EPA
TECHNOLOGY
TRANSFER
FIRST PROGRESS REPORT
                         STATIC
                         PILE
                         COMPOSTING

                         WASTEWATER
                         SLUDGE
                PREPARED BY
                U.S.
                ENVIRONMENTAL
                PROTECTION
                AGENCY


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          EPA
          TECHNOLOGY
          TRANSFER
FIRST PROGRESS REPORT
                                    STATIC
                                    PILE
                                    COMPOSTING

                                    WASTEWATER
                                    SLUDGE
              PREPARED BY
              US
              ENVIRONMENTAL
              PROTECTION
              AGENCY
EPA-625/2-77-014

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Static Compost Pile at Beltsville, Md. (USDA Photo)

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  Wastewater sludge treatment and disposal has
always been a difficult and expensive problem. This
problem has historically been far out of proportion in
the volume of wastewater sludges produced com-
pared to the volume of wastewater treated; typ-
ically, less than 1 percent has been treated. In the
last few years, sludge handling and disposal problems
have become even more severe due to more strin-
gent and definitive regulatory agency require-
ments, more complete treatment of wastewater
which generates more sludge, production of sludges
that are more voluminous and difficult to treat, and
higher costs of energy and chemicals.
  The total primary and secondary sludge produc-
tion from municipal wastewater treatment process-
es in 1975 was over 4.5  million metric tons on a
dry weight basis and is increasing at a rate of ap-
proximately 5 percent per year compounded.
  Nfew regulations, changing cost structures, and
public demands are limiting the future use of many
existing means of sludge handling. These considera-
tions will change the profile of future sludge disposal
options significantly.
  It has been estimated that the cost of sludge treat-
ment and disposal in this country is between 22 and
50 percent of the total cost of wastewater manage-
ment with the higher figure being common. Cer-
tainly this magnitude of cost fully justifies  contin-
ued extensive effort in sludge management tech-
niques.
  Conceptually, reuse of sludge for agricultural and
land reclamation purposes is a desirable alternative.
Many people view the nonbeneficial use of waste-
water sludge as waste of a resource; however, most
municipal wastewater sludges contain not only
beneficial constituents but also heavy metals,
pathogens, viruses, and parasites which could con-
ceivably pose agricultural  and public health prob-
lems. Experience has shown that well-designed and
operated systems can successfully utilize sludges in a
beneficial manner.
  Composting of primary and secondary waste-
water sludges is one means of stabilizing the sludge
for reuse purposes. Windrow composting of digested
wastewater sludge has been demonstrated for a
number of years at the Los Angeles County Sanita-
tion  District's Joint Water  Pollution Control Facility
(JWPCF) at Carson, California, and for several years
at the joint Agricultural Research Service (ARS),
Maryland Environmental Service (MES) demonstra-
tion  project at Beltsville, Maryland. Windrow com-
posting of raw wastewater sludge had proven un-
satisfactory because of odor problems.
  During the last two years, the ARS at Beltsville
has developed and demonstrated a method for com-
posting raw wastewater sludge without the re-
lease of offensive odors using a static or fixed "pile"
with forced aeration. This report describes static
pile  composting and its application to the muni-
cipalities of Bangor, Maine, and Durham, New
Hampshire.

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  Composting is the biological decomposition of or-
ganic matter by aerobic, thermophilic organisms, or
anaerobic, mesophilic organisms. Composting pro-
cesses considered herein are aerobic. Aerobic condi-
tions are maintained in the static pile by forced
ventilation as opposed to the mechanical turning of
the windrow process. The static pile method is sig-
nificant because the need for sludge digestion is
eliminated. Raw (undigested) sludge can be used
without causing odor problems. In addition, the
piles remain fixed during the composting period,
higher and more uniform composting temperatures
are developed and maintained, less land is required,
and, generally, more conventional and less costly
machinery is required as compared to windrow
composting. The forced mechanical aeration allows
operation personnel to effect some process control
by adjusting the aeration  operating cycle.
  Raw, dewatered wastewater sludge is mixed
with a bulking agent prior to formation of the pile.
The ratio most commonly used  is three parts bulking
agent to one part sludge by volume. The purpose of
the bulking agent is to increase the porosity of the
sludge, to assure aerobic conditions during compost-
ing and to reduce the moisture content of the mix to
an acceptable level (50-60%). Bark and wood chips
have been used successfully as  bulking agents but
other materials may also be suitable. Complete
mixing of the bulking agent and sludge is essential.
  A base is prepared for the pile consisting of a
perforated aeration header and approximately 30
cm of bulking agent or unscreened compost. The
base plan dimensions are the same as the bottom of
the finished pile, typically 5.5 to 7.5 meiters wide
and 12 to 15 meters long, although the dimensions
are variable. The base is important in providing
proper air distribution in the pile.
  The sludge-bulking agent mixture is piled on this
base to a typical height of 2.4 meters, forming a tri-
angular cross section. The pile is capped on all ex-
posed surfaces with a 30-cm layer of screened com-
post which insulates the active pile, limits the pre-
cipitation which penetrates into the pile, and
absorbs odors. This pile configuration can be con-
structed using commercially available front loaders
and it contains approximately 38 cubic meters (50
cubic yards) of dewatered sludge and 115 cubic meters
(150 cubic yards) of bulking agent in addition to the
base and cap materials. Other size piles  can be con-
structed.
  Additional  individual piles are normally con-
structed as sludge is available or the initial pile can
be "extended" by placing a new pile immediately
adjacent to one side of the last pile, forming a wider
continuous pile. These configurations are shown in
Figure 1.

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3.0 M
                   AIR
                    IN
         -45°±
          TYP
             V
 STATIC
COMPOST
 ~ PILE
                    -12 TO 15 M
 WATER
REMOVAL
                                                         FAN
DEODORIZED
  EXHAUST
    AIR
                                     SCREENED
                                     COMPOST
                                       (4 M3)
                            GENERAL LAYOUT
         SCREENED COMPOST

        BULKING AGENT AND
        SLUDGE MIXTURE
    UNSCREENED COMPOST.
    OR BULKING AGENT
            PERFORATED
            PIPE
                                       SUBSEQUENT PILES
                                       FOR EXTENDED PILE
                                       METHOD
                             CROSS SECTION
    Figure 1. Typical Static Compost Pile] for 40 Cubic Meters of Dewatered Sludge

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   The aeration header is attached to the suction side
 of a blower capable of producing an air flow of 200 to
 300 cubic feet per minute (for the size pile described).
 The blower discharge is piped into a smaller pile
 of unscreened compost which effectively deodorizes
 the gases drawn from the composting pile. Water
 condenses in the blower suction piping and some
 means must be provided to remove this water either
 by careful grading  of the piping or installation of a
 moisture drain or trap.
   A 7-week cycle consisting of composting and cur-
 ing has been  used  successfully. The static pile is
 operated for the first 3 weeks (or more, if necessary,
 due to weather) with the blower providing the
 forced aeration.  Interior pile temperatures and
 oxygen levels should be monitored regularly. Oxygen
 levels should  be in the range of 5 to 15 percent and
 interior temperatures should rise to and remain
 above 60° centigrade during a major portion of the
 composting period. The lowest temperatures are
 generally near the  outside of the pile. The blower
 can be operated continuously or on various on-off
 cycles during composting to maintain optimum
 conditions.
   Operating installations have demonstrated that
 pile temperatures can be maintained above 60°
 centigrade for a  week or more under severe New
 England winter weather conditions if proper com-
 posting techniques are  used. This temperature and
 time effectively cause the sludge to be pasteurized.
   Upon completion of  composting, the material in
 the pile is moved to a stockpile for curing and storage
 prior to distribution. The curing period is typically
 4 weeks and is an added safety measure prior to
 distribution because elevated temperatures are
 maintained. In most cases the compost is screened
 either prior to or after curing to control the maximum
 particle size of the compost product and to recover a
 portion of the bulking agent. The cost of the bulking
 agent can be substantial; therefore, recovery and
 reuse may be very  important to  the overall eco-
 nomics. It has been shown that wood and bark chip
 bulking agents can  be reused a number of times;
 however, these materials do deteriorate and a por-
tion is lost during each  composting cycle.
   The foregoing is only a brief description of the proc-
ess which is undergoing continual development.
The ARS is developing a manual to provide guidance
 in application of the process.

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                                                 Base for
                                                 Static Compost Pile
                                                 at Bangor, Maine
Raw Sludge Delivery
   at Bangor, Maine

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                        *?w
  iM.^*m£%&&&&&*%*'-& %z*

     Mixing Raw Sludge and Bulking Agent at Bangor, Maine
Screening of Finished Compost for Reuse of Wood Chips—Beltsville, Md.

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Beltsville, Maryland                            :
  The MES and ARS have jointly operated a dem-  :
onstration and research wastewater sludge com-   i
posting facility at Beltsville for several years. Initial  ;
work centered on windrow composting but it was  j
found to be unsuitable for composting raw waste-  j
water sludge because of odor problems. This led to j
the development of the static pile method in 1973  \
and subsequent demonstration that raw waste-     !
water sludge can be composted by the static pile   j
method without producing offensive odors. In ad-  |
dition, the static pile method produces higher com-'
posting temperatures,  requiring less space and     !
eliminating the requirement for regular turning of  i
the compost as compared to  windrow composting, i
Work is continuing, in  an effort to further improve  i
the static pile method  and develop additional per-  ,
formance data. The work  at Beltsville is funded in  j
part by the EPA Municipal Environmental Research i
Laboratory, Cincinnati.                          j
  Approximately 350 wet  tons per week of raw,    ,
dewatered wastewater sludge are composted at    j
the 10-acre Beltsville site.  This site was previously   '
used for windrow composting and is being con- '  j
verted to an efficient layout for static pile compost- i
ing. Paved composting pad areas, both covered and'
uncovered, are being constructed in addition to   j
covered storage and working areas. It is estimated  j
by ARS personnel that at least 150 wet tons per day i
of sludge could be composted on this site using the|
extended static pile method.                      •
 Static Pile Composting of Raw Sludge with
 Wood Chips at Beltsville, Md.
Finished Compost Screening at Beltsville, Md.


  The Beltsville compost product has a slight musty
odor, is moist, dark in color, and is fairly uniform in
size and consistency. The compost product can be
screened and contains an average of 1.5 percent
nitrogen and 1.0 percent phosphorus. ARS personnel
report that pathogens, including salmonella, are
reduced below detectable levels when proper com-
posting techniques are used.
  Composting has little direct effect on  the total
content of heavy metals. Their concentration is,
however, diluted by the bulking agent and there is
some indication of a reduced heavy metal uptake
by crops from compost as compared to sludge.
  The compost is an excellent organic soil condi-
tioner and can provide some nutrient value, thus
decreasing fertilizer requirements.
  The Beltsville compost product is provided to public
agencies free of charge but  it must be picked up at
the site.
  The Maryland Department of Health and Mental
Hygiene has approved the use of Beltsville compost
for turf farms, nurseries, golf courses, public works
projects, reclamation projects, park lands, and es-
tablishment of new lawns. The compost  has not
been used as topdressing or fertilizer for playgrounds
and residential lawns. Guidelines and specifica-
tions for use of compost are being prepared by the
Maryland Department of Health and Mental Hy-
giene.

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     TECHNOLOGY
      TRANSFER
For Further
Information
Write:

U.S. Environmental
  Protection Agency
Environmental Research
  Information Center
Cincinnati, Ohio 45268

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Beltsville, Maryland
  The MES and ARS have jointly operated a dem-
onstration and research wastewater sludge com-
posting facility at Beltsville for several years. Initial  j
work centered on windrow composting but it was  j
found to be unsuitable for composting raw waste-  j
water sludge because of odor problems. This led to|
the development of the static pile method in 1973  |
and subsequent demonstration that raw waste-     j
water sludge can be composted by the static pile   i
method without producing offensive odors.  In ad-  ]
dition, the static pile method produces higher com-!
posting temperatures,  requiring less space and     j
eliminating the requirement for regular turning of  i
the compost as compared to  windrow composting, i
Work is continuing, in  an effort to further improve  ]
the static pile method  and develop additional per-
formance data. The work at Beltsville is funded in
part by the EPA Municipal Environmental Research ]
Laboratory, Cincinnati.                          ]
  Approximately 350 wet tons per week of raw,    j
dewatered wastewater sludge are composted at    i
the 10-acre Beltsville site. This site was previously   i
used for windrow composting and  is  being con-    j
verted to an efficient layout for static pile compost- j
ing. Paved composting pad areas, both covered and!
uncovered, are being constructed in addition to    |
covered storage and working areas. It is estimated  j
by ARS personnel that at least 150 wet tons per day |
of sludge could be composted on this site using the!
extended static pile method.
 Static Pile Composting of Raw Sludge with
 Wood Chips at Beltsville, Md.
Finished Compost Screening at Beltsville, Md.


  The Beltsville compost product has a slight musty
odor, is moist, dark in color, and is fairly uniform in
size and consistency. The compost product can be
screened and contains an average of 1.5 percent
nitrogen and 1.0 percent phosphorus. ARS personnel
report that pathogens, including salmonella, are
reduced below detectable levels when proper com-
posting  techniques are used.
  Composting has little direct effect on  the total
content of heavy metals. Their concentration is,
however, diluted by the bulking agent and there is
some indication of a reduced heavy metal uptake
by crops from  compost as compared to sludge.
  The compost is an excellent organic soil condi-
tioner and can provide some nutrient value, thus
decreasing fertilizer requirements.
  The Beltsville compost product is provided to public
agencies free of charge but  it must be picked up at
the site.
  The Maryland Department of Health and Mental
Hygiene has approved the use of Beltsville compost
for turf farms,  nurseries, golf courses, public works
projects, reclamation projects, park lands, and es-
tablishment of new lawns. The compost  has not
been used as topdressing or fertilizer for playgrounds
and residential lawns. Guidelines and specifica-
tions for use of compost are being prepared by the
Maryland Department of Health and Mental Hy-
giene.

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Bangor, Maine
  The city of Bangor, Maine (population 38,000)
has been composting raw primary sludge since mid
1975 using the static pile method as developed by
USDA. The work at Bangor has been funded in part
by a grant from the EPA Office of Solid Waste.
  Each week the city generates approximately 40
wet tons (50 cubic yards) of sludge (approximately
20 to 25 percent solids). The sludge is dewatered and
delivered to the compost site once a week from the
wastewater treatment plant. A hydraulically op-
erated, rear loading, lift and carry type vehicle is
used to haul the dewatered sludge to the compost
site in open top containers. The compost site  is
located 3 miles from the wastewater treatment
plant and 2,000 feet from the Bangor International
Airport terminal, on approximately 66,000 square
feet of abandoned concrete taxiway. Shredded bark
is used as a bulking agent. A front-end loader is used
to move the bulking agent, mix the materials, form
the piles, and move the compost.
  After composting is complete, the product is stored
for use by the city in applications such as land rec-
lamation, ornamental plantings, parks, highway
plantings, and similar soil conditioning uses.
Durham, New Hampshire
  The town of Durham composted approximately
40 to 50 wet tons per week of raw, dewatered,
primary wastewater sludge from early 1975 to mid
1976 using the static pile method as developed by
USDA. The purpose of the work at Durham was to
determine that adequate composting tempera-
tures could be attained in a  cold northern climate and
to ascertain the costs of operation. The work was
funded in part by the New Hampshire Department
of Public Health.
  As the result of a favorable test program, static
pile composting is being incorporated into plans for
adding secondary treatment to the wastewater
treatment facility. Many of the labor intensive and
critical operations (such as sludge/bulking agent
mixing) will be mechanized to reduce  operating
costs and enhance process performance.
  Durham officials  concluded that static pile com-
posting produced a safe and usable product in a cold
northern climate and that  the system design being
developed is cost effective compared with other
disposal methods. These conclusions are based on
results of the actual full-scale test program during
1975 and 1976 and an engineering predesign study.
                          Finished Compost Screening at Bangor, Maine

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  The economics of static pile composting are
determined by the cost of producing the compost,
the cost of (or income from) disposal of the compost
product and the effect on other plant processes such
as digestion and  dewatering.
  The present static pile operations have been  in
operation for relatively short periods of time (up to
three years). Actual operating cost information  for
these first installations is preliminary in nature
because of the many experimental and research
activities carried  out at Beltsville and the short
operating history of the municipal operations. How-
ever,  it is possible to determine some general
guidelines based on observations and estimates.
  The cost of producing compost includes the follow-
ing elements:
  • Amortization of capital site improvements and
    structures.
  • Amortization of major mobile equipment costs.
  • Operation and maintenance costs.
  The required site improvements and structures
will vary depending on availability of existing
facilities, degree  of mechanization of the process,
and, to a degree, climatic parameters. Site improve-
ments related to  composting will generally include
site acess and improvements, bulking agent
storage, bulking  agent/sludge mixing area or
mechanical fixed equipment, composting pads
and appurtenances such as blowers,  screening area,
compost storage  area, support facilities (including
electrical), and fixed materials handling equip-
ment. Construction costs of $580,000 were recently
estimated for a mechanized composting installa-
tion capable of handling 120 cubic yards of dewatered
sludge per week, excluding sludge thickening, de-
watering, and mobile equipment.
  Major mobile  equipment includes screens, front
loaders, trucks, and testing equipment. The num-
ber and size of major equipment will depend on
the capacity and type of operation. Mobile equip-
ment costs of $80,000 were estimated for the 120-
cubic yard per week facility mentioned before and
included screen, front loader, and truck. Testing
equipment would cost approximately $1,000 to
$2,000.
  Operation and maintenance costs would normal-
ly include:
  • Labor for constructing the piles, handling ma-
    terials, and screening the compost.
  • Labor for regular inspection of operations and
    performing tests on the piles.
  • Electrical energy for blowers, lighting, and
    other miscellaneous uses.
  • O & M for the equipment including the front
    loader and screen.
  • Transport of materials as required.
  • Price of bulking agent, typically $2 to $4 per
    cubic yard delivered.
  Preliminary studies by ARS and MES personnel
indicate that total costs to a municipality for static
pile composting should be in the range of $20 to $50
per dry ton of wastewater sludge solids excluding de-
watering and hauling, but including land at $10,000
per acre. This cost varies with local  conditions and
with the size of the operation.
  Experience at several wastewater  sludge com-
posting and marketing operations indicates that
income from disposal of compost is  small compared
to the costs of composting. This is not a negative
factor because municipal wastewater sludge dis-
posal is not a profit making venture. Most ex-
isting  municipal operations provide the material
free of charge to users or use it within the municipal-
ity. A number of potential users have indicated a
willingness to pay for compost at a rate equal to or
less than the cost for competitive products they may
be presently using.

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     TECHNOLJOGY
      TRANSFER
For Further
Information
Write:

U.S. Environmental
  Protection Agency
Environmental Research
  Information Center
Cincinnati, Ohio 45268

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