabi-
lized
Stabilized
Hydrogeology
Deep groundwater and bedrock
Deep groundwater and bedrock
Shallow aroundwater or herlror.k
Ground slope
<20 percent
<10 percent
Rnitahla for stean terrain as
Area fill layer
Diked containment.
Sludge/refuse mixture.
Sludge/soil mixture. .
>15 Unstabilized or stabi-
lized
>20 Stabilized
>3 Unstabilized or stabi-
lized
>20 Stabilized
Shallow groundwater or bedrock
Shallow groundwater or bedrock
Deep or shallow groundwater or
bedrock
Deep or shallow groundwater or
bedrock
long as level area is pre-
pared for mounding
Suitable for medium slopes but
level ground preferred
Suitable for steep terrain as
long as a level area is pre-
pared inside dikes
<30 percent
<5 percent
prospective sludge landfill, (2) determine the extent, de-
tail, and format of the application, and (3) obtain any
permit application forms. Once this information has been
collected, the design phase can proceed in a more effi-
cient manner toward the goal of receiving the necessary
permits.
Regulations and permits relevant to sludge landfills are
found to exist on the Federal, State, and local levels.
Federal regulations relevant to sludge landfills are con-
tained largely in the Criteria for the Classification of
Solid Waste Disposal Facilities. These Criteria address
the following topic areas:
1. Environmentally sensitive areas.
2. Surface water.
3. Groundwater.
4. Air.
5. Application on land used for the production of food
chain crops.
6. Disease vectors.
7. Safety.
Environmentally sensitive areas are more specifically
identified as (1) wetlands, (2) flood plains, (3) permafrost
areas, (4) critical habitats, and (5) recharge zones for
sole source aquifers. As stated in the Criteria, disposal
facilities should not be located in environmentally sensi-
tive areas when feasible alternatives exist, unless it can
be clearly demonstrated that there will be no significant
impact on the ecosystem or human health from the op-
eration of a facility in such an area.1
Safety concerns are more specifically identified as (1)
explosive gases, (2) toxic or asphyxiating gases, (3)
fires, (4) bird hazards to aircraft, and (5) access. As
stated in the Criteria, disposal facilities should not pose
a safety hazard to facility employees, users, or the publ-
ic with respect to any of the above features. Require-
ments also exist in each of the remaining topic areas
and the Criteria should be consulted for a complete
description.
Many of the requirements in the Criteria are already
addressed in State regulations. Table 10—4 provides an
analysis of the Criteria topic areas included in State
regulations.
Several permits relevant to sludge landfills are identi-
fied and mandated by these Criteria. Generally these
include:
1. NPDES permit: required for location of a sludge
landfill in wetlands. It is also required for any point
source discharges at sludge landfills.
2. Army Corps of Engineers permit: required for the
construction of any levee, dike, or other type of
containment structure to be placed in the water at
a sludge landfill located in wetlands.
3. Office of Endangered Species permit: may be re-
quired from the Fish and Wildlife Service, Depart-
ment of the Interior for location of a sludge landfill
in critical habitats of endangered species.
State and local regulations and permits are highly vari
able from jurisdiction to jurisdiction. Depending on the
jurisdiction, one or more permits may be required for a
sludge landfill. Typical permits on the State and local
levels include:
1. Solid waste management permit.
2. Special use permit.
3. Zone change certification for a change to a zon-
ing appropriate for a sludge landfill.
120
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Table 10-3.—Design criteria3
... Trench Bulkinq _ ., .
.. ,. . solids ... M Bukmg
Method width re-
content . agent
(percent) (ft) qulred
Bulking C°^er
ratio . .
quired
Method
of cover
application
Cover
thickness Sludge
(ft) . , application
ported
ratfi (in
orill
. actual fill
In- c , requlred areas)
Pinal '
Equipment
terim
Narrow trench
Wide trench
Area fill mound
Area fill layer
Diked containment. ...
Sludge/refuse mixture..
Sludge/soil mixture
15-20 2-3
20-28 3-10
20-28 >10
>28
>20
No
No
No
No
Yes
— Yes
20-28 —
>28 —
>3 —
>20 —
Nob
Nob
Yes
Yes
Soil 0.5-2 soil:1 sludge
Soil
Soil
Soil
Refuse
Soil
0.25-1 soil:1 sludge
0 25-0.5 soil:1 sludge
Yes Land-based equipment — 2-3
Yes Land-based equipment — 3-4
Yes Land-based equipment — 3-4
Yes Sludge-based equipment — 4-5
Yes Sludge-based equipment 3 1
Yes Sludge-based equipment 0 5-1 1
4-7 tons refuse 1
ton sludge
1 soil:1 sludge
wet
Yes
Yes
Yes
No
Land-based equipment 1-2 3-4
Sludge-based equipment 2-3 4-5
Sludge-based equipment 0.5-1 2
No
No
Yes
Yes
Yes
No
— — No
1,200-5,600
3,200-14,500
3,000-14,000
2,000-9,000
4,800-15,000
500-4,200
1,600
Backhqe with loader, exca-
vator, trenching machine
Tractor loader, dragline,
scraper, track dozer
Track loader, backhoe with
loader, track dozer
Track dozer, grader, track
loader
Dragline, track dozer,
scraper
Track dozer, track loader
Tractor with disc, grader,
track dozer, track loader
aVolume basis unless otherwise noted
bBut sometimes used.
1 ft = 0.305 m
1 yd3 = 0.765 m3
1 acre = 0405 ha
-------
Table 10-4.—Analysis of Federal criteria versus State regulations2
Environmentally sensitive areas
Safety
in
TJ
State
E
o
CE
I
o>
Q.
1
1
s
'5
CT
CO
u
D
a
u
V)
a>
O
o
T3
c
3
O
3
D)
O
'X
T3
m
Percent
of
total3
Alabama X X X X X 50
Alaska X X X X X X 60
Arizona X X X X X 50
Arkansas X XXXX X X70
California XX X XXXXXXXXX100
Colorado X X XX X X 60
Connecticut X X X X X X X 70
Delaware X XXXX X 60
Florida X XXXXXXXXXX100
Georgia X X X X X X X 70
Hawaii X XXX 40
Idaho XXXX X X 60
Illinois XXXX X X 60
Indiana XX XXXXX X80
Iowa X XX XX X X60
Kansas XX X X 40
Kentucky X XXXX X X70
Louisiana X X 20
Maine X X X X X 50
Maryland XX XXXXXXX X90
Massachusetts X X X X X X X 60
Michigan XXXXX X X70
Minnesota XX XXXXXXXXX100
Mississippi X XXX X 50
Missouri X XXXXXXX X90
Montana X X X X X X 60
Nebraska X XXXX X X70
Nevada XXXX X X 60
New Hampshire XX XXXXXXX X90
New Jersey X X X X X X X X X 90
New Mexico XX X X X 50
New York XXXX X 50
North Carolina X X X X X X X 70
North Dakota XX X 30
Ohio XX X X X 50
Oklahoma X XX X X 50
Oregon X X X X X X X 70
Pennsylvania X XXXX X X70
Rhode Island XXXXXXX X80
South Carolina XXXX X 50
South Dakota X X X X X X X 70
Tennessee X XXXX X X70
Texas X XXXXXXXXX100
Utah X X X X 40
Vermont X XX X 40
Virginia XXXX X 50
Washington XX XXXXXXX X90
West Virginia XXXX 40
Wisconsin X XXXXX X90
Wyoming XXXX X X 60
Total 11/50 23/50 1/50 1/50 4/50 47/50 37/50 42/50 50/50 14/50 41/50 13/50 5/50 42/50
Percent of total .... 22 45 2 2 8 94 74 84 100 28 82 26 10 84
aEnvironmentally sensitive areas counted as one criterion for row totals.
122
-------
4. Sedimentation control permit for surface runoff into
water courses.
5. Highway department permit for entrances on public
roads and increased traffic volumes.
6. Construction permit for landfill site preparation.
7. Operation permit for on-going landfill operation.
8. Mining permit for excavations.
9. Fugitive dust permit.
10. Business permit for charging fees.
11. Closure permit.
Depending on local procedures, permits may be re-
quired from both state and local regulatory agencies.
State regulatory agencies which require such submittals
may include:
1. Solid waste management agencies.
2. Water quality control agencies.
3. Health departments.
Local regulatory agencies may include:
1. Health departments.
2. Planning and/or zoning commissions.
3. Board of county commissioners.
In many jurisdictions more than one of the State or
local agencies has authority over a disposal site. Also,
in some jurisdictions, one agency has control over
sludge-only landfills while another agency has control
over sanitary landfills receiving both refuse and sludge.
The reviewing agency may require the submittal of
information on standard forms or in a prescribed format
in order to facilitate the review process. In any event,
applicants are responsible for the completeness and ac-
curacy of the application package. The completed appli-
cation package is then reviewed by the regulatory agen-
cy. The time of the review period will vary depending
upon the regulatory agency, their attention to detail, the
number of applications preceding it, etc. From experi-
ence, this process has been found to take at least one
month and usually 6 to 12 months. After a permit is
issued, it can be valid for various durations, depending
largely upon the submittal of inspection/performance re-
ports and the outcome of on-site inspections.
Design Methodology and Data Compilation
Adherence to a carefully planned sequence of activi-
ties to develop a sludge landfill design minimizes project
delays and expenditures. A checklist of design activities
is presented in table 10-5. These activities are listed
somewhat in their order of performance. However, in
many cases separate tasks can and should be per-
formed concurrently or even out of the order shown
completely.
As shown in table 10-5, initial tasks consist of compil-
ing existing information and generating new information
on sludge and site conditions. Obviously, some of this
information would have already been collected in the site
selection phase. Generally however, additional and more
detailed information will have to be collected in the de-
sign phase.
Table 10-5.—Sludge landfill design checklist
Step Task
1 Determine sludge volumes and characteristics
a. Existing
b. Projected
2 Compile existing and generate new site information
a. Perform boundary and topographic survey
b. Prepare base map of existing conditions on-site and near-site
(1) Property boundaries
(2) Topography and slopes
(3) Surface water
(4) Utilities
(5) Roads
(6) Structures
(7) Land use
c. Compile hydrogeological information and prepare location map
(1) Soils (depth, texture, structure, bulk density, porosity,
permeability, moisture, ease of excavation, stability, pH,
and cation exchange capacity)
(2) Bedrock (depth, type, presence of fractures, location of
surface outcrops)
(3) Groundwater (average depth, seasonal fluctuations,
hydraulic gradient and direction of flow, rate of flow,
quality, uses)
d. Compile climatological data
(1) Precipitation
(2) Evaporation
(3) Temperature
(4) Number of freezing days
(5) Wind direction
e. Identify regulations (Federal, State, and local) and design
standards
(1) Requirements for sludge stabilization
(2) Sludge loading rates
(3) Frequency of cover
(4) Distances to residences, roads, and surface water
(5) Monitoring
(6) Roads
(7) Building codes
(8) Contents of application for permit
3 Design filling area
a. Select landfilling method based on:
(1) Sludge characteristics
(2) Site topography and slopes
(3) Site soils
(4) Site bedrock
(5) Site groundwater
b. Specify design dimensions
(1) Trench width
(2) Trench depth
(3) Trench length
(4) Trench spacing
(5) Sludge fill depth
(6) Interim cover soil thickness
(7) Final cover soil thickness
e. Specify operational features
(1) Use of bulking agent
(2) Type of bulking agent
(3) Bulking ratio
(4) Use of cover soil
(5) Method of cover application
(6) Need for imported soil
123
-------
Table 10-5.—Sludge landfill design checklist—continued
Step Task
(7) Equipment requirements
(8) Personnel requirements
d. Compute sludge and soil uses
(1) Sludge application rate
(2) Soil requirements
4 Design facilities
a. Leachate controls
b. Gas controls
c Surface water controls
d. Access roads
e. Special working areas
f. Structures
g. Utilities
h. Fencing
i. Lighting
j. Washracks
k. Monitoring wells
I. Landscaping
5 Prepare design package
a. Develop preliminary location plan of fill areas
b. Develop landfill contour plans
(1) Excavation plans
(2) Completed fill plans
c. Compute sludge storage volume, soil requirement volumes, and
site life
d. Develop final location plan showing
(1) Normal fill areas
(2) Special working areas
(3) Leachate controls
(4) Gas controls
(5) Surface water controls
(6) Access roads
(7) Structures
(8) Utilities
(9) Fencing
(10) Lighting
(11) Washracks
(12) Monitoring wells
(13) Landscaping
e. Prepare- elevation plans with cross-sections of:
(1) Excavated fill
(2) Completed fill
(3) Phased development of fill at interim points
f. Prepare construction details
(1) Leachate controls
(2) Gas controls
(3) Surface water controls
(4) Access roads
(5) Structures
(6) Monitoring wells
g. Prepare cost estimate
h. Prepare design report
i. Submit application and obtain required permits
j. Prepare operator's manual
Information utilized during both the site selection and
design phases can be derived either from existing sourc-
es or new sources (i.e., field investigation). A listing of
possible existing information sources has been included
as table 10-6. A listing of possible new information
sources has been included in table 10-7.
Before proceeding to the final design it is advisable 1
recontact regulatory agencies who were contacted dur-
ing the site selection process and others to try to dete
mine all of their requirements and procedures for permi
application submittals. This will also provide an opportu
nity to discuss design concepts, get questions answere<
and determine any special or new requirements. Mainte
nance of close liaison with state and local regulatory
officials throughout the design effort is normally helpful
in securing a permit without excessive redesigns.
A complete design package may include plans, specil
cations, a design report, cost estimate, and operator's
manual. Generally, the cost estimate and operator's ma
ual are prepared strictly for in-house uses, while plans,
specifications, and design reports are submitted to regi
latory agencies in the permit application. The contents
plans and specifications typically include:
1. Base map showing existing site conditions. The
map should be of sufficient detail, with contour
intervals of no more than 5 ft (1.5 m) and a scale
not to exceed 1 in. = 200 ft (1 cm = 24 m).
2. Site preparation plan locating sludge fill and soil
stockpile areas as well as site facilities. A small-
scale version of a site preparation plan has been
included as figure 10-1.
3. Development plan showing initial excavated and fi-
nal completed contours in sludge filling areas.
4. Elevations showing cross-sections to illustrate
phased development of sludge landfill at several
interim points.
5. Construction details illustrating detailed constructio
of site facilities.
6. Completed site plan including final site landscapinc
appurtenances, and other improvements.
The contents of a design report typically include:
1. Site description including existing site size, topogn
phy and slopes, surface water, utilities, roads,
structures, land use, soils, groundwater, bedrock,
and climatology.
2. Design criteria including sludge types and volumes
and fill area design dimensions.
3. Operational procedures including site preparation,
sludge unloading, sludge handling, and sludge cov
ering as well as equipment and personnel require-
ments.
4. Environmental safeguards including control of lead
ate, surface water, gas, odor, flies, etc.
Selection of Landfilling Method
As shown in table 10-2, the most significant features
affecting method selection are:
1. Sludge percent solids.
2. Sludge characteristics (stabilized or unstabilized).
124
-------
Table 10-6.—Sources of existing information
General
information
Specific
information
Source
Base map General
Topography and
sludge
Land use
Vegetation
Soils General
Bedrock.
Groundwater
General
General
Climatology..
General
County road department
City, county, or regional planning department
U.S. Geological Survey (USGS) office or outlets for USGS map sales (such as engineering supply
stores and sporting goods stores)
U.S. Department of Agriculture (USDA), Agricultural Stabilization and Conservation Service (ASCS)
Local office of USGS
County Department of Agriculture, Soil Conservation Service (SCS)
Surveyors and aerial photographers in the area
USGS topographic maps
USDA, ARS, SCS aerial photos
City, county, or regional planning agency
County agricultural department
Agriculture department at local university
USDA, Soil Conservation Service (SCS) District Managers, Local Extension Service
USGS reports
Geology or Agriculture Department of local university
USGS reports
State Geological Survey reports
Professional geologists in the area
Geology Department of local university
Water Supply Department
USGS water supply papers
State or regional water quality agencies
USDA, SCS
State or Federal water resources agencies
Local health department
National Oceanic and Atmospheric Administration (NOAA)
Nearby airports
3. Hydrogeology (deep or shallow groundwater and
bedrock).
4. Ground slopes.
One of the purposes of this section is to give specific
design information on each landfilling method. It is as-
sumed that a site and landfilling method have already
been selected. "Design Example" should be consulted
for an illustration of how a landfilling method is selected
for a given site.
Sludge-Only Trench Designs
In a sludge-only trench operation, sludge is placed
entirely below the original ground surface. Sludge is usu-
ally dumped directly into trenches from haul vehicles.
On-site equipment is used only to excavate trenches and
apply cover; equipment does not usually come into con-
tact with the sludge.
Sludge-only trenches have been further classified into
narrow trenches and wide trenches. If one of these
landfilling methods has been selected, design of the fill-
ing area consists primarily of determining the following
parameters:
1. Trench depth.
2. Trench width.
3. Trench length.
4. Trench orientation.
5. Sludge fill depth.
6. Cover thickness.
A methodology for determining these parameters is
included in table 10-8.
Trench spacing is perhaps the most important and yet
most difficult design parameter to determine. Trench
spacing is defined as the width of solid undisturbed
ground which is maintained between adjacent trenches.
Generally, trench spacing should be as small as possible
to optimize land utilization rates. However, the trench
spacing must be sufficient to resist sidewall cave-in. Fail-
ure of the trench sidewalls is a safety hazard and re-
duces the volume of the trench available for disposal.
Factors to consider in determining trench spacing in-
clude: (1) the weight of the excavating machinery, (2)
the bearing capacity of the soil (which is a factor of soil
cohesion, density, and compaction), (3) saturation level
of the soil (which may be significantly influenced by the
125
-------
Table 10-7.—Field investigations for new information
General
information
Specific
information
Method and equipment
Base map ....
Soils.
Bedrock.
Groundwater..
Property boundaries
Topography and slopes
Surface water
Utilities
Roads
Structures
Land use
Vegetation
Depth
Texture
Structure
Bulk density
Porosity
Permeability
Moisture
Ease of excavation
Stability
PH
Cation exchange capacity
Depth
Type
Fractures
Surface outcrops
Depth
Seasonal fluctuations
Hydraulic gradient
Rate of flow
Quality
Uses
Field survey via transit
Field survey via alidade
Field survey via alidade
Field survey via alidade
Field survey via alidade
Field survey via alidade
Field survey via alidade
Field survey via alidade
Soil boring and compilation of boring l:g
Soil sampling and testing via sedimentation methods (e.g., sieves)
Soil sampling and inspection
Soil sampling and testing via gravimetric, gamma ray detection
Calculation using volume of voids and t:tal volume
Soil sampling and testing via piezometers
Soil sampling and testing via oven drying
Test excavation with heavy equipment
Test excavation of trench and loading of sidewall
Soil sampling and testing via pH meter
Soil sampling and testing
Boring and compilation of boring log
Sampling and inspection
Field survey via alidade or Brunton
Field survey via alidade or Brunton
Well installation and initial readings
Well installation and mean-rand readings
Multiple well installation and comparison of readings
Calculation based on permeability and hydraulic gradient
Groundwater sampling and testing
Field survey via inspection
moisture content of the sludge deposited), (4) the depth
of the trench, and (5) soil stockpiling and cover place-
ment procedure.
A test which is used primarily to determine the ade-
quacy of soils in highway construction provides general
guidance in determining trench configurations (spacing
and depth). This test determines the stability of a soil by
means of the Hveem stabilometer, which measures the
transmitted horizontal pressure due to a vertical load.
The stability, expressed as the resistance value (R), re-
presents the shear resistance to plastic deformation of a
saturated soil at a given density.3 This test is described
under AASHO T175 (American Association of State
Highway Officials).
A general rule of thumb to follow in establishing
trench spacing is that for every 1 ft (0.3 m) of trench
depth, there should be 1 to 1.5 ft (0.3 to 0.5 m) of
space between trenches. If large inter-trench spaces are
not practical, the problem of sidewall instability may be
relieved by utilizing one of the four trench sidewall varia-
tions shown in figure 10-2. In any event, test cell
trenches should be used to determine the operational
feasibility of any trench design. Such tests should be
performed by excavating adjacent trenches to the speci-
fied depth, width, and spacing. A haul vehicle fully load-
ed with sludge should then back up to the trench to
determine if the sidewall stability is sufficient.
Using the considerations included in table 10-8, the
design parameter can be determined for a variety of
sludge and site conditions. These considerations have
been employed to develop some alternative design sce-
narios for trenches shown in table 10-9. In some cases,
sludge and site conditions may indicate that it is wholly
appropriate to utilize all of the design parameters shown
in one of these trench scenarios for application to a real
world situation. However, because of the great variety of
sludge and site conditions and their combinations, some
adaptation of one of these scenarios will be necessary
in most cases. In any event, design parameters should
not be merely extracted from these tables; parameters
should always be well-considered and tested before full-
scale application.
Narrow Trench
Narrow trenches have widths less than 10 ft (3.0 m)
and usually receive low solids sludge with solids con-
tents as low as 15 percent. Excavation and cover appli-
126
-------
-------
Table 10-8.—Design considerations for sludge-only trenches
Design
parameter
Determining
factor
Consideration
Excavation depth.
Depth to groundwater
Depth to bedrock
Soil permeability
Cation exchange capacity
of soil
Equipment limitations
Sidewall stability
Spacing Sidewall stability
Soil stockpiles
Vehicle access
Width Sludge solids content
Equipment limitations
Equipment efficiencies
Length
Orientation.
Sludge solids content
Ground slopes
Land availability
Ground slopes
Sufficient thickness of soil must be maintained between trench bottom and groundwater
or bedrock. Required minimum separation varies from 2 to 5 ft. Larger separations-may
be required for higher than normal soil permeabilities or sludge loading rates
Normal excavating equipment can excavate efficiently to depths of 10 ft. Depths from 10
to 20 ft are less efficient operations for normal equipment; larger equipment may be
required. Depths over 20 ft are not usually possible.
Sidewall stability determines maximum depth of trench. If haul vehicles are to dump
sludge into trench from above, straight sidewall should be employed. Tests should be
performed at site with a loaded haul vehicle to ensure that sidewall height as designed
will not collapse under operating conditions.
Trench spacing is determined by sidewall stability. Greater trench spacing will be required
when additional sidewall stability is required. As a general rule, 1.0 to 1.5 ft of spacing
should be allowed between trenches for every 1 ft of trench depth.
Sufficient space should be maintained between trenches for placement of trench soil
stockpiled for cover as well as to allow access and free movement by haul vehicles
and operating equipment.
Widths of 2 to 3 ft for typical sludge with solids content from 15 to 20 percent. Widths
of more than 3 ft for typical sludge with solids content more than 20 percent. Certain
sludge (e.g., polymer treated) may require higher solids contents before these widths
can apply.
Widths up to 10 ft for typical equipment (such as front end loader) based on solid
ground alongside trench. Widths up to 40 ft for some equipment (such as a dragline)
based on solid ground. Unlimited widths for cover applied by equipment (such as
bulldozers) which proceed out over sludge.
Equipment
Trenching machine
Backhoe
Excavator
Track dozer
Track loader
Dragline
Scraper
Typical widths
(ft)
2
2-6
4-22
>40
>20
If sludge solids are low and/or trench bottoms not level, trench should be discontinued
or dikes placed inside trench to contain sludge in one area and prevent it from flowing
over large area.
Trenches should be parallel to optimize land utilization.
For low solids sludge, axis of each trench should be parallel to topographic contours to
maintain constant bottom elevation with each trench and prevent sludge from flowing.
With higher solids sludge, this requirement is not necessary.
Sludge fill depth... Trench width
Cover thickness ... Trench width
Trench width
(ft)
2-3
> 3
Trench width
(ft)
2-3
> 3
Cover application
method
Land-based equipment
Land-based equipment
Sludge-based equipment
Cover application
method
Land-based equipment
Land-based equipment
Sludge-based equipment
Minimum distance
from top (ft)
1-2
3
4
Cover thickness
(ft)
2-3
3-4
4-5
1 ft = 0305 m.
128
-------
TAPE 1
TAPE 2
TAPE 4
Figure 10-2.—Trench sidewall variations.
cation in narrow trench operations is via equipment
based on solid ground alongside the trench. Illustrations
of typical narrow trench operations are included as fig-
ures 10-3 and 10-4.
The method of sludge placement in a narrow trench is
dependent upon the type of haul vehicle and upon
trench sidewall stability. Usually trench sidewalls are suf-
ficiently stable and sludge may be dumped from the haul
vehicle directly into trenches. However, if sidewalls are
not sufficiently stable, the sludge may be delivered to
the trench in a chute-extension similar to that found on
concrete trucks or pumped in via portable pumps. In
some cases (particularly in wet weather) it may be nec-
essary to dump the sludge on solid ground near the
trench and have on-site equipment push the sludge into
the trench.
Wide Trench
Wide trenches have widths greater than 10 ft (3.0 m)
and usually receive higher solids sludge with solids con-
tents of 20 percent and more. Excavation of wide
trenches is usually via equipment which enters the
trench itself. Cover application may be by equipment
based on solid ground alongside the trench, but is usu-
ally accomplished by equipment that proceeds out over
the sludge spreading a layer of cover soil. Illustrations
of typical wide trench operations are included as figures
10-5 and 10-6.
The method of sludge placement in wide trenches may
be either (1) from haul vehicles directly entering the
trench and dumping sludge in 3 to 4 ft (0.9 to 1.2 m)
high piles or (2) from haul vehicles parked at the top of
trench sidewalls and dumping sludge into the trench. For
the first of these two cases sludge should have a solids
content of 32 percent or more to ensure that the sludge
will not slump and can be maintained in piles. For the
second of these cases, sludge should have a solids
content less than 32 percent to ensure that it will flow
evenly throughout the trench and not accumulate at the
dumping location. Of course, when sludge is free-flowing,
some means will be needed to confine the sludge to
specific areas in a continuous trench. Dikes are often
used for this purpose as illustrated in figure 10-7.
Sludge-Only Area Fill Designs
In a sludge-only area fill operation, sludge is usually
placed entirely above the original ground surface. The
sludge as received is usually mixed with soil to increase
its -effective solids content and stability. Several consecu-
tive lifts of this sludge/soil mixture are usually then ap-
plied to the filling area. Soil may be applied for interim
cover in addition to its usual application for final cover.
On-site equipment usually does come into contact with
the sludge while performing functions of mixing the
sludge with so'l; transporting this mixture to the fill area;
mounding or layering this mixture; and spreading cover
over the mixture.
Sludge-only area fills have been further classified into
area fill mounds, area fill layers, and diked containments.
If one of these landfilling methods has been selected,
design of the filling area may consist primarily of deter-
mining the following parameters:
1. Diked containment width.
2. Diked containment sludge fill depth.
3. Height of sludge in each mound or layer.
4. Bulking ratio.
5. Cover thickness.
A methodology for determining these factors is includ-
ed in table 10-10.
Using the considerations included in table 10-10, the
design parameters can be determined for a variety of
sludge and site conditions. These considerations have
been employed to develop some alternative design sce-
narios for area fills which were included earlier in table
10-9.
Area Fill Mound
At area fill mound operations, sludge/soil mixtures are
stacked into mounds approximately 6 ft (1.8 m) high.
Cover soil is applied atop each lift (mounds) in a 1 ft
(0.3 m) thickness. The cover thickness is increased to 3
ft (0.9 m) if additional mounds are applied atop the first
lift. Illustrations of typical mound operations are included
as figures 10-8 and 10-9.
Sludge as received at the landfill is usually mixed with
a bulking agent. The bulking agent absorbs excess mois-
ture from the sludge and increases its workability. The
amount of soil needed to serve as an additional bulking
agent depends upon the solids content of the sludge.
Generally the soil requirements shown in table 10-10
may serve as a guideline. Fine sand appears to be the
most suitable bulking media because it can most easily
absorb the excess moisture from the sludge.
Area Fill Layer
At area fill layer operations, sludge/soil mixtures are
spread evenly in layers from 0.5 to 3 ft (0.15 to 0.9 m)
129
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Table 10-9.—Alternative design scenarios
CO
o
Sce-
nario
number
1
2
3
4
5
6
7
8
9 .
10
11
12
13
14
15
Identification
Landfillmg
method
Narrow trench
Narrow trench
Narrow trench
Narrow trench
Wide trench
Wide trench
Area fill mound
Area fill mound
Area fill layer
Area fill layer
Diked containment
Diked containment
Sludge/refuse
mixture
Sludge/refuse
mixture
Sludge/soil mixture
Site preparation
Sludge
solids
content
(percent)
15
17
25
28
26
32
20
35
15
30
25
32
3
28
20
Width
(ft)
2
2
6
8
40
60
—
—
—
—
50
100
—
—
—
Depth
(ft)
3
8
10
8
7
8
—
—
—
—
30
23
—
—
—
Length
(ft)
1,000
1,000
100
100
400
600
—
—
—
—
100
200
— -
—
—
Spac-
ing
(ft)
3
8
12
12
20
30
—
—
—
—
30
50
—
—
—
Bulk-
ing
per
formed
No
No
No
No
No
No
Yes
Yes
Yes
Yes
Yes
No
Yes
Yes
Yes
Sludge bulking
Bulking
agent
—
—
—
—
—
Soil
Soil
Soil
Soil
Soil
—
Refuse
Refuse
Soil
Bulking
ratio
—
—
—
—
2 soil 1 sludge
0 5 soil 1 sludge
1 soil 1 sludge
25 soil 1 sludge
0 5 soil 1 sludge
—
7 tons refuse 1 wet
ton sludge
4 tons refuse 1 wet
ton sludge
1 soil 1 sludge
Sludge filling
Sludge
depth
per
lift
(ft)
2
6
7
5
4
4
6
6
1
3
6
8
6
6
1 0
No
of
lifts
1
1
1
1
1
1
1
2
3
2
4
2
3
3
Sludge
appli-
cation
rate
(yd3/
acre)
1,290
1,940
3,750
3,230
4,100
4,100
3,230
12,910
2,420
7,740
12,410
13,770
2,520
4,140
1,600
Cover
ap-
plied
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
No
Sludge covering
Location
of
equipment
Land-based
Land-based
Land-based
Land-based
Land-based
Sludge-based
Sludge-based
Sludge-based
Sludge-based
Sludge-based
Land-based
Sludge- based
Sludge-based
Sludge- based
—
Cover
thickness
Im-
tenm
(ft)
—
—
—
—
—
3
05
1
1
3
05
05
—
Final
(ft)
3
3
4
4
4
5
2
1
1
1
3
4
2
2
—
Im-
ported
soil
re-
quired
No
No
No
No
No
No
Yes
Yes
Yes
Yes
No
No
No
No
No
Miscellaneous
Primary equipment
Trenching machine
Backhoe
Backhoe with loader
Excavator
Dragline
Track dozer
Track loader
Track loader, backhoe
with bucket
Track dozer
Track dozer, grader
Dragline
Track dozer
Track dozer
Track dozer
Tractor with disc
-------
Figure 10-3.—Cross-section of typical narrow trench operation.
Figure 10-4.—Narrow trench operation.
Figure 10-6.—Wide trench operation.
Figure 10-5.—Cross-section of typical wide trench operation.
131
-------
DEPTH
Figure 10-7.—Wide trench with dike cross-section.
thick. This layering usually continues for a number of
applications. Interim cover between consecutive layers
may be applied in 0.5 to 1 ft (0.5 to 0.3 m) thick
applications. Final cover should be at least 1 ft (0.3 m)
thick. An illustration of a typical area fill layer operation
is included as figure 10-10.
Diked Containment
At diked containment operations, earthen dikes are
constructed to form a containment area above the origi-
nal ground surface. Dikes can be of various heights, but
require side slopes of at least 2:1 and possibly 3:1. A
15 ft (4.6 m) wide road, covered with gravel should be
constructed atop the dikes.
Sludge may be either (1) mixed with soil bulking for
subsequent transport and dumping into the containment
area by on-site equipment or (2) dumped directly into
the containment area by haul vehicles without bulking
soil. Large quantities of imported soil may be required to
meet soil requirements for diked construction and bulk-
ing since diked containments are often constructed in
high groundwater areas.
Sludge is dumped into diked containments in lifts be-
fore the application of interim cover. Often this interim
cover is a highly permeable drainage blanket which acts
as a leachate collection system for sludge moisture re-
leased from the sludge lift above. Final cover should be
of a less permeable nature and should be graded even
with the top of the dikes. An illustration of a typical
diked containment operation is included as figure 10-11.
Codisposal Designs
Codisposal is defined as the receipt of sludge at a
conventional landfill receiving municipal refuse. Two
methods of codisposal have been identified including (1)
sludge/refuse mixture and (2) sludge/soil mixture. Design
considerations for codisposal landfills have been included
in table 10-11. The EPA document, "Sanitary Landfill
132
Design and Operation"4 should be consulted for further
information relating to design and operation of a refuse
landfill.
Sludge/Refuse Mixture
In a sludge/refuse mixture operation, sludge is deliv-
ered to the working face of the landfill where it is mixed
and buried with the refuse. Most of the considerations
relative to the receipt of sludge at refuse landfills are
operational. Nevertheless, some of the considerations re-
quire planning and design solutions.
The first problem encountered at codisposal sites is
sludge handling difficulties due to the liquid nature of
sludge relative to refuse. Difficulties include (1) the
sludge is difficult to confine at the working face since it
will readily flow, and (2) equipment slips and sometimes
becomes stuck in the sludge while operating at the
working face. These difficulties can be minimized if prop-
er planning is employed to control the quantity of sludge
received at the refuse landfill. Every effort should be
made not to exceed the absorptive capacity of the ref-
use and obviously, the maximum allowable sludge quanti-
ty will vary depending largely on the quantity of refuse
received and the solids content of the sludge. Some
suggested bulking ratios for sludge/refuse mixtures at
various sludge solids contents were included in table
10-11. In any event determinations should be made on
a site-by-site basis using test operations.
A second planning and design consideration for
sludge/refuse mixture operations concerns leachate con-
trol. The impact of sludge receipt on leachate is highly
site-specific. Generally, increased leachate quantities
should be expected. Leachate control systems may have
to be designed or modified accordingly.
A third planning and design consideration is storage
for sludge received in off-hours. In many cases sludge is
delivered around the clock, whereas refuse delivery is
confined to certain hours. Sludge storage facilities may
-------
Table 10-10.—Design considerations for sludge-only area fills
Design parameter
Bulking ratio
Cover application
Width of diked
containment
Depth of each
lift
Interim cover
thickness
Number of lifts
Depth of total
fill of diked
Final cover
thickness
Determining factor
Method
Sludge solids content
Method
Sludge solids content
Cover application procedure
Equipment used
Method
Sludge solids content
Method
Cover application procedure
Method
Sludge solids content
Cover application procedure
Method
Cover application procedure
Method
Area fill mound
Area fill layer
Diked containment
Method
Area fill mound
Area fill layer
Diked containment
Cover application
procedure
Land-based equipment
Sludge-based equipment
Method
Area fill mound
Area fill layer
Diked containment
Method
Area fill mound
Area fill layer
Diked containment
Method
Area fill mound
Area fill layer
Diked containment
Cover application
procedure
Land-based equipment
Sludge-based equipment
Method
Area fill mound
Area fill layer
Diked containment
Consideration
Solids content
(percent)
20-28
28-32
>32
15-20
20-28
28-32
>32
20-28
28-32
>32
Solids content
(percent)
>20
>15
20-28
>28
Equipment used
Dragline
Track dozer
Sludge solids
(percent)
>20
15-20
>20
20-28
>28
Cover application
procedure
Sludge-based equipment
Sludge-based equipment
Land-based equipment
Sludge-based equipment
Sludge solids content
(percent)
20-28
>28
>15
>20
Depth of
No higher than 3 ft below
No higher than 4 ft below
Cover application
procedure
Sludge-based equipment
Sludge-based equipment
Land-based equipment
Sludge-based equipment
Bulking ratio
2 soil:1 sludge
1 soil:1 sludge
0.5 soil:1 sludge
1 soil:1 sludge
0.5 soil:1 sludge
0.25 soil:1 sludge
Not required
0.5 soil:1 sludge
0.25 soil:1 sludge
Not required
Cover application
procedure
Sludge-based equipment
Sludge-based equipment
Land-based equipment
Sludge-based equipment
Width
(ft)
<40
Not limited
Lift depth
(ft)
6
1
2-3
4-6
6-10
Interim cover
thickness (ft)
3
0.5-1
1-2
2-3
Number of lifts
1 maximum
3 maximum
1-3 typical
1-3 typical
total fill
top of dikes
top of dikes
Final cover thickness
(ft)
1
1
3-^1
4-5
1 ft = 0.305 m.
133
-------
*$$&*
>rf" e^*&*& t& X^
-------
MIN. OF 15' OR AS REQUIRED
FOR CONSTRUCTION EQUIPMENT
FINAL COVER
EXTEND TO PREVENT
DISCHARGE ON SLOPE
FACE
MIDDLE DRAINAGE BLANKET
LOWER SLUDGE LAYER 10'
BOTTOM DRAINAGE BLANKET
Figure 10-11.—Cross-section of typical diked containment operation.
Table 10-11.—Design considerations for codisposal operations
Consideration
Design parameter Determining factor
Bulking ratio Method
Bulking agent
Sludge solids content
.. .. . Bulking
Method .
agent
Sludge/refuse mixture Refuse
Sludge/soil mixture Soil
Sludge
solids
content
(percent)
3-10
10-17
17-20
>20
>20
Bulking ratio
7 tons refuse:1 wet ton sludge
6 tons refuse:1 wet ton sludge
5 tons refuse: 1 wet ton sludge
4 tons refuse:1 wet ton sludge
1 soll:1 sludge
1 ton = 0.907 Mg.
COSTS
Purpose and Scope
This section presents typical costs for sludge hauling
and landfilling. Cost curves are presented in terms of
cost per wet ton VS sludge quantity received. Typical
costs are presented for (1) sludge hauling, (2) annual-
ized site capital costs, (3) site operating costs, and (4)
total site costs (combined annualized capital and operat-
ing).
These curves can be useful in the early stages of
sludge landfill planning. However, typical costs should be
used only in preliminary work. Actual costs vary consid-
erably with specific sludge and site conditions. There-
fore, use of these curves for computing specific project
costs is not recommended. Site-specific cost investiga-
tions should be made in each case.
Hauling Costs
Typical costs for hauling wastewater treatment sludge
are presented in figure 10-12. As shown, costs are
given in dollars per wet ton as a function of the wet
tons of sludge delivered to the site each day. Costs are
presented for alternative distances of 5, 10, 20, 30, 40,
and 50 mile (8.0, 16.1, 32.2, 48.3, 64.4, and 80.4 km)
hauls.
"Principles and Design Criteria for Sewage Sludge Ap-
plication on Land"5 and "Transport of Sewage Sludge"6
were the primary sources of information for data and
procedures in developing these hauling costs. Other re-
ferences7'10 are available and were also consulted and
utilized. Sludge hauling costs were originally prepared foi
the year 1975 but were updated to reflect 1978 costs.
The hauling costs shown in figure 10-12 reflect not
only transportation costs, but also the cost of sludge
loading and unloading facilities. For a plant producing
135
-------
40.00
30.00
20.00
15.00
oo
r~
O)
CC
O
^ 10.00
O
UJ
g
in
O
U
5.00
4.00
3.00
2.00
1.00
50
MILE HAUL
MILE HAUL
MILE HAUL
MILE HAUL
MILE HAUL
MILE HAUL
10
20
30
40
50
100
200
300
400
500
SLUDGE QUANTITY RECEIVED
(WET TONS/DAY)
Figure 10-12.—Typical hauling costs.
approximately 10 wet tons (9.1 Mg) per day of a dewa-
tered sludge and a 5-mile (8.0 km) haul, sludge loading
and unloading facilities were found to contribute 60 per-
cent of the total hauling costs. For a plant producing
approximately 250 wet tons (227 Mg) per day of dewa-
tered sludge and a 40-mile haul, loading and unloading
facilities contributed less than 10 percent of the total
hauling costs.
Because of the differing bases for cost computations,
certain assumptions on sludge volumes and unit costs
were utilized to produce the hauling cost curve. These
assumptions include:
1. The sludge was dewatered and had a solids con-
tent of approximately 20 percent. It was hauled by
a 15 yd3 (11.5 m3), 3-axle dump truck.
2. Hauling was performed 8 hours per day, 7 days
per week.
3. Fuel cost was $0.60 per gallon ($0.16 per liter).
4. Labor (primarily truck driving) cost was $8.00 in-
cluding fringe benefits.
136
-------
5. Overhead and administrative costs were 25 percent
of the operating cost.
6. Capital costs were annualized. A rate of 7 percent
over 6 years was used for the trucks with a sal-
vage value of 15 percent. A rate of 7 percent over
25 years was used for loading and unloading facili-
ties with no salvage value.
If conditions other than the above-stated conditions
prevail at a given site, the hauling costs in figure 10-12
should be revised upward or downward appropriately. As
an example, if 10 yd3 (7.6 m3) 2-axle dump trucks are
used, costs should be higher by factors ranging from 1.3
for a plant generating 250 wet tons (227 wet Mg) per
day with a 50-mile (80 km) haul to 1.0 for a plant
generating 10 wet tons (9.1 wet Mg) per day with a
5-mile (8.0 km) haul. Alternatively, if a 30 yd3 (23.9 m3)
dump truck is used, costs should be lower by factors
ranging from 0.6 to 1.0 for the aforementioned sludge
quantities and haul distances.
Site Costs
Typical site costs for landfilling wastewater treatment
sludges are presented in figures 10-13, 10-14, and 10-
15. As shown, costs are given in dollars per wet ton of
sludge received as a function of the wet tons of sludge
delivered to the site each day. Costs are presented for
each of the alternative landfilling methods. Scenarios us-
ing average design dimensions and application rates
were devised for the purposes of these cost calcula-
tions. These scenarios are summarized in table 10-12.
The cost curve for each method was plotted from com-
putations which assumed alternative quantities of 10,
100, and 500 wet tons (9.1, 90.7, and 453 Mg) of
sludge for each scenario.
Capital costs are summarized in figure 10-13. Capital
cost items included:
1. Land.
2. Site preparation (clearing and grubbing, surface wa-
ter control ditches and ponds, monitoring wells, soil
stockpiles, roads, and facilities).
3. Equipment purchase.
4. Engineering.
Capital costs were then annualized at 7 percent inter-
est over 5 years (the life of the site) and divided by the
sludge quantity delivered to the site in one year.
Operating costs are summarized in figure 10-14. Oper-
ating cost items included:
1. Labor.
2. Equipment fuel, maintenance, and parts.
3. Utilities.
4. Laboratory analysis of water samples.
5. Supplies and materials.
6. Miscellaneous and other.
Operating costs for one year were then divided by the
annual sludge quantity delivered to the site.
The costs shown have been derived from a variety of
published information sources10"12 and case study investi-
gations have been revised upward to reflect 1978 prices.
Several assumptions were employed in producing these
cost curves. These assumptions include:
1. Life of the landfill site was 5 years.
2. Land cost was $2,500 per acre ($6,177 per ha).
3. Actual fill areas (including inter-trench spaces) con-
sumed 50 percent of the total site area.
4. Engineering was 6 percent of the total capital cost.
5. Operating labor cost $8.00 per hour including fringe
overhead, and administration.
It should be noted that the site costs shown for codis-
posal operations were derived by dividing the additional
annualized capital cost and additional operating cost by
the sludge quantity received. Actual unit costs for typica
refuse landfills not receiving sludge may be expected to
be less.
Cost Analysis
As stated previously, these cost curves should not be
used for site-specific cost compilations performed during
design. However, they can be useful in the preliminary
planning stages of a specific sludge landfill. In addition
they are useful in developing some general conclusions
about sludge landfill costs. For instance, cost ranges
included:
1. Hauling costs ranges from $8.80 per wet ton ($9.7(
per Mg) (for a 5 mile (8.1 km) haul of 500 wet
tons (453 Mg) per day) to $34.00 per wet ton
($37.49 per Mg) (for a 50 mile (80.4 km) haul of
10 wet tons (9.1 Mg) per day).
2. Annualized site capital costs ranged from $2.20 pei
wet ton ($2.43 per Mg) (for a sludge/refuse codis-
posal operation receiving 500 wet tons (453 Mg)
per day) to $10.10 per wet tons ($11.11 per Mg)
(for a diked containment operation receiving 10 we
tons (9.1 Mg) per day).
3. Site operating costs ranged from $1.20 per wet tor
($1.32 per Mg) (for a sludge/refuse codisposal op-
eration receiving 500 wet tons (453 Mg) per day)
to $36.10 per wet ton ($39.80 per Mg) (for an are
fill mound operation receiving 10 wet tons (9.1 wel
Mg) per day).
4. Combined site costs ranged from $3.40 per wet to
($3.75 per Mg) (for a sludge/refuse codisposal op-
eration receiving 500 wet tons (453 Mg) per day)
to $46.20 per wet ton ($50.94 ton Mg) (for an are
fill mound operation receiving 10 wet tons (9.1 Mg
per day).
Also, an assessment can be made of the relative cosl
of alternative landfilling methods. A prioritized list of
landfilling methods is based on total site costs (with
lowest costs first) is as follows:
1. Codisposal with sludge/refuse mixture.
2. Wide trench.
3. Codisposal with sludge/soil mixture.
137
-------
15.00 I—
10.00
5.00 -
4.00 -
S
o
DC
O
LL
- 3.00 -
C/3
O
O
2.00 -
1.00
CODISPOSAL WITH REFUSE
100
SLUDGE QUANTITY RECEIVED
(WET TONS/DAY)
200
300
400
500
Figure 10-13.—Typical annualized site capital costs.
4. Narrow trench.
5. Diked containment.
6. Area fill layer.
7. Area fill mound.
CASE STUDY
Background and History
The Newport Township landfill, located near Wauke-
gan, II!., receives sludge generated by four treatment
plants that serve a domestic population of 232,000 with
an additional industrial inflow equivalent to 28,000 resi-
dents. The industrial inflow originates primarily from a
naval base, a pharmaceutical company and a variety of
metal finishing plants. There are three advanced waste-
water plants and one pretreatment wastewater plant
within the North Shore Sanitary District. The three ad-
vanced treatment plants use activated sludge, followed
by biological denitrification and sand filtration; the pre-
treatment plant uses trickling filters. Figure 10-16 and
table 10-13 outline sludge processing at the wastewater
treatment plant. After initial processing, sludge from the
four plants is taken to a processing plant in Waukegan
where it is elutriated and conditioned with lime and fer-
ric chloride. It is then dried to about 22 percent solids
by vacuum filtration (figure 10-17) prior to landfilling.
The site commenced operations on July 8, 1974.
Site Description
The site has an area of 282.8 acres (114 ha), with
200 acres (81 ha) to be filled. Soils consist of 2 ft
(0.6 m) of topsoil, then 20 to 25 ft (6 to 8 m) of silty
clays, followed by 6 to 15 ft (2 to 5 m) of tight blue
clay. The southwestern part of the site is a flood plain
with slopes of less than 1 percent. The flood plain is
not being used for filling operations.
138
-------
40.00
30.00
20.00
15.00
CO
CD
CC
O
"- 10.00
g
-------
50.00 i-
4000 -
30.00 -
AREA FILL MOUND
CODISPOSAL WITH REFUSE
1.00
200
300
400 500
SLUDGE QUANTITY RECEIVED
(WET TONS/DAY)
Figure 10-15.—Typical total site costs (combined annualized capital and
operating costs).
4. Landfilling of dewatered raw and digested sludges.
Figure 10-18 illustrates the estimated costs of treat-
ment, transportation and disposal for each alternative.
On the basis of these cost evaluations and a maximum
distance of 25 mi (40 km) to the landfill, it was deter-
mined that sludge landfilling would provide the most cost
effective alternative for ultimate disposal.
Following selection of the disposal alternative, eight
potential sites were chosen and evaluated using avail-
able data. Ultimately the Newport Township site was
140
-------
Table 10-12.—Cost scenarios for alternative landfilling methods
Cost
scenario
number
1
2.
3.
4.
5. ...
6
7
Cost
scenario
number
1
2
3
4
5
6
7
Landfilling method
Narrow trench
Wide trench
Area fill mound
Area fill layer
Diked containment
Sludge/refuse mixture
Sludge/soil mixture
Identification
Landfilling method
Narrow trench
Wide trench
Area fill mound
Area fill layer
Diked containment
Sludge/refuse mixture
Sludge/soil mixture
Sludge
solids
content
(percent)
22
32
30
30
25
20
20
Sludge
solids
content
(percent)
22
32
30
30
25
20
20
Width Depth Length Spacing Bulkin9 Bulking
(ft) (ft) (ft) (ft) fo^red agent
6
60
50
Cover
applied
Yes
Yes
Yes
Yes
Yes
Yes
No
6 100 9
8 600 30
30 100 30
Sludge covering
Cover
Location
equipment Int6rirr
(ft)
Land-based —
Sludge-based —
Sludge-based 3
Sludge-based 0.5
Land-based 1
Sludge-based 0.5
Sludge-based —
No
No
Yes
Yes
Yes
Yes
Yes
thickness
i Final
(ft)
4
5
1
1
3
2
Soil
Soil
Soil
Refuse
Soil
Imported
soil
required
No
No
Yes
Yes
Yes
No
No
Sludge M Sludge
depth bem~ applica-
Bulking ratio per . tion
lift .™ rate
(ft) (yd3/acre)
1 soil:1 sludge
0.5 soil:1 sludge
0.5 soil:1 sludge
7 tons refuse:1 wet ton sludge
1 soil:1 sludge
Miscellaneous
4
4
6
2
6
6
1
1 2,580
1 4,100
2 9,680
2 4,300
4 12,410
3 2,520
1 1,600
Primary equipment
Backhoe with loader, track dozer, excavator
Track loader, scraper track dozer
Track loader, backhoe, track dozer, scraper,
Track dozer, scraper, grader, wheel loader
Dragline, track dozer, scraper
Track dozer, truck loader
Tractor with disc, grader, track loader
wheel loader
-------
PLANT
NO.
1
2
3
4
PLANT
NAME
WAUKEGAN
CLAVEY ROAD
GURNEE
NORTH CHICAGO
SLUDGE SOURCES I I SLUDGE PERCENT
OR TYPE SLUDGE PROCESSING AT ORIGINATING PLANT • SOLIDS
I
|
I
WASTE ACTIVATED !-•
I
IMHOFF SETTLING -J-*
1
PRIMARY i ' »
1
1
1
WASTE ACTIVATED -f*
1
1
PRIMARY U
WASTE ACTIVATED 1
I
IMHOFF SETTLING-V
FINAL SETTLING— ^
I
GRAVITY
THICKENED
THICKENED VIA
AIR FLOATATION
FILTERS
GRAVITY THICK-
ENED IN IMHOFF
TANK
GRAVITY
THICKENED
^.GRAVITY
THICKENED
BLENDED AND
MIXED
BLENDED AND
MIXED
s.
1
1
W BLENDED AND
MIXED
, GRAVITY
1* THICKENED
1 GRAVITY
I THICKENED
ANAEROBIC
DIGESTION
L^p 5%
^ 5%
Figure 10-16.—Sludge processing ai originating plant.
selected for intensive investigation, based on the follow-
ing considerations:
1. Short haul distance (10 mi or 16 km).
2. Availability of the land for purchase.
3. A large negative reaction from the public was not
anticipated.
Accordingly, an option to purchase the land was ac-
quired for this site, and hydrogeological investigations
were begun to determine its environmental acceptability.
After discussions with the Illinois Sanitary Water Board
and the Illinois State Geological Survey regarding the
data required to obtain preliminary approval of the land-
fill site, the District proceeded with the necessary soil
borings and laboratory tests. A total of nine borings to a
depth of up to 52 ft (16 m) were performed at the site.
By the end of 1970 the District contracted to have
topographic maps made of the property. The maps of
the 450 acre area were prepared at a scale of 1
in. = 1,000 ft (1 cm = 120 m) and 2 ft (0.6 m) contour
intervals. These maps were provided to a consulting
engineering firm that the District had contracted to pre-
pare design and operation plans for the site.
Design
The design had to accommodate the following regula-
tory requirements of the Illinois State Environmental Pro-
tection Agency.
1. It had to follow the "Rules and Regulations for
Refuse Disposal Sites and Facilities" (general oper-
ational requirements—no large impacts).
2. It was required that a 150 ft (46 m) buffer be
placed between sludge deposits and the property
142
-------
Table 10-13.—Details on sludge transported from originating plant to sludge processing unit
at Waukegan
Sludge generation rate
Transport to processing unit
Plant Plant
number number
1
2
3
4
Waukegan
Clavey road
Gurnee
North Chicago
Sludge
source
Lbs per
day (dry
solids
weight)
Primary 13,530
Waste activated 15,409
Imhoff settling 13,530
(All) 11,968
(All) 22,965
(All) 1 ,420
Gallons
per day
(wet
volume)
32,446
25,177
27,038
48,643
55,071
3,405
Days
per Mode
week
5 8 in. diameter
5 8 in. diameter
5 8 in. diameter
5 5,500 gal tank
5 8 in. diameter
5 5,500 gal tank
Transport
distance
(miles)
pipeline
pipeline
pipeline
trucks
pipeline
trucks
<1
<1
<1
22
7.5
5
Total.
78,822 191,780
1 lb = 0.454 kg.
1 gal/d = 3.785 L/d.
1 in. =2.54 cm.
1 mi = 1.609 km.
PLANT NO. | PLANT NAME
1 SLUDGE SOURCE !
,
1
2
4
WAUKEGAN
CLAVEY ROAD
NORTH CHICAGO
l ,
1
IMHOFF ^FTTI IIMfi I -
1
/ A 1 1 \ 1
1
(AM )
i
I
1
1
i
I
1
i
1
I
1
1
' I
{ »
s *
L
SLUDGE
QTDR AI^F
TANK
SLUDGE
CTORAf^F
TANK
k. (INCLUDING ^ BLENDING
POLYMER
ADDITION) . ._ _.
\ p
LIME AND
FeCI
ADDITION
\
VACUUM
FILTRATION
(TO 22% SOLIDS)
1
TO LANDFILL
Figure 10-17.—Flow diagram: Sludge processing at Waukegan,
143
-------
o
DC 5
ai H
Q- <
O o
n UJ
— CC
Q w
HI Q
o -;
at
a
160
150
140
130
120
110
-
-
jX
:
\f
-//
A
IRR
1/7
A
/
/
/
1 1 1 1
LT. D-2,
IGATION -
A
r
/
s^
/ v
NOTE: C
QUANTI"
PLANNIIV
PHOSPHX
1 I 1 I
/
^^>
^ !
ALT. B-1,
LANDFIL
^
^
\LT. C-2,
DISCING
S
ALT. A,
'INCINERATION
OSTS ARE FOR 1980
PIES FROM
1G AREA W
VTE REMO\
1 I 1 1
NSSO
ITHOUT
/AL.
1 1 1 1
25
50
75
100
125
MILES TO DISPOSAL SITE
FROM WAUKEGAN STP
(ONE WAY)
Figure 10-18.—Comparative costs of sludge disposal
without phosphorus removal.
line of any residences and the center line of any
county roads.
3. The site could accept only filter cake sludge condi-
tioned with ferric chloride and lime.
4. It was required that groundwater monitoring wells
be installed at state-approved locations. Monitoring
for 22 contaminants was required annually; 5 par-
ameters quarterly.
5. It was required that gas monitoring wells at state-
approved locations be monitored for methane, car-
bon dioxide, nitrogen and oxygen.
Based on information obtained from borings, excava-
tions were limited to a 15 to 20 ft (5 to 36 m) depth. At
this depth, at least 20 ft (6 m) of silty clay with a low
permeability would separate sludge deposits from
groundwater.
Other design considerations included:
1. Relatively low solids sludge (22 percent).
2. Deep, well protected aquifer.
3. Stable soil for trench sidewalls.
4. Maximum site usage.
As a result of these considerations and the site char-
acteristics, the District chose wide trenches as the dis-
posal method.
In order to determine the stability and seepage char-
acteristics of the soil, the District excavated two test
pits on February 9 and 10, 1972.
Each pit was 24 ft by 50 ft (7 m by 15 m) at ground
level. The slope of three sides was approximately 1:1,
the fourth was 1 horizontal to 2 vertical, with a depth of
12 ft (4 m). All observations indicated that groundwater
seepage was not excessive, and that the cuts were
stable since no sloughing or caving of the banks was
observed.
An application for a permit to install and operate a
sanitary landfill, together with a detailed installation and
operating plan, was then submitted to the Illinois State
Environmental Protection Agency. The permit was issued
on March 2, 1972. In September 1973, a contract was
awarded by the District for preparation of the site in
accordance with plans and specifications prepared by
the consultant.
Public Participation
Public Interaction During S/te Approval
Although when the District initially selected the site
they anticipated little public resistance, protests began
following reports of the proposed landfill operation in the
media. However, the District performed detailed environ-
mental impact investigations and prepared an operational
plan designed to minimize impacts. The District worked
closely with various regulatory authorities including:
1. Illinois State Environmental Protection Agency.
2. U.S. Department of Agriculture, Soil Conservation
Service.
3. Lake County Illinois Soil and Water Conservation
District.
These authorities reviewed and provided input to site
plans and reports throughout the process and as a re-
sult of their support, the public reaction became less
negative.
On-going Public Relations
Operational features designed to minimize public resis-
tance were:
1. Application of cover over sludge throughout the day
in warm weather to minimize odors.
2. Application of lime over sludge in haul vehicles at
all times to minimize odors.
As a result, the only complaints received to date have
been from a resident whose property is literally sur-
rounded by the landfill. The resident's complaints are
generally justified, and they have been constructive in
nature. In general, they have centered on odors and
noise; consequently, dumping and operating procedures
have been restricted and currently run from 7 a.m. to 4
p.m.
144
-------
Operation
Site preparation, sludge loading and transport, and the
operating practices employed are discussed later. Opera-
tional considerations are presented below:
Sludge to groundwater
Soil cover thickness
Sludge application
Fill depth
Sludge exposure
Total soil usage (sludge:soil)
>10 ft (>3 m)
5 ft (1.5 m)
9,100 yd3/acre (17,200 m3/ha)
14 ft (4 m)
<1 day
1:0.6
Site Preparation
The existing on-site barn, silo, and minor outbuildings
were demolished. The remaining farmhouse was used as
an office. Structures for storing sludge and on-site
equipment were constructed. A paved, all weather ac-
cess road was constructed to within several hundred
feet of the disposal area. Approaches to the disposal
areas were covered with sand and gravel. A 6 ft (2 m)
fence was provided for the area south of Ninth Street
(figure 10-19). Lighting was installed around on-site
structures and sewer, water, and telephone services
were in place at the farmhouse.
Prior to excavating a trench the top 3 ft (0.9 m) of
soil was stripped and stockpiled.
Sludge Loading and Transport
Sludge from the vacuum filter at the Waukegan sludge
processing unit is transported via a conveyor belt that
moves from end to end of a 30 yd3 (23 m3) open dump
truck. Thus, sludge is spread evenly over the bed of the
truck. There are five open-top dump trucks with sealed
tailgates, and each makes about 5 trips to the landfill
each day. The one-way haul distance is 10 mi (16 km)
and the haul roads are compatible for truck traffic.
Operational Procedures
Individual cells 20 ft deep, 70 ft long and 22 ft wide
(6 m deep, 21 m long, and 7 m wide) at the top are
excavated by a large backhoe/excavator. Sidewalls are
B7
LIMITS OF FLOOD
PLAIN ELEV. 691
INITIAL
FINAL
SODDED.
WATERWAY
STORAGE
BUILDING
DELIVERY
ROAD
INITIAL
TRENCHING
AREA
EXISTING
RESIDENCES I
ACCESS
ROAD 4
OW-4
EQUIPMENT
STORAGE BUILDING
SODDED
WATERWAY
EXISTING
RESIDENCE
OW-2 Observation Well
O B2 Boring Location
Figure 10-19.—Site operating plant, Waukegan, III.
145
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straight on all but one side; the 70 ft (21 m) length on
the side where dumping is done has a 6 ft (2 m) wide
step halfway down for added sidewall stability. Thus, the
bottom cell width is 16 ft (5 m). Consecutive cells are
constructed with the 70 ft (21 m) sides parallel. Twenty
ft (6 m) of solid ground is maintained between the paral-
lel cells and consecutive cells proceed in a line to form
a single trench (figure 10-20). After completion of one
line of cells, a second line is begun (as shown in figure
10-19) to the side of the first line. Five ft (2 m) of solid
ground is maintained between adjacent trenches. The
trenches are graded so that leachate can be collected
at one end of the trench and returned to the Waukegan
plant for treatment. Haul vehicles back up on prepared
sand and gravel access roads to the long sides of each
cell, and sludge is dumped by the trucks in progression
from one end of the 70 ft (21 m) length to the other.
Usually the consistency of the sludge is such that it
flows out to an even grade inside each cell. However,
the bucket of the backhoe/excavator is used to spread
the sludge evenly at the end of the day. One day's
sludge usually accumulates to a 2 ft (0.6 m) thickness.
Filling proceeds to within 2 ft (0.6 m) of the surface
before proceeding to a new cell.
At the end of each day, a 6 to 8 in. (15 to 20 cm)
soil cover is applied over the sludge. After filling has
proceeded to within 2 ft (0.6 m) of the subsurface (usu-
ally at the end of a week), a 5 ft (2 m) cap of topsoil
cover (previously stockpiled) is applied to 3 ft (0.9 m)
above grade by the backhoe. After initial settlement the
cell is final graded and compacted with small bulldozers
(including a D-3 and a D-5). Additional operational
characteristics are detailed below.
The equipment and personnel at the site are as fol-
lows:
Equipment:
1 - Backhoe/excavator (Northwest with 1.5 yd3
bucket).
1 - Front-end loader (Hough with 2 yd3 bucket).
1 - Bulldozer (Caterpillar D-3).
1 - Bulldozer (Caterpillar D-5)
Figure 10-20.—Wide trench operation, Waukegan,
146
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Personnel:
1 - Superintendent.
3 - Equipment operators.
1 - Laborer.
Problems encountered during the operation of the
landfill, together with controls are detailed below:
1. Problem: Freezing temperatures make excavation of
cells and placement of stockpiled cover impossible.
Snow and rain make access to cells by haul vehi-
cles and site operation by equipment difficult.
Control: During inclement weather, soil is stockpiled
on the site inside a sludge storage building accessi-
ble via paved roads. This building is a steel frame
structure 50 ft by 50 ft by 30 ft (15 m by 15 m by
9 m) high. It is constructed on a concrete slab with
concrete sidewalls extending 3 ft (0.9 m) high. A
trench drain is located in the middle of this slab to
collect sludge moisture. This leachate is directed to
an underground 10,000 gal (37,850 I) storage tank.
Leachate is pumped out of the tank as necessary
and transported via tank truck to the Waukegan
Plant for treatment. In poor weather, all sludge de-
livered to the site is dumped into the building which
prevents the addition of moisture from precipitation
and controls odors. When weather improves, the
sludge is loaded back into dump trucks with front-
end loaders and hauled to the cells.
2. Problem: Soil runoff from denuded fill areas.
Control: Fill areas are seeded with grasses soon
after completion. All on-site drainage is channeled
through sod-lined ditches to a collection pond.
3. Problem: Odors from sludge during transport, from
uncovered sludge in cells during warm weather,
from sludge spills, and from equipment.
Control: Initially sludge transport was to be in dump
truck trailers covered with tarpaulins for odor con-
trol. However, this caused operational difficulties
and transport is now accomplished in open-top
trucks. However, after loading, the sludge is cov-
ered with a layer of lime for odor control while in
transit. In warm weather, sludge in the cells is cov-
ered during the day as well as at the end of the
day. Lime is sprinkled over any sludge spills. The
backhoe bucket (which comes into contact with
sludge) is buried in soil at the end of the day to
minimize odors.
4. Problem: Mud from site is tracked onto adjoining
roadways by haul vehicles.
Control: A washrack is located at the Waukegan
Sludge Processing Unit. It is used to clean haul
vehicles in wet weather.
5. Problem: Noise of haul vehicles and on-site equip-
ment bothers near-site residents.
Control: Per agreement with nearby residents, haul-
ing and operation is confined to between 7 a.m.
and 4 p.m.
Figures 10-21 through 10-24 illustrate the equipment
and operations at the Waukegan site.
Figure 10-21.—Stockpiling soil, Waukegan, III.
Figure 10-22.—Unloading sludge into wide trenches,
Waukegan, III.
147
-------
****"
Figure 10-23.—Placing interim cover, Waukegan, III.
Figure 10-24.—Placing final cover, Waukegan, III.
Monitoring
Background samples were taken from all wells prior to
initiating operations so that baseline conditions could be
established. Subsequent monitoring has not detected any
contamination of groundwater in on-site wells nor has
water from the collection pond and drainage ditches
contaminated surface waters. Establishing initial condi-
tions proved valuable since one of the local potable
wells showed contamination that could have been attrib-
uted to sludge disposal but was known to have preced-
ed disposal operations as a result of initial tests.
The number, location, and function of the monitoring
wells were established in conjunction with the Illinois
State Environmental Protection Agency. Figure 10—19 il-
lustrates the location of the wells and tables 10-14 and
10-15 detail the wells and monitoring parameters.
Costs
A breakdown of the on-site costs reveals that the cost
per dry ton of sludge was $14.56 ($16.05/Mg). The
costs were calculated in the following manner: first capi-
tal expenditures were divided by the total amount of
sludge received over the life of the site; next operating
costs were divided by the amount of sludge received for
the period considered (6 months in this case); finally the
figures were added to arrive at the total cost per unit of
sludge (excluding hauling costs). The intensive use of
the available land contributed to this relatively low fig-
ure. Following is breakdown of the costs by category.
Unit cost
($/dry
ton
sludge)
Site capital costs
Land
Monitoring wells
Site preparation
Total capital cost
Site operating cost (October 1977
through March 1978)
Labor
Equipment depreciation
Administration
Maintenance
Laboratory
Fuel
Operating materials & supplies...
Miscellaneous
Cost
$450,000
12,000
328,000
$2.25
0.06
1.64
790,000
3.95
Total site operating cost.
Total cost
18,200
16,450
7,300
6,850
1,450
1,250
900
650
53,050
—
3.64
3.29
1.46
1.37
0.29
0.25
0.18
0.13
10.61
14.56
Hauling costs have not been included in the total cost.
DESIGN EXAMPLE
Introduction
The design of a sludge landfill is highly dependent
upon many sludge characteristics and site conditions,
such as percent solids, climate, soil, topography, and
others. Consequently, no single design example can be
universal. However, an example can be illustrative of the
design and operating procedures which have been rec-
ommended in previous chapters.
The approach here is to present sludge characteristics
and site conditions as given design data. The design
process then proceeds to (1) select the landfill method,
148
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Table 10-14.—Summary of groundwater and gas wells and surface water
stations
Relation to fill
Monitoring
type
Groundwater
Gas
Leachate
Surface water...
Well /station
number
OW-1
OW-2
OW-3
OW-4
OW-5
OW-6
OW-7
OW-8
OW-9
OW-10
5 potable wells
Gas well 1
Sludge cell
Tank under sludge
storage building
Runoff pond
Drainage ditches
Location
(up- or down-
gradient)
Down -gradient
Down-gradient
Dp-gradient
Up-gradient
Dp-gradient
Up-gradient
Up-gradient
Down-gradient
Down-gradient
Down-gradient
Down-gradient
In-sludge
—
—
—
Dis-
tance
(ft)
200
100
100
20
100
100
100
100
100
100
>1/2 mi
—
—
—
Well specifications
Total
depth
(ft)
30
30
30
30
30
30
30
30
30
30
—
—
—
—
—
Depth below
groundwater
(ft)
5
5
5
5
5
5
5
5
5
5
—
—
—
—
Drill
rig
used
Auger
Auger
Auger
Auger
Auger
Auger
Auger
Auger
Auger
Auger
—
—
—
—
~
1 ft = 0.305 m.
Table 10-15.—Sampling and analytical program
Analyses
Monitoring
type
Groundwater
Gas
Leachate
Surface water...,
Well/station
number
OW-1
OW-2
OW-3
OW-4
OW-5
OW-6
OW-7
OW-8
OW-9
OW-10
5 potable wells
Gas well 1
Sludge cell
Tank under sludge
storage building
Runoff pond
Drainage ditches
Sample collection
technique
10 ft length of
1-in. diameter
PVC pipe, fitted
with polyethylene
foot valve on
bottom
Gas cylinder
Grab sample
Grab sample
Parameter(s)
22 parameters including
metals as dictated by
State EPA
CO2, O2, N2, CH4,
COS, H2S, SO2
Heavy metals COD, BOD,
TOG, pH, NH3, NO3
Fecal coliform
Total
times Frequency
to date
3 1 xper yr
About 20 2 Xper mo
About 20 Irregularly
About 20 Irregularly
149
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(2) compute the landfill dimensions, (3) prepare site de-
velopment plans, (4) determine equipment and personnel
requirements, (5) develop operational procedures.
It should be noted that the scope of this chapter is
confined to design only; i.e., it is assumed that the site
in the design example has already been selected. It
should also be noted that the design described in this
Chapter is somewhat preliminary in nature. A final design
should contain more detail and address other design
considerations (such as sediment and erosion controls,
roads, leachate controls, etc.) which are not addressed
herein.
Statement of Problem
The problem is to design a sludge-only landfill at the
location of a pre-selected site. The landfill is to receive
sludge from an existing municipal wastewater treatment
plant with secondary treatment. The recommended de-
sign must be the most cost-effective, well-suited for local
conditions, and in full compliance with regulatory const-
raints.
Design Data
The following information is included as given design
data and will be useful in executing the subsequent
design.
Plant Description
The wastewater treatment plant is a modern secondary
treatment facility. Further information on the facility is as
follows:
1. Service population equivalent = 500,000.
2. Average flow = 50 Mgal/d (190 ML/d).
3. Industrial inflow—10 percent of total inflow.
4. Wastewater treatment processes:
Bar screen separation.
Aerated grit tanks.
Primary settling tanks.
Secondary aeration tanks.
Secondary settling tanks.
Sand filters.
Chlorine contact tanks.
Sludge Characteristics
Sludge is primarily generated from two sources (the
primary and secondary clarifiers). The sludge is then
mixed, stabilized with lime, and dewatered. A more com-
plete description is as follows:
1. Sludge sources.
Primary settling tanks.
Secondary settling tanks.
ludge treatment.
Gravity thickening.
Mixing.
Lime addition.
Pressure filtration.
3. Sludge solids content = 30 percent.
4. Sludge quantity (dry weight basis) = 48 tons/day (44
Mg/day).
Climate
Significant factors impacting on sludge landfilling are
listed below:
1. Precipitation = 50 in./yr (127 cm/yr).
2. Evaporation = 30 in./yr (76 cm/yr).
3. Mean temperature = 32°F (0°C) for 40 days/yr.
As shown, the climate is relatively mild with cold
temperatures prevailing only slightly more than one
month per year. Precipitation is high and exceeds evap-
oration by 20 in./yr (51 cm/yr).
General Site Description
Preliminary data were collected during the site selec-
tion process. It is summarized below:
1. Depth to groundwater = 12 ft (3.7 m).
2. Depth to bedrocks = 7 ft (2.1 m).
3. Size of property = 375 acres (152 ha).
4. Property line frontage:
• 5,200 ft (1,580 m) along county road.
• 4,700 ft (1,430 m) along residences.
• 4,600 ft (1,400 m) along grazing land.
• 1,200 ft (370 m) along woodland.
5. Slopes: Uniform slope of approximately 5 percent.
6. Vegetation:
• 225 acres (91 ha) of woodland.
• 150 acres (60 ha) of grassland.
7. Surface water: None on site.
A plan view of the site is presented in figure 10-25.
As shown, the site has good access along a county
road. The site is located in a moderately developed
residential area and abuts residences. Approximately 60
percent of the site is covered with woodland. The bal-
ance of the property was recently used for grazing and
remains grass-covered.
Soil Description
Eight test borings were performed on the site to de-
termine subsurface conditions. These are located as
shown in figure 10-25. Subsurface conditions generally
are similar at the boring locations and can be summa-
rized as follows:
Depth Type Permeability
0-2 ft (0-0.6 m) Top soil High
2-9 ft (0.6-2.1 m) Silt loam Medium
>9 ft (>2.1 m) Soft shale Low
Design
Landfilling Method
Table 10-9 should be consulted for a reference. As
shown, when a trench design is selected and the solids
150
-------
0 250 500 750 1000
=z=s=a=
SCALE IN FEET
&(3&&l&ts%F
»* a-'irvi* J\i*jn • .*.*. :**'-;
PASTURE
Legend
Property Boundary
=i Road
0 Dwelling
-Jf*/Y^ii Woods
200 Contours
Figure 10-25.—Site base map.
Boring
151
-------
content is approximately 32 percent, a design similar to
Scheme No. 6 should be implemented.
Scheme No. 6 is a wide trench operation and typically
employs the following design characteristics:
1. Trench width = 60 ft (18 m).
2. Trench depth = 8 ft (2.4 m).
3. Trench length = 600 ft (18.3 m).
4. Trench spacing = 30 ft (9.1 m).
5. Fill depth = 4 ft (1.2 m).
6. Soil used for bulking = No.
7. Soil used for cover = Yes.
8. Cover thickness = 5 ft (1.5 m).
9. Off-site soil needed = No.
Scheme No. 6 allows haul vehicles to enter the trench
and dump the sludge load directly onto the floor of the
trench in 4 ft (1.2 m) high piles. The high solids content
of the sludge (30 percent) allows the sludge to be
dumped in piles without significant slumping.
Scheme Nos. 1 through 5 were not selected because
these operations require that sludge be dumped into the
trench from atop the trench sidewall. The consistency of
the low solids sludge in these operations allows the
sludge to spread out evenly in the trench. If high solid
sludge available in this example were dumped from atop
a trench, it would accumulate at the dumping location
and equipment would be needed to spread the sludge.
Design Dimensions
The width and length of individual trenches shown
above is for medium size sludge landfill operations. At
48 dry tons/day (55 Mg/day) of sludge generation, this
site falls into this category. Thus,
1. Trench width = 60 ft (18 m).
2. Trench length = 600 ft (183 m).
Trench depth is normally 8 ft (2.4 m) for this opera-
tional scheme. However, shale bedrock is at a 9 ft (2.1
m) depth. Accordingly, excavation should proceed no
deeper than 7 ft (2.1 m) to allow sufficient soil cover
over the bedrock.
3. Trench depth = 7 ft (2.1 m).
Groundwater is at a depth of 12 ft (3.7 m) below the
ground surface. A 5 ft (1.5 m) separation of tight weath-
ered shale rocks and soils was deemed adequate to
protect the groundwater.
As a rule of thumb 1 to 1-1/2 ft (0.3 to 0.5 m) of
solid ground must be maintained between trenches for
every 1 ft (0.3 m) of trench depth for the purposes of
trench sidewall stability. As shown in table 10-9, how-
ever, a trench spacing of 30 ft (9.1 m) is recommended
for Scheme No. 6, despite a trench depth of only 7 ft
(2.1 m). The trench spacing is large due to the place-
ment of large soil stockpiles between trenches. In addi-
tion, bulldozers applying cover material need sufficient
space to maneuver in this area. Thus,
4. Trench spacing = 30 ft (9.1 m).
The sludge fill depth suggested by Scheme No. 6 if 4
ft (1.2 m). Since sludge is dumped from haul vehicles
based on the floor of the trench, fill depths higher than
4 ft (12 m) are not practical. The high solids content of
the sludge means that the sludge has sufficient stability
to ensure minimal slumping without the addition of soil.
Accordingly, a sludge fill depth of 4 ft (1.2 m) is practi-
cal. Thus,
5. Fill depth = 4 ft (1.2 m).
6. Soil used for bulking = No.
In order to cover the 60 ft (18 m) wide trench fill, soil
must be applied by equipment moving out over the
sludge. A thick 5 ft (1.5 m) mantle of soil should be
adequate to support the equipment over the 4 ft (1.2 m)
layer of sludge. Soil can be taken from the 7 ft (2.1 m)
deep trench in which the sludge is landfilled. The cover
should consist of 3 ft (0.9 m) of soil to the top of the
trench, and an additional 2 ft (0.6 m) above grade to
account for future settlement. Some soil will still be
available after this initial cover application for future re-
grading needed for additional settlement. Thus,
7. Soil used for cover = Yes.
8. Cover thickness = 5 ft (1.5 m).
9. Off-site soil needed = No.
Site Development
Site development will be in accordance with the Devel
opment Plan shown in figure 10-26. Development fea-
tures included the following:
1. A 500 ft (150 m) wooded buffer should be main-
tained between the sludge fill area and the resi-
dences. A 200 ft (60 m) buffer should be main-
tained around the balance of the property.
2. Trenches should be oriented with their long axes
parallel to the topographic contours. In this manner,
trench bottoms will be evenly graded and sludge
will not flow to one end.
3. Although 30 ft (9.1 m) of solid ground is maintainec
between the long sides of adjacent trenches, 100 ft
(30 m) of solid ground should be maintained be-
tween the short sides of adjacent trenches for pas-
sage by haul vehicles.
4. Storm water runoff from fill areas should be collect-
ed by cutoff trenches along the southwestern prop-
erty line and diverted to a siltation pond.
5. In accordance with State regulations and engineer-
ing judgement one groundwater monitoring well was
located up-gradient from fill areas and three moni-
toring wells were located down-gradient from fill
area.
152
-------
0 250 500 750 1000
SCALE IN FEET
PREVAILING
WINDS
•/^ "Tff!\ f"9-i'•V»*3V« WV yii«WT"\»>73i
PASTURE
Figure 10-26.—Site development plan.
Trench
Access Road
Slltation and Erosion Pond
Monitoring Well
153
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Calculations
lated as follows:
Given a sludge quantity of 48 dry tons/day (44
Mg/day) a calculation can be made of the sludge quan-
tity on a wet weight basis:
(dry weight) ^48 dry tons per day
(percent solids)" 0.30
= 1 60 wet tons per day
A calculation can also be made of the wet volume of
the sludge:
weight of solids
density of solids
= volume of solids
density of water
_ (0.70)(160 wet tons per day)(2,000 Ibs per ton)
(62.4 Ibs/ft3)(27 ft3/yd3)
= 132 yd3 of water
total volume = solids volume + water volume
= 44 yd3 + 132 yd3 = 176 yd3
A calculation can then be made of the landfill capaci-
ty, as follows:
capacity per acre =
cubic yards of sludge per trench
area of land consumed per trench
where:
cubic yards of sludge per trench
= (trench widthXtrench length)(fill depth)
^(60 ft)(600 ft)(4 ft)
27 ft3/yd3
= 5,333 yd3
area of land consumed per trench
= (trench width + spacing)(trench length + spacing)
= (60 ft+ 30 ft)(600 ft+ 100 ft)
= (90 ft)(700 ft)
= 63,600 ft2
= 1.45 acres
5,333 yd3
capacity per acre = —r= =3,678 yd3/acre
1.45 acres
The land fill's land utilization rate can then be calcu-
. . .... .. . sludge volume per day
land utilization rate = —^ -
capacity per acre
176 ydVday
3,678 yd3/acre
= 0.0479 acres per day
The site life can then be calculated since there are
approximately 140 acres of area available for filling at
the landfill.
site size
site life =
(48 dry tons per dayX2,000 Ibs per ton) .. .. .
y (80 |bs/ft3)(27 ft3/yd3) ' = 44 yd °f SO"dS
weight of water
land utilization rate
140 acres
0.0479 acres per day
= 2,923 days-^ 365 days per year
= 8.0 years
L. ,-* gross trench acreage per trench
trench hfe = - 7:71 ^—p-
fill acreage per day
1.45 acres
0.0479 acres per day
= 30 days
Equipment and Personnel
Using the equipment selection matrix, the following
pieces of equipment would be utilized for this operation:
Description
Track dozer
Scraper (self-propelled).
Total
Quantity
1
1
The following personnel would be utilized for this op-
eration:
Description
Dozer operator
Scraper operator (as a fill-in one of the
operators will work as needed as a laborer
or check station attendant, or cover during
vacation periods)
Total
Quantity
1
Operational Procedures
Site preparation should consist of the following proce-
dures:
1. The area to be filled in the next 6 months should
be cleared using the dozer and the debris disposed
of on-site by burial and or producing wood chips.
The scraper should excavate trenches to prescribed
154
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dimensions and stockpile the excavated material
along the long sides of the excavated trench.
2. Trench excavation should be completed for each
trench before sludge filling has been initiated at the
preceding trench.
3. Excavation of trenches should proceed in each row
starting farthest away from the gate and proceeding
toward it.
4. Two trenches should be excavated near the en-
trance to the site for use during inclement weather.
Sludge unloading should consist of the following
procedures:
1. Haul vehicles should stop at the check station upon
entry to the site to register and to receive dumping
instructions if the attendant is not at the working
area.
2. The haul vehicles should then proceed toward the
designated trench, enter the trench at the ramp
from the short side, and dump the sludge at the far
end in 4 ft high piles, as shown in figure 10-27.
COVER SOIL
STOCKPILE
BULLDOZER
COVERING SLUDGE
T
100'
-- — *
X
3GE T
<
Bt^V
UNCOVERED
1 1
if
DUMP TRUCK
ACCESS RAMP
/ t
s
^ ' fifi'
\ &,
*)
^Vyv//:':'
1
}
y
:•;•!
.*.'.
::::':X;COVERED :x::;
:•.;:.•;: SLUDGE :::v:
n-je=
600'
X
t
-im'
i
F
PLAN
COVER SOIL
STOCKPILE
SOIL COVER
Figure 10-27.—Trench cross-section.
Sludge covering should consist of the following proce-
dures:
1. At the end of each day, the bulldozer applies cover
material from both sides of the trench over the
sludge in a 5 ft thick application to 2 ft above
grade.
2. End-of-the-day cover application should be ade-
quate for odor control due to the stabilized nature
of the sludge and the wooded buffers separating fill
areas from residences. However, periodic applica-
tion of cover several times during the day may be
required if odor can be detected off-site.
3. Approximately one month after the completion of
each trench, bulldozers should regrade completed
fill areas to account for settlement and periodically
thereafter if required.
4. The completed covered fill and adjoining areas
where soil had been stockpiled should be sealed
with grass after final cover regrading (1 month after
completing the fill assuming weather conditions per-
mit; e.g., during the three months of colder weather
planting will not be effective).
REFERENCES
1. Proposed Classification Criteria for Solid Waste Disposal Facilities,
U.S. Environmental Protection Agency. Federal Register, February
6, 1978, Part II.
2. Draft Environmental Impact Statement, Appendices, Proposed Reg-
ulation, Criteria for Classification of Solid Waste Disposal Facilities.
Office of Solid Waste, U.S. Environmental Protection Agency. April
1978.
3. Portland Cement Association. PGA Soil Primer. Portland Cement
Association, Chicago, IL. 1962.
4. Sanitary Landfill Design and Operation. D. R. Brunner and D. J.
Keller. EPA Report No. SW-6545. 1972.
5. Principles and Design Criteria for Sewage Sludge Application on
Land. L. E. Sommers, R. C. Fehrmann, H. L. Selznick, and C. E.
Pound. Sludge Treatment and Disposal. U.S. Environmental
Protection Agency Technology Transfer. (Chapter 9, Volume 2, p. 57.)
6. Transport of Sewage Sludge. Clean Water Consultants, Inc. U.S.
Environmental Protection Agency, 600/2-76-286. Cincinnati, Ohio.
February 1976.
7. Costs of Wastewater Treatment by Land Application. Pound, C.
E., R. W. Crites, and D. A. Griffes. Technical Report. U.S. Envi-
ronmental Protection Agency. Washington, D.C. EPA-430/9-75-003.
June 1975.
8. Sludge Processing and Disposal. A-State-of-the-Art Review. Re-
gional Wastewater Solids Management Program. Los An-
geles/Orange County Metropolitan Area. April 1977.
9. The Agricultural Economics of Sludge Fertilization. Spray Waste,
Inc. East Bay Municipal Utility District Soil Enrichment Study. Dav-
is, California. 1974.
10. Green Guide, Volume I, The Handbook of New and Used Con-
struction Equipment Values. Equipment Guide Book Company.
1977.
11. Rental Rate Blue Book for Construction Equipment. Equipment
Guide Book Company. 1976.
12. Building Construction Cost Data 1978. Robert Snow Means Com-
pany, Inc. 1978.
w U. S. GOVERNMENT PRINTING OFFICE: 1978-760-565/7 Region No. 5-11
155
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