United States
                   Environmental Protection
 Water Engineering
 Research Laboratory
 Cincinnati OH 45268
                   Research and Development
 EPA/600/S2-85/103 Jan. 1986
&ER&         Project Summary

                   Chemical  and  Microbial
                   Aspects  of  Sludge
                   Composting  and  Land
                   L J. Sikora, P. D. Millner, and W. D. Burge
                    A series of six studies was under-
                   taken to study various chemical and mi-
                   crobial aspects of the composting and
                   land application of sewage sludge. Am-'
                   monia, which is generated in sludge by
                   ammonifying  microorganisms,  was
                   shown to be virucidal. In the pH range
                   of 7 to 9, NH3, but not OH~ or NH4+, was
                   effective. Temperature effects were re-
                   lated to a single NH3 concentration.
                   Sludge and sludge compost with  high
                   concentrations of heavy metals and
                   chlorinated organic materials appeared
                   to have no inhibitory effect on soil en-
                   zyme activity, probably because of the
                   age or the highly stabilized nature of
                   the sludge and sludge compost.
                    Sludges were applied once (100
                   megagrams [Mg]/ha) or annually (20
                   Mg/ha) for 5  years to field plots.
                   N movement down the soil profile oc-
                   curred in the sludge-amended plots, es-
                   pecially in all of the split plots that re-
                   ceived additional fertilizer. Phosphorus
                   movement occurred only down to the
                   60-cm depth, or four times the depth of
                   incorporation in the  sludge-amended
                    Laboratory studies conducted to test
                   methods for improving the efficiency of
                   composting indicated that the most ef-
                   ficient system  was the temperature-
                   demand aeration system. This method
                   resulted in twice as much drying  and
                   yielded 2.5 times as much CO2 as con-
                   stant aeration composting.
                    Results of studies have shown that
                   Aspergillus fumigatus (AF) and ther-
                   mophilic actinomycetes (TA)  are
                   present in air at very low levels in most
non-agricultural sites, even when or-
ganic matter is present and tempera-
tures are occasionally higher than am-
bient. Compost and moldy agricultural
substrates are the biggest reservoirs
and sources of AF and TA. The toler-
ance of AF to broad ranges of tempera-
ture, CO2, and water content limit the
benefits of modifying the composting
process by these parameters to inhibit
this microorganism.
  This Project Summary was devel-
oped by EPA's Water Engineering Re-
search Laboratory, Cincinnati, OH, to
announce key findings of the research
project that is fully documented in a
separate report of the same title (see
Project Report ordering information at

  Applying  sewage sludge or sludge
compost to land can affect several
chemical and microbiological factors in
soils. The benefits of this practice,
which include the addition of nutrients,
trace metals, and organic matter, can be
offset by excess additions of phytotoxic
metals, nitrogen, and  organic chemi-
cals. The need to differentiate between
proper and excessive sludge additions
to soil is imperative to evaluate properly
the benefits of each  sludge  product.
Certain  sludges  have excessive
amounts of toxic materials and should
not be applied to land. Other sludges
may have elevated  amounts, but they
have no  apparent  phytotoxic conse-
quences  when added to soil at low

rates. The long-term effects on soil pro-
ductivity, surface water, and ground-
water need to be elevated along with
the short-term, first-year effects.
  This report discusses the effect of NH3
on the survival of viruses and compares
NH3 with halogens for virucidal proper-
ties. The availability of sludge N  and P
to plants and the movement of these
nutrients through the soil profile over
the long term are also  discussed. Soil
enzymes, the  key to  successful bio-
chemical transformations  in soil, were
monitored to determine the  effects of
large or repeated sludge  applications.
The data presented here provide a bet-
ter understanding of the long-term  ef-
fects of  such applications.
  Composting  stabilizes  sewage
sludges  and transforms them into  an
easily spread and stored material. The
composting process was analyzed ex-
tensively using a self-heating laboratory
composter, and the effects of tempera-
ture and aeration on the efficiency of the
composting process were determined.
These investigations improved our un-
derstanding of the optimum  compost-
ing process for producing material for
soil amendments.
  Composting is a thermophilic process
and results in a product containing nu-
merous thermophilic  organisms that
have various public health implications.
This study provides data on  the num-
bers, types, and potential  health impli-
cations  of thermophilic organisms pro-
duced  during the composting  of
sewage  sludge, the movement of com-
post and other self-heating materials,
and the eventual  distribution of these
materials to users.

Kinetics and Thermodynamics
of Viral Inactivation by
  Ammonia has been shown to be viru-
cidal in  sludge and in NH4CI  solutions.
Our studies examined the kinetics and
influence of temperature on  the inacti-
vation  of f2 bacteriophage and po-
liovirus 1 by NH3. At pH values from 6.5
to 9.5 and NH3 concentrations from 50
to 800  mg/L, the inactivation of both
viruses was pseudo-first-order. The
OH~ had no measurable  effect  on the
viruses, and the virucidal effect of NH4+
was insignificant compared with that of
NH3. The bacteriophage f2 was approxi-
mately  4.5 times  more resistant to  the
effects  of NH3 than was poliovirus.
  A general rate equation was derived
for virus inactivation as influenced by
NH3 concentration. Although NH3  is a
weak disinfectant, it may be a practical
virucide. Temperature  strongly influ-
enced inactivation rate. Poliovirus  was
inactivated at a greater rate than f2, but
the change in  the  rate of inactivation
with increasing temperature in the
range of approximately 10 to 40C was
greater for poliovirus. At higher temper-
atures, the rate of change was greater
for poliovirus. Arrhenius plots of the
data were biphasic, indicating that two
inactivation  processes  were occurring
at 300  mg/L NH3one  for the low-
temperature range and another for the
high-temperature  range (Figure 1).
However, the magnitudes of the ther-
modynamic variables for f2 were low
enough, as calculated for the low (10 to
35C) and high (35 to 60C) phases, that
inactivation could have  occurred by
breakage of nucleic acid chains. For po-
liovirus, the sizes indicated possible in-
volvement of nucleic acid at the low
range (10 to 40C)  but some unkown
mechanism for the high range (40 and
50C). The study concluded that inacti-
vation by IMH3 could play  an important
role in  the destruction of viral patho-
gens in  sludge.

Effects of Sludge and Compost
on Soil Enzymatic Activity
  Soil enzymes are important factors in
plant nutrient mineralization. They may




 *    o






Figure 1.
      be temporarily or permanently im-
      paired by soil amendments that contain
      excessive amounts of heavy metals or
      organic chemicals. A study was initiated
      to quantitate and compare the effects of
      various  sewage  sludges and sludge
      composts on important soil enzymes
      such as dehydrogenase, urease, and al-
      kaline phosphatase.
        A high-metal, high-organic chemical
      sewage sludge and its composted coun-
      terpart were tested to determine their
      effects on soil enzymatic activity. Dehy-
      drogenase activity and rate of C02 evo-
      lution of the amended soils were closely
      correlated with respect to amendment
      type and rate, and  no inhibition was ap-
      parent.  Phosphatase  activity  of all
      amendments was correlated to C02
      evolution. Net urease activity was corre-
      lated to amendment type (degree of sta-
      bilization)  and rate, and it showed no
      apparent inhibition.
        The relative level of heavy metals or
      organic chemicals therefore may not be
      a suitable indicator of the biological ef-
      fects of sewage sludge  and  sewage
      sludge composts.  Several studies have
      indicated  that inorganic metal  salts
      have inhibiting effects on enzymes,
      some at very low concentrations. These
      data indicate that, through time, metals
      are bound or chelated with organic mat-
      ter and that organic chemicals are par-
      tially degraded or  neutralized, resulting
3.2          3.3

            The relationship between the  inactivation rate constant (kj and temperature
           ( Kelvin) for f2 and poliovirus 1 (Chat).

in little or no inhibitory effect on biolog-
ical processes such as enzyme activity.

Effects of Sewage Sludge
Applications on Nitrogen
Mineralization and Phosphorus
Mobility in Soils
  Sewage sludges contain a wide range
of essential plant nutrients. Recycling
these nutrients on agricultural land can
augment commercial fertilizer sources
and thereby conserve the energy used
in their production.
  In 1978, the W-124 Regional Commit-
tee formulated a cooperative, 5-year re-
search project on the land application of
sewage sludge to answer the questions
concerning  the effects of soil type and
climate on N mineralization and P mo-
  The field  data collected at Beltsville,
Maryland, generally indicated that a 20-
Mg/ha annual application rate resulted
in yields similar to those from the rec-
ommended fertilizer application  rate,
but that slightly more N was taken up by
the  plants growing on plots receiving
sludge. The 20-Mg/ha annual  applica-
tion  resulted in a greater cumulative
yield and N uptake than the single 100-
Mg/ha application added to the plots in
1978. The application of N on the split
plots in 1981 resulted in larger, but not
significant, yield increases and N uptake
increases in most instances. During the
first and second years, phosphorus up-
take was greater in the 100-Mg/ha  plots
than in the  20-Mg/ha plots. The uptake
for the third through the fifth years was
the same for each treatment.
  Soil samples were taken with depth
after the harvest in 1983 and compared
with soil samples taken from the plots in
1978 before sludge application. Migra-
tion of N was detected to the deepest
sampling depth, which varied from 60
to 180 cm in all N~ and sludge-fertilized
plots. Phosphorus migration down to 60
cm was found in plots receiving sludge
  The movement of P does not pose a
problem  and may even  be beneficial.
The depth of P movement is within the
root zone and below the level of incor-
poration. Plants should therefore bene-
fit from the deeper  soil horizons con-
taining P.
Effect of Temperature and
Aeration on the Composting
  Composting is a process that is self-
starting, self-heating, and in certain cir-
cumstances, self-limiting. In general,
the variables that control or affect com-
posting are  the quality of the starting
materials, moisture, aeration, pH, and
  In the process of removing  water
from composts, heat is  concomitantly
removed. Vaporization is the dominant
heat removal mechanism,  removing
nearly  nine times more heat than con-
vection. Evaporation can  be accelerated
by turning piles or by increasing the aer-
ation rate. Thus the control of tempera-
ture is  best accomplished through con-
trol of vaporization  or moisture
  A laboratory composter that uses
thermistors as temperature-sensing
devices and an aeration  system, which
permits diffusion  of air into the mass,
was designed for testing  parameters to
improve the composting system. Raw,
highly  limed filter cake sludge from the
Blue Plains Wastewater Treatment plant
(Table 1) was mixed with woodchips in
a ratio of 1:1.8 (v/v) and composted.
Aeration was controlled either at preset
airflow rates or according to the de-
mand  necessary to hold the tempera-
ture desired. One study limited the tem-
perature of the insulating water bath to
55C, thereby preventing the compost-
ing organic material from reaching
60C.  A second  study aerated the
sludge-woodchip mixture at 900 or 1800
m3/h per Mg and compared tempera-
tures, moisture, volatile solids, and C02
loss. A third composter  study directly
compared composting of a sludge-
woodchip mixture under constant aera-
tion with that of a temperature-demand
  Carbon dioxide data  indicated that
the water-bath-controlled,  55C  com-
poster produced 50% more C02 than
the uncontrolled  composter that
reached 80C, probably by having a
more diverse population to degrade a
greater variety of compounds in the
mixture  (Table 1). The data obtained
from the study at two aeration rates in-
dicated that continuous  rapid aeration
did reduce peak temperatures, but it
also reduced the duration of the  com-
posting process.  In the temperature-
demand study, 2.5 times more sub-
strate decomposed than in the constant
aeration composter.  The final moisture
content of the compost from the
temperature-demand study was 33%.
  Constant, high  aeration did reduce
peak temperatures, but it did not result
in the most efficient composting  sys-
tem. Increasing and decreasing the aer-
ation rates to keep temperatures be-
tween  50 and  55C  allowed the
maximum thermophilic  population to
remain active for extended periods.
  The microbial data indicated that high
temperatures (>65C)  decreased  both
total number and diversity  of popula-
tion, which resulted in a substantial de-
cline in C02-C evolution or stabilization.
The disappearance of fungi from the
high-temperature composts and the
significant difference in CO2 evolution
underlined  the importance of fungi in
the stabilization process and the neces-
Table 1.   Carbon, Nitrogen, and Moisture Losses During Composting of Raw, Limed Sewage
         Sludge and Woodchip Mixtures under Various Aeration and Temperature Condi-

                                         Material Losses (%)
Bath controlled at 55C
900 m3/h per Mg
constant aeration
900 m3/h per Mg
constant aeration
1800 m3/h per Mg
constant aeration
Final %
900 m3/h per Mg
  constant aeration
Temperature, demand
'Grams of COZ-C lost per 100 g dry initial mixture.
*Error was due to inaccurate moisture determination.

sity of a successful compost operation
for controlling temperatures as much as
  Nitrogen loss from organic material
composting has not been studied exten-
sively, and from the data collected in
these studies, the amount of N lost was
proportional to condensate loss. Thus
increased aeration leads to increased
loss of nitrogen, but if the N loss is ac-
companied  by  an increased  loss of
volatile solids (as in the temperature-
demand study), the N content of the
final product changes only slightly.

Nutritional and Non-Nutritional
Factors in  the Growth of As-
pergillus fumigatus (AF) and
Natural Sources of Airborne AF
and Thermophilic Actino-
  The potential public health risk asso-
ciated with aerosols of Aspergillus fu-
migatus (AF) that cound  be inhaled at
sludge-composting  sites has  been a
concern to those who are responsible
for the planning and operation  of com-
post facilities. Information about the
ambient levels of AF spores in air could
be used to help evaluate the potential
impact of the aerosols on the public
health in adjacent areas.
  The work  reported here was under-
taken to increase the data base on the
quantitative differences in airborne lev-
els of AF under environmental circum-
stances that affect the growth of the fun-
gus. An extensive  literature survey was
made to determine the present knowl-
edge of the occurrence of AF in the air.
Then a series of air samples was  col-
lected from various locations (including
some suspected natural  sources) and
analyzed for viable AF.
  Studies were also made of the nutri-
tional and  non-nutritional factors in
sewage  sludge composting that affect
the growth of AF. This part of the work
aimed  to determine whether  or not
there was a  basis for managing the
composting process to produce a mini-
mum of AF growth and aerosols.
  Finally, to answer concerns about the
exposure of compost-site workers to
farmer's lung antigens  (thermophilic
actinomycetes, or TA),  air levels of
these microbes were determined con-
currently with those made for AF in the
different ambient environments.

Air Sampling for Fungi and TA
  Selected for study were habitats in
which environmental conditions were
 conducive to the growth of AF and TA.
 Air samples were obtained by using An-
 dersen six-stage, viable (microbial) par-
 ticle samplers (Andersen 2000, Inc., At-
 lanta, Georgia).* Twenty-one outdoor
 and indoor suspected sources and three
 unsuspected (reference) sources were

 Nutritional and Non-Nutritional
 Factors Affecting the Growth
  An investigation was made of the tol-
 erance limits on factors that affect the
 germination, growth, and sporulation of
 AF. The object was to suggest practical
 modes  of imposing  environmental
 stress on the organism in the compost-
 ing situation.

 Natural Airspora of AF
  The airspora  levels  of the different
 sampling sites  during each season ap-
 pear in Table 2. During winter, the air-
*Mention of trade names or commercial products
 does not constitute endorsement or recommenda-
 tion for use.
           spora in outdoor locations was gener-
           ally lower than that during other
           seasons. AF levels at the reference sites
           were also lower in winter than in sum-
           mer, and they were never greater than
           12 colony-forming units (cfu)/m3.
           Substrate Studies
             Several types of wood common to the
           mid-Atlantic region  of the United
           States, as well as oak leaves, paper pel-
           lets and cubes, and peanut hulls are ex-
           cellent substrates for AF growth  and
           sporulation when sufficient  moisture
           and  temperature are provided.

           Temperature Studies
             All of the seven isolates grew poorly
           at 55C and very slowly at 59C. At 45C,
           the growth rate was 6 to 8 times greater
           than that at 50C.

           Gaseous Environment and pH
             In chambers containing 0.5% 02 and
           23% CO2, AF spores  germinated  and
           mycelial extension  was equivalent to
           that observed on the control plates incu-
 Table 2.   Natural Airspora of Aspergillus fumigatus, 1979-80

                               Seasonal Counts (colony-forming units/m3)

During mowing
With mulch
Under trees
Of hospital
Of park
Wood area:
Nature trail
Corn field
Poultry house
Mushroom house
Brush pile
Municipal dump
Supermarket dumpster
Potting room
Low humidity
High humidity
Library stacks
Zoo - birdhouse
Boiler room
Reference sites:
School playground
University parking lot
Shopping center





















67, 100



*NS = not sampled.

  bated in air at ambient temperature.
  However, only a very limited number of
1  conidiophores and spores were pro-
  duced. Rapid growth and  sporulation
  occur at pH 6, 7, and 8, but decreased
  growth rate and sporulation are evident
  at pH 9 and 10.

  Osmotic Potential
    Decreased growth rate occurred at all
  temperatures  when the osmotic poten-
  tial of the growth medium was less than
  -40 x 102 kPa.

  Natural Airspora of TA
    Most outdoor and  indoor locations
  had fewer than 10 TA cfu/m3. Excep-
  tions  included the mushroom house,
  barn,  barnyard, and poultry house. TA
  from  other locations belonged to the
  genus Streptomyces,  and an identifica-
  tion scheme for the group was devised
  based on test  results from the type spe-
  cies and 55 compost and 35 natural air-
  spora strains.
    Results of these studies show that AF
  and TA are present in air  at very low
  levels in most nonagricultural sites,
  even if organic matter and occasionally
  higher-than-ambient temperatures are
  present also.  Thus the natural sources
  for AF and TA are very limited  in terms
  of abundant production of spores. Few
  spores are airborne  from  the natural
  sources, even during mechanical distur-
  bances such as mowing. High  levels of
  AF and TA in air are associated with
  heavily colonized  substrates. Compost
  and moldy agricultural  substrates are
  the biggest reservoirs and sources of AF
  and TA.
    Practical alterations of the sewage-
  sludge composting process to reduce
  AF growth and dispersal from compost
  sites should presently focus on the use
  of noncellulosic bulking  agents. Such
  agents would substantially reduce the
  inoculum levels entering the  process.
  The tolerance of AF to broad ranges of
  temperature,  CC>2, and water content
  limit the benefits of modifying the com-
  posting process by these parameters to
  inhibit this microbe.

    Ammonia was shown to  be virucidal
  in sludge and in NH4C1 solutions. Tem-
  perature  effects on NH3 activity were
  biphasic, indicating that two inactiva-
  tion processes were occurringone for
  the low-temperature range and another
  for the high-temperature range. The f2
  virus  was 5.4 times more  affected by
  NH3 than was poliovirus 1. As a viru-
cide, NH3 is extremely weak compared
with chlorine. Because of its high reac-
tivity with organic material, chlorine is
required in high dosages to  disinfect
sludge.  These translate into high chlo-
ride levels in the final sludge. The use of
NH3 to disinfect wastewater treatment
plant effluents is precluded by the slow-
ness of  its reaction;  but in sludge, NH3
may indeed be a practical virucide.
  The effects of  two types of sludges
and their corresponding  sludge com-
posts on soil enzyme activities indicated
that the  stabilization level of the sludge
correlated negatively with enzyme ac-
tivity. One sludge that was stored in a
lagoon for several years and contained
high concentrations of heavy metals
and chlorinated organic materials
showed no significant inhibitory effect
on soil enzyme activity. The reason was
probably that the sludge and the corre-
sponding sludge compost were highly
stabilized, with the  toxic components
either degraded or  bound to organic
  Soil profile data indicated that when a
digested sewage sludge was applied
once at 100 Mg/ha or annually at 20 Mg/
ha for 5  years, mineralized N exceeding
plant needs was found below the root
zone. The addition of fertilizer  N to split
plots increased the level of mineralized
N in the  deep soil profile. Phosphorus in
the sewage sludge also migrated down
the soil profile,  but not  to the same
depths as N. The 20-Mg/ha application
rate exceeded the nutrient needs of bar-
  A self-heating  laboratory composter
was designed, built, and used  success-
fully in studies of test methods for  im-
proving  the efficiency of composting.
The most efficient composting system
tested was one that adjusted aeration to
hold temperatures near or below 55C.
This system produced 2.5 times more
decomposition and 2 times more mois-
ture loss from the compost than did a
compost system  using a  constant rate
of aeration. The loss  of N from  the com-
post was directly related to  the  effi-
ciency of removing moisture.

  AF and TA are present  in air at very
low levels at most nonagricultural sites,
even if organic matter and occasionally
higher-than-ambient temperatures are
also present. Thus the natural sources
for AF and TA are very limited  in terms
of abundant production of spores. Com-
post and moldy agricultural substrates
are the biggest reservoirs and sources
of these  organisms. The tolerance of AF
to broad ranges of temperature, C02,
and water content limits the benefits of
modifying the composting process by
these parameters to inhibit the microbe.

  Ammonium was shown to be viruci-
dal tof2 bacteriophage and poliovirus 1.
The effect of NH3 on the inactivation of
several  human pathogens needs to be
evaluated before recommendations can
be made on the use of NH3 for reducing
pathogen numbers in sewage sludge.
  Caution should be exercised in evalu-
ating the effects of heavy metals and
chlorinated organic materials in  sewage
sludge on soil biochemical  properties.
Factors  such  as age of the sludge and
the sludge treatment process should be
considered when evaluating the effects
of chemicals whose salts  are known to
be toxic to biological processes.
  The application  of sewage sludge to
agricultural land should be coordinated
with the crop's fertilizer need. Nitrogen
mineralization rates of the sludge and
soil should be determined, and applica-
tion rates should  be adjusted  accord-
ingly. Application rates based on P min-
eralization and movement  should be
considered in soils such as  sands that
do not fix appreciable amounts of P.
  A composting system should be de-
signed to be as efficient as possible.
That is,  it should result in a stabilized,
dry product in as short a period of time
as possible. Controlling temperatures
so that they do not exceed  55 to 60C by
adjusting aeration provides a highly ef-
ficient composting  system.  However,
destruction of pathogens  under such a
system needs to be evaluated in labora-
tory and field trials.
  The sewage sludge composting proc-
ess should be altered to use noncellu-
losic  bulking agents to reduce  AF
growth  and dispersal from compost
sites. Such agents would  substantially
reduce the inoculum levels entering the
  The full report was submitted in fulfill-
ment of Interagency Agreement No.
AD-12-F-2-534 by  the Agricultural Re-
search  Service, U.S. Department of
Agriculture under the sponsorship of
the U.S. Environmental Protection
                                                                              U. S. GOVERNMENT PRINTING OFFICE: 1986/646-116/20761

     L J. Sikora, P. D. Millner. and W. D. Burge are with Agricultural Research Service,
       U.S. Department of Agriculture, Beltsville, MD 20705.
     Kenneth Dot son is the EPA Project Officer (see below).
     The  complete  report,  entitled "Chemical and Microbial Aspects of Sludge
       Composting  and Land Application," (Order No. PB 85-243 186/AS; Cost:
       $16.95, subject to change) will be available only from:
             National Technical Information Service
             5285 Port Royal Road
             Springfield, VA22161
             Telephone: 703-487-4650
     The EPA Project Officer can be contacted at:
             Water Engineering Research Laboratory
             U.S. Environmental Protection Agency
             Cincinnati, OH 45268
United States
Environmental Protection
Center for Environmental Research
Cincinnati OH 45268
Official Business
Penalty for Private Use $300
          0000329   PS