United States
Environmental Protection
Agency
Water Engineering
Research Laboratory
Cincinnati OH 45268
Research and Development
EPA/600/S2-86/023 Apr. 1986
v>EPA Project Summary
Large Soil Absorption Systems
for Wastewaters from Multiple-
Home Developments
Robert L Siegrist, Damann L Anderson, and David L Hargett
A study was conducted to evaluate
community-scale soil absorption
systems for treating and disposing of
wastewaters. Included were a survey of
current state attitudes and policies, an
overview of a number of large soil
absorption systems, and an in-depth
analysis of one system. Study
objectives were to assess the
performance of existing large-scale
absorption systems, to comment on the
viability of presently used design
methods, and to suggest improved
approaches to design.
This Project Summary was developed
by EPA's Water Engineering Research
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
back).
Introduction
Large subsurface soil absorption
systems (LSAS's) for treatment and
disposal of wastewater from subdivisions
and small communities are becoming
increasingly popular. These systems are
being designed as permanent means of
wastewater management, not as interim
solutions to be used until conventional
treatment technologies arrive.
The design and operation practices of
large, multiple-home soil absorption
systems appear simply to have evolved
•from the laboratory and field experience
gained with small, single-home systems.
However, the suitability of this practice
remains in question without field
experience involving community-scale
systems. As the size of a subsurface soil
absorption system increases to handle
the wastewater from a small community,
the design, construction, and
management practices necessary to
ensure acceptable performance become
less clear.
Procedures
The objectives of this study were to
investigate the performance of
community-scale soil absorption
systems, to identify potential deficiencies
in presently used design criteria, and to
develop recommendations regarding
design and operation practices. More
specifically, the project endeavored to
accomplish the following.
1. To determine the current attitudes,
policies, and level of use of
community-scale subsurface
wastewater absorption systems;
2. To investigate in detail the
performance characteristics of the
community wastewater absorption
system at Westboro, Wisconsin;
and
3. To characterize generally a number
of multiple-home wastewater
absorption systems in Washington.
This study was accomplished between
June 1981 and December 1983 through
the combined efforts of staff members
from several organizations.
Conclusions
1. Design infiltration rates for long-
term successful operation of
LSAS's are not well defined.
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2. Anaerobic conditions may
predominate below LSAS's, even
in sandy soils. Narrow, shallow
trenches may be required to obtain
aerobic environments.
3. Septic tank effluent may load
LSAS's too heavily, requiring a
higher degree of treatment to
remove excess organics,
suspended solids, etc., before
LSAS treatment. Criteria for
individual home wastewater
systems are clearly inadequate for
LSAS's.
4. Groundwater mounding may
present a severe hindrance to
proper wastewater treatment by
the LSAS. Present methods of
predicting the degree of
groundwater mounding under-
estimated the actual conditions
found.
5. Percolation testing as presently
practiced was inadequate for LSAS
design, and the use of vertical
hydraulic conductivity curves for
long-term acceptance rates was
also in error.
Recommendations
Based on this study, the following
recommendations are made for
engineering LSAS systems:
Site Evaluation
1. Use professional soil scientists.
2. Inspect soil morphology to a depth
of at least 2 m below the system
bottom.
3. Allow at least 1.5 m of unsaturated
soil below the system bottom.
Design
1. Flow should be based on design
population.
2. Shallow trenches should be used
instead of beds.
3. A minimum of three absorption
systems should be used to permit
resting cycles.
4. Infiltration rates should be
conservative and based on entire
site soil morphology and hydraulic
capacity.
Installation
1. Installation should be accomplish-
ed as quickly as possible to
minimize exposure of the
infiltrative surface.
2. Construction machinery (either
tired or tracked) travel over the
infiltrative area should be
prohibited, even if a thin layer of
gravel or sand covers that surface.
Operation
Rotate systems between resting and
dosing on an annual basis, avoiding cold
weather rotation; or initiate system
resting at the first sign of ponding.
Monitoring
1. Monitor LSAS influent flows at
least monthly to determine
loadings.
2. Characterize influent COD, TSS,
NH4, pH and grease initially and at
least annually thereafter.
3. Inspect LSAS's for ponding and
dosing at least monthly.
4. Monitor groundwater elevations at
least quarterly.
The full report was submitted in partial
fulfillment of Contract No. 68-03-3057
by Rural Systems Engineering, Inc.,
under the sponsorship of the U.S.
Environmental Protection Agency.
Robert L Siegrist, Damann L. Anderson, and David L Hargett are with RSE Group,
Madison, Wl 53704.
James F. Kreissl is the EPA Project Officer (see below).
The complete report, entitled "Large Soil Absorption Systems for Wastewaters
from Multiple-Home Developments," (Order No. PB 86-164 084/AS; Cost:
$16.95, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal/Road
Springfield, VAJ&161
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
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
>'\ : si <* f!jieT».f
-•,T-W,LTV j li.V.'-UvMMS
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Official Business
Penalty for Private Use $300
EPA/600/S2-86/023
0000329 PS
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United States
Environmental Protection
Agency
Water Engineering
Research Laboratory
Cincinnati, OH 45268
Research and Development
EPA/600/S2-86/025 May 1986
&EPA Project Summary
Microbial Activity in
Composting Municipal
Sewage Sludge
J. Robie Vestal and Vicky L McKinley
Research was conducted to identify the
most important operational parameters
that limit the growth and decomposition
activity of composting sludge microbiota.
Sensitive and nonselective biochemical
methods of monitoring microbial biomass
and activity were tested and used to study
the interactions between the microbial
communities and temperature, the primary
factor affecting their activity during com-
posting. Optimum temperatures for
microbial activity and biomass were
generally within the 35° to 55 °C range.
Biokinetic analyses revealed that compost
samples from low-temperature (25° to
45 °C) areas of the pile had much greater
microbial activity (measured as the rate of
incorporation or mineralization of (14C)
substrates) than did samples from high-
temperature (60° to 75°C) areas. The
microbial communities became better
adapted to increasing temperatures as
composting progressed, but their tem-
perature optimum was never greater than
55 °C. Biomass was monitored by measur-
ing the lipid phosphate content (an impor-
tant cell membrane component) of the
compost. Other parameters that were
measured included the moisture content,
total organic content, total protein con-
tent, and pH.
This Project Summary was developed
by EPA's Water Engineering Research
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 order-
ing information at back).
Introduction
Large aggregations of organic-rich mat-
ter have long been known to heat up and
become increasingly humified over ex-
tended periods. These effects are brought
about by the activity of the indigenous
microbial community, which decomposes
the usable matter for energy and growth
substrates, producing metabolic heat as a
byproduct. In organic piles of sufficient
size and insulation, this metabolic heat is
trapped and can elevate the temperatures
within the pile to in excess of 80 °C within
a few days. The production of composted
material through this process has been a
means of recycling organic waste products
throughout much of history. Recently the
process has become an important means
of disposing of municipal solid waste and
sewage sludge. The primary goals of com-
posting in solid waste management are to
rapidly reduce the pathogens, odors,
putrescible organic matter, moisture, and
bulk, and to produce a biologically stabil-
ized material.
No general agreement has yet been
reached on the best conditions and pro-
cedures for optimizing the efficiency of
decomposition (stabilization) during the
composting process, so a wide variety of
methods are currently practiced. However,
temperature is generally agreed to be
the most critical parameter influencing the
rate of composting and the quality of the
product, given reasonable initial environ-
mental conditions of moisture, free air
space, pH and nutrients, and provided that
oxygen does not become generally
limiting.
Many of the findings on optimum
temperatures for maximum decomposition
rate during composting have been in con-
flict. These discrepancies may be partly
due to the indirect and incomplete nature
of many of the studies concerning micro-
bial activity and biomass in composting
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material. Direct comparisons of decom-
position rate between different tem-
perature regimes require experimental
arrangements unrelated to the practice of
composting and produce unrealistic re-
sults. Estimates of microbial decom-
position in composting material have
typically been made using such indirect
indices as the overall temperature of the
composting pile, odors, moisture content,
carbon dioxide evolution from the com-
posting pile, or oxygen uptake by the
compostion pila In most cases, concurrent
assessments of microbial biomass were
not made, or they were aimed only at
quantifying the numbers of surviving
pathogens or other specific groups using
selective isolation techniques.
The purpose of this study was to pro-
vide a better understanding of the factors
influencing the microbial activities in com-
posting sewage sludge. The activity and
biomass of the microbial community as a
whole were accurately and consistently
measured to permit conclusions to be
made about an optimal temperature range
for rapid decomposition during com-
posting. Basic information leading to a bet-
ter understanding of rapid thermogenic
microbial successions was also obtained.
Results and Discussion
Composting was done in a full-sized
commercial composting bin using forced
aeration to regulate the overall temper-
atures of the piles. Each batch composting
run lasted approximately 2.5 weeks, dur-
ing which the material was removed and
turned once or twice.
The microbiota of composting municipal
sewage sludge from Columbus or Akron,
Ohio, was analyzed during 10 different
composting runs. A temperature gradient
existed within the composting piles, with
the central areas near the surface of the
piles being the hottest. On each sampling
day, samples were taken from several dif-
ferent areas, each with a different sam-
pling temperature. In every case, a
decrease in microbial activity occurred as
temperature increased, with overall op-
timum temperatures falling between 35°
and 55 °C. Microbial activity was
measured as the hourly rate of (14C)
acetate incorporation into microbial lipids
per /jmol of lipid phosphate biomass. The
changes in this microbial activity rate in
response to compost sampling temper-
atures during run No. 6 (see Figure 1) are
typical. Microbial biomass also decreased
with increasing temperature in most of the
compostitig runs. The biomass data from
run No. 6 (Figure 2) are typical. The same
0.14
0.10
I
g 0.06
^
|
o
,$J 0.02
I
20
40
Temperature (°C)
60
Figure 1.
Microbial activity, measured as the rate ofC*C) acetate incorporation into lipids pe
hour per umol of lipid phosphate biomass x10'\ of pooled sewage sludge compoi
samples in response to the mean sampling temperature of the pooled sample
during composting run No. 6. Sampling days are indicated by the number
associated with the data points. Activity values are the mean ± one standar
deviation of three replicates.
trends in microbial activity were found for
all of the substrates tested ((14C) acetate,
glucose, and glutamate), and the results
were similar whether the data were ex-
pressed in terms of biomass (per /^mol of
lipid phosphate biomass) or in terms of the
amounts of compost (per gram of dry
compost).
Of all the physical and chemical pa-
ramters measured during this study,
temperature had the most dramatic and
consistent effects on microbial biomass
and activity. Microbial activity and
biomass also correlated with the pH of the
compost, indicating that pH may be an in-
direct indicator of microbial activity. The
typical increases in pH during composting
are primarily a result of microbial activity,
and in addition, the microbiota may be
more active at the neutral-to-slightly
alkaline pH values found later in the runs.
This hypothesis was not tested directly
during this study, however.
During four of the composting runs,
each composting pile was divided into a
low-temperature section (mean pile
temperature ^L 55 ° to 60 °C) and a high-
temperature section (mean pile tem-
peratures up to 70 °C). Microbial activit
and biomass were higher in the low
temperature section, even when sample:
taken from the high-temperature sectioi
came from the same samplm;
temperature.
An experiment was designed to deter
mine the optimum temperatures for th<
activities of the microbial communitiei
from various temperature zones in th<
composting pile. Activities in samples f ran
low-temperature areas (25° to 50 °C) o
the pile were almost always much highe
than those in samples from high
temperature areas (60° to 75 °C), regard
less of the assay's incubation temperature
When incubated at different temperature;
during the incorporation assay, thi
samples from low-temperature areas o
the pile exhibited optimum thermal activit
at 30 ° to 55 °C. Not only did samples f ran
high-temperature areas have much lowe
levels of activity, many did not respond a
all to varied incubation temperatures, in
dicating that the microbial population:
were probably very debilitated. As com
posting progressed, the optimun
temperatures increased somewhat, in
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40
Temperature f°C/
i
60
2. Nonselective, responsive, and sen-
sitive methods for analyzing
microbial activity and biomass
should be used to monitor the pro-
cess when necessary.
The full report was submitted in fulfill-
ment of Cooperative Agreement
CR-807852-01-0 by the University of
Cincinnati under the sponsorship of the
U.S. Environmental Protection Agency.
Figure 2. Microbial biomass, measured as the lipid phosphate concentration, of pooled
sewage sludge compost samples in response to the mean sampling temperature of
the pooled samples during composting run No. 6. Samp/ing days are indicated by the
numbers associated with the data points. Biomass values are the mean ± one
standard deviation fn=3).
dicating that the microbial communities
were adapting to the higher temperatures.
Nonetheless, optimum temperatures of
the communities never exceeded about
55 °C, even in the samples from the high-
temperature areas.
Conclusions and
Recommendations
The major conclusions of this study in-
clude the following:
1. The optimum temperature range for
composting sewage sludge in a
forced-aeration batch, static-pile
system appears to be 35 ° or 45 ° to
55 °C. The lower limits of this range
are much less distinct than the up-
per limits. These conclusions are
based on measurements of the levels
of microbial activity (rates of (14C)
substrate incorporation or mineraliza-
tion) and biomass (lipid phosphate
concentration). Microbial activity and
biomass dropped off very rapidly as
composting temperatures exceeded
55 °C. Other indirect and much less
responsive indicators of microbial ac-
tivity and biomass (such as the com-
post pH and protein concentrations)
were also maximized within this
temperature range. The minimum
levels of microbial activity were
always found in compost samples at
very high temperatures (> 60°C).
2. As composting progressed, evidence
showed that the microbiota were
adapting to higher temperatures, but
no microbial communities acclimated
to temperatures above 55 °C. No
evidence indicated that extremely
thermophilic organisms (those with
optimum temperatures above 60 °C)
played a measurable role in
composting.
3. Compared with piles composted si-
multaneously at 60° to 85 °C, piles
aerated to maintain temperatures at
or below about 55 °C showed signifi-
cant improvements in the rates of
microbial metabolism and growth.
The recommendations that naturally
follow from these conclustions include the
following:
1. Composting should be done at
temperatures within the stated op-
timum range whenever possible.
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J, Robie Vestal and Vicky L McKinley are with the University of Cincinnati,
Cincinnati, OH 45221.
AtalE. Eralp is the EPA Project Officer (see below).
The complete report, entitled "Microbial Activity in Composting Municipal
Sewage Sludge," (Order No. PB 86-166 014/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
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
BULK RATE
POSTAGE & FEES
EPA
PERMIT No. G-
Official Business
Penalty for Private Use S300
EPA/600/S2-86/025
01*9044
60604
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