EVALUATION OF A
LEACHATE COLLECTION AND TREATMENT
FACILITY IN ENFIELD, CONNECTICUT
Contract No. 68-01-4438
Task #6
FINAL TASK ASSIGNMENT REPORT
SMC-MARTIN
Engineering & Geotechnical
Consultants
61 East Oakland Street
Doylestown, Pennsylvania 18901
(215) 348-7730
A Subsidiary of Science Management Corporation
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EVALUATION OF A
LEACHATE COLLECTION AND TREATMENT
FACILITY IN ENFIELD, CONNECTICUT
Contract No. 68-01-4438
Task #6
FINAL TASK ASSIGNMENT REPORT
Submitted To:
U. S. ENVIRONMENTAL PROTECTION AGENCY
Office of Water and Hazardous Materials
Washington, D.C. 20460
C. W. Rhyne (WH-564)
Project Office
Prepared By:
SMC-MARTIN, INC.
61 East Oakland Avenue
Doylestown, Pennsylvania 18901
May 1981
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FOREWORD
(By Program Director)
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ABSTRACT
Leachate generated from the Enfield, Connecticut
landfill was highly variable in terms of quantity and
quality, with both being affected by rainfall. General
improvements in the quality of the raw leachate with time
were noted.
Based on bench scale research on anaerobic treatment of
raw leachate, a Pilot Plant Facility was designed, constructed
and operated. The facility performed its intended functions
of improving the quality of leachate passing through, producing
methane gas, and allowing for examination of a full size
plant.
A number of problems were encountered during construction
and operation of the plant. Most problems of a technical
nature were eventually remedied. The raw leachate strengths
encountered, however, were only a fraction of those anticipated,
producing a low treatment/cost efficiency. The anaerobic
process proved to be almost totally self sustaining and
exhibited maximum effectiveness when treating highly
biodegradable leachate. Overall, however, the Pilot Plant
did not consistently reach removal efficiency levels
exhibited by bench scale systems.
11
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CONTENTS
Forward i
Abstract ii
List of Figures iv
List of Tables v
Acknowledgement vi
Section I Introduction'. 1
II Research and Development
Background 4
III Site Conditions and Hydrology.. 7
IV Pilot Plant Design 16
V Pilot Plant Construction 30
VI Pilot Plant Startup 33
VII Equipment Evaluation 38
VIII Process Evaluation 50
IX Economic Evaluation 76
X Recommendations 82
References 89
Appendices 91
111
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FIGURES
Number Page
I Location Map, Enfield, CT 2
I A Location of Original Leachate Collection
Wells at the Town of Enfield Landfill 3
II Completely Mixed Anaerobic Filter 6
•
III East-West cross-section, Enfield Landfill,
showing groundwater flow directions 14
III A Water Table Contours, Enfield Landfill 15
IV A Systems Facilities Flow Diagram 23
IV B Leachate Storage Tank - Plan & Section 24
IV C Treatment Plant Site Plan 25
IV D Anaerobic Reactor Vessel Plan 26
IV E Anaerobic Reactor Vessel Section 27
IV F Leachate Storage Tank, .Overflow Piping. 28
IV G System Facilities Plan 29
VI Underdrain Trench, PVC Drain Option 36
VI A New PVC Well and Drain System. 37
VII Well No. 4 - Main Collection Well 39
VII A Filter Unit, Substitute Sampling Connections
for Two (2) Thermocouples . 40
VIII C Chemical Oxygen Demand (COD) 71
IV
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TABLES
Number
Paqe
IV
VIII
VIII A
VIII B
Relationship of Organic Loading Rate to
Influent C.O.D
17
Summary of Treatment System Performance 56
Average Characteristics of Raw Leachate 58
Proposed Relationship between COD/TOC,
BOD/COD, Absolute COD, and Age of Fill to
Expected Efficiencies of Organic Removal
from Leachate 59
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ACKNOWLEDGEMENTS
This report was prepared for the United States
Environmental Protection Agency, The Office of Solid
Waste, Washington, B.C. 20460, by SMC-MARTIN, Inc.,
Consulting Engineers, King of Prussia, PA in cooperation
with Mr. Roger J. Mullins, Public Works Director, and Mr.
Thomas G. Thompson, Superintendent, Water Pollution Control
Division (Town of Enfield, Connecticut).
We wish.to thank Foppe B. DeWalle, Dept. of Environmental
Health, University of Washington, Seattle, and Edward S. K.
Chian, Dept. of Civil Engineering, Georgia Institute of
Technology, Atlanta, for their contributions to various
sections of this report and their invaluable assistance.
Also, we would like to thank all of the many people
associated with this Demonstration Project from initial
research to final evaluation through whose efforts it
was made possible.
VI
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SECTION I
INTRODUCTION
The purpose of this report is to provide a record on
the demonstration project undertaken as a cooperative effort
by the United States Environmental Protection Agency's
Office of Solid Waste, The State of Connecticut, Department
of Environmental Protection, and the Town of Enfield,
Connecticut, Department of Public Works.
The Project culminated in the operation of a pilot
plant which collected and anaerobically treated leachate
generated within the town's sanitary landfill (Figure 1).
The purpose of the pilot plant was to allow for evaluation
of the process with a full scale facility.
The total project included research, site evaluation,
design, construction and operation of the facility.
This report includes information on all primary elements
of the project and places particular emphasis on those
areas which will be important in terms of future installations
of a like process.
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ENFIELD
LANDFILL 8
PILOT PLANT
LOCATION
LOCATION MAP
ENFIELD CONNECTICUT
Figure I
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SECTION II
RESEARCH & DEVELOPMENT BACKGROUND
Anaerobic digestion of sewage sludge is a developing
process utilized in many areas of the world to reduce the
organic content of waste matter and to produce usable quan-
tities of methane gas. Full scale application of this
process in America and Europe dates back 50 to 75 years;
however, the biology and chemis.try are just now becoming
better understood.
Considerably less is known about anaerobic digestion of
other liquid organic wastes, e.g. landfill leachate. Over
the past 15 years some research has been carried out on this
subject by J.C. Young and P.L. McCarty^; E.G. Foree and V.M.
Reid (et al)^; and more recently by F.B. DeWalle and
E.S.K. Chian under contract from the United States Environmental
Protection Agency.3/4,5
DeWalle and Chian*s work resulted in a bench scale
system to anaerobically treat raw leachate. The system
utilized an upflow, anaerobic reactor (vertical column
packed with an open plastic media) with recycle provisions
to buffer the acidic raw leachate influent without the need
for chemical addition to the process.
Laboratory experimentation of this system indicated a
potential to effectively treat high organic strength leachate
with some capabilities for removing metals.^
Resultantly, their system was then utilized as the
theoretical base from which the full scale Enfield Pilot
-------
Plant developed. A compilation of various papers presented
by DeWalle and Chian pertinent to their research is included
in Appendix A of this report.
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Figure H
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SECTION III
SITE CONDITIONS AND HYDROLOGY
Site Description
The Enfield, Connecticut, landfill is situated on the
valley walls on the east side of the Scantic River in the
Connecticut River Valley region of the state. Immediately
to the west of the landfill is the broad, swampy flood plain
of the Scantic River. The uplands to the east of the valley
wall are gently rolling, huiranocky. topography typical of
glacial morraines. The landfill has been developed in two
ravines using an area method of landfilling. The southern
ravine was developed from 1967 to 1972 and covers an area of
approximately 5 hectares (12 acres). The filling of this
ravine cut off drainage from the east and resulted in the
formation of a small pond immediately east of the access
road. Water which once flowed across the land surface now.
periodically drains through the completed southern landfill.
The present active landfill also covers an area of approx-
imately 5 hectares (12 acres) and has been developed in the
north ravine since 1972. The original northern ravine was deep-
ened and broadened by excavation of the clay material along its
upper slopes. Landfilling started at the toe of the ravine
and proceeded to fill it using the area method. The site
accepts an estimated 159 to 204 tonnes per day, six days per
week, of municipal and commercial solid waste^ Each lift
is approximately 2-1/2 to 3 m (8 to 10 ft) in height.
Excavated clay material was originally used for cover; but
cover material is now obtained from sand banks immediately
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to the north of the newer landfill site. Refuse is continually
compacted and covered at the end of each working day with 15
to 30 cm (6 in to 1 ft) of sand. The western face of the
landfill is steep and the sand cover readily erodes. Leachate
discharges from the toe of the fill and from a series of
small springs and seeps along the top of the first and
second lifts. The leachate from the new landfill flows to
the west and southwest through old meander scars in the
Scantic River flood plain. Leachate from the old landfill
flows primarily to the west and joins leachate from the new
landfill shortly before discharging into the Scantic River.
Climatology
The climate of north central Connecticut is humid and
its temperature is characterized by cool winters, warm
summers, and frequent weather changes. The weather is
influenced by cool and dry continental air in winter and
warm maritime air in the summer. Heavy precipitation and
persistent northeast winds frequently accompany coastal
storms and exceptionally heavy precipitation results when
these storms take the form of tropical hurricanes. During
the summer, the area is also subject to frequent and heavy
thunder storms. Precipitation is uniformly distributed
throughout the year, so that water is potentially avail-
able for recharge throughout the year. For the period 1921
to 1950, annual precipitation averaged slightly more than
102 cm (40 in), with about one-third in the form of snow.
8
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Annual precipitation ranged from 84 cm (33 in) in 1941 to
160 cm (63 in) in 1955.
Temperature in the area also varies considerably from
season to season. The mean.annual temperature is 10°C (50°F)
and ranges from an average monthly low of -3°C (27°F) in
January to an average monthly high of 23°C (74°F) in July.
Ground is generally frozen during the months of January and
February. The pan evaporation from May to October during the
period of 1918 to 1956 had a mean.value of 12.21 cm (4.81 in)
per month.
Soils
For the most part, the soils at the landfill site have
been removed and used for cover material. Presently its
surface is primarily comprised of glacial sands with minor
areas of glacial clay toward the landfill toe. The use of
sand as cover material and the methods of spreading and com-
paction used produce a highly-permeable final cover (greater
than 15 cm (6 in) per hour). Thus, surface run off is minor,
except during high intensity storms on steep slopes and near
the toe of the landfill.
Geology
The landfill is located on the moderately steep slopes of
the eastern valley wall of the Scantic River in the Connecticut
Valley lowland or Triassic lowland physiographic division.
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The areas to the east and to the north of the site consist -of
hummocky uplands. The area to the west of the site is the low
lying river flood plain.
The triassic lowland has a nearly flat floor.formed in
easily-eroded eastward dipping sedimentary rock of triassic
age, which in most areas is covered by thick unconsolidated
glacial deposits. The triassic deposition took place in a
basin which accumulated several thousand feet of sediments
under nonmarine oxidizing conditions. The triassic bedrock,
which does not crop out in the area of the landfill, has an
eastward dip for 15 degrees. The nearest outcrops consist
of reddish-brown and gray arkosic siltstone, sandstone, and
conglomerate. Between the triassic and pleistocene time,
the area was uplifted and eroded, forming a flat wide-bottom
valley. This valley was overridden by several glacial ice
sheets which deposited a significant thickness of unconsolidated
sediments. The basal sediment consists of glacial till which
is a very poorly sorted, nonstratified mixture of clay, sand,
silt, pebbles and boulders.
Varying thickness of glaciofluvial deposits occur above
the till layer, and directly beneath the landfill is a lake
deposit of thick layers of fine silts .and clays. The hills
surrounding the landfill are underlain by water-born sands,
silts and clays, with sand predominating, in the near surface
deposits. During the post-glacial period, the flood plain of
the Scantic River was covered with a veneer of alluvial deposits
of fine sand and silt.
10
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Hydrogeology Of The Landfill Site
The hydrology of the landfill site is such that rainwater
infiltration enters the ground-water flow system on the uplands
above as well as directly through the surface of the landfill,
and flows downward and laterally towards the river. Much of the
flow occurs above the layer of silts and clays which are relatively
impermeable and which lie below the landfill. A smaller amount
of water percolates through-the silts and clays and reaches the
bedrock aquifer and the tills, sands, and gravels, where they
exist. This ground water, too, flows toward and eventually dis-
charges into the Scantic River. The flow plain below the landfill
is a major ground-water discharge area, with a significant upward
vertical gradient.
For the area in general, precipitation averages slightly more
than 102 cm (40 in) per year. A wide range of stream discharges
are reported with an average of 56 cm (22 in) rainwater equiv-
alent. The average stream flow of the Scantic River is 354,650
cubic meters (93.7 million gallons) per day or the equivalent of
51 cm (20 in) of precipitation. This runoff includes both the
surface and ground-water flows of the river. The USGS estimates
that approximately 60 percent of the total runoff is ground-water
base flow. Therefore, 31 cm (12 in) of precipitation represents
base flow and 20 cm (8 in) is surface runoff. Evapotranspiration
is.the difference between the 102 cm (40 in) of rain per year
and the total runoff of 51 cm (20 in) per year, or 51 cm (20 in)
per year. The pan evaporation record from the Hartford Municipal
District totals 73.25 cm (28.84 in) per year. The pan evaporation
generally represents the maximum potential evaporation from a
11
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free water surface, while the actual evapotranspiration from a
soil surface is nearly always lower than this figure.
In order to verify that the regional hydrology was representative
of the conditions at the landfill, the precipitation onto and
runoff from the landfill were monitored during the winter and
spring of 1975-76. The instrumentation consisted of two weirs
located beyond the toe of the landfill which monitored the surface
runoff and the surfacing seepage from the basin, which included the
north landfill.
•
The landfill water budget generally agreed with the regional
pattern. For the region, half of the 102 cm (40 in) of precipitation
manifests itself as runoff, with approximately 15 cm (6 in) being
surface runoff and 31 cm (12 in) underflow. The seasonal distribution
of the runoff in the region is: 2.5 cm (1 in) of water runs off per
month in the summer and fall, 5 cm (2 in) in the winter, and 5.8 cm
(2.3 in) in the spring. Measurements at the landfill during the late
fall and early spring yielded runoff rates of 5.6 cm (2.2 in) per
month and 6.1 cm (2.4 in) per month. These estimates, although
slightly higher than those for the region, are in good general
agreement. During the period of measurement, the precipitation was
was heavier than normal and since the landfill is not vegetated,
less evapotranspiration would occur.
The leachate generation from the landfill should be equiva-
lent to the ground-water portion of the runoff, or approximately
31 cm (12 in) per- year. Leachate generation for the new landfill
would therefore be 12,300 to 14,800 cubic meters (10 to 12 acre-ft)
per year, based on 80 to 100 percent of the annual recharge from
the 8-hectare (20-acre) basin moving through the refuse.
12
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A diagrammatic flow cross section and water table map have
been developed for the landfill and are shown on Figures III and
IIIA. The shallow near surface flow comprises the bulk of water
movement in the vicinity of the landfill while some precipitation
infiltrating east of the landfill moves downward through the per-
meable sands and enters deeper flow systems. Both the shallow and
deep flow systems discharge into the Scantic River in the vicinity
of the landfill.
13
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LEACHATE
COLLECTION WELL
LACIOFLUVIAL / DEPOSITS
ALLUVIUM
LAKE CLAY
GROUNOWATER FLOW
WATER TABLE
BEDROCK
NOT DRAWN TO .SCALE
Figurelll—Generalized east-west cross-section of the Enfield, Connecticut
Landfill showing groundwater flow directions.
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SOIL BORING
• i.EACHATE COLLECTION WELL
(Subsequently re-numbered 1 through 5
SCALE : I =3331
Map of the water table contours at the Enfield, Connecticut
Landfill—October 1975.
Figure ffiA
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SECTION IV
PILOT PLANT DESIGN
Background:
In March 1975 the Environmental Protection Agency
awarded the contract to produce plans, specifications and
the necessary bid documents for an experimental pilot plant
to SMC-MARTIN, Inc. (formerly A. W. Martin Associates,
Inc.), King of Prussia, PA.
Using the process guidelines developed by Chian and
DeWalle through their bench scale studies as a base, SMC-
MARTIN, Inc. in consultation with various Federal, State and
local officials prepared a folio of nine design drawings^
along with contract documents for construction entitled "Town
of Enfield - Leachate Treatment Facilities."
The primary design criteria included:
Reactor volume — 25,500 gallons
Detention Time — 10 to 15 days desired
— hydraulic loading rate range
required, 1.8 to 1.2 gpm
— hydraulic loading rate provided,
0.25 to 5.0 gpm
— recommended normal operating rate,-
2.0 gpm
Filter media — 24' high x 12' diameter = 2228 cu ft.
Organic loading — average 0.09 to 0.20 Ibs COD/DAY/
cu ft of media, desired.
peak 0.40 Ibs COD/DAY ft of media
desired.
16
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RELATIONSHIP OF ORGANIC LOADING RATE TO INFLUENT C.O.D.
ORGANIC LOADING
HYDRAULIC LOADING RATE
GPU. AT CJOD. SHOWN
TABLE XL
Recycle Rate — range desired (recycle/influent) ,
10:1 to 20:1
@ 2 gpra influent; range desired,
20-40 gpm
range provided, 10-50 gpm
recommended normal recycle rate =
20 gpm (including influent)
Temperature — mean temperature desired, 85°F, heat
exchanger provided
*Sludge Production — 1/4 Oth of feed volume: % solids
3.8%, expected
*Gas production — 2. 71 J. gas/-? leachate
0.46J2 gas/gr COD removed
0.32^ methane/gr COD removed
*Dependent on COD
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Description of Process
Raw leachate is secured from infiltration into collection
wells. As leachate accumulates in the well, a sump pump
operated by a self-contained switch transfers the liquid to
a storage tank. The purpose of the tank is to provide a
supply of leachate during periods of prolonged dry weather
when production rate from the landfill subsides. The tank
has a storage capacity of 55,500 gallons and is equipped
*
with a high-level control switch which will halt the oper-
ation of the well pumps when the maximum liquid operating
level is reached.
The leachate transfer pump, installed in duplicate as
a standby unit, is a positive displacement mechanically
variable-speed pump. It varies the rate of raw feed into
the system. The feed rate is adjustable to any rate up to
five gallons per minute.
The raw leachate is introduced into a recycle system
which operated at a flow rate of approximately 20 gallons
per minute. For best performance the reactor must be at a
warm temperature, in the range of 85 to 95 degrees F. and
thus a heat exchanger has been incorporated in the recirculation
loop.
The heat exchanger is a tube and shell type unit with
the leachate on the tube side and hot water on the shell
side of the exchanger. Through a temperature sensor and a
controller a motorized valve regulates the flow of hot water
18
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into the heat exchanger so as to produce a desired exit
temperature of the leachate. The warmed leachate liquor
then enters the reactor through a bottom inlet distributor
and proceeds in an up-flow mode to the top of the unit
through a twenty-four (24) foot high packing of plastic
filter media.
The filter media is made of 2' x 4' modules containing
30 square feet of surface area/cu. ft. media, and 96% voids.
The media does not filter or strain the leachate as would a
sand bed, but rather it acts similar to a sewage plant
trickling filter in the respect that its principal purpose
is to provide a large amount of surface area on which bacteria
may adhere and thrive and these organisms, in turn, decompose
and purify the organic substances in the leachate.
At the top of the unit the recycle liquor is withdrawn
through another manifold and a rate equal to the raw feed
input into the system overflows weirs into an outlet launder
and to the gas release tank. Through a water sealed outlet
the treated leachate overflows into a weir box, which measures
the final effluent flow rate, and from the box the treated
water is discharged into one of six open sand beds. It was
intended that the beds will be rotated as required.
The treatment reactor unit provides anaerobic biological
decomposition of the leachate and in this respect its action
is much like the fermentation process in a sewage plant sludge
digester. Methane gas is generated, collected in the tank's
dome and the gas's pressure causes it to travel concurrently
19
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with the liquid overflow into the gas release tank. The gas
is comprised of approximately 70% methane and 30% carbon
dioxide.
When gas production is in excess of that required by
the system, this excess is released by a pressure regulator
to a waste gas burner. As an auxiliary fuel for start-up
and to meet the requirements during periods of extremely
cold weather, a propane supply is available.
»
Description of Facility:
Raw leachate from the Enfield landfill was originally
collected in two 18" diameter galvanized steel casing wells
sunk to depths of 17-1/2' to 18-1/2' and located at the
western edge of the site (Figure IV G). These wells were
subsequently supplemented by a new collection well system
(Figures VI & VI A). The landfill in this vicinity slopes
from east to west and the wells are situated at the lowest
point in the first lift of refuse. (Approximate surface
elevation 74 ft.). The wells were fitted with 1/2 hp
submersible pumps, associated float switches, check valves
and electrical gear. Leachate was pumped from the wells
to a 50,500 gallon precast circular concrete storage tank
located several hundred feet north of the wells at approxi-
mate elevation 70 ft. (Figure IV B). The storage tank was
equipped with a float switch which cut out the well pumps
when the tank was full. Low level switches cut out the
feed pumps and actuated a visual alarm system. The tank
20
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itself had a cast in place concrete bottom and top with
precast, segmented walls. Two access hatches were located
in the top and a trapped vent-overflow system installed at
the "high water" level (Figure IV F). Additionally, the tank
%
was provided with a sump near the point of withdrawal and a
drain line to allow for removal of settlable solids.
A small precast concrete pump house was located next to
the storage tank and contained two leachate feed pumps (3/4
hp positive displacement pumps rated at .5 to 5 gpm) with
variable speed drives, a flowmeter and electrical gear. The
leachate feed pumps transfered the liquid from the storage
tank some 700 ft. north (vertical lift approximately 125 ft.)
to the treatment plant site (Figure IV C). Leachate piping
from the wells to the plant was buried polyvinylchloride (PVC).
Electrical conductors enclosed in PVC conduit were buried
in the same trench. The treatment plant itself consisted of
a concrete block building (13'x20'); a 25,500 gallon "anaerobic
filter" vessel; 6 effluent sandfilter beds, plus associated
mechanical and electrical gear. The "anaerobic reactor"
was fabricated of steel and measured 12 ft. in diameter by
approximately 35 ft. high with a shallow conical steel
top (Figure IV E). It was set on a circular concrete base,
the inside of which was conical in shape. The internal
conical concrete base section .forms a hopper in which sludge
generated from the process is collected. A withdrawal pipe and
shut off valve were installed to facilitate the removal of
21
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the sludge. The exterior of the vessel was entirely
insulated and the inside contained a proprietary plastic
media set on a steel grate above the base and extending
upward for 24 ft. (Figures IV D & IV E).
Raw leachate was fed into the bottom of the tank
through a header arrangement (Figure IV E), and as it flowed
upward through the media it was acted upon by anaerobic
bacteria (which produce methane and carbon dioxide gas).
Approximately 700 cubic feet at, the top of the vessel acts
as gas storage volume. The liquid contents of the vessel
are recycled from top to bottom (one "turnover"per 24 hrs.)
via 1-1/2 HP recycle pumps. Treated effluent overflows
into a launder (Figure IV E) arrangement several feet below
the top of the tank and was piped to a gas release tank
located in a separate, sealed off, room in the building
(liquid effluent and gas exit the vessel through the same
pipe lines). The entire gas system as installed was provided
with relief valves, pressure regulators and flame arresters
in appropriate locations. Liquid effluent from the gas
release tank was conveyed through a flow measuring device
and then via PVC piping to one of the sand filter beds.
Gas was vented through a flare or used to operate a gas
fired heater. Propane gas supplied from a 500 gallon buried
tank furished fuel for pilots on both flare and boiler.
The heating system allowed for maintaining the contents of
the anaerobic filter at a set temperature as well as providing
building heat.
22
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FLAK**
RAW LRACHATS.
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FIGURE NO.UTS - Leachate Storage Tank - Plan & Section
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FIGURE NO.BTO - Anaerobic Reactor Vessel Plan
26
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12-O" 01 A.
P5KFOKATED P/PS
OVER PLOW %
REATED LBACHATE
6 AS TO 64S
KS LEASE TANK.—
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STEEL TANK
9TEBL
SUPPORT
SKATING
PVC MEDIA
MODULE9
INLET
PIPING
9LV0&E REMOVAL
SECTION
NOT TO SC4LC
FIGURE NO.HE - Anaerobic Reactor Vessel Section
27
-------
Jccurc/y
Oi/crf/ow
f/// trap w/'M an^f- freeze
(By 0wncr)
,
(3.5O"O.O.)
3 '#c turn
3/4' P/ug
4' /.D. CJ.Dra/n
Storage Tank
S.T.B. 8-/2-7S
SECTION VIEW
N.T. S.
FIGURE 1ST F
\ COM/V. - LEACH ATE STORAGE TAUK
Overf/ow P/ping
28
-------
LlACHATg
STOK4SB
TANK-
/ /:
LI4CH4T8
COLL tCTI ON
WBLLS
1/0
POLY8THYLINK PIP*
3 AN IT A *Y LANDFILL
100'
-------
SECTION V
PILOT PLANT CONSTRUCTION
Construction of the pilot plant was broken into three
separate contracts^with bids received mid-February,
1976, after public advertisement the previous month. The
main contract for pilot plant construction (collection,
transmission, facilities and site work) was awarded to Fred
Brunoli & Sons, Inc., Avon, Conn. Two large dollar-value
hardware items were bid separately, those being the plastic
media (supplied by B. F. Goodrich), and the large steel
anaerobic reactor (fabricated by Alfred B. King Co., New
Haven, Conn.)
Drawings and component specifications were submitted by
the contractors to the engineer for review and approval.
Construction activities began in the spring of 1976, and
proceeded in a relatively routine manner with the engineer
making periodic inspections and reports on the progress at
the site. By October 22nd, 1976 the work was 95% complete
and checkout of the various facilities and subsystems was
underway.
As testing procedures continued substantial problems
arose with three of the system's major components. The
first problem to develop concerned leaking seams in the
walls of the prefabricated concrete leachate storage tank..
Resultantly the tank had to be filled and drained twice
before the leaks were finally eliminated by coating the
inside of the tank with epoxy sealant.
30
-------
Shortly thereafter as testing progressed throughout the
system, leakage became apparent from the anaerobic reactor.
A considerable amount of time and effort was required to
resolve this situation due to the number of interests involved
and the uncertain origin of the leaks, in that the tank was
covered with insulating panels. Eventually it was determined
that the problem was from nail holes, caused by the insulation
installer in the conical roof, near the point of its attachment
to the side walls. It then became necessary to remove the
roofing material and roof insulation to implement repairs.
Perhaps the most serious problem to arise, and the one
requiring the most time to resolve, involved random shutdown
and difficulty in restarting the gas-fired boiler. On
several occasions during the winter of 1976-77 the boiler
frequently malfunctioned and was off long enough to allow
the water in the heating system pipes to freeze and thereby
rupture. Each time this occurred it was necessary to isolate
the heating system, restart the boiler, thaw the frozen
pipes and make repairs to those sections which were ruptured.
This problem required nearly a full year of testing, design
reviews, meetings and investigations by an independent
consultant.7 It was finally determined that the boiler and
burner may be incompatible. Unfortunately, the matter could
not be satisfactorily resolved with either manufacturer,
requiring the engineers to select replacement equipment of a .
different design. The new equipment was then purchased,
installed and tested, with more favorable results.
31
-------
The resolution of these and other minor problems
incurred during construction extended into the spring of
1978, at which time the pilot plant was ready for startup.
32
-------
SECTION VI
PILOT PLANT STARTUP
Startup of the leachate treatment plant had been
scheduled a number of times over a period of approximately
one year beginning in the Spring of 1977 and continuing into
the spring of 1978. However, various construction and/or
equipment related problems forced repeated cancellation of
anticipated starting dates.
Following resolution of these problems, the pumping of
raw leachate to the storage tank finally began during the
first week of April 1978. Within the first few days, it
became apparent that the quantity of leachate being pumped
from the wells was much less than the yield encountered
during the initial checkout of the subsystem approximately
one year before. Investigation into the collection well's
low output indicated that silt mixed with organic material
was infiltrating the wells and burying the pumps. However,
since sufficient leachate was being collected to allow for
plant startup at a reduced hydraulic load rate, the date of
April 17 was set.
Approximately 24,000 gallons of the river water previously
used to check out the system had been maintained in the
filter vessel and was brought to a temperature of 77°F.
(25°C.) several weeks before startup. Dissolved oxygen
tests were frequently run to assure that anaerobic conditions
existed within the vessel. Arrangements had previously
33
-------
been made with the Poquonock, Conn. Water Pollution Control
Facility to obtain 1,000 gallons of sewage sludge digester
supernatant to act as "seed" material. On April 17, 1978
this material was picked up and transported via tanker truck
to the leachate treatment plant whereupon the supernatant
was transferred to the bottom section of the anaerobic
reactor. One raw leachate feed pump was put on line and the
flow rate set at the minimum rate obtainable (approximately
0.25 gpm) . The recycle rate wa.s set at 18 gpm.
The procedures and schedules which had previously been
developed for daily monitoring of the plant were immediately
put into effect. A minimum of four hours per day were
devoted to sample and data collection, testing and servicing
of equipment. An additional four hours per day, five days
per week, were spent on laboratory work.
Chian and DeWalle's paper, "Operation of an Anaerobic
Filter"^ provided the basis for process startup procedures
and data collection. The operations manual, "Anaerobic
Sludge Digestion" (EPA 430/976001) proved to be an excellent
practical guide to plant operation.
Following several weeks of process operation with no
signs of gas production, it was decided to increase the
operating temperature to 86°F. in order to increase biological
activity. Gas production began shortly thereafter (38 days
after startup). However, because of operating at the reduced
flow rate, it was not of sufficient quantity to operate the
boiler.
34
-------
Attempts to increase leachate supply throughout the
spring were unsuccessful, and by mid-1978 it became obvious
that a new collection system would be required.
The pilot plant was temporarily run at a reduced feed
rate from the storage tank while the design and construction
of a new well and collection system were under way. The new
system, called a "curtain drain" intercepted leachate both
horizontally and vertically, and performed well producing
between 2 and 5 gpm (depending upon rainfall).8
The plant ran at the 2 gpm normal operating rate during
January of 1979 until a frozen line on February 9th necessitated
backing down to a reduced rate once more. The line became
operable by the first week of March, 1979 when they resumed
pumping raw leachate to the storage tank.
35
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FIGURE "21
;BACKFILL HlTH SANK RUN
GRAVEL UHLESS OTHERWISE
HOTED
UNDISTURBED
MATERIAL-
SECTION A-A
3/8" DIAM.
SCREENED GRAVEL
UHDERDRAIH P!PE-
6" SCH. 120 PVC
PERFORATED HlTH
3/8" DIAM. HOLES
AS SHOW BELOW.
PAYMEHT LIMITS FOR EXCAVATION
BELOW NORMAL
UNSUITABLE MATERIAL TO BE
REMOVED TO THE LIMITS AS
DIRECTED BY THE ENGINEER.
BACKFILL WITH BAHK RUN
GRAVEL
6-IN.. SCHEDULE 120
PVC PIPE-PERFORATION DETAILS
NOTES:
1. JOINTING METHODS ARE TO BE APPROVED 8* THE ENGINEER
PRIOR TO CONSTRUCTION.
2. ALL CONSTRUCTION DETAILS NOT SHOHH ARE TO SE AS
SHOWN ON THE CONTRACT DRAWINGS.
UNDERDRAIN TRENCH
PVC DRAIN OPTION
NO SCALE
M ETC A LF » E OO 1
-------
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W£LL L.C. 4 ro &£
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APPKOX. CX/STT
GttOUfJO £L. 74.O
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DETAILS TO &£ APPROVED
BY ffi/GM€£f? PKIOZ TO CONSTRUCTION.
r—,?'.cr
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b'inf
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c
3)
m
-------
SECTION VII
EQUIPMENT EVALUATION
COLLECTION WELL PUMPS - Except for malfunctions caused by silting
:in the original collection wells, the well pumps performed their
intended function without any failures and required only routine
maintenance. One small problem noted, was that the pumps were
suspended by a wire rope and were fitted with flexible plastic
discharge pipe, which allowed for pump motion and consequently
the float switch occasionally hung up against the inside of the
collection well.
TRANSFER PUMPS - The transfer (feed) pumps were positive dis-
placement progressive cavity types powered by 3/4 h.p. mechanical
variable speed drives. Although performing well, it was noted
that the motors were fully loaded at a pumping rate of 2 gpm
rather than the specified 5 gpm. This discrepancy has yet to
be resolved. Aside from cases of dry pump operation which led
to internal damage, they required only routine maintenance.
RECYCLE PUMPS - The recycle pumps were centrifugal types directly
driven by 1-1/2 h.p., 1750 rpm motors. The pumps performed well
over the entire range of operation and required only routine
maintenance.
GAS-FIRED BOILER/BURNER - The original boiler and gas-fired
burner were adequately sized for the installation. However,
it was determined that flame characteristics of the burner in
the combustion chamber of the boiler produced soot in sufficient
quantities to cause burner controller malfunctions which would
38
-------
FtNCt
9V6Mt*9tM PUMP ^
seer ION 4
HOT TO 9C4LI
-------
c Secf/eroraunc/
C/obe fofrc
C/0Sff fo Tan* as
Jnju/cr//'on fo be p face of on
a// exfcr/or
1/4' P/QS//C
SECTION VIEW
. r. s.
FIGURE ZZA
• F/L
S.T.S, S-/2-76
4-22-St
Connec//ons
for Two (2)
40
-------
randomly shut the burner down. The second boiler/burner
combination was also adequately sized and performed very well,
requiring only routine maintenance.
CHEMICAL FEED SYSTEM - The chemical feed system was a small
package system and consisted of a tank with mixer and a
diaphragm metering pump. The system functioned satisfactorily
during the initial system check, but was never used in operation
as chemical additives to the process were not required.
•
PIPING AND APPURTENANCES - All the piping was found to be suitable
in terms of material; however, winter freeze-ups to the piping
buried between the collection wells and raw leachate storage
tank, and the baseboard heating pipes in the treatment facility
building were frequently encountered. The first problem stemmed
mostly from the fact that the well pumps discharged intermittently
(due to low leachate supply) and the outlet inside the storage
tank was exposed to sub-freezing air temperatures, in that it
terminated above high water level. Provisions to drain the riser
portion of these pipes could help solve this problem.
The freeze-ups to the baseboard heating pipes resulted
from a combination of the original boiler shutdowns, and the fact
that the baseboard could experience below freezing temperatures
while temperatures at higher levels in the room were actually
above the thermostat setting. Two factors which contributed to
this condition were that the concrete block building was un-
insulated with the baseboard radiator mounted directly against
the blocks at or near floor level, and that the uninsulated
process piping and heat exchanger provided enough heat in the
41
-------
building to keep temperatures at higher levels above the
thermostat setting, thereby necessitating only infrequent hot
water circulation through the baseboards.
The effluent pipeline between the weir box and sand filter
distribution box periodically plugged with a precipitate (thought
to be iron oxide). Cleanouts and/or access points in this line
could help alleviate this problem in future installations.
The gas pipeline between the building and waste gas burner
»
was improperly installed and trapped condensation (there was
apparently an improper pitch or dip at some point} which
necessitated the release of somewhat large volumes of gas from
time to time to blow out the line.
Two liquid flow meters were provided; one to measure the
raw leachate feed rate to the process and the other to measure
the recycle flow (it actually measured recycle plus feed).
Aside from occasional disassembling for cleaning, the leachate
feed flow meter performed well. The recycle flow meter however
was calibrated in increments of 2 gpm which made the necessary
precision possible, but difficult. Additionally, the upstream
piping to the meter had to be altered to provide as long as a
straight run of pipe as was possible in that unstable operation
prevented accurate readings in the early stages of plant
operation.
A gas pressure regulating device, the smallest commercially
available, proved to be unsuitable, as it was too large for the
quantity of gas produced and would not regulate the pressure.
42
-------
An attempt was made to locate a smaller valve, however, 10
or 12 different manufacturers indicated that they did not
make such a device. Since the pressure regulating valve was
essential to proper operation of the plant, the original valve
was modified by installing a smaller orifice and a needle
valve oh the stem. The modification worked reasonably well
and service to this regulator consisted of replacing only one
diaphragm.
The gas release tank which was manufactured to the engineer's
design worked well as a liquid/gas separator.
The original gas meter worked well except its installation
allowed for moisture collection from the gas which eventually.
led to its failure. A new meter was purchased and installed
with a modification of adding electrical tracing tape to its
influent pipe to prevent condensation. This solution was effective,
however, future designs may consider a drain trap or before the
meter as added protection. The only other problems noted were
related to reading the meter during periods of low gas production
(less than 100 cu. ft. per day!, in that the original meter
(calibrated in lOOcu. ft. intervals) was sized for design gas
production levels which never occurred due to low organic loadings.
HEAT EXCHANGER - The heat exchanger was a shell and tube type
and was suitable in all respects.
FILTER MEDIA - The plastic filter media along with the influent
distribution system, through test results discussed later in this
report, were indicated as haying effectively prevented short-
circuiting of leachate within the reactor.
43
-------
The media also appeared to provide an adequate surface
area for biological growth, and no "clogging" signs were ap-
parent (realizing, however, that loading rates were low and
-therefore, fewer microorganisms developed).
When the reactor is ultimately drained and its interior
inspected physically, a more detailed evaluation of the media's
performance will be possible.
COLLECTION WELLS - The five original 24" diameter leachate
•^^™^^^^^^^™^~™ »
collection wells were drilled during August 1975 in the first
lift of the landfill (see Fig. IB and 4). They were originally
numbered 26, 28, 29, 30 and 33 from north to south in the
boring lot-1-0 and subsequently renumbered 1-5. Galvanized
pipe (18" dia.) was placed in the wells. The lower 71 of the
pipe was slotted and gravel packing was placed between the pipe
and the solid waste. These wells eventually proved unsuitable.
because silt mixed with organic material continually infiltrated
the wells and buried the well pumps. All attempts at cleaning
the wells and/or raising the pumps were effective for no more
than two or three days immediately following such action. In-
sufficient leachate supply made plant operation at or near
design feed rates impossible.
By mid-1978, after repeated unsuccessful attempts to remedy
the situation, specifications and drawings for a new modified,
leachate collective system were developed. The design (Fig VI & VI A)
consisted of a well and approximately 100' of perforated underdrain.
44
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with stone and sand in such a manner as to intercept leachate
both horizontally.and vertically (a so-called "curtain drain").
The project was advertised and bid in mid-November 1978. The
-job was awarded to Baier Construction Company, Hartford, Conn.,
and construction was completed by late December 1978. The new
collection system performed well supplying between 2 and 5 gpm
(depending on rainfall) up until mid-July 1979. A month-long
drought then caused a reduction in output to approximately 1 gpm,
»
which continued throughout the summer of 1979, improving
temporarily after each rainfall.
STORAGE TANK - A vertical 50,500 gallon raw leachate storage
was constructed by Terry Hill Concrete Products, Terry Hill,
Pennsylvania and was made up of both precast concrete vertical
panels and cast-in-place concrete base. The overall tank
measured approximately 30' in diameter by 12* deep.
The original concept for leachate storage envisioned a
clay-lined lagoon; however, local officials objected to the
possibility of serious odor problems. The enclosed concrete
storage tank was very successful in eliminating this problem.
The main reason for the relatively large storage volume
was to have a steady supply of leachate during dry conditions.
The tank was successful in this respect.
Another reason was to smooth out large fluctuations in
ileachate strength (e.g. COD). The data for the storage tank
indicates a 228% variance between the low and high readings
of COD concentration (low 1120 mg/1, high 2550 mg/1). Other
leachate components exhibited similar fluctuations. At first
45
-------
glance it appears that the 50,500 gallon storage tank did
not provide the "damping" effect that it was designed for.
Before reaching conclusions in this regard it should be noted
that because of lower-than-expected leachate supply/ the storage
tank was not always filled to its design capacity. Therefore,
changes to the quality of the raw leachate entering the storage
tank would show a more pronounced effect on the overall con-
centration in the tank. In addition, the low and high figures
t
are .both within the values normally considered as low strength
when considering the broad range of values commonly found in
landfills. In order to adequately determine whether mechanical
mixing within the tank is necessary, additional testing would
be required with the tank maintaining a constantly nearly-full
volume with leachate strengths of higher concentrations to more
adequately compare the differences. The data from this 'run1
exclusively however, it appears mixing would be advantageous.
During the winter months, with most of the tank above
ground and its contents exposed to extremes in temperature, ice
would form inside to the extent that it was necessary to drain
the tank to prevent structural damage (this also meant shutting
down the process). Future designs might incorporate a buried
tank and/or installation to help alleviate this problem. Ad-
ditionally, this would maintain the raw leachate in storage
and at higher temperature such that less energy would be needed
to raise it to that required for the process.
SAND FILTER BEDS - The six sand filter beds were concrete block
construction on poured concrete footings. The walls were mostly
46
-------
below grade. These beds were adequate from a structural
standpoint and no problems arose concerning their infiltration
capacity.
ANAEROBIC REACTOR The anaerobic reactor tank was fonnd to
V
be adequate in all structural respects once the construction-
related problems were resolved. Still to be determined, pending
final inspection, is the extent of internal corrosion (if any)
and the possible need for internal coating. The plexiglass
observation window originally installed proved to be unusable
due to internal condensation and was eventually replaced with
a steel plate. A ladder on the side of the tower was eliminated
from the original design for fear of attracting "climbers".
Originally, samples were taken from the upper taps via a long
extension ladder, however this proved awkward and difficult.
Subsequently, these taps were extended to ground level. However,
two new problems were created; wintertime freeze-ups and the
need to completely flush the lines each time before samples could
be collected (see Fig. VII A). Future designs should give
consideration to these problems.
TEMPERATURE CONTROLLER - The process temperature controller
system consisted of three primary elements:
1. A thermal couple located in the process line just
downstream from the heat exchanger.
2. A positioned proportioning controller.
3. An electric motor actuated valve located in
the hot water return line between heat exchanger
and the boiler.
47
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The system functioned well until approximately two years
after initial startup, at which time a limit switch on the motor
actuated valve failed. This situation was remedied by a "factory"
service representative shortly thereafter. Minor leakage around
the valve stem was noted, but it was not serious enough to warrant
shutting down the boiler to make repairs.
A seasonal problem was encountered in regard to maintaining
a set temperature. This problem was most pronounced during the
summer months when the process temperature kept increasing in
spite of the fact that the motor actuated valve was closed. It
became necessary on many occasions to shut the boiler down in
an effort to limit system temperature. The cause of this problem
appeared to be heat transfer between the hot water in the boiler
system and the heat exchanger (via the piping and the water in
it). More specifically, the process fluid and heat exchanger
were always about 90°F. cooler than the boiler water temperature
and created a heat sink. Future designs should include longer
and/or thermally non-conductive pipe lengths between these
components to help avoid this problem.
ELECTRICAL SWITCH GEAR - All the electrical switch gear,
motor starters and boxes were properly sized and installed,
and functioned without problems. One minor wiring change was
made after the plant was in operation when it was discovered
that the recycle pumps did not restart automatically after a
power failure. Future designs should include these provisions
in all switch components in facilities which are not attended
24 hours per day.
48
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EQUIPMENT LIST
Collection Well Pumps. ENPO-CORNELL, Model 150M, 460v/3ph/60Hz,
Leachate Feed Pumps. Robbins & Myers Frame 2L3 MOYNO with
3/4 HP Reliance variable speed drive, 460v/3ph/60Hz.
*
Boiler.
A. Original. New Yorker steel boiler with Adams burner
and Honeywell controls. ' '. ' .:
B. Final. Hydrotherm Model MR-420. . -
Recycle Pumps. Goulds Pumps Inc./ Model 3196S.
• • ••••.- . " •-•»'•••• • -
Gas Meter. American Meter Division, Model AL-425. ,
Chemical Feed System. Barclay Chemical Co., mix tank & mixer.
Neptune Chemical Co., Pump Model 510-S-N3. . • '...
Liquid Flow Meters.
A. Leachate Feed. Brooks Instrument Division, Model 3602.
B. Recycle. Brooks Instrument Division, Model 3604 - 2 inch.
Gas Pressure Regulator. VAREC, Inc., Fig. 386 - 2 inchi
Flame Arresters. VAREC, Inc., 2 inch size.
Pressure & Vacuum Relief Valve. VAREC, Inc., Fig. 481, 3 inch.
Drip Trap and Waste Gas Burner. VAREC, Inc., Fig. 246 and
Fig. 238 respectively.
Heat Exchanger. Patterson-Kelley Co., Dwg. 3475-4MP.
Gas Release Tank. Manufactured by Patterson-Kelley Co.
Electrical Switch Gear, Motor Starters and Boxes. Square D Co.
Lighting & Miscellaneous Gear. Harvey Hubbell Inc.
Temperature Controller System. Honeywell, Inc.
Temperature Indicators. Honeywell, Inc.
49
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SECTION VIII
PROCESS EVALUATION
PROCESS GOALS
The bench scale studies performed by Chian & DeWalle
indicated the potential for effective treatment of high strength
landfill leachate utilizing an anaerobic reactor. They noted
much variation in effluent quality and removal efficiencies
relative to the character of the raw leachate treated, with
highly biodegradable samples producing the most favorable results.
It was concluded that when treating leachate collected from
directly within the Enfield landfill (initial COD, 32,000 mg/1),
the anaerobic reactor under optimum operating conditions could
remove as much as 90% of the COD and fatty acids. The removals
of -iron and other heavy metals were expected to be in a similar
range.
Their work with leachate collected from the toe of the
landfill (11,628 mg/1, COD) resulted in an average removal of
only slightly over 50%. However, the investigators believed
that heavy metals toxicity was experienced during this labora-
tory run, and predicted approximately 80% COD removal under
optimum treatment conditions. Suspended solids for this
leachate were reduced by an average of 70%, reaching a high
of 88%. Total iron removal was 64%. A large part of the iron
was found to be present in suspension, as analytical data on
filtered samples showed as much as a 99% difference between
influent and effluent concentrations. It was presumed that
50
-------
total iron removals in the pilot plant could reach 97% under
the assumption that suspended solids and the attending iron
would effectively precipitate in the lower portion of the
reactor unit and settle as sludge. Other heavy metal removals
were found to be generally satisfactory. Gas production
during these studies averaged 7400 cubic feet gas per 1000
pound COD removed by the process. The decrease in organic
removal efficiency encountered with the leachate from the
toe of the landfill, results from considerable degradation
which occurs during the raw leachate's travel through the
landfill, leaving a higher presence of nonbiodegradable
refractory organics which are not affected by biological
treatment.
The State of Connecticut, Department of Environmental
Protection upon reviewing the results of these studies and
the final pilot plant design and construction issued a
permit to discharge an average daily flow of 7,200 gallons
to the groundwaters in the watershed of the Scantic River
(via a seepage bed). A summary of the desired effluent
quality from the experimental plant is provided below:
*Average Daily *Maximum Daily *Average Daily
Parameter Quantity Quantity Concentration
C.O.D. 60.0 Ibs/day 210.0 Ibs/day 1000 mg/1
Suspended Solids 3.6 Ibs/day 6.0 Ibs/day 60 mg/1
Iron-(total) 2.4 Ibs/day 15.0 Ibs/day 40 mg/1
*Based on expected 90% treatment of influent (raw leachate).
51
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EVALUATION PERIOD
The time period selected for process evaluation by
the operators and the Environmental Protection Agency
extended for 107 days, between March 6, 1979 and June 20,
1979. This interval was chosen on the basis that it represents
the closest simulation by the Enfield plant to the operational
parameters derived through the bench scale models achieved
during any portion of the 'run'.
The system had been operating since February 9, 1979 at a
reduced flow rate (0.25-0.5 gpm), and possessed a suitable
environment and sufficient anaerobic microbial growth for
evaluative monitoring purposes. Efforts to increase leachate
supply the previous winter (via a new underdrain collection
system) resulted.in a hydraulic availability of 2-5 gpm, and
were considered successful. It was recognized, however,
that because of raw leachate strengths being only a small
fraction of those encountered during preliminary testing in
1976, as discussed later in this report, organic loading
rates would never reach design values.
Various samples and process readings were taken every
day and laboratory analyses were conducted on a seven day/week
basis. A summary of the specified tests, equipment and
procedures utilized in the monitoring can be found in Appendix B.
A graphical summary of the primary- operational parameters
throughout the evaluation period are contained in Appendix C.
52
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SUMMARY OF EVALUATIVE 'RUN1.
Operation
Throughout the evaluation period the process proved to
be almost totally self-sustaining with regard to maintaining
conditions favorable to anaerobic biological activity. The
pH value within the reactor averaged 7.1 (minimum 6.6,
maximum 7.8), thereby eliminating the need for acidic or
basic additives to the system. Although some of the data
»
relating to heavy metals were considered unreliable by the
operators, due to testing equipment malfunctions, there was
no evidence of heavy metal toxicity. Provisions had been
made to feed sulfides (sodium sulfide) to chemically precipitate
heavy metals, however, none was needed.
The ratio of volatile acids to alkalinity was regularly
monitored as an indicator of to what extent the organics in
the leachate feed were taken beyond the acid formation to
the methane formation regime by the microorganisms. DeWalle
recommended that the ratio not exceed 0.35. With the excep-
tion of one 3-day period, during which.the ratio peaked at
0.5, the process continually performed under that value.
All test results with regard to the oxidation reduction
potential (ORP), indicated an anaerobic raw leachate (average,
-166 mv) and increasing anaerobicity between the reactor
influent and effluent.
Hydraulic loading to the system was steadily increased
over the first eleven days of the 'run' from its pre-evalua-
tion reduced rate of 0.5 gpm to the recommended normal ©Derating
53
-------
rate of 2 gpm. For the remainder of the evaluation period
it was held constant at the latter value. Organic loading
rates were consistently and significantly lower than those
anticipated in the plant's design, resulting from drastic
changes in the character of the raw leachate which occurred
in the 36-month interval between initial preliminary testing
and the evaluation period. The most striking difference was
the change in COD, and is reflected in an .85% decrease (from
11,628 mg/1 to 1,697 mg/1, average). Explanations for
changes in the long-term quality of raw leachate such as
these are inherently speculative in nature. However, as
discussed in greater length later in this text, the factors
of leachate age and dilution/exhaustion are felt to be at
least partially responsible for the change. Based on the
original leachate strengths the anticipated design daily
organic loading to the system was 446 pounds per day.
During the 'run1 the maximum achieved was only 61.9 Ibs/day
(14% of design value).
The recycle flow was held constant at the recommended
normal operating rate during the entire evaluation period
(between 18 and 20 gpm, which included the 2 gpm raw feed).
This value proved effective in providing for a well-mixed
anaerobic reactor as specified by Chian and DeWalle, in that
test results taken concurrently from sampling points on the
reactor (1/3 point, 2/3 point and overflow) reflected similar
values.
54
-------
The process experienced frequent variations in day-to-day
temperatures (commonly + 3°F) as the result of temperature
controller malfunctions. On the average however, the process
temperature was held at 86°F from March 6 to May 1 and
increased for comparison purposes to 96°F from May 1 to June
20. ;
Performance
Overall, the Enfield pilot plant succeeded in providing
a leachate effluent quality which satisfied the criteria
specified in its discharge permit presented earlier on Page 51
It should be recognized however, that this success was due
in part to the low overall concentration of the raw leachate
treated during the evaluation period. Removal efficiencies
for certain components were lower than originally thought
possible through the bench scale studies. Table VIII below
summarizes the system's influent/effluent quality, overall
treatment effectiveness for the significant leachate components
and characteristics monitored during the evaluation period.
55
-------
TABLE VIII
SUMMARY OF TREATMENT SYSTEM PERFORMANCE
COD
Suspend
Total Carbon
Total 0
Volatil
PH
Component
Solids
>on
mic Carbon
icids
From 3/6/79-S/ 6/79
From 5/7/79-6/20/79
Reactor
Influent
1685.6
117.0
1135.0
882.5
1774. A
6.4*
7.4*
Reactor
Effluent
496.9
55.0
425.0
80.0
331.1
6.8
7.6
Removal
Efficiency
70. 5Z
53. OZ
65.3Z
91. OZ
81. OZ
N/A
N/A
Expected
Efficiency
801
over 70Z
—
-
80Z
N/A
N/A
223 NTU*
3.68
0.24
Turbidity 236 NTU*
Phosphate (Results considered unreliable)
Iron 21.9
Zinc (Results considered unreliable)
Nickel 0.58
Cadmium " Trace
Lead (No results)
Chromium 0.33
Copper 0.24
* All mg/1 unless otherwise noted.
Discussion on the plant's treatment performance for individual
leachate components and characteristics can be found in the analysis
portion of this report.
N/A
83.0%
58.7%
0.11
0.11
67.0%
54.0%
N/A
97%
56
-------
The gas produced by the process was seen to increase in
general proportion to organic loading. It is calculated
that on the average 29,980 cubic feet of gas was produced
for every 1,000 pounds of COD removed. The gas analysis
showed it was composed of 70% methane (CH4) and 30% carbon
dioxide (CC>2) , values commonly experienced in digestion of
sewage sludge. The gas was of a burnable quality and was
flared off on a continuous basis; however, at no time was
the gas production sufficient t,o operate the boiler because
of the low organic loading to the system.
PROCESS ANALYSIS
Raw Leachate Characteristics
Significant changes in the long term quality of the raw
leachate occurred in the 36-month interval between initial
preliminary laboratory testing and the field evaluation
period. One of the most noticeable changes involves an 85%
decrease in COD (from 11,628 mg/1 to 1,697 mg/1, average).
Table VIII A summarizes and compares the major characteristics
of the raw leachate collected during both periods.
Several factors are believed to have contributed to
these changes. The first, with respect to the decreased
organic content, involves the age of the landfill. As the
landfill grows older, considerable degradation of organics
occurs within it, resulting in lower concentrations of these
components in the leachate produced. The COD/TOC ratio has
been hypothesized by Chian & DeWalle through independent
studies "as providing a method of accessing the relative age,
57
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TABLE Ym A
AVERAGE CHARACTERISTICS OF RAW LEACHATE
ENFIELD, CONNECTICUT LANDFILL
Component
COD
Suspended Solids
Total Carbon
Total Inorganic Carbon
Total Organic Carbon
Volatile Acids
Alkalinity
During Evaluation
Period 1979
pH
From 3/6/79-5/6/79
From 5/7/79-6/20/79
ORP
Turbidity
Conductivity
Ammonia Nitrogen
Chlorides
Phosphorus
Sulfate
Sodium
Potassium
Calcium
Manganese
Iron
Zinc (Results considered unreliable)
Nickel
Cadmium
Lead (No results)
.Chromium
Copper
*A11 mg/1 unless otherwise noted
During Preliminary
Testing 1976
1697.5
108.0
1052.5
251.2
801.3
1724.3
2861.8
6.4*]
7.4*]
- 166 MV*
288 NTU*
2092 NMhos*
289.5
418
1.25
30.0
345.0
202.0
29.1
66.0
21.9
0.58
Trace
0.33
0.24
11,628
—
-
-
4,094
4,628
6.48*
-
-
12,300 MNhos*
184
-
19.2
308
779
735
- 790
277
430
16
1.2
.027
.38
1.7
5.6
58
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organic strength and anticipated treatability of raw leachate,
over time. Table VIII B below summarizes their hypothesis.
• —Proposed Relationship between COD/TCC. BOD/COO. Absolute COO..
and Age of FBI To Expected Efficiencies of Organic Removal from Leachate
Character oJ Luohan
COD/
TOC
HI
>U
ro-zs
<2.0
BOO/
COO
CO
X1S
0.1-OJ
<0.l
•
Ao.
o(
KB
C3)
You*
Medium
ISjrr-IOyrJ
OU
OlOjrrt
COO. in
minigmm
pcrlftsr
M
>IO.OtJO
XU- 10.000
-------
expected COD concentrations of only 500 to 10,000 mg/1.
Once again, both the leachate's age (approximately seven years
old) and concentration (1697.5 mg/1) are consistent with the
table above, lending support to Chian & DeWalle's hypothesis
and providing a possible explanation for the decreased organic
concentrations encountered during the evaluation period.
The concentration of inorganic components of the leachate
such as sulfates and metals, and of dissolved solids as indicated
/
by conductivity, were also seen to decrease significantly from
those originally measured. It is believed that these decreases
were mainly the result of an exhaustion of their sources, due
to constant leaching from within the landfill during the time
between the original testing and the evaluation period. In
addition, seepage patterns within the landfill may have changed
such that some of the original leachate supply sources were
no longer tributary to the facility's collection wells.
Throughout the 'run', the raw leachate quality was seen
to vary with rainfall. The rainfalls of April 1 through April 5
and from April 14 through April 17 produced short term increases
in the COD concentration of the raw leachate, while those of
March 6 and 7, and May 24 through May 26 produced decreases.
Although not studied in detail, it would appear that rainfall
can either dilute raw leachate, or strengthen it by carrying
out additional material. After the.extremely large .rainfall
from April 27 through April 29 (total over 4 inches), the data
on volatile acid concentrations showed an increase of 230%
which continued for most of the remainder of the 'run1. Sudden,
substantial changes to the raw leachate quality such as this,
60
-------
may indicate that large rainfall -events, through extended
infiltration, can reach new sources of pollutants which were
previously "untapped", and produce new or modified seepage
patterns from within the landfill.
A lag time of approximately eight (8) days on average was
noted between rainfall events and variations in storage tank
concentrations.
The quantity of raw leachate collected during the evalua-
tion period allowed for continuous process operation at the
recommended normal operating irate of 2 gpm. The quantity inter-
cepted by the collection wells at any given time was seen to be
a function of rainfall, and more specifically; surface water
infiltration and percolation through the landfill, in possible
combination with upsurging replenished groundwater supplies.
During periods of low collection well yield, the storage tank
supplemented raw leachate availability to the system.
Process Operability
Indicators—
Throughout the evaluation period the reactor's environment
was constantly sampled and tested to monitor whether any toxicity
was present and in general how favorable conditions within it
were to anaerobic biological activity. The data from these
tests indicated no long-term toxicity and the anaerobic process
proved to be almost totally self-sustaining. The indicators
chosen and monitored for these purposes are discussed below.
61
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pH—The pH value within the reactor remained within
acceptable limits throughout the entire evaluative 'run1 re-
quiring no acidic or basic additives to the system. The
average reactor pH was 7.1, with the data reflecting high and
low values of 7.8 and 6.6, respectively.
The raw leachate pH values (and subsequent values through-
out the system) fell into two distinct groupings.
During the first eight weeks of the 'run1 the pH of the raw
leachate varied between 6.2 and '6.7. This slightly acidic con-
dition prevailed throughout the process (except for the sludge)
and it was noted that operation was at the very lower limit of
pH normally associated with proper digester functioning (i.e.,
6.8 to 6.9).
Between May 4, 1979 and May 9, 1979 the raw leachate pH
gradually increased before a significant jump about May 9
from 6.7 to 7.3, which prevailed for the remainder of the evalua-
tion period. Initially it was thought that the pH meter was at
fault; however, subsequent events and significant changes in
other parameters indicated a change in the character of the raw
leachate, which was apparently produced by the extremely heavy
rains of April 27 - 29.
Oxidation - Reduction Potential (ORP)—The oxidation
reduction potential is measured with a pH meter fitted with
platinum and calomel electrodes. Negative readings reflect the
degree of the system towards reduction reactions or anaerobicity.
The raw leachate in the storage tank exhibited a long-term trend
of increasing anaerobicity (-70 mv to -240 mv). Increasing
62
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anaerobicity was indicated between the filter influent and
effluent (average influent -160 mv, average effluent -195 mv).
DeWalle states that an upper limit of -300 mv is usually de-
sirable for optimum anaerobic biological activity, in that a
heavy metal toxicity can more likely occur in a system possessing
more positive ORP values. Although the data from the evaluation
period falls outside the desired range, there was no evidence
of toxicity from heavy metals, possibly because of their low
*
influent concentrations.
Volatile Acids - Alkalinity—Two important parameters to
be measured in terms of any digester operation are the volatile
acids and alkalinity. The volatile acids are essentially a
measurement of the free fatty acids (readily biodegradable)
while alkalinity indicates the buffering capacity of the liquid.
The ratio of volatile acids to alkalinity must be maintained
within certain limits (DeWalle recommended operating under
0.35) for proper digester functioning. With the exception
of one 3-day period between May 10 and 13 during which a ratio
peak at 0.5, the process continually performed within that
range.
Both the volatile acids and alkalinity concentrations
remained relatively stable for approximately the first 57 days
of the evaluative 'run1. As previously discussed however, the
character of the raw leachate experienced a notable change some-
time shortly after the extremely large rainfall of April 27-29.
At that time the data in the storage tank shows sharp increases
in the concentrations of both components (from 1,182 to 3,260
63
-------
mg/1, and from 1,932 to 4,644 mg/1, respectively); which then
declined gradually over the balance of the 'run1. This
perturbation was evident throughout the entire system (delayed
by several days). This together with an unintentional process
temperature jump of approximately 18°F. on May 7 constituted
a process shock load, as indicated by a volatile acid/alkalinity
ratio of 0.5 in a recycle stream on May 11. The options available
for counteracting these rapid changes included: dumping the
contents of the storage tank, adding dilution water to the storage
tank, or reducing the influent feed rate. It was decided, however,
that no action would be taken in order to observe the durability
of the process. Resultantly, the system was able to withstand the
shock and returned to normal in just a few days.
Heavy Metals—Throughout the evaluative 'run1 the concentra-
tions on heavy metals throughout the system were low and no
toxicity problems were indicated. The overall level of iron in
the raw leachate was lowered by a factor of approximately 20 when
compared to the results of the initial testing in 1976 (21.9.
vs. 430.0 mg/1/-.respectively) . The data collected on zinc
presented a very confusing "picture" and are considered unre-
liable by the operators; however, they reported overall levels
in the raw leachate were very low (average of < 1 mg/1). No
data is available on lead concentrations due to testing equipment
malfunctions throughout the 'run'. When considering that lead
concentrations during the initial testing were very low 0.38
mg/1), it is assumed that similar or even lower concentrations
64
-------
were present during the evaluative 'run1. The plant's design
had incorporated a chemical feed system to precipitate heavy
metals if necessary, however with no toxicity indicated, it
was never utilized.
Loading Rates—
In order to achieve the desired theoretical detention
time of approximately 10 days for the reactor (25,500 gallon
volume) a hydraulic loading rate^of approximately 1.8 gpm
(rounded to 2 gpm) was required. The pilot plant was equipped
with feed pumps capable of providing the reactor with anywhere
from 0.25 to 5 gpm. For the first 11 days of the evaluative
'run' hydraulic loading to the system was steadily increased
from its pre-evaluation reduced rate of 0.5 gpm to the recommended
normal operating rate of 2 gpm mentioned above. For the remainder
of the 'run1 hydraulic loading was held constant at this rate.
The raw feed rate of 2 gpm theoretically translates to a
leachate detention time of approximately 8.6 days within the
reactor. This was confirmed by the monitoring of chlorides
(largely unaffected by the biological process) which showed a
"difference in dips" between the reactor influent and effluent
of approximately 9 days following the heavy rains of April 27-29.
This value corresponds very closely to the theoretical detention
time and thus indicates that both the design of the influent
distributor and filter media were effective in preventing Vshort
circuiting" of the leachate within the reactor.
The constant hydraulic rate utilized throughout the majority
of the evaluative 'run1 excludes examination of the reactor's
65
-------
response to variations in organic loadings and/or detention
times, data that could be of much value. Most data from the
first 11 days of the 'run1 (when the hydraulic loading rate
was varied) is considered of no value due to process adaptation
factors. Resultantly, further analysis of the effects of hy-
draulic loading on the process is not possible at this time.
Organic loading rates to a system during the evaluation
period due to the decreased raw leachate strength, as previously
discussed, amounted to only a fraction of the plant's capability.
The bench scale studies had indicated the anaerobic reactor was
capable of effectively treating raw leachate at design organic
loading rates in the range of 0.09-0.2 pounds COD per cubic foot
of filter media per day. With 2,228 cubic feet of media volume
provided, this translated to a design daily organic loading
range of approximately 201-446 pounds COD per day for the pilot
plant. The ability to provide this daily loading to the reactor
was a function of both the influent COD concentration and the
hydraulic loading rate. The combination of the constant 2 gpm
hydraulic loading rate and the consistently low raw leachate
strengths resulted in an average daily organic loading to the
reactor of only 41.7 pounds per day. (10 to 20% of design
value). The maximum achieved during the 'run' was only 61.9
pounds per day or 14% of the design rate.
Given the average raw leachate COD concentration throughout
the 'run' of 1,697 mg/1, the reactor, at a 5 gpm hydraulic
loading rate could have been provided with 104 pounds per day
COD. The leachate detention time at this rate would have decreased
66
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significantly from the design value; however, such a test
would have been of value to monitor the system's response to
this type of change.
Recycle rate
A recycle rate in the range of 10:1 to 20:1 (recycle to
hydraulic loading rate) was indicated through the bench
scale studies as providing for the desired well-mixed anaerobic
reactor. The pilot plant was equipped with pumps capable of
recycling anywhere from 10 gpm to 50 gpm. Using the 10:1
ratio and 2 gpm normal feed rate as a base, a recommended
normal recycle rate of 18 to 20 gpm was arrived at. The
recycle flow was held constant at this value throughout the
evaluative 'run1. This rate provided the anaerobic reator
with one volume, "turnover" per 24 hours. Similarity in
daily test results for the various locations throughout the
reactor where samples were taken (i.e. lower tap, upper tap,
recycle), indicate that the design recycle rate proved
effective in providing for a well-mixed anaerobic vessel as
specified by Chian and DeWalle. Scheduled variations to.the
recycle rate, if conducted, could have indicated more clearly
whether the 18-20 gpm rate was actually the optimum.
Temperature
The process temperature throughout the evaluation
period experienced frequent day-to-day variations (commonly,
+ 3°F) resulting from temperature controller malfunctions. On the
67
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average, however, the process temperature was held at 86°F.
from March 6 to May 1 and increased to 96°F. from May 1 to
June 20 for evaluative purposes.
The data indicates that during the portion of the 'run1 when
the average process temperature was higher, the COD removal
efficiency increased by nearly 5% (67.5% removal at 86°F. 72%
removal at 96°F). Also most gas production peaks during the
'run1 were seen to occur at temperatures very near 90°F. However,
no clear-cut conclusions regarding gas production as related to
process temperature .should be drawn, as the data is limited.
Rapid and extreme temperature variations were indicated
through the data as resulting in decreases to both organics
removal and gas production. The greatest temperature variation
experienced by the process occurred on May 7 (96°F. to approxi-
mately 114°F.). During this period the system was already ex-
periencing large variations in the character of the raw leachate
which had apparently resulted from the large rainfall of April 27
through April 29. This temperature jump to 114°F. was not only
rapid and extreme, but also exceeds the acceptable range for
the survival of mesophyllic organisms. This is believed to have
resulted in a stunning effect which greatly reduced their ability
to feed on the volatile acids within the system. Resultantly,
both COD removal and gas production decreased and, as previously
noted on page 60 was the only instance when the volatile acids/
alkalinity ratio deviated from within its recommended -allowable
limits during any portion of the evaluative 'run'.
68
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PROCESS PERFORMANCE
Treatment - Removal
COD - Chemical Oxygen Demand
During the evaluation period, the COD samples indicated
the following concentrations throughout the system (all in
mg/1):
Low High Average
Storage Tank: 1120 2550 1697
Filter Influent: 1190 2580 1686
Lower Tap: 350 990 581*
Upper Tap: 265 1090 517*
Recycle: 205 960 485*
Filter Effluent: 70 1050 497*
Sludge: 670 800 735
*First four (4) weeks' data thrown out before computing
averages resulting from tank dilution from previous runs.
The COD concentrations throughout the process, at the
four locations where samples were taken (lower tap, upper
tap, recycle, filter effluent) are relatively close in
magnitude representing a well-mixed leachate within the
vessel.
Figure VIII C shows how COD influent/effluent and
removal efficiency varied throughout the 'run.1 With
the respect to COD removal, the overall.reactor efficiency
averaged 70.52%, which falls short of the/80% removal felt
possible by Chian & DeWalle through their bench scale studies,
69
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Figure 3ZBT C
CHEMICAL OXYGEN DEMAND (COD)
B
p.
oo
CN
cm
c
-H
T3
tfl
O
tfl
^
•u
>-.
•K
% Removed
COD (Ibs./day)*
70
-------
Independent studies by others*-*- , have indicated that a
leachate's age may be directly related to not only, its
characteristics but its overall treatability. The Enfield
leachate during the evaluation period would best be classi-
fied as medium aged (approximately five years old). This
age leachate is less effectively treated by biological
processes than a younger highly biodegradable sample as was
used in the bench scale studies. Another contributing
factor could be the greater than desired temperature varia-
*
tions experienced by this system during the evaluation
period. These operating conditions have been seen in conventional
anaerobic sewage digesters to lead to decreased system
efficiency. Given a steady feed of younger, stronger leachate
and a more consistent process temperature it is likely that
the overall COD removal efficiency could average close to 80% as
was predicted.
Carbon
Total inorganic
(TIC)
251.25
252.5
347.5
357.5
355
345
*Data collected March 3, 1979 exhibited values which were
significantly different in the balance of the run consequently
were eliminated from all calculations.
71
Summary
of Average
Total carbon
(TC)
Storage Tank
Influent
Lower Tap
Upper Tap
Recycle
Effluent
1052.5
1135
450
447.5
465
425
Concentrations
Total organic carbon
(TOC)
801.25
882.5
102.5
90.0
110
80
-------
The process removal efficiency averaged 91% for organic
carbon producing a satisfactory effluent concentration of 80
mg/1. Total carbon removal was 62.6%. Organic carbon was
seen to represent 78% of the total carbon in the raw leachate.
The data also indicated that some organic carbon (approximately
92.5 milligrams/liter was converted to the inorganic form
and exited with the effluent).
One point of interest, still unresolved is that for
both total and organic carbon the influent concentrations
averaged higher than those in the storage tank.
Suspended Solids
Suspended Solids in Mg/1
Low High Average
49.2
42.0
29.0
29.0
30.0
27.0
166.0
176.0
253.0
91.0
111.0
87.0
123.0
819.0
108.1
117.0
53.0
61.5
49.4
55.0
492.5
Storage Tank
Filter Influent
Lower Tap
Upper Tap
Recycle
Filter Effluent
Sludge
The process averaged 53% removal of suspended solids
throughout the evaluation period producing an effluent
concentration averaging 55 mg/1. This quality effluent
72
-------
is within the allowable range for the discharge to seepage
beds as utilized on this project. It should.be noted,
however, that it is above the criteria recommended by most
government agencies for direct stream discharge (approximately
40 mg/1). The effluent concentration remained essentially
the same throughout the run (40 to 60 mg/1) even though the
influent varied by as much as 500% (42 mg/1, low; 253 mg/1,
high). This data would indicate .that in order to obtain
lower effluent concentrations of suspended solids additional
settling and/or flocculation may be necessary. The frequent
i
temperature variations experienced throughout the run may be
responsible for the higher effluent suspended solids and
related lower process efficiency through the "sloughing of
microorganisms" which is felt to have occurred.
Metals
The overall concentration of metals during the evaluation
period was low when compared to the preliminary testing
results. The process showed no signs of heavy metals toxicity
throughout the run although this could be merely the result
of the low influent concentrations experienced. The plant
was equipped with provisions to chemically feed sodium
sulfide to precipitate metals if needed^ However, none was
required. Three of the more important metals which were
evaluated are discussed below.
73
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Iron
The overall level of iron in the raw leachate was lower
by a factor of approximately 20 when compared to preliminary
testing results (21.8 mg/1-vs. 430 mg/1). Iron removal
averaged 83% during the run. Effluent concentrations were
low averaging 3.7 mg/1.
. IRON Mg/1
Low High Average
Storage - -• -
Filter Influent 12.8 28.8 21.8
Lower Tap - -
Upper Tap - -
Recycle 2.1 7.5 3.7
Filter Effluent 2.2 6.5 3.7
Sludge - -
Zinc
The data collected on this metal is considered unreliable
by the operators. Overall levels of zinc which were .in the
raw leachate were low however averaging 1.0 mg/1.
Lead
No results were obtained on tests for this element. The
problem seemed to be with the lamp used for the test (could
not zero).
REACTOR GAS
The gas produced by the process was regularly measured,
sampled and analyzed. Subsequent to an initial stabilization
74
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period of four weeks, gas production averaged 856 cubic feet
per day. In general, the rate increased in proportion to
organic loading, from a low of 100 to a high of 1,200 cubic
feet per day, with COD loading of 7.2 to 52.8 pounds per
day, respectively. It is calculated that 29,980 cubic feet
of gas is produced for every 1,000 pounds of COD removed by
the process.
Although not extensively .studied, the data indicated
that gas production is affected by operating temperature and
that peak gas rate occurs at a temperature near 90°F.
The gas analysis showed it was composed of 70% methane
and 30% carbon dioxide, values commonly experienced in the
digestion of sewage sludge. The gas was of burnable quality
and was flared off on a continuous basis; however, at no
time was the gas production at a sufficient rate to operate
the boiler because of the low organic loading to the system.
75
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SECTION IX
ECONOMIC ANALYSIS
1.0 GENERAL
Since the performance of the treatment system is
judged marginal due to the short period of acceptable
operation and the quality of leachate treated, it is
difficult to compare total equipment and operating costs
with the total COD removed. However, efforts have been
made herein to make that comparison as well as comparing
costs to quantities of leachate treated. Conclusions
and recommendations are precedent on the basis and assump-
tions made.
2.0 FUNDING
Funding for this project was received through the
United States Environmental Protection Agency on a cost
sharing basis with the City of Enfield, Connecticut,
seventy-five percent by the USEPA and twenty-five percent
(primarily construction and operation costs) by the City.
3.0 TOTAL COST
The total cost of the project is broken down as follows:
3.1 Capital Costs
Equipment Purchase and Construction $284,730.00*
Start-up and Debugging Labor 15,873.00
Electrical Power Cost 1,690.00
Propane Cost 160.00
$302,453.00
3.2 Operating Costs - Period March through June 1979
Direct Labor $ 3,565.00
Electrical Power .. 238.00
Propane 160.00
Travel 1,170.00
$"5,133.00
Four month period
Estimated Annual Cost = $ 15,399.00
*See Construction Cost Estimate, p. 81
76
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4.0 PROJECT COST
4.1 Depreciation
Assuming the straight line method of depreciation of
the capital cost of $302,453 over a useful life of 10 years
and a salvage value of $20,000 in equipment the annual depre-
ciation is represented by the relationship:
D = C-L
n
Where C = Material Cost = $302,453
L = Salvage Value = 20,000
n = Term = 10 yrs.
Then D = $302,453 - $20,000
-------
5.2 Cost/Pound of COD removed is:
CL
PC COD = COD
Where PC COD = Dollars per pound of COD removed
Cl.= Total cost per year
COD = Total COD removed per year
@ average of 28.72 removed
28,267
Pe COD = 28.72 x 365 = $2.70 per Ib. COD removed
5.3 Potential annual fuel savings cost from methane
production (1,697 mg/1) leachate
Ps = Ma x Vm x C
Ps = Potential Savings
Ma = Annual Methane Product
in CF average 800 CF/day
Vm = Average market value of natural gas
(approx. $.005/CF)
C = Coefficient of efficiency (methane/propane)
Ps = 292,000 x $.005 x .41% = $599.00
The use of modular components coupled with an established
regional network and program to treat landfill leachate could
increase cost efficiency significantly by allowing for the
reuse of components on future installations involving "young
leachate" where biological treatment appearsvmost effective.
78
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ENERGY ANALYSIS FOR OPERATION OF THE
ENFIELD LEACHATE TREATMENT SYSTEM
0 Current Usage of Pumps
All pumps operate on a 460 volt power supply.
A. Raw Leachate Well Pump - discharge is not adjustable,
pumps off or on. Nominal pump output is 5 gallons
per minute, with a current draw of about 0.7 amp.
B. Transfer Pump - discharge controlled by adjusting
pump speed.
•
Flow Rate ' Current Draw (amps)
L/min.
1.9
3.8
7.6
15.1
18.9
C. Recycle
gal./min.
0.5
1.0
2.0
4.0
5.0
Pump - discharge
Recycle Rate
L/min .
57
76
114
151
189
Energy Usage
gal./min.
15
20
30
40
50
of Pumps
2.50
2.60
2.65
2.70
2.80
controlled by throttling flow
Current Draw (amps)
2.65
2.70
2.72
2.75
2.78
The general equation used for calculating energy is:
E = I V t
where: E = energy (watts)
I = current (amperes)
V = voltage (volts)
t = time
79
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Since in this case there are three energy consumers (the three
pumps) the total energy consumed is additive and may be expressed
in the following form:
E = Jl Vl *1 + J2 V2 *2 + J3 V3 *3
where the subscripts 1, 2 and 3 represent raw leachate
transfer, and recycle pumps, respectively.
t and t are identical since the transfer and recycle pumps
operate continuously.
t-i is a function of t_ since the raw leachate well pump operates
intermittantly. Vj, V2 and Vg are the same (460 volts).
Therefore, the expression can be restated as follows:
E = Vt (FI-L + I2 * I3)
where F = fraction of total time, during which raw leachate
well pump actually operates (ratio of transfer pump
flow rate to raw leachate well pump flow rate ) .
In order that energy may be expressed in common units (kilowatt-
hours) the expression should be divided by 1,000 while time is
expressed in hours. The final expression for the energy usage
of the three pumps is then:
E + Vt (Fl! + I2 + I3)
1000
6.2 Example of Energy Usage and Cost Calculation
Assume a transfer pump flow rate of .5 gpm and recycle pump
flow rate of 20 gpm. From the tables found in I.E. and I.C.
we find respective currents of 2.50 amp. and 2.70 amp. What
is the amount of energy consumed in 30 days?
E = Vt (FI + I + I )
-i- £- O
1000
E = 460 x 24 x 30 (5/.5 x .7 + 2.50 + 2.70)
1000
E = 1741 Kw. hr.
@ $.06/kw-hr the monthly cost for electrical energy would be:
$104.46
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ENFIELD LEACHATE TREATMENT PLANT
CONSTRUCTION COST ESTIMATE - UPDATED TO JUNE 1979
Item Cost
Leachate Collection Wells
Original Well $ 5,500
Reconstructed Well 34,000
Control Building 20,800
Transfer Pump Vault 9,200
Raw Leachate Storage Tank 40,600
Reactor Tank (erected) 38,500
Reactor Media Fill • 13,400
Reactor Foundation 4,000
Gas Release Tank 800
Insulation (tank) 9,500
Insulation (pipe) 550
Seepage Beds (3) 2,700
Monitoring Wells (3) 12,000
Site Preparation 1,300
Fencing 1,800
Access Road 1,300
Mechanical 13,600
Electrical* 12,000
Propane Tank (installation only) 1,050
Water Tank & Pump 600
Chemical Feed System 640
Work Bench & Sink 200
Room Heating w/Pumps 500
Equipment: (installed cost)
Raw Well Pumps (2) 1,260
Leachate Transfer Pumps (2) 4,900
Recycle Pumps (2) 2,250
Rotameters (2) 950
Boiler & Burner 3,450
Heat Exchanger 2,330
Temp. Controller & Monitor 2,560
Gas Regulators & Safety Equip. 4,300
Raw Storage Level Controls $ 1,050
Construction Cost....$ 247,590
Contingency 15%...... 37,140
TOTAL ESTIMATED CONSTRUCTION COST $ 284, 730
* Based on electrical supply being available near site.
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SECTION X
CONCLUSIONS AND .RECOMMENDATIONS
The Enfield Pilot Plant was successful in treating raw
\
leachate anaerobically to produce an acceptable quality
effluent. Although many problems were encountered throughout
the project, the data collected and evaluated is sufficient
to provide a base from which future judgments concerning the
feasibility of the process can be made. Two factors exper-
ienced during the run, however, limited the scope of know-
ledge which was gained, namely:
the process was never given the opportunity to
perform at its design loading rates due to the
sporadic and low strength raw leachate supply which
was available at the site.
the many problems encountered with .leachate supply,
equipment and operation prevented the achievement of
a long, steady period of monitoring during which the
operators could .systematically vary individual para-
meters for evaluative purposes.
Nonetheless, from the available data collected during
the evaluation period, certain significant conclusions about
the anaerobic process can be drawn, and recommendations on
its feasibility and future use made, as follows:
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RESEARCH/CONCEPT
The anaerobic process appears conceptually to be a
viable, workable alternative for treating raw leachate. It
exhibited a great deal of stability and durability toward
changes in process environment throughout the run. It was
almost .totally self-sustaining with regard to maintaining an
environment conducive to anaerobic digestion, with no
chemical additives needed. The removal, efficiencies achieved
by the process during the evaluative run were, in general,
somewhat lower than thought possible during the bench scale
studies. However, given a more optimum set of operational
circumstances, it is likely that most could increase, in
varying degrees, to somewhere near those expected.
DESIGN
The pilot plant's design allowed for close duplication
of the operational parameters derived through the bench
scale studies (specifically, loading rates, recycle ratio,
detention time, operating temperature, etc.). The influent
distribution system and filter media proved effective in
providing for a well mixed anaerobic environment with no
evidence of short-circuiting. The major aspect of the
design open to future improvement would appear to be the
process temperature control, as many problems arose in
holding constant process temperatures.
Based on the evaluative run and the knowledge gained
through pilot plant operation, the following modifications
to the original design are recommended:
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1. The design of future collection wells should
incorporate a more sophisticated underdrainage
system to maximize the available supply of raw
leachate to the process.
2. The storage tank should be insulated and/or partially
buried to minimize the energy required to increase
the raw leachate temperature to that required by
the process. Also, some test data indicates that
a mechanical mixer may also be needed in the
storage tank to smooth out fluctuations in leachate
strength. It is not possible at this time to
determine whether this additional equipment is a
necessity, however, since the storage tank was
only partially full during most of the run and
thereby its full volume was not utilized. Also,
flow rates from the collection wells were generally
low and inconsistent, creating a minimal leachate
circulation within the tank.
3. The upper and lower sample taps should be insulated
and extended to ground level for ease in operation.
4. The burner/boiler units should be specified and
purchased as a package from one manufacturer to
eliminate the possibility of incompatability as
was experienced with the original equipment chosen
for the pilot plant.
5. The boiler water should be kept in the tube side
of the heat exchanger to minimize fouling potential,
with the process stream occupying the shell side.
84
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This may necessitate a stainless steel interior
lining for the heat exchanger, depending on the
leachate to be treated.
6. The temperature control valve should be relocated
to be in line before the heat exchanger, not
after, for improved hydraulic functioning.
7. The piping between the heat exchanger and boiler
should either be increased in length or include a
thermally nonconductive "break", to prevent heat
transfer between the boiler water and process
fluid.
In that .the approximately 9 day normal detention time
provided closely resembles the recommended bench scale
parameters, it would not appear that an increased reactor
size or reduced hydraulic loading rate would appreciably
increase process efficiency.
Since it appears that the anaerobic process is most
efficient in treating young biodegradable leachate, it would
be of advantage in future designs to utilize as many modular
and/or transportable components as possible. In this way,
as a landfill ages and the leachate produced is less efficiently
treated by biological means, it would be feasible to reuse
"standard" components of the facility at other locations.
CONSTRUCTION/STARTUP
The construction of the pilot plant was generally a
smooth, efficient operation with the engineer making site
inspections and reports as the project advanced.
A major construction related problem developed, however,
with regard to intermittent freezeups of the various under-
ground collection and transmission pipelines. The design of
these lines specified a minimum of four foot of cover over
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them. However, some of the lines eventually became uncovered,
especially where they traversed steep slopes (through erosion
of the landfill material, which was used as backfill).
Future installations should consider increased compaction
requirements and the use of more suitable earth or other
materials for backfilling.
One other problem occurred with respect to the construction
sequence for the anaerobic reactor. It should be noted that
the tank be pressure tested before the insulation is in-
stalled to uncover any internal problems at that point.
Also, more detailed procedures should be specified for
application of the insulation to prevent puncturing at the
tank, as occurred on this project.
PROCESS/OPERATION
The pilot plant achieved high removal efficiencies for
volatile acids (81.0%) and organic carbon (91.0%) indicating
that the process is most effective in treating young, high
strength, readily biodegradable leachate. Given an influent'
of this type and a more optimum process operation it is
likely that the overall COD removal would reach very near to
the 80% felt possible by Chian & DeWalle. Suspended solids
removal could also be expected to rise under more steady
state conditions (particularly, a more constant process
temperature) to minimize the "sloughing of microorganisms".
However, it would appear that coagulation and/or additional
86
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settling would be required to utilize direct stream dis-
charge. There was no evidence of heavy metals toxicity;
however, this may be atypical of the normal due to the low
overall metal concentration of the Enfield leachate. Pro-
visions to chemically precipitate heavy metals as were
included in the pilot plant's design would likely be of
benefit in future .installations. Also, due to low organic
loadings there was no appreciable amount of sludge generated
during the evaluation period, however, sludge collection
facilities should be included in any future designs in
similar proportions .to that allowed for this project.
From the limited data collected and evaluated, it is
projected that the process removal and cost efficiency would
increase under the following conditions:
1. Character of Influent—young, high-strength, readily
biodegradable leachate
(Influent COD: greater than
10,000 mg/1)
2. Hydraulic Loading Rate—dependent on organic strength
of leachate as per Table IV,
pg. 17 of this report
3. Recycle Rate—(R/I), 10:1 .
4. Process Temperature—90° to 95°F. (variations not
greater .than 2°±/day)
It is difficult to predict whether the above set of
operating parameters are actually the optimum due to the
lack of controlled variation to individual process parameters,
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which was performed during the evaluation period. It is
possible, however, that efficiency levels could reach near
those predicted in the bench scale studies once these and
possible"additional refinements to the process operation are
made.
A site visit and visual inspection of the pilot plant
made on February 5 and 6, 1981 has revealed that the facility
could be restarted with minimal expense if further evaluative
testing of the anaerobic process is desired. In view of the
funds which have 'already been invested into this concept, it
seems appropriate that if all possible, the process should
be given the opportunity to perform its intended function of
treating high-strength landfill leachate. It is recommended,
therefore, that a brief availability study be made of the
geographical area surrounding Enfield, Connecticut to determine
the feasibility of transporting high-strength leachate to
the site or a short re-evaluation of the process. If addi-
tional studies such as these are decided upon, they would be
best started during the summer months so to minimize energy
requirements and to avoid any possible problems with under-
ground pipes freezing, as were incurred previously. It
would also be of advantage to systematically vary the hydraulic
loading rate and recycle rates, tests which were not performed
in the original evaluative run, in order to more accurately
project the optimum performance and cost efficiency of the
process.
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REFERENCES
1. The Anaerobic Filter for Waste Treatment
by J. C. Young and P. L. McCarty
W. P. C. F. Journal, May 1969
2. Anaerobic Biological Stabilization of Sanitary Landfill
Leachate
by E. G. Foree and V. M. Reid
College of Engineering, University of Kentucky
January 1973, UKY TR65-73-CE17
3. Treatment of Leachate with the Anaerobic Filter Process
by F. B. DeWalle and E. S. K. Chian
University of Illinois (Published ?)
4. Kinetics of Substrate Removal in a Completely Mixed
Anaerobic Filter
by F. B. DeWalle and E. S. K. Chian
Biotechnol & Bioeng., 18, 1275 (1976)
5. Operation of the Anaerobic Filter
by F. B. DeWalle and E. S. K. Chian
University of Illinois (Published ?)
6. Heavy Metal Removal with the Completely Mixed Anaerobic
Filter"
by F. B. DeWalle, E. S. K. Chian and J. Brush
W. P. C. F. Journal, January 1979
7. Investigation of Boiler Mai-functions at Enfield Leachate
Facilities, Town of Enfield, CT Sanitary Landfill
December 31, 1975
by A. W. Martin Associates, Inc.
8. Report from Metcalf & Eddy, Inc., 50 Staniford Street,
Boston, MA 02114, dated February 16, 1979
by Donald H. Bruehl, Hydrogeologist
9. Town of Enfield, CT Leachate Treatment Facility
Set of Drawings by A. W. Martin Associates, Inc.
December 1975, Pages 1 through 9
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10. Contract Documents for Construction of the Leachate
Treatment Facilities, Town of Enfield, CT Sanitary
Landfill
December 31, 1975
by A. W. Martin Associates, Inc.
11. Demonstration of a Leachate Treatment Plant
by R. L. Steiner, J. D. Keenan and A. A. Fungaroli
of Applied Technology Associates, Inc.
for U. S. Environmental Protection Agency
90
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LIST OF APPENDICES
A. A Compilation of Research and Development Papers
by E. S. K. Chian and F. B. DeWalle
B. Summary of Tests, Equipment . & Procedures
C. Graphic Symmary of Evaluative Run
March, April, May, June 1979
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APPENDIX A
A COMPILATION OF RESEARCH AND DEVELOPMENT PAPERS
by
E. S. K. Chian and F. B. DeWalle
Composition of Organic Matter in Leachate
Collected From The Enfield Solid Waste Landfill
Treatment of Leachate With The Anaerobic
Filter Process
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COMPOSITION OF ORGANIC MATTER IN LEACHATE.
COLLECTED FROM THE ENFIELD SOLID WASTE LANDFILL
E. S. K. Chian and F. B. DeWalle
University of Illinois
Urbana, Illinois 61801
1. Introduction
It was the purpose of this study to determine the
composition of organic matter in leachate samples collected
from the solid waste landfill of the Town of Enfield (Conn.)
*
and to evaluate whether the organic matter can be treated
effectively by anaerobic trickling filter.
2. Site Location
The Enfield disposal area is located in the flood
plain and on the east valley wall of the Scantic River (Fig. 1)
This site consists of approximately 10 acres of land which
has been excavated at the eastern boundary to a reported depth
of 40 feet creating approximately 450,000 cubic yards of
capacity. The site has been used for the last 7 years and is
presently filled at a rate of 50,000 tons/year by the 46,200
inhabitants (1972 census) of the town. The southern half of
the site was filled between 1967 and 1972. It started from
the east side in 1967 and reached the west side in 1969 and
moved back to the east side in 1972. The northern half has
been filled from the west side since 1973 and is propagating
eastward.
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The Scantic River is located about 150 feet from
the western boundary of the disposal site and flows onto a
broad bedrock valley filled with glacial fluvial deposits as
much as 40 feet thick consisting of collapsed stratified
drift. This is overlaid by lake deposits with a thickness
varying from 4 to 20 feet with the thickest layer closest to
the river. The lake deposits consist of horizontally laminated
yellowish brown silty clay interchanged by silty sand. The
surface .of the flood plain is composed of 3 feet thick
reworked sand and silt and the thickness of this layer
corresponds approximately to the depth of the river. The
ground water table in this layer is varying and is located
near the surface to one foot below it. The valley wall
consists of terrace sand and laminated clay deposits. At
some locations near the fill, especially at the northeastern
corner o.f the fill, the lake deposits are not present and
the terrace sand rests directly on the fluvial deposits.
The leachate generated at the site originates
primarily from rain water infiltrating the clayey silt cover.
The sandy cover is not well sloped and numerous depressions
augment the infiltration. The construction of the disposal
area cut off a drainage swale and created a depression at the
northeastern edge of the fill. The formation of a pond at
that location (Figure 1) allows the water to recharge through
the southern section of the solid waste, thereby enhancing the
leachate formation. A section of water-laden sands underlaying
the lake deposits was observed at the southern edge of the
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fill which may facilitate upwelling water to reach the
solid waste and enhance the leachate generation.
3. Sample Collection and Analysis
The leachate is discharged at several locations
at the western base of the fill and major streams were ob-
served to originate at the northern half between sampling
points 1-1 and 2-1 CFigure 1) and at the southern half between
sampling points 5-2 and 6-1. These streams merge on the flood
plain and generally discharge in the Scantic River at location
8-1. The volume of the discharged leachate is enhanced by
small surface run-off streams at locations 1-1 and 5-1. The
majority of the leachate generated, however, will move through
the reworked surface layer above the clayey lake deposits or
through the sand in this layer, and discharge in a diffuse
front into the river.
In order to collect leachate samples for physical
and chemical analyses, six lysimeters were installed about
10 feet from the western edge of the fill (Figure 1). The
lysimeter consisted of a porous cup having an effective pore
diameter of 2 micron, mounted at the bottom end of a 5 feet
PVC pipe having a diameter of 3 cm. A 10 cm diameter hole
was drilled in the soil to a depth of approximately 3 feet.
The lysimeter was placed in the opening and the earth was
backfilled and compacted to prevent seepage along the shaft
of the lysimeter. The contents of the lysimeter were pumped
out several times before sampling and a sample was only taken
95
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after the lysimeter had been in place for 24 hours. A sample
collected with a lysimeter is only representative of the
leachate composition at the depth of the location of the
porous cup. In addition to the lysimeters, two test pits
were dug about 2 feet deep and 2 feet wide at locations 4-2
and 5-2 to collect a composite leachate sample representative
of the entire depth of the excavation. A similar sampling
procedure was used as for the lysimeters. Surface leachate
samples were collected at location 1-1 where the leachate
mixes with a small surface stream at point 8-1 (Figure 1)
before it discharges into the river.
After collection, the leachate samples were refrig-
erated and transported to the University of Illinois for
analysis. The analysis was conducted according to Standard
Methods (1971) as modified by Chian and DeWalle (.1975) . The
analysis consisted of first measuring gross parameters
such as oxidation reduction potential CORP), pH, conductivity,
absorbance at 400 nm and total and total and volatile solids.
The organic matter was analyzed for chemical oxygen demand
(COD) , biochemical oxygen demand (.BOD) , and total organic
carbon (TOC) and inorganic carbon (.1C) . Specific organic
constituents such as free volatile fatty acids were determined
with both the column partition chromatographic method and the
hydroxyl amine test. The individual fatty acids were deter-
mined with a Hewlett-Packard Research Chromatograph 57SOB
and a Linear Instruments Corporation Disc Integrator using an
acid column consisting of 0.3 percent SP1000 and 0.3 percent
96
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H3P04 on Carbopack A. Phenol was employed as an internal
standard. Carbohydrates were determined with the phenol
sulfuric acid method while aromatic hydroxyl compounds were
i
measured with the Folin-Ciocalteau test. Organic nitrogen
was determined with the Kjeldahl method after 30 minutes
digestion.
4. Results and Discussion
Results of the leachate analysis are shown in
Figures 2, 3 and 4. It is seen from these figures that the
most polluted leachate samples are observed at locations 2-1
and 5-2 and the least polluted ones are noticed at 1-1, 4-2,
and 6. Although the refuse at the southern half was placed
earlier than the northern portion, this does not seem to affect
the maximum strength of the leachate.
Substantial differences were noted between the
leachate obtained from the lysimeters as compared to that
from the test pits. At location 4, the COD of leachate from
the test pit was approximately half that from the lysimeter,
while at location 5 the test pit resulted in a leachate having
20 times higher concentration. This may indicate that the
leachate movement through the soil is confined to localized
layers which may not be detected with lysimeters since they
are restricted to one specific layer. In a test pit leachate
of different strength was drained from several layers and was
mixed before sampling. This may result in a higher average
concentration. If, however, the lysimeter is installed in a
97
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specific layer having a high leachate concentration, its
strength will be higher than that obtained from a test pit.
As the lysimeter and test pit were located several feet
apart/ the results may also indicate that the leachate
ground water flow is confined to relatively small paths from
a plain view. In order to identify the different flow paths,
more lysimeters may have to be installed to reduce the chance
of missing certain ground water flow.paths.
Further analysis of the strength of pollutants in
different leachate samples indicated that some of the variation
resulted from the varying degree of dilution. Assuming that
the leachate with the highest strength (COD = 35,905 mg/1)
was not diluted at all, the dilution factor for the other
leachate samples was calculated from the values of the conserva-
tive ions such as Cl- and Na+ (Figure 3). The highest dilution
was observed at the northwest corner at location 1-1 where
leachate intermixed with a small surface runoff stream; this
was confirmed by visual observations. The mixing apparently
also reduced the total organic strength of the leachate as
measured by COD and TOC. The southwest corner is the second
location where leachate experiences a large dilution apparently
due to upwelling ground water. However, this did not sub-
stantially lower the concentration of organic matter. The
relatively high-dilution at location 5-1 may also have resulted
in the lower COD and TOC observed, but the low concentration
at nearby location 6-1 was not the result of any dilution. The
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same can be observed for location 4-1 and 4-2. These data
indicated that processes other than dilution caused a re-
duction in the strength of organic matter.
Analysis of the data in Figures 3 and 4 indicate
that the values for the pH and ORP were inversely related.
A high pH value also corresponded with a high bicarbonate
concentration as measured by the inorganic carbon with the
total carbon .analyzer. High bicarbonate concentrations re-
sulted from the dissolution of CC>2 in water. CC>2 is formed
during the methane fermentation stage. The increase in pH
is due to the reduction of the fatty acids and the buffer
capacity of the sample. During the methane fermentation
stage the environment becomes more and more reduced thus
lowering the ORP. Since the relative amount of bicarbonate,
or. inorganic carbon, to the organic carbon indicates the
degree of biological degradation, a ratio between these two
parameters can be established with which the other parameters
such as pH and ORP can then be related. In order to obtain
a maximum ratio of unity, the ratio of organic carbon to
total carbon (organic and inorganic carbon) was used in
Figures 5 and 6. They indicate that with increasing biological
degradation or decreasing TOC/TC ratio the pH increases
while the ORP decreases.
The next step was to determine the relative changes
that the organic matter undergoes during the biological
degradation, since this may influence the effectiveness of
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the treatment process. An important parameter is the amount
of fatty acids which are the intermediates between the
degradation of the complex organics in the refuse and final
products of CH4 and C02:
(C6H12O6)n -*, CH3COOH or CH3CH2COH
CH3COOH -* CH4 + C02
2 H20
4 CH3CH2COOH -*- 7 CH4 + 5 C02
*
Figure 7 indicates that the relative amount of
fatty acids does not decrease with respect to the other
dissolved organics in the leachate during the early stage of
leachate degradation. Only when the ratio of TOC/TC de-
creases below 0.65 does the relative fatty acid concentration
decrease with respect to the other organics. Since the fatty
i
acids are the direct precursors of C02 and CH4, and since
the methane fermentation has already progressed substantially
when the ratio of TOC/TC decreases to 0.65, a constant ratio
of fatty acid to other organics indicates that this fraction
is initially replenished by the breakdown of complex organics
in the refuse. During the methane fermentation stage, the
higher molecular weight free volatile fatty acids, such as
butyric, isotontyric, valeric, isovaleric, and caproic
acids, are converted to acetic and propionic acids. Since
all of the individual free volatile fatty acids were determined
with the gas chromatography, the relative change in fatty
acid composition can be determined. The data in Figure 5,
100
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however, indicate that the relative fatty acid composition
with respect to acetic and propionic acid does not decrease,
suggesting that all acids are replenished continuously due
to the degradation of the complex organic matter, thus con-
firming an earlier conclusion.
The biological oxygen demand (BOD) follows the
similar pattern as the fatty acids, and shows a relatively
rapid decrease as compared to the other organics when the
TOC/TC ratio decreases below 0.55 (Figure 8). The relative
magnitude of the BOD was calculated with respect to COD of
the sample. This parameter is also expressed as oxygen
demand but still reflects the total organic carbon. Figure
8 tends to indicate that the relative BOD concentration even
shows a slight increase during progressing methane fermentation,
since breakdown of complex organics results in better aerobic
degradability of the sample. Further evaluation of the BOD
test showed that most of the oxygen demand is exerted during
the first 24 hours as shown for sample 8 in Figure 10. Only
one sample, i.e. 7-1, experienced a one-day delay and this
may have been due to a relatively high concentration of
complex organics that caused some inhibition, as indicated
by the high concentration of aromatic hydroxyl compounds in
that sample.
Further evaluation of the degradation of the
different organic fractions in the leachate showed that the
non-nitrogenous organics are degraded more rapidly than the
nitrogenous compounds (Figure 11). The relatively slow rate
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of removing these nitrogenous compounds is due to the slower
rate of removal of complex nitrogenous organics and the
simultaneous release of amino acids, such as glutamic acid,
during the microbial degradation of other organic matter.
In the later stages of the biological degradation, high
molecular weight organic compounds containing nitrogen are
released from the bacteria together with carbohydrates and
other high molecular weight refractory materials.
The non-nitrogenous organic fraction that is
removed along with the free volatile fatty acids is charac-
terized by the relatively high concentrations of aromatic
hydroxyl groups. Figure 12 shows that this results in a
degradation similar to Figure 11. The nature of these
organics is not yet known but may consist of slightly soluble
lignin-like material or condensation products from the
cellulosic compounds.
The breakdown of the complex organics during the
acid fermentation stage and the removal of the fatty acids
during the methane fermentation stage is followed by the re-
lease of high molecular weight organics by the bacteria when
all degradable organics are removed. Figure 13 shows a con-
tinuous increase of the relative carbohydrate concentration
with decreasing TOC/TC ratio. The excretion of these high
molecular weight organics has an effect on the flocculation
of the dispersed bacteria and may protect them from being
washed out.
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5. Conclusions
The above considerations indicate that variations
in concentrations of organic matter are affected to some
extent by the dilution of the leachate by infiltrating
surface runoff or upwelling ground water. The most important
factor, however, is the biological degradation of the re-
sulting leachate. Definitive trends were observed in which
complex organic matter was degraded to free volatile fatty
acids which in turn were converted to C02 and CH^. Analysis
of all leachate samples indicates that they are biodegradable
and are suitable for treatment by anaerobic filters. In an
anaerobic filter the same process is expected to occur as
with the individual samples discussed above. However, they
are confined in a better controlled environment and will
thus proceed at a higher rate. As the most degraded sample
(No. 6-1) has a COD of 586 mg/1 and is only diluted by 1.78
times, it may be estimated that the COD of the most concentrated
leachate sample (No. 2-1) may decrease from 35,905 mg/1 to
1040 mg/1 while being treated with an anaerobic filter.
This corresponds to 96 percent COD removal. If, however,
both dilution of the leachate with ground water and anaerobic
degradation in the soil occurs, lower treatment efficiencies
are expected.
The most important unknown that still has to be
determined is the actual leachate concentration within the
landfill before it has traveled any distance through the
103
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soil, causing the above mentioned modifications. As of now
it is not yet known whether the progressing biological
degradation of the leachate samples are a reflection of the
conditions in the soil through which the leachate has traveled
or whether they reflect the different solid waste characteristics
within the landfill. For that reason, additional lysimeters
should be placed within the fill near the west edge, opposite
to the ones already installed in the soil. Only analysis of
*
such leachate can be used to predict the concentration of
leachate to be expected for treatment by the anaerobic
filter.
104
-------
Figure 1. Contour Map of the Landfill Site
with the Sampling Points
/'"/'
•' / <' r- -\
/ I
105
Ay-
\ 'I
//
-------
TOC
(mg/0
COD
. (mg/s,)
- 40,000
. 30,000
- 20,000
- 10,000
1-1 2-1 3-1 4-1 4-2 5-1 5-2 6-1 7-1 8-1
Figure 2. COD and TOC Data of the Collected Leachate-Samples
Absorbance
1.5
A
~ / \
O Absorbance
i'- \ AORP
Dilution factor
\
OR?
mv)
40 -
50 -
60 _
70 -
80 -
90 -
100
Dilution factor
1-1 2-1 3-1 4-1 4-2 5-1 5-2 6-1 7-1 8-1
Fiqure 3. Absorbance, ORP and Dilution Factor of Collected
Leachate Samples
106
-------
Inorganic
Carbon
(mg/i)
i i i i i i
1_1 2-1 3-1 4-1 4-2 5-1 5-2 6-1 7-1 8-1
Figure 4. Inorganic Carbon and pH of Collected Leachate Samples
pH
o.
o
o
Increased biological
stabil izatjon
O
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
TOC/TC (-)
Figure 5. Effect of Increased Biological Stabilization on pH
Increase and TOC/TC Decrease
107
-------
ORP
(-mv)
10
20
30
40
50
60
70
80
90
100
o
/
0
o
o
0
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
TOC/TC
F.jaure 6. Effect of Increased Biological Stabilization on ORP
Decrease and TOC/TC Decrease .
Fatty Acids
TOC/TC
0.7
0.6
0.5
0.4
0.3
0.2
0.1
O
o-
O
P
O
1 1 1 1 1 1
1 1
0. 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
TOC/TC
Finure 7. Effect of Increased Biological Stabilization on Decrease
of Relative Fatty Acid Concentration
108
-------
BOD
COD
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
O
/O'
i
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
Finure 8. Effect of Increased Biological Stabilization on Decrease
of Relative Biochemical Oxygen Demand
03
•o
«J -r-
•r- U
4-3 ro
O)
O O
rtJ •!-
<*- O
O T-
CL
O O
O J-
1— CX
I/)
o
fO
o
c.
3.0
2.0
1.0
O
O~
_L
_L
I
_L
0 0.1 0.2.0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
Finure 9. Effect of Increased Biological Stabilization on Relative
Fatty Acid Distribution
109
-------
DO
(mg/£)
3
2
1
1:1500
(4800)
-.-'"I: 2000
f (4000) n
/rr"TT3ooQ_ X
/yy~('4'800) "
^Tf-"P (2000), ,
8-1 1:300 (1280)
_ — . • @
e^" 1:400 (1280)
, o — O fT500 (1250)
7
^ . , .
01 234501 2345
time (days)
Finure 10. BOD Curves for Sample 7-1 Showing One Day Adaptation
Period, and Sample 8-1 Representative of Other Samples
Showing no Delay in Oxygen Uptake
. TOC
Organic - N
150
100
50
O
. 0
O
' C
0 / o
/°
/ 0
o
o
1 1 S 1 1 1 1 1 ,
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
TOC/TC
Figure 11. Decrease of Non-Nitrogenous Matter During
Leachate Stabilization
110
-------
(7-1)
c.
•3
o
o.
X
o
"a o-—-
>,o i
o
c
ro
cr.
j-
o
CJ
o
01
•»->
to
-u
o
JD
03
O
O
O
O I
o:o9
0.08
O.C7
0.06
0.05
0.04
0.03
0.02
0.01
• - -cr-
—
O
o / c
o
* /
»
o
/
1 1 1 / 1 1 1 1 1 1
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
TOC/TC
Figure 12. Decrease of Aromatic Hydroxyl Compounds During
Leachate Stabilization
0.09
0.08
0.07
0.06
0.05
0.04
s
0.03
0.02
0.01
\o
\
\
\
\
o\
\
\°
X
8 x ^
,o
cc
1 1 1 1 1 1 1 1 1
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
TOC/TC
Finure 13. Increase of Carbohydrate Compounds During
Leachate Stabilization
111
-------
Treatment of Leachate With the Anaerobic Filter Process
Foppe B. DeWalle and Edward S. K. Chian
Department of Civil Engineering
University of Illinois at Urbana-Champaign
The present study was conducted to evaluate the treatability
of high strength leachate with the anaerobic filter. The
anaerobic filter consists of a supporting medium to which
anaerobic bacteria are attached.. The first step in the
anaerobic breakdown of organics consists of hydrolysis of
complex organics to their monomers which are then converted
to free volatile fatty acids by acid forming bacteria. The
last step consists of the formation of methane by methane
bacteria from the fatty acids. The major advantage of the
process is that the stabilization can be accomplished with
a relatively low production of biological solids so that
problems with the ultimate disposal are minimized. A byproduct,
the methane gas, is produced as a result of the process and
valuable energy can be recovered from the gas by subsequent
combustion. Another advantage is that the need for aeration
equipment, costly to install and operate, is eliminated.
A major disadvantage of the method is the high sensitivity
of the methane forming bacteria to acidic pH values. In
addition the methane fermenters are sensitive to heavy
metals. In order to increase the acidic pH values in the
leachate, it is necessary to dilute it with buffered effluent
of the unit, as a result of which the filter is operated as
a completely mixed system.
112
-------
Materials and Methods
In order to predict the operation of the full scale
demonstration anaerobic filter to be constructed near the
town of Enfield, Connecticut, a laboratory scale evaluation
was made at the University of Illinois using leachate
similar to the leachate that will be used to finally operate
this filter.
The anaerobic filter column is constructed of plexiglass
with an overall height of 246 cm and 20.2 cm OD (Figure 1).
The height of the filter medium in the column is 199 cm and
comprises a volume of 54.6-5 (1.93 cu ft). Additional
clearance at the top of the column represents an additional
1.4JZ. while the inlet space consists of 2.8JL. A solids
collection device is located in the bottom of the column and
has a volume of 3.8-£. A recirculation vessel with a volume
of 5.2 Ji contains effluent of the anaerobic filter that is
used to dilute the incoming untreated leachate and to raise
the pH of the mixture. The total volume of the column is
therefore 67.8 Ji of which 54.6 JL or 81% contains the media
'to which the bacteria are attached.
The media in the column consists, of plastic "surface"
slabs (Dow Chemical Midland, MI) and has a specific density
of 1.45 g/cm^. As the average thickness based on 100
measurements is 0.57 mm, the specific surface area of the
media is 34.9 cm2/cm3 filter media volume. The specific
surface area of the media in the column is 2.06
113
-------
column volume (63 ft2/ft3 column volume). The total surface
area in the column is therefore 11.3m2 (121.6 ft2) and only
6% of the column volume is taken up by the filter media
resulting in a porosity of 94%. A comparable study (McCarty,
1967) used tones instead of plastic with a resulting specific
volume of 1.1 cm2/cm3 column volume (33.5 ft2/ft3 column
volumes) and a porosity of only 42%.
Results
The initial evaluation of the filter treating the
Enfield Leachate was conducted at a relatively low loading
in order to acclimate the bacteria to the specific waste
stream. The selected loading was 23.3 Ib COD/1000 cu ft day
equivalent to a 32 day detention time. The filter was
previously operated for a one and one half year period
treating a very biodegradable leachate having an initial COD
of 30,000 mg/1. Using this leachate it was noted that 96%
of the COD could be removed at a loading of .50 Ib COD/1000
cu ft day corresponding to a detention time of 25 days
resulting in a 1400 mg/1 effluent COD. The removals observed
with the Enfield leachate having an initial COD of 11,628
mg/1 was generally smaller than in the previous study, and
the average percentage COD removal was 50% while fatty acid
removals were 70% during the first four, month period.
Several reasons, however, explain why the obtained results
are lower than previously obtained. During the initial 25
days of the operating period the bacteria were not able to
114
-------
respond to the specific waste stream and almost no COD
removals for example were observed after 9 days. A gradual
improvement was observed, however, during the next 25 days
and COD removals of as large as 88% and fatty acid removals
of 97% were observed at day 45 (Figure Id). This corresponded
with a gradual increase in gas production as shown in Figure
2c. As a result of the anaerobic conditions the sulfates
showed a gradual decrease as they were converted to sulfides
thereby precipitating the heavy metals such as iron (Figure
3a) and nickel (Figure 4). Settling of these precipitates
in the bottom section of the unit resulted in a decrease of
the effluent suspended solids.
Significant variability in effluent organic matter
concentration was observed between day 50 and day 130 after
the initial adaptation of the microorganisms had occurred.
At times the removal was as low as 30%, while it could
increase to as high as 90%. It was noted that high removals
generally corresponded with high pH values and high gas
production rates, indicating that some periodic toxicity may
be occurring. The fatty acid concentration generally
varies parallel to the COD and removals also ranged from 90%
to as low as 30%. Some of the observed toxicity may also be
due to variation in heavy metal concentrations. Evaluation
of the initial iron concentrations would indicate that high
effluent COD values correspond to high iron values. However,
more samples will have to be analyzed before solid conclusions
115
-------
can be reached. If such toxicity is occurring, addition of
sulfate or sulfide may enhance the operation of the unit;
such steps will be evaluated during subsequent studies.
When the unit is operating under optimum conditions, it is
expected that COD removals will be as large as 80%, while
fatty acids will be removed for about 90%. The lower
removals of the COD as opposed to the higher removals of the
fatty acids is the result of the presence of non biodegradable
refractory organics that are not removed by any biological
treatment process. Since the tested leachate was collected
in the floodplain at the toe of the fill, considerable
degradation .had already occurred during travel through the
soil. This resulted in a COD decrease from about 32,000 to
11,000 mg/1. Since the designed treatment plant will be
treating the leachate with a concentration of 32,000 mg/1, a
similar effluent quality will be expected, i.e. a COD of
about 2500 mg/1 and a fatty acid concentration of about 500
mg/1, which will result in a 92% COD removal and 97% fatty
acid removal.
The average removal of the suspended solids was 70%
during the first 100 day study period but was gradually
improving and reaching 88%. The high suspended solids
reductions were also reflected in the turbidity removal
which was as high as 93%. Contrary to the SS no decrease in
effluent concentration was observed with time, indicating
that other species besides the suspended solids affect the
116
-------
turbidity. The average color removal was 54% but increased
to 75% at the end of the monitoring period.
The removals of the heavy metals were generally satis-
factory and filtered iron concentrations decreased by as
much as 99%. Since the majority of the iron in the effluent
is present in the suspended solids and not in solution, the
total iron removal was only 64%. However, when the suspended
solids are effectively precipitated in the bottom section of
the unit the total iron removal will approach 97%. The
removal of soluble zinc was about 71% while total zinc
removal was 65%. Other heavy metals are still being analyzed.
The soluble calcium was decreased by 69%, while total calcium
decreased by 28% indicating that a significant fraction is
present in the suspended solids possibly as carbonates or
hydroxides. Since other metals may be present in similar
form and because these precipitates are pH dependent, the
high pH values may be more effective to reduce soluble
metals thus decreasing their toxicity. A smaller toxicity
or higher pH may in turn enhance the bacterial degradation
and result in lower effluent COD values. However, due to the
short evaluation period, no solid conclusions can yet be
made concerning the complicated interactions that occur in
the unit.
The gas production was 2.7lJ£ gas/J> leachate which
corresponded to 0.46JL gas/gr COD removed or 0.32.^ methane
gas/gr COD removed. This value is only slightly less than
1 1
-------
the theoretical value of 0.35, indicating that the methane
conversion is not affected by a possible heavy metal toxicity.
Conclusions
Based on the limited data that are available it was
concluded that under optimum operating conditions the
anaerobic filter will remove as much as 90% of the COD and
fatty acids when treating leachate that is collected within
the landfill. The removals of iron and other heavy metals
will be in a similar range. Since some variability in
effluent quality was observed in the present laboratory
study indicating possible toxicities, no solid conclusion
can yet be reached concerning expected effluent qualities of
the unit.
118
-------
I 3V.J
119
-------
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123
-------
APPENDIX B
SUMMARY OF TESTS, EQUIPMENT & PROCEDURES
OPERATORS
Town .tff Enfield, Connecticut, Water Pollution Contol
Division
Mr. Robert G. Mullins, Public Works Director
Mr. Thomas G. Thompson, Superintendent
124
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APPENDIX B
TESTS, EQUIPMENT AND PROCEDURES
STS
I
I
ATI ON
'EDUCTION:
,OTENTIAL
CONDUCTIVITY
I
TURBITIY
1
ETALS
EQUIPMENT.
Photovolt:
Model 115 A
Scale O - 14 . • .
Electrode Broadley » James
Photovolt .
Model 115 A
Scale 400 - 400• MI..V. :
Electrode Photovolir. Cat# 1120
Platinum Electrode
la"b - Line
Portable Lectro MHO Meter
Ltodel MC 3
Scale 0.1 — 100 u mhos
Range XL - Xlooo
Sargent Welch
Model S-83700
Scale 0 - 1000
Range 1 -- 1000
Perkin - Elmer
Atomic Absorptions Spectre.
Ltodel 37O A
- PROCEDURES
Standard Methods 14 Ed;
p.. 276 Glass Electrode .
Method
Photovolt, Operation
and Maintance Manual
Photovolt Operation-
and. Maintance Manual
Instructments Operation
and Maintance Manual
Standard Methods 14 Ed.
Sargent Welch Operation
and Maintance Manual
Perkini - Elmer Manual
Analytical Methods For
Atomic Absorption:
Spestropnotometry
I
:ULPATE3
Coleraan Instruments
Model 44 Spectrophotometer
Standard Methods 14 Ed;
Turbidmetic Method
Coleraan Operation and
Maintance Manual
?OTAL PO -P
Coleraan Instruments
Model 44 Spectrophotometer
S.tandard Methods 14 Ed.
Coleraan Operation and
Maintance Manual
GAS COMPOSITION:
Surrell- Gas Apparatus
Model No. 950 - 488
Burrell Manual For
Gas Analysts 7 Ed.
125
-------
APPENDIX B
TS.
uriLORIDES
CONTENTS: TESTS,, EQUIPMENT AND PROCEDURES.
EQUIPMENT'
Orion Research Inc,
Model 407 A Specific Ion Meter
Electrodes Orion lonalyzer
Model 94-17
Usual Lab Apparatus
PROCEDURES
Orion Research Manual
For Model 407 A
Orion Tonalyzer Manual.
For- Electrodes
Wastewater Analysis
Handbook p.. 14Q
Standard Methods 14 Ed,
AMMONIA,
I-ITRO&ENf
Same as Chlorids
Orion Research Manuals
Standard Methods 12 Ed.
i
OLA3HLE
.CIDSJ
Usual Latr. Apparatus
Standard Methods 14 Ed,
Procedure letter from
G.£.. Schlessinger PhD
State Chemist
Usual Lab. Apparatus
Standard Methods 14 Ed,
Procedure letter from
&..&*. Schlessinger PhD
State Chemist;
Usual Lab; Apparatus
Usual Lab Apparatus
Standard Methods 14 Ed,
See attached sheet for
reagents, procedure and
calculation • :
T... 0. C
Samples .sent out to Griswold and Fuss
Environmental Laboratories Inc.
126
-------
C.O.D.
Reagents .
1. Oxidizing solution: Dissolve 2.5 grams potassium dichromate in a mix-
ture of 500 ml. each of cone, sulfuric acid and 857. ortho-phosphoric
acid. Triturate the dichroraate with small amounts of the phosphoric
acid before adding the sulfuric acid. - - . .
2. Potassium Iodide Solution: Dissolve 55.3 grams of potassium iodide in
200 ml. of distilled water.
3. Starch Indicator Solution: Prepare according to Standard Methods.
A. .1 N thio = boil and cool 1 liter of distilled water, add 24.82 g
NA2S2°3 ? H2°* Preserve with *§ NAOH Per liter. .-..
.05 N thio = cut this with equal volume of distilled water. . .
Procedure . .'..-.; .'" . . . . . "... •
1. Pipette 25 ml. of oxidizing solution into a 500-ml. Erlenmeyer flask.
2. Pipette 5 ml. of the sample (or larger or smaller amounts depending -.
upon the strength of the waste*:) into the oxidizing solution.
3. Insert a thermometer into mixture and place on a hot plate.
-4. Bring the temperature of the mixture to 165-170°C. Do not go over
170°C. . : .. ' - - - -:-
5. Cool the mixture to room temperature.-.- ....:•..— ....... .---I-— ....
6. Add 200 ml. of distilled water. . . .
7. Add 10 ml. of potassium iodide solution. •
8. Titrate with sodium thiosulfate in the follwing manner: Add thio-
sulfate until mixture is a straw color. Add sufficient starch
indicator solution to produce a dark, opaque color. Continue adding
thiosulfate slowly until a light transparent blue color is prpduced.
The endpoint is now a few drops away. Add thiosulfate dropwise until
the blue color is dissipated leaving a greenish-blue clear solution.
9. Run a blank the same as above with the exception that distilled water
is substituted for the sample of waste;.. ;
Calculation . .
mg/1 C.O.D. = (B-S) 400 .
ml of sample
B = mis of thio to titrate blank.
S = mis of thio to titrate sample.
127
-------
APPENDIX C
GRAPHIC SUMMARY OF EVALUATIVE RUN
MARCH, APRIL, MAY, JUNE 1979
128
-------
.GRAPHIC SUMMARY OF EVALUATIVE RUN - MARCH *79
3 4 F. 6 7 6 3 /Q // /2 /3 14- 16 16 H Id 15 20 21. g 2} 24 25 2627 26 21 W 31
/ Z
30 3 1
-------
GRAPHIC.SUMMARY_QF EVALUATIVE RUN_.i. APRIL '?9
2 .3 4 5 S 7 6 -9-JO-JJ 12 13 J4.-I5 '6 J7 IS 19 20 2LJ? 73 24 Z* 2f 27 W 23 30
16 17 'B Id 2O Zl Z2 23
-------
GRAPHIC SUMMARY OF EVALUATIVE RUN - MAY '79
/ 2 3 4 S 6 7 Q S> /O II 12 13 U IS IS 17 IB 19 2O 21 22 2$ 24- 26 26 27 28 23 SO
3 A? // 12 13 14 15 /6 17 18 13 2O 21 22 23 24 25 26 27 26
30 31
-------
GRAPHIC SUMMARY OF EVALUATIVE RUN - JUNE '79
/ 2 3 4- S 6 7 B 3 10 I' II II 14 IS /g 17 18 'S 2O 2i It 2} 24 25 26 17
30
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