6061
MUNICIPAL WASTEWATER TREATMENT
TECHNOLOGY FACT SHEETS
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COLLECTION SYSTEMS
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SEWERS, SEPTIC TANK EFFLUENT PUMP PRESSURE FACT SHEET
x"
Description - A septic tank effluent pump (STEP) pressure sewer has a septic tank and a pump at each service
connection. The pumps discharge septic tank effluent into a completely pressurized pipe system terminating at a
treatment plant or a gravity sewer. Because the mains are pressurized, there will be no infiltration into them, but
Infiltration and inflow into the house sewers and the septic tanks can occur. The volume of the septic tanks is often
1000 gallons but varies widely. They remove grit, settleable solids, and grease. The pumps typically are 1/3 to 1/2
hp (0.25 to 0.37 kW) and require 110-120 V. They are designed to pump septic tank effluent; they have larger
clearances than potable water pumps, but will not pump raw sewage solids. The head and flow rate provided by
the pumps are typically about 50 ft and 15 gpm but vary widely. The working volume of the pump well is typically
about 40 gallons. The discharge line from the pump is equipped with at least one check valve and one gate valve.
Electrical service is required at each service connection. The pipe network can contain closed loops but typically
does not The sewer profile typically parallels the ground surface profile, and the horizontal alignment can be
curvilinear. Plastic pipe is typically used; it is economical in small sizes, and It resists corrosion by the septic
wastewater. The minimum diameter is typically 1 1/4 in (30 mm) for service connections and the smallest mains.
Cleanouts are used to provide access for flushing. Automatic air release valves are required at or slightly downstream
of summits in the sewer profile. Because of the small diameters, curvilinear horizontal alignment, and profile
paralleling the ground surface, excavation depths and volumes are typically much smaller for a STEP pressure sewer
than for conventional sewers, sometimes requiring only a chain trencher.
Common Modifications - A service connection at sufficiently high elevation may be served by gravity, omitting the
pump and creating a hybrid STEP/SDES (small diameter effluent sewer) system. The use of a gravity connection
in this situation is advantageous because a pump would be subject to siphoning and air-binding. Hybrid designs
are common in current practice. In-line lift stations can also be used if required by the terrain or for cost-
effectiveness.
Pipe networks with closed loops can be used to provide continuing service in case of a main break.
Two-compartment septic tanks may be more efficient at retaining solids, but single-compartment tanks have performed
well. Septic tanks with integral pump vaults are available; they reduce excavation on-lot.
Several dwelling units or other service locations can be clustered to a single septic tank, which should have an
increased volume depending on the total population equivalent it serves. Duplex pump wells may be required on
larger services. Clustered service connections have often led to disputes over billing and responsibility for nuisance
conditions and service calls (Bowne, ad.) .
Technology Status - EPA has reported funding 86 STEP Systems (USEPA, 1988); an unknown number of STEP
Systems have been built without EPA funding. The technology has been used in the US at least since 1970 (USEPA,
1977).
Applications - STEP systems are most cost-effective where housing density is low, where the terrain has' undulations
with relatively high relief, and where the system outfall must be at a higher elevation than most or all of the service
area They can also be effective where flat terrain is combined with high ground water or bedrock, making deep cuts
excessively expensive. They can be cost-effective even in densely populated areas if the terrain is sufficiently difficult
for gravity sewers.
STEP systems do not have the large excess capacity typical of conventional gravity sewers. Therefore they must
be designed with an adequate allowance for future growth if that is desired.
Where pressure sewers are indicated, the choice between STEP and GP (grinder pump) systems depends on two
main factors. First, the costs of on-lot facilities will typically be over 75% - perhaps well over 90% • of the total
system cost. Therefore, the system with the lower average on-lot cost will ordinarily have the lower total cost. STEP
systems have the advantage of allowing some service connections to be gravity connections in some cases, thus
lowering on-lot costs. GP systems must have the pumps (and grinders) at all service connections. The second
factor is the relevance of design velocities. GP systems require a higher velocity because they carry the sewage
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solids and grease. STEP systems will better tolerate the low flow conditions that occur In locations with a highly
fluctuating seasonal occupancy and in locations with slow buildout from a relatively small initial population to the
ultimate design population.
Limitations - STEP sewers are usually not as cost-effective as SDES systems, conventional gravity sewers, or flat
grade sewers where the treatment location is at a tower elevation than the service area, and the undulations are of
low relief.
STEP lines may follow rear property lines when constructed in older neighborhoods, because the house plumbing
exits the rear of the house. General purpose easements are required.
Septic tanks must be well constructed. They may collapse if poorly designed or manufactured. Septic tanks should
be watertight. Typically a large majority of existing septic tanks must be replaced in all but the most recent housing
tracts. Excessive infiltration, amounting to as much as ten times dry weather flow or more, may occur through leaking
house sewers, leaking septic tanks, or disused leaching fields connected to the septic tanks. These problems can
be avoided with proper design and maintenance. Inflow from basement drains, house footing drains, or roof drains
can also greatly exceed sewage flow and should not be allowed.
Septic tanks must be pumped at regular intervals, typically (and conservatively) once every three to five years.
General purpose easements are needed for access to the septic tanks. Septage handling and treatment must be
provided.
Because the wastewater is septic, it is essential to control odor and corrosion. Without controls, odors are typically
noticeable at lift stations and automatic air release valve locations. Odors can be absorbed efficiently and
cost-effectively in soil absorption beds (Bowker et al., 1985). Odors can also be controlled by injecting air or oxygen
into the system; by chemically oxidizing the septic tank effluent with chlorine, hydrogen peroxide, or potassium
permanganate; by adding metal salts to precipitate sulfides; by adding nitrate to decrease microbial reduction of
sutfate to sulfide; or by adding an alkali to raise the pH and decrease the emission of hydrogen sulfide (Bowker et
al., 1985).
, , . ,
Corrosion can be controlled by using corrosion-resistant materials such as plastic pipe throughout the system.
Concrete septic tanks should have a corrosion-resistant coating. Corrosion can be particularly severe in
non-corrosion-resistant conventional sewers to which the STEP system Is connected. This can be controlled by
limiting the ratio of effluent to raw wastewater or by aerating the effluent at the point of entry into the conventional
system. The techniques of odor control listed above, other than soil absorption, also control corrosion (Bowker et
al., 1985).
Solids and grease typically do not accumulate in a STEP system because they are largely removed in the septic
tanks. Biological slimes grow on the inside of the pipe, and can become significant if the velocity is consistently
below 1 fps (0.3 m/s). These slimes can be sloughed off by flushing at a velocity greater than 1 fps (0.3 m/s) (Otis,
1985).
Typical Equipment/No, of Mfrs. (Thomas Register, 1988) - septic tanks (275), septic tanks with integral pump vaults,
pump wells, pumps, float controls, electrical boxes, plastic pipe (332), plastic sewer pipe (21).
Performance - The septic tanks typically remove about 50% of BOD, 75% of suspended solids, virtually all grit, and
about 90% of grease. Therefore, clogging is not a problem. Also, the wastewater reaching the treatment plant will
typically be weaker than raw sewage. Typical average values of BOO and TSS are 110 mg/I and 50 mg/l,
respectively- On the other hand, septic tank effluent has virtually zero dissolved oxygen.
Primary sedimentation Is not required In treating septic tank effluent. Sand filters are effective secondary treatment.
Activated sludge processes are also effective. Effluent responds well to aerobic treatment, but odor control at the
headworks of the treatment plant should receive extra attention.
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Design Criteria - A wide variety of design flows has been used. A typical design flow formula is Q » 15 + 0.5D,
where Q is the design flow In gpm and D is the number of dwelling units served. The 15 gpm is the minimum flow
expected from one pump, and the 0.5 gpm per dwelling unit may be obtained by assuming an average per capita
flow of 50 gpd, 3.5 persons per dwelling unit, and a peaking factor of 4. The operation of the system under various
assumed conditions should be simulated by computer as a check on the adequacy of the design. No standard
allowances for infiltration and inflow have been established; the designer must estimate these flows based on local
conditions. A minimum velocity of 1 fps Is typically imposed (WPCF, 1986). Flows and velocities in hybrid
SDES/STEP systems call for careful designer judgment.
Septic tanks must be watertight and able to withstand pressures caused by high ground water and/or overburden
without collapse. Septic tanks may also need to be anchored to prevent flotation by high ground water. The volume
of the tank should be at least 1000 gallons for a single-family dwelling, and larger for commercial establishments or
clustered service connections. ,
Reliability - STEP systems are highly reliable; typical mean times between service calls (MTBSC). not Including
scheduled operations and preventive maintenance, range from about 3.5 to 7.7 years (WPCF, 1986). These data
include some of the earnest STEP systems constructed jn the US, Call-out maintenance usually results from some
problem with the pump, float switches, or electrical panel (WPCF, 1986). Maintenance typically must be performed
within 24 hours of the call, since a buffer volume of about 200 gallons is typically available in the septic tank.
Preventive maintenance includes annual inspection of the on-lot facilities, particularly the pump, float switches, and
electrical panel The pump wett should be cleaned if necessary, and the accumulation of septage in the septic tank
should be noted. Normal operation requires periodic pumping of septage from each tank, typically (and
conservatively) once every three to five years, but once every 10 to 12 years may be adequate (Bowne, ad.). Sewer
flushing may be required occasionally.
General easements are needed to allow access to the on-lot facilities for maintenance and septage pumping.
Environmental Impact - Construction impacts are typically lower than with conventional sewers, because excavation
is usually shallow, sometimes requiring only a chain trencher. On the other hand, a significant amount of construction
Impact is shifted on-lot, because septic tanks must be inspected, repaired, and/or replaced. When the system begins
operation, odors may be a problem at some points In the system, but they can be controlled by the methods
described above. The impacts on water quality and residuals disposal can be less than with conventional systems,
because the required treatment plant can be simpler, and the amount of residual solids (sludge and septage) Is
smaller.
Energy Consumption - The individual pumps at the service connections consume little energy. For a typical
single-family dwelling, 200 gpd of effluent will be pumped at 10 gpm, giving a pump operating time of 20 min/day.
A 1/2 hp pump will thus consume about 45 kWhr/yr. At $0.10/ kWhr, the annual energy cost of the pump is about
$4.50. . .
Costs - STEP systems can have as much as 90% or more of their construction costs on-lot. This is an added
advantage for new developments with slow buildout, since only a small proportion of the total system cost is tied
up in the initial outlay for the sewer lines.
Construction costs vary widely, depending principally on the topography, housing density, and subsurface conditions
in the service area A 1989 telephone survey yielded the following construction costs: the total construction costs
of 5 systems varied from $5,200 to $36,000 per septic tank (December, 1989 dollars), with an arithmetic average of
$16,000 per tank; the total construction cost of 3 systems varied from $9 to $54 per gpd (December, 1989 dollars),
with an arithmetic average of $32 per gpd. The accuracy of the survey data Is rather low, but It gives a rough
estimate of the magnitude and variability of costs.
The following unit costs are rough estimates of typical construction costs (Mahoney, 1989):
Pipe material and Installation cost:
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Material and Installation Costs ($/ft)
Diameter PVC pvc Polyethylene
0°) SDR 26 SDR 35 SDR 7
2 3.45 2.83
4 5.70 Z52
6 8.55 8.37
8 16.45 4.05
10 6.00
12 7.35
15 11.80
Trench Excavation and Backfill Costs (soil excavation, no dewatering needed):
40 hp chain trencher, 8 in wide, 4 ft deep $0.60/ft
backhoe, 3/8 C.Y. bucket, 0 to 1 side slope, 2 ft wide. 4 ft deep $3.16/ft
backhoe, 1/2 C.Y. bucket, 0 to 1 side stope. 2 ft wide, 8 ft deep $5.32/ft
backhoe, 1/2 C.Y. bucket, 1 to 1 side slope, 2 ft wide, 8 ft deep $17.20/ft
Septic tank (1000 gal), 50 ft service line, pump well, pump, and controls; installed (White, 1980; adjusted for inflation):
$3,500 per service connection.
These unit cost figures are not complete enough nor site-specific enough for estimating the costs of a particular
system, but they are intended to highlight the major cost elements of a STEP system and their potential variability.
Reliable data on operation and maintenance costs are difficult to obtain. Estimates of $110/yr per STEP unit plus
$430/yr per mile of sewer have been used (Gidley and Gray, 1987, adjusted for inflation). The former figure includes
energy, septage removal, preventive maintenance, service calls, and pump replacement.
References -
1. Bowker, Robert P.G., John M. Smith, and Neil A. Webster, Design Manual: Odor and Corrosion Control in Sanitary
Sewerage Systems and Treatment Plants, EPA/625/1-85/018, October 1985.
2. Bowne, William, personal communications.
3. Gidley, J.S., and D.D. Gray, "A Comparison of Conventional Sewers Using Clay Pipe with Alternative Sewers,'
report to the National Clay Pipe Institute, Lake Geneva, Wl, May 19, 1987.
4. Mahoney, William D., ed.-in-chief, Means Assemblies Cost Data 1990, R.S. Means Co. Kingston, MA 1989.
5. Thomas Register of American Manufacturers and Thomas Register Catalog File, Thomas Publishing Co. New
York, 1988.
6. U.S. EPA, Alternatives for Small Wastewater Treatment Systems: Pressure Sewers/Vacuum Sewers,
EPA-625/4-77-011, 1977.
7. U.S. EPA, Municipal Wastewater Conveyance and Treatment: Technological Progress and Emerging Issues,
1988, Office of Municipal Pollution Control (WH-595), Municipal Facilities Division,Washington, D.C.. September 1988.
8. Water Pollution Control Federation, 'Alternative Sewer Systems,1 Manual of Practice FD-12, Alexandria, Virginia,
1986.
9. White, G.B., 'Fundamental Elements and Cost Consideration of Pressure Sewer Systems," M.S.E. Problem Report,
West Virginia University, Morgarrtown, WV, 1980.
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Flow Diagram -
On-Site STEP Components: Alternative A
Separate Pump Well
Septic Tank
Pump Well
_
4 U j
House
lumbing
-1
Scum
- _
r^
-
Sludge
Check
Valve
V
Effluent
Float Switches Pump
Automatic Air
Release Valve
On-Site STEP Components: Alternative B
Integrated Pump Well
r
4" I .
Septic Tank
T
Pump Well
C
House
Plumbing
1
Scum
«
i
v
*
* ,
* /
Gate
Valve
£_/
/Main
.Check
Valve
Effluent
Pump
Float Switches
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SEWERS, SMALL DIAMETER EFFLUENT FACT SHEET
^
Description - A small diameter effluent sewer (SDES) collects effluent from septic tanks at each service connection
and transports it by gravity to a treatment plant or a gravity sewer. Synonyms include small diameter gravity sewers,
septic tank effluent drains, and small bore sewers. The volume of the septic tanks is often 1000 gallons but varies
widely. They remove grit, settleable solids, and grease, and they attenuate peak flows significantly. Both the
horizontal and vertical alignments of the pipes can be curvilinear. The pipe network contains no closed loops. Uphill
sections can be used, provided that there is enough elevation head upstream to maintain flow in the desired direction,
and that there is no backflow into any service connection. Minimum diameters can be 2 in (50 mm) or less. Plastic
pipe is typically used; it is economical in small sizes, and it resists corrosion by the septic wastewater. Cleanouts
are used to provide access for flushing. Manholes are used infrequently, usually at major junctions of main lines.
Air release risers are required at or slightly downstream of summits in the sewer profile. Because of the small
diameters and flexible slope and alignment of the SDES, excavation depths and volumes are typically much smaller
than with conventional sewers, sometimes requiring only a chain trencher.
Common Modifications - Two varieties of SDES systems have been used: the variable grade effluent sewer (VGES)
and the minimum grade effluent sewer (MGES). The VGES allows flexibility of horizontal and vertical alignment,
provided that there is enough elevation head to maintain flow in the desired direction, and that there is no backflow
into any service connection at design flow. In the MGES, minimum downward slopes are Imposed. In some cases,
horizontal alignments have been required to be straight, and larger minimum diameter constraints have been imposed.
Therefore the MGES is more conservative and more costly than the VGES.
In both the MGES and the VGES, individual service connections can be equipped with a septic tank effluent pump
unit, creating a hybrid with the septic tank effluent pump (STEP) pressure sewer. The use of STEP connections is
advantageous when excavation costs can be reduced enough to offset pumping costs. Hybrid designs are common
in current practice. In-line lift stations can also be used if required by the terrain or for cost-effectiveness.
Two-compartment septic tanks may be more efficient at retaining solids, but single-compartment tanks have performed
well.
Several dwelling units or other service locations can be clustered to a single septic tank, which should have an
increased volume depending on the total population equivalent It serves.
Technology Status - The EPA has reported funding 151 SDES systems (USEPA, 1988); an unknown number of
systems have been built without EPA funding. The earliest SDES System reported in the US was built in 1975 (Otis,
1985).
Applications - SDES systems are likely to be most cost-effective where the housing density is low, the terrain has
undulations of low relief, and the elevation of the system terminus is lower than all, or nearly all, of the service area
They can also be effective where the terrain is too flat for conventional gravity sewers without deep excavation.
SDES systems do not have the large excess capacity typical of conventional gravity sewers. Therefore they must
be designed with an adequate allowance for future growth if that is desired.
Limitations • SDES systems are usually not as cost-effective as pressure sewers if the treatment location is at a higher
elevation than the service area, or undulations are of high relief. In either case, lift stations are needed. In general,
SDES systems are not cost-effective unless the topography is such that the sewer profile can stay close to the
ground surface without using a large number of lift stations.
SDES lines often follow rear property lines if constructed in older neighborhoods, because house plumbing exits to
the rear. Topography often requires the crossing of private property also. General purpose easements are required.
Septic tanks must be well constructed and watertight They may collapse If poorly designed or manufactured.
Typically a large majority of existing septic tanks must be replaced in all but the most recent housing tracts.
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Excessive infiltration, amounting to as much as ten times dry weather flow or more, may occur through leaking house
sewers, septic tanks, or disused leaching fields connected to the septic tanks. These problems can be avoided with
proper design and maintenance. Inflow from basement drains, roof drains, or house footing drains can also greatly
•xceed sewage flow and should not be allowed.
Septic tanks must be pumped at regular intervals, typically (and conservatively) once every three to five years.
General purpose easements are needed for access to the septic tanks. Septage handling and treatment must be
provided.
Because the wastewater is septic, ft is essential to control odor and corrosion. Without controls, odors are typically
noticeable at lift stations, drop manholes, air release risers, and some service connections (through the septic tank).
Odor generation can be reduced by avoiding splashing in manholes. Odor can be absorbed efficiently and
cost-effectively in soil absorption beds (Bowker et al., 1985). Odors can also be controlled by injecting air or oxygen
Into the system; by chemically oxidizing the septic tank effluent with chlorine, hydrogen peroxide, or potassium
permanganate; by adding metal salts to precipitate sulfides; by adding nitrate to decrease microbial reduction of
sulfate to sutfide; or by adding an alkali to raise the pH and decrease the emission of hydrogen sulfide (Bowker et
al., 1985).
Corrosion can be controlled by using corrosion-resistant materials such as plastic pipe throughout the system.
Concrete septic tanks should have a corrosion-resistant coating. Corrosion can be particularly severe in
non-corrosion-resistant conventional sewers to which the SDES system is connected. This can be controlled by
limiting the ratio of effluent to raw wastewater or by aerating the effluent at the point of entry into the conventional
system. The techniques of odor control listed above, other than soil absorption, also control corrosion (Bowker et
al., 1985).
Solids and grease typically do not accumulate in an SDES system because they are largely removed In the septic
tanks. Grit can enter through manholes, and so they should be avoided, or built with closed pipes passing through.
Biological slimes grow on the inside of the pipe, and can become significant if the velocity is consistently below 1
fps (0.3 m/s). These slimes can be sloughed off by flushing at a velocity greater than 1 fps (0.3 m/sec) (Otis,1985).
Typical Equipment/No, of Mfrs. (Thomas Register, 1988) - septic tanks (275), plastic pipe (332), plastic sewer pipe
(21).
Performance - The septic tanks typically remove atooul 50% of BOD, 75% of suspended sottds, virtually all grit, and
about 90% of grease. Therefore, clogging is not a probtem. Also, the wastewafer teaching the treatment plant will
typically be weaker than raw sewage. Typical average values of BOD and TSS are 110 mg/I and 50 mg/l,
respectively. On the other hand, septic tank effluent has virtually zero disserved oxygen.
Primary sedimentation is not required in treating septic tank effluent. Sand filters are quite effective in treatment.
Effluent responds well to aerobic treatment, but odor control at the headworks of the treatment plant should receive
extra attention.
Design Criteria - Design flows of 50 to 80 gpcd (190 to 300 I/cap-day) are typically used for both VGES and MGES
systems, with peaking factors of 2 to 4 (Otis, 1985). No standard allowances for infiltration and inflow have been
established, but conservatively large per capita flows and/or peaking factors have been used instead. Alternatively,
the designer must estimate infiltration and inflow based on local conditions. Flows and velocities in hybrid
SDES/STEP systems call for careful designer judgement.
MGES design criteria are conservative. Minimum velocities of 1 to 1.5 fps (0.3 to 0.45 m/sec), with the pipe flowing
full or half-full, have been imposed; the minimum diameter has typically been 4 in (100 mm) (Otis, 1985). The
minimum velocities cannot be maintained in the upper reaches of a system except by the use of unusually steep
slopes. Minimum (downward) slopes are specified for each diameter based on minimum velocity; the criteria can
lead to steeper slopes than required in conventional gravity sewers, obviating some of the potential for cost savings
lead to steeper slopes than required in convernionai gravny sewers, ooviaimg some or tne potential for co
VGES design criteria are less stringent, taking fuller advantage of the benefits of SDES technology.
Often no
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minimum velocity constraint is imposed, and the minimum diameter is typically 2 In (50 mm) (WPCF, 1986). No slope
requirements are imposed other than to make the design hydraulically feasible.
Septic tanks must be watertight and able to withstand pressures caused by high ground water and/or overburden
without collapse. Septic tanks may also need to be anchored to prevent flotation by high groundwater. The volume
of the tank should be at least 1000 gallons for a single-family dwelling, and larger for commercial establishments or
clustered service connections.
Reliability - A pure SDES system (with no STEP units and no lift stations) has no moving parts, and is highly reliable
in operation. Call-out maintenance is typically very infrequent; the only likely cause is a construction accident
breaking a line. Preventive maintenance consists of periodic flushing of low-velocity lines. Normal operation requires
the periodic pumping of septic tanks, typically (and conservatively) once every three to five years, but once every
10 to 12 years may be adequate (Bowne, ad.). Sewer flushing may be required occasionally. General easements
are needed to allow access to the on-lot facilities for maintenance and septage pumping.
Environmental Impact - Construction impacts are typically less severe than with conventional sewers, because
excavation is typically shallow, sometimes requiring only a chain trencher. On the other hand, a significant amount
of construction impact is shifted on-lot, because septic tanks must be inspected, repaired, and/or replaced. When
the system begins operation, odors may be a problem at some points in the system, but they can be controlled by
the methods described above. The impacts on water quality and residuals disposal can be less severe than with
conventional systems, because the required treatment plant can be simpler, and the amount of residual solids (sludge
and septage) is smaller.
Energy Consumption - A pure SDES system (with no STEP units and no lift stations) requires no energy for normal
operation.
Costs - SDES systems can have as mucft as 90% of their construction costs on-lot. This is an added advantage
for new developments with siow buildout, since only a small proportion of the total system cost is tied up in the initial
outlay for the sewer lines.
Construction costs vary widely, depending principally on the topography, housing density, and subsurface conditions
in the service area A 1989 telephone survey yielded the following construction costs: the total construction costs
of 15 systems varied from $3,500 to $69,000 per septic tank (December 1989 dollars), with an arithmetic average of
$14,000 per tank; the total construction cost of 7 systems varied from $6 to $43 per gpd (December, 1989 dollars),
with an arithmetic average of $22 per gpd. The accuracy of the survey data is rather low, but it gives a rough
estimate of the magnitude and variabilities of costs.The following unit costs are rough estimates of typical construction
costs (Mahoney, 1989)
Concrete septic tank and service line installed (1000 gal) $1,200
Fiberglass septic tank and service line installed (1000 gal) $1,300-
, ., ,
Pipe material and installation cost:
Pipe Material and Installation Costs ($/ft)
Diameter PVC PVC Polyethylene
(in) SDR 26 SDR 35 SDR 7
2 3.45 2.83
4 5.70 2.52
6 8.55 3.37
8 16.45 4.05
10 6.00
12 7.35
15 11.80
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Trench Excavation and Backfill Costs (Soil excavation, no dewatering needed):
' 40 hp chain trencher, 8 in wide, 4 ft deep
backhoe, 3/8 C.Y. bucket, 0 to 1 side slope,
2 ft wide, 4 ft deep
backhoe, 1/2 C.Y. bucket, 0 to 1 side slope,
2 ft wide, 8 ft deep
backhoe, 1/2 C.Y. bucket, 1 to 1 side slope,
2 ft wide, 8 ft, deep
$0.60/ft
$3.16/ft
$ 5.31/ft
$17.20/ft
STEP unit, pump well, and controls (White, 1980, adjusted for inflation):
$2,500 per unit
These unit cost figures are not complete enough nor site-specific enough for estimating the costs of a particular
system, but they are intended to highlight the major cost elements of an SDES system and their potential variablity.
Reliable data on operation and maintenance costs are difficult to obtain. Planning estimates of $50/yr per septic tank
plus $430/yr per mile of sewer have been used (Gidley and Gray, 1987, adjusted for inflation). The former figure
includes septage removal, preventive maintenance, and service calls.
Flow Diagram -
Air
Release Valve
House
Plumbing
Onsite Septic Tank
Access Port
Main
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References -
1. Bowker, Robert P.O., John M. Smith, and Neil A. Webster, Design Manual: Odor and Corrosion Control In Sanitary
Sewerage Systems and Treatment Plants, EPA/625/1-65/018. October 1985.
2. Bowne, William, personal communications.
3. Gidley, S., and D.D. Gray, 'A Comparison of Conventional Sewers Using Clay Pipe with Alternative Sewers,' report
to the National Clay Pipe Institute, Lake Geneva, Wl, May 19, 1987.
4. Mahoney, William D., ed.-in-chief, Means Assemblies Cost Data 1990, R.S. Means Co., Kingston, MA, 1989.
5. Otis. R. J., 'Septic Tank Effluent Drainage: An Alternative Wastewater Collection Method*, Proceedings 1985
International Symposium on Urban Hydrology, Hydraulic Infrastructures and Water Quality Control, University of
Kentucky, Lexington, Kentucky, July 1985.
6. Thomas Register of American Manufacturers and Thomas Register Catalog File, Thomas Publishing Co., New
York, 1988.
7. U.S. EPA, "Municipal Wastewater Conveyance and Treatment: Technological Progress and Emerging Issues, 1988,
Office of Municipal Pollution Control (WH-595), Municipal Facilities Division, Washington, D.C., September 1988.
8. Water Pollution Control Federation, "Alternative Sewer Systems," Manual of Practice FD-12. Alexandria, Virginia,
1986.
9. White, G.B., "Fundamental Elements and Cost Considerations of Pressure Sewer Systems,' M.S.E. Problem Report,
West Virginia University, Morgantown, 1980.
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SEWERS, GRINDER PUMP PRESSURE FACT SHEET
s
Description • A grinder pump (GP) pressure sewer has a pump at each service connection. The pumps are 1 hp
(0.75 kw) or more, typically require 220 V. and are equipped with a grinding mechanism that macerates the solids.
The head and flow rate provided by the pumps are typicalry about 50 to 100 ft and 10 to 15 gpm but vary widely.
The pumps discharge into a completely pressurized pipe system terminating at a treatment plant or a gravity sewer.
Because the mains are pressurized, there will be no infiltration into them, but infiltration and inflow into the house
sewers and the pump wells can occur. In areas where the GP sewer system has replaced septic tank and leaching
field systems, these may be retained for emergency overflow, but they should be separated from the pump well by
a gate valve which is only opened when emergency overflow is needed. Otherwise, the septic tank and leaching
field can become sources of large volumes of infiltration. The discharge line from the pump is equipped with at least
one check valve and one gate valve. Electrical service is required at each service connection. The pipe network
typically has no closed loops. The sewer profile typically parallels the ground surface profile. Horizontal alignment
can be curvilinear. Plastic pipe is typically used; it is economical in small sizes, and it resists corrosion. The
minimum diameter is typically 1 1/4 in (30 mm) for service connections and the smallest mains. Cleanouts are used
to provide access for flushing. Automatic air release valves are required at or slightly downstream of summits in the
sewer profile. Because of the small diameters, curvilinear horizontal alignment, and profile paralleling the ground
surface, excavation depths and volumes are typicalry much smaller for a GP pressure sewer than for conventional
sewers, sometimes requiring only a chain trencher.
Common Modifications - Centrifugal and positive displacement pumps have been used. The latter have a discharge
nearly independent of head, somewhat simplifying design and analysis.
In-line lift stations can also be used if required by the terrain or for cost-effectiveness.
Several dwelling units or other service locations can be clustered to a single pump well, which should have an
increased working volume depending on the total population equivalent it serves. Clustered service connections have
often led to disputes over billing and responsibility for nuisance conditions and service calls (Bowne, ad.). Duplex
pump wells are often used on clustered, commercial, institutional, or other larger services.
Technology Status - EPA has reported funding 152 GP systems (USEPA, 1988); an unknown number of GP systems
have been built without EPA funding. The technology has been in use since the late 1960's. Some pressure sewer
systems using ejectors rather than grinder pumps had been built a few years earlier (USEPA, 1977; Clift, 1968).
Applications • GP systems are most cost-effective where housing density is tow, where the terrain has undulations
with relatively high relief, and where the system outfall must be at a higher elevation than most or all of the service
area They can also be effective where flat terrain is combined with high ground water or bedrock, making deep cuts
excessively expensive. They can be cost-effective even in densely populated areas if the terrain is sufficiently difficult
for gravity sewers.
GP systems do not have the targe excess capacity typical of conventional gravity sewers. Therefore they must be
designed with an adequate allowance to future growth If that is desired.
Where pressure sewers are indicated, the choice between GP and STEP (septic tank effluent pump) systems depends
on two main factors. First, the costs of on-lot facilities will be typically over 75% - perhaps well over 90% - of the
total system cost. Thus, there will be a strong motive In favor of using the system with the less expensive on-tot
facilities for a particular project STEP systems may allow some gravity service connections, thus lowering on-lot
costs. GP systems must have a pump at each service connection to grind the solids. The second factor is the
relevance of design velocities. GP systems require a higher velocity because they carry the sewage solids and
grease. STEP systems will better tolerate the low flow conditions that occur in locations with a highly fluctuating
seasonal occupancy and in locations with slow buildout from a relatively small initial population to the ultimate design
population.
GP units can be used at individual homes to discharge into a conventional gravity sewer at a higher elevation.
-------
Limitations - GP sewers are usually not as cost-effective as SDES (small diameter effluent sewer) systems,
conventional gravity sewers, or flat grade sewers where the treatment location Is at a lower elevation than the service
area and the undulations are of low relief.
OP lines may follow rear property lines when constructed in older neighborhoods, because the house plumbing exits
the rear of the house. General purpose easements are required.
Excessive infiltration, amounting to as much as ten times dry weather flow or more, may occur through house sewers.
teaky pump well covers, or disused septic tanks and leaching fields connected to the pump wells. These problems
can be avoided with proper design and maintenance. Inflow from basement drains, house footing drains, or roof
drains can also greatly exceed sewage flow and should not be allowed.
Without controls, odors are typically noticeable at lift stations and automatic air release valve locations. Odor can
be absorbed efficiently and cost-effectively In soil absorption beds (Bowker et at.. 1985). Odors can also be
controlled by injecting air or oxygen into the system; by chemically oxidizing the sewage with chlorine, hydrogen
peroxide, or potassium permanganate; by adding metal salts to precipitate sulfides; by adding nitrate to decrease
microbial reduction of sulfate to sulfide; or by adding an alkali to raise the pH and decrease the emission of
hydrogen sulfide (Bowker et al., 1985).
Corrosion can be controlled by using corrosion-resistant materials throughout the system, such as plastic pipe. The
techniques of odor control listed above, other than soil absorption, also control corrosion (Bowker et aJ., 1985).
Typical Equipment/No, of Mfrs. (Thomas Register, 1988) - pump wells, grinder pumps, float controls, electrical boxes,
plastic pipe (332), plastic sewer pipe (21).
Performance - The wastewater reaching the treatment plant will typically be stronger than that found in conventional
systems because of the lower infiltration. Typical design average concentrations of BOD and TSS are 350 mg/l each
(WPCF. 1986).
Design Criteria - A wide variety of design flows has been used. When positive displacement pumps are used, the
design flow is obtained by multiplying the pump discharge by the maximum number of pumps expected to be on
simultaneously. When centrifugal pumps are used, the same formulas as for STEP systems may be used; a typical
one is Q = 15 + 0.5 D, where Q is the flow in gpm, and D is the number of equivalent dwelling units served (WPCF,
1986). The flow of 0.5 gpm per dwelling unit may be obtained by assuming an average per capita flow of 50 gpd,
3.5 persons per dwelling unit, and a peaking factor of 4. The operation of the system under various assumed
conditions should be simulated by computer as a check on the adequacy of the design. No standard allowances
for infiltration and inflow have been established; the designer must estimate these flows based on local conditions.
A minimum velocity of about 2 fps is typically imposed.
Reliability - GP systems are highly reliable; typical mean times between service calls (MTBSC), excluding routine
operations and preventive maintenance, are on the order of 5 to 10 years (WPCF, 1986). These data include some
of the earliest GP systems constructed in the US. Higher horsepower motors (3-5 hp) may provide greater reliability
for larger service connections. Call-out maintenance usually results from some problem with the pump, grinder, float
switches, or electrical panel (WPCF, 1986). Maintenance typically must be performed within 4-6 hours of the call,
since the buffer volume in the pump well is typically only about 40 gallons. Thus maintenance personnel should be
on call 24 hours per day. An exception may be made if disused septic tanks and/or leaching fields are retained for
emergency overflow. However, the septic tank and leaching field must be separated from the pump well by a gate
valve to prevent Infiltration. The gate valve would have to be opened by the homeowner when the overflow was
needed.
Preventive maintenance Includes the annual Inspection of the on-lot facilities, particularly the pump, float switches,
and electrical panel, and the cleaning of the pump well.
General easements are needed to allow access to the on-lot facilities for maintenance.
-------
Environmental Impact - Construction impacts are typically lower than with conventional sewers, because excavation
is usually shallow, sometimes requiring only a chain trencher. On the other hand, a significant amount of construction
Impact is shifted on-let When the system begins operation, odors may be a problem at some points in the system,
but they can be controlled by the methods described above. .
Energy Consumption - The individual pumps at the service connections consume little energy. For a typical
single-family dwelling, 200 gpd of sewage will be pumped at 10 gpm, giving a pump operating time of 20 min/day.
A 1 hp pump will thus consume about 90 kWhr/yr. At $0.10/kWhr, the annual energy cost of the pump is about
$9.00.
Costs - Systems can have as much as 90% or more of their construction costs on-let This is an added advantage
for new developments with slow buildout, since only a small proportion of the total system cost is tied up in the initial
outlay for the sewer lines.
Construction costs vary widely, depending principally on the topography, housing density, and subsurface conditions
in the service area A 1989 telephone survey yielded the following construction costs: the total construction costs
of 8 systems varied from $2,000 to $74,000 per grinder pump (December, 1989 dollars), with an arithmetic average
of $22,000 per pump; the total construction cost of 7 systems varied from $6 to $41 per gpd (December, 1989
dollars), with an arithmetic average of $22 per gpd. The accuracy of the survey data is rather low, but it gives a
rough estimate of the magnitude and variability of costs.
The following unit costs are rough estimates of typical construction costs (Mahoney, 1989 a,b,c,d):
Pipe material and installation cost:
Pipe Material and Installation Costs ($/ft)
Diameter PVC PVC Polyethylene
(in) SDR 26 SDR 35 SDR 7
2 3.45 2.38
4 5.70 2.52
6 8.55 3.70
8 16.45 4.05
10 6.00
12 7.35
15 11.80
• •
Trench Excavation and Backfill Costs (soil excavation, no dewatering need):
40 hp chain trencher, 8 in wide, 4 ft deep $ 0.60/fl
backhoe, 3/8 C.Y. bucket, 0 to 1 side slope, 2 ft wide, 4 ft deep $ 3.16/ft
backhoe, 1/2 C.Y. bucket, 0 to 1 side slope, 2 ft wide, 8 ft deep $ 5.32/ft
backhoe, 1/2 C.Y. bucket, 1 to 1 side slope, 2 ft wide, 8 ft deep $17.20/fl
Simplex ginder pump, pump well, controls, 50 ft house sewer, 50 ft pressure service Rne; installed: $3.300 per service
connection.
These unit cost figures are not complete enough nor site-specific enough for estimating the costs of a particular
system, but they are intended to highlight the major cost elements of a GP system and their potential variability.
Reliable data on operation and maintenance costs are difficult to obtain. Estimates of $170/yr per grinder pump plus
$430/yr per mile of sewer have been used (Gidley and Gray, 1987, adjusted for Inflation). The former figure includes
energy, preventive maintenance, service calls, and pump replacement.
-------
Flow Diagram
On-Slte Grinder Pump Component
Pump Well
-~r
4"
House Plumbing
Float Switches x
Gate
Valve
Check \
Valve \?
Main
, Grinder Pump
Main
Sewer
Flow Direction
References -
1. Bowker, Robert P.G., John M. Smith, and Neil A. Webster, Design Manual: Odor and Corrosion Control in Sanitary
Sewerage Systems and Treatment Plants, EPA/625/1-65/018, October, 1985.
2. Bowne, William, personal communication.
3. Clift, Mortimer A., 'Experience with Pressure Sewerage", Journal of Sanitary Engineering Division, ASCE, Vol. 94,
No. SA5, pp. 849-865, October, 1968.
4. Gidley, J.S., and D.D. Gray, 'A Comparison of Conventional Sewers Using Clay Pipe with Alternative Sewers,'
report to the National Clay Pipe Institute, Lake Geneva, Wl, May 19, 1987.
5. Manoney, William D., ed.-in-chief, Means Assemblies Cost Data 1990, R.S. Means Co., Kingston, MA, 1989.
6. Thomas Register of American Manufacturers and Thomas Register Catalog File, Thomas Publishing Co. New York,
1988.
7. U.S. EPA, Alternatives for Small Wastewater Treatment Systems: Pressure Sewers/Vacuum Sewers,
EPA-625/4-77-011, 1977.
8. U.S. EPA, "Municipal Wastewater Conveyance and Treatment: Technological Progress and Emerging issues,'
1988, Office of Municipal Pollution control (WH-595), Municipal Facilities Division, Washington, D.C., September, 1988.
9. Water Pollution Control Federation, 'Alternative Sewer Systems," Manual of Practice FD-12. Alexandria, Virginia,
1986.
10. White, G.B., "Fundamental Elements and Cost Considerations of Pressure Sewer Systems,' M.S.E. Problem
Report, West Virginia University, Morgantown, WV, 1980.
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SEWERS, VACUUM FACT SHEET
s
Description - A vacuum sewer system has three major subsystems: the central collection station, the collection
network, and the on-site facilities. Vacuum is generated at the central collection station and is transmitted by the
collection network throughout the area to be served. Sewage from conventional plumbing fixtures flows by gravity
to an on-site holding tank. When about 10 gallons of sewage has been collected, the vacuum interface valve opens
for a few seconds allowing the sewage and a volume of air to be sucked through the service pipe and into the main
The difference between the atmospheric pressure behind the sewage and the vacuum ahead provides the primary
propulsive force. The fact that both air and sewage flow simultaneously produces high velocities which prevent
blockages. Following the valve closure, the system returns to equilibrium and the sewage comes to rest at the low
points of the collection network. After several valve cycles, the sewage reaches the central collection tank, which
Is under vacuum. When the sewage reaches a certain level, a conventional non-clog sewage pump discharges It
through a force main to a treatment plant or gravity Interceptor.
The vacuum interface valve is the unique component of a vacuum sewer system. These valves operate automatically
using pneumatic controls. The on-site facilities do not use any electricity. The valve is placed in a valve pit which
is buried above the holding tank. Plastic pipe is used throughout a vacuum sewer system. The gravity flow house
sewer is usually 4-inch pipe. It contains an external vent to admit air when the valve cycles, thus preventing the house
plumbing traps from being sucked dry. Typical service connections are 3-inch pipe, and mains range from 4 to 10
inches depending on the flow and layout. Joints are either solvent-welded or vacuum-certified rubber ring type.
The profile of the collection network makes use of the limited ability of vacuum propulsion to flow upward in order
to avoid excessive excavation. Where the ground slopes in the flow direction more than 0.2 %, the pipe parallels
the ground. Otherwise the pipe is laid with a downward slope of about 0.2 % until the depth becomes excessive.
When this occurs, a lift formed by two 45-degree elbows and a short length of pipe is inserted to gain elevation.
The typical lift raises the pipe by 2 feet or less, but higher lifts have been used. Division valves are usually placed
at main junctions and at 1500 foot Intervals to facilitate troubleshooting and repairs. Service lines or tributary mains
always join the continuing main from above through a wye.
Several mains may be served by a single collection station. Each main is connected directly to the collection tank
through a division valve. Air flows from the collection tank through a vacuum reserve tank to the vacuum pumps,
which discharge to the atmosphere. Dual vacuum pumps are provided to improve reliability. Both liquid ring and
sliding vane pumps have been used. Automatic controls cycle the vacuum pumps alternately to maintain the vacuum
in the desired range, usually 18 to 23 feet of water. A backup diesel-generator set is used to maintain service during
electrical outages. An airtodialing telephone alarm is provided to summon the operator in case of malfunctions.
' • i
Common Modifications - Detailed design recommendations differ among manufacturers and engineers. In some
cases, depressed lengths of pipe are substituted for holding tanks. A single interface valve may serve several
houses, a school, or a small business area Service lines may be as small as 2 inches and mains may be 2.5
inches. A few systems use vacuum toilets, which require about 1 quart per flush, contain their own interface valves,
and have their own vacuum service lines. Cleanouts may be provided to improve access to mains.
The vacuum reserve volume may be provided in the collection tank rather than in a separate vacuum reserve tank.
One manufacturer offers an ejector type vacuum pump in which sewage from the collection tank is recirculated by
a centrifugal sewage pump as the primary fluid in a multiphase jet pump. This scheme replaces the conventional
vacuum pump with an ordinary sewage pump and an ejector which has no moving parts. In addition, the structural
load on the collection tank is reduced because it Is at atmospheric pressure. Another manufacturer provides a
factory-assembled, skid-mounted central collection station which can handle design sewage flows of up to 150 gpm.
A building to house this station must be erected locally.
In addition to residential applications, vacuum plumbing Is used in office buildings, hospitals, factories, and marinas.
Vacuum plumbing is widely used on both naval and passenger ships.
Technology Status - On January 1, 1990, there were 42 residential vacuum sewer systems operating in 12 states,
including Alaska and Florida These systems serve more than 50,000 persons using 100 central collection stations,
more than 10,000 vacuum interface valves, and about 160 vacuum toilets. The first of these systems has operated
since 1970. All but 3 systems use the same brand of interface valves.
-------
Applications - Vacuum sewers are most likely to be cost-effective when excavation costs are high, population
densities are tow to moderate, and the topography is flat to moderately rolling. They are well suited for combined
sewer separation projects in urban areas where the inconvenience of construction must be minimized. Other factors
favoring vacuum sewers are the need for water conservation and the need to minimize the risk of sewage spills.
Limitations - Vacuum systems have the highest energy consumption of all collection technologies, and they require
responsive operation and maintenance programs. The propulsive force is limited so the total rise in lifts should not
exceed about 26 feet.
Typical Equipment/No, of Mfrs. (Thomas, 1988; Anonymous. 1989) - Interface valves/3, vacuum toilets/2, vacuum
pumps/26, pipe/37, valve pits/3, collection tanks/11, electrical controls/35, sewage pumps/58, diesel-generator
sets/268, prefabricated central collection stations/1.
Design Criteria - Although there are no universally accepted criteria, the following are widely used.
The maximum capacity of a 2-inch interface valve is 20 gpm.
The maximum capacity of a 3-inch Interface valve is 30 gpm.
The minimum vacuum head needed to operate an interface valve is 5 feet of water.
pipe size max flow max length minimum slope
3 inch 30 gpm 300 ft larger of 0.8*ID or 0.2 %
4 Inch 38 gpm 2000 ft larger of 0.8*ID or 0.2 %
6 inch 105 gpm no limit larger of 0.4*ID or 0.2 %
8 Inch 210 gpm no limit larger of 0.4*ID or 0.2 %
10 inch 375 gpm no limit larger of 0.4*ID or 0.2 %
ID = internal diameter
The sum of frictional and lift losses should not exceed about 13 feet of water. FrictionaJ losses may be estimated
using a modified Hazen-Williams formula The recommended height of a lift is 1 foot in pipe sizes up to 4-inches
and 1.5 feet in larger pipes. The loss due to a lift Is taken as the invert to invert rise less the internal diameter. Lifts
should be at least 5 feet apart in service lines and 20 feet apart in mains.
Use dual vacuum pumps; size each to handle airflow at design conditions. Use dual sewage pumps; size each to
handle design flow. The collection tank volume is at least three times the working volume. Choose the working
volume so a sewage pump starts every 15 minutes at design flow. Use a 400 gallon vacuum reserve tank. The
vacuum pump run time should be from 1 to 3 minutes.
Reliability - Reliability has improved greatly due to changes in hardware and design concepts. Interface valves should
be rebuilt every 10 years; controllers, every 5 years. Both jobs are performed in-shop. Central collection stations
require daily routine maintenance. Vacuum pumps may need an overhaul every 7.5 years and replacement every
15 years. Sewage pumps may need seal changes every 4 years and pump replacement every 10 years. Interface
valves jammed open, or damaged mains may require immediate attention to restore vacuum. A 1989 telephone
survey found that 15 systems (4360 valves) reported mean times between service calls (MTBSC) ranging from 0.2
to 20.5 years per valve. When weighted by the number of valves in each system, the overall MTBSC was 6.9 years
per valve.
Environmental Impact - Construction impacts may be much less than conventional sewers because of reduced
excavation. Risk of sewage spills is minimal since pipes are under vacuum. Aeration of sewage in mains reduces
odor problems.
-------
Costs • Costs are highly site-specific. These are generalized estimates based on a 1989 telephone survey of 32 out
of 42 U. S. vacuum systems, on bid tabulations, and on information from manufacturers and design engineers. AJI
costs are'December 1989 dollars ( ENR Construction Cost Index = 4679).
Based on data from 17 systems, the total construction cost of a vacuum sewer system may range from $ 7,000 to
$ 18,000 per valve. Note that one valve may serve more than one house.
A more detailed estimate can be based on the following typical installed unit costs, but wide variations from these
values are to be expected.
3-inch interface valve, pit, cover $2,000.00 each
4-inch house vent 60.00 each
4-inch gravity flow house sewer 5.00 per foot
3-inch vacuum service pipe 7.00 per foot
4-Inch vacuum main 8.00 per foot
6-inch vacuum main 11.00 per foot
8-inch vacuum main .. 14.00 per foot
10-inch vacuum main 19.00 per foot
4-inch division vaVe 350.00 each
6-inch division valve 500.00 each
8-inch division valve 700.00 each
10-inch division valve 1,000.00 each
4-inch cleanout 150.00 each
6-inch cleanout 180.00 each
150-gpm prefabricated central collection
station, including building, excluding land 116,000.00 each
The cost of custom built central collection stations for design flows in excess of 150 gpm ranges from $ 1000 to
$3000 per valve, excluding land.
Annual Operation and Maintenance:
activity
on-siie (per valve):
check valve timing
rebuild controller
overhaul valve
service calls
annual total per valve
mainline:
operate division valve
central collection station:
telephone service
daily inspection
change oil
change filters
overhaul vacuum pumps
replace vacuum pumps *
change sewage pump seals
replace sewage pumps **
annual total per station
frequency
1/1 year
1/5 years
1/10 years
1/6.5 years
1/1 year
360/1 year
12/1 year
1/2 year
1/15 years
1/15 years
2/10 years
1/10 years
parts
($)
4.40
0.70
5.10
300.00
100.00
240.00
242.00
28.00
616.00
160.00
744.00
2430.00
labor
(hours)
0.5
0.2
0.2
0.3
1.2
0.5
180.0
MO
2.0
3.0
2.0
2.0
4.0
205.0
Two 10-horsepower, 174 cfm sliding vane vacuum pumps at
$ 6.650.00 each. Sinking fund assumes 5 % interest.
•* Two 7.5-horsepower sewage pumps ( 250 gpm at 40 ft head )
at $ 4,675.00 each. Sinking fund assumes 5 % Interest.
-------
Power consumption varies with design flow, length of mains, lift, and quality of maintenance. Based on records
from 5 systems, annual power consumption ranges from 72 to 600 kWh/valve. A value of 500 kWh per valve per
year is'recommended for preliminary estimates.
These estimates are summarized by the following formula
C = 2430*NS + 205*LR*NS + 0.5*LR*NDV + 5.1*NIV + 1.2*LR*NIV
+ 500*NIV*ER
where:
C
NS
LR
NDV
NIV
ER
=annual operation and maintenance cost in December 1989 dollars.
=number of central collection stations.
=labor rate including fringe benefits and overhead in December 1989$/hour.
=number of division valves.
=number of vacuum Interface valves.
=electric power rate in December 1989$/kWh.
Flow Diagram -
vacuum
Vacuum p
Reserve
Tank
Division Sewage £
Valve Pump
References -
1. Airvac. Airvac Vacuum Sewage[sic] Design Manual. Airvac Division of Burton Mechanical Contractors Inc
Rochester, Indiana, 1989.
2. Anonymous, " A Reader's Guide to Products, Services, and Manufacturers.' Public Works, vol. 120, no 5 Aoril
15, 1989. ' '
3. Envirovac, Inc., E-vac Vacuum Sewer Systems, Rockford, Illinois, 1985.
4. Thomas Register of American Manufacturers. Thomas Publishing Company, New York, NY, 1988.
5. Water Pollution Control Federation, 'Alternative Sewer Systems," Manual of Practice No. FD-12, Alexandria,
Virginia, 1986.
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SEWERS, CONVENTIONAL GRAVITY FACT SHEET
x
Description - A conventional gravity sewer carries raw sewage by gravity. It is designed by traditional, conservative
criteria such as those embodied in Ten State Standards' (GLUMRB. 1978). Manholes are included to allow access
for cleaning. Normally, the pipes slope constantly downhill, but in adverse topography lift stations and force mains
often must be included in the collection system to avoid excessive excavation or to reach a fixed elevation at the
system outfall.
Common Modifications - To pass under an obstruction without resorting to pumping or excessive excavation,
inverted siphons can be used. An inverted siphon is a depressed sewer that flows full at low pressure with gravity
as the motive force.
Older cities frequently have combined sewers, in which both sewage and storm water runoff are carried. In dry
weather, the sewage flows in a small depression at the invert of the sewer and flows to a treatment plant. During
rain storms or times of rapid snow melt, large amounts of runoff mixes with the sewage in combined sewers and may
pass untreated through combined sewer overflows directly into a watercourse. Combined sewer overflows are
designed to divert excessive flows before they reach the treatment plant; an interceptor or storage system may collect
combined sewer overflows for later treatment.
Various pipe materials have been used, including vitrified clay, asbestos cement, reinforced concrete, cast iron, ductile
Iron, polyvinyl chloride (PVC), and acrylonitrife-butadiene-styrene (ABS).
Technology Status - Widely used for many years
Applications - Conventional gravity sewers are best suited to densely populated service areas with a relatively
constant, gentle slope toward a desirable treatment plant location.
'•,*-*•** *" " -'- i
4 4 '' . I ~ '; *
Limitations - Conventional gravity sewers can be inordinately expensive where adverse slopes require deep
excavation, many lift stations, or where the population density of the service area is low.
Performance - No treatment occurs in conventional gravity sewers except dilution by infiltration and inflow and a small
amount of aeration.
Design Criteria - A typical average flow allowance is 0.38 m3/cap-day (100 gal/cap-day), which includes Infiltration
and inflow. Alternatively, a separate allowance for infiltration and inflow can be estimated. Sewers are designed to
carry peak flow rates, usually calculated by multiplying the average flow by a peaking factor; a typical formula is
QMAX/QAVE = (18+yP)/(4+VP) where P is the population in thousands (GLUMRB, 1978). This formula yields peaking
factors ranging from about 4.2 for 8 service population of 100 to 2 for a population of 100,000. The minimum pipe
diameter is typically 200 mm (8 in). This conservative criterion avoids the clogging of the sewer by large objects.
Conventional gravity sewers are designed to avoid pressure flow at all times. They must also have sufficient
downward slope to prevent the deposition of solids and grease. To this end, they are typically designed to provide
a velocity of at least 0.6 m/sec (2 fps) when full. Manning's formula is typically used to calculate flows, slopes and
velocities. '
-------
Minimum Slopes for Conventional Gravity Sewers (GLUMRB, 1978)
Nominal
Sewer
Diameter
(mm) (in)
200
230
250
300
360
380
410
8
9
10
12
14
15
16
Minimum
Slope
(m/100 m)
(ft/100 ft)
0.40
0.33
0.28
0.22
0.17
0.15
0.14
Nominal
Sewer
Diameter
(mm) (In)
460
530
610
690
760
910
18
21
24
27
30
36
Minimum
Slope
(m/100 m)
(ft/100 ft)
0.12
0.10
0.06
0.067
0.058
0.046
Manholes are typically placed at the ends of Hoes, at every change of stope, alignment, or diameter, and at least
every 120 m (400 ft) for sewers up to 380 mm (15 in) in diameter and every 150 m (500 ft) for sewers of 460 to 760
mm (18 to 30 in) (GLUMRB, 1978).
Inverted siphons (depressed sewers) are typically designed with at least two barrels, and a minimum diameter of 150
mm (6 in). The smallest barrel should be designed to carry the minimum flow, and the inlet works (distribution box)
should be designed to split higher flows among two or more barrels in such a way as to maintain velocities of at least
0.92 m/sec (3 fps).
Design for Life Safety - Confined space hazards and explosion hazards from sewer gases must be avoided. The
principal point of human entry into conventional gravity sewers is the manhole. No one should ever enter a manhole
without a standby person at the surface, who should be in radio contact with rescue personnel trained and equipped
to perform confined space rescues. The concentrations of oxygen and toxic gases should be determined by a
portable gas monitor before entry. A portable blower and air hose should be used to ventilate the manhole. A
person entering the manhole should be on a harness attached to a hoist erected above the manhole. The standby
person should be able to hoist the entering person out of the manhole even if the latter becomes unconscious.
Reliability - Conventional gravity sewers are ordinarily highly reliable. They often require periodic flushing or cleaning
to remove deposits of solids and grease. Unlined concrete or cast iron pipes are subject to corrosion and may
require expensive lining or replacement after a few years of service. Lift stations, usually associated with gravity
sewers, require frequent maintenance and cleaning.
Environmental Impact - The environmental impact of conventional gravity sewers arises from their construction, the
release of sewer gases, and the operation of the lift stations normally associated with them.
Energy consumption - A pure gravity sewer uses no energy in operation, but flushing and cleaning consumes some
energy, and associated lift stations consume energy in operation and maintenance.
Costs - Construction costs vary widely, depending on factors such as pipe size, excavation depth, subsurface
conditions, site accessibility, type of materials, and quality of installation. Operation and maintenance costs also vary
widely and are difficult to estimate because both the O&M and accounting practices of sewer authorities vary. In
particular, It is not easy to determine what costs are incurred by different parts of the system (i.e., gravity mains, lift
stations, force mains, etc.).
-------
Flow Diagram -
On Lot Components
Main
"- 6"
Main
References •
1. Great Lakes - Upper Mississippi River Board of State Sanitary Engineers(GLUMRB), Recommended Standards
for Sewage Works, Health Education Services, Albany, NY, 1978.
2. Metcalf and Eddy, Inc. Wastewater Engineering: Collection and Pumping of Wastewater, New York, NY,
McGraw-Hill, 1981.
3. Pettit, T., and H. Unn, 'A Guide to Safety in Confined Spaces,' National Institute for Occupational Safety and
Health, Publication No. 87-113. Cincinnati, Ohio, July 1987.
4. U.S. EPA, "Construction Costs for Municipal Wastewater Conveyance Systems: 1973-1979," EPA/430/9-31-003,
January 1981.
5. U.S. EPA, "Operation and Maintenance Costs for Municipal Wastewater Facilities," EPA/430/9-81-004, September
1981.
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UFT STATIONS FACT SHEET
Description - A sewage pumping station (lift station) is a structure housing pumps that propel sewage to a higher
elevation. Its primary components are inlet works; a wet well, In which incoming sewage is briefly stored; pumps;
controls that turn the pumps on and off when the sewage in the wet well reaches specified elevations; and valves
necessary to shut down the station for maintenance or repair. The pumps discharge into a force main, (pressurized
sewer).
*
Lift stations have been classified by capacity as follows (WPCF, 1981):
Capacity
Class fl/s) (gprrrt
Very small <6 <100
Small 6-20 100-300
Medium 20-200 300-3000
Large >200 >3000
They become increasingly complex as their capacity increases. Prefabricated stations are available up to about 400
l/s (6000 gpm), but lift stations can be custom-designed and built in place at any size.
Common Modifications - Lift stations can be designed with either conventional or submersible pumps. Conventional
pumps require a dry well; only the pumps' suction piping enters the wet well. Submersible pumps are designed to
work submerged in liquid; therefore they are placed in the wet well, and the lift station requires no dry well.
Submersible pumps are coupled to piping by quick-disconnect fittings, are mounted on guide rails, and are connected
to a lifting chain so that they can be removed for service without the entry of maintenance persons into the wet well.
Non-clog pumps capable of passing solid spheres up to 2 1/2 to 3 Inches in diameter are typically used (GLUMRB,
1978). In very small stations, grinder pumps may be used. Submersible pumps are self-priming; some conventional
pumps may require external priming by water or vacuum. When non-clog pumps are used, trash baskets or bar
screens are used In the inlet works to remove solids too large to pass through the pumps. A wide variety of pumps
has been used, including various types of centrifugal pumps, turbine pumps and Archimedes screw pumps.
Lift stations should contain at least two pumps. The pumps are actuated by level controls mounted in the wet well.
The most common type of level control is the mercury float switch; others include diaphragms, bubblers, electrodes,
ultrasonic level detectors, and pressure transducers. In duplex stations, containing exactly two pumps, one is
designated the lead pump and comes on first; the other is designated the lag pump and comes on only if the lead
pump is unable to keep pace with the inflow of sewage. To equalize wear on the pumps, controls are set to alternate
the lead and lag pumps, either at every pumping cycle or at a set time interval. In stations containing three or more
pumps, the pumps may be set to come on in sequence. The pump off level is either the same for all pumps, or
they are set to go off in reverse sequence. Alternatively the third pump may be used as a standby or emergency
pump, while the first two operate as in a duplex station.
Swing disc check valves, ball check valves, and other types of check valves are used to prevent backflow through
the pumps. Plug valves, ball valves, or gate valves are typicafy used as shut-off valves to Isolate a pump for
maintenance or replacement
Telemetry can be used to monitor the operation of lift stations from a remote site.
Technology Status - Widely used for many years
Application - Lift stations are used to pump sewage uphill to avoid excessive excavation. Extant data suggests that
as more adverse topographies have been sewered, the frequency of lift stations in conventional gravity sewers has
increased significantly-
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Umltatlons - LJtt stations must be located where they will not be subject to flooding or must be protected against It
Very small lift stations can be built In the street right-of-way, but larger stations may require a house lot or larger plot
of land Lift stations require electrical power, which can be supplied from nearby power lines or from a dedicated
generator. In any case, a standby generator is required for continued operation In case the primary power source
falls. Surge control Is needed to avoid damage to pumps and piping from hydraulic transients (water hammer).
Potentially lethal hazards to maintenance workers arise from toxic and explosive gases or oxygen deficiency in
confined spaces. Ventilation is imperative »the wet well is large enough for human entry. Odors emanating from
lift stations must be controlled. A variety of odor control techniques is available. Corrosion of all metal parts within
a lift station can be severe.
All but the smallest lift stations should be Inspected daily and require frequent preventive maintenance. Trash baskets
and bar screens must be cleaned, and grease and sediment accumulations must be removed from the wet well
before they foul the pumps and controls.
Performance - No treatment is achieved except for the removal of large objects from trash baskets or bar screens
or the grinding of solids in lift stations using grinder pumps.
Design Criteria - A lift station should have more than one pump, and the pumps must be capable of delivering
maximum design flow with the largest pump out of service. The pumps must be sized for the fun range of flow rates
and heads expected; each pump should operate near its best efficiency point. Therefore, both maximum and
minimum design flows must be carefully estimated.
Fluid velocities must be capable of transporting all suspended matter and grease through the pumps and pipes. For
raw sewage, the minimum velocity is 0.6 m/s (2 fps), but at least 1.1 m/s (3.5 fps) is preferred. In sewer systems
carrying septic tank effluent, the minimum velocity can be 0.3 m/s (1 fps) or less, because most of the suspended
matter and grease has been removed in the septic tanks. Minimum velocity should also be maintained through the
wet well to avoid the deposition of solids there. To prevent scouring of the pumps and pipes by grit in raw sewage
pumping, and to prevent excessive head losses and surge control difficulties in all applications, the velocities should
not exceed 2.5 m/s (8 fps).
The pumps must be selected and located in relation to the wet well so that the net positive suction head available
(NPSHA) during the most severe conditions of operation exceeds the net positive suction head required (NPSHR).
This criterion prevents cavttation, the formation of gas bubbles in the fiufeJ within the pump when the liquid pressure
drops below the vapor pressure of the gas, which decreases efficiency and output and can severely damage the
impeller.
The working volume (volume between pump on and pump off levels) In the wet well should be large enough to
ensure that no pump operates less than five minutes at a time; this criterion is desirable to increase pump lifetime.
The working volume should also be small enough so that the retention time of sewage in the wet well does not
exceed 30 minutes; this criterion is desirable to avoid the development of septic conditions in the wet well. These
criteria may be impossible to satisfy if the range of flows is large, and the latter one is moot in a sewer system
carrying septic tank effluent.
A valve pit allowing the hydraulic feotefion of the entire Kft station should be located outside the wet well so that the
lift station can be shut down in emergencies without entry into the wet well.
Design for Life Safety - At least three types of potentially lethal hazards in lift stations must be reckoned with:
confined space hazards, explosion hazards, and electrical hazards.
Forced ventilation must be provided in any lift station large enough to be entered. The ventilation can be continuous
or intermittent; in addition, the blowers should be on whenever anyone is in the station. Continuous ventilation of
wet wells should provide at least 12 air changes per hour; and intermittent ventilation, at least 30 (GLUMRB, 1978).
Matches should also lock In the open position to prevent accidental lock-ins.
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Maintenance procedures should also be planned for life safely. No one should ever enter a lift station alone. One
person should always remain outside with radio or telephone contact with rescue personnel. No one should enter
a lift station without checking the concentration of oxygen and toxic gases within, either with a permanent or portable
gas monitor. Rescue personnel, and preferably maintenance personnel, should have self contained breathing
apparatuses (SCBA) for entry into potentially toxic or oxygen-deficient atmospheres. Persons entering the wet well
should be on tethers attached to hoists so that they can be pulled out without endangering the would-be rescuers'
lives.
To avoid explosions, electrical wiring and circuitry should be designed for Intrinsic safety, that is, no failure should
produce a discharge of enough energy to ignite explosive gases potentially present in the lift station. Other spark
sources, such as arc welding, must also be avoided.
i •-.--• . • , ,
Electrical panels should be Installed in accordance with local codes, and all applicable provisions of the National
Electric Code (NEC) and the National Electrical Manufacturers Association (NEMA) standards should be observed.
Reliability - Pumps, controls, and electrical circuits can fail. Because lift stations are often in remote locations in the
sewer system, they should be equipped with telemetry or an autodialing alarm system or both, so that maintenance
personnel can respond quickly to malfunctions. Metal parts exposed to the corrosive atmosphere in a lift station
should be corrosion-resistant, or they may frequently need to be painted or replaced. Each pump should have a
run-hour meter and a cycle counter for the scheduling of O&M operations.
Environmental Impact - Lift stations produce waste streams In addition to the sewage which ultimately reaches a
treatment plant or overflow discharge. These are gases vented to the atmosphere and cleanings from trash baskets
and bar screens. Uft stations use energy, resulting in an indirect environmental impact, and their construction
potentially impacts their immediate surroundings.
Energy Consumption - Uft stations consume energy in both pumping and maintenance.
Costs - Costs include site acquisition, construction, operation and maintenance, including energy costs.
The construction cost ts peneraJty related to the flow capacity of the lift station. At a given capacity, there is little
correlation between head and cost (Newton and Sanks, 1989). Figures 1 through 3 present the construction cost
curves of Newton and Sanks (1989) for wet well/dry well, submersible pump, and prefabricated lift stations,
respectively. Figure 4 shows the envelope of all the curves in Figures 1 to 3. A significant number of data points
lie outside the curves shown; the curves give only a general expectation of costs. The costs shown do not include
engineering, legal services, land, administration, or interest during construction. These additional costs may as much
as double the costs shown in the Figures.
Operation and maintenance costs vary considerably, partly because the policies of sewer authorities vary
considerably. For small and very small lift stations, maintenance costs can be much more significant than energy
costs, largely because of the travel, labor and overhead cost of frequent inspections. For larger stations, the life-
cycle energy cost may be 10-25% of the construction cost, and the maintenance cost perhaps half again as much.
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CONSTRUCTION COSTS Of LIFT STATIONS
WETWEll f MY y»EU (N€WTON 1 SANKS. 190)
to*.
8 io«.
1C2 103 104 !05
FLOW(QPM)
FIGURE 1. Conaruaun Costs ol Wei Wrt / Dry Wei UK Stations
(Ntwton and Sanks. 19«3| COSTS are nD«c.. 1989 Dollars
CONSTRUCTION COSTS OF LIFT STATIONS
PREFABRICATED (NEWTON AND SAMS. 1M>)
FU/tt (GPM)
FX3URE 3 Construction Com ol PrttaDreawd UK SUMns
(Ntwwn and So**. 19«9) COB tin it OK.. 1989 Dollars
CONSTRUCTION COSTS Of LIFT STATIONS
•UWCRSOU *>*» (NEWTON ANDSAMCS. 1M)
FLOW(OPM)
FIGURE 2 Corwffsxoon Con Of SuGflWlAM Pi^D Uft Staoons
fflmcn ano Sana, igai Cou
8
.1.
UPPEBCOST
to3 10* ios
FLOWIOPU)
FIGURE 4 Constnxtiori COC8 ot Utt Stations
(Nwrton and Sams. UBS', Cots ari «i DK.. 1989 Dollars
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Flow Diagram -
Wet Well
Quick-disconnect
Submersible Pump System
Sump Pump
Dry Well System
References -
1. Bowker. R.P.G., J.M. Smith, and NA Webster, Design Manual: Odor and Corrosion Control in Sanitary Sewerage
Systems and Treatment Plants, EPA/625/1-85/018, October 1985.
2. Great Lakes - Upper Mississippi River Board of State Sanitary Engineers (GLUMRB), Recommended Standards
for Sewage Works, Health Education Services, Albany, NY, 1978.
3. • Metcalf and Eddy, Inc., Wastewater Engineering: Collection and Pumping of Wastewater, McGraw-Hill, 1981.
4. Newton, D., and R.L Sanks, 'Costs', Chapter 29 in Robert L Sanks, ed.-in-chief, Pumping Station Design,
Butterworth Publishers, Stoneham, MA, 1989.
5. Pettit, T. and H. Linn, A Guide to Safety in Confined Spaces, National Institute for Occupational Safety and Health,
Publication No. 87-113, Cincinnati, Ohio, 1987.
6. Submersible Wastewater Pump Association, Submersible Sewage Pumping Systems Handbook, Lewis Publishers,
Inc., Chelsea, Ml, 1986.
7. U.S. EPA, 'Construction Costs for Municipal Wastewater Conveyance Systems: 1973-1979; EPA/430/9-81-003.
1981.
8. Water Pollution Control Federation, 'Design of Wastewater and Stormwater Pumping Stations,' Manual of Practice
No. FD-4, Washington. DC, 1981.
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FORCE MAINS
FACT SHEET
Description * A force main is a pipe carrying sewage under pressure. This fact sheet will deal exclusively with force
mains that exit lift stations in predominantly gravity flow collection systems. Such force mains typically have no
service connections entering them.
Technology Status - Widely used for many years
Applications - Force mains are used to transport sewage uphill to avoid excessive excavation in a predominantly
gravity flow collection system. They may be required within the system or at Its terminus to lift sewage to a treatment
plant.
Limitations - Surge control is needed to avoid damage to pumps and piping from hydraulic transients (water hammer).
Performance - No treatment is achieved in force mains.
Design Criteria - Fluid velocities must be capable of carrying all suspended matter and grease through force mains.
For raw sewage, the minimum velocity is 0.6 m/s (2 ft/s), but at least 1.1 m/s (3 ft/s) is preferred. In systems carrying
septic tank effluent, the minimum velocity can be 0.3 m/s (1 ft/s) or less, because most of the suspended matter and
grease has been removed in the septic tanks. To prevent scouring of the force main by grit in raw sewage, and to
prevent excessive head loss and surge control difficulties in all applications, the velocities should generally not exceed
2.4 m/s (8 ft/s). The Hazen-Williams C factors used in the design of new systems range from 100 for small, unlined
ductile iron to 150 for larger plastic pipe.
Reliability - Property designed force mains are highfy reliable. Some pipe materials, however, such as unlined
concrete and cast iron may be severely corroded or eroded after a few years and may need to be lined or replaced.
Environmental Impact - Force mains have minimal environmental impact, except during construction or in case of
a line break.
Energy Consumption - The lift stations associated with force mains consume energy in pumping and maintenance.
Flow Diagram -
— . %draulic Grade Une
Flow Direction
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References -
1. Great Lakes • Upper Mississippi River Board of State Sanitary Englneers(GLUMRB), Recommended Standards
for Sewage Works, Health Education Services, Albany, NY, 1978.
2. Sanks, Robert L, ed. In chief, Pumping Station Design, Butterworth Publishers, Stoneham, MA, 1989.
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FLAT GRADE SEWERS FACT
X
Description - A flat grade sewer carries raw sewage by gravity, ft is a variant of the conventional gravity sewer and
is designed to criteria less stringent than those embodied In Ten State Standards' (GLUMRB, 1978). In particular,
flatter slopes and smaller pipe diameters are allowed. Manholes are included to allow access for cleaning. Normally,
the pipes slope constantly downhill, but in adverse topography lift stations and force mains must be included in the
collection system to avoid excessive excavation or to reach a fixed elevation at the system outfall.
Common Modifications - To pass under an obstruction without resorting to pumping or excessive excavation, inverted
siphons can be used. An inverted siphon is a depressed sewer that flows full at low pressure with gravity as the
motive force.
Various pipe materials can be used, including vitrified clay, asbestos cement, reinforced concrete, cast iron, ductile
iron, polyvinyl chloride (PVC), and acrylonitrile-butadiene-styrene (ABS).
Technology Status - Flat grade sewers have been widely used in Nebraska for many years and occasionally used
in other states. For example, the city of Phoenix, Arizona has adopted reduced slope criteria for gravity sewers
Demonstration projects in Las Vegas, Nevada and Lacey, Washington have used 6-in lateral sewers.
Applications - Flat grade sewers are best suited to densely populated service areas with a relatively constant, gentle
slope toward a desirable treatment plant location. Because of relaxed design criteria compared to conventional
gravity sewers, flat grade sewers can also be cost-effective in many locations with lower population density and flatter
or adverse topography. Specifically, where the ground surface slope is less than 0.4%, the typical 200-mm (8-in)
conventional gravity sewer pipe will require deep excavation and lift stations, and a flat grade sewer may not.
Limitations - Flat grade sewers can be inordinately expensive when adverse slopes require deep excavation, many
lift stations, or both, or when the population density of the service area is very low. In no case will they be more
expensive than conventional gravity sewers.
Performance • No treatment occurs in flat grade sewers except dilution by infiltration and inflow and a small amount
of aeration.
Design Criteria - A typical average flow allowance is 0.38 rtf/cap-day (100 gal/cap-day), which includes infiltration and
inflow. Alternatively, a separate allowance for infiltration and inflow can be estimated (Metcalf and Eddy, 1981). Flat
grade sewers are designed to carry peak flow rates, usually calculated by multiplying the average flow by a peaking
factor; a typical formula is QMAX/OAVE = (18+yf)/(4+yp). where P is the population in thousands. This formula yields
peaking factors ranging from about 4.2 for a service population of 100 to 2 for a population of 100,000.
The minimum pipe diameter is typically 150 mm (6 In), although pipes as smail as the house sewers, typically 100
mm (4 In), could be used. In sewers not flowing near capacity, the smaller diameters have a higher velocity than
the conventional 200-mm (8-in) sewer.
Flat grade sewers are designed to avoid pressure flow at all times. They should also have sufficient downward slope
to prevent the deposition of solids and grease, but they are not so stringently designed with respect to this criterion
as conventional gravity sewers. Full pipe velocities as small as 0.27 m/sec (0.9 fps) have been used.
Manholes are typically placed at the ends of fines, at every change of slope, alignment, or diameter, and at least
every 120 m (400 ft) for sewers up to 380 mm (15 in) in diameter and every 150 m (500 ft) for sewers of 460 to 760
mm (18 to 30 in). Manhole criteria are the same as for conventional gravity sewers.
-------
Design for Life Safety - Confined space hazards and explosion hazards from sewer gases must be avoided. The
principal point of human entry Into flat grade sewers is the manhole. No one should ever enter a manhole without
a standby person at the surface, who should be In radio contact with rescue personnel trained and equipped to
perform confined space rescues. The concentrations of oxygen and toxic gases should be determined by a portable
gas monitor before entry. A portable blower and air hose should be used to ventilate the manhole. A person
•ntering the manhole should be on a harness attached to a hoist erected above the manhole. The standby person
should be able to hoist the entering person out of the manhole even If the latter becomes unconscious.
Reliability - Flat grade sewers are ordinarily highly reliable. They may require periodic flushing or cleaning to remove
deposits of solids and grease. In theory, flat grade sewers should require more maintenance than conventional
gravity sewers because of their flatter slopes and smaller diameters. Long experience in small communities In
Nebraska, however, indicates that maintenance requirements are similar to those of conventional gravity sewers.
Velocity criteria are usually applied to full pipe flow, but the amount of deposition of solids and grease depends on
the velocity in the partially full pipe during operation. The flat grade sewer is effective partly because the actual
velocities for partially fun pipes are greater in the smaller 100-mm (4-in) and 150-mm (6-in) pipes than in the 200-
mm (8-in) pipes typically required In conventional gravity sewers.
Unlined concrete or cast iron pipes may require expensive lining or replacement after a few years of service. Lift
stations, usually associated with gravity sewers, require frequent maintenance and cleaning.
Environmental Impact - The environmental impact of flat grade sewers arises from their construction, the release of
sewer gases, and the operation of the lift stations normally associated with them.
Energy Consumption - A pure gravity sewer uses no energy in operation, but flushing and cleaning consumes some
energy, and associated lift stations consume energy in operation and maintenance.
Cost - Construction costs vary widely, depending on factors such as pipe size, excavation depth, subsurface
conditions, site accessibility, typo of materials, and quality of installation. Operation and maintenance costs also vary
widely and are difficult to estimate because both the O&M and accounting practices of sewer authorities vary. In
particular, H is not easy to determine what costs are incurred by different parts of the system (i.e., gravity mains, lift
stations, force mains, etc.).
References -
1. Dewberry & Davis, 'Innovative Site Utility Installations; H-5558, US Department of Housing and Urban
Development, August 1983.
2 Gidley, J.S., 'Case Study No. 11: Ericson, Nebraska: Flat Grade Sewers.' EPA National Small Flows
Clearinghouse, West Virginia University, Morgantown, WV, September 1987.
3. Great Lakes - Upper Mississippi River Board of State Sanitary Engineers(GLUMR8), Recommended Standards
for Sewage Works, Health Education Services, Albany, NY, 19?a
4. Metcalf and Eddy, Inc., Wastewater Engineering: Collection and Pumping of Wastewater, McGraw-Hill. New York,
NY, 1981.
5. NAHB National Research Center, 'Challenge and Response -Volume I: Affordable Residential Land Development:
A guide for Local Government and Developers,' US Department of Housing and Urban Development, July 1987.
6. Pettit. T., and H. Unn, A Guide to Safety In Confined Spaces, National Institute for Occupational Safety and Health,
Publication No. 87-113, Cincinnati, Ohio, July 1987.
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7. U.S. EPA, 'Construction Costs for Municipal Wastewater Conveyance Systems: 1973-1979,' EPA/430/9-81-003,
January 1981.
8. U.S. EPA, 'Operation and Maintenance Costs for Municipal Wastewater Facilities,' EPA/430/9-81-004, September
1981.
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DISINFECTION
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CHLORINAT1ON (DISINFECTION) FACT SHEET
Description - Chlorine continues to be the most widely used chemical for the disinfection of wastewater In the U.S.
The major advantages of chlorine over alternative disinfectants are Its cost-effectiveness, Its reliability, and Its efficacy
against a host of pathogenic organisms. When chlorine (Cy is dissolved in water, a mixture of nypochlorous (HOCI)
and hydrochloric (HCI) acids is formed. Chlorine exists predominantly as HOCI below pH 7.6 and as OCr above pH
7.6. HOCI and/or OCr is defined as free available chlorine, with the hypochlorous acid being the primary disinfectant
Chloramines (NH2CI, NHCIj, and NHCy are formed when chlorine reacts with ammonia-nitrogen present in secondary
effluent. At pH 7 to 8 and chlorineiammonia-nitrogen mass ratios of 5:1 or less, monochloramine is formed; at a
tower pH, dichloramine is formed. Studies have indicated that monochloramine may be a more efficient and reliable
disinfectant than, free chlorine since the more reactive free chlorine residual is dissipated in organic reactions and is
not available for disinfection. • ......
Chlorine is typically supplied as liquified gas in cylinders. Chlorinators apply gaseous chlorine to a feed stream which
is then injected into a mixing zone in the chlorine contact chambers. Initial mixing and effective contact times are
essential for good process performance. Generally. 15 to 30 minute contact periods are required at peak flow.
Common Modifications - The two chemicals used for chlorination are chlorine gas and hypochlorite salts. Calcium
hypochlorite (Ca(OCI)j,) is in granular form, while sodium hypochlorite (NaOCI) is handled in liquid form. Sodium
hypochlorite is generally preferred over the calcium hypochlorite because of low maintenance and safety. It is,
however, more costly and requires greater storage area. In remote areas and at smaller plants (up to 0.1 mgd),
granular hypochlorites are sometimes chosen. Lithium hypochlorite (LJOCI) may be preferred in this case because
of the scaling problems associated with Ca(OCI)2. Advantages of hypochlorinalion over chlorination Include increased
safety in transporting, storing, and handling of chemicals; however, chemical costs are generally much higher. Where
reduction or elimination of chlorine discharge is necessary, dechlorination (most often with sulfur dioxide) may be
utilized.
Technology Status - Chlorination is applicable to all size plants, the process control is wen developed, the relative
complexity of the technology is considered simple to moderate, and O&M sensitivity is minimal. It remains the
dominant disinfection process for both water and wastewater. Pressure to strictly control the level of residual chlorine
in wastewater discharges has resulted in refinements for better control sysiems and contactor design. Dechlorination
is used at a growing number of plants to counter the negative effects of chlorine residuals in receiving waters.
Limitations - The effectiveness of chlorination is pH and temperature dependent Chlorine win react with certain
chemicals in the wastewater, leaving only the residual for disinfection. Wastewater components contributing to
chlorine demand include: reduced iron and sulfur compounds, ammonia nitrogen, organic nitrogen, tannins, uric and
numic acid, cyanides, phenols, and unsaturated organics. Cysts of Endamoeba histolytica and Giardia lamblia,
Mycobacterium tuberculosis, some viruses, and eggs of parasitic worms show resistance to chlorine. Consistent
disinfection In nitrified effluents containing organic nitrogen may pose problems, even when a measured free chlorine
residual is present
Chlorine is toxic to aquatic estuarine. and marine organisms. An additional hazard te the carcinogenic potential of
chtoro-organic compounds. Chlorine gas is potentially toxic when inhaled, and chlorine transport poses a risk.
Special handling is required and emergency response plans are required under right-to-know regulations for on-site
storage of gaseous chlorine. Chlorine gas and the hypochlorites are also highly corrosive.
Applications - The major application for chlorine in wastewater treatment is disinfection of pathogens and prevention
of waterbome disease- however, chlorine is also used In wastewater treatment for: control of odors, algae, flies,
sludge bulking, and foaming; prevention of septiclty and filter ponding; improving grease and scum removal; and
destruction of cyanides and phenols.
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Typical Equipment/No, of Mfrs. - chlorinators/24; chlorine analyzers/34; feeders/34; leak detectors/23; mixers/79; pH
controllers/51; scales/39.
s
Performance - Chlorination Is an effective disinfectant and can consistently meet bacterial limits generally Imposed
by discharge permits. Efficiency Is directly related to the level of treatment, and is dependent upon good mixing in
a highly turbulent regime, followed by good plug flow In the contact chamber. Chlorine doses will vary, depending
on upstream treatment levels, chlorine demand, and disinfection requirements. Typical doses range between 5 and
15 mg/L Failure to provide adequate treatment prior to disinfection will Increase chlorine requirements and/or
decrease bacteria removal efficiency.
Design Criteria - Chlorination systems encompass delivery, mixing, residual analysis, dose control, and contactor
basin. The choice between gaseous chlorine and hypochlorite is governed by economic considerations together with
safety and handling hazards of gaseous chlorine. Despite higher unit costs, it may be advantageous to use a
hypochlorite (calcium, sodium, lithium) to minimize the risks of transporting liquid chlorine through urban areas.
Mechanical mixers or diffusers are used to Introduce chlorine or hypochlorite Into the wastewater. Mixing should
occur In the most turbulent zone (velocity 2 to 3 ft/sec) of the effluent entrance to the contact chamber and be
completed in less than 3 seconds. A common method of control is a feed back compound control loop using
chlorine residual and flow as Input. Most smaller plants control dose normally on the basis of either chlorine residual
or flow.
A chlorine contacting device is typically a serpentine chamber. It Is important that short circuiting be minimized, plug
flow conditions be closely approached, comers be rounded to minimize dead flow areas, and the velocity of the
contacting stream be sufficiently high (0.1 to 0.2 fps) to prevent solids deposition. The length to width ratio should
be greater than 50 (preferably 70} and the height to width ratio of the wetted section should be less than 1. If the
effluent is transported for a long distance for discharge the effluent or outfall line may be suitable for chlorine contact.
Disinfection is dependent on contact time and chlorine dose. Values may range from a 30 minute contact time and
a chlorine dose of 3 to 6 mg/L to meet a fecal coliform requirement of 200 MPN/100 ml_ to a dose of 15 mg/L or
more and contact times greater than one hour to meet a total coliform of 2.2 MPN/100 mL Several empirical
equations are used to predict disinfection efficiency.
Dose levels will be dependent on the level of treatment; dosage ranges typically found are:
Untreated wastewater (pre-Cy 6-25 mg/L
Primary clarifier effluent 5-20 mg/L
Chemical precipitation effluent 3-12 mg/L
Trickling filter plant effluent 3-15 mg/L
Activated sludge plant effluent 2-9 mg/L
Activated sludge/multimedia filtration 1-6 mg/L
Reliability - The equipment required is not complex and chlorine is relatively easy to apply and control during
wastewater treatment. Chlorinalion destroys enteric pathogenic organisms; however, it may not be universally
effective in destroying harmful bacteria, and Its virucidal effectiveness may also be poor under some circumstances
(e.g., monochloramine is a very slow-acting virucide). The mechanical feed and contact systems are considered very
reliable.
Environmental Impact - Chlorine gas concentrations of 15 to 20 ppm for 30 to 60 minutes are dangerous; higher
concentrations for very brief periods can be fatal. Chlorination can result In the formation of carcinogenic
chloroorganics.
The USEPA has established toxiclty criteria for total residual chlorine In receiving waters. In freshwaters the acute level
Is 19 mg/L (1-hour average) and the chronic level is 11 mg/L (4-day average). The saltwater acute and chronic
criteria are 13 mg/L (1-hour the average) and 7.5 mg/L (4-day average), respectively. Due to the toxiclty of chlorine
-------
residuals at such low concentrations and the high limit of analytical detection (50 to 100 mg/L) chlorine induced
toxicity in the receiving stream is difficult to control.
Chemicals Required - Chlorine gas, liquid sodium nypochlortte, or dry calcium or lithium hypochtorite.
- Residuals Generated - The low concentration of residual chlorine remaining after treatment Is acutely toxic to aquatic
We, and Its elimination may significantly Improve the biological conditions of the receiving waters. It is not currently
possible to predict the identity of all the chloro-organtes resulting from chlorination. Some chloro-organics are potential
carcinogens, mutagens, or toxins; however, effluent levels of chlorinated by-products are below levels known to be
acutely toxic to aquatic life. Most chlorinated organic compounds produced by chlorination are polar or of low
molecular weight and do not bioaccumulate.
Potential For Improved Toxics Management - The primary rationale for wastewater disinfection is to prevent' the
spread of waterborne diseases and to protect public health. Chlorination does not offer an opportunity for improved
toxics management
Flow Diagram -
Chlorine Oas
Chlorinator
Chlorine
Solution-^.
Water
Eductor
Influent-**-
J
1
„
EffkMnt
MxingTank
Contact Tank
Energy Notes - Energy requirements for chlorination are primarily for heating, lighting, and ventilation. Total annual
energy requirements for 1,10, and 100 mgd plants are 1£100 kWh/yr/mgd, 1.800 kWh/yr/mgd, and 250 kWh/yr/mgd,
respectively. When the rate of chlorine withdrawal exceeds 1000 to 1500 Ib/day, an evaporator Is generally used to
convert the liquid chlorine to gas. Energy requirements for the evaporator (excluding mixing) can be estimated from:
kWh/yr « 11.8 x Ib Clj/day.
Costs - Estimated capital costs (1989) for 1, 10, and 100 mgd plants are $130,000, $600,000 and $3,000,000
respectively 0AM costs are estimated to be 2.6.1.4 and 0.8 cents/1,000 gal. respectively at an average dose of
6 mg/L These Increase to 3.2, £0. and 1.2 cents/1.000 gal at a dose of 10 mg/L
Chemical costs of chlorine gas and hypochlorite vary considerably depending upon the locality, demand, and
availability 1989 prices quoted for CI2 were: $0.0425 - $0.06/lb for 90 ton tank cars; $0.10/lb for 55 ton rail cars;
$0.25 to $0.275/lb for 1 ton cylinders; and $0.50 to $0.55/lb for 150 Ib cylinders. Liquid sodium hypochlortte
percent) prices quoted were $0.50/gal -$1.75/gal.
-------
References -
1. California Department of Health Services, Wastewater Disinfection for Health Practices. Sanitary Engineering
Branch, Sacramento, CA., February 1987.
2. Eastern Research Group, Municipal Wastewater Disinfection Policy Development Document. 4th Draft. Eastern
Research Group, Arlington, MA.. 1989.
3. Trussel, R.R., W.L Fisher, and K.H. Conarroe, 'Operational Experiences of Chlorination/Dechlorination Systems,'
In Alternate Effluent Disinfection Systems - Preconference Workshop Proceedings. Water Pollution Control Federation,
Alexandria, VA., 1986.
4. U.S. EPA, Design Manual: Municipal Wastewater Disinfection, Office of Research and Development, Water
Engineering/Research Laboratory, EPA/625/1-86/021, Cincinnati. OH.. 1986.
5. Water Pollution Control Federation, Wastewater Disinfection, Manual of Practice No. FD-10, Alexandria, VA., 1986.
6. Water Pollution Control Federation Disinfection Committee, 'Assessing the Need for Wastewater Disinfection,'
Journal Water Pollution Control Federation. Vol. 59. No. 10, 1987.
7. White, G.C., Handbook of Chlorination, 2nd Ed., Van Nostrand Reinhold Company Inc. New York, NY., 1986.
-------
DECHLORINAT10N FACT
pescriPtlon - The practice of dechlorination has seen dramatic growth in the past decade due to rising concerns over
chlorine toxiclty and protection of fish and wildlife. Dechlorination removes all or part of the chlorine residual and
halogenated organics remaining after chlorination, and reduces or eliminates toxicity harmful to aquatic life In receiving
Treatment with sulfur dioxide (SOg) is the most common method of dechlorination, as described by the following
reactions:
S02 + HOCI + HaO - SO*"8 + Cf + 3H+ (free chlorine)
S02 + NHaCI + 2HzO - S04* + Cr + 2H+ •»- NH4* (combined chlorine) :
S02 systems use the same types of equipment as chlorination, and are easily and economically retrofitted to existing
chlorination facilities. The material is supplied In liquefied form in canisters or cylinders. Sodium bisulfite is also used
for dechlorination, primarily with smaller plants where feed rates for SO2 are impractical.
Common Modifications - Several dechlorination agents are available. The most common agent is SO2 because of
cost and the ability to use existing chlorination equipment without modification. Sulfrte compounds are also used
(sodium sulfite, sodium bisulfite or sodium metabisulfite), primarily at smaller installations with equivalent SO2 feed
rates less than 100 Ib/day, or at large installations where storage of S02 is considered hazardous. When dissolved
in water, these salts produce the same active ion (SOa"2). Granular activated carbon (GAG) has seen only limited
success due to its inability to remove organochloramines when organic nitrogen is high, difficulties in designing
effective carbon beds, and long detention times.
Hydrogen peroxide (HjO^ has also had limited success due to its ineffectiveness in removing chloramines, problems
with side reactions, instability and cost. Aeration and holding lagoons have also been used ; however, aeration Is
ineffective in removing undissociated HOCI and chloramines. Free chlorine and to a lesser extent, chloramines, can
be destroyed by sunlight; however, decay rates are a function of cloud cover and latitude.
Technology Status - The technology of dechlorination. particularly with sulfer dioxide or sutfite, is well established.
In 1987, over 500 wastewater treatment plants practiced dechlorination. Dechlorination is encouraged and sometimes
required in many states for receiving waters designated as important for aquatic life. It is used extensively throughout
California and is required in Maryland (306 out of 335 POTWs dechlorinate) for Class 1, 2, and 4 wastewater plants.
Other states moving to restrictive limits for total residual chlorine include New Jersey, Pennsylvania, Virginia,
Minnesota and Ohio. Colorado and Oregon each have one major plant practicing dechlorination.
Applications - Dechlorination is applicable when a chlorine residual is undesirable, typically in cases where discharge
is to sensitive receiving waters.
Umitations - Chtorination/dechlorinalton is "more complex to operate and maintain than just chlorination alone. Major
difficulties are the inability to measure residuaf S02 and problems in the continuous measurement of a zero or low
chlorine residual. Many halogenated organics are also rapidly formed upon chlorine addition, and are unaffected by
application of SO*
Typical EQuipment/No. of Mfrs. - Dechlorination equipmerU/3; sulfur dioxide control systems/4; onslream chlorine
analyzers/30; chlorinators/24.
Performance - Total chlorine residual can be reduced to essentially zero with S02; however, overdosing of S02 Is
necessary for consistent dechlorination. If a contact chamber is used, aftergrowth of microorganisms, Including
-------
conforms, may occur; however, the mlcrobial increase shortly after dechtorination may not pose a risk to public
health, and application of the coliform standard at the chlorine contactor effluent may be permitted.
PeslgrfCrtterla - A major difficulty In dechlorination control is the inability to measure residual SO2 or problems In the
continuous measurement of a zero or low chlorine residual. As a result, most systems operate with a feed forward
control using flow and the chlorine residual after disinfection. Feedback control using a chlorine bias is also a
common method. On a mass basis, 0.9 parts S02 or 1.46 parts NasHSOa or 1.34 parts Na^Oj Is required to
remove 1.0 part chlorine residual. In practice, a higher dose is required to completely dechlorinate. Excess S02
provides a buffer against rapid changes In demand. The amounts of S02 added typically range from 10 to 50 percent
excess.
The maximum safe rate of S02 gas withdrawal on a continuous basis at 21 °C Is 0.9 kg (2 lb)/hr for a 68 kg (150
Ib) container, or 11.4 kg (25 lb)/hr for a ton container. For higher gas withdrawal rates, the lower half of the
containers or cylinders may be immersed in a liquid bath or surrounded with strip heaters (temperatures not
exceeding 52°C). For liquid withdrawal, the maximum rate of removal is 135 kg (300 lb)/hr. Higher withdrawal rates
are possible with pressurization or by padding with dry air or nitrogen up to 515 kPa (60 psig). Reaction with chlorine
residual is rapid, and separate contact chambers are normally not used. Contact times are typically 1 to 5 minutes.
Materials of construction are the same as with chlorination with the exception that line and auxiliary valves must have
316 SS trim instead of monel.
Reliability - No simple analytical method is presently available to determine free SOa. Process operation is therefore
difficult, and S02 overdosing is necessary to assure compliance with residual chlorine standards. The process can
be considered very reliable mechanically, and reliable from a process standpoint.
Environmental Impact - HjSO, and HCI are products of S02 dechlorination in small amounts but are generally
neutralized in the wastewater. Based on laboratory experiments, residuals of sulfite dechlorination are at least three
orders of magnitude less toxic than ozone or chlorine.
No cases of sulfur compounds effecting dissolved oxygen consumption or pH change in receiving waters or In
dechlorinated effluents have been reported. In pilot studies, no significant oxygen depletion occurred until sulfur
dioxide overdoses exceeded 50 mg/L ft is not uncommon, however, to find plants with post aeration after
dechlorination to assure that dissolved oxygen requirements are met.
Chemicals Required - Sulfur dioxide is most commonty used, followed by sodium bisulfite, sodium metabisulfite,
and sodium sulfite.
FJow Diagram -
SUfonator
RowM»t»f
Contact Chamber
Typical Chlorination Dechlorination System(wlth feed forward dechlorination control)
-------
Potential For Improved Toxics Management - Bioassay studies have shown that acute toxlclty of dechlorinated
wastewater Is less than the toxicrty of the chlorinated wastewater. While the greater part of toxiclty produced by
remOV8d ** dechlorinatlon- additional treatment (e.g., activated carbon) may be required to reduce TOX
Energy Notes - Energy requirements for 1, 10, and 100 mgd facilities are 10,000, 1,000. and 200 kWh/yr/mgd,
respectively. Facilities using more than 1,000 Ib SOj/d may use electrically heated evaporators to convert liquid S02
to gas. The energy required for the evaporator, not Including mixing, can be estimated: kWh/yr - 16.8 x Ib SCyday.
Costs - Adjustment of the 1980 I/A Assessment Manual cost estimates to 1989 (ENR Index = 4,700) yields
construction costs of $39,000, $88,000 and $244,000 for 1, 10 and 100 mgd plants, respectively. Equivalent annual
O&M costs ere $13,000, $41,000, $207,000, assuming 20 Ib SOa/Mgal.
The total cost of chlorination is reported to increase by approximately 30 to 50 percent with the addition of
dechlorination. O&M costs for 6 facilities in 1985 were reported to range from $0.08 to $0.28/1,000 gallon.
Chemical costs (1989) for S02 were 0.042 to 0.55/lb in 150 Ib cylinders; $0.165 to $0.35/lb in 1 ton cylinders; and
$0.115/lb. in 17 to 20 ton tank cars. Sodium bisulfite and sodium metabisulfite were quoted at $0.32/lb. Sodium
sulfite was $2.84/lb.
References -
1. California Department of Health Services, Wastewater Disinfection for Health Practices, Sanitary Engineering
Branch. Sacramento, CA., February 1987.
2. Eastern Research Group, Municipal Wastewater Disinfection Policy Development Document, 4th Draft, Eastern
Research Group, Arlington, MA., 1989.
3. Helz, G.R. and L Kosak-Cnanning, *Dechlorination of Wastewater and Cooling Water,' Environmental Science
and Technology, Vol. 18, No, 2, 1984.
4. Stefan, H.G. and T.R. Johnson, •Dechlorination Basin Hydraulics,* Project Report No. 250, St Anthony Falls
Hydraulic Laboratory, University of Minnesota, Minneapolis, Ml., 1986.
5. Trussel, R.R., W.L Fisher, and K.H. Conarroe, 'Operational experiences of chlorination/dechlorination systems,'
In Alternate Effluent Disinfection Systems - Preconference Workshop Preconference Workshop Proceedings, Water
.Pollution Control Federation. Alexandria, VA., 1986.
6. U.S. EPA, Innovative and Alternative Technology Assessment Manual, EPA/430/9-78-009, Cincinnati. OH.. 1980.
7. U.S. EPA, Design Manual: Municipal Wastewater Disinfection, U.S. Environmental Protection Agency. Office of
Research & Development, Water Engineering Research Laboratory. EPA/625/1-86/021. Cincinnati, OH., 1986.
8. Water Pollution Control Federation, Wastewater Disinfection, Manual of Practice No. FD-10. Water Pollution Control
Federation, Alexandria, VA., 1986.
9. Water Pollution Control Federation Disinfection Committee. 'Assessing the Need for Wastewater Disinfection;
Journal, Water Pollution Control Federation, Vol. 59. No. 10, 1987.
10. Water and Engineering Management. 1989 Buyers Guide and Reference Handbook. Water Engineering &
Management, July, 1989.
11. White. G.C.. Handbook of Chlorination. 2nd Ed., Van Nostrand Reinhold Company Inc. New York. NY.. 1986.
-------
OZONE DISINFECTION (AIR AND OXYGEN) FACT SHEET
Pescriftion '°*™ (OJ Is one of the most powerful oxidizing agents available and has been used commercially
as a disinfectant for over a century, h Is a more potent disinfectant and chemical oxidant than chlorine and will
oxidize i chemically react™ organic and inorganic substances. Ozone increases dissolved oxygen (especially when
02 to the feed gas), and can reduce BOD, COD, color, and odor in the final effluent. Ozone reacts quickly, requiring
relatrvely tow contact time. K will break down to elemental 02 in a short time; as such, on-sHe generation is
necessary. • • «
03 te produced when a high voltage alternating current Is imposed across a discharge gap containing an
oxygen-bearing gas. Some O2 molecules split and recombine with other O2 molecules to form 03. The electric
discharge is sometimes termed corona or silent arc or brush discharge, and is influenced by voltage, frequency,
dielectric material and thickness, discharge gap, and absolute pressure within the gap. Corona discharge generators
produce 03 concentrations ranging from 0.5 to 4.0 percent by weight When 02 is the feed gas, most of the O2
passes through the generator unchanged. The unused O2 is either reused in the upstream aeration basin or
recycled through the generator.
Ozone injection Into the wastewater may be accomplished via mechanical mixing devices, countercurrent or
concurrent flow columns, porous diffusers or jet injectors.
Common Modifications - Major process configurations include air feed, O2 feed, and O2 recycle systems. O2 recycle
is seldom used. Air feed is most common in plants where oxygen is not available. O2 feed is used at locations that
have pure oxygen activated sludge plants; the unused 02 (90 percent) from the O3 disinfection is used in the
biological treatment process. O3 generation equipment and power requirements are about 50 percent lower for an
O2 feed system because two to three times as much O3 is produced with high purity Oj at a given input to the
generator. The tower cost of producing O3 may be offset, however, by the higher cost of obtaining high purity 02
to feed the generator. If 02 can be used in the biological system, economics will generally favor high purity 02 feed
gas.
Low frequency generators produce 1 to 1.5 percent by weight O3 using air feed, and 2 to 3 percent by weight 03
using O2 feed at the same power requirement Medium frequency generators produce 2 to 2.5 percent by weight
03 using air feed, and 4 to 6 percent by weight O, using O2 feed at the same power requirement High frequency
generators produce the same amount of 03 as low frequency generators but with fewer dialectrics. Three types of
generators are commercially available: the Otto plate type, the tube type, and the Lowther plate type. The tube type
generator Is the most widely used for wastewater disinfection and Is capable of generating O3 from both air and 02,
which is dried and cooled to -60°F. Operating gas pressure ranges from 3 to 15 psig and peak voltage is -between
15 to 19 kV at 2000 Hz.
Technology Status - As of November 1985, 24 U.S. wastewater treatment plants disinfected with Oj, with 3 additional
plants under design or construction. Process control is considered 'developing' as opposed to Veil developed1 for
Ct the technology is considered complex in comparison to C^ and UV. Ozonation also shows high sensitivity to
O&M as opposed to minimal for Cfe, and moderate for UV.
Applications - Ozonation is an alternative to chlorination. The process does not have a residual and by- products
are considered minimal and far less detrimental than those generated through chlorination. If oxygen activated sludge
is used. O3 is economically attractive, since a source of pure oxygen is already available.
Limitations - Ozonation is energy and capital intensive, and generally requires a high quality effluent to be effective.
h is not typically considered for application to secondary level effluents. O, demand is elevated by high organlcs
and nitrites and achieving bacteriological standards is more difficult with wastewaters containing high suspended
solids. Wastewaters with very high 0, demands may not be good candidates for 0, disinfection.
Typical EQuipment/Nlo. of Mfrs. - ozone generators/5; ozonators/6; ozone decomposers/2; system manufacturers/22.
-------
Performance - Ozone te a more effective bactericide and vlrucide than chlorine. Effectiveness Is directly proportional
to dosage, exclusive of O3 demand. At dosages of 2 to 10 mg/L and contact times less than 15 minutes, ozone is
demonstrated to affect residual densities consistent with secondary and tertiary requirements, and effective virus
mactrvation. Primary factors affecting disinfection efficiency are: short-circuiting, mixing, transfer efficiency, and contact
time.
- Design Criteria - Dosages for disinfection typically range from 5 to 15 mg/L, with 15 to 30 minute contact times. The
Oj demand is ultimately dictated by the quality and quantity of wastewater treated, and the design dosage is selected
to meet the highest 03 demand.
The most efficient system was reported to be a fine bubble diffuser (2 - 5 mm diameter) in deep basins (16-20 feet
deep), with plug flow conditions achieved by staging. With respect to transfer efficiency, it is recommended that
diffusers be -installed as deep as practical, and that minimum design criteria be established at the warmest water
temperature,' the lowest pH value, and the lowest anticipated value for O3 demand (i.e., the best water quality
condition). A minimum of 3 stages should be provided in the 03 contactors, with each stage isolated to simulate
plug flow conditions and to minimize short circuiting. To achieve 200 FC/100 mL disinfection levels, the minimum
contact time should be at least 6 minutes and preferably at least 10 minutes at design peak flow rates. For more
stringent standards, the contact time should be lengthened; and pilot studies should be conducted to determine the
optimum contact times and dosage requirements.
Reliability - Mechanically reliable, and highly reliable in inactivating microorganisms. The most common operational
problems that have been identified include undersized moisture removal systems, improperly designed ozone
contactors, inefficient 03 off-gas destruction, 03 leakage from piping, inadequate air drying in air dessicant dryer,
improper sealing of the O3 contact tanks, and malfunctioning O3 concentration monitors. Key O&M design
considerations for reliable service Include: delivery of clean feed gas at -60°F; maintenance of generator coolant flow;
operation of generator within design parameters; effective contact of O3 with wastewater; and maintenance of ambient
O3 below safe limits.
Environmental Impact - 03 te considered a toxic chemical. The maximum allowable ambient O3 concentration for
an 8 hr working day is 0.0002 mg/L (0.1 ppm by volume), which is significantly less than the O3 concentration in the
off-gas, normally 1.0 mg/L (500 ppm by volume). Methods for treating excess 03 in the off-gas include thermal,
thermal/catalyst, and catalyst destruction. Although O3 is toxic to aquatic life at low concentrations, residual O3 Is
unstable in water, dissipating rapidly due to the low partial pressure above the liquid and the reactive nature of the
03 with oxidizable materials.
The reaction of O3 with organic material generally results in the destruction of the original organic molecule and
formation of a more biodegradable product with lower molecular weight. However, in some cases, particularly
pesticides, a more toxic intermediary may be formed. The possibility that 03 may produce potentially dangerous
epoxides has been suggested.
Chemicals Required - Of 39 plants using O3 for disinfection, 27 use air for feed gas and 12 use O2 (all oxygen
activated sludge plants).
Residuals Generated • Residual 03 has been shown to be toxic; however, 03 toxlclty Is no greater than residual
chlorine and it decomposes more rapidly. At dosages used in wastewater disinfection, any residual 03 would be
short-lived.
Potential For Improved Toxics Management - Ozone will oxidize cyanides, phenol and other dissolved toxic organlcs;
In combination with activated carbon, ozonation can achieve effective (>95 percent) removal of trihalomethanes. As
an alternative to chlorination, It would significantly diminish concerns related to the formation of toxic organics or to
residual toxicity in the receiving water.
-------
Flow Diagram -
Air
Treatment
-*-
Ozon*
Q*n*retor
-.*•
Ozone
Contadhg
->•
Ozon*
Destruction
^ V*nt
Oxyg«n F»rf
HahPurtty
Oxygen
+*
Ozon*
Generator
~^-
Ozon*
ContactktQ
-*-
Oxyg»n Ffecycl*
Dew Point
Treatment
i
^
Ozone
Generator
i
-**
Ozon*
Contacting
~+~
Ozon*
Destruction
Oxygen
-^ Activated
Sludg*
Ozon*
Destruction
Qffc. "Oxyoen
^" Activated
— i Sludg*
•Vwit
•V*nt
•V*nt
R*cycl* Oxygen
Diagrams showing feed-gas flow of typical ozone disinfection processes
Energy Notes - Power requirements for high purity oxygen feed systems are 3 to 4 kWh per Ib O3 per day excluding
02 power requirement, with an average O3 concentration of 2 to 4 percent weight in the parent gas. Power
requirements for atmospheric process air (-60°F dew point) are 10 to 13 kWh per Ib 03 per day including air
preparation with an average O, concentration of 1 to 1.5 percent weight in the parent gas.
References -
1. Ozone Research and Development Corporation, Ozonation Design Manual, Phoenix, KL, 1967.
2. Rakness, K.L, Brenner, R.C., Hegg, B.A., and A.G. Hill, 'Practical Design Model for Calculating Bubble Dlffuser
Contractor Ozone Transfer Efficiency.' Ozone Science & Engineering, Vol. 10. pp. 173-214. 1988.
i ,
3. Robson. M., Operational Experiences of Ozonation Facilities, Alternative Effluent Disinfection Systems
Preconference Workshop, Water Pollution Control Federation. October 5. 1986.
4. Water Pollution Control Federation, Wastewater Disinfection, Manual of Practice No. FD-10. Alexandria, VA., 1966.
5. Water Pollution Control Federation Disinfection Committee, 'Assessing the Need for Wastewater Disinfection,'
Journal. Water Pollution Control Federation, Vol. 59. No. 10. 1987.
6. Water Pollution Control Federation. Buyers Guide/1989 Yearbook. Vol. 61 (S). 1989.
7 US EPA, Design Manual: Municipal Wastewater Disinfection. Office of Research and Development, Water
Engineering Research Laboratory, EPA/625/1-66/021. Cincinnati, OH. 1986.
8. White, C.G., Handbook of Chlorination. 2nd Ed., Van Nostrand Reinhold Company, Inc. New York, NY.. 1986.
-------
ULTRAVIOLET DISINFECTION FACT SH£ET
- Lmravioiet light in the far UV range is an effective germicidal agent It is a physical process. reVing on
K , Hfl ^ 8ner£D' ** B 99netiC material *the ce" C°NA and RNA). The damage It causes results In
^inability of the cell to replicate. The optimum wavelength is between 250 and 270nm. The source of this energy
£ in almost all cases, a standard low pressure mercury arc germicidal lamp, which has Its maximum output at
253.7nnx These lamps are typically 0.75 and 1.5 meters long (arc length) and 1.5 to 2.0 cm In diameter.
UV equipment Is designed to have a number of lamps arranged In a reactor at centerline spacings ranging from 5
to 10 cm. The lamps are inserted into quartz sheaths; these lamp/quartz assemblies are submerged in the water
to provide maximum contact with the liquid. The size of the system is defined by the number of lamps; this is a
function of the lamp output and spacing, the flow rate, the Initial coliform levels, and the 'UV demand" of the
wastewater.. This demand is described by the UV transmittance or UV absorbance of the liquid, measured at 253.7
nm.
The "open channef modular system design is the most common configuration for treated wastewater applications.
It Is generally comprised of several gravity flow, open channels (depending on plant size and the degree
ofredundancy) that hold one or more banks of lamps in series. These are placed in the channel as modules that
can be easily removed for maintenance and repair. In addition to the lamp/quartz modules, the second major
equipment element is the power/control pane! which contains the lamp ballasts, operating monitors, and ground
fault interrupters. The panels are generally designed to control a channel and/or bank of lamps, and are placed in
close proximity to the lamp reactors.
Common Modifications • Nearly all UV systems use germicidal lamps that are sheathed in a quartz sleeve and
submerged in the liquid. There are some non-contact designs that suspend the lamps outside a 7 to 10 cm diameter
thin wall Teflon pipe that is transparent to the UV wavelengths and carries the liquid. Other designs have the
lamp/quartz assemblies fixed within large steel shell reactors with piped inlet and outlets. These can be gravity flow,
or under pressure. The open channel configurations can have the lamps placed horizontally or vertically in the
channel. Accessary equipment will generally include ground fault Interrupters for each module, a UV intensity meter,
and a cleaning system. ,
In-place cleaning systems have included mechanical wipers and ultrasonic transducers, both of which have proven
to be ineffective. Automated chemical recirculation may be used on some systems; these require isolation of the unit
and recirculation of a cleaning solution to restore the quartz surfaces. An aeration header Is also typically installed
in these systems (beneath the lamp assemblies) to provide additional surface scouring. Automatic, In place systems
have not been wholly effective, particularly when applied to the open channel designs. Most often manual chemical
cleaning is very effective and efficient. An auxiliary cleaning tank aids this procedure. The modules are lifted from
the channel and dipped into the tank's cleaning solution (with agitation), and then rinsed.
Liquid level control (maintained above the top lamp/quartz) In the channel is accomplished by several methods.
These include a downstream mechanical counterweight gate which works well over a wide range of flow, although
It appears to have problems at very low flows. Effluent weirs are used, but It is important to have sufficient weir
length to minimize the variation of depth over the weir. Automatic level control gates are also used, controlled by
level sensors in the channel.
Medium pressure mercury arc lamps have been used as the UV source in some applications. These tend to be
smaller lamps with significantly higher intensity at the 253.7 wavelength, and have other spectral fines within the
germicidal range. Experience is limited with these systems.
Technology Status - There are over 500 operating plants in the U.S.. representing a rapid increase from an estimated
50 plants in 1984 The earlier first generation' systems were closed shell or non-contact Teflon pipe designs, with
a small number of open channel configurations. The dominant configuration now is the open channel design wtth
modular lamp/quartz Inserts. These comprise approximately three-quarters of all operating plants, and are the
preferred design for most new plants.
-------
Design procedures for the process are In place, but design parameters that are empirically based are not fully
developed. As such, design sizing should be kept conservative. Pilot studies may be considered If treated effluent
Is available, particularly to develop data on the wastewater characteristics (initial bacterial densities, UV absorbance,
and variability), and to assess the quartz surface fouling potential (and procedures to clean the surfaces).
Applications - UV disinfection Is applicable to effluents treated to secondary levels or belter. Solids levels greater
than 30 mg/L will limit the performance of UV systems to toss than secondary requirements. UV disinfection Is
particularly applicable as an alternative to chorinatlon In cases where dechlorination is required or where there are
overriding concerns with safety. The process can be retrofitted to existing chlorination plants by Inserting the open
channel modular design Into the chlorine contact chambers.
Limitations -.-The UV process may not be suitable In cases where there is excessively high absorbance at 253.7
nm, or where there are high turbidity and suspended solids levels. Bacteria that are occluded in participates will not
be affected by the UV radiation; these will, in effect, form the performance limit for the process. A screening
calculation for biological treatment plants Is to take 25% and 90% of the square of the effluent suspended solids
(mg/L) to estimate the fecal and total cpliforms associated with the solids, respectively.
Photoreactivation of UV exposed bacteria will result in an average increase of approximately one order of magnitude
from the density Immediately after UV exposure. This is an enzymatic repair mechanism that Is catalyzed by exposure
to visible light (sunlight); most organisms have this ability, although viruses do not. Design sizing can, however, take
this repair into account In order to assure that effluent limits are met on a consistent basis.
Typical Equipment/No, of Mfrs. - UV systems are typically sold as complete units, comprising the lamp/quartz
modules, power supply and tamp ballast panels, instrumentation, channel inserts, and level control devices. There
are an estimated five manufacturers that supply the municipal market.
Performance - UV systems have been demonstrated capable of meeting limits of secondary and tertiary levels.
Colifomns associated with suspended solids can limit the lower levels attainable by the process, and photorepair
may interfere if not properly taken into account in the design of the system.
A major factor in apparent system failures has been attributed to lack of attention to cleaning, or an Inability to
effectively clean the quartz surfaces. The newer modular designs allow for easy access to the quartz; these must
be cleaned on a preventive maintenance basis.
Design Criteria - UV disinfection efficiency is defined by the dose, which is the product of the UV intensity and the
exposure time (microwatts/cm2 x seconds equals microwatt-seconds/cm2). UV intensity is a function of the UV lamp,
the lamp spacing, and the "sinks" of energy that will attenuate the radiation available for disinfection. Time is a
function of the reactor hydraulic characteristics and its proximity to ideal plug flow.
Attenuation of energy will be through three primary mechanisms. The first Is aging of the lamps, in which the UV
output of the lamp diminishes with operating time. This will usually be to a level between 65 and 75% of Its rated
output within the first 2000 hours; It will remain at this level for the remainder of its operating life. Design should be
for this "end of life" output. The second attenuation win be dependent on the transmissibility of the quartz sheath.
New quartz will transmit 90 to 95% of the UV energy, but with time, aging and surface abrasion will cause this to
diminish. Good maintenance should afiow an average quartz transmittance of 75 to 80%. The third attenuation will
be through the UV demand of the liquid itself. Design should reflect the expected transmittances at peak conditions,
and on filtered samples. Typical values of UV transmittances (at 253.7nm, in a 1 cm cell) for wastewaters undergoing
varying degrees of treatment (assuming a basically domestic plant) are 40 to 50% for a primary effluent, 55 to 65%
for a secondary plant, 60 to 70% for an advanced secondary plant, and 70 to 80% for a tertiary plant
Hydraulic design demands a close approximation of ideal plug flow, with minimal dispersion. Good approach and
exit conditions about the lamp battery are important, assuring approximately equal velocities across the reactor
cross section through the length of the reactor. In open channel designs, perforated stilling plates can be used
-------
M *****ratio
-------
The UV process does require 'expendables1. These are primarily the lamps which have an operating life between
8000 and 12000 hours, and the ballasts and quartz, which will need to be replaced on a toss frequent basis (three
to five years).
Potential for Improved Toxics Management - Use of UV light as an alternative to chlorine would serve to reduce the
toxics problems that have been associated with chtorination disinfection.
Flow Diagram -
\ss ss~*
Control/Poww
Cabhwts _.
m
n
i*nfc«l
L*v») Control
Gate
Influent
ChatvMl
S»cOon
ClwnrMl Control D*vtc*
/
/
/
/
/
/
/
#
/
/
\
Han
Efflumt
Chanoal
Typical Layout of UV Open Channel Configuration (with horizontal lamp placement)
Energy Notes - The UV process requires electrical energy to power the lamps. Overall power requirements can
be estimated on the basis of 100 watts per 1.5m arc lamp, or 60 wans per 0.75m lamp. Power utilization is based
on the actual number of lamps In operation. As a general rule, one should expect to have an average of 40 to 50%
of the system In operation at a given time.
References •
1. Scheible, O.K., Ultraviolet Disinfection, In Proceedings, Field Evaluations of Municipal Wastewater Treatment
Systems, U.S. EPA-Risk Reduction Engineering Laboratory, Cincinnati, OH., 1988.
2. Scheible, O.K. M.C Casey, and A. Fomdran, "Ultraviolet Disinfection of Wastewaters from Secondary Effluent
and Combined Sewer Overflows,' EPA/600/2-86/005, NTIS No. PB86145182, U.S. EPA-Municipal Engineering Research
Laboratory, Cincinnati, OH., 1986.
3. U.S. EPA, Design Manual - Municipal Wastewater Disinfection, U.S. EPA Office of Research and Development,
EPA/625/1-86/021, Cincinnati, OH., 1986.
4. U.S. EPA, Ultraviolet Disinfection Special Evaluation Project, Region 5, Chicago, IL, September 1988.
-------
SLUDGE
-------
WET AIR OXIDATION OF SLUDGE, LOW PRESSURE FACT SHEET
S
Description - Low pressure wet air oxidation of sludge involves the heating of sludge to a temperatures of between
150 to 210°C at a pressure of 150 to 400 psig for periods of 15 to 40 minutes with or without air. This process
should result in a sludge being dewaterable with minimal or no chemical conditioning. Thermal conditioning results
in a breakdown In the sludge cell structure, sterilization of the sludge pathogen content, and a slight solids reduction
through oxidation and solubilization of the volatile suspended solids. The warm sterilized sludge remains susceptible
to bacterial recontamination which can produce obnoxious odors and pose a disease risk.
In the low pressure wet air oxidation process, sludge is passed through a heat exchanger into a reactor vessel,
where steam is injected to bring the temperature and pressure within the reactor vessel to the necessary range.
After treatment, the sludge passes back through the heat exchanger and is then discharged to a thickener- decanter
tank. The Incoming sludge solids concentration is generally in the range of 3 to 8 percent and the sludge solids
should be screened or ground prior to thermal conditioning. The thickened conditioned sludge may be directly
applied to the land or dewatered by centrifuge, vacuum filter, plate and frame, filter press, or belt filter press.
Common Modifications - Several proprietary variations exist. Normally, air Is injected Into the reactor with the sludge.
This configuration is the most common (95 percent of low pressure wet air oxidation facilities). The process can also
be conducted at a higher temperature and pressure, generally resulting in more complete oxidation of the volatile
solids.
* .*''•*-" 1" ' ' ! ' -
Technology Status - Low pressure wet air oxidation of sludge was first introduced in Europe in 1935, but installations
in the United States did not begin to appear until the 1960s. To date over 60 installations have been installed In the
United States.
Applications • Low pressure wet air oxidation is practiced as a sludge conditioning method to reduce the costs of
sludge dewatering and ultimate disposal. The benefits include: (1) improved dewatering characteristics of treated
sludge with minimal or no chemical condatoning; (2) significantly reduced pathogen content making the conditioned
sludge more suitable for ultimate disposal by land application; (3) suitability for sludges which cannot be stabilized
biologically; and (4) reduction in size of subsequent dewatering equipment.
Limitations - The process has high operating costs, and is not normally economical at small treatment plants.
Skilled supervision and maintenance are required due to the high temperatures and pressures involved. Inadequate
operator attention has been known to result in system reliability problems. Expensive materials are required to
prevent corrosion and withstand the operating conditions. Heavy metal concentrations in sludges are not reduced.
The sludge supernatant and filtrate recycle liquor are strongly colored and contain a very high concentration of
soluble organic compounds and ammonia nitrogen. This stream must either be pretreated prior to return to the head
of the treatment plant or included in the calculation of biological system organic loading. The process produces an
odorous gas stream that must be collected and treated before release.
Typical EQuioment/No. of Mfrs. - Several manufacturers supply complete proprietary thermal sludge conditioning
processes.
Performance - Thermal conditioning of sludge results in (1) destruction of pathogens (the sludge remains susceptible
to recontamination); (2) decrease hi volatile solids loading to downstream processes of 30 to 40 percent due to
oxidation and solubilization of the volatile suspended solids; (3) reduced or eliminated need for chemical conditioning;
(4) improved thickening and dewatering properties.
Physical/Chemical/Bloloolcal Aids - Process requires an addition of heat, but eliminates or reduces the need for
chemical conditioning prior to dewatering. Scale inhibitors may be required for the boiler. Intermittent acid washing
to remove scale will be required in the exchangers, pipes, and reactor.
-------
Residuals Generated - The liquid sldestream Is generally about 75 percent or more of the sludge flow (by volume);
typical characteristics - BOD. 5.000 to 15.000 mg/l; COD, 10.000 to 30.000 mg/I; NH3-N. 500 to 800 mg/l; P, 140 to
250 mg/l; TSS, 9,000 to 12,000 mg/I; VSS. 8,000 to 10,000 mg/l; pH. 4 to 6.
The liquid sidestream is generally amenable to biological treatment but can increase the organic loading to a
treatment plant by up to 30 to 50 percent If the plant has not been designed for this additional load, pretreatment
of the liquid sidestream prior to return will be necessary. The composition of this sidestream can vary among the
various processes. It may contain a high proportion of non-biodegradable matter. This matter is largely humic acids
which can give rise to unpleasant odors. The actual chemical composition of the liquid sidestream should be
determined by detailed chemical analysis of a pilot unit A possible treatment process for a high concentration
sidestream can consist of filtration, aeration and activated carbon adsorption for non-biodegradable organics.
Design Criteria - Temperature: 150 to 210°C, Pressure: 150 to 400 psig, Detention Time: 15 to 40 minutes, Influent
Sludge Concentration: 3 to 8 percent, Steam Consumption: 600 Ibs per 1,000 gallons of sludge.
Reliability - Careful operator attention is required. Mechanical and process reliability appears adequate as long as
sufficient operator attention is provided; however, a number of installations have experienced reliability problems as
a result of inadequate operation training and attention, as well as short service lives of key components.
Environmental Impact - The liquid sidestream has a very high organic loading which may cause plant upsets and
a colored effluent. The gaseous sidestream is odorous and proper odor control must be practiced. Heavy metals
generally remain insoluble and wi« be disposed of in the sludge.
Flow Diagram
RAW SLUDGE
SLUDGE
HOLDING
TANK
SCRECN
OR
GRINDER
FEED
PUMP
EXHAUST GASES -•-
SUPERNATANT
CONDITIONED SLUDGE
References -
1. Ewing. Lewis, et. al., "Effects of Thermal Treatment of Sludge on Municipal Wastewater Treatment Costs',
EPA/600/2-78-073. June 1978.
2. Metcalf & Eddy, Inc., Wastewater Engineering: Collection, Treatment, Disposal, McGraw-Hill.
3. U.S. EPA, 'Process Design Manual for Sludge Treatment and Disposal,' EPA/625/1-79-011, September 1979.
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WET AIR OXIDATION OF SLUDGE, HIGH PRESSURE FACT SHEET
1 " **"
Description - High pressure/high temperature wet air oxidation (HPO) is a process in which sludge is completely
oxidized at high temperature, pressure and air concentration. This process can be an alternative to incineration, and
results In a similar ash residue. There are two general types of HPO equipment, aboveground and deep-well type
The deep-well type is called a Vertical Tube Reactor (VTR).
In the HPO process, sludge is first ground or screened to reduce the size of the feed solids. Next, the solids
concentration is adjusted to between 2 and 8 percent by either dilution or thickening. In the above ground systems,
a high pressure pump then pumps the sludge through a heat exchanger into a reactor vessel Air is mixed with the
sludge before entering (and sometimes In) the reactor. Steam is added in the reactor during startup. During normal
operation, the oxidation process generates excess heat and steam is no longer needed. The oxidized sludge passes
back through the heat exchanger to recover heat and is then discharged to a thickener-decanter tank. The pressure
in the reactor must be sufficient to prevent the water from vaporizing at the temperature selected for the reaction.
The VTR units do not require a high pressure pump. Pumpage is required only to overcome friction losses and
differences in elevation of the sludge storage and decant tanks. The VTR obtains the high pressures required for
the process using the hydrostatic head at the bottom of the system.
Common Modifications - Several proprietary vacations exist for HPO. for example oxygen may be .used in lieu of,
or in addition to, air as the oxidant source.
Technology Status - Wet air oxidation of sludge was introduced in the earty 1960s. There are few installations In
operation. The VTR process was developed in the 1970s and operating experience is limited to one full-scale
prototype operated with some success during 1984 and 1935. Several municipalities (e.g., Houston) have chosen
the VTR process due to its expected lower operating cost relative to the pumping requirements.
Applications - Wet air oxidation of sludge can be an alternative to incineration as a solids reduction process. The
resulting oxidized sludge is easy to dewater and does not usually require conditioning chemicals. The volume of
sludge solids may be reduced by 70 percent or more depending on the volatile solids and moisture content of the
feed sludge. The oxidized sludge is sterile and innocuous.
Limitations - The process has a very high capital cost. The operating cost may be offset somewhat by energy
recovery from the oxidized sludge. The operating cost of the VTR process may be lower than for the aboveground
units due to the lower pumping costs. Operating data are very limited for either process configuration and hence
reliable estimates of the total costs are not available. The aboveground HPO process produces an odorous gas
sidestream that must be collected and treated before release. The liquid sidestreams of HPO systems may have a
significant concentration of soluble organic compounds and ammonia nitrogen concentration which may require
pretreatment prior to returning to the head of the treatment plant. HPO systems require specialized supervision and
maintenance due to the high temperature and pressure involved. The process produces an odorous gas stream that
must be collected and treated.
Typical Equipment/No, of Mfrs. - Two manufacturers supply complete VTR processes on a privatization or purchase
basis. Several manufacturers supply complete aboveground HPO processes.
Performance - Wet air oxidation of sludge results in: (1) the oxidation of volatile solids, with reductions of up to 70
percent, (2) the destruction of pathogens, (3) Improved sludge dewatering properties, and (4) the possible removal
of some toxic pollutants.
-------
Physlcal/Chemical/BioloQical Aids - The HPO process requires addition of heat during startup until the process
become autogenous. Scale inhibitors may be required for the boiler. Intermittent acid washing to remove scale
may be required In the heat exchangers, pipes, and reactor.
Residuals Generated - The quality of the liquid sidestream improves with a higher degree of oxidation. The quality
may be similar to a thermal conditioning liquid sidestream for less complete oxidation processes. In the VTR process,
nearly complete oxidation Is claimed, but full scale operation information is lacking.
Potential for Improved Toxics Managements - When operated in the upper temperature range, the HPO processes
potentially can provide essentially complete destruction of a broad range of hazardous and toxic compounds.
Design Criteria - Temperature: 210 to 315°C, Pressure: 1,000 to 1,800 psig, Detention Time: 15 to 60 minutes,
Influent Sludge Concentration: 2 to 8 percent
Reliability - Highly trained operations personnel with machinist skills are required for HPO systems, especially for
aboveground HPO units with high pressure pumps and piping. Reliability data are not available for the VTR process.
The HPO systems have generally been abandoned by municipalities due to limitations (cost, odors, sidestream
problems and overall maintenance difficulties).
Environmental Impact - Toxic compounds may be destroyed in higher temperature units. Heavy metals remain
insoluble and pass through system and remain in the sludge. The liquid sksestream may have a high organic
loading. The gaseous sidesiream may be odorous in lower temperature processes. Potential for explosion with
improper O&M. Subsurface effects of VTR systems must be considered for each potential application site.
Flow Diagram - Above Ground -
RAW SLUDGE
SLUDGE
HOLDING
TANK
GRINDER
OR
SCREEN
FEED
PUMP
EXHAUST wzs
SUPERNATANT
OXIDIZED SLUDGE
References -
1. Kaufman, Leonard A. and Hermann Peterscheck. 'Modeling Vertech's Mile Long Multi-phase Reaction Vessel',
Chemical Engineering Science (G.B.), Vol. 41, No. 4, 1986. pp 685-692.
2. U.S. EPA. "Process Design Manual for Sludge Treatment and Disposal,' EPA/625/1-79-011, September 1979.
3. U.S. EPA. "The City of Longmont, CO., Aqueous-Phase Oxidation of Sludge Using the Vertical Reaction Vessel
System", Water Engineering Research Laboratory, Cincinnati, Ohio, January 1987.
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SLUDGE DRYING, THERMAL FACT SHEET
x"
Description - In the thermal drying process, the moisture in the sludge is reduced to 8 to 10 percent (by weight) by
hot air evaporation of the moisture. For economic reasons, the moisture content of the sludge must be reduced as
much as possible through mechanical means prior to sludge drying. The available thermal sludge drying techniques
are flash, rotary, toroidal, multiple hearth and atomizing spray.
Flash drying is the instantaneous vaporization of moisture from solids by introducing the sludge into a hot gas
stream. The wet sludge cake is first blended with some previously dried sludge in a mixer to improve pneumatic
conveyance. The blended sludge is mixed with hot gases from the furnace at about 1,200 to 1,400°F (650 to 760°C)
and then fed into a cage mill in which the mixture is agitated and the water vapor flashed. The residence time in the
cage mill is a matter of seconds. The sludge, which has been dried to a moisture content of 8 to 10 percent, is then
separated from the spent drying gases in a cyclone, with part of the dried sludge being recycled for mixing with
incoming wet sludge cake and the remainder being screened and sent to storage. The exhaust gases must be
treated to control odors.
A rotary dryer consists of a cylinder which is slightly inclined from the horizontal and revolves at above four to eight
revolutions per minute. The inside of the dryer usually is equipped with flights or baffles throughout its length to
break up the sludge. Prior to the rotary dryer, wet cake is mixed with previously heat dried sludge in a pug mill.
The system may Include cyclones for sludge and gas separation, dust collection scrubbers, and a gas incineration
step. Sizing devices may be added after th? rctary dryer to separate, crush and screen the dried sludge.
The toroidal dryer uses the jet mill principle, in which heated air is injected into a doughnut-shaped drying vessel to
create a high speed air current which dries and classifies sludge solids simultaneously. Dewatered sludge is pumped
into a mixer where It is blended with previously dried sludge to make the mixture free flowing. The blended material
is fed into the doughnut-shaped dryer where it comes into contact with heated air at a temperature of 800 to 1,000°F.
The particles are dried and broken up into fine pieces. A portion from the whirling stream of dried fine sludge
.particles and air is withdrawn, and dried solids are separated from the airstream.
The multiple hearth furnace is adapted for heat dtying of sludge by incorporating fuel burners at the top and bottom
hearths, plus down draft of the gases. The dewatered sludge cake is mixed in a pug mill with previously dried
sludges before entering the furnace. Also, fluidized bed drying has been used ahead of fluidized bed furnaces.
Atomizing drying involves spraying liquid sludge upward into a vertical tower through which hot gases pass
downward. Dust carried with hot gases is removed by a wet scrubber or dry dust collector. A high-speed centrifugal
bowl can also be used to atomize the liquid sludge into fine particles and to spray them into the top of the drying
chamber where moisture is transferred to the hot gases.
Technology Status - Although heat drying of sludge was developed more than 50 years ago, it Is not widely used.
The rotary dryer/pelletization process currently has three successfully operating facilities (Largo, FL; Cobb and Clayton
Counties, GA) and three planned facilities (Boston, MA; Tampa, FL; and Hagerstown, MD). Sludge drying facilities
in Orlando. FL and Washington, DC have been unsuccessful.
Application - Sludge drying can be an effective way to process stabilized sludge prior to ultimate sludge disposal
when the sludge is to be applied to land for agricultural and horticultural uses. Although It is an expensive process,
It can become a viable alternative If the product can be successfully marketed (e.g., Milorganite). An acceptable
product for marketing should have a total nitrogen content greater than 3.5 percent. Dried sludge sells m bulk for
up to $20 per percent nitrogen per product ton.
Limitations - Processing costs are high relative to other options and markets may not be available for the end
product. Skilled operators are required to manage sludge drying systems. Without odor control, odors can be a
problem.
-------
Typical Equipment/No, of Mfrs. - Complete heat drying systems are generally proprietary. The major equipment
components include: mixers, furnaces, cyclones, screens, dryers, wet scrubbers, dust collectors, air blowers,
heaters, spraying devices, sludge feed pumps and handling equipment.
Performance - Heat drying destroys most of the bacteria In the sludge. However, undigested heat dried sludge is
. susceptible to putrefaction in land applications If thick layers on the ground are allowed to become wet. Heat drying
does not cause any significant decrease of the heavy metals concentration in the sludge. In general, the natural
nutrient content of heat dried sludge is only about 5% nitrogen (approximately 5-10-5 N/P/K). However, ft is an
excellent slow-release nitrogen fertilizer for golf courses, orange groves, etc.
Physical. Chemical and Biological Aids - Nitrogen and phosphorus may be added to increase nutrient values of the
dried sludge.
Residuals Generated - All the solids captured in the wet scrubbers and dry solids collectors are recycled and
incorporated in the end products. Wastewater from odor control devices and coolers must be treated by recycling
through the plant
Design Criteria - The most critical consideration is to produce a high solids cake in dewatering. Approximately
1,400 BTU are needed to vaporize one pound of water, based on a thermal efficiency of 72 percent. Less fuel
would be required with additional heat recovery. Chemical scrubbers are used, or chemicals are added prior to
heat drying. Excessive drying tends to produce a sludge that is dusty or contains many fine particles, which Is less
acceptable for marketing, and should be avoided. The finer material might possibly be desirable as a binder for
chemical fertilizer or for making larger pellets. Wet scrubbers and/or solids collectors are needed. Standby heat
drying equipment is needed for continuous operation.
Reliability - Careful operator attention by trained operators is required. Although mechanical and process reliability
have been demonstrated, some equipment has proved to be unreliable and has had to be shut down (e.g., Orlando,
FL).
Environmental Impact - Potential for explosion and air pollution if the system is not property operated and maintained.
Strong odors may be produced by the process.
Flow Diagram -
EXHAUST CAS SEPARATOR AND TREATMENT I
DEWATERECT
i
SLUDGE
DRIED
SLUDGE
HEAT
AGENT
References -
1. Pollution Equipment News, 1989 Buyers Guide, November 1988.
2. U.S. EPA, 'Sludge Handling and Conditioning1, EPA/430/9-78-002, February 1978.
-------
Flow Diagram -
COOUNC At* DISCHARGE . |
SLUDGE INLET—v ^Q
COMBUSTION
A« RETURN
RABBLE Aftu
SHAFT COOUNC AIR
FLOATING DAMPER
FlUC CASES OUT
CAS EXHAUST
DRYING ZONE
SUPPLEMENT AL
FUEL
COMBUSTION ZONE
RABBLE ARM AT
CACH HEARTH
COOLMC ZONE
ASH DISCHARGE
FURNACE EXHAUST
SCRUBBER
INDUCED
DRAFT FAN
SCRUBBER
WATER
1 DRAIN
COOUNC AIR FAN
References -
1. Brunner, Calvin R., Design of Sewage Sludge Incineration Systems, 1980.
2. Brunner, Calvin R., Incineration Systems, Selection and Design, Van Nostrand Reinhold Co. NY NY 1984.
3. Chemical Engineering Equipment Buyers Guide Issue 1989. McGraw Hill. NY, NY August 1988.
4. Engineering-Science, Inc., Review of Newer European Sludge Handling, Dewatering, and Incineration Technology,
A Trip Report, Fairfax, Virginia, March 1988.
5. Engineering-Science, Inc., Proprietary Incinerator Design and Modeling. Fairfax, Virginia, November 1988.
6. Hazardous Materials Control Research Institute, Municipal Sewage Treatment Plant Sludge Management, No. 17,
Silver Spring, Maryland, 1987.
7. Hazardous Materials Control Research Institute, Municipal Sewage Treatment Plant Sludge Management, No. 18,
Silver Spring, Maryland, 1987.
8. Hazardous Materials Control Research Institute, 1987 Hazardous Materials Control Directory, Silver Sphng,
Maryland, 1987.
9. U.S. EPA, •Municipal Wastewater Sludge Combustion Technology.' EPA/625/4-85/015. September 1985.
10. U.S. EPA, -Multiple Hearth and Fluid Bed Sludge Incinerators. Design and Operational Considerations,* EPA/430/9-
85-002, September 1985.
11. U. S. EPA/Radian Corporation, Municipal Waste Combustion Study, Data Gathering Phase, 1985.
12. Water Pollution Control Federation, Incineration, Manual of Practice No. OM-11, Atexandria, Virginia, 1988.
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INCINERATION Of SLUDGE, FLUIDEED BED FURNACE (FBF) FACT SHEET
Description. The purpose of Incineration is to destroy the organic fraction of the sludge thai is generated during
wastewater treatment. During the incineration process residual moisture is first removed from the sludge cake and
then organic matter is thermally destroyed. Inerts In the sludge remain as a residual ash Sludge should be
dewatered to 55 to 85 percent moisture prior to incineration in order to minimize the energy required to remove the
residual motsttire. Fluidized bed furnaces (FBF) typically use sludge at the drier end of this range. To obtain the
information needed for process selection and design, each sludge to be incinerated must be subjected to thorough
physical-chemical analysis.
The FBF is a vertically oriented, cylindricalry shaped, refractory lined steel shell that contains a sand bed situated over
fluidizing air diffusers called tuyeres. A typical FBF is 9 to 25 feet in freeboard diameter with a 2.5 foot thick sand
bed. Dewatered sludge is usually fed into or just above the bed. Air injected at 3 to 5 psig simultaneously fluidizes
both the bed of hot sand and the incoming sludge. Temperatures of 1,300 to 1,500°F are maintained within the bed.
Typical residence times are 2 to 5 seconds. As the sludge bums, the entire ash production and some sand are
carried out the top of the FBF. The overall combustion process occurs in two zones. Within the bed (zone 1)
evaporation of water and pyrotysis of organics occur nearly simultaneously. In the freeboard area (zone 2) fixed
carbon and combustible gases are burned. Zone 2 acts as an afterburner, but may not be as efficient as a separate
unit. When needed, supplemental fuel may be injected above or directly into the bed. Sand make-up requirements
are generally 5 percent of bed volume every 100 to 300 hours of operation.
Common Modifications - A hot or warm windbox design uses heat exchanged from combustion gases to preheat
the air before injection. Cold windbox designs inject ambient air directly into the FBF. Water spray systems are
used in some units for temperature control where sludges having higher heating values are incinerated. Some
incinerator heat exchange designs use an intermediate heat exchange medium such as heated oil, hot water or
steam to transfer process heat to the influent sludge or other POTW streams. This heat exchange method tends
to be less costly and easier to replace than conventional shell and tube type exchangers. As emission standards
become stricter, multiple air pollution control units are being used in combination. A separate afterburner Is not
normally required for control of organic emissions. The vast majority of FBF incinerators Installed since 1978 use
a combination of venturi and Impingement tray scrubbers to control emissions.
Technology Status • Approximately 20 percent of wastewater sludge Is managed by the incineration process. The
FBF has gained increased popularity since its 1961 introduction. As of 1985, 38 FBFs at 33 facilities were in use,
with capacities varying from 0.7 to 145 dry tons per day. The average capacity was 23 dry tons per day. This small
capacity reflects the tendency for smaller plants to prefer FBFs over multiple hearth furnaces due to FBF's ability to
be intermittently operated and the simplified O&M requirements of FBFs.
Applications - Incineration is frequently considered as an alternative for plants handling wastewater flows greater than
10 mgd. n is a good alternative for urban areas lacking other options, provided that air pollution controls are
adequate Some sttes, however, have had difficulties in obtaining permits from regulatory agencies. With appropriate
modifications and careful operation, screenings, grit, scum and grease can also be handled. Because the sand bed
of the FBF acts as a heat s**, tf» FBF may be used for Intermittent operation with a minimum amount of start-up
time For exampto I can be restarted after a weekend shutdown with 1 to 2 hours of heating. The FBF also requires
less excess air and toss fuel than the multiple hearth design. As wan other incinerators, the potential exists for energy
recovery and recycling of ash for use hi road surfaces or building blocks or for materials reclamation.
Limitations - The fluidized bed requires a minimum amount of air to maintain bed fluidizatlon, regardless of the amount
of waste feed The FBF may therefore exhibit optimum power consumption at rts design point, but higher power
consumption at lesser feeds. Feed to the FBF must be via positive displacement pumps °r
screw/plunger type feeders. Because the air emissions contain sludge ash and elutrsted sand, higher energy verttun
scrubber systems are often required.
-------
Typical EQuloment/No. of Manufacturers - FBFa/11, Air Fans/53, Screw Pumpe/Ptoton Pumps/11, Supplemental Fuel
Bumers/2S. Preheatecs/60, Venturl Scrubbera/57, Impingement Tray Scrubbers/35. ESP/23, Bag Houses/62, Ash
Conditioning/6.
Performance • The ash volume produced Is typteaffy 30 to 40 percent of the dry solids fed to the unit As much
as 35 percent of the total heat Input to the FBF may be recovered using high efficiency neat exchangers (85 percent
efficiency).
Design Criteria - Bed loading rate to typically 44 to per ff-nr of water for a hot windbox design and 35 to per ft*-hr
of water for a cold windbox design. Bed velocity » 2 to 3 feet per second, bed expansion - 30 to 60 percent,
maximum operating temperature above the bed » 1,500°F (desired operating temperature within the bed is typically
100°F lower): Combustion air requirements should be determined by an utimate analysis of sludge combustibles.
Excess air » 20 to 45 percent
Unit Process ReHabittv - The FBF tsetf Is comprised of few mechanical components with the exception of the forced
draft fan. The majority of problems tend to occur with the auxiliary equipment needed to support an FBF system.
Sand, ash and flue exhaust from the FBF tend to cause corrosion problems with downstream scrubbers and heat
exchange equipment Slagging problems associated wtth the presence of soluble potassium and sodium have also
been reported. A common problem during hot s-andby is the drying and hardening of the sludge feed in the Injection
ports which can result m problems with screw feeders and sludge handling equipment Scaling problems with the
preheater and venturi scrubber have also been reported. Failure of the refractory dome just below the sand bed has
occurred in some Instances.
Environmental Impact • Scrubber technology to generally sufficient to meet existing paniculate emissions requirements,
but new regulations may require more complex equipment, such as wet electrostatic prectpttators, to handle sub-
micron particles, particularly for larger Installations with higher total mass emissions.
The controlled emission rates of metals and organics wffl vary as a function of sludge composition, Incinerator
operating parameters, and types of air pollution control equipment used. Emission rates must be assessed on an
Individual sludge basis. Except for mercury and to a lesser extent arsenic, cadmium, and lead, incinerators emit only
a small fraction of the metals found In sludge.
Chemicals Required • Supplemental fuel ofl or natural gas to required for non-autogenous sludges, incinerator start-
up and standby and afterburner operation, If required. When available, digester gas to often used as the primary fuel.
Other fuels Include waste oil and bunker oiL
Residuals Generated • The combustion gases and nearly aHtheashexKthetopofthe FBF. The total ash produced
to between 20 and 50 percent of the dry solids content of the sludge, and depends upon the combustible fraction
of the sludge. The oh generated may be considered hazardous V, upon leaching by current extraction procedures,
the teachate contains levels of specific metals or organJcs m excess of published standards.
Potential for Improved Toxics Management • The FBF generally results In lower emission rates for volatile organics
as compared to a multiple hearth furnace that to not equipped wtth a separate afterburner.
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Flow Diagram -
EXHAUST AND ASM
BURNER
SUPPVJTMfNTAL
FUEL
TUYERES
CAS EXHAUST
FAN
PREHEATER
J /VENTURI
RCCYO.E WATER
MAKEUP WATER
WATER
DRAIN
ASH
References -
1. Brunner, Calvin R., Design of Sewage Sludge Incineration Systems, 1980.
2. Brunner, Calvin R., Incineration Systems. Selection and Design, Van Nostrand Reinhold Co. NY, NY. 1984.
3. Chemical Engineering Equipment Buyers Guide Issue 1989. McGraw Hill. NY, NY. August 1988.
4. Engineering-Science, Inc., Review of Newer European Sludge Handling. Dewatering, and Incineration Technology,
A Trip Report. Fairfax, Virginia, March 1988.
5. Engineering-Science, Inc.. Proprietary Incinerator Design and Modeling. Fairfax, Virginia, November 1988.
6. Hazardous Materials Control Research Institute, Municipal Sewage Treatment Plant Sludge Management. No. 17,
Silver Spring, Maryland, 1987.
7. Hazardous Material Control Research Institute, Municipal Sewage Treatment Plant Sludge Management, No. 18,
Silver Spring, Maryland, 1987. '
8. Hazardous Materials Control Research Instftute. 1987 Hazardous Materials Control Directory. Sifcer Spring,
Maryland. 1987.
9. U.S. EPA, "Municipal Wastewater Sludge Combustion Technology." EPA/625/4^5/015, September 1985.
10. U.S. EPA, -Muttiple Hearth and Fluid Bed Sludge Incinerators. Design and Operational Considerations," EPA/430/9-
85-002, September 1985.
11. U. S. EPA/Radian Corporation, Municipal Waste Combustion Study. Data Gathering Phase, 1985.
12. Water PoLution Contro. Federation. Indneration, Manu* of Practk* No. OM-11. Alexandria, Wginia. 1988.
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LAND APPLICATION OF SLUDGE FACT
** ^9 dlsposal te a P"*9™*1 •"dfl* management alternative because of Its low
hr 22! recycte **" * "» ***•• " utilizes ^ p»*** *•"** a* "dogS
the sal to absorb, adsorb, and decompose waste constituents in the sludge. The primary objectives
of design and management are to provide an environmentally safe final disposal for the waste, maintain the land's
potential for future use, and gain and maintain public acceptance.
The quality of the sludge depends on the characteristics of the original wastewaters and the manner in which the
sludges are subsequently treated (e.g., aerobic and anaerobic digestion, thickening, lime stabilization, conditioning
dewatering, composting, heat drying, etc.). Sludge characteristics that are important to land application include water
content, degree of stabilization and pH. The water content determines transportation costs and the method of
application; stabilization influences btodegradability, pathogen destruction and odor potential; and pH determines the
potential for leaching metate from the soil/sludge and the subsequent metals uptake by crops. Beneficial sludge
constituents include nitrogen, phosphorous, potassium and certain trace metals that act as fertilizer nutrients, and
organic material that serves as a soil conditioner. Careful management is needed to control pathogens, toxic metals,
and toxic organics.
Land applied sludge can be an excetient substitute for commercial fertilizers and soil amendments, and can be cost
effective for both the municipality applying the sludge and the application site which accepts the sludge. The use
of wastewater sludge as a source or suppte.Ter: of fertilizer nutrient to enhance crop production is widespread in
the United States. Commercial timber and fiber production lands, as wed as federal and state forests, are potential
application sites. Sludges have also been successfully applied to disturbed or marginal lands (e.g., mining or mineral
processing operations, sandy and unproductive areas, etc.) to enhance reclamation and revegetation. Land
application to a dedicated disposal site is also practiced.
Common Modifications - Methods vary for transporting and applying sludge to the land site. The same transport
vehicle that hauls sludge to the application site can atso be equipped to apply the sludge to the land. In other cases,
the transport vehicle hauls sludge to the site and transfers it to an application vehicle and/or storage facility. Sludges
are also pumped and transported by pipeline to storage facilities at the site, and then transferred to an application
vehicle.
The sludge application method and the schedule for applying sludges are dependent on the characteristics of the
sludge and soils, and on the types of crop. Three categories of crops are usually grown: agronomic or row crops,
forage crops and grasses, and forested systems. Sludge can be applied to either the land surface (spreading or
spraying) or to the land subsurface by Incorporating (Injection, disking, or plowing) the sludge into the topsoil.
Dewatered sludge cannot be pumped or sprayed, and typically is spread over the surface and then plowed or disked
Into the soil.
Technology Status • Land treatment systems can be designed to provide an acceptable means of waste management
that is reliable and predictable. Agricultural utilization of sludge is extensively practiced. Sludge application to forest
lands and land r«damatJon sites Is practiced to a limited extent In some cases, land sites are dedicated to sludge
disposal.
Limitations - Sludge contains constituents (I.e., heavy metals, toxic organics, and pathogens) potentially harmful to
crops or animals and humans who consume the crops. However, good management practices have been developed
to limit the potential for harm that exists by way of soil and water contamination, crop damage, and accumulation
of harmful components In the food supply.
Land applied sludge is generally required to undergo a stabilization Process to Significantly Reduce Pathogens
(PSRP7 Crops for direct human consumption require either a minimum of 18 months between sludge apPl.cat,on
and growing or the sludge must undergo PSRP prior to application. These PSRP processes may «ck*a
composting heat drying, heat treatment, thermophilic aerobic digest.on, pasteurization, Irradiate, etc. Federal
regulations also include limits on cadmium, polychkxobiphynyls (PCBs) and soil pH.
-------
During periods of the year when the soil is wet, frozen or snow covered, sludge often can not be applied and
storage (e.g., stockpiles, lagoons, tanks, digesters) Is necessary. For maximum crop yield when using sludge the
application of certain additional fertilizer elements such as potassium may be required. For forest land utilization, both
control of public access and access to some forest lands for conventional sludge application equipment may be
difficult For disturbed or marginal land reclamation, some grading and other site preparation steps may be
necessary. For dedicated land disposal, land may have to be purchased or leased and build up of metals in the soil
might limit future use.
Applications - For agricultural utilization, sludge contains macronutrfents (nitrogen, potassium and phosphorous) and
micronutrients (boron, manganese, copper, molybdenum and zinc) and can be a valuable soil conditioner. For forest
land utilization, sludge contains nutrients and essential micronutrients often lacking in forest soils and organic matter
which can Increase the permeability of fine-textured clay soil or Increase the water-holding capacity of sandy soils.
For reclamation of disturbed and marginal lands, sludge organic matter can Improve granulation, reduce plasticity
and cohesion, increase water holding capacity and soil CEC, supply plant nutrients, and increase the buffering
capacity of the soil.
Typical Eoulpment/No. of Mfrs. - Surface application equipment Includes farm tractors, tank wagons, special applicator
vehicles equipped with flotation tires, tank trucks, and Irrigation systems. Subsurface application equipment Includes
tractor-drawn tank wagons with Injection shanks or tank (nicks fltted nth flotation tires and injection shanks.
Dewatered sludges require handling equipmb.it v;mDar to that used in applying animal manures, limestone, or solid
fertilizers. Dewatered sludge is typically surface-applied and then Incorporated by plowing or disking. More
specialized and/or heavy duty equipment may be used for applying sludge to forest and reclamation sites.
Performance - Land application is a viable, environmentally sound, and cost-effective technology without nuisance
or adverse environmental effects if property designed and managed. Sludges with minimum concentrations of metals
and organics can be applied at rates meeting the nitrogen or phosphorus requirements of the vegetation. It Is unlikely
that copper, zinc, and nickel will cause human health problems In properly managed systems. Cadmium Is typically
the metal of concern and may determine the life of the application site.
Design Criteria - If proper steps are taken In designing the system, very few sites are totally unacceptable for land
application of municipal sludge. However, there are a number of site-specific factors which should be assessed
adequately prior to determining whether a particular site can be used effectively for land application. These Include
soil type, flooding susceptibility, slope, depth to seasonal groundwater table, permeability of the most restrictive soil
layer, cropping patterns, vegetative cover, and organic matter content Since many suitable sites will not be Ideal,
the planner must carefully consider such factors when choosing actual application sites and designing projects.
Once a suitable application site has been selected and the process objectives defined, proper sludge loading rates
are determined. Thi» process often Involves characterizing the waste for a number of constituents. The following
constituents are generally of most concern for municipal sludges: pathogens, phosphorous, nitrogen, cadmium,
copper, nickel, lead, and zinc When sludge Is applied at rates to meet the nitrogen requirements of the crops being
grown, nitrogen losses in excess or those expected from commercial fertilizer use should not be expected.
Existing federal sludge application regulations are primarily based on cadmium content New regulations have been
proposed and are scheduled to be finalized in October, 1991. Until then, POTWs should follow the "Sewage Sludge
Interim Permitting Strategy* for permit writers. This recommends that In the absence of promulgated technical
standards, the primary source should be the document "Evidence for Writing Case-by-Case Permit Requirements for
Municipal Sewage Sludge* (December 1989).
Reliability - With proper site selection, design, and operation, land application systems are very reliable.
Environmental Impact - In 1983, over 200 hearth and environmental experts from the United States, Canada and
Europe met in Denver, Colorado to assess the state-of-the-art for sewage sludge use and disposal. The published
-------
flu?!flct ""* ™«ulalion8 w»r8 adequately Protective at puttie health and the
provided thai sewage sludge was used in accordance with those provisions. The conclusions were
that:
(1) Guidelines have been developed to enable the environmentally safe use of sewage sludge containing median
concentrations of metals and organics when the sludge Is applied at agronomic rates based upon nruoaen or
phosphorus utilization by crops; ^
(2) Concentrations of synthetic organics In sludges are generally tow, but high concentrations may exist in some
sludges. Most synthetic organics are decomposed in soil. Current Federal regulations for PCBs in sludges are
adequate to protect human health;
(3) Groundwater monitoring for nitrate-nitrogen is not needed where sludge nitrogen additions do not exceed fertilizer
nitrogen recommendations for the crop grown;
(4) Utilization of sludge for reclamation of disturbed land at rates higher than those for agricultural land, when property
Implemented and managed, improves the quality of soils, groundwater or vegetation;
(5) With proper management and safety allowances based on research data, land application is a safe, beneficial
and acceptable alternative for treatment of municipal wastewater and sludges;
(6) In terms of current detection capacity, Federal sludge disposal criteria are adequate to protect human health from
pathogenic microorganisms.
References -
1. ASCE, Land Application of Wastewater Sludge: A Report of the Task Committee on Land Application of Sludge,
Committee on Water Pollution Management, Environ. Engineer. Div., American Society of Civil Engineers, 1987.
2. Brockway, D.G., 'Forest Land Application of Municipal Sludge,' Biocycle, September 1988.
3. Crttes, R.W.. "Land Use of Wastewater and Sludge,' Environmental Science and Technology. Vol. 18, No. 5.
1984.
4. Demirjian. Y.A., A.M. Joshi and T.R. Westman, 'Fate of Organic Compounds in Land Application of Contaminated
Municipal Sludge,' Journal of Water Pollution Control Federation, Vol. 59, No. 1, 1987.
5. Jensen, R. "Sludge Management Activities in Texas; Biocycle, March 1988.
6. Mays, DA and P.M. Giordano, "Land Spreading In the Tennessee Valley," Biocycle. September 1988.
7. Loehr, R.C., WJ. Jewed, J.D. Novak, W.W. Ciarkson, and G.S. Friedman, Land Application of Wastes, Vol. II. Van
Nostrand Reinhold Co. NY, NY, 1979.
8. Page. A.L, T.Q. Logan and JA Ryan, ed., Land Application of Sludge. Lewis Pub.. Inc. Chelsea, Ml. 1987.
9 Page A.L TL Gleason J E Smith, IX Iskandar, and LE. Sommers, ed., Proceedings of the 1983 Workshop
on Utilization of Municipal Wastewater and Sludge on Land. University of California. Rivers.de. CA. 1983.
10. Reed, B. and M. Matsumoto, -Land Application of Wastewater Sludge.' Pollution Engineering, December 1988.
11. U.S. EPA. A Practical Technology: Land Application of Sludge - A Viable Alternative (a fotoout). September 1983.
M U.S. EPA, EPA Municipal Sludge Management Policy. Notice Federal Register. June 1Z Vol. 49, 24358. 1984.
13. U.S. EPA, EPA's Policy Promoting the Beneficial Use of Sewage Sludge and the New Proposed Technical Sludge
Regulations. Office of Water. Washington, D.C. June 1989.
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14. U.S. EPA, Environmental Regulations and Technology: Use and Disposal of Municipal Wastewater Sludge.
EPA/625/10-84-003. Ondnnatl, OH., 1984.
^
15. U.S. EPA, Guidance for Writing Case-by-Cas« Permit Requirements for Municipal Sewage Sludge, December
1989.
16. U.S. EPA, Handbook, Estimating Sludge Management Costs, EPA/62S/6-85-010, Cincinnati, OH., 1985.
17. U.S. EPA, Process Design Manual for Land Application of Municipal Sludge, EPA/625/11-83-016, Cincinnati, OH..
1983.
18. U.S. EPA, Sewage Sludge Interim Permitting Strategy: Notice Federal Register October 20, VoL 54, 43124.
19. Walker, J!M., -Public Acceptance: Winning Strategies for Land Application,' Btocyde, May-June 1986.
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IN-VESSEL COMPOSTING PACT SHEET
x
Description - Composting is the biological decomposition of the organic constituents of wastes. The process can
erther be aerobic or anaerobe. Those systems designed for composting municipal sewage sludge mSSoS^S
strive to be a thermophylic aerobic decomposition process in which microorganisms metabolize dewaiered organic
sludges to a relatively stable organic residue, CO,, r^O, and heal. Operating parameters are specified to assure that
the heat generated by the composting process has been sufficient to reduce pathogen content in the compost
product to an acceptable level. The resultant humus-like compost material Is an excellent low-grade fertilizer and soil
conditioner.
Irvvessel composting is a mechanical configuration of this process, In which the sludge Is treated In a closed reactor
The sludge is typically premtxed with an amendment (such as sawdust or wood chips) and recycle. Air is diffused
Into the reactor through the compost material for temperature and moisture control, and to provide oxygen for
biological metabolism. The air is typically exhausted directly to an odor treatment system before discharge to the
atmosphere. The process is usually accomplished m two stages, whereby the major composting activity taxes place
in the first stage; the second stage is used for curing and may be carried out In a second vessel and/or an exterior
pile. As an enclosed process, In-vessel composting is easier to fit for full off-gas collection/treatment. and Is generally
more automated than conventional open windrow or static pile compost systems.
Common Modifications - Reactor design can vary In configuration, incorporating either vertical or horizontal
flow-through, circular or rectanguJar tanks, and static or dynamic operation. In agitated (dynamic) reactors the
sludge/amendment mixture is mechanically mixed fin-place, or as It is moved through the reactor). This maintains
uniform heat and air distribution. In non-agitated (static) reactors the mixture may be loaded at the top and withdrawn
from the bottom (relying on gravity to force plug flow movement down through the reactor), or forced through
horizontally with a hydraulic ram. tt can even consist of a static pile system contained within a building. Air is
supplied by a variety of different blowers and pumps, depending upon the system, the air path length and the
resistance to air flow.
Technology Status - There were 19 full scale In-vessel composting plants operating In the Unites States, as of 1988,
with 24 in the design, bid or construction stages. This is a significant increase from the three that were In operation
in 1985. Sludge loading capacties range front 1 to 78 dry tons per day. Operating experience is limited at this point
and designs vary. The process can be considered an emerging technology because of the limited number of
installed plants. The control requirements and the computerized nature of the aeration and temperature control
systems Introduce a significant degree of complexity to the process.
Applications - In-vessel composting Is an alternative to conventional open-pile composting operations. The
advantages over non-enclosed composting methods include enhanced ability to collect process and curing air for
odor control Improved aesthetics, reduced impact of ambient weather conditions, reduced land requirements, and
generally tower manpower requirements. Composting is particularly applicable In areas where there is a ready
market or user for the compost product.
Limitations - By tar the most cribc* consideration for sludge composting systems to the ability to control odor.
Critical steps for successful control Induce (a) an inventory of all sources of odor, ^'^f^^™ <* ^
types and amounts (b) a determination of the typical meteorological conditions throughout each day and each
season (c) setting a level of odor detectable In the neighborhood that is acceptable to residents, and (d) based upon
mSeling anTme^urement, appropriate* determining the proper mixture of ^^^^SfSSS^S
and/or dispersion For the majority of systems the air from most all sources, including sludge transfer, mixing,
coZyingSg anS unloading. processing, curing and storage, will have to be treated by scrubbing, combust-on
and/or dispersion.
Destroying and dispersing the odors is not routine. Chemical K™^^"^™™"?*^'^
level of monitorina for successful operation. Thermal regenerative combustion may be a simple odor treatment
™
• i scr inhe future. Good communjy
should start at the facility planning stage and continue on through arting. setting an acceptable odor standard, and
-------
ongoing operation. Careful Investigation and documentation of the source of odors (both from the sludge composting
facility and elsewhere m the neighborhood) Is critical, it establishes the credibility of successful odor control for a
facility, an Important element m the facility's relationship with local neighborhoods.
Composting systems often have major problems because they have not realized that specific market uses require
specific product characteristics. This goes well beyond simply meeting EPA temperature requirements for pathogen
control Some end uses can successfully accept compost products with widely differing properties and others can
not A mixture of end uses should be available because sludge and processing conditions often may cause the final
product characteristics to differ, and a small change In product characteristics can preclude some end uses, and
hence eliminate a portion of the market
The off-gases from composting are high In humidity, organic compounds and ammonia which can cause a harsh
working environment Furthermore, these off-gases are very corrosive and, In fact, some of the organic constituents
can dissolve epoxy coatings. Consequently, great care is needed to pick the proper products for construction of
both the building and the various system components (e.g., blowers and duct work). There have been considerable
problems with materials handling equipment Many of these problems are being overcome as experience is gained
with the design and construction needs for conveyors, unloading devices, mixing devices, screening devices, etc.
If a proposed system will Include new types of components that have not previously been tested for the particular
application, careful pretesting of the proposed component Is strongly recommended.
Typical Equipment/No, of Mfrs. - In-vessel wen post systems/8; conveyers/12; dewatering systems/22; materials
handling/15; mixing/8; odor control system/3; screens/6; tubing, aeration/2,
Performance • in a survey of 8 In-vessel composting systems In 1988, 3 were operating at reduced capacity because
of odor or mechanical problems, 2 were down for modifications to structure and/or odor control systems, and 3 were
processing all available sludge. The two major problem areas experienced by most or all of the plants surveyed were
odor control and materials handling. Alt systems can achieve pathogen kills and stable end products.
Sludge/amendment/recycle ratios were variable. Depending on the site, these ratios exhibited a range of 1: 0.5 to
1.6: 0.6 to 10, somewhat higher In the use of amendment and recycle than anticipated by the original design. The
sludges were 16 to 30 percent solids; the solids content in the initial compost mix ranged between 33 and 50 percent
solids. The first stage solids output ranged from 33 to 65 percent
Design Criteria - The sludge to be composted should have a solids content of 18 to 30 percent, with a volatile
solids content greater than 50 percent The pH must be between 6 and 9, and the carbon to nitrogen ratio between
25 to 35: 1. The sludge to amendment (with recycle) ratios should yield an infeed mixture in the range of 35 to 45
percent solids. This win generally require a sludge: amendment: recycle ratio in the range of 1: 0.5 to 2:1 to 3.
The ratio and percent solids wiH depend on the quality and type of amendment and recycle. The minimum hydraulic
residence time should be 12 to 20 days, with a system sludge residence time greater than 60 days. There should
be at least 3 days residence time at a temperature greater than 55°C to meet current EPA •PFRP* pathogen
requirements.
Because of the complexity of odors produced, odor control systems employ a spectrum of removal mechanisms
(e.g., multiple wet chemica) scrubbers, Wofilters, bubbling through waste water, biologically activated suspensions,
and chemical oxidation). R Is necessary to model dispersion characteristics to screen sttes, establish maximum
allowable emissions, determine supplemented stack or ventilation needs, and develop flexible odor control plans.
Supervisors and operators should receive training in composting theory and operation. Very often, the training has
been inadequate and failures have occurred, sometimes resulting in prolong periods of shut down for expensive
repair. Visits to successfully operated sites are also recommended.
Reliability • Composting and In-vessel composting are still emerging technologies with respect to other sludge
disposal processes, and problems need to be resolved before this technology sees widespread use.
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Management - Studies show that composting can detoxify oily sludges pesticides
'
and herbicides », cflazJnon, parathton, DDT, carbaryl, etc.)
*naefObto ***** * *""*•* <**"!»* to landfarmlng and incineration, composting Is safer
Environmental Impact - Heavy metal contamination of soil and groundwater following compost application is a
concern. Cadmium and toad are most often mentioned as the driving force for regulating distribution and marketing
of sludge products; however, copper, nickel, zinc, and molybdenum may show the greatest potential for plant
accumulation and effects on man. Restrictions on land application generally appry only to heavy metal content. If
the compost is to be used for root crop or leafy vegetable production, time/temperature requirements to achieve
further pathogen reduction (PFRP) is essential.
Costs - Installed costs (1988) for six operating plants ranged between $200,000 and $700,000 per dry ton/day design
capacity, with an average of $535,000. These costs include modifications and anticipated upgrades to improve
operations. Operation and maintenance costs, based on a survey (1988) of eight operating plants, ranged between
$71 - $319/dry ton, with an average of $175/dry ton; The major components were labor, $30 • $lOO/dry ton;
amendment, $20 to $130/dry ton; power, $15 - $75/dry ton; and maintenance, $25 - $80/dry ton. Revenues from
compost sales may vary from $2 to $l9/ycP depending on local pricing policies and the quantities that are purchased.
If supply exceeds demand, the plants will stockpile, give It away, pay to have It hauled away, or sell It back to
system supplier.
References •
1. Benedict, A. H., E. Epstein and J. Alpert, 'Composting Municipal Sludge: A Technology Evaluation,' U.S. EPA,
EPA/600/2-87/021. 1987.
2. Biccycle, The Biocycle Guide to Composting Municipal Wastes, The J. G. Press, Inc. Emmaus, PA., 1989.
3. Biocycle, The Biccycle Guide to In-Vessel Composting, The J. G. Press. Inc. Emmaus, PA., 1986.
4. Donavan, J. F., •Setecting a Composting Method,' Environmental Engineering Proceedings, 1987 Specialty
Conference, American Society of Civil Engineers, Orlando, FL, 1987.
5. Goldstein, N.. W. A. Yanko, J. M. Walker and W. Jakubowskl. •Determining Pathogen Levels in Sludge Products,1
Biocycle, May/June 1988.
6. Gouin, F., •Compost Standards for the Horticultural Industry,' Biocycle, August 1989.
7. Haug, a T., •Composting Design Criteria, Part I: Feed Conditioning.' Biocycle, Vot 27. No. 7, 'Part II: Detention
Time; BtocycJe', VoL 27 No. 8. "Part III: Aeration,' Biocycle, April 1986.
8. Johnston. J.. J. F. Donovan and A. B. Plncince, 'Operating and Cost Data for In-Vessel Composting.' Biocycle,
April 1989.
9. Murray C M . -Odor Control Strategies and Experiences at the Montgomery County Composting Facility; In
Proc. ofthe Nat. Conf. on Municipal Sewage Treatment Plant Sludge Management, May 27-29., Sponsored by the
Hazardous Materials Control Research Institute, Silver Spring, MD., 1987.
10. U.S. EPA, -Composting of Municipal Wastewater Sludges; A Technology Evaluation. EPA/625/-MB/014. August
1985.
11. U.S. EPA, -Summary Report: In-Vessel Composting of Municipal Wastewater Sludge; EPA/625/5^9/016,
September 1989.
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12. Walker. J.. N. Goldstein and B. Chen, •Evaluating the In-Vwse) Composting Option. Pan I and II,' Btocyde. April
1986 and May/June 1986.
«•
13. Walker, J. M., Translating Research Into Large-Scale Production Facilities.' Btocycle. May/June 1987.
14. Wlllson, G. B. and D. Oalmat, •Measuring Compost Stability,' Blocyde, August 1986.
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CARVER-GREENFIELD SLUDGE DRYING
*•
Description - The Carver-Greenfield (C-G) Process Is a patented system for drying various types of
ntiuftng munepil wasiewater sludge. A carrier or fluidlzing oiltemixed w«h wetl
rton* 0.1 te pumped through a multiple* evapcXtion and/or mechan.cS
The evaporated water (up to 99 percent recovery) to condensed and discharged, and any entrained carrier oil is
Sf8^!^8!^ "** "I! ** feed fluldlzing tanfc ^ dried
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The City of Los Angela* (first generation) light oil C-Q plant has experienced start-up problems. Almost two years
were spent Improving mechanical equipment reliability after Its mechanical completion In late 1986. During this
period the're were numerous problems wtth various parts of the system. Substandard equipment was upgraded or
replaced, provisions were made for coping wtth equipment and piping abrasion problems, and operating methods
were modified. Some of the earlier problems with the Hyperion C-Q system and solutions are discussed In reference
4.
The transition to design, start-up and operation of the C-Q chemical process technology has been difficult for both
the designers and the municipalities. A major Investment of time and money has been required for learning the best
approach and appropriate specialists to use. Start-up of new chemical process technologies such as light oil C-
Q technology requires very specialized skills and significant funding (amounting to 10 to 20 % of the capital budget).
A team of refinery/petrochemical start-up operations specialists was assembled during the later part of 1988. They
updated the O&M manuals and established comprehensive procedures for sampling and monitoring the system.
Their experience, comprehensive approach and around-the-clock supervision paved the way for a number of
additional improvements that resulted in the attainment of continuous operation of two of the three C-Q treatment
trains at Hyperion at approximately 40% of design capacity with on-stream reliability as high as 87% during a several
month period.
There stilt have been significant periods of shut down for further modifications and improvements, e.g., the
replacement of undersized motors in slurry pumps, providing more vacuum (as called for In the original design) and
control of fugitive odor emissions. Start-up a. id taalnment of a greater percentage of design capacity was hampered
during 1989 by lack of a given skilled start-up team being consistently assigned to the task. The requirements for
starting-up and operating these facilities are clearly discussed In reference 1.
Design Criteria - Parameters affecting design Include sludge composition (solids, water, and Indigenous sludge oil
levels), application of final product, and energy prices. Multiple-effect evaporator systems are usually favored over
MVR designs when solids concentrations are greater than 15 percent and/or when steam to cheaper than electricity.
An oil to solids ratio of 6 to 1 Is typically used for municipal sludge. The evaporator pressures are between 2 and
14.7 psia generally with 3 to 5 effects.
Reliability - C-G Process plants typically have availability factors of 85 to 90 percent However, this reliability has not
yet been demonstrated for the appfcation to sludge drying wth Sght oil technology because K is an emerging
technology and a very fcnfted number of these facflWes are available for evaluation. Start-up problems have been
and are expected to be greater than for established treatments. The designer believes that redundancy Is essential
for key equipment within a process train, but does not consider redundant trains necessary.
Environmental Impact - 01 soluble orgartcs should be removed from the sludge during the sludge drying process,
and non-volatile metals should remain wtth solid particles. Volatile metals (toad and particularly mercury) may require
air pollution control devices If the dried sludge Is Incinerated. Dried sludge from the City of Los Angeles plant was
classified as hazardous waste by the California WET procedure due to cadmium; however, cadmium levels were not
found to be hazardous by the Federal EP Tcodctty hazardous waste test
Since the process Is fully enclosed and under vacuum, odor problems should be minimal, especially now that further
efforts have been made for collecting and combusting odors, including odorous vent gases. Pathogens, bacteria,
and viruses present in the sludge are destroyed due to a one hour detention time at 300 to 350°F in the de-oiler.
The oil-soluble toxic and hazardous compounds In the sludge are extracted by the carrier oB and Incinerated or
disposed of In other safe ways.
Chemicals Required - The oil makeup design requirements are: 20 Ibs/ton dry solids at $0.20/lb for light oil (narrow
fraction wtth a boiling point of 204°C); and 160 Ibs/ton dry solids at $0.08/lb for heavy oil (light gas oil, net cost after
fuel credit).
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Residuals Generated - The feed sludge Is separated into solids, water and sludge oil The gaseous emissions ire
collected and incinerated. In the heavy oil version, the sludge oil remains with the solids and is fed to an incinerator
for energy recovery. Evaporated water te condensed and returned to the wastewater treatment plant
Potential For Improved Toxics Management - The process aids in incineration of toxic materials present In municipal
sludge. By removing the water, high flame temperatures can be achieved in the incinerator, and destruction of toxic
and hazardous compounds and the formation of non-teachable ash are enhanced. In fertilizer applications, sludge
oil and oil-soluble compounds (e.g., toxic and hazardous pesticides, insecticides, etc.) are removed from the sludge,
and pathogens are destroyed. Thus far the fluidized bed incinerators at Hyperion, with their efficient scrubbing
systems, have effectively controlled emissions during the combustion of the dry sludge powder from the Carver-
Greenfield process.
Energy Notes - Current energy requirements range from 200 to 363 BTU/?b water evaporated. The manufacturer
suggests that a value no greater than 500 BTU/lb be used for preliminary estimating purposes.
Flow Diagram -
Carrier Oil
Moist
Feed -|
Solids
Flufdizing
Tj
Evaporaton
and Ho*
Exchanger*
Dried
Solids
in Oil
Flash
Still
Centrifuge
J
Sewage OU (Fuel)
Sewage Oil and
Carrier Oil
1
Solid* and
Carrier Oil
Deoiler
(Hydroextractor;
Water to POTW
I 96% Sc
I Fertili
i Solid* (Fuel or
Fertilizer)
-^ ..... ^i- iMe
. The fol.ow,ng table lists
The Figures represent C-G an
the feed is municipal sludge conim
oil plants in operation or construction, with associated costs
t^ufacturer. These estimated costs assume
mS-1989 construction at a clear and level site; process
peering fees are included; crude oil priced «
- 10 to
-------
(Dry Ton.
240
(«*••«
UWMT County
Oeotn County
Autofty.
80
Burtngkin Murtr
Ct«1v»l«rt«
ESTIMATED INSTALLED CX)ST
OF CARVER-GREENFIELD PROCESS
(MID-1989)
50 100 150 200 250 3OO 350
SLUDGE CAPACITY (DRY TONS/DAY)
References -
ESTIMATED O & M COST
FDR CARVER-GREENFIELD PROCESS
(MID-19G9)
v/o CREDITS
w/FUEL CREOITS
50 100 150 200 250 300 350
SLUDGE CAPACITY (DRY TONS/DAY)
1. Gonzates, M., F.Y.W. Uao, K.A. Pluenneke, G. Rowe, and M.J. Sieke, -Startup and Operation of Chemical
Process Technologies in ine Municipal Sector - The Carver-Greenfield Process for Sludge Drying,' U.S. EPA, Office
Of Water, EPA/430V09-8S-007, August 1989.
Z Hoteombe, T.C., Personal Communication, Dehydro-Tech Corporation, East Hanover, NJ. 07936, 1989.
3. Walker, J., Carver-Greenfield Sludge Drying Systems, Status Report, July 27, U.S. EPA Office of Municipal Pollution
Control, Washington. D.C., 1988.
4. Walker, J. and J. Zirschky, Summary of the 1987 Carver-Greenfield Sludge Drying Technology Workshop:
Problems and Solutions, U.S. EPA Office of Municipal Pollution Control. Washington, D.C., EPA/430/09-87-010,
September 1987.
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COMPOSTING SLUDGE, STATIC PILE
8hxj°6 * "*™ *** "B"* materials *e <**«•* to • stab)e
,n ^u«01T^f s °blC Or8anism8- * the static pile process, wastewater sludge is converted to
compost in a four-step process in approximately eight weeks.
Preparation . Sludge is mixed with a bulking material such as wood chips to provide the necessary structure and
porosity for aeration and to tower the moisture content of the compost mix to about 60 percent. Following mixing,
the aerated pile is constructed by placing the compost mix over a network of porous pipe that has been covered
with wood chips to insure good distribution of air. The pile Is then covered with screened or unscreened compost
for odor control and insulation. The goal is to achieve uniform aeration, sufficient moisture removal, temperature
control, and partial odor screening. The exact layout of aeration, wood chips, pile heights and Insulation to achieve
these goals may vary.
Stabilization - The aerated pile undergoes decomposition by thermophilic organisms, whose activity generates
sufficient energy to heat the aerated pile. Although higher temperatures can be achieved, optimum microbial
decomposition occurs between 45 to 60°C (113 to 140°F). Aerobic composting conditions and temperature
regulation are maintained by drawing air through the pile at a predetermined rate. The effluent air stream must be
appropriately scrubbed and dispersed to achieve good control of odor [2]. After about 21 days the decomposition
rate and pile temperature declines. The p>'.3 fc then taken down and the compost is either screened or cured
depending upon the intended use of the finished product and te moisture content Compost pile temperature must
be maintained at 55°C for a minimum of three days to assure disinfection. Periodic stability testing, germination
testing and pathogen monitoring may be desirable.
Screening - Unscreened compost should have a moisture content of between 40 to 45 percent to facilitate clean
separation of the compost from the bulking material and prevent dusting. The unscreened compost can be dried
prior to screening by aeration of the stabilized compost in storage piles of about 8 feet height following the 21 day
composting period, by restacking, or by spreading the stabilized compost out with a front- end loader to a depth of
12 inches and turning It. Screening can be performed with a rotary screen or a vibrating-bed screen. The bulking
material is usually recycled.
Curing • Either before or after screening, the compost Is stored in piles for about 30 days to complete stabilization
and to assure no offensive odors remain. The piles should be aerated while curing to prevent anaerobic odors. The
compost is then ready for utilization as a low grade fertilizer, a soil amendment, or for land reclamation.
Common Modifications • 1. Individual pile - This method is as previously described. 2. Extended pile - Each day's
pile is constructed against the shoulder of the previous day's pile, forming a continuous or extended pile, and
resulting in a savings of space and materials. Individual or extended piles can be constructed under a roof with or
without side drops, or inside a wide span building. Although the static pile process generates sufficient heat to be
left uncovered, a roof and/or partial enclosure will improve process control and reliability if the facility is located in
a cold or wet cflmate. Enclosures will also Improve the ability to control odor by collection, scrubbing and/or
dispersion Air from tt» building must be collected and treated If upflow aeration Is used. If downflow aeration is
used, the building air can be handled by dilution and dispersion, but the process air must be collected and treated.
Technoloqy Status - A December 1988 survey identified 61 operational aerated static pile facilities with 10 under
construction and 13 in planning and design m the United Stales. State of the art static pile facilities as of October
1988 include the Montgomery County Composting Facility (Site II), Washington Suburban Sanitary Comm.ss.on, Sirver
Sprina MD and sludge composting facilities at Sussex County Municipal Utilities Authorrty, Hardyston Township. NJ.
and Hampton Roads . VA. ThTuse of temperature feedback to automatically control aeration to maintain the desired
pile temperature is becoming more widespread. Promising research is ongoing in the areas of odor control and co-
composting with leaves, yard waste, and municipal and industrial solid waste streams.
Applications - The static pile method Is less sensitive to climatic conditions and allows for better odor and temperature
control than windrow composting.
-------
Limitations - 1) Odor generation and release to the main environmental problem at composting Installations. Site
cleanliness, development of an area odor Inventory, thorough knowledge of the site meteorology and a strong public
relations background provide the basis for effective odor control Close attention and high operator skill level are
required to properly operate odor scrubbers and related chemical handling facilities. 2} Planning to ensure effective
final product marketing and distribution must be accomplished 3) The design must consider variations In sludge
. and wood chip quality, and should employ a conservative estimate of sludge percent solids. If the dewatered sludge
ts 3 to 5 percent wetter than anticipated, up to 80 percent more wood chips may be required, which will significantly
increase the required composting and storage areas.
Typical Equipment • Commonly used equipment, which to readily available, Includes: front-end loaders; perforated
plastic pipe; blowers; rotary or vibrating-bed screens; odor scrubbers; prefabricated buildings.
Performance • Well-operated static pile facilities routinely produce compost which to free of salmonella and with a total
solids content of 51 to 69 percent and bulk densities of 900 to 1,500 pounds per cubic yard.
Chemicals Required • Odor scrubbers may require sodium hydroxide, sodium hypochkxite, and sulfurtc add.
Residuals Generated • Final product to compost Leachate from piles must be collected and treated.
Potential For improved Toxics Management - Heavy metals entering the process remain In the final product but
may be diluted with the addition of bulking materials. The degree of removal of organic toxic substances is not
known, but Indications are that many organics will degrade.
Design Criteria - Wood chip mix requirement for a sludge with 18 percent solids to 3.5 to 5.0 cubic yards wood
chips/wet ton of sludge; compost mix moisture content to about 60 percent; compost pile height to 8 to 10 feet;
aeration rate to 2,000 to 4,000 cubic feet per hour per dry ton of sludge; unscreened compost generation to 4.0 to
5.0 cubic yards per wet ton sludge; screened compost generation to 0.5 to 1.0 cubic yards/wet ton sludge. For
determining land requirements typical detention times are: composting • 24 days; curing * 30 days; bulking agent
storage » 60-90 days. The facilities should be manned eight to ten hours per day, five to six days per week. O&M
costs/dry ton average $154, and typically range from $125 to $175.
Reliability • Process reliability to good once pile construction techniques, aeration piping configurations and
appropriate aeration flow rates and sequencing have been established. Operator training, moisture control,
homogenous initial mix and adequate aeration have been found to be the most important factors for effective
composting. The use of a single experienced person to oversee mixing operations appears to ensure consistent
and proper Initial mot moisture content and mix homogeneity. Capability to control and record pile temperature 24
hours per day In order to meet temperature/time requirements to necessary to ensure proper pathogen control.
Emergency power In the form of Independent dual feeds or a standby generator set to desirable to provide aeration
continuity In the event of primary power source failure.
Environmental Impact - The four major concerns of adjacent communities are odor generation, notes, sightliness,
and traffic patterns. These concerns must be carefully addressed.
-------
FlowDiagram
SLUDGE
MIXING
CONSTRUCT
PILES
BULKNG
AGENT
L. •
Schematic • Individual Aerated Pile -
AIR
COVER-SCREENED
OR UNSCREENED
COMPOST
MIX-SLUDGE AND
BULKING AGENT
PERFORATED PIPE
Schematic • Extended Aerated Pile -
FORCED
AERATION
CURING
DRAIN FOR-
CONDENSATES
SCREENING
CURING/
STORAGE
USES/
MARKET
ODOR FILTER-PILE OF
SCREENED COMPOST
EXHAUST FAN
AIR
COVER-SCREENtD
OR UNSCREENED
COMPOST
MIX-BULKING ACE NT
AND SLUDOC
BULKING AGCNT BASE
PERFORATED PIPC
NON-PERFORATED PIPE
LOW POINT FOR
CONDENSATE
DRAINAGE
•^
ODOR FILTER-PILE OF
SCREENED COMPOST
OPTIONAL
CENTRAL
ODOR
SCRUBBING
FACILITIES
Section • Extended Aerated Plte -
FINISHED COMPOST REMOVED MERE-
MIXTURE TO BE COMPOSTED ADDED HERE
-------
References -
V Goldstein, Nora, •Composting Facilities In me United States, 1987 Survey,' BloCvcle. Vol 29, No. 10, pp. 27-32,
November-December, 1988.
2. Water Pollution Control Federation, tPA's Beneficial Use of Sludge Awards,' Operations Forum, Vol. 5, No. 10,
pp. 31-35. October 1988.
3. U.S. EPA, 'Composting Municipal Sludge: A Technology Evaluation,' EPA/600/2-87-021, 1987.
4. U.S. EPA, •Composting of Municipal Wastewater Sludges,' EPA/625/445/014, August 1985.
5. U.S. EPA, •Process Design Manual For Sludge Treatment and Disposal,' EPA/625/1-79-001, September 1979.
-------
T WhiCh * ""^ avallable'Include8: «™post.ni (windrow turning),
front-end loaders, rotary or vlbrat.ng-bed screens, blowers, perforated plasiic pipe, prefabricated wide-span roof*.'
Performance - Windrow composting routinely produces compost free of salmonella and with a total solids content
of up to 60 percent
Chemicals Required - None
Residuals Generated - Final product Is compost Leachate from the windrow area must be collected and treated.
Potential For Improved Toxics Management - Heavy metals entering the process remain In the final product The
degree of removal of organic toxic substances is not known, but Indicators are that many organtes will degrade.
Design Criteria - Bulking Agent requirement for a sludge with 18 percent solids « 5.0 to 7.0 cubic yards cured
compost or 3.5 to 5.0 cubic yards wood chips per wet ton of sludge; compost mix moisture content = about 60
percent; windrow dimensions * 4 to 8 feet high and 12 to 15 feet wide at base; unscreened compost generation
= 5.5 to 7.0 cubic yards per wet ton sludge (cured compost as bulking agent) or 4.0 to 5.0 cubic yards per wet
ton sludge (wood chips as bulking agent). Arec requirements can be calculated based on a mass balance of the
planned operation. Detention times for calculating area requirements are: composting * SO days; curing « 21
days; bulking agent storage (I required) « 60 to 90 days. O&M costs/dry ton typically vary from $80 to $156.
Reliability - Windrow composting has good reliability as established with a number of operating facilities. Operating
reliability is enhanced by covering key operating areas such as the mixing area. The use of all paved surfaces is
generally essential to reliability of both the windrow and static pile methods. As with the static pile process, reliability
appears to be enhanced by using only one person to oversee initial mixing operations to obtain consistency In proper
moisture content and homogeneity of the mix.
Environmental Impact - Potential for aerosol distribution of pathogens dictates careful attention to downwind land
use. Odor generation, aesthetics, noise, and traffic are concerns of great Import to nearby communities that also
must be carefully
Flow Diagram -
SLUDGE
MIXMC
uses/
I \
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COMPOSTING SLUDGE. WINDROW FACT SHEET
x
Description - Composting Is the process by which sludge or other solid organic materials are convened to a stable
disinfected form by thermophilic aerobic .organisms. In the windrow process the windrows are turned periodically
to provide oxygen to the microorganisms responsible for the degradation of the sludge organics and to remove the
heat and moisture released by the process. Windrow composting is the predecessor to static pile composting and
Involves the same basic sequential steps of compost mix preparation, biological stabilization of the sludge, and
screening. Windrow composting differs from the static pile method in the way that the compost mix is aerated. The
compost mix Is aerated In the windrow process by natural draft and by mechanically turning the windrows. In the
static pile process, aeration Is provided by mechanical ventilation of the compost mix
Preparation - A waste must have a porous structure and a moisture content of 40 to 60 percent to be compostable.
Sludge to be composted Is mixed with a bulking agent such as wood chips, sawdust, or compost to provide the
necessary structure and porosity and to adjust the moisture content of the mix to the proper range. The compost
mix is then placed In an extended windrow, typically 4 to 8 feet high and 15 feet wide. Windrows can be hundreds
of feet long depending on available space.
Stabilization • The stabflteatlon (active composting) period Is characterized by heating of the windrow as the compost
mix undergoes decompostion by thermophilic organisms. Although higher temperatures can be achieved, optimum
activity occurs between 45 to 60°C (113 to 140°F). Therefore to control the temperature of the compost mix and to
provide additional oxygen to the organisms, ti'.e «. ndrows are turned and remixed by front-end loader or a composter.
The stabilization period requires approximately six weeks. During the early part of the stabilization period the
decomposition rate and, as a result, the heat production and oxygen demand are high, while in the latter part of the
stabilization period the decomposition rate decreases. Therefore, the windrows are turned more frequently during
the early part of the decomposition period.
Curing - A curing, period of approximately two weeks is provided at the end of the active composting period to
allow the process to come to completion, provide additional moisture removal and allow temperature stabilization.
Screening • If a bulking agent such as wood chips is used, a screening step is required to remove and recycle the
bulking agent prior to use of the finished compost. If cured compost or sawdust is used as the bulking agent, no
screening is needed prior to use.
Common Modifications - A common variation of the windrow method Is to supplement aeration provided by
mechanically turning with induced aeration. This is usually done by placing the windrows over aeration pipes located
in grated trenches. The air is then drawn through the piles by mechanical blowers In a similar manner to that used
with the static pile method. The windrows can also be constructed under cover, such as a wide-span metal buildings
without side walls, to increase reliability In cold or wet climates.
Technology Statut - A December 1988 survey of compost sites Identified 34 operational windrow facilities In the
United States. Rve of these sites are aerated windrow type operations. Six more windrow composting facilities (of
which 3 are aerated windrow operations) were in the planning and design stage and there were 7 windrow pilot
projects.
Applications - The windrow composting method Is most suitable for less populated and remote sites with warm dry
climates and where minimization of capital Investment is a criteria.
Limitations • Windrow composting is land Intensive. Dust generated from mixing, windrow turning, and from the
windrow surfaces can be a problem. Los Angeles County Sanitary District indicates that the best way to control
odors and minimize complaints at Its traditional windrow composting facility is to limit the size of the compost
operation during the summer to 500 wet tons per day.
-------
Windrow Turning
References •
1. Goldstein, Nora. "Composting FacMies in the United States, 1987 Survey." Bipc^ Vo. 29, No. 10, pp. 27-32,
November-December, 1988.
2. Water PoUullan Control Federation, -EPA's Beneficial Use of Sludge Awards; Operations Forum, Vol. 5. No. 10,
pp. 31-35. October 1988.
3. U.S. EPA, -Composting MunicipaJ Sludge: A Technology Evaluation." EPWWVMWai, 1987.
4 U S EPA, -Composting of Municip* Wastewater Sludges; EPA/625/4^5/014. August 1985.
5 u S EPA "Process Design Manual For Sludge Treatment and Dfcpos*; EW/B2SM-7M01, September 1979.
-------
ON-SITE SYSTEMS
-------
SAND FILTER
FACT SHEET
- Stow sand filtration of wastewater is not a new technology. These filter* were often used by
«•"-» *S and land cosS fciLS, «^12
i» particularly applicable to treating septic tankimuent
2TJ^2l nT^8 W CfU8t8fS * resWflnc«- ** wastewater from small commerial and Institutional
developments^ It has been used extensively for this purpose over the last twenty years. With some modifications,
as explained below, sand filtration can produce a high quality effluent with a minimum of operation and majrttenance
requirements. Sand filters generally require increased land area over conventional mechanical treatment processes.
Common Modifications - Three variations of the stow sand filters are used extensively for biological wastewaier
treatment They are burled sand filters, open (single pass) Intermittent sand filters, and recirculating sand fitters.
Site specific conditions and design intent dictates the type of sand filter utilized.
Buried sand filters are constructed below grade and covered with backfill material. A 4- to 5-ft deep excavation.
lined with an impermeable membrane is prepared for the filter. Underdrains, surrounded by graded gravel or cashed
rock, are located at the bottom of the Hned pit The upstream ends of the underdralns are vented to grade. A thin
layer of fine gravel is placed over the underdrain gravel to prevent erosion of filter sand Into the underdralns. After
placement of the filter sand, another layer of washed graded gravel or crushed rock is placed over the filter surface
with the wastewater distribution piping. This pip. ig is also vented to the surface. A layer of geotextile/filter fabric Is
installed on top of the gravel and the entire filter cavity Is backfilled. Buried sand filters are commonly used for small
flows such as individual homes and small commercial establishments. These filters are designed to perform tor
periods of time up to 2 years without the need for maintenance.
Open (single-pass) Intermittent sand filters are similar to buried sand filters except that the surface of the filter is
accessible. High hydraulic and organic loadings are generally used. In cold climates, removable insulated covers
may be used. In addition to perforated distribution piping, wastewater may be applied periodically by surface flooding
(with splash plates in tne canter and/or at the comers) or through spray distribution in warm climates. Intermittent
sand filters are beds of medium to coarse sands, usually 24 to 36 inches deep underlain with gravel and collection
drains. Septic tank, Imhoff tanks or secondary effluent is intermittently applied In a generally uniform manner to the
surface and percolates through the sand to the bottom of the fitter. The underdrains collect the filtrate and convey
It to additional treatment (disinfection) processes and/or discharge.
Recirculating sand filters are open filters that utilize coarser sand and employ filtrate reclrcuiatton. Wastewater is
intermittently dosed from a recirculatton tank, which receives both settled waste (e.g. septic tank effluent) and filtrate.
A recirculation rate of 3:1 to 5:1 Is typical. A portion of the filtrate is diverted for further treatment (disinfection) or
disposal during each dose or when the recirculation tank is full, depending on the design approach".
Technology Status - Sand filters have demonstrated a capability of producing a high quality secondary effluent
Several process modifications have been Investigated at a pilot scale as a means of enhancing removal efficiency
of soluble organtea, phosphorus and coliforms. However, the application of these modifications awaits further
demonstration Enhanced nitrogen removal has been demonstrated utilizing a modified recirculating sand filter.
Treatment of septte tank effluent by anaerobic upftow filters prior to sand filtration may allow significant reduction tn
sand filter size wtth no reduction m performance.
Stow sand filtration is w«tJ-adapied to smafl tows wastewater treatment Intermittent sand filters compare favorably
m economics and performance with extended aeration package piants and tegoon systems. The use of sand flHratton
systems* puticuteV well suited for small communities that do not have the skilled personnel or me financial
!»>w3tth« operation staff required for more highly mechanized conventional treatment facilities.
and recirculating sand filters provide a proven method of advanced secondary wastewater
SS *** » ^ communities, small clusters of homes. IndMduaJ residences
Sand I filter systems are moderately inexpensM MO build and have tow energy
Additionally, operation of sand filter systems does not requ,re hghly stated personnel.
-------
Typtoal Equipment/Number of Mfrs. • Piping, washed graded gravel/crushed stone, geotextite/filter fabric and sand
media are all kxafy supplied.
*
Limitations - Land availability may Hmlt the application of Intermittent sand filters. Odors from open intermittent filters
receiving undiluted septic tank effluent may require a buffer zone between the system and adjacent dwellings.
Covered, Insulated filters may be required in areas wth extended periods of subfreezlng weather. Excessive long-term
rainfall and run-off are detrimental to uncovered. Internment and redrculating filter performance. Appropriate
measuree should be taken to divert runoff from the filter. Because intermittent sand filtration to larger/ a biological
process, wastewater should be evaluated to confirm process capability. Use of Intermittent sand filters may be limited
In areas where suitable sand to unavailable, unless a suitable substitute media to available.
Performance' - Under normal operating conditions, Intermittent sand fitters will produce high quality effluents,
consistently better than that produced by mechanical package plants, and superior to that achieved with conventional
facultative lagoons. Concentrations of BOOS and TSS of approximately 10 mg/L or less are typically achieved
through intermittent sand filtration as compared to 30 and 30 mg/L for extended aeration units. Nitrification of 80
percent or more of the applied ammonia to typically achieved. Removal of phosphorous to initially possible, but
quickly exhausted, and reduction in fecal conform bacteria to generally between two and three logarithms.
Clogging of the surface of open or redrculating filters eventually occurs as the pore space between the media grains
begins to fill with Inert and biological material, hitter clogging requires media regeneration. The removal of this top
layer of sand and replacement with dean sand to typically performed to accomplish thto. Chemical oxidation of the
dogging layer utilizing hydrogen peroxide may be attractive where media to costly. Waste sand can be disposed
of at a landfill or recycled (stabilization may be required).
Peston Criteria -
Design Factor Burled Open Redrculating
Pretreatment Minimum of Sedimentation
Media
- Effective Size 0.35-1.0 mm 0.35-1.0 mm 0.35-1.5 mm
- Uniformity Coeff. <4 <4 <4
•Depth 24-36 In, 24-36 la 24-36 in.
Hydraulic Loading <\2 gpd/ft2 2-5 gpd/ft2 3-5 gpd/ft2
(forward flow only)
Organic Loading <5 x 103 tos BODj/day/n2
Redrcuiatkxi Ratio* N/A N/A 3:1 to 5:1
Dosing Frequency >2/day >2/day 5-10 mirt/30 minutes
9
Process ReHabiary - Sand filtration to a highly stable, reliable biological treatment process amenable to variations in
organic and hydraulic loading with Uttie effect on effluent quality. Sand filter effluent to extremely low in turbidity,
which facilitates all methods of disinfection V required. Simplicity of process operation reduces risk of process upset
due to mechanical/electrical failure of more conventional systems.
Environmental Impact - Intermittent sand filters require increased land requirements presenting possible site utilization
restrictions. A buffer area to nearby dwellings may be required for open intermittent filters due to potential odor.
-------
Flow Diagram -
TYPICAL RECIRCULAT1NG INTERMITTENT! SAND PILTPB
RiwWi
ToDudurje
<
ROM V»Jve t
I
1
— ; L
1
\
». d»_
Media
*ft^ :•*/£*:»**<
Free Access
SmdFUia
Recroiliuon
Tmk
OPEN (SINGLE-PASS) SAND FILTER
INSULATED COVER
Effluent
Pump
Dianbunoo Pipe
\^WW*VUUI
/
Pe* Gravel
DischMje—•
24--36'
21CT
GndedGnvel
1M U> 1 W
CoUecuon
OpenJ<
mPipe
TYPICAL BUPIgP SAND FILTER
24 • 36 In.
P«rtor*t*d or Op*
tint Dl*trtbutor«
Graded Gravtl 1/4~ to 1 MT
>8ln.
P«rforvt*d or Optn
Joint Pip*. Tirpapcr
Ov»r Op«n Joints
-------
References •
1. MKchell, 0, Using Upflow Anaerobic Fitters As Pretreatment For Sand Filtration of Septic Tank Effluent, University
of Arkansas, 1985.
2. Sandy, AT, WA Sack, and S.P. Dbc, •Enhanced Nitrogen Removal Using a Modified Redrculating Sand Filter
(RSF2)', Proceedings of Fifth National Symposium on Individual Community Sewage Systems, Chicago, Illinois, 1987.
ASAE Publication 1-88, America Society of Agricultural Engineers, Si Joseph, Michigan.
3. State of Oregon Department of Environmental Quality, Final Report: Oregon On-Slte Experimental Systems
Program, December, 1982.
4. U.S. EPA, Disposal Systems Design Manual, EPA/625/1 ^80-012, October 1980.
S. U.S. EPA, •Wastewater Stabilization Lagoon Intermittent Sand Filter Systems,' EPA/600/2-8-032, March 1980.
6. U.S. EPA, Technology Assessment of Intermittent Sand Filters,' April 1985.
-------
TANK TmKK COLLECTION FACT SHEET
" r9CetVM " """^ "*" a home <* «™™«*X establish*** and stores
,
M ! wwi It Is pumped out and hauled to a treatment plant by a tank truck. The vaults are similar to septic tanks but
they have no outlet piping and must be water-tight The volume can be 1000 gallons on the stta Otherwise, the vault should be sized equal to the volume of the
largest pumping truck that can easily serve the location, (t would not be cost-effective to have a vault larger than
the capacity of the pumping truck.
The alarm should be located in a prominent place to attract the homeowner's attention. The alarm level should be
positioned to allow one or two clays' reserve volume after the alarm is activated. The designer should also specify
water conservation devices.
Reliability - The ay*em to highly reliable If the system operator pays attention to the need for pumping. The high
water alarm may M, and then the homeowner will eventually notice sluggish discharge from house plumbing and
surface discharge of raw sewage. To Insure performance, a maintenance contract with a hauler or utility is highly
recommended.
Safety Considerations - The vault presents confined space hazards; the atmosphere within may be deficient In oxygen
or mav contain poisonous sewer gases. No one should enter the vault unless it has been verified that the oxygen
concentration to it toast 19%. Forced ventilation should be used to bring fresh air into the vault before entry. No
one should enter the vault unless there Is a standby person outside. The person enteringshould be harnessed to
a hoist in such a way that he can be hauled out by the standby person even If he becomes unconscious.
Environmental Impact - Tank truck collection will not have a large environmental impact unless a vault begins to teak
lUucha case, ground water or surface water may be contaminated, creat,ng a potential hearth hazard
-------
Energy Consumption - A significant amount of energy Is consumed by the pumping truck In travel
x
Costs • The following table presents typical vault coats. Including excavation, material, and Installation.
Volume (gal) Coat ($) Alarm coat ($) Total Cost ($)
1220
1370
.1570
1970
2170
4770
6670
A family of four using a 2000-gallon tank and requiring pumping twice monthly would incur a coat of $100 to $200
per month. Nonresidentlal or commercial property owners can expect to pay about $2.50 to $5.00 per 100 gallons
under a long-term maintenance contract with readily available service.
Flow Diagram -
1,000
1,250
1.500
zooo
£500
4,000
5.000
850
1,000
1.200
1.600
1,800
4.400
6.300
370
370
370
370
370
370
370
A IK^^K* 1 I B^^K ^^^^PwW^p i aw^e*
AJtffTi j 1 Ipl -•
*> Pumpout ACCMS Port
\
ii "--^
_«. _«. «»
j Switc/i
1 -2 Days' R«s*rv« Vo*omt
*Vtaatta atann m a consocuous locanon
adapiwl iron fnanci
-------
SEPTIC TANK ABSORPTION BED FACT
Description - A septic lank system to the traditional, me* wide* used method of on site treatment and disposal of
«
6 the basic method of wastewater treatment and disposal, site permitting. The treatment and disposal component
include a septic tank and a subsurface absorption system. ^^
Wastewaier generated from the residence is collected and transported through the house drains to the buried septic
tank. WKhin the septic tank, gravity causes the solids to sink to the tank bottom and the grease and scum to float
The solids collected undergo some decay by anaerobic digestion. Septic tank effluent is then conveyed to the
absorption bed system. The effluent then percolates through the absorption system and into the natural soil
Absorption beds and trenches are the most commonly used option of soil absorption systems. Trenches are
shallow, level excavations, usually 1 to 5 feet deep and 1 to 3 feet wide. The bottom is filled with 6 Inches or more
of washed gravel or crushed rock over which is placed a slngie line of perforated distribution piping. Additional rock
is then placed over and around the pipe. A semipermeabie barrier is then placed at the top of the stone to prevent
backfill from migrating into the stone trench. Both the bottom and sJdewalte of the trenches serve as mfiltrative
surfaces. Absorption beds differ from trenches in that they are wider than 3 feet, may contain more than one
distribution pipe, and are recommended only In sandy, permeable soils. The bottom area of the bed effectively
constitutes the infiltrative surface.
Common Modifications - Design of subsurface disposal beds and trenches varies greatly due to specific site
conditions. In sloping areas serial distribution may be used by arranging the trenches so that each trench to utilized
to Its capacity before effluent overflows Into the succeeding trench. A dosing or pressurized distribution system may
be used to ensure complete distribution of the effluent Alternating valves may also be utilized to alternate bed/trench
use to allow drying out or resting of the system
Fiber reinforced plastic (FRP), fiberglass or polyethylene septic tanks may be substituted for conventional precast
concrete tanks which have replaced previously used steel and hand made brick tanks.
In areas where coarse aggregates are not readily available gravefless trench systems may be economically employed.
This system replaces the coarse aggregate with a finer material such as a sand fill for development of the absorption
bed.
Where high groundwater and permeable soils exist on a site, LPP (tow pressure piping) systems may be utilized.
The LPP system consists of shallow gravel trenches installed 9 to 12 inches below grade. Wastewater effluent is
then dosed into the trenches through distribution piping. Use of these systems to dependent on natural soil and
groundwater conditions. Dose volumes must not exceed void space within the trench system. Ends of laterals
must be accessible for flushing.
Technology Status - Septic tank absorption systems are the most widely used methods of orvsite wastewater
treatment and disposal. Due to Its common use and cost effectiveness, almost one-fourth of the United States
population depends on such a system.
Applications - Absorption bedsArenches are used for Individual residences and establishments generating domestic
wSewaterin rural ind suburban areas where site conditions are favorable for on-site wastewaier treatment and
disposal Property designed and constructed systems require minimal maintenance and can operaie In all chmates.
UmHations - Soil absorption systems are limited by natural sofl type and p™rtb«* bedrock **V***'*«
davations and site topography Systems may be used In soils having a percolation rate between 1 and 120 rmVin.
Ho^T'eOmiSn ySS?V» upper limit for bed/trenches. A 3 to 4 ft depth should be ma.nta.ned between the
h«£^ bo^oT am I bedrock or seasonal* ™gh groundwater. Regulations pertaining to sel back requ.rements
I™ ^^ w*" wei£, surface waiers and property lines are common s«e limKations
-------
Property operating systems present no inconvenience or Impacts to the homeowner. Systems wtth minor operating
problems may have occasional effluent ponding at grade causing wet/soggy areas wtthln the property, potential odors
and possible health hazards. Reducing water consumption m the residence should be practiced In all cases but In
particular tf minor operating problems are observed. Failed systems pose serious health hazards.
Typical Equipment/No, of Mfrs.
gravel are supplied locally.
> Septic tanks, distribution piping and bed/trench aggregate and porous barriers over
Performance • Performance Is primarily a function of site evaluation, system design and construction techniques
employed. Pollutants are removed from the effluent by physical, chemical and biological processes in the soil zone
adjacent to the field. However, chlorides and nitrates may readily penetrate coarser, aerated soils to groundwater.
Residuals Generated • As part of the treatment process, sludge and scum materials are generated within the septic
tank. Removal of this material (septage) should occur once every 3 to 5 years.
Design Criteria • Typical state-code required design flows vary between 75 gal/person/day and 150 gal/bedroorrVday.
Trench/bed depth to typicaHy 1 to 3 ft Trench width to 1 to 3 ft and bed width to greater than 3 ft. Infiltration rates
of natural soil up to 60 mln/ln to usually the uppur limit Bed/trench bottom application rates are 0.2 to \2 gpd/ft2.
Perforated distribution lateral design to 1 lateral/trench and multiple laterals/bed. Minimum depth from trench/bed
bottom to bedrock/seasonally high groundwater to 2 to 3 ft Length of distribution lateral to typically <100 ft. Spacing
between trench sWewalte to 1.5 to 6.0 ft Depth over trench/bed bottom to 0.5 to 2.0 ft. Greater cover may be
placed over systems In cold climates. Trench/bed rock amounts are .75 to 2.5 inch washed gravel or crushed rock.
Sotis wtth percolation rates less than 1 min/ln can be used V the son to amended with a layer of sandy loam or sand.
Systems with rates near GO min/ln should receive great care during construction activities not to smear or compact
inflltrative surfaces.
Process Reliability -Septic tank/absorption systems that are properly sited, designed, constructed and maintained
have demonstrated an efficient and cost effective method of on-slte wastewater treatment and disposal. Operating
without mechanical equipment, absorption systems have service lives In excess of 20 years.
The use of water conserving plumbing fixtures (tow flow toilets and shower heads) to a recommended precaution.
Retrofit of water conserving plumbing fixtures has proven effective In correcting marginal system malfunction.
Environmental Impact • Improperly designed, sited, and constructed systems can contaminate groundwaters with
pollutants. High density development utilizing absorption systems in well aerated soils can Increase nitrate levels of
surrounding groundwaters. Falling systems can result in effluent ponding creating odors, aesthetic, and public health
hazards.
Flow Diagram
-------
References -
1. Anderson, J.L, R.E. Machmeir, and M.P. Gaffran, •Performance of Gravelless Seepage Trenches m Minnesota.
Summef Meeting, American Society of Agricultural Engineers. June 1983.
2. Frltton, D.O., W.E. Sharpe, A.R. Jarrett, CA Cote, and G.W. Peterson, 'Restoration of Failing On-Lot Sewage
Disposal Systems; U.S. EPA MERL, 1984. Summarized in: Sharpe, Cole, Frltton, 'Restoration of Falling On-Slte
Wastewater Disposal Systems Using Water Conservation, Journal of the Water Pollution Control Federation, vol. 56,
NO. 7. pp 858^66.
3. U.S. EPA, 'Onsrte Wastewater Treatment and Disposal Systems Design Manual1, EPA/625/1-80-012, October 1980.
-------
SEPTIC TANK MOUND SYSTEM FACT
lI("l!Sind SyStem te * method * 0fV8*e w wwnunlly domestic wastewater treatment and
to me conventional septic tank-absorption system. a mound system is a pressure dosed.
absorptton system thai is elevated above the natural soil surface In a sand fill. Ths general design configuration
overcomes certain site restrictions such as stowty permeable soils, shallow permeable soils over porous bedrock and
permeable soils with water tables somewhat higher than otherwise allowable by local codes Ths system consists
of a septic tank, dosing chamber and the elevated mound.
The design of the septic tank-mound system is based on expected daily wastewater volume and the natural soil
characteristics. Wastewater generated by the source(s) Is collected and transported through pipes to the burled
septic tank. Within the septic tank, gravity causes solids to sink to the bottom white grease and scum float to the
top. The solids collected undergo some degree of decay by anaerobic digestion. Septic tank effluent is then
conveyed to a dosing chamber. Within the dosing chamber, effluent is stored to a volume equivalent to a design
dose. At the dose time, effluent is pumped or siphoned to the elevated absorption area and distributed through a
distribution network located in the coarse aggregate at the top of the mound. The effluent then passes through the
aggregate and Infiltrates the sand flit. The sand and the biological mat which develops treats the wastewater and
permits the spread of the filtrate over a large area of native soil cafled the basal area. The basal area required for
infiltration beneath the sand mound is determined and controlled by the hydraulic capacity of the underlying soil.
For small community systems, determination of the lateral hydraulic conductivity and estimate of groundwater
mounding beneath the bed is normafty requ»ed.
Common Modifications • Dependent upon site characteristics, the absorption area within the mound system for an
individual home can ether be a bed or a series of trenches. The shape of the mound, however, depends on the
permeability of the natural soil and the slope of the site. A rectangular mound with the long axis parallel to the slope
contour is always preferred for individual home systems and generally required for all community-sized mounds.
Natural soils having a percolation rate stower than 60 min/ln require the absorptton mound to be narrow and extend
along the contour as far as possible. The mound serving an individual home can be made more square In soils
having a percolation rate faster than 60 min/ln and f the water table to greater than 3 feet below the natural ground
surface.
In areas with colder climates the distribution piping and manifold should be sloped to drain back to the dosing tank
between doses to prevent pipe freezing. Either the check valve is removed from the pump discharge line, or a 1/4
inch deep hole is drilled into the discharge line to aitow backftow,
A synthetic geotextlle/fitter fabric is preferred over straw or untreated building paper between the top of the stone
bed/trench and the cover material to prevent clogging of the stone.
Operations monitoring and maintenance is facilitated by providing access risers with covers over the tank and pump
chamber. Operating conditions such as absorption bed ponding can be reviewed utilizing inspection wells.
Technology Status - Septic tank-mound systems have proven to be a successful on-slte wastewater treatment and
disposal system tor areas with slowly permeable soils and bedrock/high groundwater tables. Mound systems
designed and constructed as described have been in use for twenty years. The first mound systems were installed
over 30 years ago.
During construction of mound systems, special attention should be paid to assure that the basal area of the system
is property scarified, and that compaction of the basal area and downgradient water movement sues pnor to the sand
fill installation is minimized.
- A septic tank-mound system provides a proven on-sfte and small community wasiewater treatment and
wild ** conventional septic tank-absorption systems. Site restncttons overcome by
slowV permeable soils, porous bedrock and high groundwater condftor* Pnmanry used
areas, prop^V designed and constructed systems require m.nimum maintenance and can
operate in all climates.
-------
Limitations - Elevated mound systems require more space than conventional systems because of sand nil
requirements. Slope Imitations of the site are more restrictive than for conventional systems. Systems may not
operate property on sotts with a percolation rate over 120 min/»a Systems with pumps require an electrical power
source and Increased maintenance. The addition of the dosing system and sand fill raise the total construction costs
above those of conventional absorption systems. For small community systems, capacities are generally limited to
no more than 35,000 gallons per day.
Typical Equipment/No, of Mfrs. - Pump chamber, tank, septic tanks, piping, pumping equipment, and system controls
are suppled locally.
Performance • Performance of the mound system to a function of the site evaluation, design, construction and
maintenance procedures used for the system. BOO, TSS, bacteria, and viruses are effectively removed by the soil
under proper conditions. However, nitrates are not removed and are transmitted to the groundwater.
Residuals Generated - As part of the treatment process, sludge and scum materials are generated In the septic tank.
Removal of the septic tank contents (septage) should occur once every 3 to 5 years for Individual homes and more
frequently for larger systems.
Design Criteria • Typical design flow requirements for Individual homes vary between 75 gal/person/day and 150
gal/bedroom/day. Mound height at center to 3.5 to 5.0 ft Side slopes should be no steeper than 3:1. Percolation
rates of natural soils are up to 120 mln/lnch. Absorption area application rate to 1 gpd/sq. ft Basal area application
rates are 0.1 to 1.2 gpd/sq. ft Sand fU depth beneath the absorption bed to 1 ft min over slowly permeable sols, 2
ft mm. In shallow soil or high groundwater. Absorption bed/trench depth to 9 inches (min).
Absorption bed/trench stone to 0.75 to 2.5 inches washed gravel or crushed rock. Crushed limestone to unsuitable
unless dotomitic. Mound sand shall be a wed graded sand conforming to the criteria for the group SW in ASTM
Standard D 2487. Sand conforming to group SP may be used after careful evaluation of the effective grain size,
particle size distribution and compacted permeability. Distribution laterals are 1 to 3 inch diameter. Distribution
perforation is 0.25 to 0.375 Inches diameter. Spacing between holes to 2 to 10 ft Dosing frequency to 1 to 4 times
per day dependent on soH characteristics.
Process Reliability - Properly designed, constructed and operated orvstte septic tank mound systems have
demonstrated an efficient and economical alternative to public sewer systems In suburban and rural areas. System
We for property sited, designed, installed and maintained orvstte and community mound systems may equal or exceed
20 years.
In a case study of over 3,500 mounds constructed In Wisconsin, ninety-seven (97) percent of an mounds, and virtually
all mounds constructed according to modem design criteria were found to be operating satisfactorily.
Environmental Imoacj • Due to me elevated mound's size, shape and height, aesthetic issues may arise regarding
the visual impact of the system'on small flat sites. Impact may be reduced or eliminated If during design of the
system efforts are made to Incorporate the mound into the existing landscape. Drainage patterns, and land use
flexibility may also be impacted due to the mound location. Improperly sited, designed or constructed systems can
contaminate surrounding land surfaces waters when effluents are not effectively absorbed by the soil system. These
failing systems result in effluent ponding creating odors, aesthetic problems and public health hazards.
-------
Flow Diagram -
Pressure Distribution Network
Top Soil Cover
Filter
Fabric
Observation Port
From Septic Tank
and Pump Chamber
References -
1. Converse, J.C. and E.J. Tyter, Wisconsin Mound Performance,' Small Scale Waste Management Project,
University of Wisconsin, 1986.
2. Converse, J.C. and E.J. Tyler, "On-Ste Wastewater Treatment Using Wisconsin Mounds on Difficult Sites,' in
Proceedings of the Fourth National Symposium on individual and Small Community Sewage Systems, American
Society of Agricultural Engineers, 1985.
3. U.S. Department of Housing and Urban Development, 'A Reference Handbook on Small Scale Wastewater
Technology,' April 1985.
4. U.S. EPA, 'Onslte Wastewater Treatment and Disposal Systems Design Manual,' EPA/625/1-80-012, October 1980.
-------
COMMUNITY SOfl. ABSORPTION SYSTEM FACT
treatment/disposal
-------
Destan Crttaria . Alhough community toll absorption systems may have to conform to local regulations for single
dwelling systems, tnto should not be • problem since the design criteria will generally be more conservative for a
community soil absorption system than for a single home system. In addition to conformance to local regulations,
design of a community sod absorption system should Include an analysis of the extent of groundwater mounding
below a sou absorption system and the Impact of nitrate addition to the groundwater. Groundwater mounding can
be estimated In a variety of ways, but the design of the soil absorption system should Insure that the groundwater
does not mound to within 2 to 4 feet of the infiltrattve surface. Community soil absorption systems should be
designed to permit resting cycles, (Le., an additional son absorption system with an area equivalent in size to the soil
absorption system should be provided). Trench bottom application rates range from 0.2 to 1.2 gpd/Tt8 depending
upon son conditions. Design flows are normally based on local and/or state regulations, but actual flow
measurements should be used tf possible to determine either excessive Inflow/Infiltration or the degree of water
conservation practiced. Dosed systems should drain or be constructed below the frost line. Drained pipe volume
should be less than 10% of the dose volume. The pressure maintained at the end of the lateral farthest from the
manifold connection should be 1 to 2 psi.
Reliability • With proper site evaluation, a property designed, constructed, and operated soil absorption system Is very
reliable.
Environmental Impact - Possible nitrate and chkxlde addition to groundwater.
Flow Diagram •
TYPICAL TRENCH SYSTEM
Backfill
Perforated
Distribution
Pipe
Barrier
Material
in. Rock
Wattr Table or
Creviced Bedrock
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References •
1. Fieldfng, M.B.; •Groundwater Mounding Under Leaching Beds,1 Proceedings of the 3rd National Symposium on
Individual and Small Community Sewage Treatment, American Society of Agricultural Engineers ASAE Publication
No. 1-82, December 1981.
i Hampton, Mark J., Pto S. Lombardo, and D. Bruce Wile, •Determination of a Site's Hydraulic Capacity;
Proceedings of the 5th National Symposium on Individual and Small Community Sewage Systems, American Society
at Agricultural Engineers, ASAE Publication 10-87, December 1987.
3. Helm, R., J. Quinn, and W. Zyzniewski, Planning Guide for Wastewater Duster Systems in Illinois, Illinois
Department of Energy and Natural Resources, 1984.
4. Nettles. D.L, and RC. Ward, 'Design Methodology for a Large Scale Soil Absorption Bed for Septic Tank Effluent,'
Proceedings of the 4th National Symposium on Individual and Small Community Sewage Systems, American Society
of Agricultural Engineers, ASAE Publication No. 07-85, December 1984.
5. Siegrist, Robert L, et al., 'Large Soil Absorption Systems for Wastewaters from Multiple-Home Developments,'
EPA/600/2-86/023, February 1986.
6. Tyler, E. Jerry, et al.. 'Design and Management of Subsurface Soil Absorption Systems,1 EPA/600/2-85/070, June
1985.
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BIOLOGICAL SECONDARY TREATMENT
-------
Design Criteria -
Total Tank Volume:
Food/Mass (F/M):
Number of Tanks:
Number of Cycle/Day:
Tank 0«pth:
Aeration System:
Operation Policy:
Decanter.
Automatic Controllers:
Equivalent to 0.5 to 2 times the average daily flow.
0.05 to 0.4 per day depending on application.
Typically 2 or more.
2 to 6 cycles/day are typically recommended.
10 to 20 ft 15 fl to typically recommended.
Sized to deliver necessary oxygen during the react stage only. Oxygen requirements
should be estimated as for conventional activated sludge. Several aerator types have
been used successfully. Jet motive aeration appears to be advantageous since I can
be used to mix only or mix and aerate. Oxidation ditch alternative employs rotors for
bor, functions.
The time required for the five stages (including Idle) of operation have not been definitively
established. The react phase for existing SBR installations range from 0.5 to 1.5 hours.
Periods of aeration and non-aerated mbung can be manipulated to achieve denttrtfication
or phosphorus removal.
Several commercial decanter mechanisms are available, but some have been engineered.
Decanter design should preclude the possibility of discharging floating solids. Decanter
problems have characterized some of the earliest SBR systems.
Microprocessor controllers operate pumps, aerators, and varves based on timers and
float switches. Automatic controllers should be programmable.
Environmental Impact - Sludge disposal, odor potential, and energy consumption.
Flow Diagram -
Bar Screen C°mn]!nuWf Grit Chamber
Sludge Handling System
Influent
r;...v.;,.;f
£* »".*•'«%••*.*
Aeration
Settle
EfHuenj_
Discharge
| 4-Waste
1 * Sludge
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SEQUENCING iATCH REACTORS FACT SHEET
Description . A sequencing batch reactor (SBR) It a form of activated sludge treatment process. An SBR facility
typically consists of parallel reactor tanks, wtth aeration/mixing systems, decanters, and sludge withdrawal systems.
The SBR treatment process occurs In a five-stage cycle in a reactor tank. The five stages are FIN, React, Settle, Draw,
and Idle. During the 'Fill* stage, wastewater fills the tank and mixes with the mixed liquor settled during the last
cycle. The tank is typically mixed during the flu stage, and can be aerated as an option. Organic and nitrogenous
oxidation occur primarily during the 'React* stage under aerated conditions. Aeration and mixing are stopped during
the •Settle* stage to allow solids to settle. Effluent is decanted from the tank during the 'Draw stage followed by
withdrawal of solids from the bottom of the tank during the Idle* stage. This stage accounts for the time in which
one reactor has finished Its cycle and the other reactor(s) has not finished filling.
Modifications - Two patented •semi batch* systems are available that operate as generally described above but
continually accept influent flow. Also, another system to available that performs SBR functions in oxidation ditches
without the use of external clariflers. An SBR can be designed for BOD removal, nitrification, denttrtfication, or
phosphorus removal. Phosphorus removal can be by biological means.
Technology Status - There are at least 30 municipal and 30 Industrial SBR facilities m operation or under construction.
For example, Idaho Spring, Colorado; Pootesville, Maryland; and KJmbertlng Qty, Missouri treat some of their
wastewater with SBRs. SBR technology has been fully developed. The design of SBR facilities, however, varies
greatly. SBR facilities appear to be somewhat tower in cost than activated sludge facilities, and exhibit much greater
flexibility m terms of performance capability.
Applications • SBR fadflttes are used for munkdpei and industrial wastewater treatment SBR facilities are capable
of high levels of carbon oxidation, nitrification, denltriffeation, and phosphorus removal. In addition to general
application to wastewater treatment, SBRs should be considered where space is limited.
Limitations • Limitations are similar to that of activated sludge with regard to sensitivity to toxic loads. They generally
require somewhat less O&M and energy than conventional activated sludge systems. Also, the process depends
on reliability of automatic controllers for valves, pumps, aeration systems, and decanter systems.
Typical Equipment/Number of Mfrs. - SBR (Control Packages) Systems/approx 4; Aerators/at least 36; Automatic
Valves and ContrcXs/approx 15; Decantors/Approx 4.
Performance • (not necessarily all at one set of operating conditions)
BOO* Removal - 85-96%
TSS Removal - 85-96%
NH3-N OxWatton -90-95%
Total Nitrogen Removal • 85 - 90%
Total Phosphorus • < 1 mg/l effluent (biological removal)
Chemicals Required - Chemicals can be used If biological conditions for phosphorus removal are not suitable.
Residuals Generated • Essentially the same as any activated sludge system operated wtth similar solids retention time.
Process Reliability - The process appears to be at least as reliable as a conventional activated sludge process. The
process also appears to better control bulking sludge and exhibits greater flexibility with nutrient removal.
-------
References -
1. Arora, Madam L, and Peggy B. Umphres, Technical Evaluatkxi of Sequencing Batch Reactors,' EPA/68-03-1821,
September 1984.
2. Irvine, Robert L, and Uoyd H. Ketchum, "Full-Scale Study of Sequencing Batch Reactors,' EPA/600/2-83-020,
March 1983. *
3. Irvine, Robert L, Technology Assessment of Sequencing Batch Reactors,' EPA-600/2-85/007. February 1985
4. Irvine, Robert t_ and Uoyd H. Ketchum. "Sequencing Batch Reactors for Biological Waste Treatment,' in
Environmental Reviews, V.18, No. 4, CflC Press Inc., Boca Raton, FL
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TRICKUNG FB.TBV8OUDS CONTACT FACT
s
pescriptkyi-Th»trid(»ngTOef/»o)ktt contact (TF/SQ process
Typical components of the process include primary treatment, trickling filter, solids contact step secondary dartfier
and a return sludge capability. In the TF/SC process primary effluent is applied to trickling filters; trickling filter effluent
to mixed with return secondary clarifier sludge In a small aeration tank (hydraulic detention time < 1 hr)- and aeration
tank effluent Is flocculated, settled and discharged. Return activated sludge (HAS) may be aerated prior to mixing
with the TF effluent or the contact process can take place In the reaction zone of a ftocculator/cterifier. The aerated
solids contact is a solids flocculatton/aggtomeration process which captures the pin floe typical of trickling fitter
effluent It reduces suspended solids and associated BOD. The solids retention time In the aerated solids contact
tank is less than 2 days. Longer detention and solids retention times generalry connote a TF/activated sludge process
(2-stage biological system).
Common Modifications - A TF/SC can be operated by 1) aerating only the TF effluent/RAS mixture in a
ftocculator/clartfier; 2} aerating RAS only; or 3) aerating both.
Technology Status - There are at least 11 operating plants and at least 30 facilities ft planning or design phases.
The operational data base reported In the literature, however, Is based on only seven facilities.
Applications • TF/SC process Is well suited to upgrading existing TF facilities to increase flow capacity or to meet
20/20 to 10/10 BODS and TSS (mg/I), respectively.
Limitations • The TF/SC produces both primary and secondary sludges, requires a knowledgeable operator, and
consumes power for pumps and aerator* The TF in a TF/SC system to typically larger than a TF for a TF/AS
system. The TF/SC system requires an influent pump station to dose the TF.
Typical Equipment/No. Mfrs. - Clarifier equipment/38; Aeration equipment/30; Ftoculator/Ctarifiers/30; Rock media
supplied localry; Trickling filter equipment/16.
Performance - TF/SC process has been reported to achieve the following monthly average effluent quality treating
municipal wastewater when the trickling filter Itself to not overloaded.
BODS: 5 • 20 mg/I
TSS: 5 - 20 mg/l
Reliability . The existing TF/SC facilities are reported to be operating consistently and reliably. Insufficient data exist
to determine long turn reliability under a wide range of operating conditions.
Environmental Impact - Odor problems. fDter flies. Increased sludge production over TFs and consumes more
energy than TF but less than activated sludge.
Residuals Generated • Primary and secondary sludge.
-------
Design Criteria - DennMv* design standards have not been established. However, the design parameters for seven
existing facilities are presented betow(l):
TotesooAZ Oconto Fafls.Wl CorvaWs.OR Medford.OR
Design Flow (mgd)
Average Dry Weather Flow
Peak Wet Weather Flow
Design Loading (1,000 Ib/day)
BOD
SS
Primary Overflow Rate (gpd/sq ft)
Trickling Filter
Media Type
BOD Loading (ttVday/1000 cu ft)
Return Sludge Aeration Time (33% return
rate), Minutes
Aerated Solids Contact Time (total flow
Including recycle), minutes
Ftocculator Center Welt
Percent of Qartfier Area
Detention Time (total flow
Including recycle), minutes
Secondary Ctartfler
Overflow Rate Based on Total
Oartfler Area (gpd/sq ft)
Sldewater Depth (ft)
8.3
17.7
24.0
21.6
970
Plastic/Rock
55/9.1
9
13
25
440
16
0.38
0.75
0.67
0.79
370
Rock
35
8
16
38
300
15
9.7
28.0
T0.9
11.5
980
Rock
24
9
2
12
25
470
18
18.0
60.0
35.0
28.0
1030
Plastic
115
5
5
480
15
• Contact time at existing flow of 8.8 mgd plus 33% return rate is 39 minutes.
Flow Diagram -
Primary
Effluent
Trickling
Filter
XIX
Mixed
Aerated Solids , Liquor.
Contact Tank,
Secondary
Clarifier Flocculator
Center Well
Treated
Effluent
Waste Sludge
Return Sludge
Mode 1
-------
Trickling
Filter
Primary
Effluent
Waste Sludge
Mod* 2
Mixed Liquor
Return Sludge
Aeration Tank
Secondary
Clanfier
Return Sludge
Flocculator
Center Well
Treated
Effluent
Primary
Effluent
Mode 3
Trickling
Filter
Wast&Sludge
Mixed
Aerated Solids u
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EXTENDED AERATION, MECHANICAL AND DIFFUSED AERATION
FACT
DESCRIPTION. The extended aeration (EA) process is a low rate modification of activated sludge treatment. The
F/M toad.no, te in the range of 0.05 to ft 15 Ib. BOD, /d/lb MLVSS and the aerator detention time is typlc^yThourT
Primary clarification Is rarely used. The tow loading rate minimizes waste activated sludge (WAS) production by
allowing significant endogenous decay of the sludge mass. In addition the WAS produced is already partially
stabilized because of the tong liquid and solids residence times utilized. High solids retention times (SRT) are used
{20 to 40 days) allowing significant nitrification, although nitrification Is temperature sensitive and falls off at waste
temperatures below 15" C. Extended aeration plant processes typically include coarse screening and/or comminution,
activated sludge aeration including air generation facilities, clarification Including skimming and sludge return
equipment, and a disinfection contact basin with associated disinfectant (usually chlorine) storage and feeding
facilities. An aerated sludge hokSng tank is also normally provided which allows sludge digestion and facilitates
sludge handling and disposal.
Aeration may be provided by either diffused Of mechanical aerators. Both plug ftow and complete mixing flow
patterns are utilized. Aeration tanks are typically rectangular, although both square and round tanks are in use.
Common Modifications • Other aerobic suspended growth processes with tong solids residence times such as the
oxidation ditch and the sequencing batch reactor may be used. Ftow equalization is often specified upstream of EA
plants receiving highly variable or periodic flows such as from schools to avoid plant upset due to hydraulic surges.
Granular media filtration following the final clarifier Is commonly required by some states to maintain a consistentfy
high quality effluent. AJum or ferric chloride is sometimes added to the aeration tank for phosphorus removal.
Technology Status - Highly developed and widely used.
Typical Equipment/No, of Mfrs.
aeration equipment/over 10.
Package treatment plants/over 20; diffused aeration equipment/over 10; mechanical
Applications - The process is extensively applied for treatment of smafl flows (toss than 75,000 gallons/d) such as
those generated by housing subdivisions, small municipalities, isolated small businesses, institutions, and schools.
Pro-engineered 'package' plants (steel or concrete modules) are typically utilized. The process is also used for the
treatment of certain industrial wastes using a completely mixed flowsheet
Limitations -Long detention times and tow loading rates result in relate* high power «^aptal COM p«r gallon
of wasiewater treated as compared to the conventional activated sludge process. Some EA package plants
experience occasional high effluent suspended solids toss due to poor solids inventory management, high ftow
laS^Snal^esign or inadequate operator attention. As a result some states discourage the mstallaion of
I^E?Sw pS«ap«Sv^ flowVtess than around 10,000 to 15,000 gallons per day. Freeing problems
may occur in cold climates especially where above ground tanks are utilized.
Performance
BOD5 Removal
NH4 - N Removal (at 20 to 40 day SRT
35 . 95%
60-99%
sirs
0.7 . -.0 ». «- « •»— — *
B005 removed.
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Designed Criteria • A partial listing of design criteria for the EA modification of the activated sludge process is
summarized as follows:
Volumetric loading, to BOCyd/1,000 ft»
MISS, mg/1
F/M, ID BODj/d/lb MLVSS
Aeration detention time, hours
(based on average daily flow)
Standard ft3 air/lb BOD, applied
to 0,/Uj BOD, applied
Solids retention time, days
Recycle ratio (R)
Volatile fraction of MLSS
8 to 15
2.500 to 6,000
0.06 to 0.15
18 to 36
3,000 to 4,000
2.0 to 2.5 (Based on 1.5 to oyib B005 removed + 4.6 Ib O,/
NH«-N removed)
20 to 40
0.75 to 1.5
0.6 to 0.7
Process Reliability • Reliability Is good tf sufficient operator attention is provided. Particular attention must be given
to biological solids control and wasting. In addition adequate solids handling and storage capacity must be provided.
Environmental Impact - Sludge disposal; odor potential; and energy consumption.
Flow Diagram •
Screened and/or Complete Mix
Raw Wastewater
i ' Aerauon lanic
Clarifier
Return Sludge ,
Sludge
f
Excess ,.
Sludge J
Chlorination
Aerobic
Digestion
Effluent
*^
To Disposal
Energy Notes - Assumptions: Based on power for blower, froth spray pump and comminutor. Power cost + $
.07/kWh
Costs - Assumptions:
1. Construction cost includes comminutor, aeration basin, darifier, chlorine contact chamber, aerobic digester,
chlorine feed facility, building, fencing for extended aeration package plants between 0.01 and 0.1 Mgal/d. Detention
time: 24 hours (based on average daily flow).
2. Operation and maintenance costs assume sludge Is hauled from the site 5 times per year and that compliance
testing is performed monthly.
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OPERATION flND MfllWTtNRNCt COSTS
•at tewater Flaw, M
il / IMWMI i
11
CMU
KIM CMI
Construction Cost
Ulattewater Flow, M gal/d
o.io
100000
*
z «
10000
Electrical energy
o.oi Ufasteweter Flow, M gal/d
O.:o
References -
1. U.S. EPA Technology Transfer, -Wastewater Treatment Facilities for Sewered Small Communities'. EPA/625/1-
77-009, October 1977.
2. U.S. EPA, 'Package Treatment Plants - Operations Manual", EPA/430/0-77-005, April 1977.
3. Water Pollution Control Federation. 'Operation of Extended Aeration Package Plants,' MOP No. OM-7. 1985
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MISCELLANEOUS
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HYDROQRAPH CONTROLLED RELEASE LAGOONS
FACT SHEET
*floon is a lagoon used to temporally store treated effluent
A HCR ta000n' •«**»- * " *""»"< S3 control device and
" ' *** ^^ anajyste durin9 I"*™ to*"*3" P****' Sl°ra9« lagoon
» (aflef diSCharge) to M <** to Discharge). The sides ofsuxage lagoons should
to resist erosion due to changing water levels.
The «mmflow monitoring systems typically measure stream stage which is then related to stream (low. Stream
25^S ^ •1^rid ** ultrasonic "^ "**«*• by level ftoat switches or bubbler tube In a stilling well, and by
relying on the U.S.G.S. to provide daily flow estimates from a nearby gauging station.
Discharge systems can be operated automatically or semi-automatically based on Input from the stream monitoring
system The discharge system typically consists of motor or pneumatically operated valves, motor driven sluice
gates, floating weirs, or variably sized pumps.
Technology Status - There are at least 20 systems in design, construction, or operation. The existing HCR lagoons
are reponed to be working wed.
Applications - HCR lagoons are best suited to areas In which land costs are tow and stream flow Is seasonally
variable. The applicability of HCR lagoons must be analyzed in terms of seasonal stream assimilative capacity,
projected effluent quality, and the cost of storage capacity. HCR lagoons are typically used In conjunction with
lagoons, but can sJso be used with other treatment processes.
Limitations • The use of HCR lagoon technology can be limited due to land limitations, eofl conditions adverse for
constructing basins; and stringent year-round treatment requirements. Variable flow discharge schemes are not
allowable in all states.
Typical Equipment/No, of Mrfs. - Ultrasonic level sensors (bubbler/float) - at least four. Automatic valves and controls -
approximately 15.
Performance - HCR lagoons are not designed to treat wastewater. although, some treatment probably does occur.
Design Criteria - In general, HCR lagoons are designed to maintain receiving stream water quality by restricting
discharge during periods of tow flow. The permissible quantity of effluent that can be discharged should be related
to stream flow b*Md en the assimialoiy capacity of the stream. Required storage should be based on an analysis
of historical stream flow data and ttw discharge schedule stipulated by the State/local regulatory agency. Precipitation
data and nearby stream flow data for a similar drainage basin may be used If historical data is not available for the
receiving stream.
The discharge system should be designed to discharge at variable rates in order to minimize storage.
System Infiltration should be investigated and corrected If necessary.
Reliability - HCR lagoons have been very reliable in maintaining stream water quality.
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Environmental Impact? • Odor potential owing to variable lagoon levete. Animate may t*com« trapped In the lagoon
If the sides of the basins are lined with a plastic liner.
Flow Diagram •
Wastewater
Cell
Storage
Cell
Control
System
Lagoon System
Flow
Meter
Data
1 Transmission
f
Discharge Flow
Structure Meter
Receiving
Water
References -
1. HM, Donald 0., and Victor L ZJtta, •Hydrograph Control Release, State of the Art,* Mississippi State University,
MSSU-GRS-CE-80-7, September 1980.
2. Zlrschsky, John, and Rlcnard E. Thomas, "State of the Art Hydrograph Controlled Release (HCR) Lagoons,'
Journal of the Water Pollution Control Federation, Vol. 59, No. 7, July 1987.
3. ZJtta, Victor L. and Donald O. HJU, •Hydrograph Control Release: Methodologies for Predicting Storage Periods
on Ungaged Streams,* Mississippi State University, MSSU-EfRS-CE-63-1, September 1982
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SEPTAGE RECEIVING STATION " FACT 8HE£T
«.!???fle^*^nfl 8taUo" Pfovidee for the transfer, preliminary treatment, storage and equalization
ZZ I?."?!!!™? consist °f • receiving area, screening and degritting equipment and a
of a sloped ramp, washdown equipment and a coarse bar screen. This
(preferred) and open pit discharges. A channel placed in front of the bar
holding tank allows for mixing, aeration and equalization. Mixing and
«,*«„- ,« ^ maintain uniformity and keep the waste fresh. Equalization allows for controlled addition of
septage to the waste stream, thus protecting downstream processes from slug loading effects. Additional features
include sampling/monitoring equipment, solids handling pumps, and odor control
Common Modifications - Grtt removal can either precede or follow storage and equalization. If a grit chamber
precedes equalization, ft must be designed to handle the discharge of individual or multiple trucktoads of septage
as they arrive. If storage and equalization precede grit removal, the degrttdng process can be designed to handle
the average flow. Cyclone degrttters may be substituted for aerated grft chambers V average solids concentration
Is less than 2 percent Grtt classifiers are a common addition to degrttlng equipment
For colder climates, dumping pits should Include hot steam equipment for thawing frozen valves, hose lines, etc.
Vibrating screens have been used successfully in place of coarse bar screens. Vibrating screens offer smaller
openings that collect more solids but they Increase capital cost, maintenance, and energy requirements. Where
land application is Involved, longer term storage may be required during adverse weather conditions. Lagoon
storage facilities should be considered In such cases. If septage is discharged to an interceptor sewer where flows
are high, storage facilities may not be required. Odor control can be accomplished with chlorine, hypochtortte, ozone,
activated carbons, and soil gas niters.
Access to receiving stations can be automated through the use of coded plastic cards. The cards are inserted into
a computer. The computer can identify the hauler, time, date of entry and quantity of septage. Access can be
controlled at the dumping site or at a gate restricting vehicular traffic to the site. Automation allows for 24-hour
access to facilities without sacrificing control over discharges.
Technology Status - The use of septage receiving stations is widespread hi Europe, specifically Germany, Sweden
and Norway. Relatively fewer operating examples exist in the United States. Manual monitoring programs are far
more common than the automated systems. Receiving station automation is generally ymited to controlled gate
access,
Applications - Receiving stations can be placed at the headworks of a conventional wastewater treatment plant a
septage treatment plant on a land treatment site, or at a sewage collection system manhole.
Typical Equipment - Bar screens or racks (mechanically cleaned are preferred) aeration equipment; holding tank(s);
solids handling pump(s); flow controls; odor control equipment; piping, valves and hose connections.
Performance - Preliminary treatment of septage can reduce suspended solids signiftoanty. However, designers
should not assume any other oc*utant reductions. Bar screens with 0.25 Inch opemngs can remove several cube
feet of solids per 1000 gallons of septage depending on source characteristics.
Controlled addition of septage to downstream treatment facilities is recommended. This allows slow addition of
»S Wo^^mrtam^eby minimizing potential for biological and/or solids overloading of downstream
treatment facilities.
Reasonaby reliable with property designed connections, tank sizes, process equipment and 04M.
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Design Criteria -
Bar Screen
Hauler Truck Hoe* Connection
Piping and vaJves
Screen Channel
Holding Tank Capacity
< 0.25 In. spacing for mechanical screens
> 0.75 In. spacing for manually cleaned screens
4 In. diameter
8 m. diameter
6 to 10 feet m length, sloped for minimum velocity of 2 feet per second
Septage storage tank capacity should be adequate for minimum two day peak
septage volume.
Environmental Impact • Land requirements are minimal. Energy is required for pumping, mechanically cleaned bar
screens, aeration and mixing and odor control Solids will be generated that require disposal. Odors may be
associated with dumping, pretreatment (screening), and residuals disposal (land application).
r —
Raw |
Septa** t^
x*
fcxnaustAir
i_» Odor Control
fH System
__/ \_^±u^
\ 1 *— ^ i
i
i
• To
1 ^^^^^ Ti'fl iinir*nt
Processes
Dumping Receiving/ Handling Aerated Grit
Station Storage Pump(s) Chamber or
and Tank(s) Cyclone Degriuer
Bar Screen
References -
1. U.S. EPA, Handbook - Septage Treatment and Disposal, EPA 625/6-84-009.
2. U.S. EPA, Septage Management, EPA-600/8-80-032.
3. U.S. EPA, Pilot Scale Evaluations of Septage Treatment Alternatives, EPA-600/2-78-164.
4. U.S. EPA Design Manual: Odor and Corrosion Control In Sanitary Sewerage Systems and Treatment Plants,
EPA-625/1 -85-018.
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NON-WATER CAR^OE TOILETS FACT 8HE£T
?^ The maJn advantage
must be disposed SSSSSL '"j'"*"11* (30-40%) and atrength of wastewater to be dlapoaed on-site. Greywater
are descrt£^ ^ *' ^ Variad°ns * NWC toilflte "^ no**"*- *• ™ "^°° P«™anen7 types
** ,t0 **•* Wtch^ "* toitot ""a"
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Performance - Biological toilets, when well operated, can produce a soil conditioner, but Its handling should be
controlled due to biological hazards. User acceptance is fair. Incinerating toilets successfully convert waste to ash,
when operated properly. User acceptance is fair. Oil recirculatlng toilets work well but may clog during overuse
without proper maintenance. User acceptance Is also fair.
Design Criteria - Biological toilets are typically sized for up to 2-4 people. Variations exist which can be sized for
more people and/or also accept kitchen wastes. Incinerating toilets are typically designed for 2-4 people. Incineration
cycles can accommodate a maximum of approximately 4 uses. Electrical units require 120/24OV service and
consume 0.5 to 1 kw-hr per vtsft. Oil recirculatlng toilets require that accumulated wastes must be pumped out
periodically or that the concentrated wastes be treated and disposed of. Provisions should be made for flush oil
^circulation pumps and treatment/disinfection of flush oil
Reliability • Approved NWC toilets are reliable If operated correctly.
should be considered with caution.
Many non-approved designs are available and
Environmental Impact • Water consumption can be reduced by one third and on-site direct discharge of toilet wastes
may be eliminated from the ground or surface waters. Biological toilets conserve nutrients when product is used for
ornamental gardening (CAUTION: Product from toilet should not be used for gardening for human consumption).
Odors and insects may be problems.
Incinerating toilets consume energy and, may cause odors.
wastes, usually In lanofits.
ON ^circulating toilets require ultimate disposal of oily
Chemicals Required - Biological toilets require bulking agents and insect controls. Incinerating toilets require paper
Vners and odor control chemicals. Oil recirculating toilets require flushing oU, deodorizes, and disinfectants.
Residuals - Biological toilet: partially stabilized soil conditioner and excess liquid.
recirculatlng toilet: accumulated wastes and exhausted filter media.
Incinerating toilet: ash. Oil
Flow Diagram -
Toilet Wastes .
Toilet Wastes
Tata
VOIIllUCt
Toilet Waste* ^
s
Oil
RflBICUlJtiOl
t
\
"^
P
OU
Sepuuon
Treatment
Waste* ^
P
Storage
To disposal ,.
>
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1- ^~S Cl ** R L*00^- •Composting Prtvy Wastes at Recreation Sites; Compost Science/Land Utilization,
pp. 36-39, January-February 1979.
Z Lombard© & Assodates, Inc., 'State-oMhe-Art Assessment of Compost ToHets and Greywater Treatment Systems,'
Prepared for the Winthrop Rockefeller Foundation, Uttie Rock, AR, February 1980.
3. Otis, Richard J. and W.C. Boyle, "U.S. EPA Training Seminar for Wastewater Alternatives for Small Communities,
On-stte Alternatives,' August 14-18, 1978, August 28-September 1, 1978.
4. Smith, E.D., C.P.C. Poon, S.R Struss, J.T. Bandy, and R.J. Schofee, 'Appropriate Technology for Treating
Wastewater at Remote Sites on Army Installations,' U.S. Army Corps of Engineers, Technical Report N-160, April
1984.
5. State of Nevada Department of Transportation, Final Report: Experimental Project NV-81-1, Trinity Rest Area:
Clh/us Multaim Organic Waste Treatment System and Restroom Building, 1984.
6. U.S. EPA Technology Transfer, 'Alternatives for Small Wastewater Treatment Systems, On-stte Dteposal/Septage
Treatment and Disposal,' EPA/625/4-77-011, October 1977.
7. Vendor literature, Research Products/Blankenshlp (Incinerating toDets), Dallas, TX, 75220.
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