United States
 Environmental Protection
 Agency
 Municipal Environmental Resear
 Laboratory
 Cincinnati OH 45268
 Research and Development
 EPA-600/S2-81-172  Oct 1981
 Project Summary
 Dispersant  Application
 System  for the  U.S.  Coast
 Guard  32-Foot  WPB
 Michael Borst and Gary F. Smith
  This illustrated report describes
 details of the fabrication, assembly,
 and operation of a lightweight, easily
 assembled system for dispensing
 chemical dispersants on oil spills. This
 system is designed to be fitted onto
 the aft deck of the U.S. Coast Guard
 32-foot waterways patrol boat (WPB),
 a vessel stationed in many areas where
 oils are commonly transferred or
 transported. This report is intended to
 provide those detailed instructions
 necessary to the man actually doing
 the fabrication, assembly, or opera-
 tion. Sixteen illustrations and parts
 lists are also provided.
  This report was submitted in fulfill-
 ment of Contract No. 68-03-2642,
 Job Order No. 57 by Mason & Hanger-
 Silas  Mason Co., Inc., under the
 sponsorship of the U.S. Environmen-
 tal Protection Agency. This report
 covers a period from December 1979
 to January 1981, and the work was
 completed as of February 1981.
  This Project Summary was devel-
 oped by EPA's MunicipalEnvironmen-
 tal 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
 The U.S. EPA in conjunction with the
 U.S. Coast Guard (USCG), has devel-
 oped a lightweight, easily assembled
 system to fit on the USCG 32-foot
 waterways patrol boat WPB. The system
 is assembled on the aft deck directly
 behind the cabin. It can be readily
 installed on the 32-ft WPB bythree men
 in two working hours. It  includes two
 spray booms supported by a rectangular
 frame work. The spray booms are sup-
 plied water from the boat's fire fighting
 system, and chemical dispersant is fed
 into the water by an eductor. Support for
 the framework of the system is provided
 by the deck cups which ordinarily sup-
 port stanchions for the hand rail. The
 removal of the stanchions also neces-
 sitates the removal of  Search and
 Rescue (SAR) gear. SAR operations will
 therefore be impaired. Two engine
 compartment hatches are covered by
 the framework,  but access is still pos-
 sible. After drums of dispersant have
 been placed onboard, access to the
 stern hatches will be difficult, if  not
 impossible.
  The system could readily be adapted
 for use on other vessels of opportunity.
 The only limiting conditions are the
 ability to provide sufficient height for the
 spray booms and structural integrity.
The system needs an adequate supply of
water from an onboard  source. For
example, the end sections of the support
frames developed for the 32-ft WPB
could be lashed to the side handrails of
 most vessels with fore and aft stays
secured as convenient. One of the spray
booms is shown in operation in Figure 1.

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                                                Michael Borst and Gary F. Smith are with Mason & Hanger-Silas Mason Co.,
                                                  Inc., Leonardo, NJ 07737
                                                R. A. Griffiths is the EPA Project Officer (see below).
                                                The complete report,  entitled "Dispersant Application  System for the U.S
                                                  Coast Guard 32-Foot WPB," (Order No PB82-101 684, Cost: $6 50, subjectto
                                                  change) will be  available only from.
                                                        National Technical Information Service
                                                        5285 Port Royal Road
                                                        Springfield, VA 22161
                                                        Telephone. 703-487-4650
                                                The EPA Project Officer can be contacted at
                                                        Oil & Hazardous  Materials Spills Branch
                                                        Municipal Environmental Research Laboratory—Cincinnati
                                                        U S Environmental Protection Agency
                                                        Edison, NJ 08837
                                                                               US GOVERNMENT PRINTING OFFICE, 1981 -559-017/7334
    Figure  1.    Starboard spray boom in
                 operation.
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Postage and
Fees Paid
Environmental
Protection
Agency
EPA 335
Official Business
Penalty for Private Use $300
RETURN POSTAGE GUARANTEED
                                                                                                                r; rl •

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 United States
 Environmental Protection
 Agency
Municipal Environmental Researctf
Laboratory
Cincinnati OH 45268
 Research and Development
EPA-600/S2-81-170  Oct. 1981
 Project  Summary
 Density  Levels  of  Pathogenic
 Organisms in  Municipal
 Wastewater  Sludge—
 A Literature  Review
 Dana C. Pederson
  This report discusses a critical
 review of the literature from 1940 to
 1980 of laboratory  and full-scale
 studies on density levels of indicator
 and pathogenic organisms in munici-
 pal wastewater sludges and septage.
 The  effectiveness  of conventional
 municipal sludge stabilization processes
 (mesophilic anaerobic and aerobic
 digestion, composting and lime stabil-
 ization)  and  dewatering processes
 (drying beds,  lagooning/storage, and
 sludge conditioning/mechanical de-
 watering) was evaluated for reducing
 density levels of indicator and patho-
 genic organisms. An annotated bibli-
 ography presents all citations reviewed,
 with pertinent abstracts and methods
 used by researchers.
  This Project Summary was devel-
 oped by EPA's Municipal Environmen-
 tal 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
  Sludges  originating from municipal
wastewater treatment plants harbor a
multitude of microorganisms, many of
which presents potential health hazard.
Risk of public exposure to these or-
ganisms is possible when sludges are
applied to land as a means of disposal. In
recognition of this problem, and as
required by Section 405 of the Clean
Water Act of 1977 (PL 95-217), criteria
for the control of infectious disease in
the land application of sewage sludge
and septic tank pumpings were issued
by the U.S. Environmental Protection
Agency (EPA) in 40  CFR Part  257
(Federal Register Vol. 44, No.  179,
September 13, 1979).
  The "Part 257 criteria" specify what
minimum treatment of municipal waste-
water treatment  plant sludges is re-
quired prior to land application of the
residue. Acceptable treatment methods,
termed "Processes to Significantly
Reduce Pathogens," are as follows:
  • Aerobic digestion—Agitation of
   sludge  in aerobic conditions at
   residence times ranging from 60
   days at 15 °C to 40 days at 20 °C,
   with a volatile solids reduction of at
   least 38%.
  • Air drying—Draining and/or drying
   of liquid sludge on underdrained
   sand beds, or on paved or unpaved
   basins in which the sludge is at a
   depth  of 9 inches (22.9 cm). A
   minimum of three months is needed,
   two months of which temperature
   average on a daily basis is above 0
   °C.
  • Anaerobic digestion—Maintenance
   of sludge in the absence of air at
   residence times ranging from 60
   days at 20°C to 15 days at 35°C to

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    55°C, with a volatile solids reduc-
    tion of at least 38%.
  • Composting— Using the within-
    vessel, static aerated pile or wind-
    row composting  methods,  the
    sludge is maintained at  minimum
    operating  conditions of  40°C for
    five days. For four hours during this
    period, the temperature exceeds
    55°C.
  • Lime  stabilization—Application of
    lime to sludge  in  quantities  suf-
    ficient to produce a pH of 12 after
    two hours of contact.
  • Techniques demonstrated to be the
    equivalent of the above on the
    basis of  pathogen  removals  and
    volatile solids reduction
  An additional category of treatment
processes, termed "Processes to Further
Reduce Pathogens', was designated in
Appendix  II of  40  CFR Part 257 as
required if (1) affected land is to be used
within 18  months of sludge application
for the cultivation  of food crops and (2)
the edible  portion of the crop is likely to
be exposed to the sludge.  These addi-
tional processes are:
  • High temperature composting
  • Heat drying
  • Heat treatment
  • Thermophilic aerobic digestion
  • Irradiation
  In 1980, Camp, Dresser  and McKee,
Inc. (COM) undertook a literature review
of available domestic and foreign data,
from 1940 to 1980, of bacteria, viruses
and parasites densities in raw municipal
wastewater sludges, on the effectiveness
of the "Processes  to Significantly
Reduce Pathogens" and of conventional
sludge dewatermg techniques (mechan-
ical dewatermg/sludge conditioning
and sludge storage/lagooning) to reduce
levels of these organisms.
  The following organisms, categorized
into four groupings, were emphasized:
  • Indicators—Total  coliform, fecal
    coliform, and fecal streptococcus
    bacteria; Clostridum perfnngens
    (welchii); bacteriophage
  • Pathogenic bacteria—Salmonellae,
    Shigellae, Pseudomonas  sp.,
    Mycobacterium spp., Candida
    albicans, Aspergillus fumigatus
  • Enteric viruses—Enterovirus  and
    its subgroups (polioviruses, echo-
    viruses and coxsackieviruses),
    reovirus and adenovirus
  • Parasites—Entamoeba histolytica,
    Ascaris lumbricoides,  Taenia spp.,
    Schistosoma  spp.,  and others
  In addition to reporting density levels
in raw  sludge  and septage, and the
 effectiveness of conventional sludge
 treatment processes in reducing density
 levels, this review also identified design
 and operating variables that  affect
 process efficiency, compared results of
 laboratory pilot-scale studies to those of
 full-scale plants, and contrasted survival
 of  indicator  organisms to that  of
 pathogens   Methods used  by  each
 researcher  to  enumerate  organisms
 were also described, and  brief  sum-
 maries were provided of related  cita-
 tions that were encountered but were
 not actually used  in this report.

 Density Levels in Raw Sludge
  Levels of  bacteria, viruses and  para-
 sites in raw sludge are presented  in
 Table  1   Note that the densities  of
 pathogenic organisms are several logs
 less than indicator  organisms.  Also,
 there is a  noticeable lack of information
 on  the densities  of  select  pathogenic
 organisms in raw sludges and septages
 (i.e., lack of  parasite  organisms data in
 septages)

 Anaerobic Digestion
  This  process  involves  biological
 degradation of complex  organic  sub-
 stances present in wastewater sludges
 in the absence of free oxygen. Primary
 or secondary  sludge, or a  mixture of
 both, is fed continuously or intermittently
 into an airtight vessel and retained for
 varying periods of time.
  Retention times can vary from  30 to
 60 days in low-rate (unmixed) reactors
 and from 10  to 20  days in high-rate
              reactors which are mixed and heated to
              either mesophilic—30 to  38 °C—or
              thermophilic—50 to 60 °C—tempera-
              tures.  The  digester's  performance is
              indicated by  the  percent  of  volatile
              solids (VS) destroyed. Reduction  of VS
              usually ranges between 35% and 60%,
              depending  on the character of  the
              sludge, detention  time and tempera-
              ture.
                Only limited information was  found
              on levels and reductions of densities of
              organisms in low-rate digesters Longer
              detention times and higher temperatures
              are  correlated  with  greater  density
              reductions. In high-rate digesters at
              full-scale  plants, reductions of greater
              than 1 log occur in densities of bacteria
              and viruses,  with the exception of
              Pseudomonas aeruginosa (Table 2) Ova
              and cysts  of parasitic tapeworms,
              flatworms  and roundworms (with the
              exception of Trichinella spiralis) were
              able to survive this digestion  process,
              while parasitic protozoans were reduced
              to non-detectable levels.
                Comparison of laboratory/pilot-scale
              data  to those  of full-scale plants
              generally indicated that greater density
              reductions  are  accomplished in  the
              smaller-scale studies. The larger density
              reductions  are  attributed  to (1)  the
              ability to  achieve optimum digestion!
              conditions on  a smaller scale; (2) the*
              absence of short circuiting—when fresh
              sludge (and,  with it, high levels of
              organisms) is allowed to exit—in labora-
              tory/pilot-scale studies; (3)  the  dif-
              ferences in  sensitivity to the effects of
              anaerobic  digestion  of laboratory-
Table 1.     Density Levels  of Organisms in Raw Sludge and Septage (Average
           Geometric Mean of Organisms Per Gram Dry Weight)
       Organism
Primary     Secondary
Mixed
Septage
Total coliform bacteria
Fecal coliform bacteria
Fecal streptococci
Bacteriophage
Salmonella sp.
Shigella sp.
Pseudomas aeruginosa
Parasite ova/cysts (total)
Ascaris sp.
Trichiuris trichiura
Trichiuris vulpis
Toxocara sp.
Hymenolepsis diminuta
Enteric viruses0
1.2 x ro8
2.0 x ro7
8.9 x JO5
1.3 x JO5
4.1 x JO2
NR
2.8 x 103
2.1 x JO2
72 x JO2
1.0 x 70'
7.7 x 102
2.4 x W2
6. x 10°
3.9 x 102
7.1 x 10s
8.3 x 10e
1 7 x 10s
NRa
8.8 x W2
NR
1.1 x 70"
NR
1.4 x 103
<1.0 x 70'
<7.0x 70'
2.8 x W2
2.0 x 10'
3.2 x 102
1.1 x 109
1.9 x W5
3.7 x W6
NR
2.9 x 102
NDti
3.3 x 103
<5.0x 70'
2.9 x 102
0
1.4 x W2
1.3 x W3
0
3.6 x 102d
1.4 x 70"
7.2 x 10e
6.6 x 10s
NR
5.1 x 70"'
NR
2.6 x 70;
A//?
NR
NR
NR
NR
NR
NR
 a NR - No data available
 " ND = None detected
 c Plaque forming units per gram dry weight (PFU/gdw)
 d TCIDso = 50 percent tissue culture infectious dose

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 Table 2.    Density Levels of Indicator Bacteria, Pathogenic Bacteria andEnterovirus
           Following High Rate Anaerobic Digestion at 35°C for 14-15 to 21 Days

                                                     Log Reduction
Organism
Total coliform
Fecal coliform
Fecal streptococcus
Salmonella sp.
Ps. aeruginosa
Enterovirus
Density Level*
per WO ml
3 x W7C
2 x 70«c
9 x 105C
3.7 x W'a
6 x 705d
7 9 x /O'e
Meanb
2.05
1.84
1.48
1.63
0.58
1.21
Range
1.78 -2.30
1.44 - 2.33
1.10 - 1.94
0.91 - 2.08
0.15 - 1.0
1.05 - 1.36
 ^Arithmetic average of mean (geometric) values
 ^Arithmetic average
 cCount per 100 ml
 "Most Probable Number per 100 ml
 6'Plaque Forming Units per 100 ml
 grown, seeded organisms used in many
 smaller-scale studies to that of
 indigenous organisms
   The usefulness of total coliforms,
 fecal coliforms, fecal  streptococci in
 indicating both densities and reduction
 of pathogenic bacteria (Salmonella sp )
 and enteroviruses was evaluated.  No
 correlation was seen between density
 levels of indicators vs. Salmonella sp. or
 enteroviruses  Some correlation was
 seen, however, when density reductions
 of these organisms were compared.
 Indicator bacteria and  Salmonella  sp.
 levels were reduced  by similar magni-
 tudes, and fecal streptococci appeared
 to be the most conservative indicator of
 enterovirus mactivation

Mesophilic Aerobic Digestion
   In this process, wastewater sludge is
aerated  in  tanks at  temperatures
ranging from  ambient  to  37°C,  com-
monly for detention times of 10 to  20
days
   Very little  research  has been con-
ducted on the effects of aerobic diges-
tion on indicator and pathogenic bacteria,
enteroviruses and parasites Bacteria,
enteroviruses  and  parasites all show
variable response to the digester
environment,  such that  there  is  no
certainty of even a 1-log reduction in
density level.

Mesophilic Composting
  This process involves  mixing de-
watered sludge cake with a bulking
agent, such as wood chips, dry compost
or shredded municipal refuse, and then
shaping the mass  into piles,  beds  or
windrows. Due to  the  activity of the
naturally occurring microorganisms,
the compost mass will  increase  in
temperature (up to temperatures of
between 45 and 65°C) until available
food sources are exhausted The mass
then cools, and it is allowed to mature,
or "cure," in stockpiles.
  There are three principal composting
systems presently utilized'
  • Windrow—The compost  mass is
     shaped into long piles, 90 to  150
     centimeters (cm) in height, which
     are turned periodically. This com-
     posting process  is usually com-
     pleted in 6 to 10 weeks.
  • Forced aeration (Beltsville sys-
     tem)—Sludge and woodchips are
     formed into piles about  360 cm
     high for a period of 21 to 28 days.
     During  this time, air  is blown or
     pulled through the pile
  • Closed system—The compost mass
     is mixed and aerated in a rotating
     drum, or in moving elevators, for
     two  to  three weeks   During  this
     time,  temperatures commonly
     reach 70°C.
A fourth composting technique,  the
deep-pile bin system, has been used
experimentally  The technique  utilizes
aerated bins measuring 300 cm on each
side and 300  cm in height, with  the
compost mass turned periodically
  In this review of composting  data, it
was found  that most researchers
operated systems at significantly higher
temperatures and  over  much  longer
time periods than are defined by EPA for
composting as a process that  signifi-
cantly reduces pathogens (a minimum
temperature of 40°C throughout  the
composting period, with a temperature
of 55°C attained for at least four hours).
  High temperatures generated by
microbial activity in the  composting
process can inactivate or destroy many
 microorganisms present in sludge
 Within the protocol for  mesophilic
 composting, however, the temperatures
 attained are not instantly lethal to most
 indicator and  pathogenic microorgan-
 isms of concern  The effectiveness of
 the process depends, therefore, not on
 temperature alone, but rather on main-
 taining the  moderately  high tempera-
 tures throughout the composting mass
 over  a  set  period of time. Whenever
 elevated temperatures are not uniformly
 attained through  the compost mass,
 subsequent mixing of the mass  can
 cause bacterial populations from low-
 temperature zones to remoculate areas
 where bacteria had been inactivated by
 higher temperatures. In  open-windrow
 or forced-aeration systems, maintenance
 of a  uniformly  high temperature is
 difficult. The "toe" or lower outer edge
 of a static pile used in forced aeration
 composting typically remains cooler
 than  the inner portion  o.f the pile. In
 open windrow composting, turning the
 pile will cause variations in the heating
 and cooling of the pile. Generally, in the
 closed  composting  system  uniform
 temperatures  can  be routinely main-
 tained
  Information on density reductions of
 indicator and pathogenic  bacteria,
 viruses and parasites was drawn from
 both  laboratory/pilot and full-scale
 studies Total coliform and fecal coliform
 bacteria density levels decline by more
 than  3 and 4  logs, respectively. Fecal
 streptococcus appear to be quite resist-
 ant to conditions of mesophilic com-
 posting, with regrowth evident
  Salmonella densities are reduced by
 approximately 1  to 3 logs  during
 mesophilic composting, generally re-
 sulting in densities of less than, or equal
 to 10 organisms per gram dry weight of
 sludge (on  a  Most Probable Number
 basis,  or  MPN). Shigella  sonnei,
 Staphylococcus aureus and Serratia
 marcescens are also  significantly
 reduced in number, butMycobacterium
 tuberculosis will  apparently survive
 Mesophilic  composting  will  not sig-
 nificantly reduce densities of thefungus
Asperg/llus fumigatus; in  fact,  the
 temperatures encountered are optimum
 for this organisms' growth.
  Most viruses of concern appear to be
 quite vulnerable  to the temperature
 conditions of composting  Echo, reo and
 coxsackie virus densities are reduced by
three logs by temperatures within the
 mesophilic  range,  as  are  the  adeno-
virudae  Poliovirus  appears to be
 similarly susceptible  A bacteriophage

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(fg) when added to sludge was found to
be far more  resistant to  mesophilic
temperatures and, therefore, reductions
in levels of this non-pathogenic and
easily cultured  virus could provide  a
useful indication of enterovirus inacti-
vation.

  Ova  of the  roundworm, Ascans
lumbricoides,  can survive at tempera-
tures  higher than those specified for
mesophilic composting, presenting  a
potential problem in sludge treated by
mesophilic composting
Lime Stabilization
  Lime is mixed with sludge in quantities
sufficient to raise the pH to  12.0 for at
least two hours. Lime may be added (1)
to liquid sludge prior to dewatering, (2)
directly to a mixed-sludge storage tank,
followed by land  application; or (3) to a
dewatered sludge cake. The technique
most commonly used by the researchers
whose data were utilized in this review
involved the addition of lime to liquid
sludge.

  Lime stabilization can effect signifi-
cant  reductions m levels of  some
indicator  and  pathogenic bacteria and,
possibly,  of poliovirus. The  effective-
ness has been shown to be  contingent
upon the pH achieved in the stabilization
protocol.  It  appears that different
bacteria respond differently to increas-
ing  levels of pH achieved in the process.
Even  after an  effective pH  level  is
achieved in sludge, the decrease in pH
level  that occurs after  the initial
exposure and minimum contact time
can create an environment favorable to
regrowth of some bacteria.

  Fecal coliform, Salmonella spp.  and
Pseudomonas aeruginosa density levels
all appear to  be reduced by 2 logs or
greater at pH  11  or above. There is no
apparent tendency for  these micro-
organisms to regrow  Fecal  strepto-
coccus, however, are more resistant to
lime mactivation  and are able to regrow
quickly  with  decreasing pH  to  near
original densities or greater within 24
hours.

  In one study, lime treatment of
sludges inactivated Ascaris eggs; how-
ever, the lime concentrations and time
needed were  substantially greater than
is normally used for sludge condition-
ing. Also, this mactivation  of Ascaris
eggs  was  not always consistent  and
therefore cannot be relied upon.
Conventional Sludge
Dewatering Processes

Drying Beds
  In general practice, digested sludge is
placed on sand beds or paved beds that
have been provided with drainage The
sludge is  allowed  to  dry  to approxi-
mately 40% solids content, over a period
of about 10 to 15 days (under favorable
conditions)—a significantly shorter time
period than the minimum  of three
months delineated by the EPA.
  Information  was found  on the  m-
activation of  bacteria, viruses and
parasites during drying, but none of the
data conformed to the criteria specified
by the EPA. The research conducted
does,  however, focus attention on the
solids level achieved during drying. Th>s
parameter could be useful, in addition to
time, temperature, and sludge depth, as
an additional criterion for defining  air
drying of sludge.

Sludge Storage/Lagooning
  In  this  process,  anaerobically or
aerobically digested sludge is stored in
earth- or concrete-lined  lagoons at
depths of from  60 to 600 cm for periods
ranging  from several months to years.
The  performance  of  the lagoons is
affected by climate; both precipitation
and  low  temperatures will  inhibit
dewatering and the  rate of volatile
solids reduction. The two factors that
have  been studied with regard to
survival of indicators,  pathogens  and
parasites are temperature and length of
storage time At  lower temperatures, a
longer detention time is  required to
achieve reduction of density levels
  It was concluded,  based on trends
indicated by the  data reviewed, that at
temperatures of 20°C  or greater, the
minimum  storage time required to
achieve a  1 -log density reduction is one
month for bacteria, two  months  for
viruses, and greater than six months for
parasitic ova. At temperatures of less
than  20°C, more than  six months,
storage  is required to reduce  density
levels of pathogenic bacteria by 1 log,
more  than eight months for viruses, and
at least  three years for parasitic ova.


Sludge Conditioning/
Mechanical Dewatering
  For purposes of this review  (and as
commonly practiced),  dewatering in-
volves use of  vacuum filter, chamber
filter press, belt filter press, or centrifuge
to separate the liquid and solid  com
ponents of sludge. Typically sludge cake
solids content of 15 to 40% are achieved
Chemical conditioners  used to aic
sludge  dewatering include lime (CaO)
ferric chloride (FeCI3), ferrous sulfate
(FeS04), and  polyelectrolytes or  poly
nners.
  The process of mechanical dewalermc
of municipal wastewater sludges alone
has little effect on the density levels ol
pathogens  The conditioners  that are
commonly used  in  combination  with
mechanical dewatering vary in effects
Polymer has no  apparent effect on
density levels  of pathogens. Lime,
added  in concentrations to optimize
dewatering, cannot be relied on to
reduce pathogen levels because of the
variations in pH levels obtained Ferric
chloride, often used in conjunction with
lime, appears  to reduce whatever
virucidal and bactericidal  effects the
lime normally has when applied to
sludge.


Conclusions and
Recommendations
  Because a  large  body of  literature
containing comparable data is not
available,  it is  recommended  that
additional research be conducted on tha
effectiveness of sludge treatmenl
processes  in reducing density levels of
organisms. It is recommended, further,
that researchers document carefully all
pertinent aspects of their experimental
design.
  The following conclusions  appear to
be valid based on the literature reviewed-
  • Anaerobic  digestion and  lime
    stabilization consistently produce
    reductions of about 1  to 2 logs in
    densities of indicator and patho-
    genic bacteria and,  in the case of
    anaerobic digestion, m densities of
    viruses  as well At a minimum,
    effectiveness  depends on the
    processes being carried  out under
    the conditions specified  m 40 CFR
    Part 257. Neither sludge stabiliza-
    tion process appears to be particu-
     larly  effective for  inactivating
    parasite organisms.
  •  Conditions of mesophilic composting
     may inactivate common  indicator
     and pathogenic bacteria and viruses,
     provided that specified  tempera-
    tures  are  attained uniformly
    throughout the compost  mass for
     over the specified time period. The
     pathogenic fungus Asperg/llus
     fumigatus thrives under conditions
                                  4

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     of  mesophilic composting, how-
     ever, and  parasite ova appear to
     survive this process.
  • Density  reductions of bacteria by
     aerobic digestion are variable and
     of  relatively small  magnitude.
     However, there is a lack of data on
     the performance  of  this process
     and also of air drying in reducing
     densities of microorganisms.
  • Sludge lagoons can achieve 1-log
     reductions in densities of bacteria
     and viable  parasite ova,  but, de-
     pending on conditions, storage of
     one month  to more  than  three
     years may be required.
  • Mechanical dewatermg of sludge,
     with or without the use of chemical
     conditioners, has little  reliable
     effect on densities of pathogens.

  Few of the laboratory-scale studies
reviewed could be related to results
obtained at full-scale treatment plants.
Operating parameters used in laboratory
experiments differed radically from
those  at full-scale plants  For this
reason, comparing density levels was
seldom  possible In addition, laboratory
studies  often used  seeded  bacteria,
viruses,  or  parasites and it is  doubtful
whether their behavior mimics that of
naturally occurring organisms.
  No single indicator organism (either
bacteria or bactenophage) was found to
maintain a density level  of a constant
relative  value  to that of  pathogenic
organisms.  The data available made it
impossible  to determine whether this
inconsistency is due to the inability of
current techniques to enumerate patho-
genic bacteria  and enteroviruses ac-
curately, or to  the fact that  densities
actually vary.
  Of the traditional indicators, fecal
streptococci  appear to  be the  most
conservative indicator of both  the
density  levels of  pathogenic  bacteria
and enterovirus in raw sludge and of
their mactivation during sludge  treat-
ments. Additional  research is required
to identify other indicator systems, both
bacterial and viral,  whose numbers
better reflect both density and reduction
of density levels of pathogenic organisms.
  A wide variety of methods were used
to  enumerate  all of the organisms
considered in this review. Although
standard methods are available for
quantifying the  coliform and  strepto-
coccus bacteria and for Salmonella sp.,
there are no standard techniques for
other pathogens, enteroviruses,  or
parasites It is recommended that this
area be addressed so that comparable
data can be produced in future studies.
  The full report was submitted in ful-
fillment of Work Task 08 for Contract
No. 68-03-2803 by Camp  Dresser &
McKee  Inc., under the sponsorship of
the  U.S. Environmental Protection
Agency.
   Dana C. Pederson is with Camp, Dresser, and McKee, Inc.,  One Center Plaza,
     Boston, MA 02108.
   Gerald Stern is the EPA Project Officer (see below).
   The  complete  report,  entitled "Density Levels of Pathogenic Organisms in
     Municipal Wastewater Sludge—A Literature Review," (Order No. PB 82-102 286;
     Cost. $21 50, subject to change) will be available only from-
           National Technical Information  Service
           5285 Port Royal Road
           Springfield, VA 22161
           Telephone: 703-487-4650
   The EPA Project Officer can be contacted at:
           Municipal Environmental Research Laboratory
           U S. Environmental Protection Agency
           Cincinnati, OH 45268
                                                                             U S  GOVERNMENT PRINTING OFFICE 1981 --559-092/3317

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