TECHNICAL PAPER #6
UNDERSTANDING SEWAGE
TREATMENT AND DISPOSAL
By
Hank Stonerook
Technical Reviewers
Stephen A. Hubbs
R. Bruce Robinson
Ira Somerset
C. D. Spangler
VITA
1600 Wilson Boulevard, Suite 500
Arlington, Virginia 22209
USA
Tel: 703/276-1800 * Fax:
703/243-1865
Internet: pr-info@vita.org
Understanding Sewage Treatment and Disposal
ISBN: 0-86619-206-9
[C] 1984,
Volunteers in Technical Assistance
PREFACE
This paper is one of a series published by Volunteers in
Technical
Assistance to provide an introduction to specific
state-of-the-art
technologies of interest to people in developing countries.
The papers are intended to be used as guidelines to help
people choose technologies that are suitable to their
situations.
They are not intended to provide construction or
implementation
details. People are
urged to contact VITA or a similar organization
for further information and technical assistance if they
find that a particular technology seems to meet their needs.
The papers in the series were written, reviewed, and
illustrated
almost entirely by VITA Volunteer technical experts on a
purely
voluntary basis.
Some 500 volunteers were involved in the production
of the first 100 titles issued, contributing approximately
5,000 hours of their time.
VITA staff included Leslie Gottschalk
as primary editor, Julie Berman handling typesetting and
layout,
and Margaret Crouch as project manager.
Hank Stonerook, author of this paper, is a principal with
Environmental
Resources Management-Midwest, Inc.
He has published
several articles dealing with wastewater management and
disposal,
and has served as a technical consultant on international
development
projects during his affiliation with the U.S. Peace Corps.
Reviewers Stephen A. Hubbs, R. Bruce Robinson, Ira Somerset,
and
C.D. Spangler are also specialists in the area.
Hubbs is a research
engineer with the Louisville Water Company, Louisville,
Kentucky. Robinson
is an assistant professor at the University of
Tennessee where he teaches courses in wastewater management
and
treatment. Somerset
is a sanitary engineer by education and a
regional shellfish specialist with the U.S. Food and Drug
Administration
of the Department of Health and Human Services, where
he studies and evaluates the effects of sewage on
shellfish-growing
areas. Spangler, a
sanitary engineer, has been involved
in water and wastewater for a number of years.
He has worked for
the U.S. Public Health Service, the World Bank, and as a
private
consultant.
VITA is a private, nonprofit organization that supports
people
working on technical problems in developing countries.
VITA offers
information and assistance aimed at helping individuals and
groups to select and implement technologies appropriate to
their
situations. VITA
maintains an international Inquiry Service, a
specialized documentation center, and a computerized roster
of
volunteer technical consultants; manages long-term field
projects;
and publishes a variety of technical manuals and papers.
UNDERSTANDING
SEWAGE TREATMENT AND DISPOSAL
by VITA
Volunteer Henry Stonerook
I. INTRODUCTION
The treatment and disposal of domestic wastes--sewage--is
becoming
more and more important as ever-increasing rural populations
and urbanization threaten existing potable water supplies in
many
areas of the world.
Health problems and diseases are often
related to inadequate sewage treatment.
Pollution of rivers and
lakes results in fish kills and destruction of other forms
of
aquatic life. Proper
collection, treatment, and disposal of
sewage is necessary to promote healthful conditions and
maintain
the quality of the world's water resources.
Domestic wastes can conveniently be separated into body
wastes
(feces and urine) and gray water, which is all the other
liquid
wastes of the household, including both laundry and kitchen
waste
water. Body wastes
are the most hazardous due to the possibility
of contact with intestinal disease organisms.
Gray water ordinarily
has few disease organisms unless the laundry has contained
garments soiled by fecal discharges.
This paper is not meant to be an in-depth study of many
kinds and
types of sewage treatment systems in use throughout the
world.
Rather, it serves only as an introduction.
Included is a discussion
of sewage and its characteristics; the collection of sewage;
and a brief discussion of physical, biological, and chemical
treatment systems.
Appropriate sewage treatment technology,
including on-site, composting, land application, and
aquaculture
systems, are discussed as possible alternatives for
developing
nations. A glossary
of terms used in this paper and common to
discussions of sewage treatment systems is also included.
II. SEWAGE
CHARACTERISTICS
The physical and chemical characteristics of wastewater vary
according to both time of day and type of wastewater
discharged
(residential/industrial).
Table 1 presents the major pollutants
contained in wastewater, typical measurement parameters, and
the
potential environmental impact of the pollutants.
Most of these pollutants are present to one degree or
another in
any type of sewage discharge.
Residential sewage is composed of
several components, including discharges from toilets,
sinks,
bathing facilities, and laundry facilities.
Table 2 provides a
Table 1.
Principal Pollutants in Wastewater
Type of
Measurement
Environmental
Pollutant
Parameter Impact
Biodegradable
Biochemical oxygen demand
Reduce oxygen
organics
(BOD); chemical oxygen
content of
demand (COD)
receiving water
Suspended
Total suspended solids
Turbidity;
material
(TSS)
sediment
Pathogenic
Fecal coliform bacteria
Health hazard
bacteria
Ammonia
Determine amount of
Reduces oxygen
ammonia in
content; toxic
wastewater to
aquatic life;
([NH.sub.3] - N test)
promotes algal
growth
Phosphate
Determine amount of
Promotes algal
phosphate in
growth
wastewater
([PO.sub.4] - P test)
Toxic
Depends on toxin
Hazardous to
materials
present
aquatic life and
plants; may be
toxic to humans
range of flows and pollution loads in terms of the amount of
biological oxygen demand (BOD), chemical oxygen demand
(COD),
ammonia nitrogen, and orthophosphate anticipated from an
average
household consisting of 3.2 persons using conventional
"western-style"
plumbing fixtures and detergents.
Similar discharges from
developing countries might be expected to be more
concentrated as
the amount of water used per household is lower, but the
amount
of waste is about the same.
A major environmental problem caused by too much sewage
discharged
into a lake or other confined body of water is
eutrophication.
Eutrophication is a natural aging process that is greatly
accelerated by the discharge of ammonia and phosphates.
These
nutrients promote the excessive growth of algae, which
further
depletes the dissolved oxygen content of the water
body. This
Table 2.
Residential Wastewater Discharge Composition
Pollutants
Flow of
(Milligrams per Liter)
Type of
Wastewater
Ammonia Ortho-
Facility
(gpcd)(*) BOD
COD
Nitrogen phosphate
Kitchen sink
3.6 676
1,380
5.4 12.7
Bathtub
8.5 192
282
1.3 1.0
Bathroom sink
2.1 236
383
1.2 48.8
Laundry machine
7.4 282
725
11.3 171.0
Toilet
19.8 313
896
37.1 77.4
Average
(**) 310
755
20.5 71.4
(*) Gallons per
capita per day.
(**) The total
flow of wastewater is 41.4 gallons per capita per
day.
Source:
John B. Winneberger, Manual
of Grey Water Treatment
Practice
(Ann Arbor, Michigan: Ann Arbor
Science,
1974).
reduces the variety of aquatic life and the quality of the
water
itself and imparts unpleasant tastes and odors.
Limiting the
discharge of untreated or partially treated sewage will
prevent
such pollution of the water.
III. SEWAGE
COLLECTION SYSTEMS
In areas with a significant housing density, sanitary sewers
are
built to remove the wastewater to a treatment facility or
disposal
area. Although combined
sewers (sewers that collect both
wastewater and storm water) cost much less to build than do
sewers that separate wastewater from storm water, they can
become
a health hazard. For
example, with combined sewers comes the
danger that, during a rainstorm, raw sewage could enter a
bypass
conduit and pollute water used for drinking or bathing.
In
addition, the cost of treating the combined storm and
sanitary
wastes is high. Most
new sewer construction makes use of separate
sanitary sewers for these reasons.
Clay tile, concrete, asbestos-cement, and PVC plastic are
the
four most common materials used in the construction of
sewers.
These materials are chosen because of their resistance to
corrosion
and their strength and flow properties.
However, sulfide
corrosion, which occurs when wastewater is confined or slow
moving, can affect concrete and asbestos-cement sewers as
can
some industrial (toxic) materials.
Sulfide corrosion is accelerated
by high temperatures.
Clay pipe or PVC plastic may be a more
advisable choice of material under those conditions.
However,
replacement costs must be considered as well as construction
costs.
Sewage collection systems are designed according to a basic
flow
plus an allowance in infiltration through sewer joints.
Actual
wastewater discharge ranges from 40 to 50 gallons per capita
per
day in homes having flush toilets, sinks, showers, and
laundry
facilities. Allowing
for infiltration through sewer joints and
inflow from miscellaneous clear water direct connections (e.g.,
catch basins, drains), per capita flow can be expected to
range
from 70 to 100 gallons per day.
Where flows of this magnitude
occur, minimum sewer size is generally eight inches in
diameter.
Sewer sizes vary according to the flow being conveyed and
are a
function of slope, velocity, and internal roughness of the
conduit. Manholes
(holes equipped with covers) are built to
gain access to the sewers from ground level for cleaning and
inspection. The
manholes are placed at 300- to 500-foot intervals
and at those points where changes in direction and slope
occur.
Smaller sewers (i.e., those with diameters less than eight
inches) have been used in conjunction with septic or
interceptor
tanks, where many solids can settle out and not cause
obstruction
in the pipe. These
tanks constitute pretreatment facilities.
Solids collected in the tanks must be removed periodically,
i.e.,
usually at 1- to 2-year intervals, by pumping them into tank
trucks and treating the material in special treatment
facilities.
Pressure sewers, combined with grinder pumps following
storage in
a wet well or effluent pumps following settling in septic
tanks,
have also been used to transport sewage to the treatment
plant.
These systems are relatively inexpensive to construct, but
the
maintenance and power costs associated with their operation
can
be high.
Furthermore, skilled maintenance is required.
Various combinations of short collector systems and
dispersed
pretreatment or treatment facilities serve as alternative
designs
in cases where housing densities cannot justify expensive
gravity collection systems.
IV. HIGH-COST
TECHNOLOGIES FOR WASTEWATER TREATMENT
PHYSICAL, BIOLOGICAL, AND CHEMICAL TREATMENT TECHNOLOGIES
Wastewater is treated using one or a combination of
processes
including physical, biological, and chemical systems.
Process
units typical of each of these systems are given in Table 3.
Table
3. Process Units Typical of Various
Wastewater Technologies
Physical System
Biological System
Chemical System
Pumping
Aerobic systems
Precipitation
Screening
- lagoons
Coagulation
Flow equalization
- trickling filter pH
adjustment
Settling
- rotating contactors
Disinfection
Grit removal
- sludge digestion
Filtration
Anaerobic systems
- sludge digestion
- lagoons
Land treatment
Subsurface disposal
Physical Technologies
Physical systems include processes that pump, that remove
solids
by screening or settling, or that equalize flow
fluctuations.
Bar screens, both mechanical and hand cleaned, are used to
remove
large objects and serve to protect downstream mechanical
equipment.
Grit (inorganic, fine solids such as sand, coffee grounds,
egg shells, etc., which are relatively heavy) is removed by
controlled settling.
Removing grit also helps to protect pumps
and equipment from abrasion and prevent the settling of
these
materials in other treatment units.
A simple grit tank consists
of a channel through which wastewater flows at a constant
velocity
independent of the volume of discharge.
Settling tanks, which
are rectangular or circular in shape, are designed to remove
solids and are sized according to the velocity of the flow
through the tank.
Solids settle out and fall to the bottom of
the tank. These
tanks employ a subsurface scraping mechanism to
direct the settled solids or sludge to a pump well for
discharge
to the sludge treatment facility.
Overflow from the tanks exists
through a system of weirs for further treatment or
discharge. A
surface skimmer is often employed to remove floating solids
and
scum. Flow
equalization facilities are tanks that serve to
regulate and dampen the variable peaks of flow that occur
over a
normal day's time or as a result of severe inflow caused by
rain.
Biological Technologies
Biological systems employ both aerobic and anaerobic systems
to
stabilize wastewater and sludge.
The most common of these, the
activated sludge system, involves adding air to the
wastewater
to promote the growth of aerobic microorganisms that feed on
and
digest the organic material.
Detention times of two to six hours
are necessary to stabilize the waste, which requires large
tanks
capable of holding two to six hours of the average daily
flow.
Air is blown into these tanks to promote the growth of
aerobic
organisms. Large
amounts of power are required to mix and aerate
the tanks. Settling
tanks follow the activated sludge system,
and some of the settled sludge, containing a high
concentration
of microorganisms, is returned to the aeration tanks to
promote
microorganism growth.
This is a highly skilled operation and is
very expensive to build and operate.
Another type of aerobic treatment system is the trickling
filter.
Incoming wastewater, which is first settled, is distributed
at a
uniform rate over a medium of rock or plastic upon which
aerobic
organisms attached themselves and grow.
These organisms attack
the sewage, reducing it in strength.
The dead organisms and
other solids are removed in settling tanks.
Flow is also recycled
with this system.
Although not as complex as activated sludge,
this is a delicate, complex treatment method that also
requires a
high level of operator skill.
Anaerobic systems are commonly used to digest the settled
solids;
they are less commonly used as wastewater treatment systems.
Anaerobic digesters are enclosed tanks of 20 feet or more in
depth, sometimes insulated and equipped with external
heating
capabilities for cold climates.
In many cases, a floating cover
allows for the production of methane gas and the mixing of
the
sludge. Anaerobic
digesters, if well insulated or operated in
warm climates, need little or no input of energy to
function.
They usually decompose wastes at temperatures of 35 to 40
[degrees] C. Gas
produced from the decomposition can be captured and used to
provide fuel to operate natural gas pumps.
Digester performance
is a function of sludge feed rate, moisture content, the
amount
of volatile contents of the sludge, and the amount of toxic
materials present.
Large quantities of moisture and toxics will
retard sludge digestion and minimize methane gas production.
Chemical Technologies
Chemical treatment systems are designed to remove pollutants
through the addition of certain chemicals.
Capital costs for
these systems are usually low, but operating costs can be
significant.
Chemicals are used extensively in wastewater treatment
for disinfection (chlorine) and sludge thickening
(dewatering).
They are also used extensively in industrial wastewater
treatment
to adjust the pH and to remove heavy metals.
Chemical costs and
handling properties, however, make them rather poor choices
for
sewage treatment systems for developing countries.
A typical
sewage treatment plant employing screening, grit removal,
primary
settling, trickling filter, final setting, disinfection, and
anaerobic sludge digestion is presented in Figure 1.
14p08.gif (600x600)
V. ALTERNATIVE
TECHNOLOGIES
The technologies described in Section IV are designed to
treat
wastewater and sludge effectively.
They are generally very expensive,
however, and require extensive operation and maintenance.
As such, they may be applicable for larger population
areas, which can afford their construction and maintenance,
but
other, simpler methods are likely to be more suitable for
smallscale
applications.
LATRINES
For ordinary households or family groups, body wastes are
best
disposed of in a sanitary latrine.
Health authorities in most
countries have developed plans for such installations.
The most
important considerations are that the pit should be designed
so
it will not pollute ground water or permit access by insects
or
rodents. The pit
will become full over several years depending on
its size and the number of users.
When full it can be cleaned
out; this is a disagreeable job and may result in exposure
to
fresh fecal material.
A good arrangement is to have two pits.
When the first is full, the slab and building are moved to
the
second pit and the first is covered with earth and allowed
to
compost. When the
second pit is full, the first pit is cleaned
out and the slab and building moved back over it and the
second
pit is covered and allowed to compost.
If a water-seal latrine is
used, the slab and building can be permanent.
The sewage is
carried behind the latrine where it can be distributed to
one of
two pits for alternate use and composting.
Gray water is usually used for irrigation of garden plots,
shrubs, or trees and scattered to help settle the dust
around the
premises. It should
not stand to form puddles, which may result
in mosquito propagation.
Sewer systems are expensive--usually two or three times the
cost
of a water supply system.
Sewers also require a good flow of
water or material will settle in the sewers, resulting in
blockages.
In the United States between 40 and 50 percent of domestic
water goes to flush toilets.
This is a great waste of water and
can create a problem when discharged into streams and lakes,
so
expensive treatment is necessary.
STABILIZATION PONDS
If water is in ample supply water-flush toilets can be used
in
institutions such as hospitals, schools, and government
buildings.
In such installations, a plumbing system in the building
can collect the toilet wastes and gray water together and
deliver
them to a sewer that takes them a short distance from the
building
to a small stabilization pond.
Such a pond is less expensive
to build than a septic tank and tile field.
It will also have
fewer operating problems, because it will lose water from
seepage
and evaporation and the overflow can be used for irrigation.
In tropical climates the pond can be loaded at a rate of
2,500
people per acre (or 6,000 per hectare).
For a population of 500
people the pond would only be one-fifth of an acre in area,
or
about 60 feet wide and 140 feet long (approximately 20
meters
wide by 50 meters long).
The length should be about two to three
times the width. The
pond should be at least three feet deep (1
m) and should be deeper at the inlet end to allow for sludge
accumulation. The
inlet pipe should extend about one-quarter of
the way into the pond.
Over time, the pond will develop a rich
green algal culture that, with the bacteria, will break down
the
organic materials in the sewage.
Many ponds have fish, frogs, and
ducks as residents.
A properly designed pond will have little or
no odor and what odors that might occasionally occur usually
cannot be detected beyond 300 feet (100 m).
A newly constructed
pond may take some months before the bottom will be sealed
and
water will get to the design depth.
Once the pond is operating,
maintenance is simple and requires only part-time ordinary
labor
to check on the inlet flow and the retaining dikes, to cut
the
grass and weeds on the dikes, and to remove any aquatic
vegetation
in the shallow areas along the dike so as to discourage
mosquito propagation.
Various other alternative technologies for wastewater
treatment
have developed over the years.
Table 4 lists the technologies,
their intended use (wastewater or sludge), and their design
parameters, and provides comments to each technology.
Table
4. Some Popular Low-Cost Technologies
for Wastewater Treatment
Technology
Use(*) Technology Design
Comments
Parameters
Land treat-
W Land area; soil type;
Reuse potential
ment
crops grown; climate
wastewater; pre-
treatment required;
potential to pollute
water and crops;
may attract flies
and parasitic worms;
may cause odors
Composting
S Detention time; air
Soil conditioner;
requirement; moisture turning
required;
content need
additive to mix
sludge with compost
Leaching
W Soil type; topography;
Large areas required
field
groundwater; depth to
bedrock; area
Anaerobic
S Detention time;
Can produce a fuel;
digesters
moisture content soil
conditioner;
cannot treat
wastewater
Aquaculture
W Land area; climate;
Pretreatment required;
topography; crops potential
adverse health
effects
Imhoff tank
W/S Detention time;
Treats wastewater
overflow rate and
sludge; low-cost
energy; requires
maintenance; may
attract flies; may
cause odors
(*) W =
wastewater; S = sludge.
LAND TREATMENT
Land treatment relies on bacteria and organisms present in
soil
as well as the soil's physical characteristics to stabilize
pretreated sewage.
The sewage is stored in lagoons prior to
being spread over fields through channels or piping
systems. If
the sewage has been thoroughly, treated the crops grown in
these
fields can be used for animal feed.
However, for sewage that has
not been treated adequately, the land application site
should
be set aside and no crops on it should be consumed by
animals or
humans. Care should
be taken in selecting sites so that pollution
of ground water or surface water cannot occur due to
percolation or runoff from the land treatment site.
COMPOSTING
Composting of sludge and/or human and animal waste offers a
means
to solve an environmental problem and create a useful
product.
This product, a soil conditioner, contains some nutrient
value in
the form of nitrogen and phosphorous.
Composting is a natural
process that occurs when aerobic microorganisms live in an
optimum
environment that is a function of the carbon to nitrogen (C
to N) ratio of the mixture.
Care must be taken to keep this
ratio at approximately 25 to 30 parts of carbon to 1 part of
nitrogen, to maintain an adequate supply, and limit the
moisture
content to approximately 60 percent.
In many cases, a bulking
agent such as wood chips or leaves is added to help achieve
these
conditions.
Temperatures in a properly composted mixture exceed
40 [degrees] C for several days.
The compost process requires approximately
10 to 14 days, and should be followed by several weeks of
curing. Oftentimes,
the composted product is screened to recover
the bulking agent before it is used.
The screened material, if
it has aged long enough, can be bagged and stored or sold in
bulk
for use as a soil conditioner.
Adding compost to farmland can
reduce the amount of fertilizer required for crops.
LEACHING FIELDS
Leaching fields are generally used in conjunction with a
pre-treatment
device (e.g., septic or interceptor tank).
They are a
means to dispose of wastewater without having to discharge
it to
a watercourse.
Proper soil types are necessary for the construction
of leaching fields.
A tight, nonporous clay soil is generally
unsuitable since the leached sewage cannot pass through it.
The sewage then comes to the surface, causing odors and
potential
health problems. The
length of a leaching field depends on the
amount of sewage to be treated (i.e., number of persons
connected),
the type of sewage, and the types of soils present.
Where an excess of evaporation occurs, evapotranspiration
systems
are effective. These
systems employ a raised distribution field
with the crops or trees grown on top.
The vegetation draws up the
moisture and transpires it, leaving the residual solids
trapped
in the ground to be further broken down by the
microorganisms
present there. These
systems are generally limited to small
clusters of homes, but several can be scattered throughout a
community. A sketch
of a typical leaching and evapotranspiration
system is given in Figure 2.
14p13.gif (600x600)
ANAEROBIC DIGESTERS
Biogas generators are process units that make use of
anaerobic
digestion as a means to stabilize waste and produce
fuel. These
systems are designed to digest animal and human solid
wastes; or
they can be used as a treatment mechanism for sludge.
The solid
waste decomposes with the aid of anaerobic microorganisms to
produce methane gas, which can be recovered and used as a
fuel.
As with composting, an optimum carbon to nitrogen ratio
(i.e., 25
to 30 parts of carbon to 1 part of nitrogen) is required for
proper operation. A
detention time of at least 30 days is required
for stabilization.
Adding the correct amount of waste
material to the unit as well as mixing the material
thoroughly
and removing the digested product from the unit are
important
operational parameters.
Biogas generators can be designed for
small-scale use in one or several homes in many countries;
but
they only partially solve the sewage problem.
Because they cannot
handle wash water or other types of wastewater, an
additional
means of sewage treatment for these wastes must be provided.
AQUACULTURE
Aquaculture systems have become popular as a relatively
low-cost
means to provide advanced treatment where it is
required. Utilizing
specially selected aquatic vegetation, large amounts of
biodegradable material, suspended solids (SS), and other
nutrients
can be removed from wastewaters.
Water is allowed to
flow through channels at a slow rate where aquatic plants
are
grown. These plants
are harvested periodically and can then be
composted further or digested anaerobically.
The complete aquaculture
system is labor intensive, but requires minimum energy
and equipment.
Pretreatment of the waste such as in a series of
lagoons must be provided to remove the solids and partially
treat
the sewage prior to its disposal.
The resulting system requires
large land areas on which to operate.
IMHOFF TANKS
lmhoff tanks offer a treatment means that is relatively low
in
cost, produces a good effluent, and is mechanically simple.
An
Imhoff tank, shown in Figure 3, is a large, deep tank
employing
14p15.gif (600x600)
an upper compartment for settling and a lower compartment
for
anaerobic digestion.
Gases escape through vents along the sides
of the tank. Proper
tank design can limit operating problems
such as foaming, scum formation, and malodorous sludge.
In
tropical climates where the temperature does not vary
greatly,
the foaming and odor problem will be reduced.
Proper operation,
including daily cleaning of the side vents, will promote optimum
operation of the system.
Sludge withdrawal should occur only two
or three times a year, and the resulting digested product
can be
spread over land directly or applied to drying beds for
subsequent
disposal. Since the
discharge from these tanks is not of
high quality, it may require further treatment in lagoons or
leaching fields.
BIBLIOGRAPHY
Many books have been written on sewage treatment and
disposal,
and no one source is authoritative.
Several reference sources
are listed below.
Most of these are written for use in developed
countries.
Bastian, Robert K.
"Natural Treatment Systems in Wastewater
Treatment and
Sludge Management." Civil
Engineering-ASCE,
May 1982, p. 62.
Fey, Robert T.
"Cost-Minded Community Chooses Small Diameter
Gravity
System." Water and Sewage Works,
June 1978, p. 58.
Golveke, Clarence G.
Biological Reclamation of Solid Wastes.
Emmaus,
Pennsylvania: Rodale Press, 1977.
Metcalf and Eddy.
Wastewater Engineering. New York,
New York:
McGraw-Hill Book
Company, 1977.
Norris, D.P., and Troyan, J.J.
"Cost-Effectiveness of On-Site and
Community
Sewerage Alternatives." Civil
Engineering-ASCE,
December 1977,
p. 84.
Otis, R.J., and Stewart, D.E.
"Alternative Wastewater Facilities
for Small
Unsewered Communities in Rural America."
Small
Scale Waste
Management Project. Madison,
Wisconsin: University
of Wisconsin,
July 1976.
Rich, Linvil G.
Low-Maintenance, Mechanically Simple
Wastewater
Treatment Systems.
New York, New York.:
McGraw-Hill Book
Company, 1980.
Winneberger, John H.
Manual of Grey Water Treatment Practice.
Ann
Arbor,
Michigan: Ann Arbor Science, 1974.
AGENCIES TO
CONTACT FOR ADDITIONAL INFORMATION
1.
American Society of Agricultural Engineers
2950 Niles Road
St. Joseph,
Michigan 49085 USA
2.
American Society of Civil Engineers
345 East 47th
Street
New York, New
York 10017 USA
3.
EPA Small Wastewater Flows Clearinghouse
Centennial House
Morgantown, West
Virginia 26526 USA
4.
Environmental Research Information Center
Office of
Research and Development
U.S.
Environmental Protection Agency
Cincinnati, Ohio
45268 USA
5.
Inter-American Association of Sanitary
Engineering
AIDIS-USA
Section
18729 Considine
Drive
Brookeville,
Maryland 20833 USA
6.
National Sanitation Foundation
Technical
Services Division
3475 Plymouth
Street
Ann Arbor,
Michigan 48106 USA
7.
Pan American Health Organization
525 23rd Street,
N.W.
Washington, D.C.
20037 USA
8.
University of Wisconsin - Extension
College of
Engineering and Applied Science
432 North Lake
Street
Madison,
Wisconsin 53706 USA
9.
Water Pollution Control Federation
2626
Pennsylvania Avenue, N.W.
Washington, D.C.
20037 USA
10. World Bank
1818 H Street,
NW
Washington, D.C.
20433 USA
11. World Health
Organization
20 Avenue Appia
1211 Geneva 27
Switzerland
GLOSSARY OF
TERMS USED IN SEWAGE TREATMENT AND DISPOSAL
Activated Sludge System:
A biological treatment system employing
forced aeration,
aerobic growth, and recycled sludge.
Aerobic: With
oxygen. Refers to the addition of
oxygen to the
treatment or
stabilization process of wastewater and sludge.
Ammonia: A nitrogen
compound that, in combination with phosphates
or by itself,
promotes algal growth. In large
concentrations
this compound is
toxic to aquatic life.
Anaerobic: Without
oxygen. The treatment or stabilization
of
wastewater or
sludge in the absence of oxygen.
Aquaculture: A
method of sewage treatment employing aquatic
plants to absorb
pollutants.
Biochemical Oxygen Demand (BOD):
A measure of the organic materials
present in
wastewater and the amount of oxygen they
consume over a
length of time, usually five days, at 20 [degrees] C.
Biological Treatment:
Facilities that promote the growth of
microorganisms
to reduce the strength of organic material in
wastewater.
Chemical Treatment:
The addition of chemicals to wastewater or
sludge to
neutralize harmful compounds or enhance thickening
or settling
capabilities.
Combined Sewers:
Sewers that carry wastewater from homes and
businesses as
well as runoff from rain.
Composting: An
aerobic treatment method generally used for
sludges or
animal or human wastes that are essentially
solids.
Detention Time: The
time a unit of sewage is retained in a treatment
unit.
Disinfection: A
means, usually chemical, to treat wastewater to
kill pathogens.
Equalization:
Reduction of the variability of flows by holding
the sewage in a
tank so that the flow to the treatment plant
is equalized
over the day.
Eutrophication: The
excessive growth of algae in a body of water.
Evapotranspiration:
A treatment means using plants to take up
moisture and
release it to the atmosphere. Some is
removed
directly through
evaporation.
Filtration: A
physical treatment process used to remove solids by
forcing
wastewater through a graded medium.
Gravity Sewers:
Sewers that are installed at a downward slope to
convey
wastewater without the use of pumps.
Grit: Larger solids of
primarily inorganic nature in wastewater,
including sand,
egg shells, coffee grounds, which settle
out quickly when
the velocity is decreased in the grit
chamber.
Infiltration: Water
entering sanitary sewers from springs or
storm sewers.
Inflow: Water
entering sanitary sewers through leaky pipe joints
or manholes.
Lagoons: Shallow
ponds that hold wastewater and use aerobic and/
or anaerobic
methods to stabilize wastes. They are
designed
to store water
for long periods of time.
Leach: To remove
soluble constituents from (a substance) by the
action of a
percolating liquid.
Methane: The major
gas generated from the anaerobic decomposition
of sludges or
solid wastes.
Moisture Content:
The amount of water contained in a known volume
of solids (e.g.,
sludge).
On-Site Disposal: A
means of sewage treatment designed for one or
a small group of
households without connections to a central
facility.
Organics: Carbon
substances that break down in the presence of
oxygen.
Oxygen Content: The
amount of dissolved oxygen in wastewater.
Pathogens: A name
given to a group of organisms known to cause
diseases or to
upset human body functions.
pH: Potential
hydrogen. The symbol that denotes a
measurement of
the effective
hydrogen ion concentration. On a scale
of
zero to 14,
seven represents neutrality. Numbers
less
than seven
indicate acidity; greater than seven indicate
alkilinity.
Phosphates: Phosphorous
compounds that are known to promote
excessive growth
of algae if present in high concentrations.
Physical Treatment:
Physical units such as pumps, filters,
screens, or
tanks, that serve to move, screen, or contain
wastewater.
Pollutant: An
overall term used to characterize unwanted material,
chemicals, or
substances in the environment.
Pressure Sewers:
Pipes of small diameter used for conveying
wastewater after
it is pumped; these pipes are usually preceded
by some
pretreatment device.
Pretreatment: First
stage of treatment, usually screening, to
remove large
solids or grit.
Reuse: A term
employed when talking about using treated wastewater
as a water
source.
Sanitary Sewers:
Sewers designed to carry only wastewaters from
homes,
businesses, and industries.
Sludge: The material
that settles out from wastewater.
Soil Conditioner:
Soil additive that acts as a bulking agent and
holds moisture.
Suspended Solids (SS):
A measure of the amount of solids present
in wastewater;
the solids are removed by drying at a low
temperature (105
[degrees] F).
Toxic Material: A
material, usually man-made, that at certain
concentrations
can kill aquatic life or be a hazard to human
health.
Treatment Systems:
Physical, biological, or chemical systems or
combinations
used to reduce the strength of pollutants.
Trickling Filter: A
biological treatment system using aerobic
means to
stabilize wastewater by trickling through a medium
of rocks.
Wastewater/Sewage: A
combination of human waste and used water
from households,
businesses, and industrial processes.
Weir: An obstruction
placed across a stream to divert the water
to make it flow
through a desired channel, which may be a
notch or opening
in the weir itself.
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