Working for Clean Water
An Information Program for Advisory Groups
Municipal
Wastcwater Processes
Overview
What pollutants need to be removed from sewage?
How are the pollutants removed?
What is important about the stages
of pollutant removal?
How may wastewater treatment techniques
be improved?
What factors should be considered in
selecting treatment processes?
Citizen Handbook
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This program was prepared by
The Pennsylvania State University
Institute of State & Regional
Affairs
Middletown, PA 17057
Dr. Charles A. Cole
Project Director
Dr. E. Drannon Buskirk. Jr.
Project Co-Director
Prof. Lorna Chr. Stoltzfus
Editor
This unit prepared by
Lorna Chr. Stoltzfus,
E. Drannon Buskirk, Jr.,
and John B. Nesbitt
Advisory Team for the Project
David Elkinton, State of West
Virginia
Steve Frishman, private citizen
Michele Frome, private citizen
John Hammond, private citizen
Joan Jurancich, State of California
Richard Hetherington, EPA
Region 10
Rosemary Henderson, EPA
Region 6
George Hoessel, EPA Region 3
George Neiss, EPA Region 5
Ray Pfortner, EPA Region 2
Paul Pinault, EPA Region 1
Earlene Wilson, EPA Region 7
Dan Burrows, EPA Headquarters
Ben Gryctko, EPA Headquarters
Robert Hardaker, EPA
Headquarters
Charles Kauffinan, EPA
Headquarters
Steve Maier, EPA Headquarters
EPA Project Officer
Barry H. Jordan
Office of Water Programs
Operations
Acknowledgements
Typists:
Ann Kirsch, Jan Russ, Tess
Startoni
Student Assistants:
Fran Costanzi, Kathy DeBatt,
Mike Moulds, Terry Switzer
Illustrator:
Charles Sneers
Graphics support was provided by
the Office of Public Awareness,
U.S. Environmental Protection
Agency.
Photographs were provided by
U.S. Environmental Protection
Agency
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Municipal Wastewater Processes: Overview
The Problem Doesn't
Disappear
Decisions made by society years ago still
haunt us today. How do we get rid of
unwanted material? Easy. Dump it in
water. Yes, dilution in water allows the
waste to be quickly and easily transported
away. Dilution also makes the waste less
offensive. Out of sight (smell) means out of
mind!
Or does it?
Currently we have many waste removal
systems designed to operate in this way,
and have developed a lot of sophisticated
technology to go along with it. Miles of
pipe lie under our cities to collect
wastewater and carry it somewhere "out of
sight". Conventional systems are not all
that bad. They can be remarkably
dependable. Most can produce
environmentally acceptable wastewaters.
Some operate for decades beyond their
intended life spans.
However, because of high costs and other
drawbacks localities are turning to various
nonconventional methods of wastewater
management. Some communities have
inadequate sewage collection, treatment, or
disposal. These communities have a choice
whether to continue with similar adequate
facilities, or to try something different.
Sewage: Pollutant or
Resource?
Sewage presents both problems and
opportunities.
The construction of wastewater treatment
facilities historically began out of concern
for waterborne diseases. Most organisms in
sewage are harmless to humans, but
disease-causing bacteria and viruses are
present. Industrialization has created other
hazards toxic substances such as
pesticides, heavy metals, and even
radioactive materials.
/
Sewage also contains nutrients such as
organic, carbon-containing substances that
result from living things, and inorganic
matter such as nitrogen compounds.
Inorganic matter does not come from living
things, but from minerals. These materials
are not problems at low levels, but at high
levels they can degrade water quality.
These materials serve as nutrients for
bacteria and algae, which can deplete and
dissolve oxygen in lakes and streams. As
bacteria feed on organic matter, oxygen is
consumed in direct proportion to the
amount of organic matter present. Such
organisms cause a biochemical oxygen
demand (BOD). The measurement of BOD
represents the amount of this kind of
organic matter present in water. Excessive
growth of aquatic plants may also result
from nutrients.
Thus concentration as well as kind
determines whether a substance is a
pollutant or a resource.
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Removal of Pollutants
Large Solids
Sewage is more than 99.9 percent pure
water. This amounts to about two drops of
waste in a quart of clean water. Because
this small amount of pollution can cause a
lot of trouble, dirty waters must be cleaned
before being discharged into rivers and
lakes. This is neither an easy task nor an
inexpensive one.
So, what sorts of things are found in this
0.1 percent waste in sewage? How are we
going to remove them? The ways of
removing pollutants depend upon their
biological, chemical, and physical
properties.
Wastes in water exist in all three states of
matter: gases such as ammonia, liquids
such as oils, and solids such as feces or
sediment in chunks of various sizes. The
physical state of a pollutant has a direct
bearing on the selection of wastewater
treatment processes.
In wastewater treatment pollutants
generally are removed according to size.
Large chunks of solids get removed first.
Materials such as sticks and rags can be
removed by passing the wastewater
through a screen. Another approach is to
collect the large objects, grind them up,
and return them to the wastewater for
further processing. A way to deal with
floating objects is to skim them off.
Small Solids
Wastewater often contains gravel, grit, and
sand in runoff from streets. One removal
method is to allow the particles to settle
naturally. This can be done by putting the
wastewater in a basin where the water
current slows slightly, giving the small but
heavy solids time to settle with the help of
gravity.
Physical
Screening
Settling
Filtering
Adsorption
Flotation
Chemical
Precipitation
Biological
Metabolism
Suspended and Dissolved Particles
Other small organic particles are not as
heavy as the gravel, grit, and sand. They
remain suspended due to the movement of
the water. Given more time and less
agitation, these particles will settle as
well. This process is called sedimentation
and produces a clearer (clarified)
wastewater.
Organic Pollutants
Removal of the smallest organic suspended
solids is often done by biological
organisms. Three types of treatment
alternatives are often used: The trickling
filter, activated sludge, and land
treatment. In a trickling filter a film of
microorganisms grows on stones or a
synthetic medium. The wastewater is
allowed to trickle through these materials,
and the microorganisms metabolize or
digest most of the organic pollutants. In an
activated sludge system, the organisms are
suspended in wastewater with air blown in
to provide oxygen and to enhance mixing.
The third alternative is called the "living
filter," where wastewater is applied to
land, and is purified by the natural
biological, chemical, and physical processes
of the soil.
Methods to remove pollutants combine biological, chemical, and
physical approaches.
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After biological treatment, some small
suspended organic particles still remain.
Most can be removed by filtration through
a fine screen with small openings, or a
deep bed of sand.
Dissolved organic matter can be removed
both by biological treatment and by
activated carbon adsorption, a process in
which the pollutants adhere to the carbon
particles.
Inorganic Pollutants
Inorganic pollutants such as phosphorus
are usually dissolved in water. Dissolved
material is generally in the form of tiny
charged particles called ions. These ions
can be removed by various means,
including precipitation. Precipitation is
really just changing the conditions so as to
make the material insoluble in water.
Once the solubility is altered, the
pollutants can be removed by
sedimentation or filtration. Precipitation
can be carried out by adding certain
chemicals to the wastewater.
Another way is ion exchange. In this
process a more desirable ion is substituted
for the undesirable pollutant. Ammonia
nitrogen may be removed from wastewater
in this fashion.
Two other approaches, electrodialysis and
reverse osmosis, use membranes. In
electrodialysis the ionic compounds,
usually salts, are forced out of the water by
the action of an electric field. In reverse
osmosis, clean water is forced through a
membrane, leaving the dissolved solids
behind.
Dozens of other treatment processes exist.
All are based upon three types of
mechanisms: Biological, chemical, and
physical actions. These removal approaches
can be combined in many different ways to
clean up particular kinds of wastewater.
Most are patterned after natural methods of
water purification. It's just that the methods
are accelerated in time, and concentrated in
space to keep up with our huge volumes of
wastewater.
Wastewater Treatment Mechanisms
Type Function
Example
Physical
Chemical
Bar rack
Sedimentation
Sand filter
Carbon column
Sludge
thickening
Electrodialysis
Phosphorus
removal
Odor control
Disinfection
Trickling
filter
Activated
sludge
Septic tank
Land treatment
For additional information see tJie glossary and the program unit entitled,
Municipal Wastewater'Processes: Details.
Biological
Screen
Settle
Filter
Adsorption
Flotation
Selective
transport
Precipitation
Oxidation
Metabolism
Things to Consider
The advisory group can ask questions
that, in effect, direct the scope of water
quality planning. A few pertinent
questions should be asked early in the
planning process:
What assumptions are the planners
using from the outset? Are they
appropriate?
What are the reasons for using a
particular removal concept climate,
experience of engineering consulting
firm, reliability, nature or amount of
wastewater?
Are the basic design principles
well-suited to the particular problem at
hand?
What are the existing facilities? Are
these a constraining factor in
considering methods?
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Before and After Treatment
Any considerations of municipal
wastewater process should also include a
look at what happens before, and what
happens after the removal of pollutants.
Where the wastewater comes from, and
how it is collected and transported have a
direct bearing on the kinds and
concentration of pollutants that must be
removed from the wastewater. Also, the
disposal of products left after treatment
should be considered in the selection of
treatment processes.
Collection of Wastewater
First of all, how is wastewater collected so
that it can be treated? In central treatment
systems wastes from homes, businesses,
and, sometimes, industry are carried by
water through pipes called sewers which
lead to the treatment plants. Wastewater
is transported by conventional gravity
sewers, and other methods such as
pressure or vacuum sewers.
Although gravity sewers have a good
record for dependability and efficiency,
they have drawbacks. In addition to being
expensive, they may disrupt the
environment. They can require deep
excavations that cause extensive dust,
erosion, and sedimentation problems.
Odors may also be a problem where flat
terrain contributes to the slow flow of
sewage. Because gravity sewers typically
follow natural drainage paths, their
construction may disturb nearby
watercourses. They also may overflow into
adjacent watercourses from time to time.
Other methods of transporting wastes
involve the use of small diameter vacuum
or pressure sewers. These systems are
relatively new and are used only on a
small scale. They are likely to have greater
operational, maintenance, and energy costs
than gravity sewers, but cost much less to
install.
Modified onsite disposal systems also may
use small diameter sewers. Wastewater
from several conventional septic tanks can
be transported by sewers to a common
disposal area (absorption field).
Separate
Sewer
System
Sanitary sewer
Stormwater sewer
Treated
effluent
Types of Sewer Systems
There are two basic types of sewer systems
combined and separate. Combined-
sewers carry both water polluted by human
use, and water polluted as it runs off
rooftops, streets, and land during
rainstorms, snow melts, or other forms of
precipitation.
Separate sewer systems have two sets of
sewer pipes. One system called sanitary
sewers carries only wastewater from
homes, businesses, and industries. A
separate system carries rainwater polluted
by dirt and other contaminants into pipes
that are known as storm sewers. These
separate storm sewers empty directly into
water courses.
Combined sewers are common in the older
cities of the eastern United States. About
1,600 communities with a total population
of 31 million persons have combined
sewers. One problem which plagues these
systems is how to accommodate the large
quantitites of wastewater during and after
rainstorms. When storms occur, the
treatment plant often is overloaded. It is
then necessary to have some of the
wastewater bypass the plant, and flow into
the receiving surface waters without
treatment. If part of the increased load of
water were not diverted, the treatment
plant would be hydraulically overloaded,
and the purifying processes would not
function properly for a long period of time.
At times like this some wastewater gets
treated and some gets dumped into
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Combined
Sewer
System
Untreated
effluent
Combined sewer
Treated
effluent
waterways as raw sewage. Treatment
plants generally are designed to
accommodate only dry weather flows, plus
a small portion of the stormwater. Special
facilities may be constructed to treat excess
flows during storms where such flows
create pollution problems. Separate holding
tanks and equalization basins for storing
wastewater are possible remedies. Another
approach, but costly, is the separation of
sanitary and storm sewers. The cost for
this alternative around the country would
be millions of dollars. However, this
method for stormwater pollution
abatement facilities may be eligible for
federal funds if they are the most effective
means of protecting surface waters.
Sewer Funding
Sewer funding is complex. Eligibility for
EPA funds mainly depends upon the type
of sewer, installation situation, and state
priorities.
Sewer systems are composed of piping,
pump stations, manholes, and associated
items. The pipes consist of house
connections, collectors, interceptors, and
force mains. House connections carry
wastewater from the house into the sewer
system. The cost of house connections must
be borne completely by the homeowner.
The wastewater flows from these pipes into
collector sewers. New communities, or
newly developed areas of existing
communities, must bear the entire cost of
the collectors. Only communities in
existence or wastewater systems two-thirds
completed before October 1972 can qualify
for collector sewer funding. In many states,
however, collector sewers do not receive a
sufficiently high priority to receive any
funds.
The main conveyance pipe which gathers
flows from the collectors and transports the
wastewater to the treatment plant is called
an interceptor. Depending on the terrain, a
force main may be necessary to carry
water, under pressure, from a pump station
to the treatment plant. Interceptors, force
mains, and pump stations are all fundable
by the EPA which will pay 75 percent of
the cost on all eligible items. However,
only 25 percent of state allocations can be
spent on pipe-related projects such as
interceptors and pump stations.
The community, of course, must pay for all
construction costs not covered by federal or
state funding. The local users also must pay
for operation and management costs from
the time the sewers are completed.
In addition to costs, the important
considerations in wastewater collection and
transport systems include the size of the
service area, and service area
characteristics such as soils and population
projections. This last concern population
- is crucial in determining the sizes of
both sewers and treatment facilities. While
the sizes must be adequate, they must not
exceed reasonable future needs. Otherwise,
unwanted costs and undesirable
Gravity Sewers
Advantages
Dependable
Have low energy and maintenance
needs
Disadvantages
Require deep excavations
Often built along streams and lakes
Usually more environmentally
disruptive than other sewer
alternatives
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Effluent
(liquid)
Treatment
processes
Stormwater
runoff
(liquid + solids)
Disposal of Effluent and Sludge
No matter how good the treatment is, all
the pollutants are never taken out of the
wastewater. These pollutants leave the
treatment facility in two ways. There is
the treated liquid called effluent. There
also is a liquid mixture called sludge,
which contains solids that have been
removed from the wastewater.
Effluent
Before it leaves the treatment plant, the
effluent is treated further to kill any
disease-causing bacteria. This is usually
done by disinfecting the water with
chlorine. Then the effluent can be either
diluted through discharge into surface
waters; applied to land for agricultural
production, recreational use, or
groundwater recharge; placed in
containment ponds to evaporate; or reused
as process or cooling water for industry or
utilities. The use and the cost of this
reclaimed water depend on the degree of
waste removal needed, and the availability
of alternate water sources.
The quality of the effluent which leaves
the plant is of primary importance in the
protection of the receiving water. This
quality is measured by several factors:
Organic matter (biochemical oxygen
demand and suspended solids)
Nutrients (ammonia and phosphorus)
Coliform bacteria (fecal organisms)
Toxic materials.
The concentration of these substances
determines the quality of the effluent, and
represents the efficiency of the treatment
plants.
Sludge
Sludge is akin to the tail that wags the dog
in many municipalities. Proper disposal of
sludge is necessary to complete effective
waste treatment. It is a mushrooming
problem that demands larger portions of
wastewater treatment funds every year.
Sludge handling may make up half the
cost of wastewater treatment.
Sludge is largely water (90-95 percent).
The solids are separated by centrifuges,
filtration, or drying beds. Final sludge
disposal methods include burying, burning,
composting, and direct land application.
However, these methods are not without
their own problems. Incineration can result
in air pollution and generates ash that
itself must be disposed. Expensive energy
supplies also may be consumed in the
burning process, although new dewatering
methods can minimize this problem. Good
engineering design and operation, however,
can result in facilities that meet
environmental standards.
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Composting and direct land application
also have mixed benefits. Energy and
nutrients may be obtained from sludge, but
toxic agents such as heavy metals and
disease-causing organisms also may be
present. Indeed, since sludge contains
concentrated pollutants, it must be disposed
of with care. Whether or not sludge is a
resource or a problem depends upon its
contents, processing, and the market for
compost. Sludge disposal becomes much
easier and less expensive if heavy metals
and toxic materials are kept out of
municipal wastewater. This can be
accomplished through an effective
industrial pretreatment program.
Sludges must be evaluated with the
least-risk method of disposal chosen for
each community. There is no such thing as
an alternative without risk.
Questions about Sewers
and Sludges
Questions to ask about "before and
after treatment" include:
Where does the wastewater come
from, and has thought been given to
reducing this quantity of water?
How is the stormwater runoff
controlled, collected, and treated?
How is sewage collected and
transported?
If new sewers are necessary, where
are they to be built?
What are the effluent/sludge disposal
options and their related costs?
How will the disposal techniques
affect the environment?
Do the choices fit in with the values
of the community?
What environmental standards must
be met for the effluent and sludge?
Construction of a sewer system.
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Influent
Primary
treatment
Secondary
treatment
Advanced
waste
treatment
Disinfection
(if required)
Effluent
Solids
disposal
What Happens at the
Treatment Plant?
Traditionally, the stages of wastewater
treatment were designated as primary,
secondary, and tertiary, but the definition
of tertiary was unclear. Therefore, tertiary
is now referred to as advanced waste
treatment since there is a lot of overlap in
what certain processes can accomplish.
Primary Stage
This process, mainly mechanical, removes
solids which either settle or float. At best,
suspended solids can be reduced by 60
percent and the BOD by 35 percent at the
primary stage.
Basically this process involves passing the
wastewater through a screen or bar rack to
remove large floating solids. Instead of a
screen, some treatment plants use a
grinder to shred large pieces of solid
materials. Next, the wastewater flows into
a grit chamber where sand, cinders, and
small stones settle out. Suspended solids
are then removed in a sedimentation tank,
collecting on the bottom as raw sludge.
Primary treatment is a rather coarse
procedure. Only the large chunks of
wastes and solids that either float or settle
are removed. The process has little effect
upon finely suspended and soluble
pollutants. They must be removed at other
levels of treatment.
By adding secondary treatment to the
primary processes, more than 85 percent of
the BOD and suspended solids are
removed. Under controlled conditions,
biodegradable organic wastes are converted
Flow
Sedimentation tank
Bar rack
Sludge
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into carbon dioxide and water by
microorganisms in an accelerated process
similar to that which occurs in a natural
stream.
Two common types of secondary treatment
are the trickling filter and the activated
sludge processes. A trickling filter is a bed
of stones or synthetic material through
which the wastewater passes after primary
treatment. Bacteria and other organisms
on the stones consume most of the organic
matter in the wastewater as it trickles
through the bed. In the activated sludge
process, aerated wastewater and
microorganisms are held together for
several hours in a basin.
Other approaches to secondary treatment
are the oxidation pond or lagoon, carrousel
aeration, rotating biological contactor,
activated biofllter, and land treatment.
Oxidation ponds or lagoons that are not
artificially aerated offer a low energy and
operational cost alternative where land
space is available. Complexity of operation
is low for ponds as it is for land treatment.
These approaches are also biological in
nature, and provide an adequate
environment for the breakdown of soluble
organic materials. Many of these processes
with unusual names simply provide surface
areas onto which the microorganisms
attach, or create suitable conditions for
growth.
Since secondary treatment is a biological
process it is effective mainly for removing
biodegradable wastes. Care must be taken
not to introduce substances that are toxic
or damaging to the microorganisms.
Most regulatory agencies require that the
final step in secondary treatment be
disinfection to kill any pathogenic bacteria
and viruses. Disinfection is usually
accomplished by adding chlorine to
accomplish the required kill.
Secondary Treatment Processes
'BOD cnc
Trickling Filter
Activated Sludge
Oxidation Ponds or Lagoon
Carrousel Aeration
Rotating Biological Contactor
Activated Biofilter
Land Treatment
Trickling filter for breakdown of organic wastes.
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Advanced Waste Treatment
The pressures are mounting on our waste
treatment systems. As we become more
urbanized, wastes concentrate faster than
the local environment can assimilate them.
Every year industry creates new products
which also become pollutants. Our
demands for larger quantities of water
further aggravate the problem. Today
water must be used over and over in a
variety of ways. This increasing need to
reuse water calls for better waste
treatment. Advanced methods of treating
wastes satisfy some of these needs.
When secondary levels of treatment are
not adequate to protect the quality of
sensitive water bodies, more advanced
processes must be used. Treatment beyond
the conventional primary and secondary
stages can remove most of the pollutants:
nitrogen, phosphorus, non-biodegradable
organic matter, and heavy metals as well
as BOD and suspended solids. However,
the costs often are very high.
Combinations of chemical, physical, and a
few biological techniques accomplish this
additional removal of pollutants. Examples
of conventional advanced treatment
processes are chemical precipitation to
remove phosphorus, chemical reactions to
remove nitrogen, coagulation and filtration
to extract additional amounts of suspended
solids, and activated carbon to adsorb
organic compounds that cause'unpleasant
tastes or odors or are not biodegradable.
However, the increasing appearance of
hazardous substances such as
polychlorinated biphenyls (PCBs) and
synthetic chemicals is challenging even
these advanced processes. New approaches
to wastewater flow reduction and
treatment are needed. A relatively old
process, land treatment, is becoming more
and more viable as an alternative to
conventional advanced waste treatment
processes.
Advanced Waste Treatment
Processes
Phosphorus Removal
Coagulation-sedimentation
Land treatment
Nitrogen Removal
Biological nitrification-denitrification
Ammonia stripping
Ion exchange
Breakpoint chlorination
Land treatment
BOD and Suspended Solids
Removal
Coagulation-sedimentation
Filtration
Microscreening
Land treatment
>val
Organic
Activated carbon
Land treatment
Advanced techniques are not a cure-all for
our wastewater problems. Many require
chemicals that are expensive to purchase
or create residues that are difficult to
dispose. Some approaches are very energy
intensive. Many advanced techniques are
relatively new, and may not be time-tested.
The benefits of advanced waste treatment
must be weighed against the costs.
Communities must carefully consider the
need for advanced waste treatment.
10
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Concerns about Advanced
Waste Treatment
Much thought needs to be done before
planning advanced wastewater
treatment (AWT) systems. The advisory
groups can contribute by keeping the
following questions at the forefront of
the discussion:
Have community options such as
wastewater flow reduction and
changed water uses that will diminish
the need for AWT been explored?
Is AWT really needed to meet surface
water quality standards?
Has land treatment been considered
as an alternative to conventional AWT?
Can the community afford the
on-going chemical and energy expense
of AWT?
Are there sufficient disposal sites in
the area for increased sludge due to
AWT?
Will the treatment facilities have
competent personnel for dealing with
the complex AWT processes?
Efficiency of Treatment Processes
'Percent of Pollutant Removed from Domestic Wdste
Pollutant
Primary
Treatment
Secondary
Treatment
Advanced
Treatment
BOD
Suspended
Solids
Nutrients
(Nitrogen,
phosphorus)
25-30
60-65
Minimal
85-95
85-95
Minimal
90-99
90-99
90-95
Increased removal efficiencies are achieved
at increasing costs. The elimination of the
last 15 percent of major pollutants from
wastewater is several times more costly
than the removal of the initial 85 percent.
Indeed, wastewater clean-up does not come
cheap.
An advisory group can play a key role
in identifying tradeoffs between the
degree of pollutant removal and the
monetary and environmental costs.
25
Cents per 1,000 gallons
50
Type
of
treatment
75
I
100
I
Treatment beyond the secondary
level nearly doubled the cost in
1978.
Secondary treatment
+ Phosphorus
removal
+ Filtration
+ Nitrogen removal
4- Carbon adsorption
0
2.65
5.25
Dollars per month per home
7.90
10.50
11
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Planning Questions
Room for Improvement
Additional questions for advisory
groups include:
Are local environmental values
reflected in the final choice?
Are alternative and innovative
technologies as well as multiple uses of
treatment facilities considered?
Will the level of sophistication of the
treatment processes create problems in
finding qualified people to operate and
maintain the plant?
If the wastewater treatment facility
has other uses such as recreation, will
funding still be obtainable?
Will the removed pollutants create
future environmental problems at
another place or time?
Does the plan permit revisions for
increased flows, wastewater
reclamation, or water reuse in the
future?
Advisory group parti
in facilities planning.
Alternative or innovative wastewater
treatment technologies may possibly be
substituted for conventional treatment
processes. These may save energy,
operating or construction costs, or offer
some other advantages. Another
cost-saving approach is to improve the
efficiency of conventional facilities through
design changes or improved operations and
management. Such measures may avoid
the need for expensive new facilities.
Another approach involves the equalization
of sewage flows. The flow of wastewater
corresponds to our daily activities. This
routine sets a pattern of peaks and valleys
of sewage flow and strength. The purpose
of flow equalization is to dampen these
variations, and to permit the treatment
facilities to operate at greater efficiencies,
rather than constantly trying to adjust to
changing flows. Large basins for collecting
and storing wastewater are used to achieve
flow equalization.
Treatment facilities may be used
effectively for multiple uses such as
environmental education. Experience has
shown that both the facility operations and
educational experiences are improved by
this use.
It may be surprising to learn that treatment
plants do not always achieve the results
they are supposed to. Studies show that
these can be deficiencies in design or
equipment, but inadequate operations and
management (O&M) can also be at fault.
The principles of wastewater treatment
processes are few and simple, but the
technologies that use these principles are
complicated. Many processes, especially
those of advanced waste treatment, require
considerable operator training. Since
communities pay the entire cost of O&M,
some localities take funding short cuts in
maintenance and operator training. Plant
operations suffer as a result. Well-trained
and paid operators are essential to facility
operations and management.
Wastewater treatment facilities are
community resources that must be planned
in coordination with development of the
rest of the community. Plants that become
prematurely overloaded are victims of poor
planning. Similarly, plants that are too
large for a community do not operate
efficiently, and the costs of operation fall
on the few users.
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Selection of Processes
The array of treatment processes is
extensive. A major portion of facility
planning involves choosing one of them.
Over a hundred different techniques,
options, and processes exist for wastewater
treatment. In determining the best solution
to a wastewater problem, these
alternatives should be evaluated carefully
in light of specific local conditions. Among
the factors that should be considered are:
Wastewater amount and characteristics
(domestic, commercial, industrial uses)
Effluent requirements
Environmental effects
Public acceptance
Resource consumption
Sludge handling
Process complexity, reliability, and
flexibility
Implementation capability
Monetary costs
The bottom line for most people is how
much a system costs. Both nonmonetary
and monetary costs are involved.
Environmental, social, and indirect effects
such as land development are the principal
nonmonetary considerations. Monetary
costs consist mainly of capital, operations,
replacement, and management
expenditures. The costs should be
presented in a form that has meaning for
the taxpayer, such as dollars per household
per year. These costs, especially for
operations, are increasing rapidly due to
escalating energy costs.
Total Energy Consumption In
Wastewater Treatment Systems
Treatment Level
Treatment Higher than Secondary
BOD, 10-20 mg/L; SS,
5 mg/L; Total
Phosphorus, 1 mg/L
* Independent
physical-chemical 1,781 72,747
Activated sludge 2,301 26,278
plus chemical clarification
and filtration
Advanced Treatment
BOD, 1 mg/L; SS, 1 mg/L
Total Phosphorus, 0.1 mg/L
Total Nitrogen, 3.0 mg/L
Land treatment 2,701 0
Activated sludge 3,477 48,430
plus nitrification,
denitrification,
chemical clarification,
and filtration
Total requirements for a 5 million gallon per day plum including indirect
requirements for ehernicals, 1978.
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Main Points
Whether or not a substance is a pollutant
or a resource depends upon its nature,
concentration, and location.
Basic biological, chemical, and physical
mechanisms are involved in removing
pollutants from wastewater. Usually the
larger floating and suspended particles are
removed first. The remaining suspended
materials come second. The dissolved
substances, where necessary, are extracted
last.
Pollutants generally are separated by
processes that operate in three stages:
primary, secondary, and advanced. The
total cumulative removal of pollutants
increases through this series of stages.
However, costs also increase markedly,
especially from the secondary through the
advanced waste treatment stage.
Current treatment practices are being
improved through approaches such as flow
equalization, comprehensive planning, and
efficient operations and maintenance.
Considerations other than treatment the
collection of wastewater, and the disposal
of wastes, effluent, and sludge affect the
choice of wastewater treatment methods.
The disposal of sludge can be especially
troublesome.
The selection of treatment processes is
based upon many of the same factors that
are used elsewhere in facilities planning:
wastewater characteristics, effluent
requirements, monetary costs, sludge
handling, process reliability and flexibility,
implementation capability, and public
acceptance.
Costs are the main concern for most people
in selecting treatment processes.
This handbook provides background
information. Another unit entitled,
Municipal Wastewater Processes: Details,
gives specific information on comparing
and evaluating various wastewater
treatment alternatives.
Wagtewater treatment facility under construction.
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Selected Resources
Construction Costs for Wastewater Treatment Plants. Publication Number Need More
EPA-430/9-77-013. Washington, DC: U.S. Environmental Protection Agency, January
1978.125pp.
This document presents information which can be used to determine the
alternate municipal wastewater treatment process schemes that will meet
specific effluent guidelines. Procedures and information which can be used in
determining the cost of each alternative are also given. This publication is
available as MCD-37 from General Services Administration, Centralized Mailing
List Services, Building 41, Denver Federal Center, Denver, CO 80225.
Environmental Pollution Control Alternatives: Municipal Wastewater. Publication
Number EPA-625/5-76-012. Washington, DC: U.S. Environmental Protection Agency,
May 1976. 79 pp. Order #5012. (Note: An updated edition is in press at the time of this
writing.)
This document is an excellent non-technical discussion of available municipal
wastewater treatment processes. It describes the processes, gives costs and
energy requirements, and discusses their efficiency, advantages, and
disadvantages. The discussion in this handbook is based upon this document. It
is available from Technology Transfer, U.S. Environmental Protection Agency,
Cincinnati, OH 45268.
Innovative and Alternative Technology Assessment Manual. MCD-53. Washington, DC:
U.S. Environmental Protection Agency, September 1978. 388 pp.
This document contains fact sheets for 117 different wastewater treatment
process variations. Each fact sheet describes the process and its modifications
and discusses technology status, applications, limitations, equipment
manufacturers (list only), environmental impact, and references. Flow diagrams,
capital costs, and operating costs are also given. It is available from General
Services Administration, Centralized Mailing List Services, Building 41, Denver
Federal Center, Denver, CO 80225.
Primer on Wastewater Treatment. MCD-65. Washington, DC: U.S. Environmental
Protection Agency, Fall 1980. 26 pp.
This booklet is a vastly reduced version of the above publication. Although it
does not give details such as the advantages of specific treatment process, it is
valuable as a brief overview of major water quality concerns and treatment
options. It is available from General Services Administration, Centralized
Mailing List Services, Building 41, Denver Federal Center, Denver, CO 80225.
15
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Glossary
Activated Sludge waste solids that have
been aerated and subjected to bacterial action;
process for removing organic matter in raw
sewage during secondary waste treatment.
Adsorption attraction and accumulation of
one substance on the surface of another.
Advanced Waste Treatment treatment
beyond secondary or biological stage; removal
of nutrients such as phosphorus and nitrogen
and most suspended solids.
Biochemical Oxygen Demand (BOD)
amount of dissolved oxygen required in the
biological breakdown of organic matter in
water.
Biodegradable capable of being decomposed
through the action of microorganisms.
Coagulant chemical such as lime or alum
which causes a clumping together of particles
in wastewater to settle out impurities.
Colifonn Bacteria organisms found in the
intestinal tracts of humans and animals, whose
presence in water indicates pollution.
Collector sewer including laterals,
submains and mains.
Combined Sewer system that carries both
sewage and stormwater runoff.
Composting a method of organic breakdown
of matter using natural processes.
Cost-Effectiveness Analysis determination
of whether a project or technique is worth
funding; both monetary and nonmonetary
factors are involved.
Effluent treated or untreated waste
material discharged into the environment.
Electrodialysis process by which electricity
and a membrane separate mineral salts from
sewage.
Gravity Sewer collection system which
relies on gravity to transport wastewater from
homes to a central treatment or disposal
facility.
House Connection sewer that carries
wastewater from the house to a collection
system.
Insoluble material that cannot be dissolved
in a liquid.
Interceptor exceptionally large gravity'
sewer collecting waste from several
communities.
Ion Exchange exchange of one ion in water
for another; specifically, exchanging ammonium
nitrogen for sodium or calcium.
Lateral the small sewer serving individual
streets.
Main the intermediate-sized sewers
connecting submains to plants or interceptor.
Metabolism process by which food is built
up into living protoplasm, and protoplasm in
broken down into simpler compounds with the
exchange of energy.
Nitrification biological conversion of
nitrogenous matter into nitrates.
Oxidation combining of oxygen with other
chemical elements.
Oxidation Pond holding area where
organic wastes are broken down by bacteria in
the presence of oxygen.
Pathogenic disease-causing.
Polychlorinated Biphenyls (PCBs) a
group of toxic, persistent chemicals used in
making transformers and capacitors.
Precipitation process where chemicals
combine to produce a compound that can be
easily removed from a solution.
Pressure Sewer collection system in which
wastewater is pumped under pressure from
homes into a central treatment or disposal
facility.
Primary Waste Treatment first stage of
wastewater treatment; removal of floating
debris and solids by screening and
sedimentation.
Pump Station facility used to pressurize or
raise sewage to a higher elevation.
Secondary Waste Treatment bacterial
treatment of wastewater to consume organic
wastes in the presence of oxygen; pollutant
removal resulting in effluent of 30 mg/L or less
of BOD and SS.
Sedimentation letting solids settle out of
wastewater by gravity during treatment.
Separate Sewer collection system which
uses a sanitary sewer to carry only wastewater,
and a storm sewer to carry runoff from
rainwater.
Sludge concentrated solids removed from
sewage during wastewater treatment.
Soluble material that can be dissolved in a
liquid to form a homogeneous material.
Submain sewer connecting laterals to
mains.
Suspended Solids (SS) small particles of
solid pollutants in sewage that cause cloudiness
and require special treatment to remove.
Vacuum Sewer collection system in which
a central vacuum source maintains a vacuum
or small-diameter pressure mains.
Watershed the land area that drains into a
stream or river.
16
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Working for Clean Water is a
program designed to help advisory
groups improve decision making in
water quality planning. It aims at
helping people focus on essential
issues and questions by providing
trained instructors and materials
suitable for persons with
non-technical backgrounds. These
materials include a citizen
handbook on important principles
and considerations about topics in
water quality planning, an
audiovisual presentation., and an
instructor guide for elaborating
points, providing additional
information, and engaging in
problem-solving exercises.
This program consists of 18
informational units on various
aspects of water quality planning:
Role of Advisory Groups
Public Participation
Nonpoint Source Pollution:
Agriculture, Forestry, and Mining
Urban Stormwater Runoff
Groundwater Contamination
Facility Planning in the
Construction Grants Program
Municipal Wastewater Processes:
Overview
Municipal Wastewater Processes:
Details
Small Systems
Innovative and Alternative
Technologies
Industrial Pretreatment
Land Treatment
Water Conservation and Reuse
Multiple Use
Environmental Assessment
Cost-Effectiveness Analysis
Wastewater Facilities Operation
and Management
Financial Management
The units are not designed to
make technical experts out of
citizens and local officials. Each
unit contains essential facts, key
questions, advice on how to deal
with the issues, and
clearly-written technical
backgrounds. In short, each unit
provides the information that
citizen advisors need to better
fulfill their role.D
This program is available through
public participation coordinators at
the regional offices of the United
States Environmental Protection
Agency.
This information program was
financed with federal funds from
the U.S. Environmental Protection
Agency under Cooperative
Agreement No. CT900980 01. The
information program has been
reviewed by the Environmental
Protection Agency and approved
for publication. Approval does not
signify that the contents
necessarily reflect the views and
policies of the Environmental
Protection Agency, nor does the
mention of trade names or
commercial products constitute
endorsement of recommendation
for use.
This project is dedicated to the
memory of Susan A. Cole.
r.,amon >
'230 South Dearborn Street
HUnois 60604
Chicago,
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