USSR-USA JOINT COMMITTEE
ON COOPERATION IN THE
FIELD Of ENVIRONMENTAL PROTCTON
SYMPOSIUM
HANDLING TREATMENT AND DISPOSAL OF
WASTEWATEP SLUDGE
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USSR-USA JOINT COMMITTEE
ON COOPERATION IN THE
FIELD OF ENVIRONMENTAL PROTECTION
USA/USSR SYMPOSIUM
HANDLING, TREATMENT AND DISPOSAL OF WASTEWATER SLUDGE
MOSCOW, USSR
May 13-16, 1975
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PREFACE
The first cooperative USA/USSR symposium on municipal and industrial wastewater sludge was held
in Moscow, USSR from May 13 thru May 16, 1975. This symposium was conducted in accord with the
protocol of the Third Session of the Joint USA/USSR Commission held in Moscow on December 12,1974.
This symposium was sponsored under the auspices of the Working Group on the Prevention of Water
Pollution from Municipal and Industrial Sources. The United States delegation was headed by Harold P.
Cahill of the United States Environmental Protection Agency and the Soviet delegation was headed by
Professor S. Yakovlev of the All Union Research Institute on Water Supply and Sewerage.
Of the eighteen papers, sixteen are reprinted in English in this volume. The paper presented by
Turovsky was never furnished. The paper scheduled for presentation by Ostrovsky was canceled and, to
date, we have not received copies of these two papers.
This volume is reprinted in English in accord with the protocol signed by the delegation leaders on
May 26,1975 in Moscow, USSR.
ii
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INDEX
PAPERS PRESENTED AT THE
USA/USSR SYMPOSIUM
"HANDLING, TREATMENT AND DISPOSAL OF WASTEWATER SLUDGE"
(Moscow, May 13-16, 1975)
NO. PAPER PAGE
1 Seabrook, Belford L. and Whittington, William A., (US EPA), "POLICY ON MUNICIPAL SLUDGES." . 1
2 Sebastian, Frank P. (US EPA), "SLUDGE INCINERATION SYSTEMS FOR PURIFICATION AND
RESOURCE RECOVERY." 8
3 loakimis, E. G. and Davletov, A. D., (Bashkirian Scientific Research Institute of Petroleum Refining),
"MANAGEMENT OF OIL SLUDGE FROM A REFINERY WASTE WATER TREATMENT PLANT." . 27
4 Altovsky, G.S., (All-Union Scnentific Research Institute, VODGEO), "MODERN STATE AND
PRINCIPAL TRENDS IN TECHNOLOGY DEVELOPMENT FOR WASHINGTON SLUDGE TREATMENT." 36
5 Lacy, William J. and Cywin, Allen, (US EPA), "MANAGEMENT AND DISPOSAL OF RESIDUALS
FROM TREATMENT OF INDUSTRIAL WASTEWATERS." 39
6 Cywin, Allen and Lacy, William J., (US EPA) "SLUDGE CONSIDERATIONS IN THE DEVELOPMENT
OF INDUSTRIAL EFFLUENT." 53
7 Dwinskih, E. V., (All-Union Scientific Research Institute, VODGEO), 'THICKENING AND DEWATER-
ING OF WASTE WATER SLUDGES BY VIBRO FILTRATION METHOD." 63
8 Smith, James E. and Rosenkranz, William A. (US EPA), "MUNICIPAL SLUDGE MANAGEMENT
RESEARCH PROGRAM IN THE U.S.A." 68
9 Lavrov, I. S., Feodorov, N. F., and Ponomareva, V. N., (Leningrad Civil Engineering Institute),
"INORGANIC SUSPENDED SLUDGE DEWATERING." 78
10 Agranonick, R. Ya., (Municipal Water Supply, Water and Sewage Treatment Research Institute),
"DEWATERING OF SEWAGE SLUDGE BY MEANS OF CENTRIFUGES." 81
II Goldfarb, L. L., (Municipal Water Supply, Water and Sewage Treatment Research Institute),
'THERMAL DRYING OF DEWATERED SEWAGE SLUDGE." 85
12 Abramov, A. V., (All-Union Scientific Research Institute, VODGEO), "AEROBIC STABILIZATION OF
ACTIVATED SLUDGE." 88
13 Dick, Richard I., (US EPA), "THICKENING OF SLUDGES." 93
14 Konrad, William N., (US EPA), "DISSOLVED AIR FLOTATION THICKENING AS PRACTICED IN
THEU.S.." 101
15 Lynam, Bart T., Lue-Hing, Cecil, Rimkus, Raymond R., and Neil, Forrest C. (US EPA), 'THE
UTILIZATION OF MUNICIPAL SLUDGE IN AGRICULTURE." 109
16 Pirogov, L. G., (All-Union Scientific Research Institute, VODGEO), 'THE DEPENDENCE OF
DEWATERING PROCESS ON AQUEOUS PROPERTIES OF SLUDGES." 144
iii
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The following papers were also submitted but were not
available for this printing.
NO. PAPER
17 Lukinyh, N. A. and Turovsky, I. S., (Institute of Municipal Water Supply and Water Treatment,
NIIKViOB) "MAIN PRINCIPLES OF SELECTION OF WASTEWATER SLUDGE TREATMENT
METHODS DEPENDING ON ITS PROPERTIES."
18 Ostrovsky, 0. P., Suprun, J. M., Reznikov Ju, N., (Gas and Wastewater Treatment Institute at Ferrous
Metallurgy, VNIPI Chermetenergoochist ka), "PROCESSING AND DISPOSAL OF INDUSTRIAL
SLUDGES FROM TREATMENT OF FERROUS METALLURGY WASTEWATERS."
iv
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U.S. ENVIRONMENTAL PROTECTION AGENCY
POLICY ON MUNICIPAL SLUDGES
BY
WILLIAM A. WHITTINGTON
ACTING CHIEF, MUNICIPAL TECHNOLOGY BRANCH
OFFICE OF WATER PROG RAM OPERATIONS
U.S. ENVIRONMENTAL PROTECTION AGENCY
SPEAKER
BELFORD L. SEABROOK
MUNICIPAL TECHNOLOGY BRANCH
MUNICIPAL CONSTRUCTION DIVISION
OFFICE OF WATER PROGRAM OPERATIONS
U.S. ENVIRONMENTAL PROTECTION AGENCY
PREPARED FOR
U.S./U.S.S.R. SEMINAR, "HANDLING,
TREATMENT AND DISPOSAL OF SLUDGES"
MOSCOW, U.S.S.R.
MAY 12-27,197 5
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U.S. Environmental Protection Agency
Policy on Municipal Sludges
INTRODUCTION
Passage of the Federal Water Pollution Control Act
Amendments of 1972 (Public Law 92-500) instituted a
broad national program for cleaning up waterways in the
United States. The new law creates a program based on
three major elements: uniform nationwide standards,
enforceable regulations, and a permit program based on
effluent limits and geared to specific goals.
The primary aim of the Act is to "restore and
maintain the chemical, physical and biological integrity
of the Nation's waters." Under the Act each publicly
owned treatment works is required to have a permit
before discharging to navigable waters. The permit is
based on EPA effluent limitations, but more stringent
requirements may be imposed to meet approved water
quality standards.
The requirements of the Act for higher levels of
wastewater treatment will result in a substantive increase
in the quantities sludge produced by publicly owned
treatment works. Disposition of these sludges is not
simple. Methods used in the past are now restricted by
specific laws or regulations, or are subject to other
constraints in view of new information of environmental
significance.
The treatment of wastewaters for pollutant removal
produces not only relatively clean water for discharge,
but also a significant quantity of residual material. For
domestic sewage, treated in publicly owned plants, this
residual is essentially organic in nature, although measur-
able quantities of metal, minerals, and other compounds
are also invariably present. Where industrial wastewaters
are treated together with domestic sewage, the potential
for additional foreign materials in the resultant sludge is
increased. Further, pathogen organisms in sewage may
survive the wastewater treatment process and remain in
the residual.
Depending upon the composition of the wastewater
treatment plant's sludge, the quantity involved, and the
disposal method, disposal of this residual material can
have an important impact on the environment. It is
essential for wastewater treatment installations to con-
sider the proper disposal of sludge produced as well as
the proper disposal of treated wastewater. The require-
ments of the Federal Water Pollution Control Act, as
amended, emphasize the need for environmentally sound
means for sludge disposal. The national requirements for
secondary treatment for example will not only result in
production of a greater quantity of sludge than before,
but will also result nationwide in greater quantities and
possibly more concentrated forms of contaminates
present in the sludge.
Disposition of wastewater treatment plant sludges can
affect simultaneous by air, land, and water and include
considerations of human health, animal health, plant
growth, and protection of ground and surface waters
from pollution. EPA Regional Administrators consider
these matters as they evaluate sludge disposal systems
included in the design of publicly owned treatment
works for which construction grant applications are
made. Despite the still limited information available on
the comples issue of sludge utilization and disposal, the
need for definition of a base line of acceptable practice
remains.
BACKGROUND
The effluent limitation applicable to municipal waste-
water treatment plants is secondary treatment. EPA has
defined secondary treatment as a maximum 30 day
average of 30 mg/1 of 5 day biochemical oxygen
demand and suspended solids, and a maximum 7 day
average of 45 mg/1 of BODS and suspended solids. This
higher degree of treatment will result in generation of
more sludge in municipal treatment works. Table 1
shows the estimated quantities of sludge currently being
produced in comparison with the quantities of sludge
anticipated after implementation of secondary treat-
ment.
It should be noted that the information in Table I is
reported in terms of dry weight of sludge. This is done
because the dry weight affords a convenient means of
providing a consistent comparison of different types of
sludges. Actually the sludge occurs, with various
amounts of water, as a liquid slurry ranging to a drier
filter cake. Table II shows typical volumes of sludges
from various treatment processes.
There are approximately 22,000 municipal plants in
the United States today. About 5,000 of these plants are
wastewater treatment ponds, which contain the sludge
within the pond and are only infrequently emptied. The
number of municipal plants generating sludge routinely
is approximately 17,000. Table III shows a distribution,
by volume of wastewater treated, of those plants.
The current disposition of municipal sludge is not
precisely known. There is, however, sufficient data to
permit a reasonable estimate of the disposition practices
actually being used at the present time. Table IV shows
those estimates.
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TECHNICAL APPROACH
hPA, continuing the work of its predecessor agencies,
has been developing environmentally acceptable meth-
ods lor the management of municipal sludge since the
enactment of the first Federal water pollution control
laws. The initial phases of the research program were
concerned with the characteristics and dewatcring prop-
erties of primary and secondary sludge because of the
need to dcwatcr sludge for ultimate disposal. The
current program emphasis has shifted toward the devel-
opment of improved technology for returning the
sludges to the environment in an ecologically acceptable
manner. Also, the agency is required new measures, such
as source control and pretreatment, which should reduce
the heavy metals problems associated with sewage
sludges.
The agency has been aware of the growing sludge
disposal problem and the need to verify and expand the
technology that is now being utilized.
For example, a long-term land application project has
been directed at determining the beneficial uses of
sludge for strip mine reclamation and for soil enrichment
in crop production. Because of the potential human
health hazards from heavy metals uptake in plants, these
studies have carefully monitored the heavy metals
uptake in various forest and green crops.
A large increase in the amount of sludge generated
has occurred with the use of chemical participants for
nutrient control in the upgrading of secondary treatment
facilities. The agency has been actively developing new
technology for solving the problem, including recovering
and reuse of the chemical activities.
EPA will continue its comprehensive research pro-
gram for municipal wastewatcr sludge processing, utili/.a-
tion, and disposal. This program will concentrate on
demonstration of technologies which will recycle for use
sludges, or recover residual contained in sludges. It seems
likely that within the next five years a new generation of
more nearly optimum sludge disposal or utilization
techniques will be available. In the interim there remains
a need fora statement and definition of environmentally
acceptable practice based on current knowledge.
In the guidance which EPA has drafted for the
Regional Administrators, no attempt has been made to
imply that the presently known methods are optimum
for sludge utilization or disposal, but rather to state that
die adverse environmental factors associated with each
method may be tolerable under certain site conditions.
The determination of acceptability is based on the
environmental assessment and, if necessary, the environ-
mental impact statement for the specific project.
The draft guidance is contained in a technical bulletin
entitled Municipal Sludge Management; Environmental
Factors. The bulletin is divided into two distinct parts.
The first part includes methods in which the sludge is
utili/.ed as a resource. The second part includes those
methods in which the sludge is not utilized for any
beneficial purpose.
Methods which appear to have great future promise,
but which have not been used in existing facilities, are
not included in this list. As these developing methods are
demonstrated in practical use, and as supporting infor-
mation is obtained, they will be added to the list of
acceptable methods. Because it is a policy of F.PA to
encourage and, where possible, assist in development of
new advanced wastewater treatment procedures, Federal
grants funds may be awarded for the construction of
sludge utilization or disposal facilities not in the bulletin,
provided sufficient information is presented by the grant
applicant to determine that these facilities would meet
applicable statutory and regulatory requirements and
would be environmentally acceptable.
The technical approach is similar for each of the four
methods listed in the bulletin. The criteria consider
existing regulations, intermedia environmental effect,
protection of public health, and monjtoring. Wherever
possible maximum use has been made of existing EPA
regulatory material or guidelines.
Another aspect of sludge management which is of
great importance is cost-effectiveness. This facet of
sludge management, however, is not covered in the draft
technical bulletin on environmental acceptability.
The proper operation, maintenance and monitoring
of sludge utilization or disposal practices is essential to
ensure that adverse environmental affects do not result.
Grant applicants must demonstrate that they will have
managers, operators, and resources necessary to achieve
and maintain the required performance on a continuing
basis.
KEY ISSUES
In assessing the environmental acceptability of sludge
utilization or disposal methods, it soon became clear
that there were certain problem areas which occur
regardless of the particular option being studied. For
example the occurrance of trace amounts of so-called
heavy metals in sewage sludges places severe restrictions
on the option chosen. Although the severity of the
metals problem varies from method to method, heavy
metals arc a sufficiently pervasive problem to warrant
serious action by municipalities to minimize the
amounts of such metal introduced into sewage collection
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systems. Unfortunately, we know very little about the
long-term health affects of trace amounts of these
metals. Similarly, we know little about the bio-concen-
tration of these metals in the food chain and their
effects on man.
While source control and pretreatment of industrial
waste introduced into municipal treatment works will
materially assist in reducing the quantities of such
metals, there is information which indicates metals also
come from other relatively uncontrolled sources. Corro-
sion of metalic plumbing elements in soft water areas
may be a source. Street run-off may be a source in areas
where there are combined sewers.
Another pervasive problem is the unevenness of
regulatory control exercised over the various sludge
management options. This ranges from ocean disposal
(which is very strictly controlled and which cannot
legally be done at the present time without a permit) to
land application of sewage sludge which has no Federal
control and in some States viturally no State control.
For this reason the bulletin contains extensive criteria on
land application, but references existing regulations in
the ocean disposal area. To those unware of this
background material the bulletin appears much more
stringent with regard to land application than it is for
ocean disposal. In fact, there has been extensive effort to
assure proper balance in this area. While balancing the
environmental risk is the goal, equality of environmental
risk could not be obtained because of the deferring
media and management options.
LAND APPLICATION
The only sludge utilization method recognized in the
technical bulletin is land application. Because land
application of sludge conserves organic matter, nitrates,
phosphates, and certain essential trace elements, such
utilization encouraged when it is supported by the
environmental assessment.
Specifically, stabilization of sludge and subsequent
land application for enhancement of parks and forests
and reclamation of poor or damaged terrain should be
considered for the utilization of sludge. Application of
stabilized sludge to agricultural lands on which crops
entering the human food chain will not be grown may
also be regarded as an environmentally acceptable
method of sludge disposal. However, application of
sludge on land which crops entering the human food
chain will or may be grown must be examined closely in
terms of hazards to human health and future land
productivity. Priority consideration should be given to
non-agriculture uses.
The bulletin describes in some detail the information
required for design and evaluation of a site for land
application of sludges. The nature and extent of this
information must, however, be tailored to the size of the
project and a relative impact anticipated for the project.
Information should be obtained on sludge characteristics
to determine nutrient values, heavy metals, and other
constituents which may be economically recycled or
cause environmental damage. Of course, where there is
no existing plant, determining the sludge characteristics
would be difficult if not virtually impossible. In this case
reasoned estimates must be made and the monitoring
program intensified to ensure satisfactory performance.
Soil information, such as cation exchange capacity, pH,
and background heavy metals, is important where the
sludge is to be applied to agricultural lands. Extensive
background information on this subject is available
through Department of Agriculture soil surveys. Finally
the ground water characteristics in the area where the
sludge will be applied should be determined. Normally
this will consist of a thorough review of existing informa-
tion supplemented as necessary by an investigation of
soil and ground water conditions.
The general requirements for land application of
sludge include preventing odors, protecting public
health, protecting ground water, and adequate monitor-
ing. Experience has shown that public reactions to
nuisance odor conditions is one of the most limiting
factors in land application of sludges. For this reason the
sludge must be adequately stabilized prior to land
application. The stabilization method most frequently
used is anaerobic digestion, but there are numerous
other acceptable methods. Either a high degree of
reduction of volatile matter, or chemical treatment to
inhibit bacterial action, is necessary. Other methods to
prepare sludge for land application, such as anaerobic
digestion, chemical treatment, heat stabilization, or heat
drying, also may be used provided public health factors
and nuisance potential are no greater than would be
associated with anaerobic digestion. The degree of
volatile reduction achieved by anaerobic digestion is
generally not less than 40 percent to achieve a stabilized
sludge. Where other stabilization methods are used this
degree of reduction may not be applicable.
Chemical treatment typically does not significantly
reduce volatile matter but the rate of decomposition is
slowed so that any odors are disipated at very low
concentrations. Odor conditions may occur in time if
the rate of anaerobic decomposition increases, such as
by neutralization of the chemical treatment. In this case
sludge should be incorporated into the soil. At some
plants the stabilized sludge is spread on drying beds or
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temporarily stored in sludge lagoons. These methods
decrease potential odor problems from sludge applied to
land since additional stabilization occurs with time.
Digested sludge can also be further stabilized by various
composting systems.
For some projects it may be necessary to achieve
additional pathogen reduction beyond that obtained by
stabilization. The following methods have been reported
to be successful: 1) Pasteurization for 30 minutes at 70
degrees centigrade. 2) High pH treatment, typically with
lime, at a pH greater than 12 for three hours. 3)
Long-term storage of liquid digested sludge for 60 days
at 20 degrees centigrade or 120 days at 4 degrees
centigrade. 4) Complete composting at temperatures
above 55 degrees centigrade as a result of oxidative
bacterial action and curing in a stockpile for at least 30
days.
Public access to sites practicing land application of
sludge must be controlled by either positive barriers such
as fences or by remotness of the site. Where this is not
done additional pathogen reduction methods, as out-
lined above, should be used. The site also must be
designed to prevent pollution of ground water resources
and to prevent surface water run-off pollution of
streams.
There are a varity of methods used to apply the
sludge to the land. Liquid digested sludge may be
applied to the land by using a spreading method such as
a tank truck, plow injection, or ridge and furrow
spreading. Dried or dewatered stabilized sludge, or
composted material from digested sludge, may also be
spread on the land. If desired, the sludge can be
incorporated into the soil by plowing, discing, or similar
methods. Spray application of digested sludge to the
land is acceptable when the transport of aerosols beyond
the boundaries of the application area is minimized
through such means as the use of low pressure sprays, or
spray nozzles located close to ground level and directed
downward, or through remotness of the site.
Sludge application rates can be estimated based on
experience, site operating data, or test plot data.
Nitrogen substances usually limit annually application
rates. The rate of sludge application to agriculture land
must be consistent with the use of nigrogen by agro-
nomic crops to prevent nitrate pollution of ground
water. The information required to establish a sludge
application rate includes: 1) total and inorganic nitrogen
content of the sludge, 2) nitrogen, phosphate, and
potassium requirements of the crop being grown, and 3}
a soil test for available phosphate and potassium.
Supplemental fertilizer, especially potassium, may be
needed to optimize crop production. The sludge applica-
tion rates should be such that the total amount of plant
available nitrogen added is no greater than twice the
nitrogen requirement of the crop grown. It is possible
that the presence in the sludge of certain salts, phos-
phate compounds, or metals, or other materials may also
limit application rates in specific instances. The sludge is
generated relatively constantly throughout the year. The
application rate must therefore be harmonized with the
crop growing season. A mass balance is necessary to
determine the amount of sludge storage required during
intervals when the sludge is not applied to the land.
The draft technical bulletin requires the grant appli-
cant to develop and implement a plan for adequate
monitoring of each land application site where the
application rate will exceed five dry tons per acre per
year, for liquid digested sludge, or 50 dry tons per acre
over a three year period for dried or dewatered sludge.
Use of bagged sludge fertilizer products for the retail
market will not require site monitoring. The site
monitoring plan must be specifically designed for appli-
cable local conditions and it includes consideration of
heavy metals, persistent organics, pathogens, and nitrates
in ground water, surface water, sludge, and soils.
The operation and monitoring data of the system
must be periodically reviewed to ensure satisfactory
performance. Where there is not a local or State program
for this purpose, an alternative independent review will
be necessary. This could be done by a consultant or by
an agricultural extension service.
The operation and monitoring data of the system
must be periodically reviewed to ensure satisfactory
performance. Where there is not a local or State program
for this purpose, an alternative independent review will
be necessary. This could be done by a consultant or by
an agricultural extension service.
In additional to the foregoing general requirements,
the application of sludge to agricultural lands which may
be used to grow crops must be accomplished so as to
ensure crop land resources are protected and harmful
crop contaminants do not enter the human food chain.
Some projects, however, are clearly of minimal concern,
either because of their relative size and impact or
because they are controlled by other means. An environ-
mental assessment involving testing of the sludge for
heavy metals and pathogens will verify this is the case
for the particular project. In these cases of lesser
concern, the project should conform with the foregoing
general requirements, but need not necessarily conform
with eacn of the specific limits and monitoring require-
ments. Example of this type of project include:
1. Small projects where the designed flow of the
publicly owned treatment works is less than one million
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gallons per day, particularly where there are no indus-
trial users of the system and the application rates are
low.
2. Where the sludge is applied to city owned or
government controlled land dedicated to receive sludge.
3. Where the existing sludge operation is a commer-
cial activity, producing bagged products. In this case
there should be a temporary variance for nonconforming
sludges with an approved implementation schedule
established to conform with applicable limits such as
metals and pathogens. New projects should not be
exempted.
The agriculture research service of the U.S. Depart-
ment of Agriculture has suggested the following interim
criteria. The limits are based on experiments directed at
the determination of levels of heavy metals which are
toxic to plants. They are designed to keep down the
level of heavy metal being adsorbed by the plants.
Because of the great uncertainty concerning the appro-
priate level of intake by humans of these heavy metals as
part of their diet, EPA cannot say that these levels
constitute the appropriate levels for human intake. To
the extent, however, that the limits represent an attempt
to keep the levels of heavy metals at a lower point than
otherwise would be the case, these limits will make a
contribution to the protection of public health.
No greater total amount of sludge may be applied
than calculated by Equation 1 for the particular sludge
and soil.
Equation 1
Total sludge (dry wt tons/acre) =
32,700 CEC
ppm Zn + (ppm Cu) + 4 (ppm Ni) - 200
CEC - cation exchange capacity of the unsludged soil
in meg/100 g ppm - Mg/kg dry wt. of sludge.
This equation limits the heavy metal addition calcu-
lated as zinc equivalent to 10 percent CEC. The zinc
equivalent takes into account the greater plant toxicity
of copper and nickel.
Sludge having a cadmium content greater than 1
percent of its zinc content should not be applied to crop
land except under the following conditions:
1) the land areas to receive this sludge are clearly
identified in the grant application.
2) There is an abatement program to reduce the
quantities of cadmium in the sludge to an acceptable
level.
3) The project is reviewed by the U.S. Department of
Agriculture and the Food and Drug Administration.
The above criteria apply only to soil that can be
adjusted and held at a pH of 6.5 or greater for a period
of at least two years after sludge application. The criteria
provide one method to limit the amounts of metals in
sludges applied to crop lands. Other methods were
considered but not adopted at this time, either because
they do not address all the factors considered important
or it appeared they were not as consistent with the
limited data as the above criteria. As more data become
available the criteria may change. Accordingly, a high
degree of precision should not be inferred for Equation
1 or the cadmium/zinc ratio. Evaluation of borderline
cases should be based on the procedures describes
subsequently, together with an abatement program to
reduce the quantities of metals in the sludge. The 1
percent cadmium to zinc ratio is designed to protect
against unacceptable cadmium uptake in shallow, low
pH, low CEC soils growing leafy vegetables or grains. A
cadmium to zinc ratio of up to 1.5 percent could be
acceptable where the sludge is applied to marginal lands
not being cultivated.
Under certain conditions, specific organisms may
survive in the soil for extended periods. Consequently,
sludge treated land should not be used for human food
crops to be eaten raw until three years after sludge
application. Sludge applied to crops which are cooked or
processed before consumption, or pastures, or to crops
used for forage should test negative for pathogens such
as salmonella and Ascaris ova. Forest and pasture crop
should not be consumed by animals if these crops are
physically contaminated by sludge. Where there is a risk
of direct ingestion of the sludge by grazing animals, the
lead content of the sludge should not exceed 1,000
mg/kg dry sludge and the cadmium content should not
exceed 20 mg/kg dry sludge.
Other sludges may also be acceptable including some
which do not in every respect follow in the above
criteria. These sludges should only be used under
carefully defined and controlled conditions. EPA Re-
gional Administrators will work closely with grant
applicants desiring to use these sludges in land applica-
tion projects.
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LANDFILL
Sanitary landfill of sludge, either separately or along
with municipal solid waste, is acceptable when sup-
ported by the environmental assessment. Sanitary land-
fills accepting in sludge must be designed and operated
in accordance with EPA guidelines for land disposal of
solid waste. Normally, the sludge must be stabilized as
described for land application. If the landfill is not
operated by the wastewater treatment authority, a
binding agreement is required between that authority
and the operator of the sanitary landfill to ensure that
the landfill is operated in accordance with the EPA
guidelines.
Monitoring requirements for sanitary landfills include
ground water observation wells and surface water moni-
toring where the surface water could be affected directly
or by leachate from the sludge landfill.
INCINERATION
Incineration alone is a volume reduction method
rather than ultimate disposal. After incineration, ash,
either dry or in scrubber water remains to be disposed of
to the land. Ash disposal must be controlled to protect
ground water, to prevent dust, and to ensure no erosion
to surface water.
The emission from the sludge incinerator must not be
result in violation of ambient and quality standards and
must meet the EPA air pollution emission standards of
performance. Additionally, EPA has published proposed
limitations on mercury emissions from the incineration
and drying of wastewater treatment plant sludges. The
maximum amount would be 3200 grams per day. Sludge
has been shown to contain trace amounts of metals such
as mercury, lead, and cadmium, as well as persistent
organic compounds, such as polychlorinated biphenols.
The effects of these compounds which are emitted from
the incinerator must be assessed and the sludge should
be tested to determined the quantities of such com-
pounds present. If the PCB's exceed the level present in
domestic sludge (approximately 25 mg/kg dry sludge)
then special measure should be taken to ensurely 95
percent destruction of persistent organic compounds.
Increased temperature and residence time increase the
assurance of destruction.
A plan must be developed and implemented to
provide for adequate monitoring of each sludge and
incinerator. The stack gas emissions from sludge and
incinerators must be monitored and, in addition, mer-
cury either in the a sludge or in stack gas emissions must
be periodically tested to demonstrate compliance with
EPA standards. Additional monitoring for organic pesti-
cides PCB's, or heavy metals other than mercury, may be
necessary for specific projects.
OCEAN DISPOSAL
Ocean disposal of sewage sludge would be acceptable
for treatment works presently using this method only
when the sludge meets the EPA criteria and when the
disposal method is supported by the environmental
assessment. Information available to EPA from permit
applications to date indicates that those sludges cur-
rently being dumped exceed the criteria and are there-
fore being dumped under interim permits. One of the
conditions of these interim permits is the requirement
for an implementation plan to either reduce the toxic
materials to meet the criteria or find an alternative
method of disposal. Interim permits are granted for one
year only and the issuance of new interim permits is
based on the progress demonstrated by the permitee on
the implementation plan. Currently the EPA will ap-
prove only existing dumping sites presently in use for
the disposal of particular kinds of waste, unless there is
extremely strong evidence in favor of approval of a new
location.
CONCLUSION
This paper, has presented an overview of the magni-
tude of the municipal sludge problem in the United
States and some of the measures which are being
considered to controll the utilization or disposal of these
sludges. These criteria will be proposed for public
comments by all concerned agencies and will be revised
to reflect such comments before final promulgation.
-------
Table 1 Estimated Quantities of Sludge in the United States, dry tons/day
Current Secondary Treatment
(10 years)
Domestic 10,000 13,000
Industrial users of municipal plants 7,000 10,000
Total municipal sludge 17,000 23,000
Table II Range in Typical Sludge Volumes Produced, gallons of sludge/million gallons wastewater treated
Primary sedimentation 2500 - 3500
Trickling filter 500- 750
Activated sludge 15,000 • 20000
Table III Volume Distribution of Plants Generating Sludge
Size of plant Number of plants*
million gallons/day
less than 1 11,120
1-5 1,558
5-10 253
10-25 180
25-50 54
50-100 37
Greater than 100 30
Not reported 3,983
Total 17,215
* does not include wastewater treatment ponds.
Table IV Estimated Current Disposition of Municipal Sludge
Method % of Total Sludge
Landfill 25 percent
Ocean dump 15 percent
Incineration 35 percent
Land Applicatioa 25 percent
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SLUDGE INCINERATION SYSTEMS FOR
PURIFICATION AND RESOURCE RECOVERY
by
Frank P. Sebastian
Member, Working Party
Senior Vice President
Envirotech Corporation
Menlo Park, California
Working Party for the Prevention of Pollution from
Municipal and Industrial Sources
SLUDGE SYMPOSIUM
Moscow
May 12-27, 1975
under
USSR/USA ENVIRONMENTAL AGREEMENT
-------
SLUDGE INCINERATION SYSTEMS FOR
PURIFICATION AND RESOURCE RECOVERY
by
Frank P. Sebastian
INTRODUCTION
In the treatment of wastes at a sewage treatment
plant, following the various dewatering processes waste
solids and water still remain for disposal. More stringent
laws and codes have reduced freedom of choice in
disposing of such waste solids or sludge.
In a study for a midwestern U.S. town, Weller and
Condon reported relative costs for various systems as
follows:
Original Annual
Cost Cost
1.0
1.05
1.43
1.97
1.0
1.41
1.38
1.54
System
Dewatering and Incineration
of Raw Solids
Digesting, Mechanical Dewatering
and Land filling
Digesting, Mechanical Dewatering
and Incineration
Wet Combustion and Effluent
Treatment
This paper will review sludge incineration and heat
treatment for conventional primary secondary systems,
and incineration and reclamation for advanced physical
chemical systems, particularly as regards their environ-
mental impact.
USES
The multiple hearth furnace is versatile, although
originally developed in 1889 as a furnace to roast pyrites
for the manufacture of sulfuric acid. The modern
multiple hearth system has been adapted to over 120
proven uses, including:
1. Burning (or drying) raw sludge, digested sludge, and
sewage greases;
2. Recalcining lime sludge and waste pond lime;
3. Reclaiming fruit, nut and lumber waste (peach pits,
walnut shells, almond shells, sawdust and bark) for
charcoal briquettes, and reclaiming cryolite and
aluminum smelting operations;
4. Regeneration of spent activated granular carbon and
diatomaceous earth;
5. Other uses: mercury, molybdenum sulfide, carbon,
magnesium oxide, uranium, yellow cake, nickel.
The multiple hearth furnace itself is a simple piece of
equipment, consisting primarily of a steel shell lined
with refractory on the inside. The refractory can be
either castable or in brick form, depending upon the size
of the furnace. The interior is divided by horizontal
brick arches into separate compartments called hearths.
Alternate hearths have holes at the periphery to allow
the feed solids to drop into the hearth below. The center
shaft, driven by a variable speed motor, rotates the
rabble arms situated on each hearth. The rabble teeth on
these arms are placed at an angle such that the material
is moved inwards and then outwards on alternate
hearths. The shaft and rabble arms are cooled by air
introduced at the bottom. This air may be recycled as
required by the thermal process (Exhibit 1).
The sludge is fed through an inlet in the furnace roof
by a screw feeder, or belt and flapgate. The rotating
rabble arms and rabble teeth push the sludge across the
hearth to drop holes where it falls to the next hearth and
continues to the next hearth and the next, until the ash
is discharged at the bottom.
The multiple hearth system has three distinct oper-
ating zones: the top hearths where the feed is dried to
approximately 48% moisture; the incineration/de-
odorization zone where temperatures of 760°-982°C
(1400°-1800°F) are maintained, and the cooling zone
where the hot ash gives up heat to the incoming
combustion air. The warmed air rises to the combustion
zone in counterflow style and the hot combustion gases
sweep over the cold incoming sludge, evaporating the
sludge moisture to about 48%, at which point a
phenomenon called "thermal jump" can occur in the
beginning of the combustion zone. This beneficial
exchange of energy allows odorfree exhaust gas and
temperatures of 260°-593°C (SOO'-l lOO'F). The typical
temperature profile across the sludge furnace is as
follows:
Approx. Half
Hearth No. Capacity-°C
Nominal Design
Capacity-°C °F
1
2
3
4
5
6
354
748
848
787
648
163
670
1380
1560
1450
1200
325
426 800
648 1200
898 1650
787 1450
648 1200
148 300
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Thermal oxidation is reaching new high levels of
technology and performance not generally realized even
in technical circles. New data recently developed answer
favorably for the first time many questions that have
surrounded the impact on air quality from such thermal
processing systems. In addition, favorable benefits such
as energy reclamation and ash utilization from the
burning of sludge have become a reality in these sludge
processing units.
Sludge Incineration/Reclamation Benefits
Meets EPA air standards-particulates
Ruled insignificant source of emissions
Decomposes PCB's (polychlorinated biphenyls))
Decomposes pesticides-DDT, 2,4,5-T
Produces ash product-quasi-fertilizer
Recovers resources-CCh, Hme
Controls heavy metals
Energy reclamation-Closed Loop Energy System
The most comprehensive study that has been done to
date on sludge incineration was by the EPA Sludge Task
Force, the report on which was published in August
1972. It included a survey of ten furnaces throughout
the United States, including, for example, installations at
Monterey and South Lake Tahoe, California. The Task
Force study also included a report of the sludge, ash and
air emission, and of air pollutants and toxics.
The Monterey sludge incineration building was con-
verted from an existing digester to house the incinera-
tion unit. It is located on the edge of Monterey Bay
where raw sludge used to be dumped.
The South Lake Tahoe Water Reclamation Plant is
one of the most advanced wastewater treatment plants
in the world. The solids handling building contains a
sludge incineration furnace and a lime recalcination
furnace. The EPA Task Force conclusions were:
• Incineration is an acceptable alternative for sludge
disposal.
• Air emissions acceptable:
NOX
SOX
Odors
Particulates
• Apparent destruction of pesticides/PCB's
The information presented here is principally an
update of several key points that were included in the
EPA Task Force report.
EPA Task Force Abstract
A Task Force was established within the Environ-
mental Protection Agency to evaluate sludge inciner-
ation as an acceptable alternative to sea disposal.
Multiple-hearth and fluidized bed furnaces, contain-
ing scrubbing devices for particulate removal, were
selected for performance evaluation. The sludge, par-
ticulate, stack gas, scrubbing liquid, and ash were
sampled, and analyzed for heavy metals, pesticides
and oxides of nitrogen and sulfur. The results
indicated that incinerators are capable of achieving
low emission concentrations for the common pollut-
ants. Particulate samples showed a measurable con-
centration of lead. The ash samples normally showed
a higher concentration of the heavy metals when
compared with the sludge samples; however, mercury
was one of the exceptions and was not detectable in
the ash sample and assumed as lost to the stack gases.
The pesticides and PCB, present in the sludge, were
not detectable in either the ash or the scrubbing
water, and indicated complete destruction. The study
demonstrated that well designed and operated munic-
ipal sewage sludge incinerators can meet the most
stringent existing particulate emission control regula-
tion.
Since the Task Force published the report on its
findings, there have been new test results pertaining to
PCB's, pesticides, lead and mercury. The new data show
that the air quality impact can be even further reduced
over the Task Force data. In addition, the fate of PCB's
became the pivotal issue of the report insofar as fuel
conservation was concerned. These concerns have now
been relaxed.
The Task Force report recommended that, to be
certain of complete decomposition of PCB's found in a
sludge furnace, exhaust gases should be raised to 871°C
(I600°F) for two seconds.
The Task Force further reported that PCB's were
found to range from "not detected" in mountainous
areas to 105 PPM is industrial areas where PCB's were
used in manufacturing processes. The 871°C (1600°F)
temperature requirement, if imposed, would have meant
as much as a four-fold increase in the fuel cost of a
typical sludge incinerator at that time.
As soon as a copy of the preliminary Task Force
report was received, in February 1972, Envirotech
immediately undertook an independent study and found
virtually complete destruction of PCB's at 593°C
(1100°F) in only one-tenth of a second, and 95%
decomposition under normal operations. This informa-
tion was presented to the EPA and in November 1974
10
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the draft EPA Technical Bulletin on Sludge Disposal
revised the guidelines as follows: (1) check to determine
if the PCB content in sludge exceeds 25 milligrams per
kilogram, and (2) if it does, use a process that assures
95% decomposition. Since the new data showed that this
can be achieved at the normal operating parameters of a
multiple hearth furnace, no extra fuel is required to
eliminate the PCB's even when the sludge contains more
than 25 milligrams per kilogram.
The tests that led to this new guideline were
conducted by injecting PCB's into the sewage sludge at
the San Mateo, California furnace.
• 4500 PPM of Therminal FR-1 was injected into the
sludge feed;
• The furnace was operated at normal temperatures
with internal temperatures of
815°C (1500°F) to 926°C (1700°F)
• Four different afterburner temperatures were used
to develop sample decomposition data:
337°C (640°F)
365°C (690°F)
493°C (920°F)
632°C(1170°F)
• The analysis was done by certified independent
laboratories.
The results showed what 95% of the PCB's were
destroyed at 371°C (700°F) using 0.1 second exhaust
gas detention time. At 593°C (1100°F), 99.9% of all
PCB's were destroyed, also at an exhaust gas detention
time of 0.1 second.
What is the significance of PCB in sludge? Perhaps it
would be helpful to review briefly some background
information on PCB. PCB's have some unique properties
that have made them very useful in industrial applica-
tions for the last forty years. PCB's were first produced
commercially in the U.S. in 1929. Since then they have
been produced by one U.S. manufacturer and several
manufacturers outside the U.S.
The main properties that distinguish PCB's are: they
are inert chemicals; they are insoluble in water; they are
adhesive; they are extremely heat resistant; and they are
toxic to many organisms. Chemically, they are very
similar to the well known chlorinated hydrocarbons or
pesticides. Due to their remarkable stability, PCB's have
found many uses, particularly in industry.
The major user of PCB's has been the electrical
equipment industry, followed by heat transfer systems,
use as hydraulic fluid, and, finally, use as plasticizers
which originally, but no longer, included carbonless
carbon paper, and in paints and glues. In 1966, PCB's
were first identified as being present in some food
products and, since, have been found throughout the
environment.
Based on these findings, the sole producer of PCB's in
the United States voluntarily limited production of these
chemicals in 1971. The latter three of these uses have
been scverly limited and suitable substitutes have been
found for the PCB's. At this time, the U.S. government
is recommending the use of PCB's only in electrical
equipment, sucli as transformers and capacitors, which
presently have no suitable substitute for PCB's.
A U.S. government interdepartmental task force on
PCB's identified where PCB's exist in the environment.
It was estimated that in North America the air environ-
ment contains 20,000 tons of PCB's; land environment,
250,000 tons; and the water environment, 30,000 tons.
These totals represent a great majority of the PCB's that
have been produced in the last forty years. Worldwide
totals for these three sectors of the environment would
run much higher. Significant to this report is that the
government pinpointed the principal means of cycling
through the environment for PCB's as being in waste-
water systems.
The cycle consists of waste streams, receiving waters,
fish, animals and, finally, man. PCB's, like their close
pesticide relatives, the DDT, ODD, dieldrin-chlorinated
hydrocarbons, tend to concentrate in the higher levels of
the food chain and in the fatty tissues of animals. The
cycle begins with waste streams from industrial manu-
facturing or accidental spills into sewers or streams.
From there the PCB's enter receiving waters were
aquatic organisms ingest them, and as mentioned above
they concentrate in the top of the food chain. Also,
wildlife, which increasingly serve man as an early
warning system, take the PCB's and concentrate them in
their bodies when they consume water laced with
PCB. Finally, the chemicals find their way into man.
The U.S. government does not believe that PCB's
represent an immediate threat to human health. How-
ever, this tendency to concentrate in the food chain,
plus the long lived characteristics of PCB's make them a
long range threat. The U.S. government has recognized
them as such and some New York reports show a direct
correlation in fish with age.
In September 1972 a United States Geological Survey
report made headlines in the newspapers across the U.S.
A survey of streams and lakes in 39 states detected
PCB's in 17 of the 39 states. In many places where PCB's
would not be expected to exist, such as remote lakes and
rivers, scientists were surprised to find PCB's present.
This omnipresence, coupled with the non-biodegrad-
ability, is obviously the reason the U.S. EPA is
concerned about the fate of PCB in sludges. Fortunately,
the current sludge incineration technology has been
11
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shown to offer a safe alternative to eliminate any
concern over PCB contamination in the air or on land
from that process.
AIR QUALITY IMPACT
For comparison with stringent air quality regulations,
further tests were conducted at the same San Mateo
installation. The air quality tests there were also very
favorable. Three tests for hydrocarbons showed 0.7, 2.2
and 0.4 PPM, and three tests for carbonyls showed 3.4,
7.6 and 3.4 PPM-all very low fractions of the 25 PPM
allowable for the Bay Area Air Pollution Control District
(BAAPCD). Similar low values were obtained for par-
ticulates-.019, .021 and .017 PPM compared to the
.125 allowable of 0.15 in terms of grains per standard
dry cubic foot.
To offer some perspective as to how significant
incineration impact is on air quality, a comparison can
be made on a per capita or person versus per automobile
impact on air quality, using a typical U.S. automobile
traveling 12 miles per day. Taking the actual U.S.
standards on hydrocarbons, hydrocarbon emissions for
1970 U.S. cars were 55.2 grams, in 1975 18.0 grams, and
1977 standards were 4.89 grams-a substantial reduction
(Exhibit 2). On a per capita basis, the air impact from
incineration is .019 grams per day per person. The
carbon monoxide comparison is similar, at 564,180 and
40.8 grams per day emissions for an automobile, and
only .057 grams per person per day from incineration.
Nitrogen oxide carries a similar story: improvements
from 49.2 in 1970 to 37.2 grams in 1975, and 24.0
grams in 1977. The impact per person is 0.29 grams.
The Tahoe plant, mentioned earlier, was one of the
plants studied by the Task Force. This plant was a
conventional activated sludge plant that has been up-
graded by adding lime and carbon tertiary treatment to
produce an ultra high quality effluent water. The
effluent water will meet U.S. "laboratory tests" for
drinking water standards. The sparkling product is
pumped to a new 3.785 million cubic meter, one billion
gallon reservoir, Indian Creek, where it is u,sed for trout
fishing, recreation and crop irrigation.
Further, environmental impact improvements have
been achieved since Tahoe was built, as the EPA Task
Force report mentioned. Two 5.71 meter, 18.75 ft.
6-hearth furnaces were under construction "when the
BAAPCD reduced its allowables in 1970. Tests were
conducted on the improved Palo Alto furnace design
following completion in 1973. The actual emissions were
a small fraction of the reduced allowables for hydro-
carbon emission, carbonyls, SCh (a new requirement)
and participates (Exhibit 3).
This advanced facility is frequently visited by both
U.S. and foreign environmental groups and has been
inspected by several Soviet delegations under the USSR/
USA Environmental Agreement. It was our honor to
host Dr. Yury Izrael's delegation there in July 1973 and
the Working Party for Prevention of Pollution in
October 1974. During these visits we sipped together
"Tahoe champagne" as the reclaimed water is called by
the local plant operators.
About the time that the Palo Alto tests were
completed, Livermore, California, a small community
east of San Francisco, was denied a permit to build its
wastewater treatment plant as required under the Clean
Water Act. This was due to the fact that this valley,
which is famous in the U.S. for its white wine, was
already exceeding the secondary air quality standards.
Therefore, no more construction could be started, not
even to clean up the wastewater. At the invitation of the
municipality and its consulting engineer, the impact on
air quality from the new Palo Alto furnace was
presented to the Bay Area Air Pollution Control District
Board (Exhibit 4). A study showed that in the Liver-
more valley automobiles were the source of 28,000
pounds per day of NOX emissions. If sludge were hauled
from a treatment plant by truck, emissions from the
truck would be ten pounds per day into the valley,
traveling just to the edge of the valley, and the truck
would still have to be driven some additional distance
where it could be unloaded. Within the valley itself there
would be a ten pound NOX impact.
Earlier data indicated that 62 pounds per day of NOX
would be emitted from the sludge incinerator if lime
reclamation were included with it, compared to 50
pounds per day for sludge only. However, based on the
Palo Alto plant performance, it was determined that the
NOX impact on the valley would be about the same
whether incinerated or hauled away by truck. Here
again, this does not include the truck emissions outside
the rim of the valley. Based on these results, the Bay
Area Pollution Control District ruled that sludge inciner-
ation was an insignificant source of emission and no
permit was required to proceed to build the waste
treatment plant.
A further comparison of air emissions on a per capita
basis with the automobile on a per day basis shows the
NOX emissions, based on the Palo Alto tests, were .037
grams per day per person, and a 1976 automobile
traveling 12 miles per day is estimated to emit .4 grams
per mile of NOX. Sludge incineration emissions per
12
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capita are about equal to driving a U.S. car one-tenth of
a mile.
The test results from San Mateo and Palo Alto were
studied by EPA personnel concerned with solid waste
and the disposition of residuals.
EPA concerns involved excess DDT which has been
banned in the U.S. and also disposition of the pesticide
2,4,5-T. The Solid Waste Division of EPA was interested
in the possibility of injecting DDT into sludge as a means
of processing DDT through the furnace to remove it
from the environment. The EPA contracted for tests to
be performed by Versar, Inc., an independent labora-
tory. Following pilot scale tests, full scale tests were run
at the Palo Alto installation. DDT was injected into the
sludge (Exhibit 5) at the rate of 908 grams per hour. The
ash at the bottom of the furnace contained 0.000027
grams/hour. In the airstream with no afterburner oper-
ating there was .0044 grams per hour and 3 grams per
hour were contained in the scrubber water which is
returned to the headworks. The overall removal or
decomposition efficiency was determined to be
99.669%. It was concluded that any DDT that is
normally contained in the sludge is destroyed in the
furnace, and that additional DDT up to 5% that might
be added to the sludge would also be similarly decom-
posed. Similar tests were conducted for 2,4,5-T with
similar results-99.989% decomposition (Exhibit 6).
There has been some expressed concern about the
fate of heavy metals that might be contained in sludge.
The EPA contracted for additional tests at Palo Alto as
to the fate of lead and mercury in the sludge. In the case
of lead, there was plenty in the sludge since electronic
industry wastewater is treated at the Palo Alto municipal
plant. It was found, much to the surprise of many
people, that the lead in sludge is not volatilized into the
atmosphere.
The sludge input contained 5570 grams/day, the ash
from the furnace contained 4900 grams'/day. Scrubber
water picked up 623 grams/day and only 47 grams/day
entered the atmosphere through the exhaust airstream.
Overall, removal efficiency was found to be 99.15%
(Exhibit 7).
The mercury results are probably even more sur-
prising. The EPA Task Force report assumed, as had
others, that all the mercury in the sludge was volatilized
and went into the atmosphere. However, the Versar
testing contractor developed different theories after
studying the pesticide results, and obtained EPA support
for tests on the fate of mercury in sludge when
incinerated. The sludge feed contained 67 grams per day
of mercury, but a high percentage-39.55 grams per
day-of that mercury went through the furnace with the
ash. As mentioned previously, the EPA Task Force
found no measurable quantity of mercury in the ash.
The scrubber water which is returned to the plant
headworks contained 20.95 grams/day. Only 6.50 grams
per day went into the atmosphere. Overall, the process
controlled 90.2% of the mercury (Exhibit 8).
LIME RECLAMATION
In these energy and material conscious days, reclama-
tion is all important. Reclamation in the multiple hearth
furnace is a normal operating procedure. For instance,
the Lake Tahoe Water Reclamation Plant uses a separate
multiple hearth furnace to recalcine or reclaim lime that
is used in the treatment process. Since this is a
manufacturing process—that is, taking the lime-rich
sludge and reclaiming the valuable lime treatment
chemical-it does not fall under the sludge furnace air
quality regulations. A further benefit of reclaiming lime
is that there is a unique opportunity to lower emissions
to the atmosphere in the process. When lime is added to
facilitate settling of the solid matter, the alkalinity pH of
the wastewater is raised substantially. In order to reduce
the pH, the exhaust gases from the furnace are highly
cleansed in the methods already described—they are not
released to the atmosphere but are reused. To capture
the C02 that is required by the process, the gases are
compressed and bubbled into the bottom of a recarbona-
tion basin where the C02 and trace components in the
gases are transferred to the wastewater. Thus, the gases
are further scrubbed clean. This system has been in
operation at the South Lake Tahoe Water Reclamation
Plant since 1968.
ENERGY RECLAMATION
A further industry development is that of energy
reclamation from sewage plants. In addition to the
reclamation of the fuel value of sewage sludge to reclaim
chemicals on site for reuse, a further step has been taken
in three municipal plants currently under construction
involving the use of third generation multiple hearth
furnace systems which we call Closed Loop Energy
Systems (Exhibit 8). In these systems a sludge heat
treatment step is installed to break loose the water
bound in the biological cells to enable normal dewater-
ing equipment (vacuum filters or centrifuges) to be used
to obtain up to a 250% increase in the normal solids
content of the sludge. This brings the sludge to a fuel
value approximately equal to that of soft coal. The heat
treated sludge is them processed through a similar but
differently designed furnace to convert itself to a sterile
13
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but potentially useful ash without the need for auxiliary
operating fuels and with sufficient heat left over to
provide process heat and steam at the treatment plant.
Three sludge handling and disposal systems, designed
with a "closed circuit energy loop" to conserve fuel, are
currently under construction in the U.S. for Granite
City, Illinois; Chcsapeakc-Eli/abeth, Virginia; and the
Western| Branch! Plant'at Prince, Georges County, Mary-
land.
Granite City, Illinois
At Granite City the existing wastewater facility is
currently being upgraded with activated sludge treat-
ment to handle the 23 MGD flow and to treat sludge in a
"recuperative" BSP system. The influent consists pri-
marily of domestic waste with a small industrial com-
ponent.
This system includes:
• Two 6000 CPU BSP Heat Treatment units to
thermally condition hydrous sludges used waste heat
recovered from the furnace.
• One 18(9u $x 7 hearth furnace designed to reduce
11,000 Ib/hr of cake to 1000 Ib/hr inert ash without
use of support fuel.
• One heat recovery boiler to convert the furnace's
16.9 million PTU&hr of waste heat to 8,255 Ib/hr
steam for thermal conditioning of the raw sludge.
• (The Eimco/BSP system also includes an 18 GPM
BSP Scum Concentrator to segregate grease and
fibrous trash and to put it into the furnace as fuel at
a controlled rate, and an Arco Impingement scrub-
ber to control emissions.)
The $10 million expansion at Granite City will also
include two Einico 80' <(> x 18' primary clarifiers, two
Eimco 70' gravity sludge thickeners; and an Environ-
mental Operating Services contact for a startup and
training assistance program.
Chesapeake-Elizabeth, Virginia
The Chesapeake-Elizabeth waste treatment facility in
Virginia, one of many being executed for the Hampton
Roads Sanitation District, includes:
• Two 70' i x 10' Eimco Sludge Thickeners.
• One 9300 GPH BSP Heat Treatment unit.
• Two 18'9" 0x7 hearth BSP furnace systems and an
Environmental Operating Services startup and train-
ing assistance program.
• Two heat recovery boilers to convert 3,319,000
BTU/hr. of waste heat into 6200 Ib/hr of steam for
the BSP Heat Treatment Process.
Western Branch, Maryland
The Western Branch facility at Prince Georges
County, Maryland is the latest of the three new "Closed
Energy Loop" projects. It consists of upgrading an
existing 15 MGD plant to reduce the sludge volume
containing 51,700 pounds of dry solids per day over
99% in a virtually "fuel-less" system. The plant primarily
processes municipal waste with a small industrial com-
ponent. It includes two 6000 GPH BSP Heat Treatment
systems and two 14'3" $ x 7 hearth BSP furnaces. The
5500 Ib/hr waste heat recovered from the autogenous
combustion is 25% more than the 4666 Ib/hr necessary
to power the heat treatment system.
The economics of the CLES arc based on the fact
that the combustion is the flowsheet containing the
closed loop concept is self-sustaining. The excess heat
from the combustion is sufficient to run the heat
treatment system's heat treatment requirements. There-
fore, the fuel required in CLES is essentially zero
(Exhibit 9).
Regarding the actual cost comparison between the
Closed Loop Energy System and the conventional
system (Exhibit 10):
1. Costs include both operating and amortized capital
costs of installed heat treatment and multiple hearth
furnace systems.
2. All costs have been reduced to "dollars per ton" of
dry solids, and include all the actual solids generated
by a complete primary secondary treatment flow-
sheet.
3. Annual costs are computed by multiplying the sludge
generated (tons/year) by the cost ($/ton).
The following conclusions are apparent:
1. Despite the fact that a slightly greater quantity of
sludge is generated using the Closed Loop Energy
System, savings are consistently realized regardless of
plant flow;
2. Annual cost savings vary depending on the economies
of scale realized. (A particular piece of equipment
may be employed at a higher rate of utilization which
would affect the savings.) For example, this phenom-
enon has occurred at the 75 MGD plant flow.
Conventional system costs at 75 MGD appear to be
somewhat out of line, probably due to lower equip-
ment utilization rates.
ASH AS POTENTIAL FERTILIZER
Other reclamation potential for sludge incineration-
in addition to energy and CO: recovery-exists in the
potential fertilizer value of the ash.
14
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In Japan, more than 50,000 tons of ash from multiple
hearth furnaces have been sold on an experimental basis
by cities to fertilizer companies for sale in 20 kilo bags.
The fertilizer value is
0.1% nitrogen
6.0% phosphate
1.0% potash
To indicate the high potential fertilizer value in ash, a
comparison can be made" with typical values of nutrient
found in wet sludges and used in typical sludge to land
projects such as at Denver, Colorado.
Using the value of $0.48 per kilogram ($440 per ton)
for nitrogen, $0.88 per kilogram ($800 per ton) for
phosphate, and $0.07 per kilogram ($6.00 per ton) for
potash, the wet sludge at Denver has been valued at
$0.013 per kilogram and $12.22 per ton. By compari-
son, using the same values, and due to the fact that the
ash is more concentrated, the ash from the sludge
furnace at Palo Alto—a typical secondary sludge—would
have a value of $0.053 per kilogram and $48.50 per ton,
four times as much as wet sludge.
The ash from an advanced waste treatment facility
such as Tahoe, of course, removes a higher percentage of
phosphate. Principally, due to the higher phosphate
content of the ash, it has a potential value of $0.088/
Kilogram and $80.50 per ton.
COSTS
Before closing, a comment about costs based on U.S.
experience might be useful.
At the Tahoe Water Reclamation Plant, published
figures show an operating cost of $0.154 per kilogram
($13.98 per ton) of dry solids dewatered.
Total operating and capital cost is $0.053 per
kilogram ($47.92 per ton) for the sludge incineration
process. This amounts to less than 5% of the total cost
for complete treatment, which is about $0.105 per cubic
meter (40^/1000 gallons) for the 28,400 cubic meter
(7.5 MGD) capacity. Large plant flows would reflect
economics of scale and lower costs by as much as
one-half.
The Environmental Engineers' Handbook, published
in 1974, reports multiple hearth incineration cost for
cities of one million population of 144 per capita per
year and 64^ per capita per year for cities of 100,000
population.
A 1973 study of one of the large population areas in
the U.S.—the Metropolitan Boston area-shows that
incineration/reclamation of sludge is the lowest cost and
lowest energy use alternative, in comparison to land
disposal and wet oxidation. The energy cost alone for
land disposal was 60% higher than for sludge incinera-
tion.
Fuel costs and labor and material costs have
risen sharply since these data were developed but,
as mentioned earlier, the new Closed Loop Energy
Systems furnaces eliminate the need for auxiliary
operating fuel.
The ash is an environmentally superior product
for it has been purified of DDT, 2,4,5-T and PCB,
as well as many other chemicals found in sludge
that are on the EPA toxic chemicals list (e.g.,
chlordane. dieldrin, endrin, toxophene). Quantities of
heavy metals in excess of allowable would need to
be removed through pre-treatment for any fertilizer
usage of sludge or ash.
In summary, the new sludge oxidation technology
offers the following advantages:
Meets EPA air standards-particulates
Ruled insignificant source of emissions
Decomposes PCB's (polychlorinated biphenyls)
Decomposes pesticides—DDT, 2,4,5-T
Produces ash product—quasi-fertilizer
Recovers resources—CCh, lime
Controls heavy metals
Energy reclamation-Closed Loop Energy System
As the USSR and the US move to higher quality
levels in both the air and water sectors, the overall
environmental impact of technology must be considered.
In the allocation of environmental resources in urban
communities, advanced thermal processing technology
deserves to be fully considered for its resource recovery
and purification, benefits, as well as for its "disposal"
aspects.
REFERENCES
"Advanced Waste Water Treatment as Practiced at
South Tahoe," EPA, August 1971, No. 17010ELQ08/71
"Advances in Incineration and Thermal Processes,"
Frank P. Sebastian, Short Course: The Theory and
Design of Advanced Waste Treatment Processes, Univer-
sity of California, Berkeley, September 30-October 1,
1971
15
-------
"Accepted Methods for the Utilization or Disposal of
Sludges," EPA No. 430/9-75-XXX, Technical Bulletin,
November 1974
The Environmental Engineers' Handbook, Chilton
Book Company, Philadelphia, Pa., 1974
"PCB's Spotted in Nation's Water Resources", U.S.
Geological Survey, September 1972
"Problems in the Design of Sludge Incinerating
Systems," Proceedings, 16th Annual Conference of
Sanitary Engineering, University of Kansas, Bulletin of
Engineering and Architecture, No. 56, January 1966
"A Study of Pesticide Disposal in a Sewage
Sludge Incinerator,", Frank C. Whitmore and Robert
L. Durfee, Versar Incorporated, Contract No.
68-01-1587, prepared for EPA, Tenth Report and
Final Report, 1974
"Sewage Sludge Incineration,", EPA Task Force, No.
EPA-R2-72-040, August 1972, NTIS No. PB-211 323
16
-------
BSP
ENVIROTECH
SLUDGE
OXIDATION SYSTEM
EXHAUST
STACK
I.D. FAN
SCRUBBER
17
-------
TOTAL OXIDATION vs. AUTO
HYDROCARBONS
1975 AUTO
1977 AUTO
OXIDATION! .019
0 10 20 30 40 50
GRAMS/DAY
-------
PALO ALTO EMISSIONS
300 PPM
•c:
25 PPM 25 PPM
<3
0 £
§ £
1 s
g 5
S 3
Q
^ BW
0.75 : '.. •;r;'
>(>^
CM
O
(O
HI
0
8
DC
LL
3
(/)
10.2
.... - ;.
0.15
GR./SDCF STANDARDS
(0
•sr
O
CO
CO
K
LU
UJ
§
3
O
F
CC
^
0.054
ACTUAL
19
-------
ENVIROTECH
to
o
NOX EMISSIONS
LIVERMORE VALLEY
AUTOS
SLUDGE
HAULING
SLUDGE
OXIDATION
10.0 MINIMUM
62 MAXIMUM
50 SLUDGE ONLY
10.1 PALO ALTO PERFORMANCE
28,000
LB/DAY
-------
Exhibit 5
DDT Removal in a Multiple Hearth
Furnace
input "
908
gms/hr
Multiple
Hearth
Furnace
After-
burner
0.0146 gms/hr
Scrubber
0.0036 gms/hr
.00039 gms/hr
Overall Removal Efficiency =/b08-.0186\1QO= 99.99%
V 908 /
source: EPA/Versa r
-------
2,4,5-T Removal in a Multiple Hearth
Furnace
.0030 gms/hr
in Air Stream
ro
K>
input
183
gms/hr
1
Multiple
Hearth
Furnace
I
afterburner
not in use
0.000036 gms/hr
t
Scrubber
.015 gms/hr
Overall Removal Efficiency = / 183-0.018 VinQ=QQ9RQ%
V 183 /
source: EPA/Versar
-------
Exhibit 7
Lead Removal in a Multiple Hearth Furnace
K>
Daily Input
5570 gms/day
' Multiple
Hearth
Furnace
1
47 gms/day
in Air Stream
623 gms/day
in Scrubber
4 9OO gms/day
in Ash
Scrubber x? 623
Removal Efficiency = I ^90 .
source: EPA/Versar
-------
ENVIROTECH
MERCURY REMOVAL IN A
MULTIPLE HEARTH FURNACE
Daily Input
Tahoe 28.0gm/day
Monterey 62.5 gm/day
Scrubber
Removal _.
Efficiency = Tahoe
Multiple
Hearth
Furnace
T
Ash
28.0
In Air Stream
Tahoe 1.195 gm/day
Monterey 10.82 gm/day
t
Scrubber
Tahoe 26.805 gm/day
Monterey 51.68 gm/day
/
V
Monterey 51.68 100 = 83
~
-------
Closed energy loop, sludge handling systems incorporates
heat treatment, incineration, and heat recovery
EIMCO thickener
Reactor
KJ
in
Heat exchanger
High pressure
pump
EIMCO decant tank |Steam)
Vacuum filter (existing)
ARCO Scrubber
Waste heat boiler
BSP scum concentrator
BSP multiple hearth furnace
-------
ENVIROTECH
COST COMPARISON OF
CLOSED ENERGY LOOP SYSTEM
vs CONVENTIONAL SYSTEM
(0
K)
so
45
£n 40
o
35
CE 30
liJ
°- 25
20
CONVENTIONAL
©
CELS
25 50 75 IOO
PLANT CAPACITY, MGD
-------
MANAGEMENT OF OIL SLUDGE FROM A REFINERY WASTE
WATER TREATMENT PLANT
by E.G. loakimis
A. D. Davletov
Bashkirian Scientific Research Institute
of Petroleum Refining
(USSR)
SUMMARY
Oil sludge sources at refineries, its quality and
utilization methods are discussed. Operating data for oil
sludge incineration in fluid bed incinerators, rotary drum
kilns, and incinerators equipped with atomizing burners
are presented. Incinerators of different design are com-
pared. Various approaches to improve incinerator capac-
ity by the reconstruction of main assemblies as well as
operating data for incinerators equipped with rotary
burners are presented.
Refinery and petrochemical waste water treatment
gives rise to a significant quantity of oil sludge whose
disposal problem has not been yet solved. Some refin-
eries have been still storing oil sludge.
Oil sludge is largely formed by solids entering
industrial sewage with make-up water, as a result of
equipment corrosion and the plant site cleaning, with
storm run-off as well as by dust blown in from air in the
cooling towers, and biological growths in recirculating
cooling systems. Oil sludge is also produced in storage
tanks both for crude and dewatered, desalted oil.
The above impurities entering the refinery sewer
system and moving along the conduits become en-
veloped with petroleum products and while settling out
in the treatment facilities form oil sludge which contains
up to 10 to 20% of solids and up to 30% of petroleum
products.
Conventional methods for oil sludge discharge and
transportation from the treatment facilities lead to
highly water-diluting the oil sludge entering a gathering
pond, petroleum products and solids content being as
low as 1 to 2%. As the oil sludge accumulates in
gathering ponds, a partial separation of petroleum
products and water takes place. The separated petroleum
product after proper treatment returns to the refinery
for reuse, the water free from settled solids being fed to
the primary waste water treatment unit.
The oil sludge consists of several layers. Upper layers
contain from 40 to 65% of petroleum products and 1 to
2% of solids while lower layers contain as low as 13 to
20% of petroleum products and as high as 15 to 40% of
solids.
In recent years, many refineries and petrochemical
plants have put into operation biological treatment
facilities producing waste activated sludge in amounts as
high as 2 m3 per 1000 m3 of influent waste water, with
water content of 97 to 98%, which contributes to total
refinery wastes.
A study of different methods of oil sludge utilization
(viz. stripping, thickener usage, various solvent extrac-
tion, etc.) has revealed their incapability of providing
complete petroleum product separation; petroleum
product content in residual solids being 3 to 5%, their
dumping is not feasible. Oil sludge management by
burning rather than utilization has proved to be the most
efficient and reliable means providing for essentially
complete oil sludge disposal, ash of no harmful effect
being a result of the incineration.
In the Soviet Union, the following methods for oil
sludge incineration have been tested on pilot and large
scales:
1) rotary drum kiln incineration;
2) incineration in a furnace with bubble burners;
3) incineration in a fluid bed of heat carrier;
4) incineration in a furnace with atomizing burners.
Studies of rotary drum kiln incineration performed in
our country on a pilot scale have shown the combustion
to be incomplete, about 28% of non-burned substances
being carried away with off-gases in spite of a two- or
three-fold air excess.
One of GDR refineries is operating an oil sludge
incinerator with a rotary drum kiln (Fig. 1).
This kiln is intended for the incineration of oil sludge
containing 2 to 4% of solids at a temperature of about
700°C.
The Soviet Union has gained a large-scale experience
in incinerating the oil sludge in furnaces with bubble
burners; the system is simple. The oil sludge is pumped
from a gathering pond to a vessel where it is heated,
freed from water then pumped into the kiln. Incinera-
tors with bubble burners are capable of incinerating aged
emulsions and oil sludge containing minor quantities of
solids (up to 5%) and at least 35 to 40% of petroleum
products, the 1,5m diameter and 3.5m high kiln
capacity being 5 to 6 tons/hr (Fig. 2). The incinerators
27
-------
with bubble burners are simple in construction but have
some limitations. The main limitations of these incinera-
tors involve the lack of ash-catching facilities and the
periodic shut-downs for slag removal.
Fluid-bed oil sludge incineration is of greater practical
use. Such units have been constructed in Japan, FRG,
France, and USA. In the Soviet Union, some fluid-bed
oil sludge incinerators having a design capacity as high as
1.5 m3/hr /Fig. 3/ have been constructed.
The technological incineration process carried out in
this type units involves the oil sludge pretreatment in
sewage regulators followed by incineration in a sand
fluid bed of a vertical kiln. The kiln is equipped with
mechanic burners for the atomization of fuel, oil sludge,
and cooling water. The off-gases cooling down to 250°C
was achieved by water injection into the kiln top zone
and scrubber. The volatile ash catching was effected
from off-gases in the scrubber and a set of cyclones.
The experience gained in operating a fluid bed
incinerator has shown that when incinerating oil sludge
containing 25 to 28% of petroleum products and as high
as 18% of solids the incinerator capacity was about
Im3/hr, the fluid bed temperature varying between 400
and 450°C. Attempts to raise the temperature above
450°C were unsuccessful for the following reasons:
1) feeding the oil sludge into a fluid bed produced
gasification of its organic portion followed by the
burning of petroleum product vapours over the
mentioned bed;
2) the cold air quantity introduced for fluidization is
well above that needed for the sludge burning;
3) the use of cold air for fluidization.
As a result of the fluid bed low temperature the oil
sludge has no time to be burned, which leads to sand and
sludge agglomeration.
Supplemental fuel fed both to the fire box and the
fluid bed did not contribute to a higher temperature of
the fluid bed.
To provide for a normal operation of the incinerators
with a fluid bed intended for oil sludge, it is necessary to
heat the air for fluidization to 600°C, to have a watch
incendiary burner above the heat-carrying agent bed. At
one of the refineries a unit is being constructed with due
regard for all the mentioned limitations. Recently, along
with the above units, incinerators with atomizing burn-
ers have been used. As the experience in pneumatic
burners has shown, their stable operation is adversely
affected by all kinds of foreign matter present in the
sludge and often leading to clogging the burners. The use
of screens at the feed pump suction does not prevent
burners from clogging but makes it much more difficult
to operate the pumps due to frequent screen replace-
ments. The unstable operation of pneumatic burners
adversely affects the operation rhythm of the whole
unit. Most of these limitations are not peculiar to the
rotary burner whose performance can be affected only
by a foreign matter size of more than 10 mm.
One of the operating incinerators was reconstructed
to change from fluid bed to torch burning under the use
of a rotary burner /Fig. 4/.
The reconstruction involved modernization of the
following procedures: the sludge intake and pretreat-
ment, the sludge feed to the incinerator and its
atomizing, cooling off-gases/Fig. 5/.
To withdraw the oil sludge from gathering ponds, two
pumps (screw and sanitary) were installed in series as a
part of the floating assembly. The screw pump sub-
merging into the oil sludge discharges it into the suction
of the sanitary pump, the latter pumping the sludge to
the pretreatment. However, the thickened bottom sludge
cannot slip down into the screw pump suction.
Therefore, a scraper device is provided which makes it
possible to feed the sludge into the pump suction. The
screw receiving window is equipped with a screen to
retain major inclusions. On its way to settling tanks the
oil sludge is passed through a preheater where its
temperature rises to 60 to 80°C as a result of the direct
contact with steam. The heated sludge is settled in a
tank, the separated water being drained into a gathering
pond. After the treatment, petroleum products of the oil
sludge average about 26 to 34% and solids 3 to 11%.
From the trapped oil treatment facilities the oil
sludge goes to sewage regulators from where it is
pumped to combustion.
As the operating experience has shown, mechanical
agitators installed in the sewage regulators are often put
out of the action and do not provide sufficient mixing
and the sludge composition equalization. To maintain a
more constant sludge composition fed to the
combustion, the oil sludge was recirculated using a
pump.
To provide for the fuel combustion, the rotary burner
has a watch incentiary burner operated on supplemental
fuel with a consumption of 1 to 3%. The lower part of
the incinerator is made of a two-layer steam- or
air-cooled conic bottom destined to the slag and ash
discharge. Vibrators installed on the conic bottom surve
to improve the slag discharge. Slag is discharged without
shutting down the unit.
According to the experience gained in the operation
of a vertical furnace, its lining made of fireclay brick
cannot withstand temperatures higher than 1000°C—it
melts, especially when feeding alcaline wastes, and is put
out of the operation after 2 to 3 months. Therefore, the
lower two thirds of the furnace lining were replaced by
the lining made of chromomagnesite brick with a
28
-------
subsequent increase in the lining life up to 17 to 18
months.
Cooling off-gases is a combined procedure. The
off-gases are cooled by water injection in the furnace
and scrubber, then in the air cooler made of ribbed cast
iron tubes, the off-gases with dust blown in being passed
through the intertubular space and the cooling atmos-
pheric air-through the tubular space. To clean the
ribbed tube surface from ash deposits, a shot blasting
device has been mounted providing for a complete
cleaning of the cooler dusty surfaces by cast iron shot.
The device is switched on once per shift for some
minutes.
The inclusion of the above and other improvements
in the unit scheme has made it possible to reach an
average capacity of 2.7 tons/hr, a maximum capacity of
4 tons/hr being achievable when burning the sludge
containing 25 to 27% of petroleum products, 5 to 10%
of solids.
Operating the unit makes it possible to dispose of all
the oil sludge produced, which contributes to a con-
siderable improvement of the waste water treatment
effect for the refinery treatment facilities.
The flow diagram of the most promising oil sludge
incinerator is shown on Fig. 6.
The oil sludge from treatment facilities goes to a
pretreatment tank where it is freed from water excess
and petroleum products and is then fed to a sewage
regulator. The oil sludge heated to 60 to 80°C goes from
the sewage regulator to a rotary burner and is burned in
a fire box of the incinerator. The off-gases leaving the
incinerator are cooled by water injection, freed from
dust in a set of cyclones and discharged into the
atmosphere. The ash trapped in a cyclone accumulates in
a bunker and is dumped periodically. The above scheme
makes it possible to most economically incinerate the oil
sludge.
29
-------
Oil eludge
» Air
Rotary tubular kiln
xj ifuel oil
» *
IV Ash
Ash
Fig.I,, Rotary drum kiln
I - rotary tubular kiln
2 - off-gas chamber
Streams: I-oil sludge;jj-air;^|-fuel oil;|y-ash
30
-------
S200
Fig.2.Kiln with bubble burner
I-housing;2-fireproof lining;3-heat insulation;
4-supporting belt;5-feedlng pipeline;'6-primary air;
7-bubble s^ate^-secondary air;9-orifices for the suction
of atmospheric air
31
-------
Fig.3. Oil sludge incineration in a fluid bed
I-floating pump assembly;2-sev7ase regulators-vertical kiln:
p-2.6m,H-8,55i;4-scrubber of VTI type;5-battery cyclone;6-stack;
7-air blower;8-flue gas blower;9-sludge punp;IO-fuel pump;
II-v/ater for cooling
32
-------
/"\
V
-.«t..i.i '. . *.*^t..',,*. • -*'-- •.*. Itu* »-
Fig.4. General view of rotary burner
33
-------
f
I •
Fig.5» General view of oil sludge incinerator
34
-------
Fig,6. Flow diagram of the most promising oil sludge
incinerator
I-oil sludge pretreatment tank;2-sewage regulator;3-furnace
with a rotary burner;4-a set of cyclones;5-stack;6-flue gas
blov;er;7-bunker for ash;8-v;ater supply;9-slag removal;lO-air
blowerJI-fuel supply;I2-sludge supply;IJ-sludge supply
35
-------
MODERN STATE AND PRINCIPAL TRENDS IN TECHNOLOGY DEVELOPMENT
FOR WASTEWATER SLUDGE TREATMENT.
by G. S. Altovsky, Ail-Union Scientific Research Institute
VODGEO.
Sludge treatment is among the most difficult, ex-
pensive as well as less developed wastewater treatment
problems put recently forward.
The object of sludge treatment is to get an end
product the properties of which either enable it to be
utilized or make it possible to minimize a deleterious
effect on environment.
In the USSR as in many other countries the principal
treatment method of municipal wastewater sludges was
for a long time anaerobic digestion followed by drying
on sludge beds and wastewater sludges were discharged
in storage devices. However a necessary change to
mechanical methods of sludge dewatering was due to
low operating capacities of installations, to unfavorable
sanitary conditions and also to lack of area in industrial
districts of our country. Soon after the Great Patriotic
War the construction of the first large installations for
vacuum filtration and heat drying was accomplished at
Moscow municipal sewerage plants. The plant construc-
tion for mechanical dewatering is now being carried out
in many large and medium-sized towns and at industrial
enterprises in the USSR. As a result of a qualitative
composition variety of municipal and industrial waste-
waters and used treatment methods, such sludges are
formed that are quite different by their physical-
chemical properties, therefore it does not allow some
universal treatment means and methods to be developed.
Today a technological sludge treatment process is
multistage and involves the following consecutive stages
as thickening, stabilization of organic matter, condition-
ing, dewatering, utilization and disposal. Modern engi-
neering enables the several feasible treatment methods to
be used at every of these stages, the efficiency of the
methods depends on sludge physical-chemical properties
and on local conditions for treatment plant construc-
tion. Therefore the choice of a rational technologic
treatment scheme is a complex engineering-economic
problem the solution of which in many cases requires
the performance of the experimental researches in some
variants.
The important scientific and practical problems as
concerns the wastewater sludge treatment are to give
objective evaluation to currently use'd methods and
apparatus, to establish the scope of its rational use, to
find out the most promising trends in further scientific
research and test design works and to coordinate
activities in this field.
We suppose that the USSR-US symposium on sludge
treatment will contribute in solving these problems.
The given report deals with principal sludge treatment
methods used and improved in our country in technolog-
ical sequence of their employment.
The sludge thickening is the first stage of treatment
that allows simultaneously an original sludge volume to
be reduced at minimum energetic expenditures as well as
the capital and operating costs to be decreased at
consecutive treatment stages.
The most widely used method is gravity thickening in
sedimentation tanks-thickeners, the construction of
which differs little from usual primary sedimentation
tank (either radial or vertical one). The gravity thick-
ening duration depending on sludge properties is in
6 to 24 hours range. In most cases this method for
sludge treatment gives suitable results at not high
operating expenditures. However it does not always
ensure a sufficient extent of thickening. Particularly
in the case of treatment of the activated sludges
discharged from wastewater biological treatment
plants the maximum concentration for solid sludge
is only of 3%.
It is known that the increase of sludge thickening
intensity provides large opportunity for simplifying all
the technologic treatment scheme. At current trend of
using the heat methods (drying or incineration) in the
last stage of sludge treatment the increase of thickening
intensity enables to refuse from such expensive stages as
conditioning and mechanical dewatering namely the
whole technologic process is reproduced by two stages as
thickening-drying (for utilized sludges) and thickening
and incineration (for not utilized sludges).
Therefore over the past years we study such processes
as flotation, centrifugal separation and vibrothickening.
The extent of method improvement is various.
In regard to flotatory thickening the research is
carried out in pilot and full scale and the process for
activated sludge thickening is as present implanted at
many enterprises of our country. With this method the
solids concentration achieves up to 7% and the treat-
ment time can be reduced by 3-4 times versus the gravity
thickening.
As concerns the centrifugal thickening of activated
and other sludges the studies are now carrying out and
are aimed at the choice of more rational construction for
disk type centrifugal separators.
36
-------
The sludge vibrothickening method involving the
filtering via vibroscreens and the using of submerged
type vibromembers is in the stage of researches. The
available results allow this method to be considered the
most promising one due to process high rate, to
inconsiderable electroenergy consumption and to high
intensity of thickening. However the equipment pro-
vision for this process has not still complete.
The object of wastewater sludge stabilization is to
break down the sludge organic matter that is subjected
to biological destruction in order to prevent its septicity.
It is necessary to provide this treatment stage only if the
detention period of sludges on outdoor areas is long (e.g.
during drying on sludge beds) as well as when sludges are
used as agricultural manure without heat drying.
As outlined above the principal stabilization method
in our country is so far anaerobic digestion in digestion
tanks. In spite of the fact that the method has some
advantages in the near future it will be obviously valid
only for large municipal biological treatment plans. In
the case of waste water sludge treatment, anaerobic
digestion is not essentially advantageous as the process is
sensitive to both many components contained in waste-
water sludges and sharp load fluctuations. The aerobic
stabilization method consisting of biological oxidation
of sludge organic matter in such installations as aeration
tanks is an alternative to anaerobic digestion.
Aerobic stabilization advantages are the large process
stability, the ease of operating and the lower plant
construction costs.
The aerobic stabilization process has recently been
put into practice at many biological treatment plants of
low and average capacities. The stabilization period for
activated sludges of various wastewater types is on the
average in the 8 to 11 day range. Stabilization of 1 kg of
activated sludge organic matter requires about 0.7 kg of
oxygen. The increased energy expenditures on aeration
refer to disadvantages of the aerobic stabilization
method. Under the same conditions the aerobic stabi-
lization process is estimated to be more advantageous
than digestion for the plant capacities up to 100,000
m3/day. However the method can be employed at larger
plants if digestion process has no utilization for outlined
above reasons.
In our country only the reagent method is so far used
for sludge conditioning prior to the mechanical dewater-
ing. Ferric chloride and lime are predominantly used as
reagents. The reagent consumption is very considerable
and treatment cost amounts up to 40% of total
investments spent on sludge dewatering.
Heat treatment (Porteous' process) is considered to
be an adganced sludge conditioning method among
promising others. Based on the laboratory tests and on
the experience of foreign achievements, the apparatus
and device development for heat treatment is being
currently carried out in some consecutive modifications.
The scheduled plant construction, both in pilot and full
scales is scheduled that makes it possible to begin
process implantation. It is known that a disadvantage of
the heat treatment process is heavy pollution of super-
natant and filtrate (COD is in the range of 10-15 g/1)
caused by conversion of the large amounts of solid
organic matter to dissolved one. Recycling the polluted
liquors for retreatment considerably increases aeration
tank loads (by 15-20%). We are now studying the local
treatment feasibility of both supernant and filtrate
without mixing it with the total effluent flow. Sorption
and bioxidation methods are being examined.
In our country sludge conditioning by using high
molecular polyelectrolytes (flocculation additives) has
not yet employed in full scale. The process studies are
aimed to find out and develop the more economic and
efficient types of flocculation additive. In the USSR
three main processes of vacuum filtration, pressure
filtration and centrifuging are extensively used for
wastewater sludge mechanical dewatering. Vacuum fil-
tration is now the most developed and improved process
used in many towns and at industrial enterprises of our
country. The object of research and design works
currently performed in this field is to improve and
modernize the vacuum filter construction, to intensify
the process and to determine experimentally process
technological parameters for the particular kinds of
some wastewater sludges.
In our country pressure filtration for wastewater
sludge dewatering has been recently used. In the USSR
the automatic compartment pressure filters of type
FPAKM are now manufactured that proved to be
suitable for dewatering of many kinds of wastewater
sludges. The filter pressing enables the greater extent of
sludge dewatering to be accomplished verus vacuum
filtration and centrifuging. So in the case of sludge
treatment of municipal sewage the cake water content is
achieved in the range of 50% if the efficiency by sludge
dry weight is about 15kg/m2/h. However as concerns
the filter pressing efficiency, as a rule it is generally
second to vacuum filtration and centrifuging. Therefore
the filter presses are advisable in cases when the last
treatment stage of sludges requires the use of heat drying
or incineration.
In our country the centrifugal method for sludge
dewatering is not yet extensively used. However the
evident advantages (compactness, good sanitary condi-
tions, ease in operating, wide range for control of
process variables) allow this method to be considered as
an advanced one. The solid-bowl centrifuge development
37
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of a particular type with a capacity up to 50m3/h is
being carried out, allowing this effective method for
dewatering to be more widely used in the future.
Vibrofiltration is one of the new methods for
mechanical dewatering. The process attracts attention by
its high efficiency and comparatively low capital and
operating expenditures.
Tests performed on the laboratory vibrofilter model
for municipal wastewater sludge dewatering gave the
following results:
- efficiency is in the range of 100-160 kg/m2h
— cake water content is about of 80%
- losses of solids together with filtrate is of 10-20%
(the sludge is digested under thermophilic condi-
tions and is treated by ferric chloride and by lime).
The pilot vibrofilter is now mounted and the experi-
mental works will be continued by using it.
Sometimes the heat drying is required in the last
treatment stage if the wastewater sludges have utilization
as agricultural manure.
This process provides also the sludge disinfection in
addition to extra wastewater decrease.
The drum kilns for heat drying of the dewatered
sludges are used at two treatment plants of Moscow
municipal sewerage system.
The new technical approach to this process is the use
of dryers with gas counter current that reduces the
capital expenditures by 3-4 times and the operating ones
by 15% versus the drum dryers. Based on this principle
two experimental lines have been constructed. One line
is for the heat drying of wastewater sludges in Orechovo-
Zuevo, the other one is for the drying of lignin sludge at
a cellulose plant.
Incineration is recognized as one of the most radical
methods for disposal of unutilized organic sludges.
In the USSR certain experience is available in
incineration of process liquor sludges produced at
wastewater treatment of the petroleum refinery plants.
The incineration of dewatered sludges was not used up
to now. However in the very near future it will be
appropriate beyond all shadow of doubt to put into
practice this method at many industrial enterprises.
Taking into consideration a variety of physical-chemical
and heat-physical properties of wastewater sludges pro-
duced from different industrial processes and the arisen
difficulties concerning the development of a universal
furnace device several types of kilns are currently being
tested (as with fluidized layer, multihearth and cyclone
ones) for subsequent experiments at using of different
kinds of sludges.
Summarizing all the outlined above, the main prob-
lems that are brought forward before our scientific
research, test design institutes and industrial enterprises
in the field of wastewater sludge treatment can be
classified into the following groups as:
1. Development and improvement of assembled de-
vice and apparatus manufacturing for sludge heat
treatment including:
a) heat treatment for sludge conditioning prior to
dewatering,
b) heat drying of dewatered sludges for its utili-
zation in agriculture.
c) incineration of unutilized sludges to reduce its
mass.
2, Development and improvement of equipment and
plant constructions for sludge vibrothickening and
dewatering.
3. Development and improvement of efficient floccu-
lation additives production for sludge condition-
ing.
4. Development and improvement of modernized
centrifugal separators for sludge thickening and
dewatering.
5. Carrying out the complex investigations on agri-
cultural and sanitary-hygienic evaluation of waste-
water sludges.
38
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MANAGEMENT AND DISPOSAL OF RESIDUALS FROM
TREATMENT OF INDUSTRIAL WASTEWATERS*
by
William J. Lacy and Allen Cywin**
INTRODUCTION
The Water Pollution Control Act and Amendments of
1972 and the Clean Air Act require industry to treat
their liquid and gaseous wastes in accordance with best
treatment practices.
The subject of this paper is similar to the topic of a
recent (Feb. 3-5, 1975) Conference namely "National
Conference on Management and Disposal of Residues
from the Treatment of Industrial Wastewaters." The
proceedings have been published and are part of the
eleven reports (list attached) we are submitting to you.
It is our intention to present a summation of what
the speakers actually said.
Mr. Roger Strelow, Assistant Administrator, Air and
Waste Management, U.S. Environmental Protection
Agency, indicated industrial residues are expected to
double in the next 10 years. Some will consist of toxic
residues, which if improperly disposed on the land can
cause harmful effects from leaching, sublimitation-
evaporation, runoff, or direct contact.
Hazardous waste residue regulations are currently
lacking. Public pressure for legislation has been limited
probably because the problems are not quite understood
and/or solution may be out of sight.
However, the Office of Solid Wastes Management
Program is preparing guidelines for acceptable storage,
treatment and disposal of residues which are imminently
hazardous.
EPA is urging process improvements to reduce the
amount of residues generated by industry:
The method is by reducing pollution in the environ-
ment and the cost of treatment by recovery of resources
for reuse by the industry or by others as a means to
conserve energy.
Mr. George Rey, EPA's Industrial Pollution Control
Division presented a detailed technical analysis of
industrial residue disposal and an overview of the EPA
R&D effort. The intermedia transfer of pollutants was
under study by the Federal Water Pollution Control
Administration in 1966 and was the forcerunner of
current EPA efforts.
Open cycle and closed cycle systems with total
environmental control were discussed.
EPA's program is viewed as an integrated effort of
industrial wastewater treatment, and water reuse, residue
reuse, and disposal.
A residue management check list for industry was
presented.
"Zero discharge" as an economically viable goal may
be achievable when we consider water reuse and resource
recovery.
Mr. John P. Lehman, Office for Solid Waste Management
Programs indicated that residue disposal is of interna-
tional concern with U.S. lagging behind a number of
countries. He presented amounts of residues from
various sources i.e. industrial waste residues of 260
million dry tons/year which is twice the amount of
municipal solid wastes and 30 times that of municipal
sewage solids.
Moreover between 1971 and 1983,industrial residues
from pollution control are expected to double these
quantities.
At least 10 million dry tons/year of residues may be
toxic 40% of residues are inorganic and 90% are liquid.
Although technology is available there is no economic
or legislative requirements to solve problems. Proper
disposal techniques may cost 550/ton.
Residue disposal with exception of pesticides and
radioactivity is not subject to current Federal regula-
tions.
A strong Federal regulatory program is needed which
will deal with the residue problems from "cradle to
grave."
Mr. Murray Newton, presented a discussion of State
standards and programs for hazardous residues disposal.
Much of the Federal activity on hazardous wastes
management has occured during the last year.
Minnesota, California, and Oregon, have comprehen-
sive hazardous wastes management programs which
control "life cycle" of residues. Most other states have
programs which have discrepancies because they are not
comprehensive.
*Presentation at the U.S./USSR "Handling Treatment and Disposal of Sludges and Industrial Residual", Symposium Moscow,
USSR, May 5-8,1975.
"Respectively, Directors of the Industrial Pollution Control Division, R&D and Effluent Guidelines Development Division, U.S.
EPA, Washington, D.C.
39
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EPA's Office of Solid Wastes can currently provide
some financial -and technical assistance to states to
develop hazardous waste management programs.
Current problems in residue disposal programs are:
1. Administrative or political
2. Concentration of problems in a limited number of
states
3. Free movement of residues is prohibited
4. Lack of database
We can expect increased activity in legislation and
programs.
However, with or without Federal legislation, the
States must move ahead and not wait for the political
action.
Mr. John Monteith of the Canadian EPA pointed out
very clearly that environmental policy in Canada is
influenced by the factors of geography and climate and
the multiplicity of governing bodies. Also, discussed was
the degree of responsibility assumed by each of these
bodies—total, shared or liaison.
Legislation on the Federal level is in the formative
stage. It includes the proposed Environmental Contain-
ment Act and the Ocean Dumping Act. Research
programs under the Canada/Ontario agreement for Great
Lakes Water Quality include waste characterization and
sampling-methodology. Land disposal of sludges cover
heavy metals and persistent organics.
Mr. Lawrence D. Kramer, Minnesota Pollution Control
Agency stated the ability to control solids disposal on
land sites involves learning where such sites have been
located, and to establish requirements for each site. That
includes operation, an adequate system of monitoring,
and reporting the results. Consideration is being given to
establishing regional plants for detoxifying sludges be-
fore land disposal.
Dr. Thomas Short, EPA reported that a survey of
industrial solids disposals as well as liquid concentrates
in Ventura County indicates the need for a centralized
treatment plant to accept all industrial waste concen-
trates. A survey quantifying the volume and quality of
these wastes indicates the variability is such it is not
practical to handle such wastes in existing municipal
wastewater treatment plants. Solids now sent to landfill
sites may be diverted to this centralized treatment
facility. Joint industrial-municipal studies are underway
to evaluate the detoxification of all wastes for land
application of organics and for ocean disposal of
inorganics.
Ms. Marsha Gorden, Development Sciences Inc. pre-
sented an excellent description of an EPA sponsored
project on the history of traditional in-plant manage-
ment of environmental problems which indicated re-
gional systems may be more effective because of
economics of scale. The five case histories on intermedia
impact of industrial residuals illustrated differing ex-
amples of public and private control over the treatment
and recovery of mercury, cheese whey, organic solvents,
and mixed metal bearing wastes.
Mr. Samuel Morekas, EPA presented an assessment of
hazardous waste practices in several industries. He
pointed out that potential hazardous wastes are increas-
ing at a rate of 5-10%/yr. His offices currently have
many industries under study. These studies include:
inorganic chemicals industry, alkalies and chlorine,
industrial gases, inorganic pigments, industrial inorganic
chemicals. States are involved where the various cate-
gories of wastes predominently occur. Also being devel-
oped are: Summary of treatment and disposal practices
for various wastes and typical costs of selected wastes by
various treatment or disposal methods.
In conclusion tentative indications are that land
disposal methods in most cases do not provide adequate
containment, nor is there sufficient monitoring of these
wastes.
Mr. William T. Bush, Atlanta Water Bureau raised the
question is a water plant a source of industrial waste
effluents? Most would say NO, But because of the high
turbidity in the water and Al (OH)3 precipitate, the
answer is YES.
Alum sludge treatment investigations were started in
1967, centrifuging, air flotation none of which didn't
prove satisfactory. Following evaluation of unit opera-
tions the city of Atlanta engineers chose pressure
filtration with diatomaceous earth pre-coat. They re-
ceived bids in 1969, and started operating the plant in
1972.
Results: Plant operating at 5.9% solids which is then
concentrated to 46% solids and pressed yielding 518
million gallons of H20 and 8,673 tons of solids
recovered from producing 15 billion gallons of water.
The equipment used are the first two pressed of their
type in VS. EPA provided 55% of funds required to this
project.
He concluded that (1) Pressure filtration definitely
works, (2) Water is returned to reuse, (3)Dewatered
solids can easily be handled.
Mr. Kenneth Ladd, Southwest Public Service Com-
pany stated that the Southwest Public Service Co. used:
(1) Secondary treated sewage effluent for cooling,
(2) They are able to treat water up to 3% solids, (3) The
cooling tower blowdown was used for irrigation of
40
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selected agriculture crops, (4) Southwest Public Service
Co. built a coal fired plant, using low sulfur Wyoming
coal and installed electrostatic scrubbers, (5) They used
the limestone content derived from the sewage treat-
ment plant by using a "Mudcat" to pick up the
materials, (6) Projections of solid waste to be produced
by electric utilities burning coal were given, (7) Looking
for local uses for mixed sludge, fly ash and bottom ash,
and soil, (8) They are also investigating uses of above
components individually.
Mr. Laszlo Pasztor, Dravo Corporation gave a description
of EPA data on power plants including scrubbing media
utilizing 90% lime and/or limestone.
Thiosorbic process which uses lime with 5-6% Mg was
described. He also described how the Calcilox* process
works with an additive which is a waste product from
the steel industry and is used to stabilize flue gas
desulfurization sludges.
1 ton of 1% coal yields 160 pounds of sludge, equal
to 8% of weight of coal. By 1980, the industry will
produce 35X 106 tons (dry) of sludge annually.
He gave various potentially useful application for
stabilized flue gas desulfurization sludge.
Mr. F. N. Davis, Utah Power and Light stated that a
power company (Utah P&L) is assessing the effectiveness
of brine concentration as a technique for ultimately
closing the wastewater cycle. Concentrated brines are
rendered suitable for land disposal via natural evapora-
tive-dewatering mechanisms.
Dr. K. Willard, EPA is exploring two thermal systems
(pyrolysis) to effect an economical disposition of bark
residues from the pulp and paper industry. Potential
economic advantages are associated with the conversion
of the bark which can be converted into by products
such as oil and that the related hot gas can be used in
electricity generating gas turbines.
Mr. Jacquish, Barber-Coleman, Corporation described
wet oxidation, as a specific technology, which has been
investigated relative to its usefulness in stabilizing spent
ordinance (Military) materials. Pilot scale studies have
documented the technical feasibility with costs accept-
able to the Department of Defense.
Dr. Ronald D. Neufeld, University of Pittsburgh sug-
gested that the normal biological sludge environment of
a sewage treatment plant may in fact be the key in the
scavenging of transition metals in industrial-municipal
wastewaters. This type of information has a bearing on
the degree of pretreatment that may ultimately be
required for industrial dischargers into municipal sys-
tems. The quantities and qualities of sludges produced is
likewise related to pretreatment.
Mr. Howard Brown, Manufacturing Chemists Association
explained that process techniques involved ion exchange,,
solids concentration by precipitation centrifugation, and
evaporation; by perfiltration, and electrolytic oxidation.
In each instance the process has been scaled up for
practicable and feasible application and acceptance and
for economic evaluations and cost/environmental con-
trol effectiveness determinations.
It was significant that none of the papers presented at
this session of the conference resulted in a waste
material for disposal, the accent being on reuse or new
use.
Dr. Craig Brandon, Clemson University paper was on the
recovery of textile dye concentrates for reuse within the
industry utilizing reverse osmosis techniques.
Mr. John W. Wade, Toledo Pickling and Steel Service
dealt with the production of waste sludges from the
pickle acid rinse water waste lines in a steel mill and with
potential for by-product use as a concrete additive
and/or fertilizer.
Dr. R. H. Cherry, Jr., Battelle-Columbus Laboratories
reported on an EPA sponsored project. General purpose
of work was to develop a technique for recovering the
metals spent electroplating baths and rinse waters.
Recycle waters to rinse operations also detoxify existing
sludge stores.
Seven platers installations were visited to gain back-
ground in sludge sources and production technology and
to review waste treatment techniques.
Mr. Peter L. Kern, The New Jersey Zinc Company
discussed Ti02 production which produces a waste
H2S04 waste stream containing metallic sulfates.
A process was developed with EPA's help to reclaim
sulfuric acid. Concentrated sulfuric acid from this waste
and a 2 Ton/day pilot setup has been successfully
handled.
A spray drier evaporates water and produce H2S04 to
get a dry metal laden solid. This material is quite soluble
which if not reused makes disposal a significant problem.
Vapors are condensed in multiple stages to give
concentrate sulfuric acid (85%).
The process loses a small amount of acid as mist and
SO.
New Jersey Zinc Company has designed 345,000
metric ton/yr. commercial plant to process waste H2S04
41
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at a total cost of $7,800,000 or S77/T (metric) acid
recovered.
Fuel demands and residuals remain serious problems
to be solved.
Dr. J. T. Lawhon, Texas A&M University discussed
treating cottonseed wheys from protein isolation from
cottonseed flour by semi-permeable ultiafiltration and
reverse osmosis. The process produces 45-95 Ibs/ton of
the waste material as a solid waste residual.
Ultrafiltration membranes are utilized to retain pro-
teins, and passed most of remainder for additional
treatment.
A second non protein whey fraction was recovered by
the reverse osmosis membrane.
Spray dried protein concentrate from the UF mem-
brane were used as protein fortifiers in breads, non-
carbonated beverages, and as whippingdessert products.
Dr. Sheldon Bernstein, Amber Laboratories, reported
that saccharomyces fragile s are easily grown on acid or
sweet whey-continuously in an aerated fermentor-cell
counts equals several billion/ml as a high grade protein
feed material.
Sterility is not a problem due to low pH. Lactose is
carbohydrate substrate.
Ethyl alcohol can be produced and recovered with
lower cell yield.
Using centriftigaticn, food grade yeast can be pro-
duced. However, the supernatant streams does create a
disposal problem.
Protein quality appear to be good. They whey is low
in sulfuric amino acids. No toxicity was exhibited in rat
feeding.
Dr. Richard L. Olson, Resources Conservation Company
presented a unique dewatering system using an alphatic
amine capable of processing a wide variety of municipal
and industrial sludges is being developed by his com-
pany.
This system, Basic Extracting Sludge Treatment
(B.E.S.T.) has had extensive laboratory evaluation dur-
ing past two years.
System prototype tests are currently being con-
ducted. B.E.S.T. appears capable of handling large
number of organic and inorganic sludges. Results vary
depending upon sludge type. Good results obtained with
municipal sludges. Pulp and paper sludges were also
tested with similar success.
Variable results were obtained with steel industry
sludges.
Dr. D. Rebhan, Farbwerke-Hoescht-Unde Corporation
reported on a new process developed by Hoechst
whereby hydrocarbons and their chlorinated deriva-
tives are completely converted by chlorination to
CC14+HC1. Ethylene and propylene are favorable
starting materials. In constrast to combustion tech-
niques, this process conserves the carbon value of the
utilized wastes. It is a completely closed recycle system.
A semi-commercial plant producing 8,000 tons/yr. CC14
operating since 1970.
A commercial plant (50,000 ton/year) is under
construction. Another plant (36,000 tons/year) is being
planned for the U.S.S.R.
Mr. Joost J. Gallay, Imperial Holding AG in his paper
described the design of gasification burners. These
burners are used on ships which incinerate chemical
waste. It was claimed that the cost of incinerating many
hazardous wastewaters is lower than treatment. Conse-
quently, many manufacturers prefer thermal disposal.
These ships were originally designed to incinerate
liquid chlorinated hydrocarbons. However, their gasifi-
cation burners have permitted the burning of high water
content waste.
Some plants generate large volumes of chemically
contaminated water. Thermal disposal of such large
volumes is too expensive. Volume reduction is necessary.
However, this involves an increase in sodium concen-
tration of the waste which results in serious corrosion of
the lining of the combustion chamber. Work is under
way to attempt to solve this problem.
A third incineration ship will be commissioned at the
end of 1975. This ship will have a furnace capable of
incinerating both liquids and sludges.
Wastes would not be incinerated unless approval was
received from the regulatory agencies of the countries of
origin.
Dr. A. Sadana, Enviroengineering, Inc. indicates that two
new refinements of the Carver-Greenfield multi-effect
evaporator process have been successfully used to
treat/reduce wastes residues from a pharmaceutical
processing operation and a pet food plant. The first
refinement is the inclusion of a pyrolyzation step which
decomposes the organic material in the dried solids
(pharmaceutical wastes) into volatile hydrocarbons to be
fed to the boiler burner as fuel, thus promoting energy
recovery and resulting in a minimum amount of ash. The
second refinement is the drying of dilute and concen-
trated pet food waste stream simultaneously and recov-
ering by-product fit for resale. Both refinements to the
multievaporator process close the "aqueous loop" and
approach zero discharge. The technical aspects and
economics of implementing the two refinements of the
42
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multievaporator process to the two waste streams were
discussed.
Mr. Jesse Conner, Chemflx, Inc., described a silicate
based system for solidification of liquids as an approach
to their "neutralization" with respect to "environmental
impact."
Mr. Robert A. Stadelmaier, Chem-Trol Company dis-
cussed a regional approach to handling sludges from
physical chemical wastewater treatment processes. Firm
approach is to recover substances of value from the
sludges.
Mr. Robert Landreth, EPA presented discussion of
chemical fixation of hazardous, concentrated wastes
particularly those from sulfur oxide scrubbers prior to
land application.
Mr. Donald Carruth, President of the Eagle Foundation
presented the background and a description of events
leading to a demonstration of the destruction of
hazardous substances by incineration at sea. The pre-
sentation was formally discussed by a representative of
the Environmental Protection Agency.
The EPA scientist indicated that the permit issued for
actual burning was for a one time operation and did not
amount to an endorsement of this technique.
Mr. Alfred Lindsey, EPA reported conventional sanitary
landfill of hazardous or potentially hazardous waste can
lead to the contamination of surface or groundwater due
to leachate and runoff problems, particularly in areas
where the annual precipitation rate exceeds the evapo-'
transpiration rate. Methods were proposed to modify the
conventional sanitary landfill to ensure proper disposal
of chemical and hazardous industrial wastes.
His paper examined some of the techniques currently
available to prevent, collect, treat, monitor, and manage
chemical waste landfill leachates. In addition, hazardous
waste preparation techniques, employed to minimize
waste hazardous prior to secure landfill disposal, were
presented.
Mr. Edwin E. Slover, Union Carbide Corporation,
reported that waste activated sludge from its own
industrial waste treatment unit is used by this moderate-
sized, multi-product chemical plant to supplement the
soil added to stabilize hazardous solid waste blended
into the plant's licensed chemical landfill.
The unique "flow-through" design of the chemical
landfill permits all leachate to be collected and siphoned
to the waste treatment unit for reprocessing.
Final dewatering of the sludge is done in temporary,
clay-floored beds and shallow basins serving the treat-
ment unit until an ultimate dewatering process is
selected to meet 1977 Federal effluent permit standards.
In combination, the treatment unit, the beds, and the
special chemical landfill provide a low energy, closed,
wate-disposal cycle for the biosolids.
Mr. George E. Brown's, Mallinckrodt, Inc., report dealt
with the development of a land application system for
an industrial waste water high in nitrogen content. The
land application is an integral part of the waste water
treatment system.
Mallinckrodt, Inc., operates a synthetic organic chem-
ical manufacturing plant north of Raleigh, N.C. The
products from which the waste water is obtained are
organic pharmaceutical and medicinal chemicals. The
overall treatment system consists of in-plant neutrali-
zation, equalization, an anaerobic lagoon, two aerated
basins in series, clarification and sludge recycle, and land
application by spray irrigation. The spray irrigation of
the treatment plant effluent together with wastes sludge
is proposed and is not yet installed. Because of severe
limitation of discharges to the local Neuse River, land
application is the only system found to be technically
feasible for the disposal of the final effluent.
In summation Dr. Lazar, EPA indicated that the
hazardous waste disposal problem has assumed particu-
larly significant proportions because of the progressive
implementation of air and water pollution control
programs, ocean dumping bans, and cancellation of
pesticide registrations. The net result has been an
increased tonnage of land-disposed wastes, with adverse
impact on public health and the environment. The
problem is manifested in groundwater contamination via
leachate, surface water contamination via runoff, air
pollution via open burning, evaporation, sublimation and
wind erosion, poisonings via direct contact and through
the food chain, and fires and explosions at land disposal
sites. The subject presentation cites case studies that are
associated with these various mechanisms of damage.
43
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EPA-660/2-74-Q55
June 1974
Environmental Protection Technology Series
Physical-Chemical Treatment of
Municipal Wastes 3y Recycled
Magnesium Carbonate
Cffica of P.cssarch and Dovel
US. Er']r2,-.^=r.t»» Prcir-ctior.
\VashinQicn. D.C. 2D-VSD
-------
EPA-67G/2-74-008
January 1974
Environmental Protection Technology Series
f ••'
u;:.. ;i:ng
Office ef Rcscezich end DDveS???r,snt
U.S. s-T.vironr.enl:! Pr^tectiwn /'^rnc
y/3£;iington, D.C. 20^50
45
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13LEA
WATER POLLUTION CONTROL RESEARCH SERIES Q 12050 DSH 03/71
Ths Impact ov luiBiy
on Activated Skidge Systems
ENVIRONMENTAL PROTECTION AGENCY • WATER QUALITY OFFICE
46
-------
R-GGO/2-73-032
unary 1974
Environmental Protection Technology Series
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47
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EPA-K2-73-232
MAY 1G73 Environmental Protection Technology Series
Methods for
Pulp and Paper Mill Sludge
Utilization and Disposal
Office of Research and Monitoring
U.S. Environmental Protection Agency
Washington. D.C. 20460
48
-------
WATE3 POLi.UT.TON CONTROL RESEARCH SERIES f) 11010 EVE 01/71
* i m r- ?•- p • f\ *'•
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50
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EPA-660/2-74-086
DECEMBER 1974
Environmental Protection Technology Series
a'i vj i. ^Lral '.': k 'i V« *.* v -;; 'i. V" a V L 1 ».<• s. 1 i
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51
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EPA 625/1-74-006
PROCESS DESIGN MANUAL
FOR
SLUDGE TREATMENT AND DISPOSAL
US. ENVIRONMENTAL PROTECTION AGENCY
Technology Transfer
October 1974
52
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INDUSTRIAL SLUDGE DISPOSAL PRACTICES*
by
William J. Lacy and Allen Cywin**
The United States Environmental Protection Agency
is responsible for establishing national regulations for
industrial water pollution control.
These regulations establish the base level for control-
ling the amount of pollutants that might be discharged
to the surface waters of the United States. More
stringent requirements may be imposed upon industrial
dischargers should these base level limits not be good
enough for protecting water quality at the point of
discharge.
These limits are to be applied to all similar plants
across the country. They are to be in force by July 1,
1977.
In establishing these limits, U.S.E.P.A. is required to
consider a number of factors such as the non-water
quality impact of the regulations.
There follows selected abstracts referring to sludges
from the documents which support the regulations.
Apple, Citrus and Potato
The disposal of most of the solid wastes from the
fruit and vegetable processing industry is directed
toward animal feed. Solid waste consists of cull fruits
and vegetables, discarded pieces, and residues from
various processing operations. For example, the net
energy and total digestible nutrient content of dried
potato pulp is very nearly the same as U.S. No. 2 corn.
One exception of waste utilization as animal feed occurs
when excessive amounts of pesticides have been used
during the growing season.
Screening devices of various designs and operating
principles remove large-scale solids such as peel, pulp,
cores, and seeds prior to waste water treatment. These
solids are then either processed for co-products, sold for
animal feed, or land filled.
The solid material, separated during waste water
treatment, containing organic and inorganic materials,
including those added to promote solids separation, is
called sludge. Typically, it contains 95 to 98 percent
water prior to dewatering or drying. Some quantities of
sludge are generated by both primary and secondary
treatment systems with the type of system influencing
the quantity. The following table illustrates this:
Treatment System
Sludge Volume as Per-
cent of Raw Wastewater
Volume
Dissolved air flotation
Anaerobic lagoon
Up to 10%
(Sludge accumulation in
(these lagoons is usually
(not sufficient to require
Anaerobic and aerated lagoons (removal at any time
Activated sludge 10-15%
Extended aeration 5-10%
Anaerobic contact process approximately 2%
The raw sludge can be concentrated, digested, de-
watered, dried, incinerated, land-filled, or spread in
sludge holding ponds. In most cases, as stated previously,
the sludge goes to animal feed.
Sludge from air flotation with polyelectrolyte chem-
icals added has proven difficult to dewater, and thereby,
presents problems in disposal by any of the afore-
mentioned handling processes. Also, certain polyelec-
trolyte chemicals rendered the sludge inadequate for
animal consumption.
Sludge from secondary treatment systems is normally
dewatered or digested sufficiently for hauling and sale as
animal feed or fertilizer or for land fill. The final dried
sludge material can be safely used as an effective soil
builder. Prevention of runoff is a critical factor in
plant-site sludge holding ponds. Costs of typical sludge
handling techniques for each secondary treatment sys-
tem generating enough sludge to require handling equip-
ment are already incorporated in the costs for these
systems.
Silt water from cleaning root commodities such as
potatoes is usually handled separately from the food
processing water which goes through secondary treat-
ment. The silt water being accumulated in the bottom of
the ponds is removed annually and disposed of by
adding it to pond dikes. These ponds are generally
•Presentation at the U.S./USSR "Handling Treatment and Disposal of Sludges and Industrial Residual", Symposium Moscow, USSR,
May 5-8, 1975.
**Respectively, Directors of the Industmal Pollution Control Division, R&D and Effluent Guidelines Development Division, U.S.
EPA, Washington, D.C.
53
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abandoned after useful performance, with new ponds
being established.
In addition to the solid wastes generated as a result of
food processing, solid waste is also generated in terms of
trash normally associated with activities. This material
may be disposed of at the plant site or collected by the
local municipality with disposal by incineration of
sanitary land fill. The solid wastes or trash comprises
packaging materials, shipping crates, and similar dry
combustible materials.
Sanitary wastes are usually handled by a separate
system in the plant (in most cases municipal) and
consequently are not involved in the food processing
waste water treatment. The sanitary wastes are of low
volume and quite efficiently treated in standard sanitary
waste treatment facilities.
Building, Construction, and Paper
Solid waste control must be considered. The water-
borne wastes from the asbestos industry may contain a
considerable volume of asbestos particles as a part of the
suspended solids pollutant except for the roofing and
floor tile subcategories. Best practicable control tech-
nology and best available control technology as they are
known today require disposal of the pollutants removed
from waste water in this industry in the form of solid
wastes and liquid concentrates. In some cases these are
non-hazardous substances requiring only minimal cus-
todial care. However, some constituents may be haz-
ardous and may require special consideration. In order
to ensure long term protection of the environment from
these hazardous or harmful constituents, special consid-
eration of disposal sites must be made. All landfill sites
where such hazardous wastes are disposed should be
selected so as to prevent horizontal and vertical migra-
tion of these contaminants to ground or surface waters.
In cases where geologic conditions may not reasonably
ensure this, adequate legal and mechanical precautions
(e.g. impervious liners) should be taken to ensure long
term protection to the environment from hazardous
materials. Where appropriate the location of solid
hazardous materials disposal sites should be permanently
recorded in the appropriate office of legal jurisdiction.
Consideration should also be given to the manner in
which the solid waste is transferred to an industries
waste disposal area. Solids collected in clarifiers, save-alls
or other sedimentation basins should first be dewatered
to sludge consistency. Transportation of this asbestos
containing sludge should be in a closed container or
truck in the dump state so as to minimize air dispersal
due to blowing. Precautions should also be taken to
minimize ah- dispersal when the sludge is deposited at
the waste disposal areas.
The quantities of solids associated with treatment and
control of waste waters from paper, millboard, roofing,
and floor tile manufacturing are extremely small. For
example, the reported volume of dewatered waste solids
from a paper plant is 1.5 cum (2 cu yd) per month.
Solids are wasted only when elastometric binders are
being used, which is 25 to 35 percent of the time.
Another example is that provided by one of the larger
floor tile plants in the country. The sludge and skim-
mings from the sedimentation unit amount to about 625
liters (165 gallons) per week. Unlike other asbestos
manufacturing wastes, this material is highly organic and
is disposed of by a commercial firm that incinerates it.
The treatment facility at this plant is not highly
efficient, but is believed to capture at least 50 percent of
the waste solids.
Contrary to the above categories, the waste solids
associated with asbestos-cement product manufacture
are significant in volume. The reported losses at one pipe
plant are in the order of 5 to 10 percent of the weight of
the raw materials. The losses of asbestos fibers arc kept
to a minimum in this industry, to 1 percent or less, and
the fiber content of the waste solids is low. The solids
have no salvage or recovery value.
In summary, the solid wastes disposal associated with
the application of treatment and control technologies in
the asbestos manufacturing industry does not present
any serious technical problems. The wastes are amenable
to proper landfill disposal. Full application of control
measures and treatment technology will not result in
major increases at most plants. In many cases, complete
recycle will result in lower losses of solids.
Beet Sugar Processing
The large volumes of dirt and solid material removed
from sugar beets at the processing plant pose a perplex-
ing problem for permanent disposal. Generally, almost
50 kg of soil/kkg (100 Ibs/ton) of beets sliced is
contributed by a typical beet sugar processing plant.
Where holding ponds are employed, solids accumulated
in the ponds are removed annually and disposed of by
adding the material to pond dikes. These ponds are
generally abandoned after useful performance, with new
holding pond facilities being established.
Sugar beets stored in large piles at the plant site or in
outlying areas such as railroad sidings may be exposed to
rodent activity and additional pollution from truck or
railroad car unloadings. Rainfall may assist the spread of
existing contamination.
In addition to the large volumes of soil delivered to
the plant with the incoming beets, solid waste is also
54
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generated in terms of trash normally associated with
municipal activities. Disposal of this material may be at
the plant site or the waste material may be collected by
the local municipality with disposal by incineration or
sanitary landfill. The solid waste or trash consists of
packaging materials, shipping crates, and similar dry
combustible materials.
Sanitary landfills are generally best suited for non-
combustible material and organic wastes which are not
readily combustible such as decomposed beets, weeds,
and peelings. Composting offers a viable alternative for
disposing of organic materials such as decomposed beets,
weeds, and peelings. Experience with this method in the
disposal of municipal wastes has proved more costly
than sanitary landfill operations, however. The sanitary
landfill is probably the lower cost alternative, provided
that adequate land is available.
Consideration of suitability is a prime factor in
location of a landfill site. Requirements in selection of a
landfill site include sufficient area, reasonable haulage
distance, location relative to residential developments,
soil conditions, rock formations, transportation access,
and location of potential ground water polluting aqui-
fers. Location of sanitary landfills in sandy loam soils is
most desirable. Proper sloping of the landfill soil cover
to promote runoff rather than ground percolation is
necessary to prevent ground water pollution. Other
factors to be considered include no obstruction of
natural drainage channels, installation of protective dikes
to prevent flooding when necessary, location of the base
of the landfill operation above the high water table, and
consideration of possible fire hazards. The general
methods and desirable practices in operation of muni-
cipal sanitary landfill operations are equally applicable
to disposal of solid waste from beet sugar processing
plants. Open burning of combustible wastes on the plant
site is an undesirable and often unlawful method of solid
waste disposal.
Dairy Product Processing
The main non-water pollutional problem associated
with treatment of dairy wastes is the disposal of sludge
from the biological oxidation systems. Varying amounts
of sludge are produced by the different types of
biological systems. Activated sludge systems and trick-
ling filters produce sludge that needs to be handled
almost daily.
Waste sludge from activated sludge systems generally
contains about 1% solids. The amount of sludge pro-
duced ranges between 0.05 to 0.5 kg solids per kg BOD5
removed.
Sludge from trickling filters consists of slime sloughed
off the filter bed. This sludge settles faster than activated
sludge and compacts at solids concentrations greater
than 1% solids. The amount of sludge generated will be
less than that produced by activated sludge systems.
Aerobic and anaerobic digestion of sludge generated
from activated sludge systems is recommended to render
it innocuous, thicken it, and improve its dewatering
characteristics. Sludge thickening can precede digestion
to improve the digestion operations. Digested activated
sludge and thickened trickling filter sludges can be
vacuum-filtered, centrifuged or dried on sand beds to
increase their solids content for better "handleability"
before final disposal.
Flat Glass
Landfilling of properly dewatered sludges from the
flat glass industry is an appropriate means of disposal.
The wastes are largely inorganic and incineration, com-
posting, or pyrolysis would not be effective in reducing
their volume. The dewatered solids are relatively dense
and they are stable when used as fill material. If disposed
of using proper sanitary landfill techniques, solids from
flat glass manufacturing should cause no environmental
problems.
With the exception of plate glass manufacturing, the
volume of sludge associated with the various control and
treatment technologies is relatively small. The lagoons
used for plate glass suspended solids removal also serve
as sludge disposal sites. The levees are generally raised to
keep pace with the rising sediment level. At older plate
plants large areas of low-lying land have been filled in. In
some cases this is reclaimed as part land by spreading
topsoil over the dry sludge solids.
Three types of waste solids are produced by the
treatment systems indicated for the float, solid tempered
automotive, and windshield manufacturing processes.
These are (1) coagulation-sedimentation sludge asso-
ciated with tempering waste waters, and (2) spent
diatomaceous earth, and (3) brine residue associated
with at least one treatment alternative for each of the
subcategories. The coagulation-sedimentation sludge is
assumed to be dewatered by centrifuge to about 20%
dry solids and the typical volume produced is estimated
to be 0.38 cu m/day (13.5 cu ft/day).
Spent diatomaceous earth has an estimated moisture
content of 85% but is dry to the touch. This material is
stable and should be suitable for landfill. Estimated
production of diatomaceous earth waste is less than 0.23
cu m/day (8 cu ft/day) for each of the subcategories.
The salt residue that will be produced by a total
recycle system will present the biggest disposal problem.
To prevent ground water contamination, it must be
55
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permanently stored in lined basins. Only as much water
as will evaporate can be allowed into the basin. The land
used for salt storage will be permanently spoiled. The
salt residue produced by the tempering and laminating
processes is conservatively estimated to be 0.56 cu
m/day (20 ft/day). Salt storage costs are directly related
to the cost of land and the type of lining used.
Grain Processing
The treatment of grain milling waste waters will give
rise to substantial quantities of solid wastes, particularly
biological solids from activated sludge or comparable
systems. Several avenues are available for the disposal of
these solids including digestion and landfill, incineration,
and other conventional methods of handling biological
solids. Alternately, the solids can be dewatered and
added to the animal feed already being produced at
these mills. This practice has found some acceptance in
the grain milling industry, particularly in the corn wet
milling segment, and is strongly recommended. Addi-
tional discussion of soils recovery and sludge disposal is
contained in Section VII.
Unbleached Kraft and Semichemical Pulp
In addition to sludges produced by effluent treat-
ment, the following wastes are or can be produced at
mills in the subcategories covered by this survey:
Unbleached Kraft Mills
(and Kraft-NSSC)
Bark
Rejects and Screenings
Grits and Dregs
Log wash water
Ash
Waste paper
Garbage
Trash
NSSCMitts
Bark
Rejects and Screenings
Chemical ash
Ash
Waste paper
Garbage
Trash
Paperboard from Waste Paper Mills
Trash
Waste Paper
Fly ash
Garbage
Linerboard mills which bark roundwood on the
premises produce sufficient bark to fire a boiler for
steam generation so the necessity for its disposal is
eliminated. Others receive their wood supply in the form
of chips which are a by-product of lumbering operations,
and no bark is involved.
Rejects and screenings from linerboard mills are
either reprocessed, burned in incinerators or in the
bark-fired boilers or disposed of by land fill. The latter
procedure represents no problem for most of these mills
because of the large mill sites containing considerable
usable land. Grits and dregs from the causticizing system
of the recovery plant are inorganic solids which are
generally water carried to a land disposal site. This is
facilitated by their small quantity which amounts to
about 22.5 kg/kkg (45 Ibs/ton) of pulp produced.
Ash from bark- and coal-fired boilers and screening
rejects are as a rule discharged hydraulically to ash
ponds. There the solids settle and compact and the clear
supernatant water is discharged to the mill effluent
system. In some instances, ash and rejects are hauled to a
disposal area away from the mill site. Wet handling of
these materials avoids their being blown into the
atmosphere.
Overflow, from log washing operations which con-
tains silt and fine bark particles generally joins the
stream carrying ash from the mill.
Waste paper, garbage, and trash attendant to produc-
tion or accessory operations and activities are either
incinerated on the site or hauled away for disposal by
contractors engaged in this business.
NSSC corrugating board mills generate most of the
kinds of solid wastes created at linerboard mills and
handle them in a similar manner. One exception is that
most of these mills are relatively small operations which
do not produce enough bark to justify a steam-generat-
ing bark boiler. The bark is usually disposed of in
incinerators designed for this purpose.
At NSSC mills where spent liquor is burned in
fluidized bed units, ash consisting of a mixture of
sodium carbonate and sodium sulfatc is produced. This
is usually sold to kraft mills to be used as a make-up
chemical replacing salt cake in the recovery system.
The paperboard from waste paper mills, trash such as
rags, wire and other metals, glass, and plastics, is
removed in the breaker beater and stock cleaning
operations. This material, and grit from the rifflers, is
disposed of by land fill on the mill premises or hauled to
a suitable location for disposal in this manner.
The remaining solid wastes such as ash, waste paper,
etc., are handled as described above.
Particulate emissions from incineration of bark and
other solid wastes must be controlled by effective
devices such as big filters or scrubbers.
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Leather Tanning and Finishing
Solid waste from tanneries and tannery wastewater
treatment includes the following: (1) fleshings, (2) hair,
(3) raw hide trimmings, (4) tanned hide trimmings,
(5) sanding and buffing dust, (6) lime sludge, (7) chrome
sludge, (8) biological sludge, (9) grease, (10) general
plant waste.
Most tanneries recover fleshings and raw hide trim-
mings for sale to rendering plants or conversion into glue
at the tannery site. Tanned hide trimmings are often sold
as by-products. Office and general plant waste is either
hauled away by a local refuse disposal service or
disposed of on-site.
In save-hair operations, the tannery has facilities for
washing, drying, and baling of the hair. The baled hair is
sold as a by-product.
Sanitary landfills are best suited for disposal of
tannery waste. Incineration and high temperature treat-
ment are not recommended for sludges containing
chrome, since chrome may be reduced from the trivalent
to the hexavalent state.
Tannery sludges containing chrome should not be
spread on the land until further efforts are^made to
define the impact of these waste materials iipon the
environment.
The selection of proper site for landfill operations is
of prime consideration. Requirements in the selection
include: sufficient area; reasonable haul distance; re-
mote location relative to residential, commercial, and
recreational developments; soil conditions and rock
formations; accessibility to existing transportation net-
works; and proximity to existing groundwater supplies.
The soil cover should be sloped such that precipitation
will run off rather than percolate and pollute ground-
water sources. Other factors to be considered include
provisions to prevent the obstruction of natural drainage
channels, location to avoid flood waters, and the
consideration of possible fire hazards.
Major Inorganic Products
The slurries, water soluble solids and water insoluble
solids obtained from control and treatment of inorganic
chemicals industry water-borne wastes have to be con-
tained, or disposed of, in a safe and economical manner.
Provided that the solids are insoluble in water, most
solid wastes from the inorganic chemicals industry may
be land dumped or land-filled. Costs are $0.22 to
$0.66/kkg ($0.20 to $0.60/ton) of solids-for simple
dumping or landfilling. Large scale operations without
cover cost less than $l.ll/kkg ($1.00/ton). If cover is
involved for appearance or zoning requirements, the
costs may increase to $1.05 to $2.2O/kkg ($2.50 to
$2.00/ton).
If the evaporation-rainfall situation for the disposal
area is favorable (as is the case for much of the
southwestern U.S. and some other areas of the country),
then landfill in an impervious, lined pan is feasible for
soluble solids. Operation costs are similar to those for
landfill with no cover, $0.22 to S0.66/kkg ($0.20 to
$0.60/ton).
Landfilling of containerized soluble solids in plastic
drums or sealed envelopes is practicable but expensive.
Blow-molded plastic drums, made from scrap plastic
(which is one of the present major problems in solid
waste disposal) could be produced for $ll-22/kkg
($10-20/ton) capacity at 227 kg (500 Ib) solids per drum
and a rough estimate of $2.50-5.00 cost/drum. A more
economical method, particularly for large volumes,
would be sealed plastic envelopes, 750 microns (30 mils)
thick.
At $1.10/kg ($.50/lb) of film low density polyeth-
ylene costs about lOtf per 0.0929 sq m (1 sqft). Using
the film as trench liner in a 1.8 m (6 ft) deep trench
1.8m (6/ft) wide, the perimeter (allowing for overlap)
would be approximately 7.5 meters (25 feet). At a
density of 1.6 gm/cc (100 Jb/cu ft) for the solid, costs of
plastic sheet/kkg would be $2.00 ($1.75/ton). With
sealing, the plastic envelope cost would be approxi-
mately $2.20/kkg ($2/ton). With landfill costs of
$2.20/kkg ($2/ton) additional, the total landfill disposal
costs would be about $4.40/kkg ($4/ton).
The above figures for soluble disposal using plastic
containers, bags or envelopes are only rough estimates.
Also, the technology would not be suitable for harmful
solids or in situations where leaching contamination is
critical.
Red Meat Processing
Solid wastes are the most significant non-water
pollutants associated with the waste treatment systems
applicable to the meat packing industry. Screening
devices of various design and operating principles are
used primarily for removal of large-scale solids such as
hair, paunch manure, and hog stomach contexts from
waste water. These solids may have some economic value
as inedible rendering material, or they may be landfilled
or spread with other solid wastes.
The solids material, separated from the waste water
stream, that contain organic and inorganic matter,
including those added to aid solids separation, is called
sludge. Typically, it contains 95 to 98 percent water
before dewatering or drying. Both the primary and
secondary treatment systems generate some quantities of
57
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sludge; the quantity will vary by the type of system and
is roughly estimated as follows:
Treatment System
Dissolved air flotation
Anaerobic lagoon
Aerobic and aerated lagoons
Activated sludge
Extended aeration
Anaerobic contact process
Rotating biological contactor
Sludge Volume as Per-
cent of Raw Wastewater
Volume
up to 10%
sludge accumulation in
these lagoons is usually
not sufficient to require
removal at any time.
10-15%
5-10%
approximately 2%
unknown
The raw sludge can be concentrated, digested, de-
watered, dried, incinerated, land-filled or sub-surface
injected on-site, or spread in sludge holding ponds. The
sludge from any of the treatment systems, except air
flotation with polyelectrolyte chemicals added, is amen-
able to any of these sludge handling processes.
The sludge from air flotation with chemicals has
proven difficult to dewater. A dewatered sludge is an
acceptable land fill material. Sludge from secondary
treatment systems is normally ponded by the meat
industry plants on their own land or dewatered or
digested sufficiently for hauling and deposit in public
land fills. The final dried sludge material can be safely
used as an effective soil builder. Prevention of run-off is
a critical factor in plant-site sludge holding ponds. Costs
of typical sludge handling techniques for each secondary
treatment system generating sufficient quantities of
sludge to require handling equipment are already in-
cluded in the costs for these systems.
Smelting and Slag Processing
The solid waste produced by treatment of waste
waters in the industry derives principally from the
smelting operation as waste from air pollution control
devices. The solid waste from air pollution controls is
produced whether a dry or wet system is utilized and
varies only in that the former produces a slurry or
sludge, the latter a fine dust. The slurry or sludge is
generally accumulated in sludge lagoons, while the dry
dust may be bagged and landfilled or simply piled. More
careful attention should be directed to the disposal of
these potentially harmful materials. Possible improve-
ments might be landfilling in a sealed site, or encapsu-
lation in concrete or polymers. There has been little
success in efforts to agglomerate these solids for recharg-
ing to the smelting furnaces, although it is probable that
dry dust could be utilized more easily than wet sludge.
Steel Making
Beehive Coke-Solid Waste Disposal: Solid wastes will
be generated by processing the scrub water and reusing
coke fines in the system.
Sintering - Solid Waste Disposal: The solid waste from
the waste system will be internally consumed in the
sinter process.
Blast Furnace (Iron)-Solid Waste Disposal: There
should be no problem in disposing of the solid waste
which will be generated. It can be internally consumed
in the sinter process plant.
Blast Furnace (Ferromanganese) - Solid Waste
posal: Same as iron making blast furnace (iron).
Dis-
Basic Oxygen Furnace Operation Semi-Wet Systems -
Solid Waste Disposal: The solid waste that will be
generated by the fume collection system for the BOF
(semiwet) process of steelmaking should present no
problem. It can be internally consumed in the sinter
process plant.
Basic Oxygen Furnace Operation Wet Systems - Solid
Waste Disposal: There should be no problem in dispos-
ing of the solid waste generated by the fume collection
system for the BOF (wet) process for the manufacture
of steel. It can be internally consumed in the sinter
process plant.
Open Hearth Furnace Operation - Solid Waste Disposal:
The solid waste that will be generated by the fume
collection for the open hearth system should present no
problem. It can be internally consumed in the sinter
process plant.
Electric Arc Furnace Operation Semi-Set Systems - Solid
Waste Disposal: The solid waste that will be generated
by the fume collection system for the electric furnace
(semiwet) process of steelmaking should present no
problem. It can be internally consumed in the sinter
process plant.
Electric Arc Furnace Operation Wet Systems - Solid
Waste Disposal: There should be no problem in dispos-
ing of the solid waste generated by the fume collection
system for the electric furnace (wet) process for the
manufacture of steel. It can be internally consumed in
the sinter process plant.
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Vacuum Degassing - Solid Waste Disposal: The solid
waste that will be generated by the creation of a vacuum
for the degassing process should present no problem. It
can be internally consumed in the sinter process plant.
Continuous Casting - Solid Waste Disposal: The solid
waste generated can be consumed internally in the sinter
plant.
Synthetic Resins
Biological sludges are the principal disposal problem
resulting from end-of-pipe treatment of waste waters.
Occasionally chemical sludge (such as from neutraliza-
tion and precipitation of an inorganic chemical) is of
concern. Biological sludges are most frequently sub-
jected to some type of continued biological degradation.
Aerobic digestion is the most frequently used method.
When lagoons are operated in the extended-aeration
mode, the solids accumulate in these lagoons or in
polishing lagoons. The long-term consequence of these
operations is a gradual filling of the lagoons. They then
must be dredged or abandoned. Presently, sludges from
end-of-pipe wastewater treatment plants are stabilized
by biological means and disposed of to landfills. Prior
treatment to dewater the biological sludges by chemical
or mechanical means will probably be increasingly
employed. However, the problem of landfill disposal
Type of Plant
(1) Cellulosic-based
(2) Phenolics, epoxy, nylon,
acrylics, polyesters
(3) Polystyrene, PVC, APS/SAN,
polyethylene, polypropylene
remains. Consequently, one of the long-term aspects of
waste water treatment is ascertaining that appropriate
landfill sites have been obtained. The cost of sludge
disposal from plastics and synthetics plants will be
essentially equivalent to the cost of sludge disposal from
municipal sewage treatment plants. The same type of
disposal methods are applicable, but there will be
significant variations in the amounts of sludge generated.
Estimates based on raw waste loads reported in the
Celanese report (8) indicate the range of dry solids to be
disposed of would be as follows:
Type of Plant
(1) Cellulosic-based
(2) Phenolics, epoxy, nylon
acrylics, polyesters
(3) Poly sty rcne, PVC, ABS/
SAN, polyethylene, poly-
propylene
Units/lOOO/Units of
Product
25-50
10-25
1-10
Burd (11) reports that lagooning or landfilling cost
(capital and operating) lie in the range of $1 to $5 per
ton of dry solids. Utilizing the higher value, the range of
disposal costs per pound of product becomes:
I/Pound of Product
0.00625-0.0125
0.00250-0.00625
0.00025-0.0025
of Product
0.0138-0.0276
0.00551-0.0138
0.00055-0.00551
Burd also reports capital and operating costs for incin-
eration to be S10 to $50 per ton ($1 l-$55/kkg). Due to
the rapid increase in fuel costs and the relatively small
volume of sludge at individual plants, $50 per ton is
probably more nearly the cost that will prevail in this
industry. Consequently, sludge incineration costs might
be expected to be in the following ranges:
Type of Plant
(1) Cellulosic-based
(2) Phenolics, epoxy, nylon
acrylics, polyesters
(3) Polystyrene, PVC, ABS/SAN
polyethylene, polypropylene
59
I/Pound of Product
0.0625-0.125
0.250-0.0625
0.00250-0.0250
tf/kq of Product
0.1378-0.2756
0.00551-0.0138
0.00551-0.0551
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The ysarly volume of biological sludges (acre feet) generated for each 10,000,000 Ibs. of product is estimated to be
the following:
Type of Plant
(1) Cellulosic-based
(2) Phenolics, epoxy, nylon
acrylics, polyesters
(3) Polystyrene, PVC, ABS/SAN,
polyethylene, polypropylene
Biological Sludges Only
Acre Feet/Year CU Meters/Year
0.4-0.80
0.10-0.40
0.04-0.10
The most significant sludge disposal problem is the
volume of sludge generated during the removal of zinc
from rayon plant waste waters. These sludges, mixed
with calcium sulfate, are presently being lagooned. An
EPA demonstration project for zinc removal and re-
covery has been completed. Undoubtedly, the future
disposal of zinc sludge will depend upon economics as
well as the need to meet effluent limits. Although large
diked land areas are required for lagooning and, conse-
quently, large-scale flooding might be considered a
hazard, zinc sludge tends to attain a jelly-like consist-
ency, which would prevent this. This means that, if a
dike wall breaks, large amounts of the contained sludge
will not flow from the filled lagoon.
Petroleum Refining
The major nonwater quality consideration which may
be associated with in-process control measures is the use
of and alternative means of ultimate disposal of either
liquid or solid wastes. As the process Raw Waste Load is
reduced in volume, alternate disposal techniques such as
incineration, ocean discharge and deep-well injection
because of the potential long-term detrimental effects
associated with these disposal procedures. Incineration
may be a viable alternative for highly concentrated waste
streams.
Phosphorus Derived Chemicals
Solid waste disposal will be the chief non-water
quality are impacted by the proposed guidelines. Neutra-
lization of acidic waste streams with lime or limestone
will increase the amounts of sludge, especially when
soluble phosphates and sulfates are precipitated. Installa-
tion of dry air pollution control equipment will reduce
the water content of wasted solids. In addition, return of
collected solids to the process may be feasible. Arsenic
rich solid residues accumulate from the purification of
493-986
123493
49-123
phosphoric acid and of phosphorous pentasulfide. Burial
in a controlled area is the standard disposal method.
Special disposal methods as mentioned previously in this
section may be necessary to prevent leachate from
reaching surface or ground waters.
Textile Mills
The solid wastes from the textile industry are
generally disposed of by landfill. The solid materials,
separated during waste water treatment, containing
organic and inorganic materials, including those added to
promote solids separation, is called sludge. Typically, it
contains 95 to 98 percent water prior to dewatering or
drying. Some quantities of sludge are generated by both
primary and secondary treatment systems with the type
of system influencing the quantity. The following table
illustrates this:
Treatment System
Dissolved air flotation
Anaerobic lagoon
Extended aeration
Aerobic & aerated lagoons
Activated sludge
Extended aeration
Anaerobic contact process
Sludge Volume as Percent
of Raw Wastewater
Volume
up to 10%
(Sludge accumulation in
these lagoons is usually
sufficient to require
removal at any time)
10-15%
5-10%
approximately 2%
The raw sludge can be concentrated, digested, de-
watered, dried, incinerated, land-filled, or spread in
sludge holding ponds. Sludge from secondary treatment
systems is normally dewatered or digested sufficiently
for hauling to a land fill. The final dried sludge materials
can be safely used as an effective soil builder. Prevention
of runoff is a critical factor in plant-site sludge holding
ponds. Costs of typical sludge handling techniques for
60
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each secondary treatment system generating enough
sludge to require handling equipment are already incor-
porated in the costs for these systems. All other
non-water quality environmental impacts of the alter-
native treatment and control technologies described
appear to be minor.
Tire and Synthetic
Solid waste disposal is a major problem confronting
the industry as a whole. Typically 3,100 kg (6,800 Ibs)
of solid waste are generated by a tire plant each day.
Additional solid waste results from the drumming of the
waste solutions for off-site disposal. Many manufac-
turing plants, particularly in the northern states, are
finding it difficult to locate and arrange for service at a
satisfactory landfill sites. Fortunately, the additional
solid waste generated by the proposed treatment tech-
nology is very small relative to the normal solid waste
generated by the production facility.
Sludge cake is produced by vacuum filtration of the
primary coagulation solids and the digested biological
solids. Sludge disposal costs were based on sanitary
landfill. Sludge incineration costs were not evaluated
because the economics depend, to a large degree, on the
accessibility of a landfill site and on the relative costs for
sludge haulage and site disposal. The annual quantities of
solid waste generated are:
Primary coagulated solids 2,940 cu m (3,900 cu yd)
Biological solids 245 cu m (325 cu yd)
Solid wastes are produced by chemical coagulation
and clarification, wasted biological sludge, and spent
activated carbon. For cost purposes, it is proposed that
these all be hauled to a landfill. The annual quantities of
solid wastes are listed below:
Primary coagulated solids
Biological Solids
Spent carbon
214 cum (283 cu yd)
62 cu m (82 cu yd)
126cum(167cuyd)
Solid waste generation with this treatment system is
associated with biological solids and spent activated
carbon. The activated carbon canisters may be returned
for regeneration off-site by the supplier. However,
annual operating data have been based on disposal of the
spent carbon at a landfill site. The annual quantities of
solid waste gerated are:
Biological solids
Spent carbon
102 cum (135 cu yd)
140 cum (185 cu yd)
Synthetic Resins
Biological sludges are the principal disposal problem
resulting from end-of-pipe treatment of waste waters.
Occasionally chemical sludge (such as from neutrali-
zation and precipitation of an inorganic chemical) is of
concern. Biological sludges are most frequently sub-
jected to some type of continued biological degradation.
Aerobic digestion is the most frequently used method.
When lagoons are operated in the extended-aeration
mode, the solids accumulate in these lagoons or in
polishing lagoons. The long-term consequence of these
operations is a gradual filling of the lagoons. They then
must be dredged or abandoned. Presently, sludges from
end-of-pipe wastewater treatment plants are stabilized
by biological means and disposed of to landfills. Prior
treatment to dewater the biological sludges by chemical
or mechanical means will probably be increasingly
employed. However, the problem of landfill disposal
remains. Consequently, one of the long-term aspects of
wastewater treatment is ascertaining that appropriate
landfill sites have been obtained. The cost of sludge
disposal from platics and synthetics plants will be
essentially equivalent to the cost of sludge disposal from
municipal sewage treatment plants. The same type of
disposal methods are applicable, but there will be
significant variations in the amounts of sludge generated.
Estimates based on raw waste loads reported in the
Celanese report (8) indicate the range of dry solids to be
disposed of would be as follows:
Type of Plant
(1) Cellulosic-based
(2) Penolics, epoxy, nylon
acrylics, polyesters
Units/1000/Units of Product
25-50
(3) Polystyrene, PVC, ABS/SAN,
polyethylene, polypropylene
10-25
1-10
Burd (11) reports that lagooning or landfilling cost
(capital and operating lie in the range of $1 to 55 per
ton of dry solids.
Utilizing the higher value, the range of disposal costs
per pound of product becomes:
Type of Plant tf/Pound of Product 4/kg of Product
(1) Cellulosic-based 0.00625-0.0125 0.0138-0.0276
(2) Phenolics, epoxy,
nylon, acrylics,
polyesters 0,00250-0.00625 0.00551-0.0138
(3) Polystyrene, PVC,
APS/SAN/
polyethylene,
polypropylene 0.00025-0.0025 0.00055-0.00551
61
-------
SUMMARY
Burd also reports capital and operating costs for
incineration to be $10 to $50 per ton ($ll-$55/kkg).
Due to the rapid increase in fuel costs and the relatively
small volume of sludge at individual plants, $50.00 per
ton is probably more nearly the cost that will prevail in
this industry. Consequently, sludge incineration costs
might be expected to be in the following ranges:
Type of Plant ^/Pound of Product #kg of Product
(1) Cellulosic-based 0.0625-0.125 0.1378-0-0.2756
(2) Phenolics, epoxy,
nylon acrylics,
polyesters 0.250-0.0625
0.00551-0.0138
(3) Polystryrene, PVC,
ABS/SAN,
polyethylene
polypropylene 0.00250-0.0250 0.00551-0.0551
The yearly volume of biological sludges (acre feet)
generated for each 10,000,000 Ibs of product is esti-
mated to be the following:
Biological Sludges Only
Type of Plant Acre Feet/Year Cu Meters/Year
(1) Cellulosic-based
(2) Phenolics, epoxy,
nylon acrylics,
polyesters
0.4-0.80 493-986
0.10-0.40 123493
(3) Polystyrene, PVC,
APS/SAN, polyethylene,
polypropylene 0.04-0.10
49-123
The most significant sludge disposal problem is the
volume of sludge generated during the removal of zinc
from rayon plant wastewaters. These sludges, mixed
with calcium sulfate, are presently being lagooned. An
EPA demonstration project for zinc removal and re-
covery has been completed. Undoubtedly, the future
disposal of zinc sludge will depend upon economics as
well as the need to meet effluent limits. Although large
diked land areas are required for lagooning and, conse-
quently, large-scale flooding might be considered a
hazard, zinc sludge tends to attain a jelly-like consist-
ency, which would prevent this. This means that, if a
dike wall breaks, large amounts of the contained sludge
will not flow from the tilled lagoon.
Considerable work has been done and is being
reported in this conference on residual recovery and
reuse. Examples include the recovery of product fines,
usable water and thermal energy. There are many
products that are recovered now but there are many
more that could be recovered in the future.
A trend by industry in the direction of "closing the
loop" has been established and it is becoming obvious
that it may be an intelligent thing to do. Accordingly,
Effluent Guidelines Development Program with the
technical base of the EPA industrial research, develop-
ment, and demonstration (RD&D) program is oriented
toward the elimination of discharges of pollutants into
the navigable waters of the U.S.A.
Waste treatment must be considered not an add-on
but an integral part of the manufacturing process and
the cost of treatment must be charged against the
product. The waste disposal operations result in a net
cost to the industry producing the waste, but you will
hear at this conference examples of how product
recovery and utilization practices reduce the cost of
treatment and frequently prove to be cheaper than other
methods of disposal.
In the treatment of industrial discharges, by-product
recovery frequently accompanies water reuse and water
conservation. Recycled water may utimately be the
major valuable product because of increasing water
supply costs, increasing water treatment costs, and
mounting charges for using municipal sewerage facilities.
Industrial wastes contain the gambit of toxic chemi-
cals, hazardous materials and heavy metals. Direct
discharge of these wastes into streams and rivers is
objectable as this is a gross insult to the environment.
These wastes cannot be sent through sewage treatment
plants as they contain toxic materials. Hence, the
pretreatment and reduction of waste load is of import-
ance in the waste treatment plant operations.
Frequently, waste streams can be eliminated or
reduced by process modifications or improvements. A
notable example of this is the use of save rinse and
spray-rinse tanks in plating lines or dry caustic peeling
and hot air blanching in the canning industry. These
measures bring about a substantial reduction in waste
volume and a net savings of energy, conservation of
materials and protection of our environment-not to
mention being more economical.
In closing, I want to again thank you for the
opportunity of addressing you today and leave this
thought that both industry and government must be-
come attuned to "WASTE NOT WANT NOT" or "A
PENNY SAVED IS A PENNY EARNED" philosophy in
the future to preserve the environment and protect our
national resources.
62
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THICKENING AND DEWATERING OF WASTE WATER
SLUDGES BY VIBRO FILTRATION METHOD
by
Dvinskih, E. V., All-Union Scientific Research Institute
VODGEO
Present day methods of mechanical dewatering, that
is, vacuum filtration and centrifugation in most cases
require sludge conditioning that considerably compli-
cates and increases the cost of the sludge treatment
process. The application of vibro-filtration method in
sludge thickening and dewatering without addition of
chemicals is of concern.
Vibro-filtration as a new trend in the separation
technology of industrial suspensions has been recently
introduced. The main feature of this type of filter is the
use of vibrations of filtering media in order to intensify
the liquid-solid separation process. The destruction of
sludge structure and the reduction of its resistance to
filtration, the continuous regeneration of filtering media
and furthermore, the increase in working pressure
differential caused by arising inertial forces take place
during the separation process.
Depending upon the objective of filtration and
properties of filtered suspensions pressure or open
(gravity flow) vibrofilters are used.
The Gravity flow vibro-filters with harmonic vibra-
tions of filtering media with frequency of 100 Hz are
being more widly used for thickening and dewatering of
industrial suspensions and waste water sludges. The
dewatering process occurs at the movement of thickened
sludge, produced by directed vibrations or filtering
media slope.
We have carried out theoretical and experimental
investigations of waste sludge dewatering process on a
model of continuous gravity vibro-filter with directed
vibrations of the filtering media in the frequency range
of 20 to 100 Hz and the acceleration to lOg.
The studies were conducted on municipal and indus-
trial sludges. The construction of the joint of the model
to a vibration stand permitted to change the angle of
filtering media slope oi in the range of 0 - 18° and the
direction of vibrations^ from 20 to 90° (Fig. 1). The
EDC - 200 vibration stand allowed to regulate continu-
ously the frequency of 20 to 100 Hz and the accelera-
tion of vibrations of 1 to lOg.
Metal screens with 40-120 mlczones meshes were
used as a filtering media. The studies of the relationship
of filtration rate to vibration parameters were conducted
on filling filtration funnels. The filming was used to
record the rate of the process. The investigations of
process kinetics showed that vibro-filtration process
occurred in two stages in the absence of excess static
pressure. Fig. 2.
First the layer of vivro-fluidized sludge with solids
concentration Cj, that is higher than solids concentra-
tion of incoming suspension, Co forms on the filtering
screen. The resistance to filtration of this layer depends
on the degree of its fluidization, that is on vibration
parameters of the screen and on the depth of the layer,
on the other hand. The solids concentration in the
suspension above the layer is equal to the solids
concentration in initial suspension. When the layer of
incoming suspension above the sludge layer reduces to
zero the first stage of filtration process finishes and the
second one starts, during which the reduction of the
sludge layer occurs due to the separation of filtrate. The
solids concentration in the layer constantly increases,
but solids concentration gradient on the layer depth
stays equal to zero throughout the second stage of
filtration process.
Mathematical model of both stages of the process was
obtained on the bases of linear law of filtration.
Equation 1.
where
V — volume of suspension;
/(0- coefficient of permeability;
fi - kinematic coefficient of viscosity of liquid
phase;
P - pressure differential;
l_ - length of filtration path;
S - area;
•£• — time;
U - total depth of suspension layer above
filtration media;
^ - depth of vibro-fluidized sludge layer;
£/ - depth of suspension layer above sludge
layer.
Both stages of vibro-filtration process are schemat-
ically presented in Fig. 3.
The driving force of the process P consists of
hydrostatic pressure Ph (V), determined by the depth of
63
-------
the filtered suspension above filtering screen, and pres-
sure Pu (V) arized in the suspension by the action of
inertial forces.
Equation 2.
A)
where
— crest value of vibration acceleration;
— weight of suspension;
— relationship of vibration acceleration to
gravity acceleration.
j-f; a =
Having determined the sludge weight through its
volume for each stage of filtration process respectively in
Eq. 2, after integration we obtain the mathematical
description for both stages of vibro-filtration process.
The first stage is described by Eq.3
_ VoM+U
~ B
Vo M-LL Vo-V
~~
where
are specific weights of liquid and solid phases;
constant coefficient, determining resistance to
filtration of the vibro-fluidized sludge layer during the
first stage of filtration.
The Second stage of vibro-filtration process is de-
scribed by equation 4.
where fl-
f\
YI sludge volume above filtering screen at the beginning
of the second stage when t = tj, and Vs n sludge volume
when t - Ks- experimental coefficient responsible for
resistance of vibro-fluidized sludge layer during the
second stage of filtration.
The typical kinematic curve of activated sludge
vibro-filtration with initial concentration of 6,5 g/1. at
vibration frequency of filtering media of SOHz and
acceleration of 4g is presented in Fig. 4.
The experimental values are shown as points. The
curve AC and AD are calculated according to equation
of both stages on the basis of experimental values of K-
andKs.
The curve AC describes the first stage of vibro-filtra-
tion process with the formation of vibro-fluidized sludge
layer on the screen as it is evident from Figure 4, the
curve is in satisfactory agreement with experimental
values to a certain time t, then deviates downward. It
means that by the moment of time t the first stage
finishes and the second one starts. As experimental data
showed, the vibro-filtration process of organic sludges
occurred in two stages when solids concentration in
sludge is less than 15 gr/1. As the concentration of
incoming organic sludges usually is higher therefore only
the second stage of dewatering process of this type of
sludges takes place.
Qualitative investigations of the process with the use
of high-speed filming showed, that in the course of
filtration the sludge layer didn't separate from the
porous media even at the acceleration of 8-10g.
The final moisture of sludge depends on the accelera-
tion and the frequency of vibrations, and for tested
sludges dewatered at frequency of 50Hz and the
acceleration of 8g. during the same time was as follows:
-for thickened activated sludge 93-94%
-for primary sludge 84-86%
—for digested coagulated sludge mixture 82-83%
—for the mixture of primery and thickened activated
sludges 86-88%.
—for sludges from wood-fibred slabs plants 82-86%
—for sludges of blust-furnace gas-cleaning process
.25-28%
The solids content in the filtrate depends on the
vibration parameters of porous media, its permeability
and sludge properties.
One more significant feature that is, the screen must
be rigid should be taken into consideration besides
common requirements for filtering media. So metal
screens were used during experiments. The application
of synthetic cloth didn't give positive results during
dewatering of waste water sludges.
The cloth dissipates the energy of vibrations, not
transferring it to the sludge layer.
The relationships of filtrate concentration to
vibration parameters have a parabolic shape. These
64
-------
dependences have almost the same character for all
investigated sludges, and differ in numerical values of
filtrate concentration. As the major amount of filtrate is
produces at the beginning of the process in order to
minimize losses of solids with filtrate, it is better to
carry out the dewatering process in two stages: maxi-
mum possible thickening of sludge at accelerations in the
range of 2 of 5 g; and subsequent dewatering of sludge
to produce a cake with minimum moisture at accelera-
tion of 8-10 g.
In this case the loss of solids with filtrate is
considerably reduced. The results of these studies
indicated, that the dewatering of waste sludges in the
frequency range of 30 to 50Hz is optimal.
The dewatering of sludge on the gravity vibro-filters
occurs at the sludge movements on the filtering caused
by the action of directed vibrations. Therefore the
direction of vibratings^S and the angle of filtering media
slope above the horizontal cL belong to the basic
parameters of vibro-filtration process. The relationship
of rate of movements to vibration parameters was
obtained experimentally (Eq.5).
where c£#p-angle of slope, at which the vibration
movement of sludge stops, (its value for tested sludges is
from 12-15°).
It was found experimentally, that the angle>8 is
55-70°). angle GL-6-8° at the dewatering of sludges
under optimum conditions.
The results obtained on bench-scale continuous
vibro-filter unit during vibrofiltration process are given
in Table 1.
According to the results of investigations the pilot
model of vibro-filter was developed and constructed and
will be applied in the dewatering of sludges from
pig-breeding farms.
Considerable losses of solids with filtrate and rela-
tively high final moisture of dewatered sludge reduce
efficiency of vibro-filtration process.
Nevertheless the analyses of experimental results
shows, that vibro-filtration belongs to the promising
developments in the field of intensification of thickening
and dewatering of some type of sludges and permits to
separate the considerable part of free water from sludge
without conditioning.
Approximated tecknical-economic calculations in-
dicate, that the use of sludge vibro-thickening with
consequent heat drying or incineration, in most cases
allows to exclude complicated and expensive condition-
ing process prior to mechanical dewatering from the
technological scheme.
Fi However additional expences on heat will be
required but the cost of extra fuel doesn't exceed
expenses on addition of chemicals and dewatering.
TABLE 1
1st stage
Thickening process
2nd stage
Dewatering process
Type of sludge
Initial moisture
content (%)
Final
moisture
content
capacity
kg/sq.m.
per h.
Final
moisture
content
capacity
kg/sq.m.
h.
lotai
capacity
kg/sq.m.
Solids
loss.
1. Primary sludge 93-94
2. Thickened 97,5-98
activated sludge
3. The mixture of 96,6
primary and
thickened acti-
vated sludge
4. Primary sludge 98-98,5
from wood-fibred
slab plant
5. Sludge from wet 75-80
blust furnace
ease leaning process.
89-90 30-50
95,5-96.5 12-16
92-94
91-93
35-42
30-35
50-60
900-1200
84-86 60-90 20-30 15-30
93-94 20-30 7-12 8-12
86-87 50-65
20-25
85-87 100-110 25-30
8-15
10-15
28-32 2000-2500 1000-12000 12-15
65
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Figure 1. Bench scale vibrofilter unit.
1. Vibrator.
2, Filtering screen.
3. Feed sludge.
4. Dewatered sludge.
5. Filtrate.
Figure 2. Schematic diagram of a laboratory unit for
investigations of vibro-filtration process.
1. Vibrator.
2. Filtration tunnel.
3. Samplying pipes.
4. Cylinder volumes.
5. Gamers.
Figure 3. Vibro-filtration process.
1st stage of vibro-filtration process.
2nd stage of vibro-filtration process.
Figure 4. Kinetics of activated sludge vibro-filtration.
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67
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MUNICIPAL SLUDGE MANAGEMENT RESEARCH
PROGRAM IN THE U.S.A.
BY
James E. Smith, Jr., Ph.D.
Sanitary Engineer
Ultimate Disposal Section
Advanced Waste Treatment Research Laboratory
and
William A. Rosenkranz Director
Municipal Pollution Control Division
Environmental Protection Agency
PRESENTED AT
US/USSR SEMINAR
HANDLING, TREATMENT AND DISPOSAL OF SLUDGES
MOSCOW, USSR
May 1975
68
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MUNICIPAL SLUDGE MANAGEMENT PRACTICE
AND RESEARCH PROGRAM IN THE U.S.A
INTRODUCTION
The United States Environmental Protection Agency,
Municipal Wastewater Sludge Research and Development
program is designed to resolve the health and ecological
issues and to preserve and utilize this resource in a
beneficial manner.
I don't know if there is a similar expression in your
language, but there is an old expression in English
appropriate to this approach to solving sludge problems.
It is: "make a silk purse out of a sow's ear".
The persons attending this Symposium, on both sides,
are aware of the complexities of sludge management
systems and the difficulties that must be overcome in
finding environmentally acceptable solutions.
We view our approach or research plan as having the
primary purpose of developing and demonstrating new
or improved technology which can be placed into
practice throughout the United States.
Ours is not completely a government program. It is a
cooperative program conducted in partnership with the
Water Pollution Control Agencies and Universities of our
States, local governments, industry and other Agencies
within the Federal government. The difficulties of
processing, utilizing and disposing sludge are faced by
the local communities. We, therefore, look to them for
participation by testing the newest technology under
local conditions where the practicability, efficiency, cost
and operating problems can be determined under actual
operating circumstances.
Industry participates through its development pro-
grams and manufacturing capabilities. It is advantageous
to individual companies because the market potential for
equipment and systems is improved if performance and
cost data are available from full-scale projects.
Environmental concerns are the principal driving
force behind the effort to develop improved tech-
nology. They range from undesirable odors to the
potential for contaminating the human food chain
when sludges are placed on agricultural land. The
engineering aspects, such as improved means of
dewatering, have cost factors and simplicity of
operation as driving forces.
Utilizing the partnership arrangement mentioned ear-
lier, we view the program as a broad-based approach to
problem-solving.
We first recognize the environmental constraints
imposed by the nature of the sludges. These constraints
are imposed by the constituents of environmental
concern: the trace metals, bacteria, viruses, intestinal
parasites, process chemicals contributed by industry,
nutrient materials, organics and PCB's (Polychlorinated
biphenols).
The technology improvements we are developing
must be designed to produce an end product which has
either removed or inactivated the problem constituents.
Hopefully, that objective can be accomplished by
simultaneously producing a useful product or by serving
a useful purpose, such as power production.
Our discussions with your experts here in the Soviet
Union in 1973 and again in the United States in 1974
clearly indicated that the sludge problems faced here are
not substantially different from those in the United
States or, as a matter of fact, in all of the urbanized
areas of the World. Approximately 60 percent of the
municipal sludge generated in the United States is
currently being applied to the land in a number of ways
including liquid spreading, landfill and trenching (see
Table 1).
Without clear delineation of environmental impact
and public health factors associated with land appli-
cation, we cannot be assured, or even confident, that
current practices do not adversely affect our environ-
ment. Once the damage is done, it is extremely difficult
to undo. Nitrate contamination of a groundwater aquifer
due to placement of sludge on the land for example,
will exert its effect for many years. We are, therefore,
studying the health and ecological factors involved in
land application of sludge.
At the same time, we are evaluating technology which
can be employed to eliminate or minimize specific
problems. Pasteurization, other heat treatment methods
and lime stabilization are being studied as alternatives
for resolving the bacterial, virus and intestinal parasite
issue.
A cooperative effort with the U.S. Department of
Agriculture and the Food and Drug Administration is
directed to the definition of the impact of trace metals
on the human food chain through the production of
crops and meats grown on land to which sludge has been
applied. Evaluation of the uptake of metals in the crops,
and in animals grazed on land to which sludge has been
applied are part of this effort. Studies of this type in the
United States and in other countries should provide the
information needed to establish guidelines which will
inform the users of municipal sludges of the limitations
of use applicable to the constituents of concern. They
will also provide guidance on the techniques of appli-
cation which will permit them to utilize sludges in an
acceptable manner.
69
-------
I wish to note here, since the technical problems are
so similar, that we are also conducting extensive studies
of land application of treatment works effluents.
Incineration will be discussed in detail by others
during the Symposium. Since about 25 percent of the
municipal sludge generated in the United States is
disposed by means of incineration, I would note at this
point that the technical questions concerning the en-
vironmental aspects of this method have not been settled
to complete satisfaction. Air emissions of some of the
sludge constituents, such as the metals and PCB's are still
of concern to local authorities. This is not to say that
incineration is not an acceptable means of sludge
disposal. It can be a satisfactory disposal means. As I
have already indicated, others will discuss these matters
in more detail.
While sludge utilization and disposal is a problem to
some degree for each municipality and for those who
plan and oversee pollution control remedial activities,
the coastal metropolitan areas have a problem of larger
proportion. Approximately 15 percent of the municipal
sludge produced is ocean dumped. Recent legislation
requires control of the dumping of hazardous materials
to the ocean. All who would dispose of such materials at
sea must now do so only with a permit issued by the
Environmental Protection Agency. Municipal sludges,
because of their constituents, fall under the re-
quirements of this legislation. It is planned that ocean
dumping of sludges will be discontinued within the next
few years, which removes a major disposal alternative
from the hands of municipalities along the coast.
Land-based alternatives must then be utilized. Scarcity
of suitable sites for land application within reasonable
hauling distance, air pollution control requirements and
socio-economic aspects then place additional pressures
on those who seek environmentally acceptable sludge
technology.
Table 1 outlines the direction of research and
development referenced early in this presentation. We
hope to include any technology which offers potential
for cost effective solutions. Environmental constraints
cause us to examine technologies such as pasteurization
and sterilization for solution of problems identified with
bacteria, viruses and intestinal parasites when applying
sludge to the land. Other heat treatment technologies
such as the Porteus process, will also contribute to the
solution and improve dewatering characteristics.
Wet oxidation offers the potential for sterilizing the
sludge and to produce useful by-products including
thermal energy and saleable chemicals such as acetic
acid. Application of this method may also make it
feasible to recover trace metals from the sludge. The
small amount of residual solids from the wet oxidation
process is sterile and should pose no major problem of
disposal.
Composting and heat drying are being studied in
respect to the use of the resulting materials for soil
conditioners and low-grade fertilizers. When properly
applied, these methods also produce a material which is
acceptable from the standpoint of biological quality.
Pyrolysis offers the potential, especially when
sludge is utilized in combination with municipal,
solid wastes, to accomplish large reduction in vol-
ume, production of low BTU gas, tars and oils and
other useful materials.
Coincineration with solid wastes in systems which
will include heat recovery or power production may be
an applicable approach and is under study.
Application of these new approaches to solution of
the "sludge problem" is in the development stages. A
wet-oxidation process which offers a great deal of
potential will be built and tested at pilot scale within the
next two years.
Each technology has its specific advantages and
disadvantages. The costs, operation and maintenance and
general acceptance of each will determine how it is used
or considered for application in different locations.
Recognition is being given to socio-economic aspects
of the problem as we proceed with the program. The
experience of many communities indicates that success-
ful application of any of the technologies will depend to
a significant extent on public acceptance. This is a factor
too often ignored in planning a sludge system for
incorporation into the plans for wastewater management
systems. Those who would be subjected to odors,
groundwater contamination, air emissions or other im-
pact on the environment should have a say in what
technology is applied. If we accept that as a requirement
for sludge systems we must recognize that careful
evaluation of all technologies is of first importance. Such
evaluation will be of limited value, however, if we do not
also effectively communicate this information to the
public.
During the past five to eight years improvements in
process have been made and technologies previously
little used or new to United States practice have been
introduced and evaluated by means of demonstration
projects. These include pressure filtration, top-feed
vacuum filter, lime stabilization, heat treatment, land
disposal by trenching, aerobic digestion, composting and
land reclamation.
These are tools communities can use in combination
with traditional processes such as anaerobic digestion,
flotation thickening, incineration, and others to form
sludge management systems currently satisfactory for a
large number of locations.
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They do not, however, provide all the answers for
solving the more difficult sludge management problems
faced by the larger cities and cities located in areas
where potential environmental damage is a major
problem.
For this reason we are proceeding with a research
program directed to the development and demonstration
of technology not previously applied or adapted to
sludge management. Pyrolysis and wet-oxidation are
examples of processes which fall in this category. Such
emphasis is of recent beginning and it will be two or
three years before sufficient data will be available to
make judgements with regard to applicability and cost
effectiveness of the new processes. With moderate
success it will be possible to formulate new sludge
management systems, improve system efficiency and
cost factors and ultimately to demonstrate that sludge
can not only be managed in an environmentally ac-
ceptable manner, but can also be an asset to the
environment.
SLUDGE HANDLING ALTERNATIVES
In general, as a treatment plant's effluent improves,
greater quantities and more complex types of sludge are
produced. These are the factors that make sludge
treatment and disposal such a great challenge. Sludge
handling processes can be classified as shown in Fig. 1.
Within each of these categories are listed numerous
process alternatives. The challenge in putting together a
total process is the evaluation of the numerous alterna-
tives and the elimination of inappropriate methods.
Little comment is required about the need for thick-
ening other than the fact that it is used to increase a
sludge's solids concentration while maintaining fluidity.
Sludge stabilization processes aim at converting raw or
untreated sludges into a less offensive form with regard
to odor, rate of putrefaction and pathogenic organism
content. Sludge conditioning is a pretreatment of thick-
ening or dewatering process. A dewatering method
removes sufficient water from sludge so that its physical
form is essentially changed from that of a fluid to that
of a damp solid. Most of the techniques shown in Fig. 1
are familiar to the pulp and paper industry. One
dewatering technique that is relatively new and has
potential for solving future and present problems is the
belt filter press. Several manufacturers are currently
marketing in the United States variations of a horizontal
belt filter press. One such device is shown in Fig. 2.
These devices generally utilize the following steps:
chemical conditioning possibly followed by gravity
thickening and introduction of the conditioned and
thickened sludge onto a porous belt with simple pressure
or "squeezing" of the sludge by roller-pressing; com-
bined pressing and shearing of the cake; and finally,
discharge of the sludge cake. In some designs, the porous
belt is actually a camllary material or a slight vacuum is
applied before squeezing the sludge. These devices are
undergoing steady development and offer potential
benefits of low capital and maintenance cost, simple
operation, and a higher cake solids than centrifuges or
vacuum filters.
Sludge reduction processes are those that yield a
major reduction in the volatile sludge solids (see Fig. 1).
None of the techniques shown are strangers. Incineration
and wet oxidation are well-known processes, but there
have been no full-scale applications of pyrolysis of
sewage sludge as yet. Final disposal methods, the last
classification shown in Fig. 1, refer to the disposition of
sludge in liquid, cake., dried, or ash form as a residue to
the environment. Essentially all the techniques shown
are self-explanatory.
In the above presentation of methods available for
the treatment and disposal of sludge, the discussion
followed the process flow sequence; that is, sludge was
taken from the clarifier through various treatments and
finally disposed. Actually, the disposal procedure should
be determined first, since its selection often dictates the
choice of treatment methods. For example, if a sludge is
to be incinerated, biologically stabilizing it would be
highly undesirable since this would reduce the sludge's
volatile solids content and, therefore, its caloric content.
Effectively thickening and dewatering the sludge would,
however, be desirable since this minimizes the need for
auxiliary fuel in burning.
Total costs for some sludge handling processes are
given in Table IV. Major expenses are associated with the
mechanical dewatering, digestion, and incineration proc-
esses, while gravity thickening is low in cost.
IMPACT OF UPGRADING WASTEWATER
TREATMENT BY THE ADDITION OF
CHEMICALS ON SLUDGE PRODUCTION
Adding chemicals such as alum, lime, ferric chloride,
or polyelectrolytes in the primary and secondary treat-
ment processes can upgrade present treatment plant
efficiencies. The chemicals enhance the removal of
suspended solids, BOB, and phosphorus. Better removal
of suspended solids in the primary clarifier, however,
also increases primary sludge production and decreases
waste activated sludge production. The total mass of
sludge solids to be dewatered will increase primarily due
to greater removal of incoming solids and the precipi-
tates formed by the chemical additives.
71 Envircrsmsi^d! PrctecrSisn Agency
Lfcrary Room 2404
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Knowing what happens to the sludge mass and
volume when chemicals are added into the treatment
processes is of considerable interest. Although data are
very limited, some have been obtained for phosphorus
removal systems from a review of 13 case histories,
which include both pilot and plant scale studies (3).
Table V shows the effect of adding chemicals in primary
treatment. Although with lime addition the sludge solids
concentration was either changed only slightly or greatly
increased depending upon the amount of lime added to
the wastewater, the sludge mass and volume were
considerably increased. With aluminum (A1+++) and
iron (FC+-H-) addition, sludge mass increased but not to
the extent that occurred with lime. Sludge volume,
however, was equal to or greater than that obtained with
lime. Addition of AH-H- and Fe+++ clearly had a
detrimental effect on the sludge solids concentration.
Similar data for the addition of A1+++ and Fe+++ not to
the primary darifier but to the activated sludge process
are given in Table VI. Although large increases in sludge
solids and volume occurred, surprisingly, the sludge
solids concentration was not as seriously affected as it
was with the addition of A1+++ and Fe+++ salts to the
primary system. Table VII shows the effect of tertiary
treatment by lime, AH-H-, and FC+-H- addition on sludge
protection. In each case, a large amount of dilute sludge
solids was produced. The smallest amount of sludge mass
was produced with iron addition; the greatest with lime.
The data just presented dearly indicate that the
addition of chemicals in vastewater treatment can cause
large increases in the mass and volume of sludge to be
processed. With the addition of Al-m- and Fe-m- salts,
the resultant sludge may be very dilute (1 to 2% solids).
Further the use of inorganic chemicals increases the
inorganic content of the sludge, which means there will
be more ash to dispose of it the sludge is incinerated,
and the sludge will have a lower volatility and, therefore,
lower caloric content. Plants employing chemical addi-
tion will probably need a more elaborate and costly
sludge treatment and disposal scheme than that used
with conventional sludges. Learning that more complete
wastewater treatment can produce additional sludge
disposal burdens is not a new experience. When only
primary sludge was produced, the operator had a simple
fibrous material to work with. It was basically incom-
pressible, generally came from the clarifier with a solids
concentration of about 5%, and could be readily gravity
thickened to an 8 to 10% solids concentration. With
little chemical conditioning, this material is readily
dewatered by a rotary vacuum filter at rates of from 24
to 49 kg D.S.*-/m2-hr. (5 to 10 Ib D.S./ft2 -hr), and high
*D.S.-dry solids
cake solid concentrations of from 25 to 30% result. The
sludge cake was often autocombustible. A completely
different situation arose with the need to handle large
quantities of waste activated sludge. This material
typically leaves the clarifier with a very dilute solids
concentration of from <1 to ..1.5% and is gelatinous in
nature. The sludge is generally very compressible and
will only thicken by gravity to about a 2.5% solids
concentration. Even with considerable chemical condi-
tioning, it dewaters on a rotary vacuum filter only
poorly. Consequently few plants dewater straight waste
activated sludge. It is generally first mixed with primary
sludge, and this combination is thickened and de-
watered. The combination, however, typically dewaters
more poorly than the primary sludge alone.
IMPACT OF CHEMICAL ADDITION IN PRIMARY
TREATMENT ON SLUDGE HANDLING
The difficulty faced in handling chemical process
sludges sparked in the initiation of a research project to
define the ability of conventional thickening and de-
watering techniques to process chemical-primary sludges.
At Salt Lake City, Utah, the Envirotech Corporation,
under contract to the U.S EPA, has been studying the
characteristics of sludges produced when either FC+++ or
A1+-H- salts arc added to raw wastewater. A dual train
pilot system, each train of which has the capacity to
process 152 1/min (40 gpm), is operated on raw
wastewater. Each train consists of a primary clarifier,
with sludge removal to a thickener. An FC-H-+ salt is
added to remove phosphorus in one train and A1+++ salt
is added in the other train. Phosphorus-laden chemical
primary sludges thus produced are studied as to their
thickening characteristics in gravity and dissolved air
flotation pilot systems and as to their dewatering
characteristics by pilot vacuum filtration and centri-
fugation units (4). Preliminary results of pilot scale
gravity thickening tests are presented in Table VIII. The
solids concentration in the sludge leaving the clarifier in
the Fe+++ salt-dosed train was slightly higher than that
leaving the clarifier in the A1+++ salt-dosed train. In each
case, indications are that a sludge's thickening properties
vary inversely with the quantity of A1+-H- or FC+++ it
contains, and the chemical primary sludge thickens
better when polyelectrolyte is added to the wastewater.
In general the A1+-H- sludge thickened very poorly. The
best results were obtained with the sludge produced
from a low A1+++ and polymer dosage to the raw
vastewater. A feed sludge of about 2.7% solids was
generated. When this feed sludge was loaded to the
thickener at a rate of 20 kg D.S./m2-da (41b
D.S./ft2-da), a solids concentration of 4.2% was
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produced. The Fe+++ sludges thickened much better
than the A1+++ sludges. Similar thickening results were
obtained for the sludge produced when polymer and
both high and low levels of Fe-m- were added to the
wastewater. Best results were obtained for a feed solids
concentration of about 2.5% and a loading rate of about
20 kg D.S./m -da (4 Ib D.S./ft -da); this gave final solids
concentration of 5.2%. Hathaway and Farrell recently
studied the gravith thickening of A1+++ and Fe+++
primary sludges in bench top tests (5). In agreement
with the work of Envirotech, they found that A1+++ and
Fe+++ primary sludges have very low thickening rates.
However, dilution of A1+++ primary sludges with efflu-
ent before thickening, by Hathaway et al., produced a
dramatic increase in the thickening rate and increased
the thickened solids concentration. The beneficial effect
of dilution on Fe+++ primary sludges was also sub-
stantial. Further, the addition of polymers in the
thickening step substantially increased the thickening
rate and thickened solids concentration for both the
A1+++ and FC+++ primary sludges. The preliminary
results of pilot-scale, dissolved air flotation thickening
tests on unconditioned sludge by Envirotech are pre-
sented in Table IX. The effects of level of A1+++, level of
FC+++, and polymer addition to wastewater were not as
clear as in gravity thickening. Further, the degree to
which the A1+++ and Fe+++ primary sludges could be
thickened differed little, and when these results were
compared with those of gravity thickening, it was
surprising to see little difference. Hathaway and Farrell
in similar dissolved air flotation testing obtained results
that were superior to those they obtained with gravity
thickening (6). However, they used polyelectrolyte to
condition the sludge prior to thickening. A1+++ and
Fe+++ primary sludges were thickened on an average to
6.2 and 5.2% solids concentrations, respectively, when
solid loading rates of from 5 to 20 kg D.S/m2-hr (1 to
4 Ib D.S./ft2-hr) were employed. As the A1+++ or Fe+++
concentration in the sludge increased, they noted that
the float solids concentration decreased.
A 15 cm (6-inch) Sharpies sold-bowl centrifuge was
employed by Envirotech to determine the sludges'
dewatering characteristics (4). Preliminary data are
shown in Table X for a "G x Pool Detention Time"
value of 500 g-min (G is the centrifugal force in
multiples of force of gravity). During testing, the
centrifugal force at mid-depth in the bowl averaged 1950
g's or about 5000 rpm, and the centrifuge's pool volume
was 1.556 1 (0.411 gal). The poor solids capture is
evident for the instances where the sludges were not first
conditioned by the addition of polyelectrolyte. How-
ever, capture was still on an average 85% better for the
unconditioned Fe-t-H- sludges than it was for the
unconditioned Al-m- sludges. With appropriate polymer
conditioning, high level solids capture was obtained for
both A1+++ and Fe+++ primary sludges. Good cake solid
concentrations were obtained for all sludges without the
use of polymer, although in general the Fe+++ sludge
cakes were about 26% drier than the A1+++ sludge cakes.
With polymer conditioning, the cake solids concen-
tration for the Fe+++ sludge cakes, however, were on an
average 50% drier than the A1+++ cakes. Results of
pilot-scale vacuum filtration tests are shown in Table XI.
In all instances reported in these preliminary test results,
the vacuum employed was equivalent to 0.69 kg/cm2
(20 in. mercury), cake discharge was good, and solids
capture was very high (98-99%). A review of the test
results shows that the A1+++ primary sludge produced at
a low A1-H-+ dose filtered better than the higher dose
level sludge. The low dose level Fe+++ primary sludge,
however, filtered at essentially the same rate as the
sludge with a larger amount of Fe+++ in it. In comparing
the low level A1+-H- and Fe+++ primary sludges, it is
noted that the A1+++ sludge filtered with a greater
production rate than the FC+++ sludge, but that the
Fe+++ sludge gave a drier cake. The A1-H-+ sludge gave a
significantly lower production rate than the FC+++
sludge in the high level salt addition studies, however.
and the cake solids for both sludges were not signifi-
cantly different. An overview of the data readily shows
that an increase in either the filter's feed sludge solids
concentration or level of lime addition caused greater
filter production rates. The production rate could also
be increased by decreasing the filter's cycle time. Cake
dryness increased with lime addition.
The addition of lime to primary treatment generates
another type of upgrading sludge. Investigators at EPA's
Blue Plains Pilot Plant (District of Columbia) have
conducted tests on the thickening and dewatering
properties of lime sludges (6). For a high lime sludge
(pHMl.5), it was calculated that with a solids loading
of 26.4kg D.S./m22-hr (5.42 Ib D.S./ft2-hr), 12%
underflow solids could be obtained. Similarly at a solids
loading of 18 kg D.S./m2-hr (3.7 Ib D.S. ft2-hr), it was
calculated than 20% total solids in the underflow could
be obtained. With low lime sludges (pHMO.5), a 2%
clarifier underflow solids sludge could be thickened to a
6 to 9% solids concentration at only a loading rate of
approximately 9.2kg D.S./rn2-hr (1.9 Ib D.S./ft2-hr).
The investigators cautioned, however, that these data
had not been verified in continuous thickening tests. The
low lime sludge could be dewatered on a vacuum filter at
a rate of 10 to 15 kg D.S./m2-hr (2 to 3 Ib D.S./ft2-hr)
and give a 28 to 29% cake solids concentration. The high
lime sludge, however, could be dewatered at a rate of 29
to 45 kg D.S./m2-hr (6* to 9 Ib D.S./ft2-hr) and give a
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cake solids concentration of 35 to 36%. Blue Plains does
have a low magnesium content wastewater, and the high
lime sludge was found to contain only 3 to 4%
Mg(OH)2. Mulbarger has discussed in detail the relation-
ship between magnesium in a sludge and a sludge's
dewaterability (7).
Van Fleet et al. have reported on chemical sludge
handling experiences in Ontario (8). When 90mg/l of
alum and 0.4mg/l of a polymer were added to
wastewater at the 76 m3/min (29 MGD) West Windsor
primary plant for phosphorus removal, the solids con-
tent of the primary sludge dropped from 11.5 to 7.6%.
Further total solids production increased from 0.10 to
0.216 kg D.S./m3 of plant flow treated (800 to 1800 Ib
D.S./MG of plant flow treated). The corresponding
vacuum filter yield and filter cake solids content
dropped from 55.2 to 28 kg D.S./m2-hr (11.3 to 5.8 Ib
D.S./fts-hr) and from 31.1 to 19.2% solids, respectively.
Sludge conditioning with ferric chloride and lime was
more difficult, with chemical costs rising from $3.42 to
$10.47 ton (metric) $3.10 to $9.50/ton) of dry solids
produced. Somewhat similar experiences occurred at the
Little River conventional activated sludge plant in
Ontario when 150 mg/1 A1+++ were added to the raw
waste. However, when 125 mg/1 of lime as Ca(OH)
instead of A1+++ were added to the Little River Plant's
raw waste, sludge treatment improved. The sludge solids
concentration and vacuum filter yields went up and
chemical conditioning costs per ton of solids processed
went down. Sludge production, however, was increased
by close to 50%.
SOME POTENTIAL SOLUTIONS
Waste chemical and activated sludges have been
shown to be two sludge types not readily handled by
conventional technology. This factor sparked the initia-
tion of several research projects reported on here.
LIME STABILIZATION
The addition of lime in sufficient quantity to elevate
the pH of a raw sludge to between 12.2 and 12.4 for a
lime sludge contact time of 30 min. is an effective,
simple, and relatively inexpensive alternative to other
sludge stabilization schemes (9). With the lime addition
technique just described, the pH of the sludge should
remain above 11.0 for better than 2 weeks. Paulsrud and
Eikum's results agree with these findings and their
determination of the time doses required to keep
different types of sludge at a pH greater than 11.0 for 14
days is shown in Table XII (10). Results of lime
stabilization are destruction of pathogenic bacteria
(Table XIII), good dewatering on sandbeds, elimination
of obnoxious odors, and the possibility of as much as a
50% ammonia-nitrogen reduction (11) Battelle-North-
west has estimated the costs of lime addition to a pH of
12.2 to the costs of lime addition to a pH of 12.2 to
12.4 including all operation and maintenance costs to
range from $9/ton (metric) D.S. ($8/don D.S.) for
primary sludges to approximately $17/ton (metric) D.S.
($15/ton D.S.) for biological sludges (9). Lime stabili-
zation has immediate application in situations where a
plant through upgrading or because of a digester failure
suddenly has large amounts of sludge that require quick
stabilization.
AUTOTHERMAL THERMOPHILIC AEROBIC
DIGESTION
Past and recent laboratory studies have indicated
benefits for the elevation of an aerobic digester's
temperature to 40, 50 or 60°C. The rate of volatile
solids destruction significantly increases with an increase
in temperature. At the higher temperatures, only several
days are required for the biodegradation of sludge solids
as opposed to a few weeks. In fact, during cold weather
a typical aerobic digester may only accomplish 10 to
15% volatile solids destruction in a week.
Recent laboratory, pilot and plant scale studies of the
aerobic digestion process have shown that considerable
heat is released by the microorganisms during their
metabolism of organic sludge solids. Working with
oxygen instead of air in a closed plant scale aerobic
digester at Speedway, Indiana, and at normal loading
rates, 1.28kg Vs/m3day (0.08 Ib Vs/cu ft-day), the
temperature was found to rise to about 33°C and remain
near this temperature in year-round operation. The
system was essentially independent of the external air
temperature. Pilot work at Denver with an open aerobic
digester using pure oxygen and sludge loading rates of
about 4.81 kg VS/m3 day (0.3 Ib VS/cu ft-day) resulted
in a temperature rise to near 33° C despite very cold air
temperatures. Covered pilot digesters were operated at
Tonawanda, New York, at feed sludge loading levels of
8.01 to 9.61 kg VS/m3 day (0.5 to 0.6 Ib VS/cu ft-day).
These units achieved temperatures near 60°C.
Advantages to be derived from an autothermal
aerobic digestion process are a much smaller volume
reactor requirement because of the high loading rates
and rapid solids destruction. Operation at thermophilic
temperatures (45-60°C) will produce a pasteurized
sludge suitable for land disposal. Preliminary results
indicate that the digested sludge settlers and dewaters
better than raw sludge and sludge from a conventional
aerobic digestion system.
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The Los Angeles, California, Hyperion Activated
Sludge Treatment Plant routinely reduces 247 metric
tons (272 tons) per day of solids to 111 metric tons
(122 tons) per day by mesophilic anaerobic digestion.
They have recently been experimenting with thermo-
philic anaerobic digestion. Temperature differentials of
± 1.7°C in a day or two upset tank stability, but a
successful operational temperature range has been estab-
lished between 46 and 51°C. Since the particle size of
thermophilic sludge is more coarse than the mesophilic
sludge, the dewatcrability on vacuum filters and cen-
trifuges produces a drier cake and uses less chemicals as
studied on pilot and full size equipment. However,
filtrate-centrate concentrations from dewatered thermo-
philic sludge are higher in grease, COD, and heavy
metals.
After weighing the additional energy and heat re-
quirements of thermophilic operations against the bene-
fits derived from the dewatering process, results indicate
that anaerobic digestion at a thermophilic temperature
range can be an important and economic step in the
total sludge disposal problem. Los Angeles is currently
the only location in the United States utilizing thermo-
philic anaerobic digestion.
ASH CONDITIONING
In laboratory dewatering gests using sludge incinera-
tor ash as a conditioner, the filter yield of ash-
conditioned sludge (ash-free basis) was found propor-
tional to ash dosage and to approximately double at
dosage levels of 1.3, 3.7, or 3.1 kg ash/kg sludge solids
for waste activated, raw primary, or digested primary
sludge, respectively. The moisture content of dewatered
ash-conditioned sludge (ash-free basis) generally in-
creased somewhat for all sludges. Interestingly, the
filtrate from dewatering of the ash-conditioned sludge
was of a high quality (12). The properties of ash that
enable it to improve dewatering of sludge include partial
solubilization of its metallic constituents, its sorptive
capabilities, and the irregular shapes of the particles. In
Indianapolis, Indiana, the city recently began using
sludge incinerator ash to condition a mixture of primary
and activated sludge before dewatering. The dramatic
effect of ash addition on the average performance of the
plant's rotary vacuum belt filters is shown in Table XIV.
Indianapolis succeeded in increasing its filter produc-
tivity by as much as 500% and decreasing its cake
moisture by as much as 22%. The filtrate quality has also
improved, and from a cost viewpoint, the cationic
polymer requirement has been reduced by approxi-
mately 55%. These data were obtained in late 1972; at
that time the plant was handling approximately
189,569 kg D.S./da (418,000 Ib D.S./da) and the ratio
of ash to dry sludge solids varied from 0.25 to 0.50. The
ash handling facilities required almost no investment and
no additional operating cost. The relative location of the
ash slurry line to the gravity sludge thickeners provided
for easy ash addition, and only a tap, a short feed line,
and pump needed to be installed (13).
THERMAL CONDITIONING OF SLUDGE
In heat treatment, temperatures of from 149 to
260°C (3000 to 500°F) and pressures of 1034 to
2758 kN/m2 (150 to 400 psig) are attained for pro-
tracting periods. The steps usually involved in the
process include sludge storage, grinding, preheating, high
pressure and temperature react, thickening and decant-
ing, auxiliary liquor treatment, off gas deodorize and
steam. Significant changes in the nature and composition
of wastewater sludges result. The effect of heat treat-
ment has been ideally likened to syneresis, or the
essentially cellular material. These cells contain intra-
cellular gel and extracellular zoogleal slime with equal
amounts of carbohydrate and protein. Heat treatment,
breaks open the cells and releases mainly proteinaceous
protoplasm. It also breaks down the protein and zoogleal
slime, producing a dark brown liquor consisting of
soluble polypeptides, ammonia nitrogen, valatile acids,
and carbohydrates. The solid material left behind is
mineral matter and cell wall debris.
Dewaterability is usually significantly improved by
the solubilizing and hydrolyzing of the smaller and more
highly hydrated sludge particles which then end up in
the cooking liquor. While analysis of this liquor from
domestic wastewater sludges indicates the breakdown
products are mostly organic acids, sugars, poly-
sacharides, amino acids, ammonia, etc., the exact
composition.
TOP-FEED ROTARY VACUUM FILTRATION
The City of Milwaukee, Wisconsin, under an EPA
grant, performed a pilot-scale study of dewatering waste
activated sludge containing Fe+++ salts by top-feed
vacuum filtration. The Fe+++ was added into the
activated sludge system for phosphorus removal. Gravity
thickened FC+++ activated sludge was conditioned with
ferric chloride and filtered on a 1 m (4 ft) diameter, 2 m
(6 ft) face vacuum filter in both the bottom-feed and
top-feed modes at the Jones Island Plant. The top-feed
filter was compared on a slide-by-slide basis with the
large bottom-feed production filters. Production rates to
7.91 kg D.S./m2-h r(1.62 Ib D.S./ft2-hr) at 14.5% cake
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solids were produced in the top-feed mode as compared
with 6.83 to 7.62 kg D.S./m2-hr (1.40 to 1.56 Ib.
D.S./ft2-hr) at 13.6 to 14% cake solids for the bottom-
feed filters. Discharge of filter cake from the top-feed
unit was far superior to that from the bottom-feed units
(14).
MOVING BELT FILTER PRESSES
#
A general description of these relatively new sludge
dewatering devices was given earlier. While little per-
formance data are available on the devices, EPA partially
assisted in development of one unit, a capillary de-
watering device which is shown in Fig. 3 and will be
described here (15). Conditioned sludge is distributed
over the screen logitudinally through a series of openings
that creata a uniform liquid level. This portion of
operation releases free water which drains through the
screen. Solids concentration is increased by approxi-
mately 25%. After the initial free water release, the
screen carrier comes in contact with the capillary belt,
which is the unusual feature of the device. The addi-
tional dewatering comes from the capillary action of this
.belt; the capillary dewatering zone is shown in Fig. 4.
The carrier screen and sludge continue along the
longitudinal plane after capillary dewatering where it is
pressed by a single compression roller, which extracts
additional liquid for a final dehydration. The sludge cake
transfers from the belt to the smooth compression roller;
it is collected by a doctor blade, falls in clumps onto the
screen, and is carried to a discharge chute.
Considerable data were obtained on a pilot plant scale
at the Long Road treatment plant near Pittsburgh,
Pennsylvania (Table XV). Feed capacities from 10 to
22 kg D.S./m2-hr (2 to 4.5 Ib D.S./ft2-hr) were achieved
with cake solids at discharge ranging from 15 to 18% for
activated sludge. Machine capacities more than twice
these values may be possible. It was found that the
device operated without coagulant addition at a penalty
to solids capture. With polyelectrolyte addition of
5 kg/ton (metric) D.S. (10 Ib/ton D.S.) at an equivalent
cost of $4.41/ton (metric) D.S. ($4/ton D.S.), sludge
solids capture of 95% was obtained when the machine
was operated at 9.8 kg D.S./m2-hr (2.0 Ib D.S./ft2-hr).
At higher machine capacities, i.e., 20kg D.S./m24u
(4.0 Ib D.S./ft2-hr) or higher, the system operated more
economically with use of ferric chloride conditioner.
Overall machine operation depended on chemical ad-
dition, sludge solids loading, and screen mesh size. Total
cost estimates for capillary dewatering ranged from
$21.34 to $43.74/ton (metric) D.S. ($19.36 to
$39.67/ton D.S.) processed in plants of the 5 to 11
m3/min (2 to 4 MGD) size (15).
PRESSURE FILTRATION OF SLUDGE
Experience in the United States with pressure filtra-
tion of municipal sludges has been limited. A recent
installation of pressure filtration was made at the Cedar
Rapids, Iowa, 75.2 m3/min (28.6 MGD) two-stage trick-
ling filter plant to dewater an anaerobically digested
mixed primary and secondary sludge. EPA participated
in the evaluation of its performance. A combination of
recycled ash and chemicals is used before dewatering to
condition the 25,397kg (56,0001b dry basis) of di-
gested sludge per day (16). Sludge cake discharges from
the filter with a cake solids content in the range of 62 to
64%, and the cake's appearance is dense, dry, and
textured. Although the Cedar Rapids plant normally
dewaters digested sludge, full-scale tests have also been
successfully run on raw primary sludge. The costs at
Cedar Rapids are related to the concentration of feed
solids. At 4.5% solids, the average total capital and
operating costs were $29.58/ton (metric) D.S.
($26.83/ton D.S.), and at 6.5% solids, $20.07/ton
(metric) D.S. ($18.2Q/ton D.S.). Incineration has norm-
ally been achieved without the use of supplemental fuel.
The Kenosha, Wisconsin, activated sludge wastewater
treatment plant recently installed two Edwards and
Jones filter presses to dewater its digested sludge.
Performance requirements for the presses are that they
process a 3 to 6% digested sludge working 16 hours a
day, 5 days a week, and remove approximately
9,5255 kg (21,000 Ib) of dry solids per day. Sludge is
fed into the press at a maximum pressure of 7.03
kg/cm2 (100 psi), and a complete cycle takes 3 to 4
hours. Each press produces 3-cm (1 inch) thick cakes of
about a 40% solids concentration. Sludge conditioning
requires 3 to 5% ferric chloride and 12 to 15% lime on a
dry weight basis (17).
PYROLYSIS
Pyrolysis is the destructive distillation of organic
materials under pressure and heat in the absence of
oxygen. Through the pyrolysis process, the organic
portions of waste are reformed into lower molecular
weight compounds. These compounds can be in the
form of a combustible gas, tar and oil, and a solid "char"
which also has an appreciable heating value. Generally
the "pyrolyzing" process is carried out in an externally
heated closed reactor chamber. Process temperatures can
be as low as 500°C (932°F) or in excess of 900°C
(1652°F) at atmospheric pressures. At the lower tem-
peratures the reaction product is predominantly solid
and at higher temperatures, gas is more prevalent. The
volatile gasses can be siphoned off and used to heat the
76
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reaction chamber. The process can be thermally self-
sustaining providing the heating value of the waste is
high enough.
Since the combustion of sludge normally requires the
use of auxiliary fuel, EPA intends to investigate at two
sites on a plant scale the copyrolysis of sludge and solid
wastes mixtures. At one site the production of a useful
gas will be emphasized while at the other, products other
than gas will be emphasized.
PURETEC WET OXIDATION OF DIGESTED SLUDGE
Philadelphia will shortly demonstrate the use of this
process at their Northeast Plant. The unit will process
daily 15 tons of dry sludge solids, which is equivalent to
a wastewater flow of 60,000 m3/day. In the process,
sludge is brought to a pH of about 3 with sulfuric acid,
heated to 232°C and contacted with air at a pressure of
about 4,137 kN/m2. The sludge flows through a series of
compartments, each equipped with an agitator, in a
single horizontal cylindrical vessel. A gaseous and a
liquid stream are removed. Benefits anticipated with this
process include: 75 to 85% COD destruction, the
generation of surplus thermal energy, the conversion of
nitrogen compounds to recoverable ammonia and the
rendering of metals cxtractable. The predominant
organic compound in the resultant solution is acetic
acid.
LITERATURE CITED
1. Stanley Consultants, "Sludge Handling and Dis-
posal, Phase I-State of the Art," Report to Metro-
politan Sewer Board of the Twin Cities Area,
Nov. 15, 1972.
2. Ralph B. Carter Company, "Carter Automatic Belt-
Filter Press," Marketing Brochure, Hackensack, N.J.
(1971).
3. Adrian, D. D., and Smith, J. E., Jr., "Dewatering
Physical-Chemical Sludges," Progress in Water Tech-
nology, Vol. I, Applications of New Concepts of
Physical-Chemical Wastewater Treatment, Sept.
18-22, 1972, Pergamon Press, N.Y., N.Y.
4. Villiers, R. V., Personal Communication concerning
progress under USEPA Contract No. 68-03-0404,
"Dewatering of Primary Chemical Sewage Sludges,"
with the Envirotech Corp., Jan. 1975.
5. Hathaway, S. W., and Farrell, J. B., "Thickening
Characteristics of Aluminum and Iron Primary
Sewage Sludges," Proc. of Research Symposium on
Pretreatment and Ultimate Disposal «f Wastewater
Solids, USEPA Publication No. EPA-902/9-74-002,
May 21-22, 1974, p. 197.
6. Bennett, S. M., Personal Communication, Jan. 1975.
7. Mulbaiger, M. C., Grossman, E. Ill, Dean, R. B., and
Grant, O. L., J. Water Pollution Control Fed.
41:2070(1969).
8. Van Fleet, G. L., Barr, J. R., and Harris, A. J., J.
Water Pollution Control Fed. 46:582 (1974).
9. Counts, C.A., Shuckrow, A. J., and Smith, J. E.,
Jr., "Stabilization of Municipal Sewage Sludge by
High lime Dose," Proc. of Research Symposium on
Pretreatment and Ultimate Disposal of Wastewater
Solids, USEPA Publication No. EPA-902/9-74-002,
May 21-22, 1974, p. 73.
10. Paulsrud, B., and Eikum, A. S., Norwegian Institute
for Water Research, personal communication, April
1974.
11. Farrell, J. B., Smith. J. E., Jr., Hathaway, S.W. and
Dean. R. B., J. Water Pollution Control Fed. 46:113
(1974).
12. Smith, J. E., Jr., Hathaway, S. W., Farrell, J. B., and
Dean, R. B., "Sludge Conditioning with Incinerator
Ash," Proc. 27th Annual Purdue Ind. Waste Conf.,
Engineering Extension Series 141, Pt. 2: 911
(1972).
13. Doyle, Carlos, Indianapolis Sanitary District, per-
sonal communication, Jan. 1973.
14. Leary. R. D., Ernst, L. A., Douglas, G. R. Geino-
polis, A., and Mason, D. G., J. Water Pollution
Control Fed. 46:1761 (1974).
15. Lippert, T. E., and Skriba, M. C., "Evaluation and
Demonstration of the Capillary Suction Sludge
Dewatering Device," USEPA Publication EPA-
670/2-74-017 (March 1974).
16. Gerlich. J.W., and Rockwell, M. D., "Pressure Fil-
tration of Waste Water Sludge with Ash Filter Aid,"
USEPA Publication No. EPA-R2-73-231 (June
1973).
17. Swope, H.G., Water and Sewage Works 121:108
(1974).
77
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INORGANIC SUSPENDED SLUDGE DEWATERING.
by Lavrov, I. S., Feodorov, N. F. and Ponomareva, V. N., Leningrad
Civil Engineering Institute.
It is known that a great mass of multicomponent
sludge suspension (with humidity 98-99%) is collected
on the industrial treatment facilities. These colloid
systems include negatively and positively charged parti-
cles which settle down badly. Such sludges must be
deposited out of the community region in such ground
from which they can not get into the aquiferous layers.
The very procedure is very expensive in addition to the
difficulty to find the needed geological structure of the
ground throughout the country territory. It forces to
obtain the maximum concentrated sludge of small
volume and with the simple procedure of depositing.
The methods of settling and mechanical dewatering
with the help of filters and centrifuges are used for
thickening with prior treatment by chemical reagents. It
results in humidity lowering up to 80-90%.
In the last period the electrical method of water
removal is becoming spread especially in some techno-
logical processes. In order to prove the usefulness of the
electrical method in waste water sludge treatment the
scientists of the Leningrad Institute of Civil Engineers
(LISI) have carried out some experimental tests. Two
groups of mostly characteristic sludges were chosen.
Those were the sludges from the recycling water systems
and from some technological waste waters of several
industrial plants. The first group consists of flocculant
sludges of metal hydroxides as those after the galvanic
work. The second one consists of more consentrated
silicate-oxide dispersion as those from the ceramic,
refractory and abrasive industries. As far as the con-
sentrating process of dispersion systems depends on their
physical-chemical properties the following parameters
were investigated: chemical composition of solid and
liquid phases, electrical conductivity, acidity, dispersion
degree, stability, Z-potential and the coagulants and
flocculants influence.
The average data state that the basic properties of
heterogenous, multidispersive, multicomponent systems
are characterized with the solid phase from 1,03 to 10%,
alkalinity from 0,6 to 34Sppm, volume weight from
1,00 U*9l,07g/cm3 and the particle size from 1 to 20
mm with the pick on the distribution curve in the range
2-5 mm. The chemical structure of the investigated
sludge was controlled by spectrochemical analyses.
The dispersion system mainly consisted of the metal
oxides: silicon 2,9-55,3%, aluminium 2,25-33,9%, man-
ganese 1,97-22,9%, magnesium 0,2-73%, chrome
0,65-12,14% and small content of cadmium and copper.
The compactness of the solid phase was 1,98-2,91 g/cm3
and that of the liquid phase was from 1,00 to l,09sp.
The electrical conductivity was from 6,2.10~4 to
1,0.10~2 1/om.cm.
The refractory suspension had relatively high aggraga-
tive and kinetic stability in the wide range of solid phase
concentration 0,5-10% weight. The value of Z-potential
is in the range -10+ -50mv with electrical conductivity of
liquid phase 10~4 -10~5om~' cm'1
The injection of aluminium sulphate in refractory
suspension lead to the distortion of its stability. The
points of coagulant doze 40 + 75mg/l were those at
which the suspension started to settle as non stable one
with the particle enlargement from 2 to 30 mm. Both
Z-potential and system stability lowering is the result of
the increasing of antiion content and compression of
double ion layer. The particle recharge had not been
observed (Fig. 1).
The injection of poly aery lamide into the refractory
suspension as a flocculant from 0,1 to 25 mg/1 lead to
the particle settling acceleration and to the particle
enlargement from 100 to 500 mm. The reduction of
Z-potential and the increasing of sludge volume ware
noted as well. The similar influence of flocculant on
hydrooxide sludge was observed when the content of
polyacrylamide was increased up to 250 mg/1.
Thus during the investigation of physical-chemical
sludge properties the usage of flocculants was shown to
be the most proper way in case of separation followed
by compression in hydrooxide systems. It is mostly
effective to combine the coagulant and the flocculant
for better concentration of solid phase, particular, for
the refractory suspension.
The process of dispersive particle interactions when
the electrical field is used is known to be the result of
double ion layer deformation, dipol-dipole interaction.
Under this influence the dispersive particles become
closer to each other and form the convertable or
nonconvertable aggregates, depending on the summary
curve shape of the potential energy of particle inter-
action. Using the theoretical explanation of the influ-
ence of electrical field on suspension system it is possible
to determine parameters of the electrical treatment
process for some certain objects of the investigation.
This is achieved with the help of the analytical methods.
The behaviour of the chosen systems in the electric
field had been checked on the devices of types BCA-UL
or YUH-1, consisting of the source of stable voltage and
78
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a working chamber. The range of voltage was E=5-150
v/cm. As the tests showed the dispersive particles in the
nonstable hydrooxide sludge started moving, coagulating
and aggregating under the influence of the electrical
field. This process was characterized by the differential
distribution curves accordingly to the particle size up to
the moment of the electrical field influence and after it
(correspondently 2-5 mm and 400-700 mm) at E=10
-20v/cm. By the experiment it was proved that the
sludge compression is practically finished in five minutes
after the moment of the electrical field laying-on. At the
same time the electrical current that flowed through the
system was increasing to some stable value. Changing of
Physical-chemical properties of the system was observed
along with the particle aggregation (Fig. 2). If the change
of limit settling volume is taken as a criteria to evaluate
the system stability in case of electrical field influence
within the range E = 5-40 v/cm., one can notice that the
minimum dispersion stability is corresponding to the
maximum limit settling volume; E= 10-20 v/cm for
positively and negatively charged systems. Within this
voltage range the typical changing of Z-potential was
observed. But it can not be explained up to now. The
flocculant, chaotically formed sludge results from the
electrical treatment, with less resistance to filtration.
The concentration of the dispersion system, prior being
aggregated in the electrical field, may be done either
mechanically (Table 1) or with further electrodewatering
with the simultaneous filtrate removal under the gravity
field.
Table 1
Influence of the electrical treatment of systems
at E optimal on the vacuum-filtration parameters.
(vacuum - 500 mm of mercury column,
filtration cycle - 2 minutes)
Type of sludges
Sludge after galvanic work*
Sludge from electrode shops
Hydrodynamic specific resistance
r.lO'°cm/g
before electrical
treatment
72,2
28,4
64,5
after electric
treatment
44,1
11,5
16,0
Efficiency of vacuum filter
kg/m2 Jiour
before electric
treatment
6,7
10,5
6,07
after electric
treatment
14,6
26,4
12.9
*Diffeient industrial samples of hydrooxide sludges with equal concentration of the solid phase were taken for testing.
It was proved by the tests that the dewatering process
of studcd systems was correspondently increasing for a
number of electrodes stainless steel < coal < aluminium
< brass. 82% humidity was achieved with the usage of
brass and aluminium electrodes.
The refractory suspensions are more aggregatively
stable (Fig. 2). The nonconvertable coagulation was
evaluated on the base of the suspension transparency. It
changes jumplike at the critical voltage of field. The loss
of the system stability under the influence of the
electrical field in range E from 10 to 150 v/cm is
accompanied by lowering Z-potential without the mean-
ingful changing of the electrical conductivity of liquid
phase. These changings in the system stability can be
explained by Deriagin-Landay-Ferway -Overback theory,
the polarizational interaction of separate particles being
taken into consideration. The common usage of rea-
gental and electrical methods is especially reasonable for
the separational processes. The electrical treatment of
the refractory suspensions gives the possibility to lower
E from 125 v/cm to 50 v/cm when 10-25 mg/1 of
aluminium sulphate is injected in these suspensions (the
limiting doze 40-75 mg/1). The application of the
electrical field results in more intensive aggregation,
because the forces of dipole-dipole interaction are
proportional to the third degree of radius of particle
79
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interaction. Therefore the injection of the coagulant in
small doses causes the spontaneous process of suspen-
sion coagulation. These doses change the particle dis-
persability unconsiderably and have no on the system
stability with the following usage of the electrical field.
To increase the concentration of the solid phase in
necessary to carry out the electrical treatment of the
refractory suspensions in two stages. It allows to get the
weight concentration of the solid phase 25-62% depend-
ing on the field voltage.
On the base of the past experiments the technological
scheme of the sludge concentration with the usage of the
electrical field is proposed (Fig. 4). It has been proved
that the dewatering of sludge with the help of the
electrical treatment is economically better than that
with the mechanical method. For example, the costs for
the hydrooxide sludge dewatering (one plant is taken)
are 39,900 roubles when the vacuum-filtration costs
are 20600 roubles with the usage of the electrical
field.
Subscription to Figures
I. S. Lavrov, N. F. Fedorov, V. N. Ponomareva
"Inorganic suspension sludge dewatering."
Fig. 1 Dependence of the specific electrical conductivity
(1), Z-potential (2), limiting sedimentation vol-
ume (3), and light transparency (4), of the
refractory suspension on the content of alumin-
ium sulphate.
Fig. 2 Dependence of Z-potential (1,1), limiting sedi-
mentation volume (2,2), specific resistance (3) of
the hydrooxide suspension on the field voltage;
1,2,3 - for the initial suspension; 1, 2 - for the
suspension after washing.
Fig. 3 Dependence of the specific electrical conductivity
(1), Z-potential (2), limiting sedimentation vol-
ume (3) and light transparency (4) of the
refractory suspension on the field voltage and
aluminium sulphate at E=100v/cm (1,2,3).
Fig. 4 The technological scheme of the sludge concen-
tration with the usage of the electrical field.
1 - electrocoagulator
2- vacuumfilter
3- electrical dewatering machine
4- the source of constant current
— unstable suspension
— stable suspension
80
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DEWATERING OF SEWAGE SLUDGE BY MEANS OF CENTRIFUGES
Agranonick R.Ya.
Cand.Sc., Senior researcher Municipal Water Supply,
Water and Sewage Treatment Research Institute.
The method of sewage sludge dewatering by means of
the continuously operating centrifuge with dewatered
sludge scroll discharge has become rather popular lately.
The advantages of the sludge centrifugation method
compared to the conventional methods widely used in
this country, such as drying in beds or mechanical
dewatering in rotating vacuum filters are as follows:
The units are compact; mechanical dewatering can be
performed without addition of chemicals; dewatered
transportable sludge of low moisture content is pro-
duced under normal sanitary conditions.
The scroll discharge centrifuge is notable for its high
centrifugal force G, compactness, continuous initial
sludge supply and produce discharge and relatively low
energy consumption per 1 m3 of treated sludge.
The main scroll centrifuge performance parameters
are sludge dry residue detention efficiency, centrifuge
capacity and cake moisture content.
Table 1 illustrates centrifuge performance results
obtained on different types of sewage sludge; no
chemicals were added.
TABLE 1
Sludge dry residue detention efficiency and cake mois-
ture content with the sludge being dewatered by
centrifugation.
Type of sludge
raw or digested
primary
Dry residue
detention
efficiency ,%
45-65
cake
moisture
content,%
65-75
digested primary
and activated
sludge mixture 25-40
raw activated sludge
of the following
ash content
28-35% 10-15
38-42% 15-25
65-75
70-80
65-75
Actual value of sludge dry residue detention effi-
ciency was calculated by the following formula:
where:Coc,Ck and Cop are dry residue, cake .and
centrate concentrations, respectively.
Centrifuge performance parameters depend on the
bowl geometric size and centrifuge operating conditions:
the bowl speed, the discharge cylinder diameter and the
feed pipe position, and also on the initial sludge
properties, such as: the solid phase density and disper-
sion composition; bound water quantity; the liquid
phase viscosity and some other properties, the depend-
ence of separate parameters for different types of
sludges differing considerably. Thus the centrifuge ca-
pacity increase during raw sludge processing results in a
slight cake moisture content increase and vice versa in
humidity decrease in processing activated sludge.
The investigations of dispersion composition showed
that about 90% activated sludge solids are of 0,15 mm
size, whereas only 45% of such solids are contained in
raw sludge, therefore dry substance detention efficiency
is 30-40% higher than that of activated sludge.
Industrial effluent influx into municipal aeration
stations, sewage flow and composition fluctuation,
sewage treatment station arrangement and operating
conditions variations in separate units cause change in
sludge physicochernical properties and consequently in
the centrifuge performance efficiency.
Chemical conditioning and heat treatment promote
centrifuge performance efficiency increase. However,
preconditioning being very expensive, much attention
was given to centrifugation without chemical condition-
ing. In connection with high suspended solids loss with
centrate there were developed several technological
treatment schemes:
1) utilization of centrifugated excessive activated
sludge centrate as return sludge,
2) centrate discharge to the preliminary settling
tanks after raw and digested sludge centrifugation;
3) combined aerobic and anaerobic digestion of
centrate activated sludge mixture;
4) digested sludge centrate drying in beds.
Activated sludge centrifugation yields the greatest
amount of suspended solids in the resulting centrate.
Meanwhile the amount of dry residue after centrifuga-
tion exceeds that of the dry residue formed in the
activated sludge growth process in the course of sewage
treatment.
Hence, there has been offered a method by which
secondary activated sludge is centrifugated, intestinal
worms in the resulting cake are destroyed and the
centrate is used for biological sewage treatment instead
81
-------
f return activated sludge or in mixture with the
iatter.(2).
The method was laboratory tested in the models of
aero tanks; the centrate produced in the process of
secondary activated sludge centrifugation (the sludge
was taken from Lublino aeration station) was used in
one of the models, and in the other-return activated
sludge. The experiments were conducted on contact
basis and the models also worked as aerator-clarifler
units. Sludge concentration in the aerotanks was from
0,86 to 2,79 gr/1. Air consumption was measured by
means of rcometer and made up from 15 to 30 m3/m3
of sewage.
Comparison of return sludge and centrate sewage
treatment results indicated that centrate can be used for
sewage water treatment instead of return activated
sludge centrate. Sewage treatment quality is competitive
with that of return activated sludge sewage treatment.
At contact time from 1 to 24 hours BOD5 decreased to
73-5 mg/1. When sewage was centrate-treated, and to
65-5 mg/1. When return activated sludge was utilized.
In both cases the amount of suspended solids reduced
to 55-8 mg/1. Return activated sludge index fluctuated
from 65 to 118, and that of centrate-from 80 to 127.
The amount of pollutant, obtained in the aerotanks
where return activated sludge was used fluctuated from
46 to 172 mg.BOD5/g of sludge dry residue depending
on the initial BODS, aeration and sludge doze, and from
44 to 158 mg.BODs/g of sludge dry residue when
centrate was used. Since laboratory work is not suffi-
cient when testing aerotanks continuously utilizing
centrate as return activated sludge, the experiments were
conducted in 1,5-2 thou-sand m3/day treatment plants.
These experiments results are listed in table 2.
Aeration duration varied from 8 to 10 hours. Aera-
tion intensity was maintained continuously at
4,3m3/ma/hour. Activated sludge growth at '4-5 g/1
sludge concentration averaged 100 g/1 of sewage or 4.15
kg/hour. Centrifuge capacity being 4m3 /hour it caught
8.0 kg/hour of sludge dry residue on the average. It took
4 15 24
' '—= 12.4 hours/day of centrifugation to remove all
O.U
the surplus sludge from the system; only 11-13% of the
secondary activated sludge being fed to the centrifuge.
According to table 2, the results of the two compared
sewage treatment schemes were roughly equal. The
treated sewage BOD5 varied from 4.6 mg/1 in summer
time to 20.6 mg/1 in winter time, the suspended solids
amount fluctuating from 2.2 mg/1 to 25 mg/1, respec-
tively.
Thus centrifugation for the purpose of surplus acti-
vated sludge separation and centrate utilization for
sewage treatment did not deteriorate the treated sewage
quality as compared to the convenient scheme of
treatment.
Centrate addition to circulating sludge in aerotanks
results in the surplus activated sludge treatment scheme
simplification, since there is no more need in sludge
thickening, digesting and drying in beds. All the enumer-
ated operations are replaced by centrifugation of a
portion of taken directly from secondary clarifiers
activated sludge. This sludge amount is determined on
the basis of its growth and operating dose.
When primary sludges are centrifugated, the simplest
method of centrate treatment consists in its discharge to
preliminary settling tanks(3).
Centrate discharge to preliminary settling tanks re-
sults in the settled sewage SS concentration increase in
influent and clarified sewage and also in the increase of
the amount of sludge formed in clarifiers. SS concen-
tration in the influent sewage with continuous and
multiple centrate addition to the latter can be calculated
by the formula mentioned below, provided the settled
sewage concentration increases in proportion to the
initial sewage concentration increase:
, ..
l l-m(l-K)
Where: Cn - suspended solids concentration in sew-
age-centrate mixture,
Cj - SS concentration in influent sewage,
M - SS carrying out with centrate coefficient,
K - SS carrying out of clarifiers coefficient
In the cases when SS carrying out of preliminary
settling tanks increase is inadmissible, i.e. condition
KCn=const. preservation is indispensable, influent sew-
age plus centrate mixture concentration can be calcu-
lated by the following formula:
-r ^ C,-m (I-K)
-+——
Having substituted values Ci=ltK- 0,6
in formulae (2) and (3), we receive:
rn=0.525
Experiments in Usenko vessels showed, that settling
duration should not be prolonged for the first condition
realization, i.e. when K=const (fig. I). Nevertheless SS
amount in settled sewage increase by 15-30%, the latter
circumstance should be taken into account when digest-
ing in biological treatment units. Raw sludge centrate
82
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TABLE 2.
COMPARISON OF THE QUALITY OF SEWAGE TREATMENT IN FULL-SCALE
AEROTANKS BY MEANS OF RETURN ACTIVATED SLUDGE AND SLUDGE-CENTKATE MIXTURE
o>
CJ
period ot experiments
tarrying out
1'cbruary
March-April
May
Juno
influent sewage characteristics
BODS, mp/1
153-200
1 10-112
69-78
120
S. S. tng/1
148-150
65-166
39,-75
100
activated sludpe concentration in
aerotanks, my/l.
after convenient
scheme
4, 5-4. 6
4, 0-4, 2
4, 5-4, 8
4,8
after new seru-me
4, 5-4. 6
4, 2-4, S
4, 5-4, 6
5,0
characteristics of treated sewage in aerotanks
in the one operating after the
conventional scheme
BODs.mn/t.
10. S-20. 6
15,2-22,0
4,6-12,0
7
SS, mg/1
14,2-25,0
14, 2-17,0
2,4-5,2
6
in the one opera tint: after the new
scheme
BO i:>s, ing/ 1
10,8-19,4
15. 1-19,0
4,7-11,0
7
SS, mg/1.
13-18,8
13.4-15,0
2, 2-4, 8
4
-------
plus unthickened surplus activated sludge mineralized
mixture centrifugation is of considerable interest.
The centrate volume to surplus activated sludge
volume ratio corresponded to their real ratio in treat-
ment plants which equalled 1:10. Air consumption made
up 2-3 m3/m2/hour.
The mixture ash-free substance decomposition de-
pendence on aeration duration is shown in fig. 2.
Maximum ash-free substance composition in the
course of 8-10 days reached 35-40%. Extension of
aeration duration over 10 days did not cause any
considerable ash-free substance decomposition rise.
Mineralized mixed liquor taken from the aero tank-
stabilizer, settles better then initial sludge-centrate mix-
ture. The mineralized mixture dry substance detention
by centrifugation efficiency is 1.5-2 times more then
that of initial mixture dry substance detention.
Comparison of digested sludge and centrate drying
efficiency in the laboratory drying beds with an artificial
slag-sand foundation and in the half-size beds with
natural foundation and drainage showed, that in 12 days
of 6.5% concentration sludge drying, the sludge bed
thickness reduced from 35 to 24 and that of centrate
from 35 to 8, the dried centrate being of 10.9%
concentration and pasty, and the digested sludge • of
93% concentration and fluid:
During 3 summer months there were carried out two
digested sludge fillings and a 0.7 m bed was dried in one
half-size bed. During this very period in the other drying
bed four centrate fillings were realized and a 1.4 m bed
was dried.
By the end of this period the initial sludge drying bed
drainage was clogged up with sludge solids and prac-
tically did not function, whereas in the bed, designed for
centrate drying, the dried sludge cracked, which resulted
in subsequent satisfactory drainage functioning.
Sludge dry substance concentration decrease after
sludge centrifugation, and more rapid centrate thicken-
ing in drying beds indicate, that digested sludge prelimi-
nary centrifugation results in drying beds area reducing
by 2-3 times.
Chemicals pretreatment of sludge before centrifuga-
tion promotes centrate treatment schemes simplifica-
tion. High molecular cation flocculants are the most
efficient ones for this purpose; by means of some of
them 200-300 mg/1 SS containing centrate can be
produced; the latter does not need any special treat-
ment.
Chemical agents application in centrifugation and the
choice of centrate treatment scheme are determined by
techno-economical calculation.
CONCLUSION
Sewage sludge mechanical dewatering by means of
solid-bowl scroll centrifuges has a number of advantages
in comparison with other sludge treatment methods. The
method is particularly useful in low capacity - to 50000
m3/day plants; sludge dewatering without chemical
treatment is the principal advantage of the method.
There are worked out several schemes of centrate
treatment since large amounts of SS are carried out with
centrate.
The centrifuges design perfection and flocculants
application, simplifying centrate treatment schemes pro-
mote the sphere of centrifuges application expansion.
LITERATURE CITED
1. Turovsky, I. S., Agranonick, R. Ya. "Sewage sludge
centrifugation and centrate treatment schemes".
GOSINTI, OMT, 6/90-70, 1970.
2. Turovsky, I. S. "A method of sewage treatment".
Authorth certificate, USSR, 170418,1965.
3. Turovsky, I. S., Agranonick, R. Ya. "The centrifuga-
tion of sludge from municipal aeration stations
preliminary settling tanks", "Water supply and sewer-
aee design", Glavpromstroiproekt, 1969, series 2,55.
84
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THERMAL DRYING OF DEWATERED SEWAGE SLUDGE
Goldfarb, L. L.
Cand. Sc.
Municipal Water Supply
Water and Sewage Treatment
Research Institute
Mechanically dewatered sewage sludge large volume,
high moisture content and pollution with pathogenic
microorganisms and intestinal worms ova make it
necessary to process sludges.
Due to high organic substance content, sludges can be
utilized as fertilizers or fuel. In both cases therman
drying is the most expedient method of sludge treat-
ment. Thermally dried sludge presents a disinfected, dry,
loose, granulated or powdery produce, its weight and
volume being considerably reduced. Drying of mechani-
cally dewatered sludges presents a problem on account
of their pasty condition and high adhersion capacity.
To dry mechanically dewatered sludges continuous
convcctive dryers - rotating, belt, loop and pipedryers-
are used.
In most cases a 500-800° C furnade gas is used as a
drying agent. Dryed sludge presents a loose, powdery or
drainy substance with a moisture content of 540%.
Rotating dryers have relatively high capacity of a single
unit but low moisture removal (60 kg/m3/hour); the
latter circumstance causing the mits big sizes, and high
weight resulting in gross capital costs, and in the
extension of sludge thermal drying shops construction
terms. Rotating dryers are also characterized by large
fuel quantity consumption. Belt and loop dryers have
similar drawbacks, furthermore, they cannot be success-
fully automated.
Pneumatic pipe-dryers with mechanical drinders,
popular in the USA and some other countries, are the
most effective ones of the dryers employed abroad.
Their drawbacks are units big hight and the availability
of moving parts in the high temperature zone.
The analysis of the methods and apparatus used to
dry dewatered sludge and other pasty material indicate
that the creation of a special apparatus on the basis of
modem convective drying methods with regard for
sludges individual properties is expedient.
In recent years an all-round investigation of thermal
drying was carried out by the Municipal Water Supply,
Water and Sewage Treatment Research Institute of the
Academy of Municipal Economy. Sludge drying kinetics
was studied by meaks of laboratory hydrometer, used to
fix sewage mass variations in the process of convective
drying.
The results indicated that dewatered sludges have
similar drying rate curves.
Drying of sludges is going on at constant (1st period)
and stalling rate (the second period). In the second
period the drying rate stalls on a complex dependence,
drying rate curve including three sections: linear, convex
and concave. The obtained results analysis indicates that
the moisture in sewage sludiges, evaporated by means of
vacuum-filters or centrifuges, is mainly bound with
capillary and adsoption forces. Capillary moisture re-
moval in the second period (p.3) is accompanied by the
evaporation zone deepening, a dry thickening crust being
formed on the sludge surface.
The great bulk of moisture is removed from sludges in
the first period and in the bordering upon it linear
section of the second period.
According to the theory, rigid drying regimes appli-
cation in these sections is quite efficient, such regimes
securing high intensity of external heat-and massex-
chlange. To prevent sludge superheating and the thermal
decay of its organic substance of further heating it is
necessary to decrease the drying agent temperature and
rate, simultaneously increasing the sludge-heat-carrier
contact time, thus passing on to a milder drying regime.
A produssire counterjets method used to dry mechani-
cally dewatered sludges efficiently intensifies the
process. The process going on in counterjets, percussive
fusion of two oncoming axial-summetric jets of suspen-
sion of sludge in gas takes place. In the zone of jets
collision there arises solids oscillatory movement from
one jet to the other, thus increasing the material
concentration in the unit; besides the suspension of
sludge in gas is considerably turbulized. One of advan-
tages of the method is the utilization of gases high
velocity, limited only with the material granding condi-
tion and the boosting pipes walls wear, in the latter the
suspension of sludge in gas oncoming movement takes
place.
Due to the high gas velocity, the phases have
sufficiently high relative velocity; material transporta-
tion about the unit is improved and also the material
dispersion is provided.
To ensure the required variable drying regime there is
offered an original method, consisting in consecutive hot
85
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gases sludge handling in the counteijet regime and
airgushing by means of a portion of dried sludge return
for drying; the scheme securing the process intensifi-
cation by the material concentration increase, the
material temperature levelling up and the amelioration
of its feeding into the unit.
Besides a portion of the dried sludge return provides
the regulation of the produce humidity and granulo-
metric composition. According to the offered method
the mechanically dewatered sludge drying is carried out
in the counteijet dryers. Their principal elements are as
follows (fig 2): 1) a drying chamber, made of two
horizontal boosting pipes coaxially fit in the vertical
connecting pneumatic pipes; 2) centrifugal air-passing
separator. Combustors of aircraft gas-turbine motors
having worked off their flying life are used to produce
the drying agent. Natural gas or kerosene are utilized as
fuel.
For thermally dried sludge or mazut utilization there
are developed special chamber; sludge thermal drying
being carried out, fuel is required only for warming-up
and brightening of the unit.
The counteijet dryer operates in the following way.
The sludge is fed into the dryer through the receiving
ports of the boostng pipes (1). The 600-800° C fuel gas
halting the velocity of 100-400 m/sec is fed into the
dryer from the combusters (3) through the nozzles. (2).
The indicated velocity is provided by the compressed air
(0.11-0.15 MPa-Mega Paskal) feeding into the com-
busters. To provide the required temperature and com-
bustion of the gas, produced by fuel combusting, the air
is fed into the combusters at a quantity of 4-5 normal
m3/kg of die evaporated moisture. The humid sludge,
fed to the nozzles shears, is caught up and comminuted
with the hot gas and moved in the two oncoming jets.
When the streams are collided in the center of the dryer,
supplementary sludge dispersion and its intensive drying
take place. The sludge dried solids of inadequate
humidity and coarseness are returned to be dried again
through the pipe (7) after they are classified in the
separator (8).
The waste gas, having passed through the system of
suction and purification are released to the atmosphere.
The produce is transported from the separator to the
bunker (10).
The counteijet dryers are notable for a high volu-
mentrie stress on evaporated moisture, reaching
700-1000 kg/cm3/hour, and a low specific heat con-
sumption per proccss-3.4-3.8 M /kg of evaporated
moisture. The waste gas temperature does not exceed
100-150°C at the dried sludge moisture content of
30-45% and less.
The dryers are compact, simple to manufacture and
operate. The dryer is fully automated.
As a result of the investigation carried out in the
laboratory and full-scale counteijet dryers there was
offered a generalized method estimation of units for
different process regimes.
The main unit estimation parameters are its diameter
and the length of the active zone of the drying chamber
boosting pipes. The boosting pipes diameter is deter-
mined on the basis of the required dryer capacity
according to the estimated volume of gas and its
accepted velocity and is checked up by means of a
criterion heat exchange in oncoming jets equation,
formulated by the authors: Mn= 1.9 Re° •* 3
The boosting pipes active zone length is accepted to
be equal to the doubled value of the maximum solids
hardover into the oncoming jets and is calculated by the
empirical formula:
H*
By way of changing boosting pipes diameter and
length when utilizing the appropriate separator size,
chosen according to gas consumption, the dryers
capacity variation in a wide range can be produced.
Presently, the counterjet dryers are invisaged in a
number of municipal sewage treatment plants projects.
One such 150,000 m3/day unit has been operating at
Orekovo-Zuevo aeration station since 1973.
The drying unit is located at the sludge vacuum-filtra-
tion shop, taking up about 35 m2 area; the unit hight is
10 m. The unit dries up to 120 t/day of vacuum-filter
de watered raw sludge. Capacity to the evaporated
moisture equals 2.2-3.3 t/hour. In the process of drying
the sludge humidity reduces from 75-80% to 35-40%.
Fuel /natural gas/ and air consumption per 1 kg of
evaporated moisture equals 0.09-0.108 normal m3 and
3.7-5.0 normal m3, respectively.
The dried sludge presents a loose grandous product,
the size being predominantly 1,3 mm.
Due to the presence of nitrogen, phosphorus, cal-
cium, potassium, boron, cobalt, manganese, copper,
sodium, zink, etc, the dried sludge is successfully used as
an orcano-mineral fertilizer.
The counterjet dryer utilization instead of the rotat-
ing dryer at Orenoko-Zuevo aeration station resulted in
150,000 roub capital costs reducing, i.e. by 3-4 times;
operating costs reduced by 15%.
Counteijet dryers were also tested on different
industrial effluents. One such dryer has been tested at
Baikalsky cellulose plant; it was used to dry lignin
86
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sludge. The dried sludge was incinerated in the cyclone
furnace.
The counterjet dryer is expedient to be widely
utilized at treatment plants due to their high reliability
and simplicity, satisfactory operating figures and low
capital and operating costs.
The counterjet dryers are recommended to be used at
40000 to 1 000 000 m3/day aeration stations.
DESIGNATIONS
Nu - Nussilt criterion (heat exchanging)
Re - Rein old criterion
AT • principal sludge solids size
la - the active zone length,m
D - boosting pipes diameter.m
H - The distance between the boosting pipes open ends
S7 - volume density of the dried sludge particles, kg/m3
S - gas density at the mean temperature values in the
boosting pipes, kg/m3
CONCLUSION
Counterjet dryers are the most efficient and eco-
nomic apparatus for the thermal drying and dewatering
of mechanically dewatered sewage sludge. The dried
sludge is expedient to be utilized as organo-mineral
fertilizer.
87
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AEROBIC STABILIZATION OF ACTIVATED SLUDGE
by Abramov, A. V., AU-Union Scientific Research Institute VODGEO
Sludge treatment is one of the most labour-consum-
ing and expensive parts of the general waste water
purification system. Technological schemes of sludge
treatment are notable for being complicated and multi-
form. Stabilization of organic sludges is an important
link in the technological chain of their treatment, which
results, on the one hand, in the reduction of sludge mass
and, on the other hand, in creating satisfactory sanitary
conditions on subsequent stages of their treatment.
The aerobic stabilization process carries out in con-
ventional aeration tanks, hereafter they will be referred
to as stabilization tanks. Two main technological
schemes of the stabilization process - a conventional one
(scheme I) and a scheme with recycling involved (scheme
II) are shown in Fig. I.
Being an alternative to anaerobic stabilization, that is
to digestion, aerobic stabilization favourably differs
from it due to less capital costs it requires and due to its
simplicity and reliability in operation.
This paper reflects the results of investigations into
the main regularities of the excess activated sludge
aerobic stabilization. Degradation of biological mass of
activated sludge takes place as a result of stabilization.
Kinetics of degradation has been studied by many
authors. The results of their studies can be summarized
in the following basic points:
1. The whole organic matter of the activated sludge
can be relatively divided into two parts: an inert part, Si,
which remains unchangeable in the course of stabiliza-
tion and an active part, Sa, which is subjected to
degradation. Hence, the degradation value cannot exceed
a certain value A called degradation limit and defined
by the equation
35o*S/ Si
where So and Sag are respectively values of total
quantity of activated sludge and of the active part of
activated sludge biological mass at zero tune.
The degradation value Oj at time of t is defined
by the expression:
where St is the quantity of activated sludge biological
mass at time of t. It is apparent that at is always less
than A.
2. The active part degradation rate is described by
the first-order equation, where k is the degradation rate
constant:
The oxygen uptake rate in the stabilization process is
proportional to the biological mass degradation rate with
the stoichjometric coefficient of v :
,
v
dt
dt
where Gt is quantity of oxygen consumed by the
activated sludge by a period of time t.
G
Specific quantify of oxygen g =
i.e. the
quantity of oxygen needed for stabilization of a unit of
the activated sludge biological mass, is defined by the
equation:
From the engineering point of view the required time
of stabilization, t, and the specific oxygen uptake, g, are
obviously the basic design parameters.
With the structure of flow in view, the equation for
the required detention time may be derived on the basis
of Equations 1 - 3:
for a complete-mixing reactor + - _ — f . , —
for a plug-flow reactor
tnf =
for a multi-cell reactor
where n is the number of cells.
88
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It follows from Equations 6-8 that the value t is
defined in the first place by the values A and k, i.e. the
constants of the process, and in the second place by the
degradation value a^.
It is known from literature that A and k are not
considered strict constants, but depend on a number of
factors hereafter named variables, these dependences
being unknown for the most part. As for the value at, it
follows from Equations 7-9 that if a^ -»• A, then
t —» cx> . It is obvious, that we should choose a
minimum permissible value of at or, to put the other
way round, a stability criterion. At present the uniform
stability criterion is not available in the Soviet and
foreign practice.
Thus in order to obtain the needed calculation
equations for definition of values t and g it is necessary
firstly to find out functional dependences between
values A and k and the variables, and secondly to choose
the stability criterion.
The investigations were conducted in the bench-scale
installations, activated sludge involved was grown on
synthetic substrates. Real sludges of municipal and
industrial waste waters were also studied in the experi-
ment. In all tests the biological mass of activated sludge
was measured both as the organic matter of mixed liquor
(MLVSS) and as COD of mixed liquor, the former
defined as the losses during the incineration of mixed
liquor.
The regressive analysis determined that kinetics of the
biological mass degradation process expressed in mg/1 of
MLVSS and COD is adequately described by the
first-order equation. Hence, (see Equations 6-8) in order
to obtain the same value at the time needed for
stabilization in the plug-flow reactor will be much less
that in the complete-mixing reactor. The construction of
stabilization tanks being similar to that of the conven-
tional aeration tanks which are complete-mixing tanks in
case of a long period of aeration, their sectioning by
means of light cut-cross baffles provided with orifices is
considered to be necessary.
The investigations into kinetics of oxygen uptake in
the process of aerobic stabilization carried out by using a
dissolved oxygen analyser showed that the quantity of
oxygen consumed by activated sludge over a certain
period of time is equal to the COD reduction value over
the same period of time. Kinetics of the mixed liquor
COD reduction, as mentioned above, is described by the
equation of the first-order reaction. So we obtain a
simple and reliable method of experimental determina-
tion of oxygen quantity demanded for stabilization of
various kinds of activated sludges as well as any organic
sludges.
Composition of waste water, sludge age, temperature,
both sludge and disolved oxygen concentrations were
chosen as variables capable of affecting the values A and
k.
It was experimentally determined that neither sludge
concentration (within ranges investigated from 7,5 to 20
g/1) nor oxygen concentration (within ranges investi-
gated from 1,0 to 8.5 mg/1) affect the constants of the
process.
Experimental studies of the temperature effect upon
these values showed that within the investigated range
from 5 to 30°C the value A didn't depend upon the
temperature, the change of k is adequately described by
the well-known Phelps equation:
which is identical to the overwhelming majority of
chemical and biological processes.
Numerical value of the constant 9 for two investi-
gated types of sludges, i.e. for the activated sludge of
municipal waste waters and activated sludge grown on
synthetic subtrate, was identical and equal to 1.084. A
very close value of 8 obtained by P. Benedek
(Hungary) and equal to 1.080 gives us the reason for
considering the value 6 being practically identical for
all kinds of activated sludge.
In order to check the effect of sludge age upon values
A and k experiments were carried out with six activated
sludges of different age (from 3 to 37 days) grown on
synthetic substrates and real waste waters. The values A
and k were determined to have been reduced as the age
of the sludge increased, this relationship is adequately
described by fractional-linear functions of the type:
Ci
where C] • C4 are empiric coefficients,
T is sludge age, days.
Graphic forms of Equations 10-11, where the value S
is expressed in units of COD and MLVSS are shown in
Fig. 2.
As mentioned above, the uniform stability criterion is
not available in the world practice. That is why for
69
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approximate evaluation of stability we suggest that the
off-gas quantity evolved from aerobically stabilized
sludge during its anaerobic final digestion should be
compared with the quantity of off-gas evolved from the
municipal waste water sludge after digestion in digestion
tanks.
Digestion tanks of one of the Moscow aeration
stations were chosen standards. Tests for final digestion
of digested sludge samples taken from this station
showed that the specific gas evolution averaged 125
mg/1 of MLVSS, fed for final digestion. Thus we
assumed that the sludge can be considered stabilized if
its specific gas evolution value did not exceed 125 mg/1
of MLVSS fed for final digestion.
As experiments showed, the quantity of gas released
per unit of MLVSS degraded in the process of final
digestion averaged 848 mg/1 MLVSS and depended
neither upon the type of sludge nor upon the degree of
stabilization.
Having determined the gas release values of stabilized
and incoming sludges of 125 and 850 mg/1 respectively,
one may write down the following:
then
where 0 is the stability criterion showing the maxi-
mum permissible relation of the active organic matter to
the inert one in the stabilized sludge.
Now we can derive the calculation formula for
determination of basic parameters for the aerobic
stabilization process, that is for t and g.
Having put formulae 9, 10, 11 and 13 into Equation
7 we obtain:
where Tt • design temperature in the aeration tank, °C;
T2 is design temperature in the stabilization tank,
°C.
Graphic for equation 14 at design temperature in the
stabilization tank T2 = 20°C is presented in Fig. 3.
hi order to apply the formulae obtained for the ideal
plug-flow reactor to the recommended multi-cell reactor,
coeficient a was introduced. Then we obtain:
Joint solution of equations 7,8, 10 and 11 gives us
the following expression for the calculation of coeffi-
cient a
_ n
1 + 0.53*?
0,058'?:
The value a depends upon the number of cells n
and upon sludge age *£" . Sectioning of a single-cell
reactor (a mixing reactor) leads to the sharp reduction
of cC and therefore tmc, however the efficiency of
sectioning reduces as the number of n decreases. More
than 8 cells is not considered to be appropriate. At
n=8, cC is equal to 1.05-1.15.
On the basis of the previously proved equality
between the quantity of oxygen consumed and the
amount of COD removed one can derive the equation
for determination of g:
It is seen from formula 17, that g depends on sludge age
only. The graph of Equation 17 is presented in Fig. 4.
Being rather complicated formulae 14-17 are obvi-
ously not available for engineering calculations. Within
the sludge age ranged from 2 to 30 days they can be
substituted for more simple and approximate ones:
3.0+0.5^-0.2 n
0.960+0.
1+0-
For approximate calculations one can assume that at
the most wide-spread sludge age of 2-10 days the
stabilization time at calculated temperature in the
stabilization tank of 20° C is equal to 8-10 days.
90
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Increase or decrease in temperature by 10°C in its
turn decreases or increases stabilization time respectively
2.2 times.
Specific amount of air at the aeration tank depth of
5m and at diffused aeration with the incoming sludge
concentration of 30 g/1 will be of 460-670 m3 per m3
of the incoming mixed liquor, or at t=8 • 10 days it will
be 2.4 - 2.8 m3 per in3 of the stabilization tank volume
per hour.
It should be noted, however, that formulae 18 and 20
are valid only for the sludge grown on wastewater
containing negligibly small amount of suspended solids
as compared to the excess sludge amount. The above
stated results were obtained on such waste waters
exactly. Quantitative and quantitative composition of
suspended solids can effect on stabilization parameters,
this effect is impossible to be determined.
The above stated is valid also for the cases of
stabilization of raw sludge and secondary sludge mix-
ture. Therefore when waste water fed to aeration tanks
contains great amount of organic suspended solids or in
case of stabilization of primary and secondary sludge
mixture, it is preferably to determine stabilization
parameters experimentally. On the basis of investigations
carried out we suggest the following rather simple
procedure of experiment which does not take more than
a fortnight.
1. The process of stabilization of activated sludge or
primary and secondary sludge mixture is being carried
on under the contact conditions which are modeling the
process in the plug-flow reactor. MLVSS and COD of
mixed liquor are determined in the course of the
experiment.
2. Constants A and k, as well as Si and corresponding
3j are calculated from the obtained curves of the
biological mass concentration decrease (in units of
MLVSS and COD).
3. The value tpf is being determined by formula 7.
4. The value G being equal to the value of mixed
liquor COD reduction is determined either graphically or
analytically.
Application 1.
Fig. 1 Technological schemes of aerobic stabilization
process.
1. feed waste water
2. aeration unit
3. secondary settling tank
4. effluent
5. returned sludge
6. excess sludge
7. sludge thickener
8. supernatant
9. stabilization tank
10. stabilized sludge
1 1 . stabilized sludge recirculation.
Fig. 2 Relationship between A and k constants and
sludge age.
Fig. 3 Relationship between tpf and Cf and TI at T2
= 20°C.
Fig. 4 Relationship between g and sludge age.
91
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02
-------
THICKENING OF SLUDGES
RICHARD I. DICK
University of Delaware
Newark, Delaware
from Proceedings of the National Conference on Municipal Sludge Management, Pittsburgh, Pennsylvania,
June 11-13, 1974, Information Transfer Incorporated, Washington, D.C., 21-28 (1974).
ABSTRACT
The extent to which sludges are thickened has a
significant influence on the overall cost of sludge
treatment and disposal. Yet, rational approaches to the
design and operation of thickeners to accomplish an
optimal degree of thickening have not traditionally been
implemented. The purposes of this paper are to review
basic thickening concepts and to illustrate that appre-
ciable cost savings may be realized by avoiding the use of
conventional, arbitrary, design loadings for thickeners.
Instead, thickeners should be designed to achieve a
degree of sludge concentration which, in concert with
other sludge treatment processes, minimizes overall
sludge treatment and disposal costs.
INTRODUCTION
Thickening inevitably is involved in all schemes for
treatment and disposal of sludges. Often, separate
thickeners are used to reduce the volume of sludge
contributed by wastewater treatment processes prior to
subsequent sludge treatment and disposal. However,
even if a separate thickener is not provided, thickening is
still involved in sludge treatment and disposal schemes.
This is because facilities which separate solids from the
wastewater treatment process and divert them to sludge
handling and disposal facilities normally involve use of
sedimentation basins. Such basins serve to clarify waste-
water prior to discharge and, indeed, frequently bear the
name "clarifier." In addition to accomplishing clarifica-
tion, these sedimentation basins also are expected to
concentrate or "thicken" the solids separated from the
wastewater. The concepts of thickening discussed in this
paper relate as much to the thickening function of
sedimentation basins as to thickening occurring in
separate sludge thickeners. In either case, clarification
also is going on and must be considered in the design.
In spite of the frequent use of separate thickeners in
sludge treatment and disposal schemes, as well as the
more common occurrence of thickening within sedimen-
tation basins, the design and operation of such facilities
has not usually been accomplished on a rational basis.
Thickeners ordinarily have been designed using arbitrary
design standards with a little consideration being given
to the performance which should be anticipated or to
the possible benefits of constructing a thickener of
different size. Also, in design, the interaction of thick-
eners with other treatment and disposal processes has
not been rationally evaluated. Yet, because the perform-
ance of thickeners influences the performance of other
processes, some optimal degree of thickening must be
appropriate for each particular sludge and sludge treat-
ment and disposal scheme. Similarly, those charged with
the operation of thickeners usually have not explored,
on a rational basis, the manner in which their facilities
should be operated to make optimal use of the installed
thickener capacity.
The technology for making rational assessments in
the design and operation of thickeners would seem to be
available. The purpose of this paper is to review those
concepts and to show their utility in design and
operation of wastewater treatment facilities. To do this,
thickening theory will be briefly reviewed, the inter-
actions of thickening with other sludge treatment and
disposal processes will be discussed, and the economic
implications of these interactions will be illustrated.
The Rational Analysis of
Thickener Performance
Rational bases for design of thickeners and for
analyzing the performance of existing thickeners have
been presented3 and reviewed2'4 elsewhere and the
concepts will only be capsulized here. The following
discussion is oriented to gravity thickeners, but is
applicable to flotation thickeners by substituting the
rate for the settling velocity and reversing the direction
of the movement of tank content due to sludge removal.
The basic concept in thickener design is to provide
sufficient area so that the solids loading per unit area per
unit time (the applied flux, ordinarily expressed as
Ib/sq ft/day) does not exceed the rate at which solids
can reach the bottom of the gravity thickener (or top of
the flotation thickener). The rate at which solids can
reach the bottom of a thickener depends on the rate at
93
-------
which they settle under the influence of gravity and the
rate at which they are transported through the thickener
due to removal of thickened sludge. That is
Gi -
(i)
where G/ is the possible flux of solids through a layer of
concentration cf v{ is the gravity settling velocity of the
sludge solids at concentration c/; and u is the bulk
downward velocity in the thickener produced by the
removal of sludge from the bottom of the tank.
Equation 1 is an expression of the possible rate of solids
transport per unit area for any concentration in a
continuous thickener (one from which thickened sludge
is continuously withdrawn). Batch thickeners are a
special case in which the cju term in Equation 1 is zero.
It should be noted that the cj\>i term in Equation 1
depends only on the physical properties on the sludge
and is not susceptible to control by the designer or
operator of the thickener unless physical, biological, or
chemical alteration of sludge solids (as by use of a
polyelectrolyte) is practiced. In contrast, the magnitude
of the cju term in the equation depends on the rate at
which thickened sludge is removed from the bottom of
the tank, and is therefore susceptible to control by he
thickener designer and operator.
For optimal performance of a thickener, sludge
removal equipment must be designed to uniformly
collect thickened sludge from the bottom of the tank so
that
U =
(2)
where Qu is the volumetric rate of removal of thickened
sludge from a continuous thickener of area A. Thus, it is
seen that the capacity of a thickener for receiving sludge
solids can be increased by increasing the rate of removal
of thickened sludge. While this may be a desirable course
of action for an overloaded thickener, it conflicts with
the basic goal of thickening-the production of a
concentrated thickening underflow. This is because
Qti = oFQF/cii
(3)
and it is desired to maximize the underflow concentra-
tion, cu. Equation 3 was obtained from a mass balance
on a thickener receiving feed sludge at a volumetric flow
rate, Qf, with a suspended solids concentration, cf,
assuming that the clarified effluent from the thickener
was essnetially free of suspended solids.
If the relationship between settling velocity, v/, and
concentration, c/, is known (see Reference 2 for proce-
dures and difficulties in determining the settleability of
sludges), and if a value of u is selected, then the value of
the batch flux and underflow flux in Equation 1 can be
determined for each possible concentration of sludge
which might exist in a thickener.
Figure 1 illustrates the variation of these two terms in
Equation 1 with suspended solids concentration and
shows the resulting total flux, Gj, possible for each
concentration of sludge which might exist in a thickener.
It is seen that, in the higher range of concentrations
which typically exist in thickeners the value of G/ passes
through a minimum. It is this limiting capacity for
transmitting solids to the bottom of a thickener, GI,
which limits the capacity of thickeners. Thus, one must
ascertain that solids are not applied at a rate greater than
A - CFQF/GL
(4)
It should be noted that, because u, the underflow
velocity, is controlled by the designer or operator of a
thickener, the value of GI is controllable. Thus, for a
thickener receiving a given solids load (cfQf), the value
of GI in Equation 4 can be varied to give any desired
thickener area. However, from Equation 1, it can be seen
that if a high value of GI is selected, a high value of u,
the underflow velocity, must also be used. From
Equations 2 and 3, it is seen that the use of a high
underflow velocity would result in the removal of dilute
sludge from the thickener. When a new thickener is
being designed, area, and thus underflow velocity, are
unknown. Thus, the solution outlined above becomes a
laborious trial and error situation. This difficulty can be
circumvented by use of a graphical solution2. This
simplified procedure is highly recommended for design
and routine analysis of the performance of existing
thickeners.
Interaction of Thickening with
Other Sludge Treatment and
Disposal Processes
To illustrate the influence of gravity thickening of the
economics of sludge treatment and disposal, the cost of
thickening a typical municipal sludge to various con-
centrations was compared with the savings resulting
from the improved thickening in the cost of various
sludge treatment techniques. To illustrate the effect of
the size of the waste treatment facility on the economics
of thickening, calculations were conducted for cities of
10,000, 100,000, and 1,000,000 people.
94
-------
TOTAL
FLUX
TRANSPORT
DUE TO
SEDIMENTATION
TRANSPORT
DUE TO
SLUDGE REMOVAL
G:
o"
Figure 1: Determination of Allowable Loading on a Thickener.
Sludge Quantities
The following equation was developed to estimate the
quantities of sludge to be treated by the various sized
cities:
Production
of
Sludge
suspended solids
removed in
primary clarifier
nonbiodegradable volatile
solids in raw waste which
become incorporated in
activated sludge
nonvolatile suspended
solids carried into
activated sludge process
synthesis of
activated sludge
solids
any organic precipitates
formed during biological
treatment
autooxidation of
biological
solids
suspended solids
lost in
effluent
This equation may be written as
Cp-b tf'PBOo)°BOD
/ ---- ~
The meaning of symbols in
below along with dimensions.
(5)
Equation 5 is indicated
95
amount of biological synthesis per unit of
BOD removed, M suspended solids/M BOD
(0.5).
fraction of mixed liquor volatile suspended
solids which are autooxidized daily, dimen-
sionless, (0.12).
Environmental Fraction Agency
Lfbrary Reom ^.
'.reet, SW, WSM Pfvl-213
, D.C,
S'.
-------
CBOD = concentration of BOD in raw waste, M/L3,
(178mg/l).
cp = concentration of inorganic precipitants
formed during biological treatment, M/L3,
(Omg/1).
cse = concentration of suspended solids in effluent
from treatment plant, M/L3, (15 mg/1).
ess = concentration of suspended solids in raw
waste, M/L3,(205 mg/1).
f = fraction of volatile suspended solids entering
aeration tank which are not biologically oxi-
dized, dimensionless, (0.3S).
h = fraction of suspended solids entering aeration
tank which are volatile, dimensionless, (0.75).
L = organic loading intensity in activated sludge
process, M BOD removed/M volatile sus-
pended solids in aeration tank, (0.4).
rofiOD = fraction of BOD entering the secondary
process which is removed (based ort filtered
effluent sample), dimensionless, (0.90).
PBOD = fraction of BOD removed in primary settling
tank, dimensionless, (0.33).
PSS = fraction of suspended solids removed in pri-
mary settling tank, dimensionless, (0.6).
Q = wastewater flow rate, L3/T, (at 135 gpcd).
S = daily production of waste sludge solids, M/T.
Equation 5 is a modification of Eckenfelder's Equa-
tion 11.3* with the addition of terms to account for
primary sludge, any organic solids precipitated in the
biological reactor9, incorporation of non-volatile solids
contained in the raw waste into activated sludge, and the
loss of solids over the final sedimentation tank weir.
Values of the various constants as assumed for purposes
of this illustration are indicated in parentheses in the
preceding list. All of these values are subject to variation
from waste to waste and none are necessarily applicable
to any particular plant. In the absence of information on
the amount of inorganic precipitants formed during
biological treatment, this contribution toward sludge
production was ignored. A waste flow rate of 135 gpcd,
a per capita suspended solids loading of 0.23 Ib/day, and
a per capita BOD contribution of 0.2 Ib/day were
assumed based on data presented by Loehr7. No
allowance was made for the probable variation in quality
and quantity of waste as a function of the size of the
municipality.
Based on the assumed values, sludge production per
million gallons of wastewater flow would be 1,425
Ib/day of which 1,020 Ib/day would be primary sludge,
and 405 Ib/day would be waste secondary solids. The
magnitude of this sludge production is perhaps on the
low side of reported experience.
Cost of Gravity Thickening of Sludges
To obtain an indication of current probable costs of
thickening and to achieve a basis for illustrating the
interaction of thickeners with other processes of sludge
handling and disposal, estimates were developed for the
cost of thickening sludge to various degrees in munici-
palities of various sizes. This was done by assuming
sludge settling properties (settling velocity as a function
of concentration), determining the allowable loading on
a thickener to concentrate the sludge to varying degrees,
sizing the thickener, and estimating the cost of construc-
tion and operation of the thickener of the necessary size.
REQUIRED THICKENER SIZE. As described in an
earlier section, the required size of a thickener is a
function of the extent to which it is desired to
concentrate sludge and of the settling characteristic of
the sludge being thickened. In this illustration, the
settling properties of a combined primary-secondary
sludge were assumed and expressed in the form of an
equation used by Dick and Young5
(6)
where vf is the settling velocity of sludge at con-
centration Cj and a and n are constants characterizing the
properties of the particular sludge being considered. For
purposes of this illustration, a was taken as 0*045 ft/min,
and n as 2.57, when v,- is expressed in ft/min and c,- in
percent.
The allowable solids loading (the limiting flux) for
achieving various degrees of concentration of the sludge
were calculated and are shown in Figure 2 along with the
resulting required total thickener area for a city of
100,000. Because no differences in sludge production
between cities of various sizes was considered, the
required thickener areas for achieving various degrees of
sludge concentration for cities of 1,000,000 and 10,000
are on an order of magnitude more or less than the
values shown in Figure 2.
THICKENER COSTS. In addition to requiring an
understanding of factors affecting process performance,
optimal integration of sludge treatment processes re-
quires information on the cost of treatment by various
techniques as a function of the level of process perform-
ance. Unfortunately, rational selection, design, and
operation of sludge treatment processes is hampered by
a dearth of such cost information. In the case of gravity
thickening, such data are in particularly short supply.
This is, perhaps, because thickening normally is the
cheapest step in sludge treatment and disposal and, thus,
thickening costs often tend to be lumped into the cost
96
-------
30
20
«n
9
e
z
z
10
4000
3000
- 20OO
o
UJ
K
3
O
- 1000
2 4 6 6
SLUDGE CONCENTRATION. PERCENT
10
Figure 2: Required Size of Thickeners for Concentrating
Hypothetical Sludge to Varying Degrees in City of .100,000
People.
of other sludge processing techniques. Additionally,
sludges vary widely in their thickening characteristics,
and unit costs for thickening would be expected to vary
accordingly. As with all current cost estimations, infla-
tion also imposes complications. In Burd's review1 of
the state of the art in sludge handling and disposal, it
was generalized that separate sludge thickening costs
from two to five dollars per ton of dry solids. Smith1 3
presented equations for the cost of construction of
gravity thickeners as a function of area. In neither case
was the thickening cost related to the degree of sludge
concentration achieved. That was accomplished here by
estimating the cost of the thickeners sized (Figure 2) to
give various degrees of sludge concentration.
Capital costs for thickeners of various sizes were
obtained by adjusting cost data presented by Smith13 to
April, 1974 on the basis of the Engineering News Record
Construction Cost Index (the April, 1974 value being
1940) and then increasing the cost by 25 percent to
account for contractor's profit, contingencies, and engi-
neering. The resulting capital cost equation was
(7)
Extensive data on the operation and maintenance of
gravity thickeners as a function of their area were not
available. In the absence of such information, costs
reported by Smith13 on operation and maintenance
costs for primary clarifiers as a function of their area
were used. It was reasoned that the equipment and
operational requirements were similar to separate thick-
eners. Arbitrarily, Smith's operational and maintenance
costs were adjusted by use of the Engineering News
Record Construction Cost Index to make some allow-
ance for changes in costs of labor and materials since his
work was published. The resulting equation for an
annual operating and maintenance costs as a function of
thickener area was
(8)
To obtain an overall cost of thickening to various
degrees, annual costs (operation and maintenance plus
amortization of capital costs) were calculated. Then, as
shown on Figure 3, costs of thickening to various
degrees for various sizes of municipalities could be
expressed on the basis of total cost per unit of sludge
production. For this purpose, the approximate current
interest rate on Grade A municipal bonds (6V4 percent)
was used with a 20-yr amortization period.
Thickening and Dewatering of Raw Sludge
The yield of sludge dewatering devices is increased
when water is removed from sludge (as by gravity
thickening) prior to being fed to the dewatering device.
This is because less water must then be passed through
the somewhat impermeable sludge cake in the course of
dewatering than would be necessary if the excess water
was not removed previously by thickening. Additionally,
the degree to which sludge can be mechanically de-
watered increases when concentrated sludge is fed to the
dewatering equipment8
To illustrate the optimal integration of thickening
and dewatering processes, the cost of sludge dewatering
by vacuum filtration was considered. Then, the total
cost of the combination of the thickening and dewater-
ing processes could be evaluated to determine the proper
design for each of the two processes.
The effect of feed sludge concentration of filter yield
was taken from data presented by Schepman and
Cornell12 which indicated that
(9)
97
-------
024 6 8 10
THICKENED SLUDGE CONCENTRATION. PERCENT
Figure 3: Costs of Thickening Hypothetical Sludge to Varying
Degrees.
where Y is the filter yield in Ib dry solids/hr/sq ft, and
cu is the concentration of sludge in the thickener
underflow. Extrapolation of the Schepman and Cornell
data was necessary to include the range of interests here,
but the extrapolated data agreed closely with informa-
tion on relationship between feed solids concentration
and filter yield presented in Quirk1 °.
Capital costs for vacuum filters were taken from
information presented by Smith13. As with the capital
costs for thickeners, Smith's estimates were adjusted to
the April, 1974 Engineering News Record Construction
Cost Index of 1940 and then 25 percent was added for
contractors profit, contingencies, and engineering. Capi-
tal costs were amortized at 6.5 percent for 20 yr. Costs
for labor, power, and maintenance were taken from
estimates prepared by Quirk10 and, arbitrarily, were
adjusted to current costs by use of the Engineering News
Record Construction Cost Index. Chemical costs for
sludge conditioning were taken as $12/ton of dry solids
and were not considered to vary with the size of the city
or the extent to which the sludge was thickened.
Resulting total costs for thickening and dewatering
are shown in Figure 4. The contribution of thickening
and vacuum filtration (including conditioning) to the
total cost is illustrated for the city of 1,000,000. Total
costs curves are shown for all three cities. The relative
contribution for thickening and dewatering to the total
cost for cities of 10,000 and 100,000 people can be
obtained by comparing Figures 3 and 4.
It is seen from Figure 4 that the optimal degree to
which the sludge considered here should be thickened
for this city of 10,000 people of about 8 percent. For
the two larger cities, a total cost became relatively
insensitive to the degree of thickening at a concentration
of around 8 percent, but a true optimum was not
reached within the range of concentrations considered.
While the thickening costs involved in reaching these
high concentrations are in excess of the costs normally
considered for thickening, results would suggest that,
with this sludge and thess estimates of capital and
operating costs, more money should be spent for
thickening than is normal practice. However, because
sludge properties vary from plant to plant, the more
important point is that great savings in the combined
cost of thickening and dewatering is possible by use of a
rational approach to design of sludge treatment systems.
120
too
o
o
o
o
o
o
o
o
TOTAL- CITY
OF 10.000
TOTAL- CITY
OF IOO.OOO
TOTAL - CITY
OF I.OOO.OOO
VACUUM FILTRATION
CITY OF 1.000,000
THICKENING-CITY
OF 1.000.000
0 2 4 6 8 10
THICKENED SLUDGE CONCENTRATION. PERCENT
Figure 4: Optimal Integration of Thickening and Dewatering.
98
-------
Overall Costs of Thickening and
Transporting Sludge by Truck
To illustrate the effect of thickening on another
phase of sludge handling, overall costs of thickening and
subsequent trucking were evaluated for thickeners de-
signed to achieve varying degrees of sludge concentra-
tion. For this purpose, trucking costs were taken from
estimates prepared by Riddell and Cormack11 for
trucking sludge a distance of 25 miles. Riddell and
Cormack's data (which were developed for sludge at 3.5
percent concentration) were adjusted to evaluate the
cost of transporting different volumes of sludge contain-
ing the same total amount of dry solids. Figures then
were adjusted for inflated labor and materials costs by
use of the Engineering News Record Construction Cost
Index.
Total overall costs for thickening and transporting
sludge 25 miles by truck for various sized cities are
illustrated in Figure 5. Again, the breakdown of costs is
shown only for the city of 1,000,000 people, but the
relative contributions of trucking and thickening for the
cities of 100,000 and 10,000 people can be obtained by
comparing Figures 3 and 5. As before, a true optimum
was not achieved within the range of sludge concentra-
tions considered. That is, even though sludge thickening
became far more expensive than usual, the incremental
cost was justified by the reduction in the cost of
transporting the sludge.
SUMMARY AND CONCLUSIONS
Thickening is involved in all schemes of sludge
treatment and disposal. If a separate gravity or flotation
thickener is not used, then thickening still is involved
because it occurs in the sedimentation tanks which
produce the sludge. Thickening has a great influence on
the cost of sludge treatment and disposal because the
cost effectiveness of sludge treatment and disposal
techniques depends on the concentration of solids in the
sludge.
Traditionally, thickeners have been sized in an arbi-
trary fashion without regard to the thickening properties
of the sludge being treated or to the degree of thickening
desired. Yet the size of a thickener does effect the
amount of thickening achieved and this effect can be
estimated if the settling characteristics of the sludge are
known. This allows thickeners to be designed and
operated to achieve any desired degree of sludge
concentration. The degree to which sludge should be
concentrated in a thickener depends on factors such as
the nature of the sludge, the size of the community, and
120
TRUCKING -
CITY OF
I.OOO.OOO
THICKENING-CITY
OF 1.000.000
0 24 6 8 O
THICKENED SLUDGE CONCENTRATION. PERCENT
Figure 5: Optimal Integration of Thickening jnJ Tim kin*
the types of other sludge treatment and disposal
processes involved in the system.
The effect of designing thickeners to accomplish
varying degrees of solids concentration on sludge treat-
ment and disposal costs are illustrated herein. Integrat-
ion of the design of thickeners with the design of other
processes offers significant potential for reducing costs.
While this approach to the design of sludge treatment
and disposal facilities requires appreciably more informa-
tion about sludge treatability than normally is available,
the results suggest that the potential cost savings warrant
the cost of conducting the special studies required.
ACKNOWLEDGMENTS
This work was supported in part by funds provided
by the United States Department of the Interior as
authorized under the Water Resources Research Act of
1964, Public Law 88-379.
REFERENCES
1. Burd, R. S. "A Study of Sludge Handling and
Disposal," Water Pollution Control Research Series,
Federal Water Pollution Control Administration, Publi-
cation WP-20-4, Washington, D.C., (1968).
2. Dick, R. I. "Thickening," Advances in Water
Quality Improvement-Physical and Chemical Processes,
99
-------
E. F. Gloyna and W. W. Eckenfelder, Jr., Editors,
University of Texas Press, Austin, Texas, 358-369
(1970).
3. Dick, R. I. "Role of Activated Sludge Final
Settling Tanks," Journal Sanitary Engineering Division
American Society of Civil Engineeers, 96, SA 2,423-436
(1970).
4. Dick, R. I. "Gravity Thickening of Waste
Sludges," Proceedings of the Filtration Society, Filtra-
tion and Separation, 9, 2,177-183 (1972).
5. Dick, R. I. and Young, K. W. "Analysis of
Thickening Performance of Final Settling Tanks," Pro-
ceedings of the 27th Industrial Waste Conference,
Purdue University, Extension Series, (1972).
6. Eckenfelder, W. W., Jr. "Industrial Water Pollution
Control," McGraw-Hill Book Company, New York, 275
PP,(1966).
7. Loehr, R. C. "Variation of Wastewater Quality
Parameters," Public Works, 99, 5, 81-83, (1968).
8. McCarty, P, L. "Sludge Concentration—Needs,
Accomplishments, and Future Goals," Journal Water
Pollution Control Federation, 38, 4,492-507, (1966).
9. Menar, A. B. and Jenkins, D. "Fate of Phosphorus
in Waste Treatment Processes: Enhanced Removal of
Phosphate by Activated Sludge,n Environmental Science
and Technology, 4, 1115 (1970).
10. Quirk, T. P. "Application of Computerized Anal-
ysis to Comparative Costs of Sludge Dewatering by
Vacuum Filter and Centrifuge "Proceedings 23rd Indus-
trial Waste Conference, Purdue University Engineering
Extension Series No. 132, Part 2, 691, (1969).
11. Riddell, M. D. R. and Cormack, J. W. "Selection
of Disposal Methods for Wastewater Treatment Plants,"
Proceedings of Conference on Waste Disposal from
Water and Wastewater Treatment Processes, University
of Illinois, Urbana, Illinois, 125-130, (1968).
12. Shepman, B. A. and Cornell, C. F. "Fundamental
Operating Variable in Sewage Sludge Filtration," Sewage
and Industrial Waste, 28, 12,1443, (1956).
13. Smith, R. "Preliminary Design and Simulation of
Conventional Wastewater Renovation Systems Using the
Digital Computer, Federal Water Pollution Control
Administration, Water Pollution Control Research
Series, WP-20-9,( 1968).
100
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DISSOLVED AIR FLOTATION THICKENING
AS PRACTICED IN THE U.S.
By
William N.Konrad
Director-Market Development
Envirex Inc.
A Rexnord Company
Waukesha, Wisconsin, U.S A.
101
-------
DISSOLVED AIR FLOTATION THICKENING1
AS PRACTICED IN THE U.S.
By
William N. Konrad2
One of the most essential requirements in the disposal
of solids from wastewater treatment plants is that of
thickening or reducing the water content of sludge in
order to insure the effectiveness of subsequent disposal
processes. The utilization of thickening by gravity
sedimentation is well known, quite well documented,
and has been employed successfully in this field.
However, since the early 1950's, and since the increased
usage of the activated sludge process, where larger
volumes of sludges are generated, the application of
dissolved air flotation for thickening has increased in the
United States. Today, a large majority of the designers
requiring thickening of biological sludges utilize dis-
solved air flotation as an integral part of their sludge
handling process, since dissolved air flotation has not
only demonstrated its ability to reduce the hydraulic
loading on subsequent units, it has also allowed an
increade in applied solids loadings in these processes.
Figure No. 1 illustrates where flotation thickening is
used in the various sludge handling schemes employed
by municipal wastewater treatment plants.
Generally, dissolved air flotation is not applied on
primary sludge alone;however, there have been instances
where designs are based on sludge mixtures where
occasionally primary sludge alone has been thickened.
The primary reason for not using dissolved air flotation
on primary solids is that it is generally possible to obtain
the necessary concentration in the sedimentation basin.
Also, when thickening of primary sludge is required, the
use of a gravity thickening device will be the most
economical to achieve the desired results.
This figure essentially shows the application of
dissolved air flotation thickening on secondary sludges,
either humus sludge or activated sludge, and with or
without the addition of primary sludge.
It should be noted that dissolved air flotation has
been applied on aerobically digested sludge, but it has
been used very selectively. In a number of pilot plant
operations, results obtained have been poor and erratic.
One successful installation utilizing this process has
demonstrated that it can achieve a 4% sludge concentra-
1 Paper presented at United States-Soviet Seminar on "Han-
dling, Treatment, and disposal of sludges," Moscow, Russia-May
12-27,1975.
Director-Market Development, Envirex Inc., A Rexnord
Company, Waukesha, Wisconsin, UJSA.
tion at a solids loading of 20#/sq. ft-day (97.65 kg./sq.
meter-day) without the use of chemical aids. This is one
area that requires further research before general usage
can be claimed.
Concentrating humus alone has not found general
application since trickling filters are generally used in
small municipalities. It has been shown to be uneconom-
ical to use flotation thickening where a small amount of
sludge is generated. In larger plants employing trickling
filters, we find that the humus sludge is handled with the
primary sludge and should an activated sludge plant also
be located on the same site, the humus sludge will be
handled with the activated sludge. For purposes of
design, we have assumed that humus sludge does behave
like activated sludge. The applied load generally is not
very great and permits a conservative approach.
One increasing area in the application of dissolved air
flotation is that preceding anareobic digestion, which,
incidentally, is also increasing in use in the United
States. In Addition to Better utilization of digestion
volume through water reduction, the dissolved air
flotation thickener has demonstrated effective separa-
tion of grit from the sludge flow. One installation which
we are familiar with, which concentrates mixtures of
primary and activated sludge, has removed over a cubic
yard (3/4 cu. meter) of grit from 12,000 Ibs. (5450 kg.)
of primary sludge each day. Being able to do better
degritting prior to digestion decreases maintenance costs
and provides additional volume for digestion.
This figure also shows thickening before vacuum
filtration or centrifugation. One area of caution is where
dissolved air flotation is utilized with checicals. We have
experienced cases when the chemical used in dissolved
air flotation process acted antagonistically with the
vacuum filter performance.
The design criteria for dissolved air flotation thicken-
ing is shown in Figure 2. Design surface loading rates as
well as the expected thickened concentration of the
sludge are illustrated. (Normally a 4% concentration is
an optimum desirable design concentration.) This data
reflects the situation where chemicals are not used to aid
the thickening process. When chemicals are used, they
are generally applied when activated sludge alone is
thickened. In these cases the surface loading rates can be
increased by three to six times that shown in Figure 2,
with essentially the same thickened sludge concentration
102
-------
resulting. Also when chemicals are used, approximately
three to ten Ibs. (1.35 to 4.5 kg.) of polyelectrolytes are
required per ton (907 kg.) of sludge thickened. There
have been cases where the sludge was very difficult to
concentrate and requirements as high as 20 Ibs./ton (9
kg./907 kg.) of polyelectrolytes have been reported.
The subnatant, which is relatively clear underflow,
will contain about 15% of the solids that were fed to the
unit when no chemicals are used. When a polyelectrolyte
is used, the subnatant will be clearer and underflow
concentrations of less than 5% can be expected. The
subnatant in either case is usually returned to the
aeration tank.
When selecting the size of the dissolved air flotation
thickener and whether to use or not use chemicals, the
designer has several options. The use of checicals allows
for the size of the flotation unit to be smaller, but the
operating and maintenance costs will be greater. A
number of designers have used a conservative approach
in loading, which increases the size of basins but
provides a lower operating cost. Others use the conserva-
tive approach and make provisions for the later addition
of chemical feed equipment as anticipated solids loads
increase; while others use the conservative approach but
install the chemical feed equipment initially. In these
cases, the chemicals may be added initially in very small
amounts to improve the subnatant. Where mixtures of
primary and activated sludge are thickened, the loadings
are generally those shown in Figure 2, and the chemical
usage relegated to cleaning up the subnatant and not to
increase the applied loadings.
To assist in finalizing a Design, and when sludge is
available, it is common practice to use a pilot dissolved
air flotation unit to obtain accurate design data. Figure
No. 3 is a picture of such a unit. If a unit such as this
cannot be used, a bench scale test procedure has been
developed for predicting the loading rates and the
resultant thickened sludge concentration. The apparatus
used for this test is shown in Figure No. 4. It is beyond
the scope of this text to describe the test details and
method of correlation. However, over the last 15 years, a
correlation between the sludge concentration developed
in the bench test to that of a full scale unit has been
established with a high degree of confidence.
DESIGN PARAMETERS OF THE UNIT PROCESS
In the unit process for dissolved air flotation there are
several parameters of design which must be considered.
Some of these parameters are spacing and speed of
flights which remove the surface thickened sludge,
frequency of removal, tank configuration, source of
pressurized flow and the air to solids ratio (A/S ratio).
Experience over a number of years has dictated that
the spacing of flights and speed of skimmer be such that
intermittent operation be employed to obtain the
optimum in concentration of sludge removal. We have
found optimum spacing to be approximately three feet
(1 meter), a variable speed of 2 to 8 feet/min. (0.61 to
2.44 meters/min.), and intermittent operation with the
timing dependent on tank length, mass loading and
desired concentration. Generally this will be between 10
and 25 percent of the time. We also recommend scraping
away from the influent end of the tank. Side-by-side
tests of duplicate units with only the direction of
skimming changed yielded superior results with the
skimming in the direction of flow. The reason is that
removal is at a point of minimum eddirs and maximum
sludge blanket thickness.
The tank configuration found to be most successful
in obtaining optimum concentration is rectangular.
Length to width ratios of three to five to one are
generally recommended to allow optimum concentra-
tions in the sludge blanket and (to balance removal
capacity. Tank depths include a sludge concentration
time, a flow-through zone, and a depth below this zone
to accommodate bottom sludge or grit removal equip-
ment. Some designers have attempted to use hydraulic
overflow rates in the design of thickeners, but overflow
rates are meaningless since the overriding criterion in
establishing the area of the thickener is the applied mass
loading.
The source of pressurized flow is also a consideration
of the Designer. There are three options available: One is
the effluent from the thickener itself; the second is the
utilization of plant effluent; and the third is the
utilization of screened primary tank effluent.
Utilizing subnatant from the thickener tank offers the
disadvantage of requiring a back-up source of flow to
restart the unit should there be a failure in the air
system. The utilization of plant effluent offers a
relatively clean source of pressurized flow, but consider-
ation must be given to the added hydraulic flow recycled
to the treatment plant. This can be a significant amount
to add to a plant facility. The third system has
demonstrated reasonable success in the United States,
and in this case the pressurized flow is screened primary
effluent and essentially is borrowed for the dissolved air
flotation system before being returned to the aeration
tank. Because the pressurized flow is returned to the
aeration tank, it does not impose a hydraulic load in the
treatment system.
Of all of the variables mentioned, the one that is of
most significant value is the air to solids (A/S) ratio. This
ratio is the amount of air applied to a given amount of
sludge. The ratio is unitless—kilograms of effective air
103
-------
blended with each kilogram of sludge to be thickened.
Since dissolved air flotation has become a major process
in the handling of municipal sludges, there has been
much controversy as to the optimum A/S ratio which
should be used as well as how this solids ratio should be
obtained.
The literature has indicated that the pressurizing
process should be between 40 and 80 psig (2.8 and 5.6
kg./sq.cm), and the A/S ratio should have a range of
0.01 to 0.04.
Figure No. 5 shows what a dissolved air flotation
thickener physically looks like. In this process an
external or recycled flow is put under pressure and fed
to the unit and mixed with the raw sludge whereby the
pressure is released to atmosphere and small microscopic
bubbles come out of solution and float the sludge to the
surface.
For a given volume of flow to be pressurized, the
higher the operating pressure, the more air that can be
put into solution. This is one way to increase the
amount of air being put into contact with the sludge;
thus, the higher the pressure, the higher the A/S ratio.
Another way to increase the A/S ratio is to maintain the
same pressure but to increase the volume of pressurizing
flow for the same amount of sludge being blended.
W. J. Katz and A. M. Geinopolos in the mid-1950's
indicated that an optimum operating pressure for a
dissolved air flotation unit would be about 40 psig. (2.8
kg./sq.cm). Even though you may place more air into
solution at a higher operating pressure, the higher
pressures release air bubbles that are of an ineffective
size (the effective bubble size is under 100 microns).
Larger size bubbles pass through the sludge rather than
lifting and compact the sludge. R. F. Wood and R. I.
Dick in work done in 1974 have reconfirmed the
benefits of operating at 40 psig. (2.8 kg./sq.cm) rather
than 70 or 80 psig. (4.9 or 5.6 kg./sq.cm).
To operate at a lower pressure has a real economical
impact also, because there is a significant cost difference
between air saturating a given flow volume at 40 rather
than 80 psig. The requirement for higher feed pumps,
larger air compressors, and higher pressure coded pres-
sure tanks contribute significantly to the initial cost of
the process and the high horsepower pumps and air
compressors increase operating costs.
Figure No. 6 shows some of the results which R. F.
Wood and R. I. Dick have produced with regard to
increasing the A/S ratio by increasing the pressure. These
results which are depicted in figure No. 6 prove to be a rl
contribution to the art. These results would not only
indicate that attempting to operate at a higher A/S ratio
by increasing the pressure is of no benefit, but, in fact, it
is detrimental to the thickening process. Again, the
reason for this detrimental effect of higher pressures on
thickening is that the size of the bubble formed is such
that it passes through the sludge rather than lift and
compact it.
FIELD PERFORMANCE DATA
Another way to increase the A/S ratio is to operate at
the optimum pressure and increase the volume of flow
to be pressurized. In the summer of 1973, we had the
opportunity of evaluating high rate loadings and various
air to solids ratios on a full scale dissolved air flotation
thickener. R. F. Wood and R. I. Dick confirmed in the
laboratory that increasing A/S ratio by increasing the
operating pressure proved to be detrimental to the
process. We attempted to confirm this work on a full
scale unit having an effective surface area of 150 sq. ft.
(14 sq. meters). We not only wanted to again confirm
that operating at 40 psi (2.8 kg./sq.cm) was optimum,
but we also wanted to determine what the optimum A/S
ratio is by changing the pressurized flow volume.
Approximately 14 days were spent at the site doing a
full scale analysis. The objectives of the test work were
as follows:
1. With all other parameters being equal, to deter-
minine the efficiency of the unit at 40 psig and 60
psig (2.8 and 4.2 kg/sq.cm) operating pressure.
2. At whichever pressure the unit performed better,
to determine the amount or volume of pressuriz-
ing flow which may be required to obtain opti-
mum performance (variation of A/S ratio by flow
volume). Optimum performance was measured by
the maximum thickened sludge concentration
which resulted from a given solids loading. The
solids loading of the thickener were from 48 to 54
Ibs./sq.ft./day (234 to 263 kg./sq. meter-day) with
the use of chemicals. Chemical dosages were kept
constant for all tests. The duration of the test
ranged from 6 to 12 hours. This duration is
important because it indicates stability in the
operation of the unit. It is very possible to operate
at substantially higher loadings but for short
periods of time only. However, one cannot op-
erate this process continuously at a sustained
higher level for any length of time because the
entire process begins to deteriorate very rapidly.
What is implied here is, when a unit begins to fail,
it does not fail instantly, but it fails by gradual
deterioration of the subnatant.
These two test objectives show an attempt to
determine what happens when the A/S ratio is changed
by changing the pressure and then by keeping the same
pressure and changing A/S ratio by changing the volume
of recycle flow which contains the dissolved air.
104
-------
Conclusions on Field Tests (determination optimum
A/S)
1. Increase in the operating pressure from 40 to 60
psig indicated deterioration of the performance of
the process. With other parameters held equal, the
unit produced a scum concentration of 3.9% while
operated at 60 psig (4.2 kg./sq. cm) (A/S equal to
0.026), while at 40 psig (2.8 kg./sq. cm) (A/S is
equal to 0.018), the scum concentration was 4.1%.
What is interesting to note here is that the effluent
suspended solids concentration in the underflow
was 26 mg/1 while operating at 40 psig and 200
mg/1 while operating at 60 psig. This data reaf-
firms the conclusion outlined by R. F. Wood and
R. I. Dick.
From these observations, it has been concluded
that a change in air to solids ratio by increasing
the pressure provided to be detrimental to the
operation and that 40 psig (2.8 kg./sq. cm) is the
optimum operating pressure.
2. Since 40 psig (2.8 kg./sq.cm) proved again to be
the optimum operating pressure, the operating air
to solids ratio was then changed by the changing
of the recycle flow volume. Figure No. 7 shows
the results. These results show conclusively that
there is optimum air to solids ratio when operating
at 40 psig (2.8 kg./sq.cm) and that higher air to
solids ratios again prove to be detrimental. As can
be seen from Figure No. 7, the design point with
respect to air to solids ratio proves to be about
0.014 at 40 psig (2.8 kg./sq.cm)
This A/S ratio can be converted directly to a
practical design approach by using 100% recycle
or pressurized flow for every 1/2 percent of
influent sludge concentration while operating at
40 psig (2.8 kg./sq.cm). This value results in an
A/S ratio of about 0.015.
As the various parameters discussed are more
fully understood and a better understanding of the
importance of operating with the optimum A/S at
40 psig (2.8 kg./sq.cm) (optimum operating pres-
sure), the application of dissolved air flotation for
sludge thickening will increase. This process has
demonstrated that it has the capability of per-
forming an economical and necessary function in
the entire sludge handling scheme.
Flgm No. 1
COMMON SLUDGE HANDLING SCHEMES
Incineration. Landfill, Fertilizer or OcMn Diipoul
105
-------
Figure No. 2
DESIGN LOADINGS FOR FLOTATION THICKENING
Type of Sludge
Surface Loading
Ibs/day/ft2
Thickened Concentration
Primary
Activated
Primary & Activated
Primary & Trickling Filter
20- 30
8- 15
20 - 30
20- 30
7 - 12
3 5
5 10
5 10
This data is for thickening without the use of chemicals.
Figure No. 3
Pilot Unit
106
-------
Figure No. 4
Bench Scale Testing Apparatus
Figure No. 5
Dissolved Air Flotation Thickener
107
-------
Figure No. 6
1000
600
400
I* 200
s
urlNL
U 80
« 60
£ 40^
20
10
0 20 40 60 80 100 120 140
PRESSURE OF SATURATION, psig
Effect of pressure on rise rate.
From R.F. Wood and R.I. Dick.
5
Jx«
SJ*
g
s
SI
1J.N30N03
%
§
$
Q -
THICKENE.
j»
i
2
0
(
I
0
1
A
o\8
\
FIG
URE
NO.
EFFECT OF AIR TO SOLIDS
RATIO ON THICKENED SLUD
CONCENTRA TION AT 40 PSH
^^
© ^t
0£>l 0.015 O.OS
K 0
O.C
~-^~~
X3
7
GE
Off<
AIR TO SOLIDS RATIO, A/S
108
-------
THE UTILIZATION OF MUNICIPAL
SLUDGE IN AGRICULTURE
By
Bart T. Lynam, General Superintendent
Cecil Lue-Hing, Director of Research and Development
Raymond R. Rimkus, Chief of Maintenance and Operations
Forrest C. Neil, Chief Engineer
Presented at
United States/Soviet Seminar on
"Handling, Treatment and Disposal of Sludges"
Moscow, U.S.S.R.
May 12 - 28, 1975
109
-------
THE UTILIZATION OF MUNICIPAL
SLUDGE IN AGRICULTURE
By
Bart T. Lynam, General Superintendent
Cecil Lue-Hing, Director of Research and Development
Raymond R. Rimkus, Chief of Maintenance and Operations
Forrest C. Neil, Chief Engineer
INTRODUCTION
The disposal of the solid residues from wastewater
treatment has traditionally been the most difficult
problem facing municipally and privately owned treat-
ment faculties. In general, there exists sufficient tech-
nology to remove various pollutants from wastewater,
but the disposal of the resulting solids has been a
difficult technical as well as social problem.
Sludge Production
There is no known information available on the
quantities of sludge currently being produced world-
wide. However, there are some estimates of the munici-
pal sludge (excluding privately owned industrial waste-
water treatment faculties) produced in the U.S.
Dean (1973) has estimated that the actual national
production of sludge in 1972 was approximately 10,000
dry tons (9,072 metric tons) per day. The estimate is
probably lower since it is based only upon the sewered
population and includes the effect of process variations
such as digestion and incineration. By 1990, he esti-
mated that the quantity of sludge will increase to 13,000
tons (11,800 metric tons) per day.
Extrapolation of this U.S. data to sludge quantities
produced on world scale is tenuous at best since
wastewater treatment is not developed to the same
extent on a worldwide basis. An accurate estimate would
include a study of the wastewater practices of various
nations in order to arrive at even a rough estimate.
Clearly, as the nations of the world reach for higher
standards of living, while preserving the quality of the
environment, there will be an increasing demand for
more sophisticated and advanced wastewater treatment
processes. Older waste treatment practices which pro-
duced little if any solids will soon give way to processes
which, in general, will generate larger quantities of
sludge. Also, traditional sludge disposal techniques such
as lagooning will progressively lose social acceptance and
thus will require new and more innovative approaches to
existing solids disposal techniques.
In addition, as the population of many nations
becomes more urbanized, it will become increasingly
difficult to find locations in or around large cities where
sufficient space can be allocated for solids disposal. That
is, wastewater solids will become increasingly out of
place in relation to their point of origination.
Ultimate Sludge Disposal Alternatives
There are many combinations and variations of sludge
disposal alternatives available to municipalities but the
basic processes are:
1) Land Spreading
2) Incineration and Ash Disposal
3) Ocean Disposal, and
4) Land Fill
Incineration
Incineration essentially involves the combustion of
the organics contained in sludge. Normally, this means
that approximately 30 - 53% (dry weight) of the sludge
remains in the form of ash which must be disposed of.
The primary advantage claimed for incineration is that it
reduces the volume of the material for disposal. How-
ever, the process requires much energy in order to burn
the high-water-content sludge, while the fertilizer value
of the sludge is simultaneously destroyed. The process
also incurs significant costs for sludge dewatering, and
the ash does require a land disposal site. The incineration
process also releases significant quantities of pollutants
to the air including volatilized metals. Air pollution
control technology for removal of metals is expensive
and is not likely to meet the emerging and increasingly
110
-------
stringent governmental regulations. For The Metro-
politan Sanitary District of Greater Chicago (District),
incineration is estimated to cost from $60 - $120 per dry
ton ($54.3 -$111 per metric ton) of sewage sludge solids
excluding any costs for removal of metals and gaseous
pollutants from stack gases.
The current fuel shortage has cast an additional
gloomy shadow on sludge disposal by incineration. The
steadily increasing cost and decreasing availability of gas
and oil will affect the desirability if not the feasibility
and practicality of this process in the foreseeable future.
Table 1 presents some data on auxiliary fuel con-
sumption in seven cities of the U.S. (Olexsey and Farrell,
1974). The weighted average consumption of number 2
fuel oil necessary to burn 1 ton (.907 metric tons) of dry
solids is 51.6 gallons (195 liters). If this figure is rounded
to 50 gallons (189 liters) per ton nationwide and one
assumes that the practice of sludge incineration were
adopted nationally, then the U.S. would require at least
9 X 108 gallons (340 X 10s liters) of crude oil per year.
In 1972, the nation was consuming about 50 X 108
gallons (19 X 108 liters) per year (Olexsey and Farrell,
1974). Clearly, unless alternative methods for sludge
disposal are available to municipalities, sludge incinera-
tion will be at variance with the long term fuel
conservation goals which many nations have adopted.
In addition to the energy required to incinerate
sludge, one must also consider the fact that incineration
destroys the nigrogen and other agronomic nutrients
contained in the sludge. This nitrogen must be replaced
and, of course, it takes energy to make the required
inorganic fertilizer for replacement. For example, the
replacement of one ton of nitrogen fertilizer requires
917 gallons (348 liters) of crude oil. Clearly if we can
recycle the nitrogen content of sludge for agricultural
production, we can reduce the amount of energy
required for fertilizer manufacture and the correspond-
ing cost of food production.
Ocean Disposal
Ocean disposal offers, to coastal cities, a readily
available ultimate sink for sludge. This has been prac-
ticed by many U.S. cities including Los Angeles and New
York. However, this means of disposal is not available to
inland cities and has many disadvantages. Any nutrient
value contained in the sludge is wasted while the
organics present tend to deplete the dissolved oxygen of
the disposal site. Such disposal could significantly affect
coastal fishing areas as well as reduce ocean bathing
areas. This method of disposal has come under increased
governmental scrutiny and may soon be severely re-
stricted. Costs are very low for this process and include
only transportation costs although some cities are
beginning to digest their sludge prior to ocean disposal.
Landfill Operations
Landfill operations are practiced by many cities and
included under this general term is sludge lagooning.
Landfill operations waste the organic content of sludge
while considerable expense is involved in sludge dewater-
ing either for lagoon decanting operations or prior to
landfill operations. Disposal sites often are useless for
other purposes following landfill and some are never
returned to the tax rolls. Few sites can be used for 20 to
30 years after being landfilled with municipal sludges.
Oftentimes, such sites will produce methane gas which
could cause a potentially dangerous situation for other
land uses.
Land Spreading
Land spreading of sludge has become a method which
is being increasingly considered by many municipalities
in the U.S. and indeed, throughout the world. If offers
the advantage of recycling nutrients back to the land at
low cost, and of reclaiming lands bespoiled by strip
mining. Sludge is first stabilized by anaerobic digestion
or other suitable means before application on land. Such
stabilization eliminates obnoxious odors and fly prob-
lems. Yield of grain and forage crops are increased by
the nutrients and water supplied by irrigating with
digested sludge. Digested sludge organic matter accumu-
lates in and imparts favorable characteristics to soils
because of its normally high humus content. The process
of land spreading of sludge affords the opportunity for
urban areas to recycle the fertilizer value of sludge to the
fanning areas from which much of the organic materials
and nutrients originate. With the current shortage of
fuels, and the high requirements for inorganic fertilizer
production, sludge recycle for agricultural production
offers a ready opportunity to reduce the energy require-
ments of the agricultural sector. Also, since many
municipalities can offer their sludge at practically no
cost to the farmer, a significant cost savings is effected
both for the farmer and the municipality which pro-
duces the sludge.
SLUDGE APPLICATION TO LAND
One of the most widely publicized operations is the
Rye Meads Works of the Middle Lee Regional Drainage
111
-------
scheme in England. Portions of the liquid digested
domestic sludge produced, is taken by tanker trucks to
local farms and spread as liquid referred to as "Ryganic"
(personal communication with B. T. Lynam, 1974). The
remainder of the sludge is dewatered on open beds and
the resultant dry sludge then applied to land. The plant
serves 300,000 people and a drainage area of 125 square
miles (324 sq km) Approximately 60,000 gallons per
day (228,000 I/day) of liquid Ryganic and about 1,000
tons (907 metric tons) per year of solid Ryganic were
being applied in 1971.
Liquid Ryganic is delivered and spread free within a
7*4 mile (12 km) radius of the Rye Mead Works. Because
there is a large demand for liquid Ryganic during the
spring and summer, customers are advised to place
orders as early as possible.
Based upon the recommendations of the Hertford-
shire Institute of Agriculture, liquid Ryganic is usually
applied at a rate of 5,000 gallons per acre (7650 1/ha)
which contains 100 Ibs. N and 115 Ibs. P2OS per acre
(112 and 129 kg/ha of N and P2O5, respectively) using
1,000 gal. tankers (3785 1) spreading over an 8-ft. (2.4
m) strip. Yields of grass, barley and other crops in the
area are excellent and, as noted above, the demand by
local farmers is high.
The Metropolitan Sanitary District of Greater
Chicago (District) has embarked upon a program to
utilize the digested sludge from its treatment plants on
land in the central portion of the State. Currently, the
District owns over 15,000 acres (6,030 ha) of land about
200 mfles (320 km) south of its 900-square-mile (2340
sq km) drainage area. Liquid digested sludge containing
approximately 4% solids is barged down the Illinois
River and then pumped through a 10.8 mile (17.3 km)
pipeline to holding basins. During the application season
which principally occurs during the months of April
through October, liquid sludge from the holding basins is
applied either by means of spray guns or soil incorpora-
tion. To date, rates up to 30 dry tons per acre (67.2
mT/ha) per year have been applied during the growing
season to fields which were principally planted in com.
Approximately 6,000 wet tons (5,440 metric wet
tons) of 4% liquid digested sludge is currently being
transported daily to the site in Illinois. In 1974, about
475 dry tons per day (431 mT) are being removed from
the District's West-Southwest secondary treatment facil-
ity which currently has a design capacity of 900 million
gallons (3510 X 10* 1) per day.
SLUDGE PROPERTIES
Sewage sludge is derived from the organic and
inorganic matter removed from wastewater at sewage
treatment plants. The nature of sludge depends on the
wastewater sources and the method of wastewater
treatment. If waste solids are to be evaluated as a soil
amendment or as a fertilizer, it is important to under-
stand their chemical and biological properties. A com-
parison of sludge analyses from various treatment plants
would be confounded by the individual treatment
processes; therefore, some of the more common waste-
water treatment methods will be described.
The first treatment process is usually gravity separa-
tion of solids from wastewater. This process is com-
monly known as primary settling or primary treatment.
Secondary sewage treatment may be accomplished by
physical-chemical or biological processes. The physical-
chemical processes include chemical precipitation using
lime, alum, or ferric chloride. Biological secondary
treatment includes trickling filters or some modification
of the activated sludge process where aerobic suspended
bacteria treat primary treated wastewater. These bio-
logical processes result in nutrient consumption by
microorganisms and the formation of biological floes
which are later settled out and subsequently pumped to
concentration chambers for further processing.
The wastewater solids separated by these primary and
secondary water treatment processes may then be dried
for marketing as a low analysis dry fertilizer, or
subjected to various stabilization treatments. Some
current sludge stabilization processes include: aerobic or
anaerobic meso- or thermophilic digestion.
Following any of these latter processes the stabilized
sludge may be further concentrated by drying beds,
vacuum filtration, pressing, centrifuging, or lagooning
with supernatant drawoff.
Some typical fertilizer value of sewage sludge can be
seen in Table 2 which gives the concentrations of the
major plant nutrients from various sources in the Eastern
United States. The N, P, and Ca are the dominant
elements present which can aid plant growth. The
storage of the processed sludge can affect the nitrogen
content considerably. Peterson et al. (1973) reported
total N and NH3-N from an aged lagoon to average 2.6
and 1.2%, respectively. The current sludge N and NH3-N
content entering the lagoons averaged 6.8% and 3,1%
respectively. The Chicago (District) sludge in Table 2 is
from a heated high rate digester and it has an NH3-N
content of 3.1%. The seven state mean presented in
Table 2 has an NH3-N content of 0.7%.
The metal contents of sewage sludges from Chicago,
seven states in the USA, and 42 locations in England and
Wales (Berrow and Webber, 1972) are presented in Table
3. The range of metal contents is extreme in this table. It
is likely that some large industrial waste loads are
released into some of these sewer systems. A comparison
112
-------
TABLE 1
AUXILIARY FUEL CONSUMPTION FOR SLUDGE INCINERATION
IN CITIES DUXING 1972
(Olcxsey & Farrell, Mews of Envir. Res., May 3, 1974}
City
Jersey City, IJ. J.
Providence, R.I.
Toncv.-anilo, H.Y.
Rochester, N.Y.
Hartford, Conn.
St. Louis, Mo.
St. Paul, Minn.
Sludge Production
(dry tons/day)
15
30
6
17
25
55
275
Fuel/dry
tons of solids
28
28
17
42
160
22
45
* Gallons cl No. 2 oil
IAJir.1: 2
Major riant Nutrients Present in VarLus Sewage Sludge Sources.
Constituent
Total N
NH3-N
P
S
K
Ca
Hg
No
% dry v;t. basis
Chicago V/SW
Renjjs
4.2-9.6
1.5-5.0
1.1-8.1
0.35-1.3
0.2-0.8
0.3-4.8
0.6-1.7
0.2-0.7
Median
6.8
3.1
2.8
0.98
0.4
2.1
1.1
0.25
1U.-24 cities
Range
2.6-9.8
0.1-6.1
0.7-4.9
-
-
.
•
-
Mean
5.4
1.8
2.4
-
-
-
-
-
7 States in USA*
Range
0.03-17.6
0.0005-6.7
0.04-6.1
-
0.008-1.9
0.1-25
0.03-2.0
0.009-2.7
Mean
3.2
0.7
1.8
-
0.3
5.1
0.5
0.4
' These diti »rt from Agric Experiment Stations Committee
on Uliliia'iioti and Disposal of Municipal. Industrial, and
Aviculivral Processing Wastes on land and reptetent
select cities in seven slates.
THE METROPOLITAN SANITARY DISTRICT
OF GREATIR CHICAGO
ENGINEERING DEPARTMENT
r.J.K.AW.B. MARCH 1973
113
-------
TABLE 3
f.klal Content of Voriocs Sewage Sludge Sources.
Lleicl
T.g
J»$
B
Da
Ca
Bi
Cd
Co
Cr
Cu
Fa
Go
Hg
la
li
i\n
flo
Ni
Pb
Sc
Si
Sr
Ti
V
Y
ZB
Zr
/ug/g dry wt. basis
CLica-jo 173W
Rcsge
120-312
11-4120
680-2270
15400-49000
0.8-7.5
120-550
186-840
304-1160
1670-4850
Median
197
2400
1330
36300
3.2
370
355
680
2770
7 Sic-tes ir, USA
Range
6-230
4-757
21-C920
1-18
17-99000
84-13400
400-CJOOOO
18-7100
5-39
10-3515
13-19700
13-27800
Mean
53
114
618
5.3
3290
1260
12900
400
27
426
1670
2900
Greet Britain"
Range
5-150
15-1000
150-1000
1-30
12-100
60-1500
2-260
40-8800
200-2000
6000-62030
1-20
30-150
10-150
150-2500
2-30
20-5300
120-3000
2-15
40-700
80-2000
1000-4500
20-400
15-100
700-49000
30-3000
Median
20
50
1500
3
25
-
12
250
cno
21COO
3
60
40
400
5
80
700
5
120
300
2000
60
40
3000
150
lUpublished data from Ajric. Expt. Stations Committee
M Uliluatioi anj Disposal el Muaicipal. Ud«striil.
nd Ajncoltifil Pmtssi»| Wastts Mli«4.
IB< Wtkier. 1972. j Sci. H Ajric. 23,93 100
THI MtlBOPOllTAN SANITARY DISIIICI
Of CRIATIR CHICAGO
INCINiERINC DIPARTMSNT
O.F.M.AW.*. MARCH 1973
114
-------
of the metal data from Chicago, which has strict
regulations on metal contents of sewage released to the
sewers from industrial sources, with the seven states of
the USA and Great Britain shows the effects of
industrial waste regulations. The Chicago sludge has less
Cr, Ni and Pb than the other seven states reported.
However, in comparison to Great Britain the District
sludge has a higher metal content. The continued
improvement in wastewater treatment will result in a
greater metal content of the resulting sludges. This is in
the best interest of man in that the protection of our
water resources is paramount to our future.
The residual pesticide content of sewage sludge is
usually very low. Chawla etal. (1974) reported the total
organochlorine insecticide content of four cities in
Ontario, Canada to range from 20 to 103 ug/1 and the
polychlorinated biphenyls (PCB) contents for these
sludges ranged from 74 to 112 ug/1. Analyses of five
wastewater treatment plants sludge sources from the
District showed the PCB content to be < 50 ug/1.
The physical characteristics of sewage sludge depend
on the type and extent of the wastewater treatment and
the method of sludge stabilization. For example, a
granular dense sludge may be produced from primary
wastewater treatment, while the waste-activated sludges
from secondary wastewater treatment results is a sludge
containing mostly bacterial cells which may be viscous
and difficult to dewater. Digested waste-activated sludge
has liquid properties up to a total solids content of 8 to
12%. At a total solids content of 10-15% this sludge is a
gel which can be stirred to form a solution but reverts to
a gel in a day or two. The sludge solids content must be
at least 20 - 30% before it can be handled as a solid. To
obtain this solids content, extended holding with good
drainage and solar radiation is necessary. The pumping
of sewage sludge with up to 10% total solids can be done
with special techniques. Field irrigation sprinklers work
best with sludge solids of up to 5 to 7%.
SLUDGE APPLICATION RATES ON LAND
Crop Production
The annual application of sewage sludge should be
adequate to produce maximum crop yields. With sludges
as reported in Table 2 and 3 this translates to the
nitrogen requirements of the crop. If perennial grasses
are grown the annual nitrogen removal may be 300
Ibs/acre (336 kg/ha). The annual N needs for com (Zea
maize) may be 180 Ibs/acre (202 kg/ha) with good corn
yields. The grass has another advantage in that it has a
longer growing season and has a high water use which
reduces the potential for N leaching.
As with any fertilizer system, the N content from
sewage sludge is not completely available to the plants.
In sludges, the NH3 or readily available N content is
approximately 45% of the total N with freshly digested
material, and if the sludge has been stored in lagoons or
dried on exposed beds the soluble NH3 fraction may be
30 to 35% of the total N. The remaining sludge N is in
the organic form which is mineralized in the soil at the
rate of about 20 - 50% the first year and from 3 - 20% in
successive years. These rates are a function of soil-
moisture and temperature as well as the relative stability
of the sludge.
The method of sludge application also affects the N
utilization efficiency. If surface application without soil
incorporation, e.g. sprinkling, is used 11 to 60% of the
applied NH3-N can be lost by volatilization (Ryan and
Keeney, 1975; and Peterson, et al. 1974). If the liquid
sludge is immediately incorporated into the topsoil,
about 80% of the NH3 is retained and available for plant
uptake.
The denitrification of the N02 and N03 has been
estimated to be as high as 20% under moist soil
conditions which are very common with liquid sewage
sludge applications. These rates will vary with the
placement of the sludge in the soil. No incorporation
will result in the least and subsurface application will
result in the highest denitrification rates.
Another means of immobilizing the nitrate is by the
soil micro-flora. This can be accentuated with large
additions of a high carbon source, e.g. straw, which
create an accelerated growth of hetertrophic microorga-
nisms which will consume the N. This management tool
can be used to retain the soil nitrogen until the crop
needs it.
The nitrogen cycle depicting the fate of sludge N as
well as estimated transfer rates is summarized in Figure
I. As this discussion may have suggested, it is not
possible to formulate uniform rules for the rate of
sewage sludge application on productive land. However,
if the rate is set to supply the N needs of the crop, good
production can be assured.
Reclamation of Spoils
The amelioration of disturbed lands, e.g. coal mine
spoil, wastepits, and other manipulated lands, has been
successfully accomplished with sewage sludge (Peterson,
etal. 1971; Lejcher and Kunkle, 1973; Sutton, 1973).
Disturbed lands usually require pH control and
fertilization if revegetation is to be successful. Barren,
acidic or alkali lands are very likely to have severe
erosion problems. Rapid restoration of such areas is in
the best interest of the area. High rate applications of
115
-------
FIGURE I
N cycle illustrating the fate of sludge N with estimated transfer coefficients where appropriate.
(From Beauchomp and Moyer, 1974, with'transfer coefficients added by authors)
NH3
VOLATILIZATlON(.2-.8)
PLANTS12-.6)
SLUDGE N
ORGANIC N
(0.2-0.5 first year)
(mineralization)
SOIL
MICROORGANISMS
GASEOUS LOSSESU5-.2)
(denltrification)
LEACHING LOSSES(0-?)
THE METROPOLITAN SANITARY DISTRICT
OF GREATER CHICAGO
ENGINEERING DEPARTMENT
PU.O MARJ27*
-------
sewage sludge on such lands has been shown to be the
best restorative procedure for these ecosystems (Peter-
son and Gschwind, 1972). This concept insures a rapid
establishment of vegetation which checks erosion and
leaching of the undesirable constituents, e.g., H2SO4, Fe
and Mn.
SITE SELECTION, DESIGN & MANAGEMENT
Topography & Soil Factors
Site development should be based on the following
four sets of parameters for environmental control:
1. The site plan should be developed so that it would
not cause air, land or water pollution now or in
the future.
2. The site plan should implement the principle that
organic solid material from urban areas is not a
waste product to be discharged but rather, a
valuable organic material to be recycled for
beneficial use.
3. The plan should be developed to provide a
maximum multiple-use development.
4. The site should be developed in close liaison with
environmental regulatory agencies to insure maxi-
mum protection of the natural environment.
Tne District developed a program of site analysis in
order to insure that the preceding criteria would be met
on its land utilization site in Fulton Co. Illinois. The site
for development was studied in three general areas. The
first was a series of environmental characteristics which
were investigated to insure against an existing or
projected environmental hazard to the soil or to the
surface and subsurface water systems. The second was
the development of multiple-use potential of the site in
relation to existing and projected urban development to
make certain that there would be a compatibility with
the planning program at the local, county, state and
regional levels. A third area for consideration was the
construction of a continuously monitored environmental
protection system.
The environmental survey involved an inventory of
physical characteristics of the land. These included
slope, surface and subsurface geology, and hydrological
characteristics.
The District performed surface and subsurface soil
investigations in two phases. The first phase involved 25
soil borings that were utilized as a basis for the design of
the sludge holding basins and related earthwork. In
addition to the regular testing program, consolidation
and permeability tests were performed, time-settlement
and moisture density curves were derived, and field
percolation tests were performed. The second phase of
the work involved 35 borings that were used for the
purpose of establishing general soil properties, existing
groundwater conditions, and nature of underlying
geologic formations across the entire site.
The boundary lines for the site were located by
placing monuments in the field at every property corner.
Each corner was located on both the local township and
section grid, as well as on the Illinois State plane
coordinate grid. Topography maps were prepared to the
scale of 1:1,200. Contour intervals were shown at 2 ft
(0.609 m or 0.6 m), and the topography was extended
for a distance of 1,000 ft (304.8 m) outside the
boundary lines of the District site to provide informa-
tion on local drainage. Individual topographic sheets
were indexed to sections, and each sheet contained the
topography for half a section of land (320 a., 129.5 ha).
All topographic and planimetric information was shown
in these sheets, and supplementary information, such as
water depths, was determined by actual field surveys.
Because the key to successful development is the
control of water on the District's site, the District set up
a program that involves:
1. An initial hydrological survey and complete log of
existing water quality data;
2. The design and construction of an instream
monitoring system, the holding reservoirs, and the
recycling system; and
3. Development of an ongoing identification of water
quality for local, state, and federal review.
Site Preparation
Prior to sludge application on the District's site each
field is leveled by construction equipment to maximum
slopes of approximately 6%. Fields vary in size from
approximately 10 acres (4.05 ha) to more than 100 acres
(40.5 ha). Berms are placed around the field so that all
surface water runoff is directed to adjacent retention
basins for temporary storage and analysis prior to release
to the water course. Retention basin capacity is designed
to receive the runoff from a 100 year frequency storm,
which for the District disposal area amounts to more
than five inches (127 cm) of water. Rocks and other
debris were removed from the field during site prepara-
tion. Those areas that were scarified and which would
not become part of the productive field were seeded to
permanent grass for erosion control. Complete surface
water collection is accomplished by directing application
field runoff to retention basins. The water is then
analyzed prior to release to insure that it meets State of
117
-------
Illinois water quality standards. In addition, several small
streams that run through the property are monitored at
points where they enter and leave District property. The
United States Geological Survey, Illinois Environmental
Protection Agency and the Fulton County Health
Department also monitor some of these streams as well
as several other locations within the property.
Numerous shallow wells have been located through-
out the property for purposes of supplying groundwater
for monitoring purposes. Shallow wells for groundwater
monitoring purposes surround the sludge holding basin
that was put into operation first. Extensive use of
grassed waterways reduces the sediment load that leaves
the fields during heavy rains. These waterways also
provide for additional utilization of nutrients prior to
entry of the runoff into retention basins.
Site Management
The basic aim of the District is to be able to apply as
much sludge to a particular location as the environ-
mental limitation will permit for rapid restoration of
productivity. In this regard, an agricultural cropping
program is a vital component. To date, the District has
contracted with local farmers for completely caring for
most field crops from planting on through harvest. Most
sites in the United States, utilizing sludge as soil
fertilizer, have the agricultural cropping done by local
farmers.
Sludge is applied at the District's site by using
contract employees to operate District owned appli-
cation equipment. Supervision of contract employees is
done by a small permanent District staff who reside in
the vicinity of the application site. Transportation of
sludge to the District's land utilization site is entirely
done by a private contractor who uses river barges and
pipeline.
Throughout the United States, many combinations
are used for sludge transportation, site application and
site management. Most small sanitary districts either
transport sludge to the site by truck and apply it or
permit farmers to haul sludge to their own application
site. Usually, most site management involving agricul-
tural operations is done by local farmers. Because of
increased precautions against environmental contami-
nation, there has been a definite trend, in the United
States, toward land utilization of municipal sludges.
Utilization can be either for land reclamation or fertility
utilization by conventional agricultural crops.
Publk Relations
One of the greatest difficulties with implementing
land utilization or disposal programs for sludge in the
United States has been with public acceptance. The
general public is not sufficiently aware of the nature of
stabilized sludges so that a rational consideration of such
programs seldom occurs. This problem becomes more
acute when large projects are proposed in rural areas.
An educational program would appear to be a
necessary and integral part of any large scale land
utilization program. It does not appear sufficient to
recite the value of the material relative to its nutrient
and organic matter content. The public needs to be more
fully informed of the product stability and lack of
public health risk, odor potential and water contami-
nation potential so that unfounded anxieties may be
relieved.
The land disposal site, be it utilization, landfill or
reclamation, can be operated to minimize problems in
the public sector. Only well stabilized material should be
brought to the site to prevent odor and vermin prob-
lems. Storage and application operations should be
conducted in such a manner as to prevent loss of the
material which occurs primarily through water move-
ment. In land utilization systems, tillage of the applied
solids into the soil at an early date has a positive effect
on odor control and in reduction in the possibility of
contaminated surface runoff. Good housekeeping prac-
tices can produce effective results.
IRRIGATION SYSTEMS
When large volumes of liquid sludge are to be applied
to established crops, several application methods can be
used. Figure II shows a traveling sprinkler with a single
nozzle volume gun. Nozzles range in size from 1 to 2
inches (25 to 50 mm) for sludge application. Nozzles
must be operated with sufficient pressure to break the
liquid stream into very small drops to avoid damage to
the crop and soil. Practices which re conventional for
irrigating water with traveling sprinklers also apply for
sludge irrigation.
Figure III shows a typical layout for a traveling
sprinkler. Width of a single pass depends upon nozzle
size and pressure but is normally 300 to 500 feet (91 to
152 m). The mobile pipe or hose is constructed in sizes
up to five inches (12.7 cm) in diameter and in lengths of
660 feet (201 m). Propulsion across the field is
accomplished by a small engine which drives a winch to
retrieve an anchored cable. Application travel speeds are
in the order of several feet per minute but can be varied
to suit most field conditions. When one pass is com-
pleted the hose is disconnected, emptied of sludge and
then wound on a reel for transport to the next area of
application. A small tractor is sufficient for moving the
sprinkler and hose reel and a crew of two is adequate for
118
-------
Figure II. Traveling sprinkler applying liquid sludge to
a corn crop.
HGUKE 'ILL
PUMP UNIT
119
THE METROPOLITAN SANITARY DISTRICT
OF GREATEH CHICAGO
EWiWf.FniNC DEPARTMENT
W II (III J 0 MAIIOI U71
-------
operating a traveling sprinkler. The most predominant
concern with large-sized nozzles for sprinkler application
has been with downwind drift of small droplets.
Liquid sludge can also be applied by center-pivot
irrigation machines to existing crops. Actual operation
of these machines for sludge application has been
relatively limited at this time in the United States. The
same range of nozzle sizes that were used on traveling
sprinklers can also be used for center-pivot machines.
Some opportunity is present for development of a low
pressure application device in conjunction with the
center-pivot machine. The main reason for interest in
low pressure application is in reducing spray drift. The
primary advantage of the center-pivot machine is in the
reduction of operational labor. When in conventional use
for applying irrigation water, center-pivot machines
operate unattended for long periods of time; motive
power is supplied by electrical means.
Combinations of ridge and furrow, gated pipe and
flooding systems have been used to apply sludge to
fallow fields or fields with growing crops. Regardless of
the application method, excessive liquid sludge should
not be applied because of possible deleterious affects of
water-logged crops and environmental contamination.
Soil Incorporation & Injection Systems
In the past several years in the United States,
incorporation devices have been developed which mix
liquid sludge into the soil. Injection devices have been
used for a number of years to place liquid livestock
manure beneath the soil surface and are now being used
for municipal sludges. The distinction between these two
methods is as the names imply, but in addition, an
incorporation device - usually a conventional agricultural
disk harrow with attached sludge distribution manifold -
applies sludge to the entire cross-sectional area of the
soil being tilled whereas an injector usually applies
sludge to bands or slots formed in the soil by a tool
shank. Most injectors presently use self-contained tanks
for the liquid while incorporation devices use a trailing
hose similar to a traveling sprinkler. However, either
device could use either method for sludge supply.
Incorporation devices place the sludge into the soil
where it is less subject to erosion and runoff than surface
application. Offensive odors can be more completely
controlled by placing sludge quickly into the soil. While
incorporation devices destroy all vegetative cover, an
injector can apply to a grass cover without serious
damage to the grass. Both devices need large tractors to
operate at any appreciable flow rates. Figure IV shows
an incorporation unit while Figure V shows an injector.
Slurry, Cake and Solids Handling Systems
Most of the problems associated with handling of
municipal sludges are related to their physical properties.
Slurries can be handled with pumping equipment and
pipelines; however, the viscosity of such sludges may
result in pumping difficulties. In established lagoons,
pump problems are sometimes encountered with en-
trained gases formed during decomposition. These gases
enter the pump suction line and loss of prime or
cavitation is often observed. Problems such as these
should be considered in initial design.
High viscosity of slurries causes a considerably greater
variation in pipeline pumping losses as the pipeline
length changes, as compared to lines conveying water.
Pump and pipeline transfer systems can presently convey
sludges with up to 12-15% sludge solids content.
Technological improvements are likely to increase these
limits. Presently, the limitation on solids content for
applying sludges by high pressure, large volume nozzles
appears to be between 5 and 7%. Systems using smaller
nozzles and lower pressures are more restricted in
handling the solids without blockage.
When transporting dry sludges, one cannot depend
upon friction, gravity or inertia, when used in conjunc-
tion with conveying devices, to move the solids to where
they are intended to go. The adhesive nature of sludges
at various moisture conditions might cause the sludge to
stick to the conveying device. Solid sludges are usually
spread by conventional manure spreaders while loading
is readily done with end loaders.
Liquid sludges contain abrasive components such as
sand and other inert materials which will wear on pump
shaft bearings and must be considered in pump design.
Corrosive problems, related to conveying of sludges, are
usually not significant because sludge has nearly a
neutral pH.
SOIL AND CROP RESPONSES
TO SLUDGE APPLICATION ON LAND
Sewage sludge when applied to soils provides a readily
available source of plant nutrients and it is an effective
soil amendment. The chemical quality of sewage sludges
is dependent upon wastewater sources and the methods
of wastewater treatment as discussed earlier in the
section on sludge properties. Sludges applied to land
provide major plant nutrients such as N, P, K, micro
plaht nutrients such as Cu, Fe and Zn and organic matter
for improving the soil structure (e.g., better aeration and
water holding capacity). The effectiveness of sludge as a
soil improving agent depends upon the composition of
120
-------
Figure. IV. Disk incorporation with trailing supply hose,
Figure V . Injection unit showing three injectors.
121
-------
the sludge, the characteristics of the soil to which it is
applied and the plant species to be grown (U.S.D.A.,
1974).
The nutrient content of municipal sludges vary
considerably and nitrogen, phosphorus and potassium
levels is about one-fifth of those found in typical
chemical fertilizers (Table 2). Much of the N and P in
sludge is in organic combination and it must be
mineralized before becoming available to plants. The
rate of mineralization for N and P is dependent upon
local conditions such as soil type, temperature, soil pH,
soil water and other soil chemical and physical charac-
teristics.
Crop Types
Crop selection for sewerage sludge application to land
is of great importance and it merits thorough considera-
tion if the system is to be successful. Crops normally
grown in sludge application schemes are perennials
(forage and fruit crops) and annuals (field crops). In
some instances forest and landscape vegetation are
satisfactorily grown.
Crops selected for use should be evaluated with
respect to (1) water requirement and tolerance;
(2) nutrient requirements (e.g., nitrogen), tolerances,
and removal rates; (3) optimum soil conditions for
growth capability; (4) sensitivity to various inorganic
ions; (5) compatability with the climate and growing
season; (6) the ease of cultivation and harvesting and
(7) the demand and market value of the harvested
product (Sopper, 1973; U.S.E JA., 1974).
Crop Responses
Crop responses to sewage sludge application has been
evaluated by The Metropolitan Sanitary District of
Greater Chicago for many years. In 1966 it became
apparent to the District that it would soon be unable to
handle increasing volumes of sludge by lagooning and
heat drying. To determine the environmental effects of
sludge on agricultural lands experimental corn plots were
developed from a 7-acre (2.8 ha) field at the Hanover
Park Wastewater Reclamation Plant in 1968. The
original experimental design was a randomized block
with five replications and three sludge loading rates of 0,
J4, and J4 inch (0, 6 and 12 mm) of sludge/week. Sludge
was applied to the plots at weekly intervals in furrows
between growing corn rows.
Com yields from 1968 to 1973 are presented in Table
4. Sludge applications consistently produced yield in-
creases for corn grown on the Drummer silty clay loam
sofl with poor natural drainage.
In another experiment on the Northeast Agronomy
Research Center of the University of Illinois near Joliet,
Illinois, digested sludge from wastewater treatment
plants operated by the District has been applied at
various rates each growing season on 20 X 44 ft. (6.1 by
12.2m) plots on a Blount silt loam soil continuously
planted to corn since 1968 (Hinesly et ai, 1974). The
maximum loading rate of sludge was 1 inch (2.54 cm) of
liquid containing 2 to 4% solids applied by furrow
irrigation as often as weather conditions and available
labor permit. Lesser amounts of sludge were applied on
1/2 and 1/4 maximum treated plots on the same day
sludge was applied on the maximum treated plots. Each
spring before plowing the control plots received 300
Ib/acre (333 kg/ha) of N and 100 Ib/acre (111 kg/ha) of
P as a broadcast application. All plots received an
application of 100 Ib/A (11 kg/ha) of K each spring
before plowing until 1974 when the K fertilizer applica-
tion was doubled. Limestone has been applied at rates
calculated to maintain the soil pH between values of 6 to
6.5. The four treatments were replicated four times in a
randomized block design.
The amounts of sludge applied each year on maxi-
mum treated plots are shown in Table 5. It may be
noted that sludge solids contents varied from slightly less
than 2 to almost 4% by weight. Such a variation in
sludge solids content contributes to a variation in annual
applications of solids which has varied from a low of
11.4 tons/acre (25.6 mT/ha) in the wet growing season
of 1972 to a high of 57.2 tons/acre (128.4 mT/ha) in the
relatively dry growing and harvesting season of 1971.
Corn grain yields in response to sludge applications
are shown in Table 6. Grain yields were significantly
increased (1% level) by sludge treatments over those
obtained from heavily fertilized control plots in only
1970 and 1973, when total applied sludge solids on
maximum treated plots amounted to 118 and 139
ton/acre (52.7 and 62.2 mT/ha) in each of the respective
years. Although yield increases with increasing sludge
applications have been highly significant in only two of
the six years, it was noteworthy that the sludge
applications at the high rates used never resulted in a
yield decrease on the poorly drained Blount silt loam
soil where pH conditions have not always been
optimum.
Since 1969 a similar experiment has been conducted
with digested sludge on the Blount silt loam using
soybeans (Hinesly, et al, 1974). Soybean yield responses
were compared with respect to applications of phos-
phorus 105 Ibs/A/yr. (118 kg/ha/yr.), water and sludge
applied at the rates shown in Table 7. Yields responses
of soybeans to sludge, phosphate and water treatments
are shown in Table 8.
122
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TABLE 4
Corn yields from 1968 through 1973 for the Hanover Park experimental
com p;.-,•;; v.'i.itij have received liquid sludge froni 1968 tnrocqh 1973.
Weekly
Application
Rate
mm
Check
6
12
Total Sludge
Applied
1968-1973
Metric ions/ho
of solids
0
116
182
Year
1968
1969
1970
1971
1972
1973
Corn - Yield
mectric tons/ha at 15.5% moisture
2.07
3.95
4.01
2.57
8.72
8.91
1.51
2.89
2.95
3.45
5.33
6.08
0.69
4.33
4.95
1.82
4.89
6.21
I'/MM.ii
Tofn! iansin-.on animal upplicTfions of digested iludge by
f'jrfov; irrissition during and following corn growing season.
M ax iHI urn rate per application wus 25.4 mm. Appropriately
lesser amounts were applied 0-1 the same day on 0.25-
ar.j 0.5-na7,inuir, treatsd plot* (Unpublished Dnta, Hinesly, ef al).
Year
1968
1969
1970
1971
1972
1973
Liquid Sludge
ram
171.45
254.00
228.60
254.00
127.00S/
127.00
279.40
Average
Solicls Content
percent
3.01
1.91
2.31
3.99
2.16
2.02
2.23
Annual
Sludqo Solids
lit/Sin (T/A)
51.52 (23)
48.31 (21.5)
52.67 (23.5)
100.97 (45)
27.40 (12.2)
25.61 (11.4)
62.15 (27.7)
Accumulative
Sludqe Solids
Ht/lia (T/A)
51.52 (23)
99.33 (44.5)
152.50 (68)
253.47 (113)
280.87 (125)
306.48 (136.7)
368.63 (164.4)
Applied after corn harvest.
THI METROPOLITAN SANITARY DISTRICT
OF OREATIR CHICAGO
ENGINEERING DEPARTMENT
D.F.M.4W.B. MARCH 1975
123
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TABLE 6
Continuous corn groin yields during 6 years with various
rcics of digested sbdge irrigation on Bloont silt loam
(Unpublished Data, Ilinesly, at cl).
Year
1968
1969
1970 "
1971
1972
1973 "
Average
RoJo of Application
0
1/4 tlax
1/2 Max
Max
Metric tons per hectare
4.16
8.96
5.53
6.06
8.94
4.00
6.28
6.03
9.34
7.48
6.50
8.62
6.05
7.34
7.16
9.42
7.62
6.92
8.99
6.72
7.81
7.02
9.44
8.63
7.88
8.82
7.63
8.24
•Tuitmtnl illtcls itt ligaiiicint it 1 pirctnl l*vtl.
ISO In 1970 ind 1973 it 1 84. in* 1 8S Ml/ha,
TABLE 7
Total maximum annual applications of digested sludge by furrow irrigation during and
following soybean growing season. Maximum rate per application was 25.4 mm.
Appropriately lesser amounts were applied on the same days on 0.25- and 0.5-maximum
treated plots (Unpublished Data, Hinesly , et al).
Year
1969
1970
1971
1972
1973
Liquid Sludge
mm
203.2
228.6
254.0
76.21/
25-;4
50.8.1L/
Average
Solids Content
percent
2.11
2.60
4.31
3.38
1.90
2.70
Annual
Sludge Solids
Mt/ha (I/A)
42.76 (19)
59.28 (26)
109.19 (49)
25.69 (11)
4.81 (21)
13.68 (6.1)
Accumulative
Sludge Solids
Mt/ha (T/A)
--
102.4 (45.7)
236.92 (105.7)
241.73 (107.8)
255.41 (113.9)
tf Applied I lief »*ybtan harvtst
fc/ Applied on r-tmtnttt plots only liter s«ybun hanrtst
THI METROPOLITAN SANITARY DISTRICT
Of GREATER CHICAGO
ENGINEERING DEPARTMENT
R.J.O.ftW.B. MARCH 197S
124
-------
Soybean yields in Table 8 when analyzed statistically
by analysis of variance were shown to have been
increased significantly by sludge application during each
of the five years. However, in 1972, the response to
maximum sludge treatments was negative. Annual appli-
cations of superphosphate did not affect soybean yields
even though the site soil, a silt loam was somewhat
deficient in available phosphorus. In 1972 when sludge
applications had a significant negative affect on soybean
yields, the plant toxicity symptoms observed may be
attributed to phosphorus toxicity, a soil-plant salt
interaction or both.
The phosphorus or salt interaction observed between
soybeans and sludge reinforce the need for careful
selection of the sludge application rates used. However,
application of sludge to agricultural soils at rates based
on yearly nitrogen requirement of crops and a total
application rate based on sludge phosphorus levels would
prevent such interactions.
Metal Translocation
Of concern is metal uptake by crops from soils
receiving sewage sludge. Paris, Berlin and Melbourne
have operated "sewage farms" to dispose of sewage and
sludge for several decades. Rohde (1962), however, has
claimed that soils at the sewage farms operated by Paris
and Berlin have become exhausted due to high accumu-
lated levels of Zn and Cu. Leeper (1972) reviewed
Rohde's work and that of Troone, et al. (1950) who
reported on Mn deficiency in vegetables at the Paris farm
and reinterpreted their data. According to Leeper, the
problem at the Paris farm was not Zn and Cu phyto-
toxicity, but rather Zn deficiency which Troone, et al
(1950) reported had occurred around Paiis before 1925.
Melbourne has operated a sewage from since 1897 at
Werribee, Australia. Johnson, et al. (1974) analyzed
tissue from selected sites on the farm and they con-
cluded that in regard to food chain effects, forage
contained neither excessive nor deficient amounts of
trace elements. These results are very significant for
helping to determine the long-term effects of sludge
application to land.
The Agronomy Department of the University of
Illinois has been conducting for 7 years experiments to
evaluate the environmental effects of sludge application
to land as mentioned previously. Metal uptake by
agronomic plants in these experiments has been studied.
Table 9 shows the element concentration in the tissues
of mature corn receiving sludge at the rate described in
Table 5.
The Zn and Cd contents in com leaf, grain, and
mature plant residues were increased by greater annual
applications of sludge. However, metal concentrations in
corn plant tissues were not elevated by increasing years
of sludge application at the high rates used in this
experiment. Concentration levels of Zn and Cd reached a
fairly constant value in corn plant tissue and these levels
were not changed by increasing accumulative amounts of
sludge applied in subsequent years. With respect to Cu
and Ni concentrations in the corn plant tissue, these
levels were not changed by increasing accumulative
amounts of sludge applied in subsequent years. With
respect to Cu and Ni concentrations in the corn plant
tissues, there was in some years little apparent relation-
ship with the amount of sludge applied. For example, in
1971, the Cu levels in corn grain were significantly
reduced by increasingly greater application rates of
digested sludge. There is evidence that the Cd, Cu, Ni
and Zn levels in tissue do not reflect the accumulative
amounts of digested sludge applied during the experi-
ment.
Table 10 shows the element concentration in the
tissue of soybeans receiving sludge at the rate described
in Table 7. An examination of the data shows that Zn,
Ni, and Cd contents of soybean tissues were increased by
different sludge application rates. Compared to the
amounts in plants from control plots, the Cu concentra-
tion in plant tissues either remained the same or
decreased. The greatest increase in metal concentration
occurred in 1972 when the phosphorus or salt inter-
action occurred. With respect to the treatments the data
suggest that plant metal levels remain nearly the same
each year and they do not reflect the accumulative
yearly applications of sewage sludge.
The corn and soybean data presented in Tables 9 and
10 show that under the local soil, climatic and experi-
mental conditions during the seven year study
(1968 - 1974) that no phytotoxic conditions or ab-
normal metal concentrations resulted from heavy metal
translocation in a Blount silt soil receiving up to 164
tons/acre (369 mT/ha) of sludge on continuous corn and
up to 114 tons/acre (255 mT/ha) on continuous
soybeans. However, it must be noted that each sludge
application system is unique, containing specific condi-
tions and characteristics, and because of this, crop
response with respect to yield and element contents
should be periodically evaluated.
ANIMAL RESPONSES
An excellent use of the fertilizer value of municipal
sludges is the application to pasture land. Excellent
stands of forage crops can be produced from the
nutrient and water content of municipal sludge.
125
-------
TABLii 8
Soyl'ean yiald responses to phosphorus, sladge and water
applications (Unpublished data, Ilinesly, et al).
Yeur
1969
1970
1971
1972
1973
p
Ka/ha
0
118
0
118
0
118
0
118
0
118
0 mm
2.28
2.53
1.93
1.89
1.77
1.53
2.04
2.27
1.68
1.49
Rate of Slat!
6.4 ram
Yield (I
3.02
3.00
2.76
2.57
1.93
1.87
2.55
2.65
1.90
1.64
98 Agitation
12.7 mm
Ac trie ton per
3.24
3.16
2.98
2.84
2.10
2.08
2.31
2.84
2.00
2.08
25.0 mm
hectare)
3.36
3.50
2.84
3.19
2.13
2.12
0.93
0.21
2.11
1.97
Y/oter-
2.92
3.48
2.57
2.59
1.50
.74
.64
.98
.10
.22
W*l
i 1972
i
i 1973
4.9
6.6
8.9
7.5
—
5.9
8.4
6.6
5.7
6.6
8.6
7.5
—
6.7
4.1
5.9
3.0 9.0
7.8
6.3
13.1 14.0 14.9
10.8
13.0
11.4
10.7
13.0 12.0
14.0 14.0
13.0
12.5 12.2
9.6
9.5
13.0 : 14.0
11.0 14.0
' NICKEL ppm
| 1970
! 1971
j 1972
! 1973
3.5
2.7
3.0
3.A
_
3.0
2.0
3.7
4.7
4.5
5.1
4.5
..
5.2
6.3
6.3
4.3
5.5
10.9
5.4
6.1
7.4
4.2
5.3
10.1
11.7
6.5
8.6
9.4
13.4
9.9
8.4
10.5 10.5
15.7
10.2
17.8
16.5
9.9 10.6
' " CADUIIKJ onm
S 1970
1971
1972
1973
0.'.2
0.26
0.53
0.5C'
—
O.cO
0.54
1.70
0.90
2.14
0.^7 1.10
—
3.16
4.46
2.00
10.3
7.0
13.9
4.2
0.12
0.35
0.19
0.20
0.12 0.3S
0.33
0.35
0.25
0.47
0.55
0.60 1.08
0.96
1.61
1.00 3.06
0.36 ! 0.59 ! 0.79
126
-------
TABLE 9
Average contents of several chemical elements in tissues of corn continuously
grown and annually fertilized with various loading rates of digested sludge.
Values are ppm dry weight of plant tissues (Unpublished Data, Hinesly, et al).
Year
lefif
I'.r.
'.i Max
Grain
.V..i«; MDI Ci, ; MJ< .: MJX. MJ»
Mature Plant Residues
u
i MJX /: r..n
Ma>
liUC pun
1970
1971
1972
1973
53
28
56
60
85
95
139
113
123; 212
15SJ 259"
253! 381"
223 1328- '
32 i 40 > 50 I 65
24 i 36 i 36 | 53"
22 i 29 i 40 | 50"
29 ! 37 i 51 ! 58"
43
39
133
94
237
193
340"
337"
CO;JPtS p?m
1970
1971
1972
1973
8.9
10.4
12.4
7.4
9.0
9.2
13.6
7.3
10.2 j 8.7
9.51 5.6
14.3115.4'
6.6! 7.2
2.5 i 3.6 i 2.9 1 4.2
2.4 ! 2.6 i 2.2 • 2.0 '
2.8 1 3.0 j 2.9 i 3.1
2.4 i 2.6 ! 2.6 2.0
10.0
2.3
8.2
2.3
8.5
2.7
7.8
3.0
M!C!'£Lppni
1970
1972
1973
1.5
1.5
3.5
1.1
1.9
1.5
2.9
2.6: 4.3
2.3! 2.6
1.9! 2.4"
1.7! 3.0
2.3 i 3.0; 2.2 ; 3.1
O.S i O.G- 1.2 ! 3.5"
0.6 iO.8 j 1.3 2.2"
1.2! 0.9: 1.3 1.7
1.4
0.7
1.2
0.7
1.6
0.7
2.0
1.4'
CARi.4!(JM ppm
1970
1971
1972
1973
0.9
0.2
1.1
04
3.0
;3.4
9.0
7.3
5.3; 11.6
7.5 10.3"
6'.9* UJ-
0.300.600.79 1.00"
0.14 0.700.65 0.92"
0.14 0.45 0.83 1.10"
0.080.15 0.35 0.61"
0.4
03
4.8
0 8
8.9
4?
13.2"
12.9"
IftOiJ Dcra
1970
1971
1972
1973
* ') •'
i \ i
i ' '
15;
156
34
,93
iia
Ui 1 112
95 90
154 i 144
12^ i 118
! 1 I
36 ! 33 i 34 ; 36
19 ' 16 : 20 19
30 i 30 j 32 35
211
90
231
99
286
82
166
61
uA'JGAlicSE P?ro
1970
1?7T
19/2
1973
cr.
c-i
6;
•' S3
57
60
40
| 92 i 116 '
! 79; 151 "
] 126! 130"
! «l 54"
5.0' 6.0 ! 5.5 8.2"
3.4 2.4 3.1 4.6"
8.2 6.8 6.3 6.6"
35
29
38
31
47
38
72'
! 36
" Sigr.ificani al £?> Icvpl.
" Sisiuific«iiit 81 I7i lev*:.
ISD's:
leaf
Gftin
Plant Residues
ZliK
1970= 82
1971= 42
1972=136
1973= 77
1971 = 10
1972= 13
1973= 6
1972= 72
1973= 60
COPPER
1970= n.s.
1971= n.s.
1972= 1.3
1973= n.s.
1970 =
1971 =0.4
1972= n.s.
1973= n.s.
1972= n.s.
1973= n.s.
UICKEL
1970=
1971= n.s.
1972= 0.7
1973= n.s.
1970= n.s.
1971 =
1972= 0.4
1973= 0.4
1972= M.S.
1973=0.6
leaf
Grain
Plant Residues
CADMIUM
1970= 6.6
1971= 4.2
1972= 7.4
1973= 5.8
1970 = 0.20
1971=0.40
1972 = 0.5?
1973 = 0.06
IRON
1970 =n.s.
1971 =n.s.
1972 =n.s.
1973= n.s.
1970 =
1971 = n.s.
1972= n.s.
1973= n.s.
1972= n.s.
1973= n.s.
MANGANESE
1970= 22
1971= 36
1972= 76
1973= 14
1970 =
1971 = 2.1
1972= 0.8
1973= 0.9
1972= 23
1973= n.s.
n.s.- not significant
127
-------
In experiments performed by Fitzgerald and Jolly
(1974), where Sudax grass was fertilized by means of the
spray application of liquid digested sludge from the
Metropolitan Sanitary District of Greater Chicago, it was
found that such grass contained 7.85% to 23.01%
protein, 20.67% to 27.95% fiber, 0.42 to .57% calcium,
0.25% to 0.44% potassium, 0.01% to 1.21% nitrate, and
was negative for cyanide and arsenic. Dehydrated
sorghum-sudan grass was found by Schneider (1974) to
average 15.3% crude protein, 9.7% digestible crude
protein, 19.4% crude fiber and 58.6% total digestible
nutrient. Sudax is a sorghum - sundangrass hybrid, and
the quality of sludge fertilized Sudax compared favor-
ably with that tested by Schneider. Fitzgerald concluded
that sludge fertilized forage contained a sufficiency of
those elements known or believed to be essential to
animal nutrition.
Clearly, if municipal sludge is a satisfactory fertilizer
for many crops, it should be useful in fertilizing forages.
The Fitzgerald study confirms this basic premise.
Of concern to some individuals regarding the use of
sludge fertilized forage for animal feed is the possibility
of problems with animal health. Naturally, the grazing
animals will have direct contact with the sludge while
they are grazing. This is not to say that grazing animals
should come into contact with municipal sludge immedi-
ately following application. On the contrary, it is
advisable to allow an 8 to 10 day resting period
following sludge application to pastureland or alterna-
tively that the applied sludge be allowed to dry before
resuming grasing.
The Board of Works Sewage Farm at Werribee,
Australia was established in 1897 as a sewage farm
serving the City of Melbourne, Australia which has a
population of about 2.5 million people (Johnson et al.,
1974). The daily amounts of raw sewage arriving at the
farm vary but the average flow in 1973 was 144 MGD
(546,000 m3/day). This farm is about 10,376 acres
(4,200 ha) and is a raw sewage irrigated pastureland. The
irrigated pastures are sown with a mixture of grasses and
legumes to provide balanced production. Raw sewage is
applied in a flood irrigation method to a depth of
4 inches (10mm). Just before irrigation, the grasing
animals are removed and the surface is allowed to dry
one week before they are returned.
Despite the fact that the pasture is irrigated with
essentially raw sewage, the health of the animals bred at
the farm is excellent and there is no prohibition of the
sale of the animals for human consumption. Between
July 1946 and June 1972, out of a total of 116,266
animals marketed there were only 29 rejections or
0.025%. In an Australian area where pastureland is used
with no sewage products, namely, Victoria and
Tasmania, a rejection rate of .041% was recorded based
on examination of 506,625 animals and 208 rejections.
Clearly, the Australian data indicates that if there is
no difficulty in the rejection rate of animals foraging on
pastures fertilized with raw sewage, one can conclude
that there should be no difficulty with the use of
digested sewage sludge.
Fitzgerald and Jolly (1974) studied the possibility of
transmission of parasitic organisms from digested sludges
sprinkled on Sudax grass to cow& and/or calves. In this
study, 91 pregnant Hereford-Angus-Charolais cows
were released on municipal sludge fertilized Sudax
pasture. The sludge being liquid digested sludge from the
Metropolitan Sanitary District of Greater Chicago. A
control herd of 19 pregnant cows were pastured on
Sudax in a land area not receiving digested sludge.
At monthly or shorter intervals fresh individual or
random fecal samples were examined to determine the
species and relative abundance of parasites of each herd.
In addition frequent visual observations of the animals
were made. A comparison was made of the parasite
species present, egg and oocyst discharge quantity, and
visual clinical signs between the 2 groups of animals to
determine the effects of sludge on the health related
factors in the pasture environment.
After the examination of 614 fecal samples from the
cattle foraging on the sludge fertilized pasture and 255
samples from the control herd, it was found that there
was no significant difference between the two groups. In
Figure VI is plotted the nematode egg discharge during
14 months of the study. Generally, the test and control
herds followed a similar pattern with levels of nematodes
remarkably similar. The average discharge of coccidian
oocysts seen in Figure VII was actually higher in the
control than the test animals over a 14-month period.
Fitzgerald and Jolly (1974) concluded from this
study that sludge irrigation had not introduced unusual
or additional common bovine pathogens to the pasture
environment, nor otherwise increased the incidence of
common bovine disease. Digested sludge in the pasture
environment had not influenced the normal parasitic
load of the herd.
The available evidence indicates that the use of
municipal sludge as a fertilizer for pastureland is a
practice without hazard to the health of the grazing
animals. There is no available evidence to suggest that
the health of grazing cattle would be affected. It would
appear that many countries in the world would wish to
pursue the use of municipal sludge in growing forages for
cattle production. As the demand for meat increases
among the nations of the world, and with the increasing
problems of obtaining fuel for producing sufficient
nitrogen fertilizer, it would seem that municipal sludges
128
-------
800
200-
150-
a
O.
£
JOO
U
50-
FIGURE 30;
Somple data ova per gram of feces per animal based on
random or individual monthly field samples
(Unpublished data , Fitzgerald,et al).
/~
Test Cattle
0-1
N. / *
/ \ /
' A»g. S«?
' \ 1 \
IX / .'
l\ / J
\^\/x
-------
FIGURE 3ZH
Cumulative total coccldian oocysts per gram of feces
per animal based on random or individual monthly
field samples (Unpublished Data, Fitzgerald,et al).
2500--
2000 t
o
a
o
a.
0?
&.
iO
*-
10
5K
O
o
O
1500
1000-
500
Control Animals
Tent Animals
A tig S«p OcJ Mov Dec Jan F«b ' Mar Apr Moy Jun ' Juf Aug u
1973
1974
THE KETROPOUTAN SANITARY DISTRIC
OF GREATER CHICAGO
ENGINEERING DE
130
MAR. 1975
-------
would be a useful product in increasing the productivity
of the pastureland.
ENVIRONMENTAL MONITORING OF
SLUDGE APPLICATION TO LAND
As noted previously, the land application of sewage
sludge is practiced successfully in the United States and
many countries throughout the world. Cities such as
Melbourne has operated "sewage farms" to dispose of
sewage for many decades. Even though sludge is benefi-
cial as a fertilizer and soil amendment, its application to
land must not result in significant degradation of local
waters and the soil ecosystem.
The term monitoring as defined by Blakeslee (1973)
means observing, the performance of the system, check-
ing the quality of affected natural systems such as
surface and groundwaters and evaluating environmental
impacts as quality changes occur. In short, the informa-
tion obtained from monitoring should be consistent with
the changes expected or predicted to occur during the
design of a land application system.
The type of monitoring program employed depends
to a great extent on the size and purpose of the project.
Large scale land application systems would require
extensive monitoring of the environmental components
at a high frequency, while small scale projects would
require less extensive monitoring at less frequent inter-
vals. However, all projects need to assess the quality of
sludge applied and the impact of sludge on the quality of
surface and groundwaters and on the soil plant system at
some prescribed frequency.
In any sludge application system, the quality of
surface and groundwater needs to be assessed before,
during and after sludge applications. Guidelines and
suggestions for water monitoring of land application
systems in the United States are available from the
Environmental Protection Agency and from state regula-
tory agencies.
As mentioned earlier, the District is currently recy-
cling sewage sludge on approximately 15,000 acres
(6.075 ha) of calcareous strip-mined land in West Central
Illinois. A comprehensive environmental monitoring
system was developed in 1971 and is being used to
continuously evaluate the surface and groundwater
quality at the site. The District started collecting water
quality data from 1971 to the present at monthly
intervals. This included sampling of major streams
entering and leaving the property and strip-mined
reservoirs. It should be noted that this is a large scale
project and that smaller projects would require less
extensive monitoring.
The chemical-physical-biological quality of surface
waters streams and strip-mine reservoirs at the District's
Fulton County, Illinois land reclamation site is moni-
tored on a monthly basis for the 24 chemical characteris-
tics shown in Table 11. In addition to fecal coliform
counts determined in each stream and surface water
body monitored, enteric virus levels are also measured
on a monthly basis on major streams entering and
leaving the property.
In addition, each agricultural field is bermed and
drained into a field runoff basin to prevent direct runoff
into the local waterways. These basins are designed to
capture and contain from the adjacent field receiving
sewage sludge. The basins are designed to capture runoff
from an equivalent 100-year storm in the region. Any
possible contamination in the field runoff water result-
ing from sewage solids applied to the field are also
captured and contained by these basins.
Samples from the field runoff basins are analyzed to
determine the percent suspended solids, biological oxy-
gen demand and fecal coliform concentrations of their
content. If the concentrations of these water quality
parameters are within acceptable limits set by the Illinois
Environmental Protection Agency, the contents of the
field runoff basins are discharged to the receiving stream.
If the concentrations are not acceptable, the contents of
the field runoff retention basin may be held until
sufficient reduction of the offending constituent is
attained or, at the discretion of the project manager,
may be pumped back on to the field serviced by the
field runoff basin in question. Good soil conservation
practices on the application fields are essential in
reducing field runoff problems and maintaining the
water quality requirements of field runoff basins needed
for release. Groundwater monitoring is also an important
part of a monitoring system on lands receiving sewage
sludge. Groundwater monitoring wells or periodic deep
soil corings are used to monitor groundwater quality.
Blakeslee (1973) indicates that monitoring wells must be
designed and located to meet the specific geologic and
hydrological conditions at each site. Groundwater
quality should be monitored in the upper most water
table near the application site. Consideration must be
given to the following:
1. Geological soil and rock formations existing at the
specific site.
2. Depth to an impervious layer.
3. Direction of flow groundwater and anticipated
rate of movement.
4. Depth to seasonal high water table and an indica-
tion of seasonal variations in groundwater depth
and direction of movement.
Eu-rircnmentsl Protection Agency
131 Lferary Room 2404
40-i !Vi "Street, SW, VV3M PM-213
Wellington, D.C. 2046Q
-------
MONITORING WELL AT LAND RECLAMATION SITE
FULTON COUNTY, ILLINOIS
FIGURE SHI
Lock— 2^.,
Electrical Control— ^.
4'-0"x4'-0" Concrete Pad-
!
i
To
o
c
o
1
1
o
1
rjf
tiif
. — *•
?
!•>-« • /»
u- .... i i ^ — W«ll Covar
»
1
<
Pfpo Contoring
Device ^-^r
Sfolrtes-i Screen ^i
'
J=M"
4 f
c
• |
<
«
«
•*
••i
>*r
i
!•» •-
!'.« '•
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•It u.
H
A
U^ ... — — Glnha V/nlvn
/®'° Airline
1Q, Well Seal
.! v* 9 .*•;*•„•-,
*
A
'r
*
4
*»
1 r—
• *"i
• j «•
-1 .B
* "f •'
.'.' ••
»*" •
*l
/i!S
^:.:
^-Concrete
\*^
^--Bleeder
« 77^*
a
HI
l" Discharge t5
.^ Pipe £
CO
V
^
Nipple
i
£
C
S
^-Gravel
*"*'
9
4D
to
Q.
E
O.
_S~Pump
ej- Stainless Screen
Washout Nozzle
132
-------
5. Nature, extent, and consequences of mounding of
groundwater which can be anticipated to occur
above the naturally occurring water table.
6. Location of nearby streams and swamps.
7. Potable and nonpotable water supply wells.
8. Other data as appropriate to the specific system
design.
Again, it should be emphasized that the extent of the
groundwater monitoring system is related to size and
nature of the land application site.
The District has an extensive groundwater monitoring
system at its strip-mine reclamation area in West Central
Illinois. Part of the environmental protection system
established at the site in 1971 is 25 groundwater
monitoring wells situated on both nondisturbed and
strip-mined areas. These wells were used to determine
base line levels of 24 physical-chemical-biological charac-
teristics (Table 11) prior to applications of digested
sewage sludge. The groundwater monitoring wells are
sampled monthly. Three of these wells are municipal
water supplies for the three adjacent towns of St. David
(15m deep), Bryant (488m deep) and Cuba (488m
deep), Illinois, respectively.
The District's monitoring wells were drilled with
hollow auger drills to rejection at the shale layer
underlying the coal seam and currently beneath the mine
spoil area, typically 35 - 70 ft. (10.7-21m) below
surface datum. Figure VIII illustrates the typical well
construction for these monitoring wells note that the
poured concrete surface pad and continuous concrete
grouting around the 4 inch (10cm) black iron well
casing insure sealing of the well from surface water
infiltration and contamination.
The frequency and the type of sampling for surface
and groundwaters as suggested by Blakeslee (1973) is
listed below. Note that the District at its strip-mine
reclamation site has exceeded Blakeslee suggestions.
Background water quality. A minimum of three
monthly samples should be collected from each
monitoring well prior to placing the storage or
disposal facility in operation. In cases where back-
ground water quality adjacent to the site may be
influenced by prior waste applications, provision of
monitoring wells or analysis of water quality from
existing wells in the same aquifer beyond the area of
influence will be necessary.
Operating Schedule. Samples should be collected
monthly during the first two years of operation.
After the accumulation of a minimum of two years of
groundwater monitoring information, modification of
the frequency of sampling may be considered.
Sample Analysis
Water samples collected for background water quality
should be analyzed for the following: (Note: Param-
eters for groundwater monitoring at industrial waste
disposal sites must be established on an individual basis
depending on the composition of the wastes applied).
1. Chloride
2. Specific Conductance
3. pH
4. Total hardness
5. Alkalinity
6. (a) Ammonia nitrogen
(b) Nitrate nitrogen
(c) Nitrite nitrogen
7. Total phosphorus
8. Methylene blue active substances
9. Chemical oxygen demand
10. Any heavy metals or toxic substances found in
the applied wastes.
After adequate background water quality information
has been obtained, a minimum of one sample per year,
obtained at the end of the irrigation season in the case of
seasonal operations, should be collected from each well
and analyzed for the above constituents.
All other water samples collected in accordance with
the operating schedule should be analyzed for chlorides
and specific conductance as indicators of changes in
groundwater quality resulting from the sludge applied. If
significant changes are noted in chloride and/or specific
conductance levels, samples should immediately be
analyzed for the other parameters listed above to
determine the extent of water quality deviation from
background levels.
Soil and Vegetation
In any land application program a systematic sam-
pling of soil and vegetation is desirable. The objective of
monitoring for soils and plants is to evaluate and prevent
the possible buildup of compounds added to the soils
which may result in plant toxicity and human food
chain accumulation. Of particular concern are the so
called heavy metals in sewage sludges.
A review of the possible fate and effects of trace
elements in sewage sludge when applied to agricultural
lands has been made by Leeper (1972) and Page (1974).
A discussion of soil-plant relationships as related to
applications of municipal sludge on land is given by
Melsted (1973). Heavy metals of major concern in soil
monitoring considered to be a potential hazard to plants
133
-------
or the food chain are: B, Cd, Cr, Cu, Hg, Ni, Pb and Zn.
Of these Cu, Ni and Zn are considered by many
researchers (Berrow and Webber, 1972; Leeper, 1972;
and Page, 1973) to have the greatest potential to cause
phytotoxkity to plants.
It should be noted, that District field research data
with corn and soybeans from 1968 to date indicates that
if sewage sludge is applied to soils at an annual rate
consistent with the yearly nitrogen requirements of the
crop, and if sludge is applied at a total accumulative rate
based on the sludge phosphorus levels then heavy metals
problems in the food chain and plant phytotoxicity will
not occur.
In monitoring the effects of applying municipal
sludges on the soil two approaches are possible, or they
can be used together. Melsted (1973) indicates that one
approach is to make a systematic soil analysis and the
other is to make a systematic plant analysis. Soil analysis
require that the analytical values be correlated to plant
composition so that dependable predictions of plant
composition can be made. Plant analysis requires that
the normal composition and upper tolerance level be
known and set for an indicator plant or the crop grown
at the land application site. Typical ranges in soil metal
composition is given by Bowen (1966) and Swaine
(19SS). Melsted (1973) in Table 12 shows the probable
available form, average composition range for selected
agronomic crops and suggested tolerance level of heavy
metals in agronomic crops. In any land application
system, evaluation of the heavy metal content of soils
and/or plants before sludge application is essential to
evaluate future buildup of metal levels.
To determine the effect of sludge application on land,
the District at its Hanover Park, Illinois research farm
and its 15,000 acre (5,075 ha) mine-spoil reclamation
site conducts yearly sampling of soils and crops. As an
example, the metal content of com leaves grown in 1972
and grain grown in 1972 and 1973 at the Fulton
County, Illinois land reclamation site is presented in
Table 13. The summaries are grouped by non-sludged
and sludge fertilized fields. The metal and organic
carbon content of spoil banks and place lands at the
reclamation site are presented in Tabble 14.
It should be noted that if sludge is applied to lands
growing crops not in the human food chain trace
element uptake would not be a significant consideration.
In the case of cotton or trees for example, there would
be little need to monitor the metal contents of these
plants since the crop grown is not ingested directly or
indirectly by humans.
The extent of soil and crop monitoring depends upon
the type and scale of a land application system. For
small land areas receiving sludge as a fertilizer the
Ontario, Canada Ministry of the Environment (1973)
suggests periodic soil sampling to measure soil pH for
possible liming and P, K, Mg, and Ca. Plant analysis of
each crop on annual basis should be considered for N, P,
K, Ca, Mg, Mn, Fe, Zn, Cu, and B. The sludge used
should be analyzed at least every three months for total
solids, volatile solids, pH, N, P, K, either extractables
and heavy metals.
Public Health Aspects
In any operation where municipal sludge is applied to
the land, there will be public concern regarding the
possibility of disease transmission to the surrounding
populace. Although no exhaustive epidemiological study
has been done on a municipal sludge application project,
there exists much peripheral information which indicates
that such public health problems are not significant.
Naturally, in the spreading or application of sludge to
land, one must expect that aerosols will be generated.
Agitation by the wind and/or application equipment is
inevitable.
Studies by (Ledbetter et al., 1972; Ledbetter, 1973)
indicated that workers at sewage treatment plants had
no more incidence of respiratory diseases than similar
workers at other sites. Absenteeism among sewage plant
workers was found to be lower than among all other
occupational groups studied by Melnick (McLean,
1967).
The above three references indicate that although
sewage plant workers are exposed to aerosols from
activated sludge aeration tanks which contain only
partially treated sewage, they are not subject to higher
disease incidence than among other industrial groups. It
should be remembered that sewage plant workers are in
very close proximity to such aeration tanks, while in a
sludge application operation, local inhabitants would be
located at much greater distances and would not be
exposed to or be in contact with the application
operations. It may therefore be concluded that aerosol
disease transmission from municipal sludge application is
not a significant consideration.
There is other indirect evidence to suggest that
disease transmission is not a significant problem with
municipal sludge application sites.
It is a well known fact that anaerobic municipal
sludge digestion is a highly effective process in coliform
reduction. This is in fact, one of the benefits of such
digestion which is pointed out in such standard text-
books as Fair and Geyer's (1963) Elements of Water
Supply and Wastewater Disposal. Clearly, anaerobic
digestion reduces the pathogens present in sludge as
indicated by the coliform reduction. Normally, coliform
134
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TABLE 11
The diemical-physical-biclogical- characteristics
measured in surface and ground waters at the
Fulton County Land Reclamation site.
N-Kjeldahl
N-HH3
Total P mg/l
CF mg/l
mg/l
mg/l
mg/l
»g/l
Alk as CaCOj rag/I
Conductivity yumhos/cm
K mg/l
Ma , mg/l
Ca mg/l
Mg mg/l
MDf
0.01
1.0
1.0
1.0
0.1
0.01
1.0
1.0
1.0
1.0
1.0
Zn
Cd
Cu
Cr
Ni
Mn
Pb
Fe
Al
Se
Hg
Fecal
mg/l
mg/l
mg/l
mg/l
mg/l
mg/l
mg/l
»g/l
mg/l
«g/i
/•9/I
Coliform
per 100 ml
MDf
0.1
0.01
0.01
0.02
0.1
0.01
0.03
0.1
1.0
0.1
•
0.1
2
" Minimum detection limi; 01 iaJornory
JVT vitas less thin these arc ;cported ai zero.
TAIiLt 12
The Probe
and
Borivrn
Cadnivia
Cobiilt
(inner
Iron
Hcnqanese
Mercury
lithium
llitkcl
Lead
Strontium
Zinc
iblc Aroilable Form, the Average Composition Range for Selected Agronomic Croci,
the Authors Soqgcsted Tolerance Level of Heavy Metals In Agronomic Crops
When Used for Monitoring Purposes (Melsled, 1973).
Probable
Available
Form
Do*4
Cd'4
Co'4
Cu*4
Fe*4
tin44
rig**
li*4
Ni**
Pb*4
Sr*4
Zn*4
.Common
Average
Composition
Range' ppm
Cations
10-100
0.05-0.20
0.01-0.30
3-40
20-300
15-150
0.001-0.01
0.2-1.0
0.1-1.0
0.1-5.0
10-30
15-150
Suggested
Tolerance
level"
ppm
200
3
5
150
750
300
0.04
5
3
10
50
300
Arsenic
Dtron
Chromium
fluorine
Iodine
Molybdenum
Selenium
Yanadiuki
Probable
Available
Form
AsO«"
HBOV-
Cr04—
r
Se04—
Common
Average
Composition
Range' ppm
Anions
0.01-1.0
7-75
0.1-0.5
1-5
0.1-0.5
0.2-1.0
0.05-2.0
0.1-1.0
Suggested
Tolerance
Level"
PDRI
2
150
2
10
1
3
3
2
'Avetege values lor coin, soybeans, .ilbita. led clovei when.
eats, batlev and Brasses mown undei noimal soil conditions
Greenhouse, both soil and so ution. values omitted
"V.iuei nt lor corn leaves at 01 ogaosile and below etr level al tasiel slant
soybeans - ike vomgest naltiu leaves and petioles on the plant adei first pod
fotT.atien. letumes - apper stem atttinas 'f eifly Mower stage, cerdls - the whole
plznt* at boot stage, and grasses - whole plants it eaily hay cutting stage.
THI MtriOrOllTAN SANITARY DISTRICT
OF CRIATIt CHICAGO
INOINEIIINO DIPARTMINT
R.J.O.AW.I. MARCH 1975
135
-------
TABLE 13
METAL CONTENT OF CORN LEAVES AND GRA!M
HARVESTED UN MSOQO LAND IN FULTON COUNTY. IIUI.'OIS
BEFOHE AND AFTER SLUDGE APPLICATION
SAMPLE SOURCE
ANtf YEAR
LEAVES-1972
MOM- SLUDGED
SLUDGE KtRTIUZHD
GRAIN-1972
KON-SLIJOGED
SLUDGE FERTILIZED
GRAjN-1973
N ON- SLUDGED
SUJDGE KERTIUZF.D
K Mg
1.6 0.36
1.6 0.29
0.07 0.16
O.i1 0.15
0.31 0.12
0.52 0.13
Ca
0.61
0.49
0.035
0.025
0.057
0.07
Na
102
216
47
17
30
20
Zn
NA
NA
NA
NA
24
2A
Fe
227
364
46
40
28
25
Mn
-Aig/g
58
50
10.9
9.3
7.2
8.1
Cli
DRY
13.7
27.7
2.3
2.5
3.3
3.4
Ni
WT.-
7.0
6.7
NA
NA
0.8
0.5
Cr
1.7
NA
NA
NA
0.4
0.3
Pb
8.6
NA
NA
NA
0.3
0.3
Cd •
1.3
3.1
-HA
NA
0.4
0.3
IIA MO ANALYSIS
TABLE 14
MHTAIS, EXCHANGEABLE CALCiUM AND ORGANIC CARBON CONTENT OF SPOIL MATERIAL
AM> PLACE LANDS IN FULTOH COUNTY PRIOR TO THE APPLICATION OF DIGESTED SLUDGE
SAMPLES COLLECTED IN THE SPRING OF 1972.
SITE
SAMPLED
SPOILS
MEAM
MINIVUM
MAXIMUM
PLACE LAND
MEAN
MINIMUM
MAXIMUM
Mn
154
70
208
146.1
92.0
258.C
Zn
31.7
11.1
69.4
31.4
10.3
63.7
01 N
Cu
— yg/
•4.79
1.90
19.1
2.62
1.48
3.73
HCI
Cd
'q OF
0.2
0
1.36
o.o a
0
0.68
EXTRACTABLE^
Cr Ni
OVEN DRY SOIL-
V22
0
3.40
1.23
O.30
3.17
6.7
3.2
10.0
7.5
3.2
12.7
Pb
3.52
0
8.50
4.55
2.23
7.94
Al
509
384
620
540
317
741
EXCH
Ca
• %
0.83
0.63
1.12
0.36
0.20
0.72
ORGANIC
CARBON
%
0.61
0.24
1.56
1.64
0.92
4.55
•> THREE SUCCESSIVE S MINUTE EXTRACTIONS OF 1.5 GRAMS SOIL WITH 15 MILLILITERS OF ACID.
THE METh'OPOLIT.UJ SANITARY RI81T1ICT OF GREATER CHICAGO
136
-------
reductions over 99% are reported for anaerobic diges-
tion.
Naturally, virus levels in sludge are of concern to
many in addition to bacteria. Although no definitive
evidence exists regarding the die-away of viruses
"indigenous to digested sludge, there is evidence available
regarding the die-away of viruses seeded into digested
sludge.
The District has conducted two studies designed to
investigate the reduction in virus levels in digested
sludge.
In the first study (Bertucci et al., 1974) the coliphage
or bacterial virus (MS-2) was inoculated into pilot
anaerobic digesters. It was found that between 87.7 to
96.3% of the viruses were inactivated in 24 hours and
between 99.0 and 99.6% in 48 hours of anaerobic
digestion. This data is presented graphically in Figure IX.
In a second study (Bertucci etal., 1973) four Enteric
picornaviruses were inoculated in pilot anaerobic digest-
ers. Figure X presents the die-away curves for the four
viruses studied. After 24 hours of digestion, there was
found to be an average of 94.4%, 99.11%, 90.04% and
60.60% inactivation for poliovirus type 1, coxsackievirus
type A-9, coxsackievirus type B-4, and echovirus type
11, respectively. The respective inactivation after 48
hours were 98.80%, 99.93%, 98.65% and 92.90%.
Laboratory studies regarding the die-away of viruses
was also conducted by Meyer et al., (1971). He used a
swine entervirus (ECPO-1) which has bio-physical prop-
erties similar to human enteric viruses. After gas produc-
tion had stabilized in six laboratory digesters fed with a
mixture of primary and waste activated sludge, they
were inoculated with 10s plague forming units of the
swine virus. After inoculation, 20ml of fluid was
periodically withdrawn from the digesters and mixed
with milk and fed to germfree piglets. The feces of the
piglets were then collected and assayed for viable virus.
The virus was not found in the feces of piglets fed sludge
material which had been inoculated and digested for a
period of time of five days or longer. He concluded that
heated anaerobic digestion for 14 days would provide a
considerable margin of safety with regard to the destruc-
tion of viruses.
One can conclude from these studies that the
anaerobic digestion process is highly effective in reduc-
ing virus levels in sludge. More work is needed on this
aspect of sludge digestion and ultimately the state of the
art will advance so that the quantities and types of
indigenous viruses can be monitored. However, the
available data indicates that concern about virus-caused
diseases is not warranted.
There are many opinions about methods to prevent
possible public health problems at sludge application
sites. Some have even suggested such extraordinary
precautions as liming municipal sludge to pH 11 for 3
hours to destroy all pathogens. While in some European
countries, pasturization of municipal sludge by heating it
to 70°C for 30 minutes has become a widely accepted
practice.
Liming of sludge to pH 11 for 3 hours requires the
addition of over 5000 mg/1 of lime to digested sludge
(MSDGC Report. 1971). This dosage figure is based
upon laboratory experiments whereby digested sludge
(4.2% total solids) was mixed with various amounts of
lime and the resultant pH was recorded. Adding such
quantities of lime to sludge is expensive and significantly
increases the amount of sludge to be disposed of. The
'iming of sludge to pH 11 would add about 12 Ibs. (5.4
kg) of lime to every 100 Ibs. (45 kg) of sludge processed
or would increase the sludge to be disposed of by 12%.
Pasteurization of sludge (30 minutes at 70°C) is
expensive, costing about $20 per dry ton ($18/metric
ton) of solids (Dotson, 1971) and is a source of many
maintenance problems due to scale buildups on heat
exchangers.
It is the opinion of the Metropolitan Sanitary District
of Greater Chicago that anaerobic digestion followed by
sludge storage are adequate methods of controlling
pathogen levels in municipal sludge applied to land.
Sludge storage should be 60 days at 20°C or 120 days at
4°C.
The District has conducted studies regarding the fecal
coliform die-away resulting from the storage of liquid
digested sludge. These studies revealed that, for tempera-
tures averaging about 10°C, fecal coliform in stored
digested sludge was reduced from 800,000 ctns/100 ml
to 20 ctns/100 ml in 33 days.
Table 15 shows the fecal coliform content of stored
digester supernatant (liquid portion of the sludge) over a
period of 41 days. Clearly, the decrease in fecal coliform
content is shown quite dramatically.
Berg (1966) suggested also that long term storage was
the simplest method for reducing viruses and other
pathogen organisms. From laboratory studies, Berg
determined the time in days to achieve 99.9% reduction
in the number of viruses and bacteria by storage of
sewage at different temperatures. The die-away data are
presented in Table 16.
It can be seen that storage of sewage for 120 days at
4°C and 60 days at 20° would be more than adequate in
reducing the viruses and bacteria studied by Berg.
In addition to anaerobic digestion followed by
storage, the District is strongly in favor of controlling
public access to municipal sludge application sites. Such
control is not only desirable from the point of view of
public health^but also safety.
137
-------
TABLE 15
FECAl COllfORH COUNTS OF AN EXPERIMENT
CONDUCTED OF STORED DIGESTER SUPERNATANT EXPOSED TO
ATMOSPHERIC CONDITIONS FROM
OCTOBER 24,
1973 THROUGH NOVEMBER 10, 1973
DAY
SAMPLED
0
1
2
3
4
7
8
9
10
11
14
15
15
17
FECAL confer.;.; COUNTS
(per 100 niilMitsr)
800,000
9,000 "
20,000
8,000
6,000
8,000
16,000
6,000
8,000
4,000
6,000
2,000
3,000
4,000
DAY
SAMPLED
13
21
22
24
27
28
29
30
31
34
35
36
38
41
FECAL COUFORM COUK'S
her ICO milliliter)
2,000
<2,000
<2,000
200
500
100
300
130
240
<20
<20
<20
<20
<20
* F.C. count jusl prior tc lagoanmg.
** F.C. coont aher Ligoening.
TABLE 16
Effjrfs of storoge: Laboratory study demonstrating days required
for 99.9% redaction of virases and bacteria IB sewage (Berg, 1966).
Organism
Polioviras 1
Echcviras 7
Edovirps 12
Coxscckieviras A9
Aerobacter nfronoaes
Esciiericliir. cell
Slrcntccotcus faecalis
Ko. of Days
Teraperatorc *C
4'
110
130
60
12
56
48
48
20P
23
41
32
--
21
20
26
2r
17
28
20
6
10
12
14
THI MtTROPOUTAN SANITAtT DISTRICT
OF CttATCH CHICAGO
ENGINEERINO DEPARTMENT
«.J.O.*W.».
138
-------
100%
THE METROPOLITAN SANITARY DISTRICT OF GREATER CHICAGO
FIGURE IX
507,
PERCENT SURVIVAL OF MS-2
WITH TIME IN
A^AFRQSICALLY PASTING SLUDGE
L07o
\
\
0.57o
~O Experiment No. T
—o Experiment No. 2
—® Experiment No. 3
—IB Experiment No. 4
Regression
24
-------
iOO.O
THE P4ETROPOLITAN SANITARY DtSTRICT OF GREATER CHICAGO
FIGURES:
(0.0-
Poliovirus Type 1
Coxsackievirus Type A-9
Coxsackievirus Type B-4
Ecbovirus Type 11
INACTiVATION OF POLIOVIRUS TYPE 1, COXSACKIEVIRUS TYPE A-9,
COXSACKiEVIRUS TYPE B-4, AND ECHOVIRUS TYPE 11 IN ANAEROBICALLY
DIGESTING SLUDGE
^(Curves represent the geometric means of all ths runs for each virus)
0.01 £~
'0
48
-------
COSTS FOR THE UTILIZATION OF MUNICIPAL
SLUDGE IN AGRICULTURE
The question of cost is an important one no matter
how desirable a particular process may be from an
environmental point of view. Municipalities must not
only protect the environment, but realistically spend the
tax dollars collected from those they service.
To this end, costs for the District's Fulton County
operations in Illinois are presented in Table 17. As can
be seen, the total capital and maintenance and operation
(M&O) costs are SI.57 per wet ton (S1.43/mT) and
$5.18 per wet ton ($4.78/mT), respectively. Total costs
are $6.75 per wet ton (S6.02/mT). Capitol costs for the
Fulton County operations amount to 23% of the total
costs while approximately 41% of the M & O costs are
taken up for transportation and 32% for application.
Naturally, the costs presented here are for a particular
situation which may or may not be true for other types
of operations. One must calculate costs for the particular
system to be used.
LITERATURE CITED
Berg. G. 1966. Virus transmission by the water vehicle.
II Virus removal by sewage treatment procedures.
Health Library Science 2: (2) 90.
Berrow, N. L., and J. Webber. 1972. Trace elements in
sewage sludges. J. Sci. Fd. Agric. 23:93-100.
Bertucci, J., C. Leu-Hing, D. R. Zenz and S. J. Sedita..
1974. Studies on the inactivation of four enteric
picornaviruses in anaerobically digesting sludge.
MSDGC Report 74-19, August.
Bertucci, J., C. Lue-Hing and D. R. Zenz. 1973.
Inactivation of viruses in anaerobically digesting
sewage sludge. MSDGC Report, May.
Blakeslee, P. A. 1973. Monitoring considerations for
municipal wastewater effluent and sludge application
to the land. In Proceedings of the Joint Conference
on Recycling Municpal Sludges and Effluents on
Land. National Assoc. of State Univ. and Land-Grant
Colleges, Washington, D.C.
Bowen, H. J. M. 1966. Trace Elements in Biochemistry.
Academic Press, London and New York.'
Chancy, R. L. 1973. Crop and food chain effects of
toxic elements in sludges and effluents. In Proceed-
ings of the Joint Conference on Recycling Municipal
Sludges and Effluents on Land. National Assoc. of
State Univ. and Land-Grant Colleges, Washington,
D.C.
Chawla, V. K., D. N. Bryant, and D. Leu. 1974.
Disposal of chemical sewage sludges and land and
their effects on plants, leachate and soil systems. In
Sludge Handling and Disposal Seminar, Sept. 18-19,
Environment Canada, Ontario.
Dotson, G. K., Smith, J. E., Jr. 1971. Persistence of
pathogens in sludge treated soils, EPA - NERC - Cin-
cinnati, Interanal Report, September.
Fair, G. M., and J. C. Geyer. 1963. Elements of Water
Supply and Waste Water Disposal. John Wiley and
Sons, Inc., N.Y.
Fitzgerald, P. R., and W. R. Jolley. 1974. The use of
sewage sludge in pasture reclamation: parasitology,
nutrition and the occurrence of metals and polychlo-
rinated byphenyls. Unpublished report to the Metro-
politan Sanitary District of Greater Chicago from the
College of Veterinary Medicine, University of Illinois,
Urbana.
Hinesly, T. D., O. C. Braids, R. I. Dick, R. L. Jones, and
J. A. E. Molina. 1974. Agricultural benefits and
environmental changes resulting from the use of
digested sludge on field crops. Report from the
University of Illinois, Urbana, to the Metropolitan
Sanitary District of Greater Chicago, unpublished.
Johnson, R. D., R. L. Jones, T. L. Hinesly, D. J. David.
1974. Selected chemical characteristics of soils,
forages and drainage water from the sewage farm
serving Melbourne, Australia Department of the
Army, Corps of Engineers.
Ledbetter, J. 0., L. M. Jauck, and R. Reynolds. 1972.
Health hazards from wastewater treatment practices.
Amer. Ind. Hygiene Conf., San Francisco, Calif.
Ledbetter, J. 0., 1973. Health hazards from wastewater
treatment practices. Env. Letter 4:225-32.
Leeper, G. W. 1972. Reactions of heavy metals with
soils with special regard to their application in sewage
waste. Dept. of the Army, Corps of Engineers.
Lejcher, T. R. and S. H. Kunkle. 1973. Restoration of
acid spoil banks with treated sewage sludge. In W. E.
Sopper and L. T. Kardos (ed). Recycling Treated
Municipal Wastewater and Sludge Through Forest and
Cropland. The Perm State Univ. Press. University
Park.
McLean, D. M. 1967. Transmission of virus infections
by recreational water. P. 25. In G. Berg (ed)
Transmission of Viruses by Water Route. Inter-
science, N.Y.
Melsted, S. W. 1973. Soil-plant relationships, some
practical considerations in waste management. Pro-
ceedings of the joint conference on recycling munici-
pal sludges and effluents on land.
Meyer, R. C., F. C. Hinds, H. R. Isaacson, and T. D.
Hinesly. 1971. Porcine enterovirus survival and
anaerobic sludge digestion. Presented at the Inter-
national Symposium of Livestock Wastes, Columbus,
Ohio April 22.
141
-------
TABLE 17
COSTS FOR SLUDGE MANAGEMENT SYSTEM-MSDGC FULTON COUNTY ILLINOIS
OPERATIONS (Interest Rota 5 7/87,, Cost ii 1975 Dollars).'"
Sludge Management
System Component
1. Flotation Concentration
Digestion
2. Transportion
(barge-200 miles)
3. Holding Basins
4. Land
5. Site Preparation
6. Application System
7. Monitoring
Capital Costs
Amortized
$/Wet Ton
0.72
Contractual Agmt.
0.07
0.19
0.09
0.41
0.09
M t 0 Costs
Anneal
$/Wet Ton
1.33
2.14
•
••
•
1.6S
0.06
TOTAL COST * S6.7S/W.T.
N» o»er»tmg costs isscmel. Tfcisi c«» lit included
in *p;lic*tion M & 0 costs.
Net ip»licab!c *** Uiinttrmg Ntwt Rtctrd Indtx • 2400.
THI METtOPOUTAN SANITAIT DISTRICT
OF GHf ATEt CHICAGO
ENGINEERING DEPAtTMENT
R.J.O. * W.». MARCH 1973
142
-------
Olexsey, R. A., and I. B. Farrell. 1974. Sludge
incineration and fuel conservation, News of Environ-
mental Research USEPA, May 3.
Ontario Ministry of the Environment. 1973. Processed
organic waste training seminar, May 1-3, 1973. 880
Bay Street, Suite 344, Toronto, Ontario M5S 128.
Page, A. L. 1974. Fate and effects of trace elements in
sewage sludge when applied to agricultural lands. A
literature review study. Office of Research and
Development, U.S. Environmental Protection
Agency, National Environmental Research Center,
Cincinnati, Ohio.
Peterson, J. R., C. Leu-Hing, and D. R. Zenz. 1973.
Chemical and biological quality of municipal sludge.
In W. E. Sopper and L. T. Kardos (ed) Symposium on
Recycling Treated Municipal Waste Water and Sludge
Through Forest and Croplands. The Pennsylvania
State University, University Park.
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143
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THE DEPENDENCE OF DEWATERDMG PROCESS ON AQUEOUS PROPERTIES
OF SLUDGES
by
Pirogov L. G., All-Union Scientific Research Institute
VODGEO
The interaction of solid phase, which forms a basic
structure of sludge, with liquid phase and basic relation-
ship, defining its passage through sludge, may be shown
at consideration of dewatering process in general as
liquid penetration through porous medium by the action
of external forces.
According to Darcy-Weisbach Equation for pressure
gradient at laminar liquid flow through porous medium
the following relationship is true:
where: AP— pressure differential
B - height of specimen
Ji — coefficient of resistance
J1 - characteristic linear parameter for porous
media
J* - density of liquid
V - average flow rate through sections
The relationship of A to& may be expressed as:
(2)
in which
(3)
where: £ - a number, constant for a given system of
characteristic parameters.
/H- viscosity of liquid.
The actual value of flow rate through pore channels may
be found from equation (I) taking into account Equa-
tions (2) and (3)
(4)
._
c s* e
The average actual value of flow rate through pore
channels in case Darcy's law is true, is given in Equation
(4). Darcy's Law itself may be written In the form
(5)
where
W — filtration rate
/(/7 — coefficient of permeability.
The relation between actual, average flow rate and
filtration rate for porous medium, where only part
of its area participates in filtration process, may be
expressed by the following relationship:
V
-K
(6)
/f?Q_ - active porosity.
A comparison of Equations (4) and (5), considering
equation (6) results in
Kn
(7)
Then
Kn=
(8)
C
Taking relations of certain geometric values such as total
porosity and specific surface area as characteristic
linear parameter for porous medium, we'll obtain
m
(9)
In accordance with modern hydrodynamics theory (I)
then Equation (4) becomes:
. 5.1 (io)
Taking into consideration relationships expressed by
equations (9) and (10), the following equation will be
true:
5.IS*
144
-------
Relationship (II) determines value of coefficient of
permeability, characterizing filtration capacity of porous
medium and therefore complex of hydrodynamic prop-
erties and physical-chemical phenomena occurring at
boundary of liquid-solid phases.
Interaction between solid and liquid phases at the
boundary is a determining factor both in the formation
of various categories and forms of bounds of liquid with
the basic structure of sludge and in the destruction of
these bonds as affected by this or that dewatering
process.
Using works by Rebinder P.A. (2), Likov A. V. (3),
(4), (5); Kazansky M. Ph. (6) the author carried out
investigations (7), the results of which required more
accurate definition according to Rebinder classification
of categories of osmotically combined water. It was
separated into two types: osmotic proper and entrapped
by the basic structure of the sludge. The introduction of
entrapped water into this classification allowed to create
the uniform method for calculation of physical con-
stants related to water balance, structural and filtration
characteristics as well as the degree of sludge thickening,
which is obtained at this or that unit after handling.
Actual values, calculation equations and consequence
of calculation of the whole complex of characteristics
are presented in Tables I, 2, 3, 4 and 5.
Some filtration characteristics and limit residual
moisture contents obtained by calculation according to
the author's method and by sludge filtration tests
according to other investigators, are given in Tables 6
and 7.
Suggested method of investigation of sludge aqueous
properties is applied to any two-phase "solid-liquid"
system under condition of their isotropy.
Taking into consideration that a great number of
materials in nature and technics is isotropic two-phase
solid-liquid systems, the developed method can find
a side application in water and waste water treat-
ment as well as in adjoining fields of science and
technics.
TABLE 1
Nature of
bond
Category and
type of bonds
Symbols for
water weight
differentiated
on category and
type of bonds.
Phy sical-mechanical
bond
Total
amount $
of water
in sample
1.
Si
Excess
water
2.
-
Water in
macro-
pores
-5
>10cm
3.
-
Physical-chemical bond
Osmotic Water
Osmotic
proper
4.
,
Entrapped
5.
gs
Micropores.
-5
«10cm
6.
-
Adsorbed Water
Polyrnole-
cula adsor
ption
7.
Si
Monomolecu
lar adsorpti
on
8.
g>
Total
amount of
adsorbed
water.
9.
g.
145
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TABLE 2.
PHYSICAL CONSTANTS
Specific weight
of liquid phase
10
Specific weight
of solid phase
11
Volume of
specimen
12
Total surface area of
pore volumes in sample.
13
TABLE 3.
STRUCTURAL CHARACTERISTICS
Total porosity
14
Active porosity
15
Total surface area of pore
volumes in sample
in micro-
porous
systems
16
in macro-
porous
systems
17
Characteristic
linear parameter
18
TABLE 4.
Basic filtration characteristics
Coefficient of
permeability
19
Specific resistance
Volume
20
Weight
21
Coefficient of
filtration
22
TABLE 5.
Mechanism
of water
removal
Symbols for
removed
water
Dewatering
process
during which
a certain
category of
water is
removed
Separation
during
thickening
process
gravity
thickening
Compression
of basic
structure
without
deformation
Vacuum
filtration
Compression
of basic
structure
with its
deformation
Pressure
filtration
or centri-
fugation
Change in water
aggregate
condition
Heat drying.
146
-------
TABLE 6.
Type of investigated
sample
1.
Calculated values, obtained by author's
method
Specific resistance
r*
2.
Coefficient of
filtration
kf
3.
Experimental values of filtration characteristics obtained by other
investigators.
Specific weight
resistance
rb
4.
Coefficient of
filtration
kf
5.
Name ol author
6.
Luberetsk sand -
Sludge from filtration
plant.
At solids concentra-
tion
33 275. 1010
49 438.1010
51 458.1010
Sludge from
Chimkent lead plant
Sludge moisture*
67.5 927. 1010
67.6 914.1010
69.7 778.1010
70.6 732.1010
70.8 720.1010
71.9 656.1010
Grey Clay Moisture**
53.6
43.3
35.6
25.3
Clay from KUCHINO
Moisture**
31.5
31.3
Kf°°-l, 38 - Kfuo = 1.95 NedrigaV.P.
10 2 10~2 Afinogenov I. A.
(VNII VODGEO)
1420-M600.1010 LcventonO. L.
336.10 (VNII VODGEO)
726.810.1010
362.0.1010
513.9. 1010 Orlovsky Z. A.
443.3.1010 Mongait I. L.
405.2. 1010 Pishkina N. 1.
346.6.1010 (VNII VODGEO)
449.0.1010
Kfl°°=9.26 K'° = 30.10'9 Nedriga V. P.
IT9
15.2.10 Pavilonsky V. M.
4.6.10"9 (VNII VODGEO)
2.15.1Q-9 - 5-27-10"?n
2.71.10'10 1.06.10 10
K10°=0.569.10-9 K10°=1.5.10-9
Q
0.56.1Q-9 2-2.5.10
*Moisture = 100% if = gb
*'Moisture is 1007r if =
147
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148
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