&EPA
             United States
             Environmental Protection
             Agency
            Office of Water
            Office of Wastewater Management
            Washington DC 20460
EPA 832-R-04-001
September 2004
Primer for Municipal
Wastewater Treatment
Systems



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Primer for Municipal                Treatment

Clean Water Act Requirements for Wastewater Treatment	4

The Need for Wastewater Treatment	5

Effects of Wastewater on Water Quality	5

Some of the Key Challenges Faced by Wastewater Treatment Professionals Today         6

Collecting and Treating Wastewater_
   Centralized Collection	6
      Combined Sewer Systems	7
      Sanitary Sewer System	9
Pollutants:	8
   Oxygen-Demanding Substances	8
   Pathogens	8
   Nutrients	8
   Synthetic Organic and Inorganic Chemicals	8
   Thermal	8
Wastewater Treatment
Primary Treatment 	
Preliminary Treatment 	
Primary Sedimentation
Rasir Wastewater Treatment Processes
Physical
Biological
Chemical
Secondary Treatment 	
Attached Growth Processes
Suspended Growth Processes
Lagoons 	
1 and Treatment
slow Rate infiltration
Rapid Infiltration 	
Overland Flow
Constructed Wet lands 	
Disinfection 	
Chlorine
O7one
9
	 9
	 9
11
10
10
10
10
	 11
11
12
	 13
14
14
	 15
15
	 15
	 16
16
      Ultraviolet Radiation
Pretreatment	16

Advanced Methods of Wastewater Treatment	17
   Nitrogen Control	17
   Biological Phosphorus Control	18
   Coagulation-Sedimentation	18
   Carbon Adsorption	19

The Use or Disposal of Wastewater Residuals and Biosolids                           19
   Land Application	20
   Incineration                                                                20
   Beneficial Use Products from Biosolids	21

Decentralized (Onsite or Cluster) Systems	21
   Treatment                                                                 22
      Conventional Septic Tanks	22
      Aerobic Treatment Units	22
      Media Filters                                                            22
   Dispersal Approaches	23
      Absorption Field	23
      Mound System	23
      Drip Dispersal System	24
      Evapotranspiration Beds	24
   Management of Onsite/Decentralized Wastewater Systems	24

Asset Management	24
   Operation	25
   Maintenance                                                               25

Common Wastewater Treatment Terminology	25

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                  Timeline of Federal Water
             Pollution Control Acts and Programs
 Secondary Treatment Regulations
                                       Federal Water Pollution Contol
                                         Act Amendments of 1972
1974
1975
                                      Clear Water Act Amendments of 1977
National Pretreatment Program Rule
      National Municipal Policy
  Secondary Treatment Regulations
                                       Clear Water Act Amendments
                                          of 1981, PL 97-177
                                      Clear Water Act Amendments of 1987
       Phase I Storm Water Rule
    Part 503 Standards for Use and
     Disposal of Sewage Sludge
                                       CSO Control Policy
       Phase II Storm Water Rule
                                       Federal Clean Water Action Plan

        Confined Animal Feeding
            Operation Rule
   Clean Water Act Requirements for
          Wastewater Treatment

The 1972 Amendments to the Federal
Water Pollution Control Act (Public Law 92-
500-, known as the Clean Water Act (CWA),
established the foundation for wastewater
discharge control in this country. The CWA's
primary objective is to 'restore and maintain the
chemical, physical and  biological integrity of the
nation's waters.'

The CWA established a control program for
ensuring that communities have clean water
by regulating the release of contaminants
into our country's waterways. Permits that
limit the amount of pollutants discharged
are required of all municipal  and industrial
wastewater dischargers under the  National
Pollutant Discharge Elimination System  (NPDES)
permit program.  In  addition, a construction
grants program was set up to assist publicly-
owned wastewater treatment works build the
improvements required to meet these new limits.
The 1987 Amendments to the CWA established
State Revolving Funds (SRF) to replace grants as
the current principal federal funding source for
the construction of wastewater treatment and
collection systems.

Over 75  percent of the  nation's population is
served by centralized wastewater collection
and treatment systems. The  remaining
population uses septic or other onsite systems.
Approximately 16,000 municipal wastewater
treatment facilities are in operation nationwide.
The CWA requires that municipal wastewater
treatment plant discharges meet a minimum of
'secondary treatment'.  Over 30 percent of the
wastewater treatment facilities today produce
cleaner discharges by providing even greater
levels of treatment than secondary.

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        Primer  for  Municipal
Wastewater  Treatment
                                          Systems
     The Need for Wastewa-
     ter Treatment
     Wastewater treatment is
     needed so that we can
     use our rivers and streams
     for fishing, swimming and
     drinking water. For the first
     half of the 20th century,
     pollution in the Nation's
     urban waterways resulted in
     frequent occurrences of low
     dissolved oxygen, fish kills,
     algal blooms and bacterial
     contamination. Early efforts
     in water pollution control
     prevented human waste
     from reaching water supplies
     or reduced floating debris
     that obstructed shipping.
     Pollution problems and their
     control were primarily local,
     not national, concerns.
     Since then,  population
     and industrial growth have
     increased demands on our
     natural resources, altering
     the situation dramatically.
     Progress in  abating pollution
     has barely kept ahead of
     population growth, changes
     in industrial processes,
     technological developments,
     changes in land use,
     business innovations,
     and many other factors.
     Increases in both the
     quantity and variety of goods
produced can greatly alter
the amount and complexity
of industrial wastes and
challenge traditional
treatment technology. The
application of commercial
fertilizers and pesticides,
combined with sediment
from growing development
activities, continues to be a
source of significant pollution
as runoff washes off the
land.
Water pollution issues now
dominate public concerns
about national water quality
and maintaining healthy
ecosystems. Although a
large investment in water
pollution control has helped
reduce the problem, many
miles of streams are still
impacted by a variety of
different pollutants.  This,
in turn, affects the ability of
people to use the water for
beneficial purposes. Past
approaches used to control
water pollution control must
be modified to accommodate
current and emerging issues

Effects of Wastewater on
Water Quality
The basic function of the
Wastewater treatment plant
is to speed up the natural
processes by which water
purifies itself. In earlier
years, the natural treatment
process in streams and
lakes was adequate to
perform basic Wastewater
treatment.  As our population
and industry grew to their
present size, increased
levels of treatment prior
to discharging domestic
Wastewater became
necessary.

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          (Dafa form U.S. Public Health Service multi wasfewafer inventories:
                           2000 USEPA Clean Watershed Needs Survey)
           Population Receiving Different Levels of
                    Wastewater Treatment
     220
  c
  o
 -a
  (D
  >
  !__
  (D
 C/3
  C
  O
  D
  CL
           Before the CWA
                             After the CWA
1  Raw discharges were eliminated by  1 996
2 Data for the "no-discharge" category were unavailable for 1 968
             Some of the key challenges faced by wasfewafer
             treatment professionals today:

                Many of the wastewater treatment and collection facilities
             are now old and worn, and require further improvement,
             repair or replacement to maintain their useful life;

                The character and quantity of contaminants presenting
             problems today are far more complex than those that pre-
             sented challenges in the past;

              • Population growth is taxing many existing wastewater
             treatment systems and creating  a need for new plants;

              • Farm runoff and increasing urbanization provide ad-
             ditional  sources of pollution  not controlled by wastewater
             treatment; and

                One third of new development is served by decentralized
             systems (e.g., septic systems) as population  migrates further
             from metropolitan areas.
Collecting and Treating
Wastewater
The most common form
of pollution control in the
United States consists of
a system of sewers and
wastewater treatment plants.
The sewers collect municipal
wastewater from homes,
businesses, and  industries
and deliver it to facilities
for treatment before  it is
discharged to water bodies
or land, or reused.

Centralized Collection
During the early days of our
nation's history, people living
in both the cities and the
countryside used  cesspools
and privies to dispose of
domestic wastewater. Cities
began to install wastewater
collection systems in  the late
nineteenth century because
of an  increasing awareness
of waterborne disease and
the popularity of indoor
plumbing and flush toilets.
The use of sewage collection
systems brought dramatic
improvements to public
health, further encouraging
the growth of metropolitan
areas. In the year 2000
approximately 208 million
people in the U.S. were
served by centralized
collection systems.

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Combined Sewer Systems
Many of the earliest sewer systems were combined sewers, designed to collect both sanitary
wastewater and storm water runoff in a single system. These combined sewer systems were
designed to provide storm drainage from streets and roofs to prevent flooding in cities.
Later, lines were added to carry domestic wastewater away from homes and businesses.
Early sanitarians thought that these combined systems provided adequate health protection.
We now know that the overflows designed to release excess flow during rains also release
pathogens and other pollutants.
                            Simplified Urban Water Cycle

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Pollutants
Oxygen-Demanding Substances
Dissolved oxygen is a key element in water quality that is necessary to support aquatic life.
A demand is placed on the natural supply of dissolved oxygen by many pollutants in waste-
water. This is called biochemical oxygen demand, or BOD, and is used to measure how well
a sewage treatment plant is working. If the effluent, the treated wastewater produced  by a
treatment plant, has a high content of organic pollutants or ammonia, it will demand  more
oxygen from the water and leave the water with less oxygen to support fish and other aquatic
life.
Organic matter and ammonia are "oxygen-demanding" substances.  Oxygen-demand-
ing substances are contributed by domestic sewage and agricultural and industrial wastes
of both plant and animal origin, such as those from food processing, paper mills, tanning,
and other manufacturing processes. These substances are usually destroyed or converted
to other compounds by bacteria if there is sufficient oxygen present in the water, but the dis-
solved oxygen needed to sustain fish life is used up in this break down process.
Pathogens
Disinfection of wastewater and chlorination of drinking water supplies has reduced the oc-
currence of waterborne diseases such as typhoid fever, cholera, and dysentery, which remain
problems in underdeveloped countries while they have been virtually eliminated in the U.S.
Infectious micro-organisms, or pathogens, may be carried into surface and groundwater by
sewage from cities and institutions, by certain kinds of industrial wastes, such as tanning and
meat packing plants, and by the contamination of storm runoff with animal wastes from pets,
livestock and wild animals, such as geese or deer.  Humans may come in contact with these
pathogens either by drinking contaminated water or through swimming, fishing, or other
contact activities.  Modern disinfection techniques have greatly reduced the danger of water-
borne disease.

Nutrients

Carbon, nitrogen, and phosphorus are essential to living organisms and are the chief nutri-
ents present in natural water.  Large amounts of these nutrients are also present in sewage,
certain industrial wastes, and drainage from fertilized land.  Conventional secondary bio-
logical treatment processes do not remove the phosphorus and nitrogen to any substantial
extent -- in fact, they may convert the organic forms of these substances into mineral form,
making them  more usable by plant life. When an excess of these nutrients overstimulates the
growth of water plants, the result causes unsightly conditions, interferes with drinking water
treatment processes, and  causes unpleasant and disagreeable tastes and odors in drinking
water.  The release of large amounts of nutrients, primarily phosphorus but occasionally ni-
trogen,  causes nutrient enrichment which results in excessive growth of algae.  Uncontrolled
algae growth blocks out sunlight and chokes aquatic plants and animals by depleting dis-
solved  oxygen in the water at night.  The release of  nutrients in quantities that exceed the
affected waterbody's ability to assimilate them results in a  condition called eutrophication or
cultural enrichment.

Inorganic and Synthetic Organic Chemicals
Avast array of chemicals are included in this category. Examples include detergents, house-
hold cleaning aids, heavy metals, pharmaceuticals, synthetic organic pesticides and  her-
bicides, industrial chemicals, and the wastes from their manufacture. Many of these sub-
stances are toxic to fish and aquatic life and many are harmful to humans. Some are known
to be highly poisonous at very low concentrations.  Others can cause taste and odor prob-
lems, and many are not effectively removed by conventional wastewater treatment.
Thermal

Heat reduces the capacity of water to retain oxygen.  In some areas, water used for cooling
is discharged to streams at elevated temperatures from power plants and industries. Even
discharges from wastewater treatment plants and storm water retention ponds affected by
summer heat can  be released at temperatures above that of the receiving water, and elevate
the stream temperature.  Unchecked discharges of waste heat can seriously alter the ecology
of a lake,  a stream, or estuary.

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        Workers install sewer line
Sanitary Sewer Systems
Sanitary sewer collection
systems serve over half the
people in the United States
today.  EPA estimates that
there are approximately
500,000 miles of publicly-
owned sanitary sewers
with a similar expanse of
privately-owned sewer
systems. Sanitary sewers
were designed and built
to carry wastewater from
domestic,  industrial and
commercial sources, but
not to carry storm water.
Nonetheless, some storm
water enters sanitary sewers
through cracks, particularly
in older lines, and through
roof and basement drains.
Due to the much  smaller
volumes of wastewater
that pass through sanitary
sewer lines compared to
combined sewers, sanitary
sewer systems use smaller
pipes  and lower the cost of
collecting wastewater.
Wastewater Treatment
In 1892, only 27 American
cities provided wastewater
treatment.  Today, more
than 16,000 publicly-owned
wastewater treatment plants
operate in the United States
and its territories. The
construction of wastewater
treatment facilities
blossomed  in the 1920s and
again after the passage of
the CWAin 1972 with the
availability  of grant funding
and new requirements
calling for minimum levels
of treatment.  Adequate
treatment of wastewater,
along with the ability to
provide a sufficient supply
of clean water, has become
a major concern for many
communities.

Primary Treatment
The initial stage  in the
treatment of domestic
wastewater is known as
primary treatment. Coarse
solids are removed from
the wastewater in the
primary stage of treatment.
In some treatment plants,
primary and secondary
stages may be combined
into one basic operation.
At many wastewater
treatment facilities, influent
passes through preliminary
treatment units before
primary and secondary
treatment begins.
Preliminary Treatment
As wastewater enters a
treatment facility, it typically
flows through a step called
preliminary treatment. A
screen removes large floating
objects, such as rags, cans,
bottles and sticks that may
clog pumps, small pipes, and
down  stream processes.  The
screens vary from coarse to
fine and are constructed with
parallel steel or iron bars
with openings of about half
an inch, while others may
be made from mesh screens
with much smaller openings.

Screens are generally placed
in a chamber or channel and
inclined towards the flow of
the wastewater.  The inclined
screen allows debris to be
caught on the upstream
surface of the screen, and
allows access for manual
or mechanical cleaning.
Some plants use devices
known as comminutors or
barminutors which combine
the functions of a screen and
a grinder. These devices
catch  and then cut or shred
the heavy solid and floating
material.  In the process, the
pulverized matter remains
in the wastewater flow to be
removed later in a primary
settling tank.
"the ability to
provide a sufficient
supply of dean
water continues to
be a major national
concern"

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Basic Wastewater Treatment Processes
 Physical
 Physical processes were
 some of the earliest methods
 to remove solids from
 wastewater, usually by
 passing wastewater through
 screens to remove debris
 and solids. In addition,
 solids that are heavier than
 water will settle out from
 wastewater by gravity.
 Particles with  entrapped
 air float to the top of water
 and can also  be removed.
 These physical processes are
 employed  in many modern
 wastewater treatment
 facilities today.
Biological
In nature, bacteria and
other small organisms in
water consume organic
matter in sewage, turning
it into new bacterial cells,
carbon dioxide, and other
by-products.  The bacteria
normally present in water
must have oxygen to do
their part in  breaking down
the sewage.  In the 1920s,
scientists observed that these
natural processes could be
contained and accelerated
in systems to remove organic
material from wastewater.
With the  addition of oxygen
to wastewater, masses of
microorganisms grew and
rapidly metabolized organic
pollutants. Any excess
microbiological growth
could be removed from
the wastewater by physical
processes.
Chemical
Chemicals can be used to
create changes in pollutants
that increase the removal
of these new forms by
physical processes.  Simple
chemicals such as alum,
lime or iron  salts can be
added to wastewater to
cause certain pollutants,
such as phosphorus, to floe
or bunch together into large,
heavier masses which can
be removed  faster through
physical processes.  Over the
past 30 years, the chemical
industry has developed
synthetic  inert chemicals
know as polymers to
further improve the  physical
separation step in wastewater
treatment. Polymers are
often  used at the later
stages of treatment to
improve the  settling of excess
microbiological growth or
biosolids.
                                                                                    sr




                                                                                    ;s
                                                                              III «_M
After the wastewater has
been screened, it may flow
into a grit chamber where
sand, grit, cinders, and small
stones settle to the bottom.
Removing the grit and gravel
that washes off streets or
land during storms is very
important, especially in
cities with combined sewer
systems.  Large amounts
 of grit and sand entering a
 treatment plant can cause
 serious operating problems,
 such as excessive wear of
 pumps and other equipment,
 clogging of aeration devices,
 or taking up capacity in tanks
 that is needed for treatment.
 In some plants, another
 finer screen is placed after
 the grit chamber to remove
  any additional material that
  might damage equipment or
  interfere with later processes.
  The grit and screenings
  removed by these processes
  must be periodically
  collected and trucked to a
  landfill for disposal or are
  incinerated.

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Basic Treatment... primary stage
 Primary Sedimentation
 With the screening
 completed and the grit
 removed, wastewater still
 contains dissolved organic
 and inorganic constituents
 along with suspended
 solids.  The suspended solids
 consist  of minute particles of
 matter that can be removed
 from the wastewater
 with further treatment
 such as sedimentation or
 gravity  settling, chemical
 coagulation,  or filtration.
 Pollutants that are dissolved
 or are very fine and remain
 suspended in the wastewater
 are not  removed effectively
 by gravity settling.

 When the wastewater enters
 a sedimentation tank, it slows
 down and the suspended
 solids gradually sink to the
 bottom. This mass of solids
 is called primary sludge.
 Various methods have been
 devised to remove primary
 sludge from the tanks.
 Newer plants have some type
 of mechanical equipment
 to remove the settled solids
 from sedimentation tanks.
 Some plants  remove solids
 continuously  while others do
 so at intervals.
Secondary Treatment
After the wastewater has
been through Primary
Treatment processes, it
flows into the next stage of
treatment called secondary.
Secondary treatment
processes can remove up to
90 percent of the organic
matter in wastewater by
using biological treatment
processes. The two most
common conventional
methods used to achieve
secondary treatment are
attached growth processes
and suspended growth
processes..

Attached Growth
Processes
In attached growth (or fixed
film) processes, the microbial
growth occurs on the surface
of stone or plastic media.
Wastewater passes over
the media along with air to
 Solids removed from
automated bar screens

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Sequencing Batch
Reactor
provide oxygen.  Attached
growth process units include
trickling filters, biotowers,
and rotating biological
contactors. Attached growth
processes are effective at
removing  biodegradable
organic material from the
wastewater.

A trickling filter is simply
a bed of media (typically
rocks or plastic) through
which the  wastewater passes.
The media ranges from
three to six feet deep and
allows  large numbers of
microorganisms to attach
and grow.  Older treatment
facilities typically  used
stones, rocks, or slag as the
media bed material.  New
facilities may use beds made
of plastic balls, interlocking
sheets of corrugated plastic,
or other types of synthetic
media.  This type of bed
material often provides
more surface area and
a better environment for
promoting and controlling
biological treatment than
rock.  Bacteria, algae, fungi
and  other microorganisms
grow and  multiply, forming
a microbial growth or slime
layer (biomass) on the
media.  In the treatment
process, the bacteria use
oxygen from the air and
consume most of the organic
matter in the wastewater  as
food. As the wastewater
passes down through the
media, oxygen-demanding
substances are consumed by
the biomass and the water
leaving the media is much
cleaner.  However, portions
of the biomass also slough
off the media and must settle
out in a secondary treatment
tank.
Suspended Growth
Processes
Similar to the microbial
processes in attached growth
systems,  suspended growth
processes are designed
to remove biodegradable
organic material and
organic nitrogen-containing
material  by converting
ammonia nitrogen to
nitrate unless additional
treatment is provided. In
suspended growth processes,
the microbial growth is
suspended in an aerated
water mixture where the air
is pumped  in, or the water is
agitated  sufficiently to allow
oxygen transfer. Suspended
growth process units include
variations of activated
sludge, oxidation ditches and
sequencing batch reactors.

The suspended growth
process speeds up the work
of aerobic  bacteria and
other microorganisms that
break down the organic
matter in the sewage  by
providing a rich  aerobic
environment where the
microorganisms suspended
in the wastewater  can work
more efficiently. In the
aeration  tank, wastewater  is
vigorously  mixed with air and
microorganisms acclimated
to the wastewater in a
suspension for several hours.
This allows the bacteria

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and other microorganisms
to break down the organic
matter in the wastewater.
The microorganisms grow
in number and the excess
biomass is removed by
settling  before the effluent
is discharged or treated
further.  Now activated
with millions of additional
aerobic bacteria,  some of
the biomass can be used
again by returning it to an
aeration tank for  mixing with
incoming wastewater.

The activated sludge
process, like most other
techniques, has advantages
and limitations. The units
necessary for this treatment
are relatively small, requiring
less space than attached
growth processes. In
addition, when  properly
operated and maintained,
the process is generally
free of flies and odors.
However, most activated
sludge processes  are more
costly to operate than
attached growth processes
due to higher energy use
to run the aeration system.
The effectiveness of the
activated sludge process
can be impacted by elevated
levels of toxic compounds in
wastewater unless complex
industrial chemicals are
effectively controlled through
an industrial pretreatment
program.

An adequate supply of
oxygen is necessary for the
activated sludge process to
be effective. The oxygen
is generally supplied by
mixing air with the sewage
and biologically active
solids in the aeration
tanks by one or more of
several different methods.
Mechanical aeration can  be
accomplished by drawing
the sewage up from the
bottom of the tank and
spraying it over the surface,
thus allowing the sewage
to absorb  large amounts  of
oxygen from the atmosphere.
Pressurized air can be forced
out through small openings
in pipes suspended in the
wastewater.  Combination
                                                            Centerfeed well of a clarifier for
                                                            removing excess biomass
of mechanical aeration and
forced aeration can also be
used. Also, relatively pure
oxygen, produced by several
different manufacturing
processes,  can be added
to provide oxygen to the
aeration tanks.

From the aeration tank,
the treated wastewater
flows to a sedimentation
tank (secondary clarifier),
where the excess biomass
is removed. Some of the
biomass is  recycled to the
head end of the aeration
tank, while the remainder is
"wasted" from the system.
The waste biomass and
settled solids are treated
before disposal or  reuse as
biosolids.

Lagoons
A wastewater lagoon
or treatment pond  is a
scientifically constructed
pond, three to five feet
deep, that allows sunlight,
      Secondary Treatment Suspended Growth Process

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Wastewater Lagoon
                     algae, bacteria, and oxygen
                     to interact. Biological and
                     physical treatment processes
                     occur in the lagoon to
                     improve water quality.  The
                     quality of water leaving the
                     lagoon, when constructed
                     and operated properly, is
                     considered equivalent to the
                     effluent from a conventional
                     secondary treatment system.
                     However, winters in cold
                     climates have a significant
                     impact on the effectiveness
                     of lagoons, and winter
                     storage is usually required.

                     Lagoons have several
                     advantages when used
                     correctly.  They can be used
                     for secondary treatment
                     or as  a supplement to
                     other  processes.  While
                     treatment ponds require
                     substantial land area and
                     are predominantly used
                     by smaller communities,
                     they account for more
                     than one-fourth of the
                     municipal wastewater
                     treatment facilities in this
                     country.  Lagoons remove
                     biodegradable organic
                     material and some of the
                     nitrogen from wastewater.
Land Treatment
Land treatment is the
controlled application of
wastewater to the soil  where
physical, chemical, and
biological processes treat
the wastewater as it passes
across or through the  soil.
The principal types of land
treatment are slow rate,
overland flow, and rapid
infiltration.  In the arid
western states,  pretreated
municipal wastewater has
been used for many years
to irrigate crops.  In more
recent years, land treatment
has spread to all sections of
the country.  Land treatment
of many types of industrial
wastewater is also common.

Whatever method is
used, land treatment can
be a feasible economic
alternative, where the land
area needed is readily
available, particularly
when compared to costly
advanced treatment plants.
Extensive  research has been
conducted at land treatment
sites to determine treatment
performance and study
the numerous treatment
processes involved, as
well as potential impacts
on the environment, e.g.
groundwater, surface  water,
and any crop that may be
grown.
Slow Rate Infiltration
In the case of slow rate
infiltration, the wastewater
is applied to the land and
moves through the soil
where the natural filtering
action of the soil along
with microbial activity and
plant uptake removes most
contaminants. Part of the
water evaporates or is used
by plants. The remainder is
either collected  via drains or
wells for surface discharge or
allowed to percolate into the
groundwater.

Slow rate  infiltration is
the most commonly used
land treatment technique.
The wastewater, which is
sometimes disinfected before
application, depending on
the end use of the crop and
the irrigation  method, can
be applied to the land by
spraying, flooding, or ridge
and  furrow irrigation.  The
method selected depends on
cost considerations, terrain,
and  the type of crops. Much
of the water and most of the
nutrients are used by the
plants, while other pollutants
are transferred to the soil
by adsorption, where many
are mineralized or broken
down over time by microbial
action.

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           Biologically Degradable Wastewater Treated in the U.S. has
            increased since 1 940, however, treatment efficiency has
            improved so that pollution has decreased.
     80,000


     70,000
   ">C
   •! 60,000
   c
   0

   1 50,000

   u>
   4 40,000
   § 30,000
     20,000

     10,000
             1940   1950   1960
                           1970  1980  1990  1996     2016
                              Year
     165 gal/capita-day is based on data in the Clean Water Needs Surveys for 1 978
     through 1986 and accounts for residential, commercial, industrial, stormwater, and
     infiltration and inflow components.
Rapid  Infiltration
The rapid infiltration
process is most frequently
used to polish and recover
wastewater effluents for
reuse after pretreatment by
secondary and advanced
treatment processes. It is
also effective in cold or
wet weather and has been
successfully used in Florida,
northeastern and arid
southwestern states. Large
amounts of wastewater
are applied to permeable
soils in a limited  land area
and allowed  to infiltrate
and percolate downward
through the soil into the
water table below. If the
water is to be reused, it can
be recovered by wells.  The
cost-effectiveness of this
process depends on the soil's
ability to percolate a large
volume of water quickly and
efficiently,  so suitable soil
drainage is important.
Overland Flow
This method has been used
successfully by the food
processing industries for
many years to remove solids,
bacteria and nutrients from
wastewater.  The wastewater
is allowed to flow down a
gently-sloped surface that is
planted with vegetation to
control  runoff and erosion.
Heavy clay soils are well
suited to the overland flow
process. As the water flows
down the slope, the soil and
its microorganisms form a
gelatinous slime layer similar
in  many ways to a trickling
filter that effectively removes
solids, pathogens, and nutri-
ents.  Water that is not
absorbed or evaporated is
recovered at the bottom of
the slope for discharge or
reuse.
Constructed Wetlands
Wetlands are areas where
the water saturates the
ground long enough to
support and maintain
wetland vegetation such
as reeds, bulrush, and
cattails.  A "constructed
wetlands" treatment system is
designed to treat wastewater
by passing it through the
wetland.  Natural physical,
chemical, and biological
wetland processes have  been
recreated and enhanced
in constructed wetlands
designed specifically to treat
wastewater from industries,
small communities, storm
runoff from urban and
agricultural areas, and acid
mine drainage.  Significant
water quality improvements,
including nutrient reduction,
can be achieved
                                       Constructed Wetlands

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                                   Land Treatment - Rapid Infiltration
Disinfection
Untreated domestic
wastewater contains micro-
organisms or pathogens that
produce human diseases.
Processes used to kill or
deactivate these harmful
organisms are called
disinfection.  Chlorine is the
most widely used disinfectant
but ozone and ultraviolet
radiation are also frequently
used for wastewater effluent
disinfection.

Chlorine
Chlorine kills micro-
organisms by destroying
cellular material.  This
chemical can be applied to
wastewater as a  gas, a liquid
or in a solid form similar to
swimming pool disinfection
chemicals.  However, any
free (uncombined)  chlorine
remaining in the water,
even at low concentrations,
is highly toxic to  beneficial
aquatic life. Therefore,
removal of even trace
amounts of free chlorine
by dechlorination is often
needed to protect fish
and aquatic life. Due to
emergency response and
potential safety concerns,
chlorine gas is used less
frequently now than in the
past.

Ozone
Ozone is produced from
oxygen exposed to a high
voltage current.  Ozone is
very effective at destroying
viruses and bacteria and
decomposes back to oxygen
rapidly without  leaving
harmful by products.  Ozone
is not very economical due to
high energy costs.

Ultraviolet Radiation
Ultra violet (UV) disinfection
occurs when electromagnetic
energy in the form of  light in
the UV spectrum produced
by mercury arc  lamps
penetrates the cell wall of
exposed microorganisms.
The UV radiation retards the
ability of the microorganisms
to survive by damaging
their genetic material. UV
disinfection is a  physical
treatment process that
leaves no chemical traces.
Organisms can sometimes
repair and reverse the
destructive effects of UV
when applied at low doses.
Pretreatment
The National Pretreatment
Program, a cooperative
effort of Federal, state,
POTWs and their industrial
dischargers, requires industry
to control the amount of
pollutants discharged into
municipal sewer systems.
Pretreatment protects the
wastewater treatment
facilities and its workers
from pollutants that may
create hazards or interfere
with the operation  and
performance of the POTW,
including contamination of
sewage sludge, and reduces
the likelihood that  untreated
pollutants are introduced into
the receiving waters.

Under the Federal
Pretreatment Program,
municipal wastewater
plants receiving significant
industrial discharges must
develop local pretreatment
programs to control
industrial discharges into
their sewer system. These
programs must be  approved
by either EPA or a  state
acting as the Pretreatment
Approval Authority. More
than 1,500 municipal
treatment plants have
developed and received
approval for a Pretreatment
Program.

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Advanced Methods of
Wastewater Treatment
As our country and the
demand for clean water
have grown, it has become
more important to produce
cleaner wastewater effluents,
yet some contaminants are
more difficult to remove
than others. The demand
for cleaner discharges has
been  met through better
and more complete methods
of removing pollutants at
wastewater treatment plants,
in addition to pretreatment
and pollution prevention
which helps limit types of
wastes discharged to the
sanitary sewer system.
Currently, nearly all WWTPs
provide a  minimum of
secondary treatment.  In
some receiving waters, the
discharge of secondary
treatment  effluent would
still degrade water quality
and inhibit aquatic life.
Further treatment is needed.
Treatment levels beyond
secondary are called
advanced treatment.

Advanced treatment
technologies can be
extensions of conventional
secondary biological
treatment to further
stabilize oxygen-demanding
substances  in the wastewater,
or to remove  nitrogen and
phosphorus. Advanced
treatment may also
involve physical-chemical
separation techniques
such as adsorption,
f I occu I at ion/precipitation,
membranes for advanced
filtration, ion  exchange,
and reverse osmosis.  In
various combinations, these
processes can achieve any
degree of pollution control
desired.  As wastewater is
purified to higher and higher
degrees by such advanced
treatment processes, the
treated effluents can be
reused for urban, landscape,
and agricultural irrigation,
Monitoring a discharger as part of a Pretreatment Program
industrial cooling and
processing, recreational uses
and water recharge, and
even indirect augmentation
of drinking water supplies.

Nitrogen Control
Nitrogen in one form
or another is present in
municipal wastewater and
is usually not removed by
secondary treatment.  If
discharged into lakes  and
streams or estuary waters,
nitrogen in the form of
ammonia can exert a
direct demand on oxygen
or stimulate the excessive
growth of algae.  Ammonia
in wastewater effluent can be
toxic to aquatic life  in  certain
instances.

By providing additional
biological treatment beyond
the secondary stage,
nitrifying bacteria present
in wastewater treatment can
biologically convert ammonia
to the non-toxic nitrate
through a process known as
nitrification. The nitrification
process is normally sufficient
to  remove the toxicity
associated with ammonia in
the effluent. Since nitrate
is also a nutrient, excess
amounts can contribute to
the uncontrolled growth of
algae. In situations where
nitrogen must be completely
removed from effluent, an

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                                                                      Nitrification Process Tank
additional biological process
can be added to the system
to convert the nitrate to
nitrogen gas. The conversion
of nitrate to nitrogen gas is
accomplished by bacteria
in a process known  as
denitrification. Effluent
with nitrogen in the  form of
nitrate is  placed into a tank
devoid of oxygen, where
carbon-containing chemicals,
such as methanol, are added
or a small stream of raw
wastewater is mixed in with
the nitrified effluent. In  this
oxygen free environment,
bacteria use the oxygen
attached  to the nitrogen in
the nitrate form releasing
nitrogen gas. Because
 CHEMICAL
nitrogen comprises almost
80 percent of the air in the
earth's atmosphere, the
release of nitrogen into the
atmosphere does not cause
any environmental harm.
Biological Phosphorus
Control
Like nitrogen, phosphorus
is also a necessary nutrient
for the growth of algae.
Phosphorus reduction is
often  needed to prevent
excessive algal growth
before discharging effluent
into lakes, reservoirs and
estuaries.  Phosphorus
removal can be achieved
through chemical addition
and a coagulation-
sedimentation process
discussed in the following
section. Some biological
treatment processes
called biological nutrient
removal (BNR) can also
achieve nutrient reduction,
removing both nitrogen
and phosphorus.  Most of
the BNR processes involve
modifications of suspended
growth treatment systems
so that the  bacteria  in these
systems also convert nitrate
nitrogen to inert nitrogen gas
and trap phosphorus in the
solids that are removed from
the effluent.
Coagulation-
sedimentation
A process known as chemical
coagulation-sedimentation
is used to increase the
removal of solids from
effluent after primary
and secondary treatment.
Solids heavier than water
settle out of wastewater by
gravity. With the addition of
specific chemicals, solids can
become heavier than water
and will settle.

Alum, lime, or iron salts
are chemicals added to
the wastewater to remove
phosphorus. With these
chemicals, the smaller
particles 'floe' or clump
together into  large masses.
The larger masses  of
particles will settle faster
when the effluent reaches the
next step--the sedimentation
tank.  This process can
reduce the concentration of
phosphate by more than 95
percent.

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Although used for years in
the treatment of industrial
wastes and in water
treatment, coagulation-
sedimentation is considered
an advanced process
because it is not routinely
applied to the treatment of
municipal wastewater.  In
some cases, the process
is used as a necessary
pretreatment step for other
advanced techniques. This
process produces  a chemical
sludge, and the cost of
disposing this material  can
be significant.

         ADSORPTION
Carbon adsorption
Carbon adsorption
technology can remove
organic materials from
wastewater that resist
removal by biological
treatment.  These resistant,
trace organic substances can
contribute to taste and odor
problems in water, taint fish
flesh, and cause foaming
and fish kills.
Carbon adsorption consists
of passing the wastewater
effluent through a bed or
canister of activated carbon
granules or powder which
remove more than 98
percent of the trace organic
substances.  The substances
adhere to the carbon surface
and are removed from the
water.  To help reduce the
cost of the procedure, the
carbon granules can  be
cleaned by heating and used
again.

The Use or Disposal of
Wastewater Residuals
and Biosolids

When pollutants are removed
from water, there is always
something left over.  It may
be rags and sticks caught on
the screens at the beginning
of primary treatment.  It  may
be the solids that settle to
the bottom  of sedimentation
tanks.  Whatever it is, there
are always  residuals that
must be reused, burned,
buried, or disposed of in
some manner that does not
harm the environment.

The utilization and disposal
of the residual process solids
is addressed by the CWA,
Resource Conservation
and Recovery Act (RCRA),
and other federal laws.
These Federal laws re-
enforce the need to employ
environmentally sound
residuals management
techniques and to
beneficially use biosolids
whenever possible.  Biosolids
are processed wastewater
solids ("sewage sludge")
that meet rigorous standards
allowing  safe reuse for
beneficial purposes.
Currently, more than half
of the biosolids produced
by municipal wastewater
treatment systems is
applied to land as a soil
conditioner or fertilizer and
the remaining solids are
incinerated or landfilled.
Ocean dumping of these
solids is no longer allowed.

Prior to utilization or
disposal, biosolids are
stabilized to control odors
and reduce the number of
disease-causing organisms.
Sewage solids, or sludge,
when separated from the
                                                                                                         Biosolids Digester

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Land Application of Biosoilds
wastewater, still contain
around 98 percent water.
They are usually thickened
and may be dewatered
to reduce the volume to
be transported for final
processing, disposal, or
beneficial use. Dewatering
processes include drying
beds, belt filter presses,
plate and frame presses,
and centrifuges. To  improve
dewatering effectiveness,
the solids can be pretreated
with chemicals such as lime,
ferric chloride, or polymers
to produce larger particles
which are easier to remove.
Digestion is a form of
stabilization where the
volatile material in the
wastewater solids can
decompose naturally and the
potential for odor production
is reduced. Digestion without
air in an  enclosed tank
(anaerobic solids digestion)
has the added benefit of
producing methane gas
which can be recovered and
used as a source of energy.
Stabilization of solids may
also be accomplished by
composting, heat treatments,
drying or the addition
of lime or other alkaline
materials.  After stabilization,
the biosolids can  be safely
spread on land.

Land Application
In many areas, biosolids
are marketed to farmers as
fertilizer. Federal  regulation
(40 CFR Pert 503) defines
minimum requirements
for such land application
practices, including
contaminant limits, field
management practices,
treatment requirements,
monitoring, recordkeeping,
and  reporting requirements.
Properly treated and
applied biosolids are a
good source of organic
matter for improving soil
structure and help supply
nitrogen, phosphorus, and
micronutrients that are
required by plants.
Biosolids have also been
used successfully for many
years as a soil conditioner
and fertilizer, and for
restoring and revegetating
areas with poor soils due to
construction activities, strip
mining or other practices.
Under this biosolids
management approach,
treated solids in semi-
liquid or dewatered form
are transported to the soil
treatment areas. The slurry
or dewatered biosolids,
containing nutrients and
stabilized organic  matter, is
spread over the land to give
nature a hand in returning
grass, trees, and flowers to
barren land. Restoration of
the countryside also helps
control the flow of acid
drainage from mines that
endangers fish and other
aquatic life and contaminates
the water with acid, salts,
and excessive quantities of
metals.

Incineration
Incineration consists of
burning the dried solids
to reduce the organic
residuals to an ash that
can be disposed or reused.
Incinerators often  include
heat recovery features.
Undigested sludge solids
have significant fuel value as
a result of their high organic
content.  However, the water
content must be greatly
reduced  by dewatering or
drying to take advantage
of the fuel potential of
the biosolids. For  this
reason, pressure filtration
dewatering equipment is
used to obtain biosolids
which are sufficiently dry
to burn without continual
reliance on auxiliary fuels.
In some cities, biosolids are

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Composted Biosolids
mixed with refuse or refuse-
derived fuel prior to burning.
Generally, waste heat is
recovered to provide the
greatest amount of energy
efficiency.

Beneficial  Use Products
from Biosolids
Heat dried biosolids pellets
have been produced and
used extensively as a
fertilizer product for lawn
care, turf  production, citrus
groves, and vegetable
production for many years.
Composting of biosolids
is also a well established
approach to solids
management that has been
adopted by a number of
communities. The composted
peat-like product  has shown
particular promise for use
in the production  of soil
additives for revegetation  of
topsoil depleted areas, and
as a potting soil amendment.

Effective pretreatment
of industrial wastes
prevents excessive levels
of unwanted constituents,
such as heavy metals
(i.e. cadmium, mercury,
and lead) and persistent
organic compounds from
contaminating the residuals
of wastewater treatment and
limiting the potential for
beneficial use.

Effective stabilization
of wastewater residuals
and their conversion to
biosolid products can be
costly. Some cities have
produced fertilizers from
biosolids which are sold to
help pay part of the cost
of treating wastewater.
Some municipalities use
composted,  heat dried,
or lime stabilized biosolid
products on parks and other
public areas.

Decentralized (Onsite
and Cluster) Systems

A decentralized wastewater
system treats sewage from
homes and businesses
that are not  connected to
a centralized wastewater
treatment plant.
Decentralized treatment
systems include onsite
systems and cluster systems.
An onsite system is a
wastewater system relying on
natural  processes, although
sometimes containing
mechanical components,
to collect, treat, disperse
or reclaim wastewater
from a single dwelling or
building. A septic tank and
soil adsorption field is an
example of an onsite system.
A wastewater collection  and
treatment system  under  some
form of common ownership
that collects wastewater from
two or more dwellings or
buildings and  conveys it to
a treatment and dispersal
system located on a suitable
site near the dwellings or
buildings is a cluster system.
Decentralized  systems
include those using
alternative treatment
technologies like media
filters, constructed wetland
systems, aerobic treatment
units, and a variety  of soil
dispersal systems. Soil
dispersal systems include
g-shaped Digesters

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Septic tank and distribution box
                        pressure systems such as
                        low pressure pipe and drip
                        dispersal systems. These
                        systems treat and disperse
                        relatively small volumes
                        of wastewater, and are
                        generally are found in
                        rural and suburban areas.
                        While septic tanks and soil
                        absorption systems have
                        significant limitations,
                        decentralized systems can
                        effectively protect water
                        quality and public health
                        from groundwater and
                        surface water contamination
                        if managed properly (i.e.
                        properly sited, sized,
                        designed, installed,
                        operated, and maintained).
                        Nitrate concentrations in
                        groundwater that exceed the
                        drinking water standards can
                        cause health problems.

                        Treatment
                        Onsite wastewater systems
                        contain three components:
                        a treatment unit which treats
water prior to dispersal
into the environment; a
soil dispersal component
which assures that treated
water is released  into the
environment at a  rate which
can be assimilated; and a
management system which
assures proper long term
operation of the complete
system. Disinfection
of the treated effluent
may be provided  prior
to dispersal. A typical
onsite system consists of a
septic tank followed by an
effluent distribution system.
Alternative treatment systems
include aerobic treatment
and sand filtration systems.

Conventional Septic
Tanks
A septic tank is a  tank buried
in the ground used to treat
sewage without the presence
of oxygen (anaerobic).  The
sewage flows from the
plumbing  in a  home or small
business establishment into
the first of two chambers,
where solids settle out.  The
liquid then flows into the
second chamber.  Anaerobic
bacteria in the sewage  break
down the organic matter,
allowing cleaner water
to flow out of the  second
chamber.  The liquid typically
discharges through a sub-
surface distribution system.
Periodically, the solid matter
in the bottom of the tank,
referred to as septage, must
be removed and disposed of
properly.

Aerobic Treatment Units
Aerobic treatment units
are also used to provide
onsite wastewater treatment.
They are similar to septic
tanks, except that air is
introduced and mixed with
the wastewater inside the
tank. Aerobic (requiring
oxygen) bacteria consume
the organic matter in the
sewage. As with the typical
septic system, the effluent
discharge from an aerobic
system is typically released
through a sub-surface
distribution system or may be
disinfected and discharged
directly to surface water.
Aerobic treatment units also
require the removal and
proper disposal of solids that
accumulate in  the tank.

Media Filters
Media filters are used to
provide further treatment
of septic tank effluent,
and provide high  levels of
nitrification. They can be
designed to pass the effluent
once or multiple times
through the media bed.
Media, such as sand, acts as
a filter. The media is placed
two to three feet deep above
a liner of impermeable

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 Onsite aerobic treatment unit
material such as plastic
or concrete. Septic tank
effluent is applied to the filter
surface in intermittent doses
and is further treated as it
slowly trickles through the
media.  In most media filters,
wastewater is collected in
an underdrain then either
pumped back to the filter
bed or to other types of
treatment.

Dispersal Approaches
Traditional onsite systems
include treatment units
followed by a drainfield or
absorption field.  Wastewater
from the treatment unit  is
dispersed  through a suitable
soil layer where it receives
additional treatment by the
soil microorganisms and
filtering properties of the
soil.  If the soil  is  unsuitable
for the installation of a soil
absorption field, alternative
methods can be used to
further treat or distribute the
treated effluent. The most
common alternative dispersal
systems include low pressure
pipe, mounds,  drip disposal,
and  evapotranspiration beds.

Absorbtion Field
When soil conditions permit,
the most common method
to disperse septic tank or
aerobic system effluent is an
absorption field consisting
of a  series of perforated
parallel pipes laid in trenches
on gravel or crushed stone
or as a direct discharge to
the soil through trenches.
Typically, effluent flows into
the absorption  field from
a distribution box which
maintains an even flow of
effluent to the absorption
field. From there, the
effluent drains  through the
stone and into  the soil which
provides further treatment.
Mound System
When the soil is not
conducive to percolation or
when the groundwater level
is high, a mound system is
commonly used.  A mound
system is a distribution
system constructed above
the original  ground level
by using granular material
such as sand and  gravel
to receive the septic tank
effluent before it flows to
the native soil below. The
effluent flows to a dosing
tank that is equipped with a
pump.  Here the effluent is
stored  until there is sufficient
liquid.   Once the liquid is
pumped out, it moves evenly
throughout the mound before
reaching less permeable
soil or  ground water.  The
granular material  acts as
a treatment  medium and
improves the removal of
Mound system under construction
(photo courtesy of Ayres Associates)

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                                             Licensed wastewater treatment plant operator
Sewer line maintenance
                 pollutants in ways that
                 may not be provided by
                 substandard native soils.

                 Drip Dispersal System
                 Where soils are very thin or
                 have reduced  permeability,
                 drip dispersal  systems can
                 be utilized. The typical drip
                 system operates like drip
                 irrigation at a  moderately
                 high pressure. The
                 components of a drip system
                 include filters to remove
                 solids, a network of drip
                 tubes to disperse liquid into
                 soil, tanks to hold liquid, and
                 controllers  to regulate the
                 flow to the  drip system.

                 Evapotranspiration Beds
                 Evapotranspiration  (ET)  bed
                 is an onsite dispersal system
where pretreated wastewater
evaporates from the soil
surface or is transpired by
plants into the atmosphere.
Usually, ET beds are used  in
arid climates and there is no
discharge either to surface
or ground water. Vegetation
is planted on the surface of
the sand bed to improve the
transpiration process and
landscaping enhances the
aesthetics of the bed.

Management of Decen-
tralized Systems
Ensuring performance of
decentralized wastewater
treatment systems is an
issue of national concern
because these systems are
a permanent component
of our nation's wastewater
infrastructure. Twenty-
five percent of households
nationwide and one-third
of the new homes being
constructed are served  by
onsite systems. Many of
the existing systems do not
perform adequately due
to a lack of management.
Therefore, EPA promotes
the sustained management
of decentralized wastewater
systems to enhance their
performance and reliability.
EPA strongly encourages
communities to establish
management programs for
the maintenance of onsite
systems in addition to
improving local requirements
for onsite system siting and
system design. Communities
benefit from effective
onsite system management
programs by enjoying
improved protection of public
health and  local surface
water and groundwater
resources, preserving rural
areas, protecting property
owners' investments through
increased system service
life, and avoiding the need
to finance costly central
wastewater collection and
treatment systems.

Asset Management
America's public water-
based infrastructure - its
water supply, wastewater,
and storm water facilities,
and collection/distribution
systems - is integral to our
economic, environmental
and cultural vitality.
Much of this country's
public wastewater system

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infrastructure has crossed
the quarter-century mark,
dating back to the CWA
construction  grant funding
of the 1970s. Many of our
collection systems date from
the end of World War II and
the population boom of the
post war era. The oldest
portions of the collection
system pipe network exceed
100 years of service.
Significant parts of this
infrastructure are severely
stressed  from overuse and
the persistent under-funding
of repair, rehabilitation,
and replacement. In an
increasing number of
communities, existing
systems are deteriorating,
yet the demand for
new infrastructure to
accommodate growth
presses unabated.  A
revitalized approach to
managing capital wastewater
assets for cost effective
performance is emerging
in this country. This asset
management approach
focuses on the cost effective
sustained performance of the
wastewater collection and
treatment system assets over
their useful life.

Operation
Wastewater collection and
treatment systems must
be operated  as designed
to adequately protect
water quality and human
health.  Most systems are in
operation every day of the
year, rain or shine.  Licensed
and trained operators are
responsible for the day-
to-day performance of the
wastewater system.  Their
responsibilities include
budget and business
administration, public
relations, analytical testing,
and mechanical engineering
as well as overseeing the
collection system and
wastewater treatment
processes.

Maintenance
Wastewater collection and
treatment systems must
provide reliable service
and avoid  equipment
breakdowns. Most
equipment breakdowns
can be avoided if system
operators inspect the
equipment, including
sewer lines and manholes,
regularly.  Preventive
maintenance uses data
obtained through the
inspections in a systematic
way to direct maintenance
activities before equipment
failures occur. A good
program will reduce
breakdowns, extend
equipment life, be cost-
effective, and help  the
system operators better
perform their jobs.
Common Wastewater
Treatment Terminology

Activated Sludge is a suspended
    growth process for removing
    organic matter from sewage
    by saturating it with air and
    microorganisms that can
    break down the organic
    matter.
Advanced Treatment involves
    treatment levels beyond
    secondary treatment.
Aeration Tank is a chamber for
    injecting air and oxygen into
    water.
Aerobic refers to a life or a
    process that occurs in the
    presence of oxygen.
Aerobic Treatment Units
    provide wastewater
    treatment by injecting
    air into a tank, allowing
    aerobic bacteria to treat the
    wastewater.
Algae are  aquatic plants which
    grow in sunlit waters and
    release oxygen into the
    water. Most are a food
    for fish and small aquatic
    animals, but some cause
    water  quality problems.
Alternative System A
    wastewater treatment or
    collection system utilized
    in lieu of a conventional
    system.
Anaerobic refers to a life or a
    process that occurs in the
    absence of free oxygen.
Bacteria are small  living
    organisms which help
    consume the organic
    constituents of sewage.
Barminutor is a device mounted
    on bar screens in a
    wastewater treatment plant
    to shred material, such
    as rags and debris, that
    accumulates on the bars.
Bar Screen is  composed of
    parallel bars that remove
    larger objects from
    wastewater.

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Black Water is the term given
    to domestic wastewater that
    carries animal, human, or
    food wastes.

Biological Nutrient Removal
    (BNR) is the use of bacteria
    to remove nutrients from
    wastewater.

Biomass is microbial growth.

Biosolids are treated sewage
    sludge solids that have
    been stabilized to destroy
    pathogens and meet
    rigorous standards allowing
    for safe reuse of this material
    as a soil amendment.

Biotower is a unit in which the
    waste is allowed to fall
    through a tower packed with
    synthetic media on which
    there is biological growth
    similar to the trickling  filter.

BOD  (Biochemical Oxygen
    Demand) is a  measure
    of oxygen consumed in
    biological processes that
    break down organic matter
    in water.

Carbon Adsorption is a method
    to treat wastewater in which
    activated carbon removes
    trace organic matter that
    resists degradation.

Chlorination is the process
    of adding chlorine gas or
    chlorine compounds to
    wastewater for  disinfection.

Chlorinator is a device that adds
    chlorine, in gas or liquid
    form, to wastewater to kill
    infectious bacteria.

Clarifier also known as a settling
    tank, removes solids from
    wastewater by gravity settling
    or by coagulation.

Clean Water Act (Federal
    Water Pollution Control Act)
    originally enacted in 1948
    and amended in 1972, 1981
    and 1987, the Clean Water
    Act has as its objective the
    restoration and maintenance
    of the "chemical, physical,
    and biological integrity of
    the Nation's waters."

Coagulation is the clumping
    together of solids to make
    them settle out of the
    sewage faster. Coagulation
    of solids is improved by the
    use of chemicals such as
    lime, alum, iron salts, or
    polymers

Combined Sewers carry both
    sewage and stormwater
    runoff.

Comminutor is a device to catch
    and shred heavy solid matter
    at the headworks of the
    wastewater treatment  plant.

Composting is the natural
    biological decomposition
    of organic material in the
    presence of air to form
    a stabilized, humus-like
    material.

Conventional Systems are
    wastewater treatment
    systems that have been
    traditionally used to collect
    municipal wastewater in
    sewers and convey it to a
    central facility for treatment
    prior to discharge to surface
    waters. Either primary or
    secondary treatment may be
    provided in a conventional
    system.

Denitrification is the  reduction
    of nitrite to nitrogen gas.
    Denitrification is carried
    out in wastewater treatment
    tanks by bacteria under
    anoxic conditions. The
    bacteria use the nitrate for
    energy, and in the process,
    release nitrogen gas. The
    nitrogen gas, a major
    constituent of air, is released
    to the atmosphere.

Diffused Air is a technique by
    which air under pressure
    is forced into sewage in
    an aeration tank. The air
    is pumped into the tank
    through a perforated pipe
    and moves as bubbles
    through the sewage.
Digestion of solids takes place in
    tanks where volatile organic
    materials are decomposed
    by bacteria, resulting
    in partial gasification,
    liquefaction, and
    mineralization of pollutants.

Disinfection is the killing of
    pathogenic  microbes
    including pathogenic
    bacteria, viruses, helminths,
    and protozoans.

Dispersal/Percolation involves
    a volume of wastewater
    applied to the land,
    penetrating  the surface,
    and passing through the
    underlying soil.

Dissolved Oxygen (DO) is
    the amount  of free oxygen
    in solution in water, or
    wastewater effluent.
    Adequate concentrations
    of dissolved oxygen are
    necessary for fish and other
    aquatic organisms to live
    and to prevent offensive
    odors.

Eligible Costs are those
    wastewater reduction
    activities that can be funded
    with State Revolving Fund
    (SRF) loans.

Effluent is the treated liquid that
    comes out of a treatment
    plant after completion of the
    treatment process.

Eutrophication  is the normally
    slow aging  process by
    which a lake evolves
    into a bog or marsh and
    ultimately disappears.
    During eutrophication, the
    lake becomes enriched
    with nutrients, especially
    nitrogen and phosphorus,
    which support the excess
    production of algae and
    other aquatic plant life.
    Eutrophication may be
    accelerated by many human
    activities.

Evapotranspiration is the
    uptake of water from the
    soil by evaporation and by

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    transpiration from the plants
    growing thereon.

Floe is a clump of solids formed
    in sewage by biological or
    chemical action.

Flocculation  is the process
    by which clumps of solids
    in sewage are made to
    increase  in size by chemical
    action.

Gray  Water refers to domestic
    wastewater composed of
    wash water from sinks,
    shower, washing machines
    (does not include toilet
    wastewater).

Grinder Pump is a mechanical
    device which shreds
    wastewater solids and raises
    the fluid pressure level high
    enough to pass wastewater
    through small diameter
    pressure  sewers.

Grit Chamber is a small
    detention basin designed to
    permit the settling of coarse,
    heavy inorganic solids, such
    as sand, while allowing the
    lighter organic solids to pass
    through the chamber.

Groundwater is the zone
    beneath the ground surface
    saturated with water that  has
    seeped down through soil
    and rock.

Impervious means resistant to
    penetration by fluids or by
    roots.

Incineration  involves combustion
    of the organic matter in
    sewage sludge, producing a
    residual inert ash.

Infiltration is the penetration  of
    water through the ground
    into sub-surface soil or the
    passing of water from the
    soil into a pipe, such as a
Influent refers to water,
    wastewater, or other liquid
    flowing into a reservoir,
    basin or treatment plant, or
    any unit thereof.
Inorganic refers to compounds
    that do not contain carbon.

Interceptors are large sewer
    lines that collect the flows
    from smaller main and trunk
    sewers and carry them to the
    treatment plant.

Intermittent sand filter involves
    a bed of sand or other
    fine-grained material to
    which wastewater is applied
    intermittently in flooding
    doses.

Lagoon  is a shallow  pond  in
    which algae, aerobic and
    anaerobic bacterial purify
    wastewater.

Land Application  is  the
    controlled application of
    wastewater or biosolids onto
    the ground for treatment
    and/or reuse.

Lateral  Sewers are small pipes
    that are placed in the
    ground to receive sewage
    from homes and businesses
    and convey it to  main, trunk
    and interceptor sewer lines
    leading to the wastewater
    treatment plant.

Mechanical Aeration uses
    mechanical energy to  inject
    air from the atmosphere into
    water to provide oxygen to
    create aerobic conditions.

Media Filters involves a bed of
    sand or other fine-grained
    material to which wastewater
    is applied, generally to
    physically remove suspended
    solids from sewage.
    Bacteria on the media
    decompose additional
    wastes. Treated water drains
    from the bed. Solids that
    accumulate at the surface
    must be removed from the
    bed periodically.

Microbes is shorthand for
    microorganisms.

Million  Gallons Per Day (MOD)
    is a  measurement of the
    volume of water.
Mound System is an effluent
    disposal system involving a
    mound of soil built up on the
    original ground surface to
    which effluent is distributed.

National Pollutant Discharge
    Elimination System
    (NPDES) is a program
    established by the Clean
    Water Act (CWA) that
    requires all wastewater
    discharges into "waters of
    the United States" to obtain
    a permit issued by the US
    Environmental Protection
    Agency (EPA) or a state
    agency authorized by the
    EPA.

Nitrification is the biochemical
    oxidation of ammonium to
    nitrate.

Nitrogenous Wastes are wastes
    that contain a significant
    concentration of nitrogen.

Nutrients are elements or
    compounds essential as
    raw materials for plant
    and animal growth and
    development.

Organic Matter is the
    carbonaceous material
    contained in plants or
    animals  and wastes.

Overland Flow is land treatment
    which involves the controlled
    application of wastewater
    onto grass-covered gentle
    slopes, with  impermeable
    surface soils. As water flows
    over the grass-covered soil
    surface,  contaminants are
    removed and the water is
    collected at the bottom of
    the slope for reuse.

Oxidation  involves aerobic
    bacteria breaking down
    organic matter and oxygen
    combining with chemicals in
    sewage.

Oxidation  Pond is an aerated
    man-made pond used for
    wastewater treatment.

Ozonation is a disinfection
    process where ozone is

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    generated and added to
    wastewater effluent to kill
    pathogenic organisms.

Pathogens are disease-causing
    microorganisms, including
    pathogenic bacteria, viruses,
    helminths, and protozoans.

Percolation is the movement
    of water through sub-
    surface soil layers, usually
    continuing downward to the
    groundwater.

Permeability is a measure of
    the ease with which water
    penetrates or passes through
    soil.

Phosphorus is a nutrient that
    is essential to life, but in
    excess, contributes to the
    eutrophication of lakes and
    other water bodies.

Pollution results when
    contaminants in human,
    animal, vegetable, mineral,
    chemical or thermal waste
    or discharges reach water,
    making it less desirable
    for domestic, recreation,
    industry, or wildlife uses.

Polymer is a long chain organic
    compound produced  by
    the joining of primary units
    called monomers. Polymers
    are used to improve settling
    of suspended solids,  remove
    solids from wastewater,
    and improve dewatering of
    biosolids.

Pressure Sewers are a system
    of pipes in which the water,
    wastewater or other liquid is
    transported under pressure
    supplied by pumps.

Pretreatment  involves treatment
    of wastes or wastewater by
    industries  performed prior
    to the discharge to the sewer
    system.

Primary Treatment is the
    initial stage of wastewater
    treatment that removes
    floating material and
    material that easily settles
    out.
Pump is a mechanical device
    for raising or lifting water or
    other fluid, or for applying
    pressure to fluids in pipes.

Receiving Waters are
    waterbodies (i.e. rivers,
    lakes, oceans, or other
    water courses) that receive
    discharges of treated or
    untreated wastewater.

Rotating Biological Contactor
    (RBC) is a wastewater
    treatment process involving
    large, closely-spaced
    plastic discs rotated about a
    horizontal shaft. The discs
    alternately move through
    the wastewater and the air,
    developing a biological
    growth  on the surface of the
    discs that removes organic
    material in the wastewater.

Sanitary Sewer is the collection
    system for transporting
    domestic and industrial
    wastewater to municipal
    wastewater treatment
    facilities. Stormwater is not
    directed into this system but
    is handled by a separate
    system.

Secondary Treatment is the
    second stage in most
    wastewater treatment
    systems in which bacteria
    consume the organic matter
    in wastewater. Federal
    regulations define secondary
    treatment as meeting
    minimum removal standards
    for BOD, TSS, and pH  in
    the discharged effluents
    from municipal wastewater
    treatment facilities.

Sedimentation Tanks are
    wastewater treatment tanks
    in which floating wastes are
    skimmed off and settled
    solids are removed for
    disposal.

Seepage is  the slow movement
    of water through small
    cracks or pores of the soil,
    or out of a pond, tank  or
    pipe.
Septage refers to the residual
    solids in septic tanks or
    other on-site wastewater
    treatment systems that  must
    be removed periodically for
    disposal.

Septic Tanks are a type of  onsite
    wastewater treatment system
    in which the organic waste
    is decomposed and solids
    settle out. The effluent
    flows out of the tank to a
    soil adsorption field or other
    dispersal system.

Sequencing Batch Reactors
    (SBR) are a variation
    of the activated sludge
    process where all treatment
    processes occur in one tank
    that  is filled  with wastewater
    and  drawn down to
    discharge after treatment is
    complete.

Settleable Solids  are solids that
    are heavier than water and
    settle out of water by gravity.

Sewers are  a system of pipes
    that  collect and deliver
    wastewater and/or
    stormwater to  treatment
    plants or receiving waters.

Soil Absorption Field is  a
    subsurface area containing
    a trench or bed with  a
    minimum  depth of 12
    inches of clean stones and
    a system of piping through
    which treated  wastewater
    effluent is distributed into the
    surrounding soil for further
    treatment and disposal.

Slow  Rate Land Treatment
    involves the controlled
    application of wastewater
    to vegetated land at  a few
    inches of liquid per week.

Storm Sewers are a  separate
    system of pipes that carry
    rain  and snow melt from
    buildings, streets and yards
    to surface waters.

Suspended  Solids are the  small
    particles suspended in  water
    or wastewater.

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Transpiration is the process
   by which water vapor is
   released to the atmosphere
   by living plants.

Trickling Filter is a fixed film
   process that involves a tank,
   usually filled with a bed of
   rocks, stones or synthetic
   media, to support bacterial
   growth used to treat
   wastewater.

Ultraviolet Radiation (UV) is a
   disinfection process where
   wastewater is exposed to UV
   light for disinfection.
Virus is the smallest form of
    a pathogen which can
    reproduce within host cells.

Wastewater Treatment Plant is
    a facility involving a series
    of tanks, screens, filters, and
    other treatment processes
    by which pollutants are
    removed from water.

Water Table is the elevation of
    groundwater or saturated
    soil level in the ground.
            For  more  information  see
                  www.epa.gov.owm

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