v'/EPA
                                  United States
                                  Environmental Protection
                                  Agency
                                  Municipal Environmental Research
                                  Laboratory
                                  Cincinnati OH 45268
                                  Research and Development
                                  EPA-600/S2-82-092  Jan. 1983
Project Summary
                                  A  Critical  Review of
                                  Wastewater  Treatment Plant
                                  Sludge  Disposal  by Landfilling
                                  James C. S. Lu, Robert J. Stearns, Robert D. Morrison,
                                  and Bert A. Eichenberger
                                   Current  landfilling practices are
                                  reviewed for the disposal of sludges
                                  from wastewater treatment plants
                                  (WWTP). Major emphases of the report
                                  include (1) assessments of the possible
                                  impacts  of sludge landfilling on the
                                  environment and the public health, (2)
                                  available control technologies and
                                  management options,  (3) sludge
                                  treatment processes and the charac-
                                  teristics  of WWTP sludges, and  (4)
                                  design approaches and  operational
                                  procedures for  current sludge land-
                                  filling practices.
                                   Codisposal landfills (which dispose
                                  of sludge along with refuse or soil) are
                                  generally favored over  sludge-only
                                  methods (which dispose of sludge
                                  alone in  either trenches or area fills).
                                  Advantages of the codisposal landfills
                                  are that they are the least costly
                                  alternative, they generate the least
                                  public opposition, and they provide for
                                  more effective  land use. However,
                                  codisposal  sites do  have greater
                                  potentials for increased odor, aerosol,
                                  noise, and public health risks.
                                   This Project Summary was developed
                                  by EPA's Municipal Environmental
                                  Research Laboratory, Cincinnati, OH,
                                  to announce key findings of the
                                  research project that is  fully docu-
                                  mented in a separate report of the
                                  same title (see Project Report ordering
                                  information at back).

                                  Introduction
                                   Disposal of wastewater treatment
                                  plant (WWTP) sludge has historically
                                  occurred by land burial, ocean dumping,
                                  internment in evaporation (or percola-
                                  tion) lagoons and ponds, incineration,
                                  agricultural  use, and land spreading.
                                  But annual increases in sludge produc-
                                  tion, current bans on ocean dumping of
                                  sludge, and the high costs of incineration
                                  have  intensified the need for sludge
                                  landfilling.  Recent sludge disposal
                                  research assesses the site-specific
                                  problems of sludge landfilling as well as
                                  the environmental benefits.
                                   Sludge landfilling (with or without the
                                  addition  of municipal refuse) presents
                                  many environmental and public health
                                  risks and managerial options. Environ-
                                  mental and public health risks include
                                  leachate contamination  of water and
                                  soil resources, destruction of native
                                  fauna and  flora,  obnoxious odors,
                                  aerosol and dust generation, pathogen
                                  transmission, and other related nuisances.
                                  Management decisions about sludge
                                  landfills  encompass a range of topics
                                  uncommon to conventional refuse
                                  landfills,  including acceptable types of
                                  sludge for landfilling, the degree of
                                  sludge stabilization or dewatering
                                  required, and appropriate sludge/refuse
                                  mixing ratios for codisposal. The degree
                                  of environmental and public health risks
                                  posed by sludge landfills will be greatly
                                  influenced by such management deci-
                                  sions.
                                   This study reviews current landfilling
                                  practices for the  disposal of sludges
                                  from wastewater  treatment plants.
                                  Major subjects covered in the report are
                                  as follows:

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1. Sludge treatment processes and
   the physical, chemical, and micro-
   biological characteristics of WWTP
   sludges;
2. Design  approaches  and opera-
   tional  procedures for  current
   sludge landfilling practices;
3. Potential environmental and public
   health impacts of sludge landfilling
   procedures; and
4. Available pollution control  tech-
   nologies and management options.

Characteristics of WWTP
Sludge
  The physical,  chemical, and micro-
biological  quality  of sludges  from
municipal wastewater treatment plants
depends on the nature of incoming raw
wastewater and the effectiveness of the
treatment plant process. Most of the
sludge is readily biodegradable, though
measurable quantities  of  persistent
organics,  metals, and  minerals are
invariably present. The sludge may also
contain pathogenicorganismsthat have
survived the  wastewater  treatment
process. Without wastewater pretreat-
ment, industries may  be  the major
source for contributing  trace  metals,
refractory  organics, or  salts to the
WWTP sludges.
  WWTP sludge is generally classified
according to the stage of wastewater
treatment (primary, secondary, or
tertiary). In addition, the  sludge may be
categorized  by the various  sludge
treatment processes, including thicken-
ing, stabilization, disinfection, condi-
tioning,  dewatering, drying, and high-
temperature processing. Within each of
these categories are numerous process
alternatives that ultimately affect the
disposal options for the sludge.
  Sludge moisture content and  per-
meability are critical physical  charac-
teristics that  can have pronounced
impacts  on leachate generation and
sludge engineering properties. Excessive
residual moisture will complicate hand-
ling and  landfill operations and hasten
the formation of landfill leachates. Even
dewatered sludge has poor engineering
properties  because it is largely non-
compressible  and  has  little  bearing
strength.
  The chemical characteristics of WWTP
sludges  often  impose limitations on
sludge disposal options. Though the
concentration and mobility of chemical
constituents vary greatly, sludge can be
highly contaminated. Sludge consti-
tuents that are potentially  harmful to
the  environment include  nitrogen,
phosphorus, trace  metals, major inor-
ganic ions, and certain organic  com-
pounds. Industrial wastewater can be a
particularly important source of  trace
metals and synthetic organic compounds.
  Sludge microorganisms that may be
of health concern are bacteria, viruses,
parasites, and fungi. Bacteria, viruses,
and parasites (including protozoa,
helminths,  and  nematodes) are con-
sidered primary pathogens  and are
incorporated into the sludge during its
formation in  wastewater  processing.
Fungi are considered secondary sludge
pathogens because they  are  only
numerous in sludge when given the
opportunity to grow during some treat-
ment or storage process. The concen-
trations of  these  microbes can  be
diminished through  various sludge
processing practices such as anaerobic
digestion, aerobic digestion, lime stabi-
lization, composting, and heat and
radiation treatment. But, the literature
reviewed in this study clearly indicates
that many pathogens actually survive
wastewater  and  sludge  treatment
processes.  Thus WWTP  sludges can
pose various health hazards.

Current Sludge Landfill
Practices
  Current  landfilling practices for
WWTP sludge disposal fall into three
major categories:
  • Sludge-only trench
     narrow trench
     wide trench
  • Sludge-only area fill
     area-fill mound
     area-fill layer
     diked containment
  • Codisposal
     sludge/refuse mixture
     sludge/soil mixture

Each of these landfilling methods can
demonstrate site-specific advantages in
terms of design approach, operational
procedures, or effectiveness in protect-
ing the  environment and  the public
health.

Sludge-Only Trench
  Disposal of sludge  in a sludge-only
trench  involves the  excavation of a
trench into which the sludge is placed.
The excavated soil is then placed over
the sludge as a cover, thereby eliminating
the need for substantial soil import. The
practice is usually limited to areas with
suitable  hydrogeological conditions or
in locations where surface application
or other alternatives are not viable.
  Sludge-only trenching  represents
potential despoiling of prime agriculture
soils,  since the nutrient rich topsoil i
mixed and buried in a subsoil/surfac
soil mixture.  Another disadvantage i
the occasional need  for sludge limin
before placement  in the trench. Thi
approach  can  have its advantage!
however,  such  as reduction of odor:
immobilization  of heavy metals, an
reduced pathogen levels.
  Methods for sludge-only trenchin
are generally  designated as  wid
trenches (greater than 3.0 m, or 10ft) c
narrow trenches  (less than 3.0  m
Variables affecting the depth and lengt
of trenches  include the  followim
depth to bedrock,  high water table,  sc
stability,  and operational  limitatior
(i.e., site configuration, equipment, ar
physiographic characteristics). Thoug
the narrow-trench operation is usual
land-intensive, associated enviror
mental  and  public  health  risks  ai
relatively minimal. Wide-trench sludc
disposal often creates a greater potenti
for leachate generation, vectors, odor
and  possible'public health impact
Liners can minimize the risks of leachai
generation. Odors, vectors, and publ
health impacts are related to the largi
sludge  exposure  periods and  greati
sludge application rates.

Sludge-Only Area Fill
  Sludge-only area fill  is a method I
which WWTP sludge  is disposed <
above the original  ground  surfac
Three methods may be used for area-f
sludge applications—area-fill moun
area-fill layer, and diked containmer
The sludge-only area fills require mixir
with soil as a bulking agent to provii
sludge stability. Since sludge-only an
fills are usually located where a hi;
groundwater  table or near-the-surfai
bedrock prevails, difficulties often arii
in obtaining  sufficient onsite soils.
common design feature of sludge an
fills is the inclusion of surface wat
drainage  control  measures. Leacha
from the sludge and surface runoff fro
the site require control measures sui
as upland runoff diversion ditches ai
onsite leachate collection systems.

Codisposal
  Codisposal  is the practice of disposi
of sludge in a conventional refu
landfill. This method can offer signifies
cost savings through economies of sc<
(e.g.,  additional land acquisition a
equipment costs are expected  to
low). Codisposal landfilling methods £

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 viewed favorably when compared with
 sludge-only  alternatives  because of
 advantages such as lower capital costs,
 less public opposition, and more effective
 land use. Conventional codisposal
 approaches  include the use of both
 sludge with refuse mixtures and sludge
 with soil combinations.  Both  practices
 are increasingly used as viable disposal
 options.
   Municipal  refuse can absorb large
 volumes of sludge moisture and prevent
 or delay  attainment of landfill field
 capacity. Thus the sludge/refuse mix
 ratio is a critical operational specification
 for codisposal practices. A proper mix
 ratio ensures that water released from
 the  sludge can be intercepted  by the
 refuse  without depleting  the  refuse
 adsorption capacity.  Major factors
 governing sludge/refuse mix ratios are
 sludge solids content (or moisture
 content), refuse composition, and depth
 of d'isposal.
   In a sludge/soil operation,  sludge is
 mixed  with  soil  and the  mixture  is
 applied as a cover for areas of a refuse
landfill. In this operation, the sludge is
disked or mixed into indigenous soil and
later retrieved for use as an intermediate
or final  cover.  Use  of sludge/soil
mixtures requires greater manpower
and  equipment and may have greater
environmental and public health impacts
than mixing sludge with  refuse.
Environmental and  Public
Health Impacts
  Various  environmental impacts are
associated with the landfilling of WWTP
sludges. Sludge landfilling can adversely
affect leachate composition, leachate
volume production, air quality, and land
quality. Because of  the toxic and
pathogenic nature of  many WWTP
sludges, their placement in  a  landfill
may lead  to  the formation  of highly
contaminated leachates  or surface
runoff that could migrate from the
landfill site. But the critical factor
influencing environmental impacts is
the method of sludge application.
  The risk of  transmitting disease is of
major concern for the various sludge
    disposal practices. The direct pathways
    for disease transmission from  sludge
    landfilling operations include aerosols,
    vector transport, direct contact, ground-
    water, and surface water runoff. The
    groundwater and surface water runoff
    pathways present the greatest risks for
    disease transmission. Although the po-
    tential health effects  and virulence of
    sludge and refuse contaminants have
    been well documented,  no known out-
    breaks of disease have occurred among
    persons exposed to  sludge  landfilling
    operations.
      The literature suggests that good
    design and operation can mitigate many
    of the  potential environmental and
    public health problems. For instance,
    codisposal  practices were found  to
    produce weaker leachates than munici-
    pal refuse landfills. But the potentials
    for increased odor, aerosol, and noise
    are greater at codisposal sites. Possible
    risks to the  public health are  also
    greater because more viable contamin-
    ants are available to enter the ground-
    water. An acceptable sludge disposal
Table 1.    Suitability of WWTP Sludges for Landfilling According to Potential Odor and Operation Problems


                   Type of Sludge
                     Sludge Only Landfilling         Codisposal Landfilling
                   Suitability        Reason        Suitability        Reason
Liquid - Unstabilized
  Gravity-thickened primary, WAS* and primary, and WAS
  Flotation-thickened primary and WAS, and WAS
    without chemicals
  Flotation-thickened WAS with chemicals
  Thermal-conditioned primary or WAS

Liquid - Stabilized
  Thickened anaerobic digested primary and primary,
    and WAS
  Thickened aerobic digested primary and primary,
    and WAS
  Thickened lime stabilized primary and primary, and WAS
Dewatered - Unstabilized
  Vacuum-filtered, lime-conditioned primary
Dewatered - Stabilized
  Drying-bed-digested and lime-stabilized
  Vacuum-filtered, lime-conditioned digested
  Pressure-filtered, lime-conditioned digested
  Centrifuged,  digested, and lime-conditioned digested
Heat-Dried
  Heat-dried digested
                       NS

                       NS
                       NS
                       NS
                       NS

                       NS
                       NS
                       S
                       S
                       S
                       S
OD, OP

OD. OP
    OP
OD, OP
    OP

    OP
    OP
NS

NS
NS
MS.
MS

MS
MS
                  S
                  S
                  S
                  S
OD, OP

OD, OP
OD, OP
OD, OP
    OP

    OP
    OP
High-Temperature-Processed
Incinerated dewatered primary and primary, and WAS
Wet—Air Oxidized Primary and Primary, and WAS
S
NS
—
OD, OP
S
MS
—
OD, OP
* Abbreviations: WAS - Waste-activated sludge
               NS   = Not suitable
               MS  = Marginally suitable
               S    = Suitable
               OD  = Odor problems
               OP   = Operational problems

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    alternative  must include measures for
    minimizing the environmental  and
    public health impacts.

    Control Technology and
    Management Options
      Landfill ing of WWTP sludge can be an
    acceptable  disposal method, providing
    environmental and public health impacts
    are controlled. Control technologies
    that can be implemented are as follows:
      1. Leachate and groundwater control,
         including  collection, treatment,
         ultimate disposal, and monitoring.
      2. Surface water control, including
         run-on control, and runoff  reten-
         tion and treatment.
      3. Air emissions control, including
         control of gases, odor, dust,  and
         volatile sludge constituents.
      4. Erosion control to minimize wind
         and water erosion.
      5. Mud control to prevent equipment
         from   slipping onsite  or tracking
         mud offsite.
      6. Vector control to limit  vector
         access and to discourage burrow-
         ing animals.
      7. Aesthetic considerations, including
         site closure  planning  and  visual
         barriers.
      8. Noise control to prevent excessive
         noise.
      9. Personal health and safety control
         for onsite workers and others near
         the facility.
      Management options depend on
    current WWTP sludge landfill practices,
    the types of WWTP sludges placed in the
    fill, related environmental and  health
    impacts, and other special constraints
    of WWTP sludge la ndfilling. Appropriate
    control technologies should be applied
    for anticipated environmental impacts.
    Consideration should be  given to
         operational  factors  such as  sludge
         dewatering and stabilization or special
         regulatory constraints that exist in most
         states.
           The feasibil ity of various management
         options is primarily influenced by the
         selected landfill method and the type of
         incoming sludge (Table  1). Additional
         considerations include cost evaluations,
         regulatory limitations, and geographical
         distinctions.

         Conclusions
           Codisposal landfills  are generally
         favored  over sludge-only  alternatives
         because they are the least  costly,
         generate the least public opposition,
         and provide for more effective land use.
The  potentials  for  increased odor,
aerosol, noise, and public health risks
are greater at codisposal sites.
  The  need for sludge  stabilization
depends strictly on the landfill site and
the engineering  design.  Sludge de-
watering, .however, is imperative for all
landfilling operations. Available control
technologies such  as leachate  and
methane gas control must be applied at
sludge landfill sites to prevent odor and
operational problems and to ensure
overall public acceptance.
  The  full report was  submitted in
fulfillment of contract No. 68-03-2886
by Calscience Research, Inc., under the
sponsorship of the U.S. Environmental
Protection Agency.
           James C. S. Lu, Robert J. Stearns, Robert D. Morrison, and Bert A. Eichenberger
             are with Calscience Research, Inc., Huntington Beach, CA 92647.
           Wendy J. Davis-Hoover and Laura Ringenbach were the EPA Project Officers
             (see below for present contact).
           The complete report, entitled "A  Critical Review of  Waste water Treatment
             Plant Sludge Disposal by Landfilling," (Order No.  PB 83-111 518; Cost:
                   $25.00, subject to change) will be available only from:
                   National Technical Information Service
                   5285 Port Royal Road
                   Springfield, VA22161
                   Telephone: 703-487-4650
           For information, contact Norms Lewis:
                   Municipal Environmental Research Laboratory
                   U.S. Environmental Protection Agency
                   Cincinnati,  OH 45268
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United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
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