United States
Environmental Protection
Agency
Industrial Environmental
Research Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S2'83-119 July 1984
&ER& Project Summary
Management of Industrial
Pollutants by Anaerobic
Processes
Alan W. Obayashi and Joseph M. Gorgan
A study was made of the anaerobic
degradation of organic matter to
methane, a byproduct which could
recommend wider use of the anaerobic
waste treatment as a short-term
solution for lessening U.S. demand for
oil in an energy crisis. The anaerobic
process requires less energy than does
the aerobic biological process which
does not produce a usable byproduct.
The study investigated two major
aspects of anaerobic treatment: devel-
opment of the process, and process
control parameters. Other areas of
study included biodegradation of
organic compounds, toxicity effects,
and microbial sulfur recovery.
This Project Summary was developed
by EPA's Industrial Environmental
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).
Anaerobic Treatment Processes
The anaerobic degradation of organic
matter to methane is a complex
interaction of three groups of bacteria
(illustrated in the full report). The first
group of bacteria are the fermentative
bacteria which hydrolize the complex
long chain organics and ferment them to
fatty acids, alcohols and other soluble
organics. The second group of bacteria
are the acetogenic bacteria which
degrade propionate and longer chain fatty
acids to acetate, H2 and C02- Presently
this is the only known pathway for long
chain fatty acids and alcohols, since there
are no documented cases of a
methogenic bacteria being isolated
which can degrade these organics di-
rectly to methane. For the third group of
bacteria, the methanogens, the
substrates for growth determined to date
are H2, acetate, formate and methanol.
A review of the literature suggests that
the rate limiting step in anaerobic
digestion may be the conversion of
propionic and acetic acid to methane gas.
However, one reference indicated that at
high solids retention times (greater than
10 days) the rate limiting step in the
digestion of sewage sludge at 35°C is the
hydrolysis of organic solids. The same
study reports that cellulose hydrolysis is
the rate limiting step in the digestion of
municipal solid wastes.
In spite of their present significance
and future potential, anaerobic waste
treatment processes have not enjoyed a
favorable reputation. This lack of popular-
ity stems from the many misconceptions
held by design engineers concerning the
microbiological and biochemical
fundamentals of the anaerobic digestion
process. Anaerobic waste treatment is
thought of by many as a sensitive process
which is easily upset and difficult to
control. The anaerobic digestion process
also has a reputation for producing
obnoxious odors and requiring long initial
startup periods and high temperatures
(35°C) for effective waste stabilization.
Another reason may be that direct
treatment processes have yet to be
proven on specific industrial effluents.
Nevertheless, anaerobic waste
treatment does have several fundamen-
tal advantages over aerobic biological
treatment processes. First, anaerobic
-------
treatment attains a high degree of waste
stabilization with very little sludge pro-
duction (less than 5% of the biodegrad-
able organic matter is converted to cell
material) which reduces the nutrient
requirement in the influent waste
stream. A second advantage of the
anaerobic process is that 90% of the
biodegradable fraction can be converted
to a usable end-product in the form of
methane (CH4) gas which can be used to
heat the waste stream to give a higher
rate of stabilization or to supplement
inplant power requirements. Using direct
anaerobic digestion processes,high
organic loadings along with short hy-
draulic retention times (three hours and
greater) can be achieved.
Because of the current energy situation
throughout the country and the need for
energy conservation, use of anaerobic
processes by industry will undoubtedly
increase. Many researchers see energy
conservation as the only practical short-
term solution for the U.S. to become self-
sufficient in energy production. More and
more interest is being evinced by the
anaerobic processes which require little
energy and supply a valuable power
source, methane gas. Anaerobic
biological processes on the other hand,
require a high energy input and produce
no usable byproduct.
In the final report, two major aspects of
anaerobic treatment are reported in detail:
the development of the processes and the
process control parameters. In the
development aspect, the anaerobic
processes are reviewed in a chronologi-
cal order, i.e., from the simplest to the
higher rate processes, e.g., anaerobic
sludge blanket process. The final report
also summarizes the application of
anaerobic processes to a variety of waste-
waters. In the process control aspect,
three areas are covered (1) pH and alka-
linity, (2) nutrient requirements, and (3)
temperature effects on biological
processes.
Biodegradation of Organic
Compounds by Anaerobic
Processes
Recent advances in technology have
led to the production of many new and
potentially dangerous compounds, some
of which eventually turn up as a
constituent in wastewater. Each of these
new substances, representing a wide
array of compounds ranging from
phenols to pesticides, presents problems
for its ultimate disposal. Wastewater
treatment plants are experiencing many
problems and challenges in dealing with
these hazardous wastes. Many new and
innovative techniques for their treatment,
including anaerobic processes, are being
investigated. As is the case in any waste
treatment method, anaerobic processes
will not breakdown all organic
compounds. In the final report, complete
details are presented on how anaerobic
processes function to breakdown large
numbers of organic wastes. Also, the
applicability of anaerobic processes to
new wastes are evaluated in a three-step
evaluation: (1) formulation of a definition
of the term biodegradation and setting of
standards for the degree of biodegrada-
tion; (2) a comparison of tests on aerobic
and anaerobic processes to determine
relative biodegradabilrty; and (3) a
summary of previous work involving the
biodegradation of organic by anaerobic
processes.
Toxicity Effects in Anaerobic
Processes
Adequate knowledge of the toxicity of
relevant toxins and inhibitors in any
biological process is essential for an
optimal application of the process.
Despite the many advantages of
anaerobic treatment, the application of
methane fermentation is not widely used
in this country for treatment of industrial
wastewaters.
Much of this reluctance to use an-
aerobic processes stems from the belief
that the methane fermentation systems
cannot tolerate the chronic or slug doses
of toxic substances found in industrial
wastewaters. The presence of toxicants
may have caused inhibition which even-
tually led to failure of the process, particu-
larly in the case of anaerobic sludge
digestion. However, it should not be
assumed that methanogens are more
sensitive to toxicants than facultative
organisms.
During the past fifteen years, there
have been numerous documented
studies of the possible inhibitory effects
on the anaerobic digestion process from
different compounds commonly found in
these systems. In many instances in
which digester performance had
decreased, the source of the upset could
be traced to the presence of a compound
that was inhibitory to the microorganisms
involved in the digestion process. These
compounds originate from waste streams
generated by the different industrial
processes.
The control of sulfur pollution is a
widespread problem associated mainly
with hydrocarbon processing and power
production. For example, the mining of
coal results in acid mine drainage, the
burning of coal results in CaSO4 sludges
(SO2 scrubbing) and coal and oil
desulfurization results in H2S waste
streams. Of the two forms of sulfur
pollution SO24 is a major problem with no
reliable method of control.
Microbial Sulfur Recovery
The problem with sulfur disposal are
related primarily to energy production
and, to a smaller extent, to the mining
industry. As more emphasis is placed on
the use of hydrocarbons such as oil and
coal for energy production, sulfur control
and disposal become a more pressing
problem.
One form of sulfur pollution is the
generation of CaSO4 sludges which is a
result of the scrubbing of flue gases from
coal fired plants. In addition, H2S waste
streams are generated from the desulfur-
ization of coal and oil. This problem is
generally handled by using physical-
chemical processes which convert the
H2S to elemental sulfur. Other more
limited areas in which high sulfates
(acidic wastes) are a problem include acid
mine drainage (coal mining), acid wastes
from mining operations, and wastes from
ethanol distilleries.
Currently, H2S waste streams are
handled by physical-chemical processes,
with the major objective being the
recovery of elemental sulfur. Presently,
when high sulfate wastewaters are
neutralized they are either discharged or
stored in lagoons where they continue to
be a problem.
The biological conversion of high
sulfate wastes or hydrogen sulfide waste
streams to the more desirable form of
elemental sulfur has not been developed
beyond the laboratory stage. The kinetics
of sulfate reduction and the kinetics of
hydrogen sulfide conversion to elemental
sulfur have been the subject of very few
published studies on the applied bio-
process production of elemental sulfur.
These studies are discussed in more
detail in the final report. Also, a brief
summary of the microbiology of sulfur
transformations is presented in the final
report.
Microbiology of Sulfur
Transformations
All organisms require sulfur with the
major need in the incorporation of sulfur
-------
in proterns. In addition, microorganisms
can use sulfur in a manner similar to the
way that organisms use the various forms
of nitrogen; that is, as both an energy
source and as an electron acceptor. The
various oxidation states and the forrns in
which sulfur exists in the environment
are discussed in the final report. Of
particular interest is the anaerobic
portion of the cycle, the reduction of
sulfate to hydrogen sulfide, and the
oxidation of sulfides to elemental sulfur.
Alan W. Obayashi and Joseph M. Gorgan are with the Illinois Institute of
Technology, Chicago, IL 60616.
William A. Cawley is the EPA Project Officer (see below).
The complete report, entitled "Management of Industrial Pollutants by Anaerobic
Processes," (Order No. PB84-133 024; Cost: $22.00, 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:
Industrial Environmental Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
US'GOVERNMENT PRINTING OFFICE; 1984 — 759-015/7750
-------
United States Center for Environmental Research
Environmental Protection Information
Agency Cincinnati OH 45268
Official Business
Penalty for Private Use $300
AGENCY
REtlUN 5 LiBKAKY
230 S DEARtlORN STREET
CHICAGO IL 60604
------- |