Pollution Abatement in the Fruit and
Vegetable Industry
BASICS
OF
POLLUTION CONTROL
U.S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF TECHNOLOGY TRANSFER
WASHINGTON. D. C.
-------
Pollution Abatement in the Fruit and Vegetable Industry
Volume 1
BASICS OF POLLUTION CONTROL
U. S. ENVIRONMENTAL, PROTECTION AGENCY
Office of Technology Transfer
Washington, D. C.
1975
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While the recommendations in this publication are based on scientific studies
and wide industry experience, references to operating procedures and methods,
or types of instruments and equipment, are not to be construed as a guarantee
that they are sufficient to prevent damage, spoilage, loss, accidents or injuries,
resulting from use of this information. Furthermore, the study and use of this
publication by any person or company is not to be considered as assurance that
that person or company is proficient in the operations and procedures discussed
in this publication. The use of the statements, recommendations, or suggestions
contained, herein, is not to be considered as creating any responsibility for
damage, spoilage, loss, accident or injury, resulting from such use.
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TABLE OF CONTENTS
List of Figures iv
I. INTRODUCTION
Distribution of Water I - 1
The Pristine State I - 1
Natural Pollution and Self -Purification 1-2
Assimilative Capacity 1-3
Effect of Waste Discharges 1-4
Environmental Legislation 1-5
II. ANATOMY OF POLLUTION CONTROLS
Materials Balance II - 1
Management and Pollution Controls II - 3
WATER POLLUTION PARAMETERS
Flow in - 1
Dissolved Oxygen III - 2
Biochemical Oxygen Demand III - 3
Chemical Oxygen Demand III - 5
Solids in Wastewaters
Settleable solids III - 6
Total solids III - 6
Suspended solids III - 8
Dissolved solids HI - 9
Other Parameters
pH III- 9
Temperature III - 11
Nutrients III - 11
ii
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IV. SAMPLING
Grab Samples IV - 1
Composite Samples IV - 1
Sample Storage IV - 3
V. TREATMENT METHODS
Screening V - 1
Primary Treatment V - 3
Secondary Treatment
Biological treatment V - 4
Physical - Chemical Streatment V - 7
Land Disposal V - 9
VI. REFERENCES VI - 1
GLOSSARY OF TERMS VII - 1
111
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LIST OF FIGURES
1. Distribution of water on earth 1-2
2. A hypothetical oxygen - sag curve 1-4
3. Balance of principal materials of a food processing
plant II 2
4. Dissolved oxygen meter with recorder III - 2
5. First and second stage BOD curve III - 4
6. Steps in the determination of total and fixed solids III - 7
7. The pH scale, with values of some materials III - 10
8. Temporal fluctuations in a food plant waste load IV - 2
9. Bar rack with automatic rake V 2
10. Vibrating screen for separation of solid particles V - 2 a
11. Parabolic or tangential screen V - 2
12. Sectional diagram of a circular clarifier V - 3
13. Aeration basin with floating surface aerators V - 5
14. Top view of trickling filter packed with plastic media V - 6
15. Schematic of a full flow pressurization flotation system V - 8
16. Spray irrigation disposal of food processing wastewater V - 10
IV
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I. INTRODUCTION
We travel together, passengers on a little spaceship,
dependent on its vulnerable supplies of air and soil. . .
preserved from annihilation only by the care, work,
and I will say the love, we give our fragile craft.
In his inimitable.eloquent address, the late Adlai E. Stevenson might readily
have- included reference to our vulnerable and limited natural resource of wa-
ter. For of all environmental elements, man's existence on Earth is depen-
dent foremost on the availability of fresh water.
DISTRIBUTION OF WATER
Examination of the distribution of water on this planet (Figure 1) reveals that
the greatest quantity, 97.13 percent, exists in the oceans of the world. The
second major quantity, 2. 24 percent, exists as ice and snow in the polar re-
gions. These sources are, of course, unavailable for domestic use without
extensive treatment and/or transportation. Of the remainder of Earth's wa-
ter, the largest supply, 0. 612 percent, that is used for human consumption,
exists as ground or subsurface waters. The wide-spread dependence on wells
for fresh water attests to its distribution and availability. Only a relatively
small portion, then, exists as surface water in the lakes (0. 00^%) and the
streams (0. 001%) of the world.
THE PRISTINE STATE
Water in its pure state is a simple molecule consisting of two hydrogen atoms
attached to a single atom of oxygen. However, water molecules have the
unique property of being able to dissolve an extremely wide variety of sub-
stances. Therefore, in its natural state water contains varying concentrations
of dissolved minerals, organic matter and atmospheric gases, all of which are
technically speaking, pollutants.
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WATER DISTRIBUTION
(PERCENT)
Streams
"&; aoooi
Figure 1. Distribution of water on earth.
During the discussions accompanying many recently-enacted pollution control
laws, desires were expressed for returning the quality of our Nation.'s waters
to a pristine state. When the term "pristine" is mentioned, one immediately
envisions a stream of crystal-clear water flowing through pastoral meadows
and lush forests. This pristine stream would support and sustain a myriad of
wild creatures -- mammals, birds and fish of wide variety.
NATURAL POLLUTION AND SELF-PURIFICATION
Yet even in such a seemingly idyllic setting, pollutants are generated. Rocks
and soil are eroded by the passage of the stream, adding suspended solids to
the water; trees and plants shed their leaves, or die and fall to rot, adding
organic matter; the animals, birds and fish, all functioning naturally and living
their normal life cycles, further add to the organic load imposed upon the stream.
These normal and continuous contributions of water contaminants have been
termed natural pollution.
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The effect of natural pollutants on lakes is well known. Countless lakes naturally
filled with detritus, eventually eutrophicating to become marshes, bogs, and
stagnant ponds. In time these dried to form the very pastoral meadows, and
ultimately the lush forests, through which the envisioned pristine stream flows.
However, the effect of pollutants on a stream contrasts markedly. Each stream,
flowing along its course, has the capability to purify itself of various materials.
In the slow-flowing stretches, suspended solids settle to the stream bed, there
forming sandy bottoms. As a stream tumbles and falls over rocks and other
obstacles in its path, oxygen is entrained in and dissolved by the water. Even
as a stream slowly flows through forest or meadow, oxygen is absorbed from
the air at water's surface. The dissolved oxygen not only sustains fish, plants
and other large aquatic life, but also sustains a large group of microorganisms
which are especially responsible for the stream's self-purification.
Aerobic bacteria, microorganisms which require oxygen, rely on organic
matter in water for food. These microorganisms, in utilizing the pollutants
in the stream, convert the organic matter into cellular material during growth,
or degrade the organics to nonputrescible compounds through^heir metabolic
process. During the process dissolved oxygen is consumed. In a free-flowing
stream, the rate at which bacteria consume dissolved oxygen to stabilize natural
pollutants only infrequently exceeds the rate at which the stream is physically
oxygenated. Thus, sufficient dissolved oxygen is normally present to sustain
the needs of a variety of aquatic life.
ASSIMILATIVE CAPACITY
The rate at which dissolved oxygen is consumed is directly related to the con-
centration of pollutants present in water. That is, the higher the concentration,
the more active are the bacteria, and hence the higher the rate at which oxygen
is used; the lower the concentration, the lower the consumptive or deoxygenation
1-3
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rate. When the consumptive rate exceeds the oxygenation rate of a stream, the
level of dissolved oxygen in the water begins to decrease. Since minimum
levels of dissolved oxygen are required by fish and other aquatic life, exces-
sive oxygen depletion will result in biological stress and, ultimately, fatality.
The quantity of pollutants which may be added to a stream without deleterious
effects on aquatic organisms, is called the assimilative capacity of the stream.
EFFECT OF WASTE DISCHARGES
Waste discharges, whether domestic sewage or industrial wastewaters, impose
demands upon the assimilative capacity of the receiving water. When a heavy-
load exceeding the assimilative capacity is discharged, the dissolved oxygen
content of the stream will be greatly depressed. However, provided no further
waste discharges occur downstream, the dissolved oxygen content of the
stream will eventually be re-established. A graph depicting the profile of
the dissolved oxygen content in such a situation is called an oxygen-sag curve
(Figure 2). Reoxygenation rates depend upon a number of factors, including
8
c
N
X
o
TJ
9)
t—I
O
to
waste discharge
r e oxy g ena tion
Time of flow, days
Figure 2. A hypothetical oxygen-sag curve.
1-4
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the initial dissolved oxygen content of the stream, the pollutional strength
of the waste discharge, the relative volumes of the two, and the character-
istics of the down-stream flow (fast or slow, smooth or turbulent).
Unfortunately, waste discharges occur at numerous points along most streams,
thereby precluding sufficient reoxygenation. Thus, the self-purification capa-
bilities of such streams are seriously hampered. When excessive waste loads
are discharged under these conditions, the consequences become evident by
large fish kills and nuisance conditions with serious public health significances.
The increasing frequency of such occurrences in many of the Nation's lakes
and rivers eventually led to the formation of environmental groups, each
demanding protective legislation. Politicians immediately joined in the clamor,
often using environmental issues as major platform planks. Naturally, envrion-
mental legislation soon followed and the Age of Ecology was born.
ENVIRONMENTAL LEGISLATION
During the late '50s and through the 60's, several important Congressional
acts were passed. Although some of these were not individually effectual,
they served as precursors to the most significant piece of environmental legis-
lation enacted to date. On October 18, 1972, Congress established Public Law
92-500, the Federal Water Pollution Control Act Amendments of 1972 (FWPCA).
This act essentially rewrote and consolidated several preceding laws in an
effort to create a mechanism by which to attack and resolve the Nation's wa-
ter pollution plight.
The FWPCA establishes as a national goal the elimination of pollutant dis-
charges into navigable waters by 1985. This is popularly called the "zero
discharge" concept. In an effort to meet this goal, the Administrator of the
Environmental Protection Agency (EPA) is directed to establish for each ma-
jor industry group a set of effluent limitations -- that is, specific restrictions
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on the quantity of pollutants that an industrial plant will be permitted to dis-
charge. These limitations are to be based on reductions which are considered
to be achievable through in-plant process changes, as well as end-of-pipe
wastewater treatment.
The Act requires that by July 1, 1977, effluent limitations reflect the applica-
tion of the "best practicable control technology currently available"; by July
1, 1983, the limitations are to be based on application of the "best available
technology economically achievable"; and performance standards for all new
sources must be based on the "best available demonstrated technology. " Fac-
tors to be considered in the establishment of effluent limitations include the
age of equipment and facilities, the processes employed, and costs to achieve
the specified reductions.
Also of direct interest to industrial wastewater dischargers, the FWPCA es-
tablishes a permit program known as the National Pollutant Discharge Elimi-
nation System (NPDES). The assure that effluent limitations are being met
and that designated water quality standards are maintained, all wastewater
discharges are required to obtain a permit. Although the permit program
was initially administered by EPA, a mechanism is provided to shift admini-
strative responsibilities to individual states. (Most states now have or will
soon be granted administrative authority.)
When NPDES discharge permits are issued, conditions are prescribed to as-
sure compliance with all appropriate regulations, including, but not limited
to, protection of designated beneficial uses of the receiving water, specifica-
tion of effluent limitations, and a schedule o'f construction of adequate waste-
water treatment facilities to meet the limitations. The permits also prescribe
s elf-monitor ing procedures required of all discharges. The self-monitoring
program generally consists of data collection and record keeping; reports
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must be periodically submitted to the appropriate regulatory agency. To
meet the requirements specified in the permits, companies will generally
have to expend considerable funds for pollution abatement.
The provisions of the FWPCA briefly described above primarily effect
direct discharges -- i. e. , those industrial plants which discharge waste-
water directly to receiving streams. The Act, however, also contains
provisions which affect industrial users of publicly-owned treatment works.
Industrial users can be significantly affected by performance standards
and effluent limitations which are imposed upon publicly-owned facilities.
Since industrial waste loads may constitute a significant portion of the
total load being treated at a municipal plant, the type and size of that
facility may be greatly affected by the industrial load, thus influencing
the total cost of new or expanded facilities to meet imposed regulations.
For municipalities to take advantage of Federal construction grants, the
Act requires each municipality to establish a revenue recovery program
•which insures that industrial users will contribute their proportionate
share of the total capital costs. Additionally, each municipality is
required to establish a schedule of user charges, based on flow rate
and strength, which will assure that each recipient of wastewater
treatment services, both industrial and non-industrial, will pay its
proportionate share of the total operating and maintenance costs. Thus
industrial users of publicly-owned treatment works may incur significant
costs for the privilege of utilizing such facilities.
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II. ANATOMY OF POLLUTION CONTROLS
Food processing operations inherently, require the use of water. And
as long as water is used, wastewaters requiring treatment will be generated.
The degree of treatment will be dictated by the quantity of pollutants, as well
as discharge requirements. Several options exist by which reductions in the
discharged effluent may be achieved. In almost all food processing plants, the
problem of pollution abatement can be attacked in two broad areas -- inside
the plant and at the "end of the pipe. " Company-management will inevitably
be required to decide where and how working capital can most effectively be
directed to ultimately resolve a problem.
MATERIALS BALANCE
Examination of materials balance (Figure 3) may provide insight into how
these areas are inter-related. Incoming materials include numerous items,
but principally raw commodities (fruits/vegetables), water, energy, supplies
(packaging materials and similar items), and product ingredients (sugar, salt,
spices, etc.). These are utilized in various processes to produce a principal
product. The processing operations utilize both energy and •water, and
generate residuals* which are discharged from the plant. Some residual
materials may be processed into by-products; the remainder are generally
considered to be "•wastes". The wastes are in various forms -- gaseous
(heat and stea'm), liquid (wastewater and dissolved product components),
and solid (solid residuals and suspended solids contained in the wastewater).
Assuming that supplies and ingredients are totally utilized (if they are not,
these materials will contribute to the waste load), the major inputs into the
processing operation are raw commodities, water and energy. All
*Residuals are defined as those materials from incoming items which
remain after the production of all primary commodities.
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INPUTS
Raw Commodities
Water
Energy
Supplies
Ingredients
- $
t
Heat
Steam
-$
OUTPUTS
I Principal Products
I By-products
•
Pollutants
Waste water
Solid Residuals
Figure 3. Balance of principal materials of a food processing plant.
of these must be purchased and, thus, represent costs to the company. There
is generally little that can be done to change the cost for raw commodities;
the prices are established •well before the processing step. However, the
costs to obtain water and energy are dictated by the quantitites consumed by
the operations. Minimizing the need by optimizing operating efficiencies will
result in minimizing costs.
Of the several output items, only the principal product results in an
appreciable income. If by-products can be feasibly manufactured, these
may also result in an income, albeit generally significantly less. The re-
maining outputs either do not directly affect finances, such as dissipated
energy lost as heat, or else incur costs for. handling and disposal. The
•
most significant expenses are associated with the management of waste
materials, namely, processing wastewaters with the pollutants contained
therein and solid residuals,for which there is no current usefulness.
H-2
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To appreciate the relationship between the main input and output items, one
has only to realize that:
1. The total quantity of raw commodity initially purchased
equals the sum of the salable products, solid residuals
and discharged pollutants.
2. The volume of purchased water equals the generated waste-
water volume plus the small volume of water lost as steam
or used in the principal product.
By optimizing processing operations to reduce the quantity of generated wastes,
the quantity of salable products must necessarily increase; by reducing water
consumption, the quantity of generated wastewater requiring treatment will
correspondingly be reduced.
MANAGEMENT AND POLLUTION CONTROLS
Pollution controls, whether through process modifications or end-of-pipe
treatment, or a combination of the two, will require capital expenditures.
Company-management's responsibilities must include:
1. Knowledge of existing operations.
2. Understanding of the problems and the available alterna-
tive solutions.
3. Decision as to where maximum benefit-cost ratios exist.
4. Dedication of resources (capital and man-power) to achieve
resolution of the company's environmental problems.
To assist food processing plant owners, managers, supervisors and their
engineering and operation personnel in developing an effective pollution
control program, the primary pollution control parameters, the basic aspects
of pollution control programs, and a brief introduction to the major treat-
ment processes are discussed in the following sections of this manual. De-
tails pertaining to pollution abatement through process modifications are
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contained in the second volume of the series, In-plant Control of Food Pro-
cessing Wastewaters. Treatment alternatives are described in detail in
the third volume, Wastewater Treatment in the Food Processing Industry.
U-4
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III. WATER POLLUTION PARAMETERS
The potential effects of wastewater discharges, either upon a receiving
stream or a treatment system, can best be evaluated by accumulating spe-
cific information with which to determine the "waste load" associated with
the discharge. Waste loads are used by engineers to design appropriate
wastewater treatment facilities, by regulatory authorities to specify effluent
limitations, and by municipalities to levy surcharges for sewer services.
There are two aspects of industrial waste loads which are of primary con-
cern. The first is the volume or quantity of wastewater -which must be
treated and/or disposed. This is referred to as the hydraulic load. The
second consideration is the pollutional strength of the wastewater, or the
quantity of pollutants contained therein. For most food processing wastes,
the pollutants of major concern are biochemical oxygen demand (BOD) and
suspended solids (SS). These are collectively referred to as the organic
load. The hydraulic and organic loads comprise what is referred to as the
raw waste load (RWL).
Other water pollution parameters, in addition to flow, BOD and suspended
solids, which may be of concern to fruit and vegetable processors, are also
briefly described below. The reader, however, is directed to References
1 and 2 for details (reagents, equipment, supplies and procedure) of the
analytical methods.
FLOW
Flow measurements are a basic requirement for monitoring all discharges.
Hydraulic loads can only be determined by accurate flow records, prefer-
ably kept on a continuous basis. Since the hydraulic load largely dictates
the required size of a treatment facility, each processing plant should pro-
vide some means for obtaining and recording this information.
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Numerous types of equipment or combinations of equipment are commer-
cially available for measuring both large and small flows. These include
meters, weirs, flumes, and special devices; these, as well as simple
flow measuring techniques, are described in detail in the following volume
(also see Ref. 3).
DISSOLVED OXYGEN
Dissolved oxygen is defined as oxygen which is dissolved in water or other
liquid. This should not be confused with the presence of air bubbles which
may be visible in water since such bubbles are still in a gaseous state.
Although dissolved oxygen is not generally a significant parameter when
dealing exclusively with waste streams, it is of major importance in receiv-
ing waters and in certain waste treatment sys terns, aerobic conditions must
be maintained in the latter to preclude development of odors associated with
stagnation.
Dissolved oxygen (DO) may be measured either by wet chemical analysis or
by instrument (Figure 4); the procedures are discussed elsewhere. Dis-
solved oxygen concentrations are expressed as milligrams per liter (mg/1 DO),
which is approximately equivalent to parts per million (ppm).
Figure 4. Dissolved oxygen meter with recorder.
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The quantity of dissolved oxygen which can be maintained in water is directly
related to atmospheric pressure and inversely related to water temperature.
Thus, the lower the temperature and the higher the pressure, the greater will
be the maximum maintainable DO level. Although it is possible to obtain rela-
tively high concentrations of dissolved oxygen, a concentration of 9 mg/1 DO is
generally regarded to be saturation under ambient conditions. A minimum of
5 mg/1 is considered to be desirable for sustaining game fish (trout, salmon,
etc.).
BIOCHEMICAL OXYGEN DEMAND
For many years, investigators have attempted to measure the strength of
wastewater containing dissolved organic compounds in terms of their effect
upon streams or other bodies of water into which the wastes are discharged.
The standard method for measuring this effect is the biochemical oxygen de-
mand (BOD) test. The test was developed by determining the amount of oxy-
gen required to microbially stabilize known quantities of decomposable organic
matter.
The BOD test is based on an apparent direct relationship between the pollution-
al strength of organic wastes and the amount of oxygen that will be required
(oxygen demand) in biochemical reactions to convert the materials to carbon
dioxide, water and inorganic nitrogen compounds. The oxygen demand is re-
lated to the rate of increase in microbial activity which is, in turn, proportional
to the concentration of nutrients in the organic wastes. These relationships
also represent the mechanism for stream self-purifications.
In the standard laboratory BOD test, samples of wastewater are seeded with
an inoculum, diluted with previously aerated water (if necessary), and incuba-
ted at 20 C. After a specified period the dissolved oxygen content is deter-
mined; the BOD is based on the depletion of oxygen from the sample during the
III-3
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bO
s
p
•
o
2nd stage
(nitrification)
1st stage
(carbonaceous)
I
5-day BOD
Incubation time, days
Figure 5. First and second stage BOD curve.
incubation period. Since complete stabilization of organic wastes require
prolonged periods (Figure 5), laboratory analysis is limited to two periods.
The 5-day BOD, which is used most widely, represents most of the oxygen
necessary to stabilize the carbonaceous and readily oxidized materials.
Since fruits and vegetables are largely composed of carbohydrates, the 5-
day BOD value is of greatest significance to this industry. The 20-day,
or second stage, BOD value is used to estimate the ultimate BOD; this
value represents oxygen required to stabilize nitrogenous and other slowly
oxidized materials.
Laboratory results are reported as milligrams per liter (mg/1). However,
effluent limitations and sewer service charges are based on pounds of BOD.
To determine the latter quantity, accurate flow measurements must be avail-
able. Pounds of BOD may then be calculated as foUows:
III-4
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Ibs BOD = BOD (mg/1) x total flow (gallons) x 8. 34
1,000,000
It is apparent that from this equation "dilution is no solution to pollution. "
For any waste the concentration of pollutants can be readily reduced by sim-
ply using more water, but the increase in volume will result in the same num-
ber of total pounds of pollutants. Instead, the BOD load can be effectively re-
duced only by simultaneously reducing water usage and BOD generation.
CHEMICAL, OXYGEN DEMAND
Chemical oxygen demand (COD) represents an alternative to biochemical oxy-
gen demand (BOD) for measuring the pollutional strength of wastewaters.
Simply described, the COD test measures the amount of oxygen consumed
during chemical oxidation of waste constituents. The test is relatively quick
and highly reproducible, thereby eliminating the two primary disadvantages of
the BOD test.
When considering the use of COD for measuring the pollutional strength of
wastewater, one must bear in mind that the BOD and COD tests involve
separate and distinct reactions. Chemical oxidation measures carbon and
hydrogen, but not amino nitrogen, in organic materials. Furthermore, the
COD test does not differentiate between biologically stable and unstable com-
pounds. For example, cellulose is measured by chemical oxidation but is not
measured biochemically under aerobic conditions. Despite these differences
a number of investigators have found a reliable and useful relationship between
BOD and COD for certain types of wastes. The COD is especially useful for
routinely monitoring wastewater discharges.
The primary disadvantage of the COD test is its susceptability to interference
by chloride. Thus, wastewaters containing high salt concentrations, such as
sauerkraut and pickle brines, cannot be readily analyzed. However, the
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standard method for COD is designed to remove interferences at low chloride
concentrations and can be used for analyzing processing wastewaters.
SOLIDS IN WASTE WATERS
Solids, or particulates, present in screened wastewaters are of concern for
several reasons. When discharged into receiving streams, the particulates
may remain in suspension to create turbid conditions. They may float and ag-
glomerate to form unsightly scum blankets, or they may settle on stream beds
to form anaerobic sludges. In wastewater treatment systems, settleable and
floatable solids must be removed so that they will not interfere with the effi-
ciency of treatment.
Settleable Solids
Information on the amount of settleable solids in wastewaters provides a basis
with which to predict the sludge load in settling basins, clarifiers, stream
beds, or sewer lines. The laboratory method is semi"quantitative and is use-
ful only for estimating the volume of sludge which can be anticipated.
Total Solids
Total solids determinations measure all matter which are contained in a water
or wastewater sample. Included in the determination are suspended matter,
which contribute to the turbidity of water, as well as dissolved components,
such as sugars and salts. Despite the fact that some volatile organic com-
pounds may be excluded in the analysis, which is conducted at the boiling point
of water, total solids is a useful tool for the qualitative determination of the
pollutants contained in wastewater samples (Figure 6).
Total solids, which is the residue remaining after evaporation of water from a
sample, can be further subdivided into fixed and volatile fractions. The fixed
solids, determined by weighing the residue remaining after combustion, is re-
HI-6
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2. Evaporating dish
placed in drying oven
for one hour at 103°C.
1. Evaporate sample
to dryness on
steam table.
7.
Total fixed
solids de-
termined by
weighing re-
sidue after
combustion.
Cool combusted
sample.
3.
Evaporating
dishes trans-
ferred to
desiccator
for 45 min-
utes to cool.
4. Total solids
determined by
weighing dried
sample.
5« Sample heated in muffle
furnace for 20 minutes
at 600° C to burn the or-
ganic material.
Total
Volatile Solids =
Total Solids -
Total
Fixed Solids
Figure 6. Steps in the determination of total and fixed solids.
in - 7
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garded as representing the inorganic matter contained in the sample; the vola-
tile solids, which is that portion of the total solids lost upon combustion, rep-
resents the organic matter.
Suspended Solids
Suspended solids (SS) in wastewater is the solid matter parameter of greatest
interest. This test is used by regulatory agencies as an index of potential for-
mation of sludge deposits and turbid conditions in receiving waters; effluent
limitations are therefore placed on allowable SS discharges. Engineers and
treatment plant operators utilize SS information to determine the quantity of
solids which will require removal; in activated sludge treatment systems (des-
cribed under Treatment Methods), suspended solids determinations reflect the
operating efficiency of the system.
Suspended solids is defined simply as that matter which will not pass through a
filter. For fruit and vegetable processing wastewaters, SS is considered to be
all materials which pass through a 20-mesh screen but are retained on a filter.
The laboratory determination is made by filtering a wastewater sample, and
drying and weighing the residue retained on the filter. As with total solids, the
total suspended solids (TSS) thus obtained may be further subdivided into fixed
•
(FSS) and volatile (VSS) components by combustion.
*\
Laboratory results are expressed as milligrams SS per liter (mg/1). However,
as in the case of BOD, SS limitations are expressed in pounds. The conversion
of units, which requires accurate flow data, is identical to BOD:
SS (mg/1) x total How x 8. 34
pounds SS = 1,000,000
Again, dilution will effect no change in the total pounds. Rather, the organic
load, consisting of both BOD and TSS can only be effectively reduced by simul-
taneous reductions in water usage and pollutant generation at in-plant sources.
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Dissolved Solids
Since as much as 85% of the BOD of fruit and vegetable processing wastewaters
maybe attributable to dissolved organic matter, the total dissolved solids
(TDS) determination is often of interest. TDS measurements are made by
filtering samples, and drying and weighing the residues in the filtrates. Fixed
(inorganic) and volatile (organic) fractions may be determined by combustion.
When brines, such as used for storing olives, pickles and sauerkraut, are
discharged, the TDS test is often used to estimate the quantity of salt contain-
ed in the wastewater.
OTHER PARAMETERS
The tests discussed above constitute the parameters of major concern to fruit
and vegetable processors. In specific situations, those tests which are de-
scribed below may also be of importance to this industry.
£H_
pH is a measure of the hydrogen ion concentration in water and indicates the
acidic or alkaline character of the water. A pH measurement does not, how-
ever, indicate a liquid solution's buffering capacity -- that is, its capacity to
accept acid or alkali without corresponding changes in the hydrogen ion concen-
tration. The pH values are expressed by a numerical scale from 0 to 14; the
mid-point, 7. 0, being neutrality (Figure 7). The 0 to 7 range is the acid scale;
the 7 to 14 range, the alkaline scale. Measurements are most suitably made
potentiometrically with an appropriate pH meter.
The pH of fruit and vegetable processing wastewaters may very from 3. 5 to
11. 5, depending upon the product being packed and the type of operations con-
ducted within the plant. Natural occurring waters generally have pH values
between 5. 5 and 8. 5. Accurate pH measurement and control of plant effluents
are often essential for successful treatment and disposal.
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14 T
(BASIC)
11 • •
9 •
NEUTRAL 7
(ACIDIC)
5 «
3 • •
caustic (lye) solution
weak or dilute
alkaline solutions
[ most effluent limits
*••• most ground waters in U. S.
y»|.- pure water = pH 7
\ most vegetables
L..... most tree fruit, tomato
^ \ ... berries
>..... citrus juices
weak or dilute acids
0 ^» mineral acids, cone.
Figure 7. The pH scale, with values of some materials.
in- 10
-------
Temperature
Since the dissolved oxygen concentration in water is inversely related to tem-
perature, effluent limitations based on water quality standards generally in-
clude temperature limits. The temperature of plant effluents may be of little
or not consequence to some processors but may be of significant concern to
others. The degree to which temperature may be a problem is determined by
the types of operations which contribute to the temperature and the relative
flows in the plant effluent as compared to the receiving stream.
Container and compressor cooling waters and evaporator condenser effluents
are the major sources of heated wastewaters in food processing plants. These
streams maybe discharged in several fashions. When mixed with processing
wastewaters prior to treatment, temperatures in the final discharge will have
minimal effects on receiving streams. When mixed with treated wastewaters
prior to discharge, the final temperature will be determined by the degree to
which the heated effluent is diluted by the treated waste. The severest impact
on a receiving stream will occur when heated wastewaters are discharged di-
rectly; in this case the effect will be determined by the flow and temperature
of the discharge vs. the flow and temperature of the receiving stream. Cool-
ing ponds or towers may be-required in extreme situations.
Temperature measurements can be manually taken by periodically checking the
discharge with a mercury-filled glass thermometer or by any one of a number
of commercially available temperature measuring devices. Where continuous
readings are desirable, suitable temperature sensors and recorders are also
available.
Nutrients
Aside from carbonaceous organic matter which are measured largely as BOD,
nutrients of primary concern are organic nitrogen and phosphorus-containing
in-n
-------
compounds. Both of these are required for multiplication of microorganisms.
Nitrogen (n) and phosphorus (P) are largely responsible for algal "blooms':1
which cause eutrophication of lakes and streams. To optimize efficiencies of
biological wastewater treatment systems, nitrogen and phosphorus concentra-
tions are adjusted according to the BOD concentration in the wastewater; the
generally recommended ratio of BOD to total N to total P is 100:5:1. Fruit and
vegetable processing wastewaters are normally nutrient deficient.
The laboratory nitrogen determination of greatest interest to this industry is
the total kjeldahl nitrogen (TKN) analysis. Most of the organic nitrogen com-
pounds are converted to ammonia which can then be meausred colorim etrical-
ly or by titration; results are reported as mg/1 TKN.
Phosphorus occurs almost exclusively in the form of various types of phos-
phates (PO .). Detergents used for product washing and plant cleanup are pri-
mary sources of phosphates in fruit and vegetable processing effluents; these
phosphates are water soluble. Insoluble forms of phosphates may be found
in sediments and in waste sludges. In the laboratory procedure wastewater
samples may be analyzed solely for soluble forms of phosphate or may be
treated to solubilize all phosphates. All of the several available laboratory
methods for measuring phosphate are colorimetric; results are reported as
mg/1 P.
111-12
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-IV. SAMPLING
The most vital part of an effluent monitoring program is the procedure used
to collect wastewater samples. Only with appropriate sampling procedures
can laboratory analyses yield accurate information relative to a plant's dis-
charge. Optimally, the best information can be developed by continuous in-
line sampling, with instantaneous analysis and recording. For some parame-
ters, such as temperature and pH, this is very practical. However, the cost
or the unavailability of suitable instrumentation renders continuous monitoring
infeasible for most parameters. As a compromise, laboratory analyses are
performed on samples which are collected and preserved in a manner that will
yield representative or typical data.
GRAB SAMPLES
A sample which is collected on a one-time basis is called a grab or discrete
sample. A grab sample, as implied by its name, may be simply collected by
manually dipping a container into a wastewater stream. However, laboratory
results obtained from such a sample will provide but a single data point, re-
flecting only those conditions which exist at the time the sample is drawn.
Since wastewater characteristics from food processing operations vary widely
throughout the production day, a single grab sample is of little value. If, on
the other hand, numerous grab samples are collected and separately analyzed,
temporal fluctuations in the waste load will be revealed (Figure 8). This type
of information is extremely useful, not only for determining at which periods
of the day the loads tend to peak, but also for calculating meaningful daily (or
other period) averages. Automatic sampling equipment capable of collecting
a series of discrete samples are commercially available.
COMPOSITE SAMPLES
As previously indicated, laboratory results from numerous grab samples taken
within a period of time can be used to calculate meaningful averages for that
IV-1
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2000
1500
°. 1000
o
PQ
500
Tf Vv
Tf Vv
6A
12N 6P
Time of day
12M
6A
Figure 8. Temporal fluctuations in a food plant waste load.
time interval. However, this procedure for obtaining daily (or other)
averages places a heavy burden on laboratory personnel. To minimize
laboratory efforts which obtaining meaningful data, a single sample con-
sisting of the combination of numerous discrete subsamples, or aliquots,
may be used. Such samples are referred to as composites. Composite
samples will yield excellent average values, but cannot reveal peak and
low data points within a specified temporal interval (Figure 8).
Composite samples can be readily obtained by merely collecting a
containerful of wastewater at regular intervals. For example, a half-
liter sample can be obtained each hour -over a twenty-four hour period,
thereby resulting in a composite sample of approximately three gallons.
Laboratory results obtained by analyzing a single sample collected by
IV-2
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this procedure, which can be referred to as fixed time-fixed volume (TV),
F F
will closely approximate the average obtained by individually analyzing each
aliquot. Relatively inexpensive devices are available to automatically collect
TV composite samples. This procedure is quite satisfactory for non-
fluctuating flows.
When discharge flows fluctuate widely, a single aliquot in a TV composite
F F
may seriously influence analytical accuracy of the entire composite sample.
To minimize the effect of an individual aliquot, flow-proportioned aliquots
should be taken. For example, when aliquots are collected once per hour,
the volume should be adjusted according to the flow rate at that time (1 liter
at 1000 gpm, 250 ml at 250 gpm, etc.). This may be referred to as fixed
time-variable volume (TV). This procedure, for which a few automatic
sampling devices are available, will yield laboratory results in close agree-
ment to the true average.
Best results short of continuous on-line analysis are obtained by analyzing
samples composited on a "per unit flow" basis -- that is, a composite con-
sisting of aliquots, each of which represents a unit volume of discharge
(e.g., per 1000 gallons). Automatic sampling equipment operated in con-
junction with various accurate flow-measuring devices are available for this
purpose. These samplers obtain an aliquot of fixed volume for every 1000
gallons, or other unit, of wastewater discharged (TV). Thus, representa-
tive samples are obtained regardless of wide fluctuations in the discharge rate.
SAMPLE STORAGE
Since organic matter in wastewaters can degrade rapidly, it is important
to analyze samples as quickly as possible to assure sample integrity and
valid results. Analysis of composite samples, by the nature of collection
IV-3
-------
procedures, must inevitably be delayed. Therefore, these samples must
be iced or held under refrigeration during compositing and up to the time
laboratory analyses can be performed. When unavoidable prolonged delays
are anticipated, other preservation techniques should be followed; these
are discussed in greater detail in Volume 2 and in Reference 3.
IV-4
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V. • TREATMENT METHODS
Wastewater discharge permits (NPDES permits) contain limitations on
the quantity of pollutants which can be discharged into receiving streams.
For food processing wastewaters, permittees are all required to reduce
their raw waste loads by often extensive treatment. Industrial users of
municipal treatment systems are generally also required to minimally
pretreat their wastewater to the extent of removing large particulate
matter. The following discussions generally describe the main treat-
ments for food processing wastewaters. Details of each, with discussions
of specific treatment processes and schemes, are contained in Volume 3
of this series.
SCREENING
The basic and primary pretreatment step for all wastewaters is the
removal of large materials which are detrimental to equipment operations
and to the efficiency of the remainder of the treatment system. Screens
of various types are used to remove such materials. Screens may range
from parallel bars (bar racks) spaced at up to two-inches (Figure 9) for
removing rocks, rags and wood, to tightly woven metal or fabric cloth
for removing fine particles (Figure 10).
Woven screen cloths are used in rotating cylindrical screens and in
vibrating flat-bed screens utilized extensively by food processors.
These cloths are sized according to mesh, the number of openings per
inch. Thus, a 10-mesh cloth contains ten openings per lineal inch.
However, the percent open area, which is affected by the diameter of
the wire or fabric used in the weave, is not reflected by mesh desig-
nations. For fine screen cloth the size of each opening (e. g. , lOOfi) is
used in place of mesh. For most fruit and vegetable wastewaters, 20-
mesh to 40-mesh screens have proven most effective.
V-l
-------
Figure 9. Bar rack with automatic rake.
Figure 10. Vibrating screen for separation of solid particles.
V - 2
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Dewatered
Solids
Figure 11. Parabolic or tengential screen.
V - 2a.
-------
A design gaining in popularity is the parabolic or tangential screen
(Figure 11). The screening surface consists of a curved steel sheet
containing slits through which water can pass but on which solids are
retained. By introducing wastewater tangentially to the top of the
curved slope, the retained solids are gravitationally forced to the
bottom discharge. Dewatering of solids is facilitated by the decelera-
tion of retained materials at the bottom of the slope. Size designation
is by mesh-equivalent or by the measurement of the slit width.
PRIMARY TREATMENT
Primary treatment refers to removal of floatable and readily settleable
materials. This is always a necessary initial step in the treatment of
domestic sewage. Settling tanks and clarifiers (Figure 12) are designed
to reduce influent flow rates so that floatable and settleable materials
will be naturally separated from the wastewater. Mechanical devices
are incorporated to continuously remove scum and sediment from the
units.
BRIDGE
EFFLUENT
/ONONEWftLV SC^ER-,
SQUEEGEE
PLOW
Figure 12. Sectional diagram of a circular clarifier.
V-3
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Waste-water from washing certain commodities, such as root vegetables
and mechanically-harvested tomatoes, contains high concentrations of
soil. Under these circumstances, primary treatment may be required
to prevent sedimentation of soils in subsequent treatment works. However,
primary treatment will have little effect in reducing the BOD loads asso-
ciated with fruit and vegetable processing wastewaters. Generally,
screening is all that will be required for solids removal.
SECONDARY TREATMENT
Secondary wastewater treatment systems are designed to reduce organic
loads. Under practical situations, BOD and suspended solids removals
of 85 to 90 percent are achieved. Effluent limitations generally require
the minimum of secondary treatment for all discharges into receiving
streams. The numerous types of systems which are available for this
purpose are classified into two broad categories -- biological and
physical-chemical.
Biological Treatment
Biological systems are so named because microorganisms are depended
upon to reduce organic loads. System designs attempt to optimize environ-
mental conditions for the support and growth of suitable micro-fauna. The
simplest of biological systems is a lagoon or stabilization pond, usually
four to six feet deep. Lagoons are sized to retain waste flows for long
periods (as much as 30 days or more), during which time organic materials
are degraded. Aerated lagoons are equipped with mechanical devices
(Figure 13) to increase the dissolved oxygen concentration in lagoon water,
thereby increasing the efficiency of treatment and reducing required re-
tention times. Both stabilization ponds and aerated lagoons are used widely
by food processors.
V-4
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Figure 13. Aeration basin with floating surface aerators.
The activated sludge process, with its many variations, is the most
sophisticated biological treatment procedure. An activated sludge system
basically consists of an aeration tank followed by a clarifier. Wastewater
is continuously introduced into the aeration tank; nutrient balances are
maintained to optimize the growth of microorganisms within the tank.
The organisms are removed from the system effluent by the clarifier;
the clarified treated wastewater is discharged and the recovered
organisms (activated sludge) are mixed with the influent wastewater
to achieve maximum degradation rates. Retention times required by
this process are relatively short (a few hours for weak wastes to a few
days for stronger wastes).
V-5
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The operating principle of trickling filters (Figure 14) is unique among
biological processes. Instead of providing an environment in which micro-
organisms are suspended within a liquid, trickling filters are vertical tanks
containing rock, plastic or wood media which provide large surface areas
upon which microorganisms form a film, or zoogleal slime. The media is
arranged within the system to provide a high percentage of void spaces,
thereby assuring maintenance of aerobic conditions. Wastewater is applied
slowly over the top of the packing and allowed to slowly trickle down through
the media. Organic matter contained in the wastewater is adsorbed on the
slime and degraded by the microorganisms. The BOD of the effluent col-
lected at the bottom of the unit is thus considerably reduced.
Figure 14. Top view of trickling filter packed with plastic media.
V-6
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Physical-Chemical Treatment
Physical and/or chemical processes may provide effective secondary
treatment when a. high percentage of the organic load is attributable
to solids contained in the wastewater. For most fruit and vegetable
processing wastes, most of the BOD is due to dissolved organic matter.
Therefore, biological systems will generally be required. However,
physical-chemical processes may be required in conjunction with
biological treatment in situations where extremely stringent discharge
requirements must be met.
Colloidal particles -- suspended solids which are extremely fine and
tend to remain suspended in water -- are most problematic. Chemical
flocculation has been demonstrated to effectively facilitate their re-
moval. When certain chemicals are mixed with wastewater, the
particles are physically encouraged to agglomerate, thereby forming
larger particles (floe) which can then be readily separated. Effective
chemicals include ferric chloride, alum, and a wide variety of synthe-
sized polyelectrolytes.
When flocculated materials are relatively heavier than water, separation
can be most readily achieved by sedimentation. However, some floes
can remain close to the density of the water and will not readily settle.
In such cases, air flotation has proven quite effective (Figure 15). In
this process minute bubbles of air are introduced into a tank of waste-
water. As the bubbles rise to the surface, they become attached to floe
particles, thus encouraging the particles to float. The floe can be re-
moved from the system with skimmers.
Suspended solids may also be removed by various filtration techniques.
Vacuum filters, widely used by potato processors for dewatering settleable
V-7
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AIR PRESSURE
SYSTEM
AIR
PRE-SCREENED
CANNERY WASTE
PRESSURE AIR-LIQUID
TANK DISSOLVING
SYSTEM
FLOTATION SYSTEM
1st. STAGE
PUMP
• — ' RETENTION
Znd STAGE TANK
PUMP
LIQUID PRESSURIZATION
SYSTEM
FLOATABLE SETTLED
SOLIDS COARSE SOLIDS
SOLIDS TO DISPOSAL
CLEAN
WATER
DISCHARGE
Figure 15. Schematic of a full flow pressurization floatation system.
solids, employ rotating drums covered with extremely fine-mesh
filter cloths. The drums are partially vacuated and immersed partly
in wastewater. The water phase is drawn through the fabric cover;
the suspended solids are retained as a coating on the outer surface.
The solids are removed by scraping the exposed drum surface and
collecting the dislodged solids. Fine suspended solids may be removed
by sand filtration. By passing wastewater through a bed of fine sand,
suspended materials are retained within the bed while water passes
through. The bed must be periodically cleaned by backwashing, thus
dislodging trapped solids which are collected in a concentrated stream.
When a filter bed consists of a mixture of size-graded materials, such
as sand, garnet and anthracite, the process is named mixed-media
filtration. Filtration rates are greatly improved by use of mixed-media.
V-8
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Refractory compounds -- that is, materials which are difficult to remove
by conventional processes -- can often be removed by carbon adsorption.
Activated carbon has the unique property of being able to "hold onto" a
wide variety of compounds. Refractory compound concentrations contained
in wastewater will be significantly reduced by passage through columns of
activated carbon. When the adsorptive capacity of a column is reached,
the carbon must be regenerated, typically by incineration to combust the
adhering pollutants. The carbon can then be reused to treat additional
volumes of wastewater.
LAND DISPOSAL
The EPA generally considers land disposal (with no associated run-off)
as satisfying the WPCA goal of "zero discharge". Effluent limitations
for several industrial categories, such as beet sugar processing, speci-
fy zero discharge through land disposal. Under practical conditions,
land disposal of large volumes of wastewater is limited to either flood
or spray irrigation, both techniques are widely used by fruit and vege-
table processors.
Flood irrigation , as the term implies involves spreading wastewater over
designated fields. Disposal is accomplished by percolation of wastewater
into the soil and by evaporation. In check irrigation, the field is divided
into diked sections or "checks". Wastewater is applied by flooding the
checks on a rotational schedule; each check is allowed to dry before further
wastewater applications are made. In ridge-and-furrow irrigation, the
field is prepared by creating parallel furrows or ditches. Wastewater is
applied by flooding the furrows; the ridges facilitate disposal by absorbing
water from the furrows. Crops may be planted on the ridges to further
facilitate disposal through evapotranspiration.
V-9
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Spray irrigation involves application of wastewater through impulse sprinkler
heads (Figure 16). As in flood irrigation, spray fields are normally divided
into sections and wastewater applications are made on a rotational schedule.
Disposal is accomplished by evaporation and percolation. Cover crops,
generally a mixture of water-tolerant grasses, are planted to facilitate dis-
posal through evapotranspiration. Percolative spray irrigation systems are
designed for complete disposal -- that is, all applied wastewaters are disposed
of through percolation and evaporation, thereby resulting in zero run-off.
Overland flow systems, which are gaining in popularity, are intentionally de-
signed for excessive application with resultant runoffs. These systems are
engineered to utilize soil bacteria for degradation of organic matter
contained in the wastewater. The quantity and pollutant content of the
collected runoff is thus considerably reduced. In principle, this system
is a combination percolative spray irrigation and biofilter (trickling filter).
Figure 16. Spray irrigation disposal of food processing wastewater.
V-10
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REFERENCES
1. U.S. Environmental Protection Agency. Methods for Chemical
Analysis of Water and Wastes (Document Number EPA-625-/6-74-003),
EPA Office of Technology Transfer, Washington, D.C. (1974)
2. Standard Methods for the Examination of Water and Wastewater,
(13th ed.), American Public Health Association, N. Y. (1971)
3. U.S. Environmental Protection Agency. Handbook for Monitoring
Industrial Wastewater, EPA Office of Technology Transfer, Washington,
D.C. (1973)
VI-1
-------
GLOSSARY OF TERMS
Definition of Selected Terms
used in
Water and Waste Management
vn-i
-------
A
acidity -- The quantitative capacity of aqueous solutions to react with hy-
droxyl ions. It is measured by titration with a standard solution of
a base to a specific end point. Usually expressed as milligrams per
liter of calcium carbonate.
activated carbon -- Carbon particles usually obtained by carbonization
of cellulesic material in the absence of air and possessing a high
adsorptive capacity.
activated sludge -- Sludge floe produced in raw or settled wastewater by the
growth of zoogleal bacteria and other organisms in the presence of
dissolved oxygen and accumulated in sufficient concentration by return-
ing floe previously formed.
activated sludge process -- A biological wastewater treatment process in
which a mixture of wastewater and activated sludge is agitated and
aerated. The activated sludge is subsequently separated from the
treated wastewater (mixed liquor) by sedimentation and wasted or
returned to the process as needed. The treated wastewater overflows
the weir of the settling tank in which separation from the sludge takes
place.
adsorption -- A taking up of gases or liquids by the surfaces of solids or
liquids with which they are in contact.
advanced waste treatment -- A term including any treatment process ap-
plied for renovation of wastewater that goes beyond the usual 90-99%
oxygen demand and organic solids removal of secondary treatment.
May include nitrogen, phosphorous, other minerals, taste, odor, color,
and turbidity removal by a variety of conventional and special processes
as required to renovate wastewater for intended reuse.
-------
aerobic -- (J) A condition characterized by an excess of dissolved oxygen
in the aquatic environment. (2) Living or taking place only in the
presence of molecular oxygen.
alkalinity -- The capacity of water to neutralize acids, a property im-
parted by the water's content of carbonates, bicarbonates, hydrox-
ides, and occasionally borates, silicates, and phosphates. It is
expressed in milligrams per liter or equivalent calcium carbonate.
Natural waters are generally neutral or slightly alkaline. The
alkalinity of water may range from a few milligrams per liter to
several hundred. Domestic sewage is usually slightly more alka-
line than the water from which it is derived.
alum -- A chemical substance (usually potassium aluminum sulfate),
gelatinous when wet, used in water-treatment plants for settling
out small particles of foreign matter.
anaerobic -- (1) A condition in which dissolved oxygen is undetectable in
the aquatic environment. Usually characterized by formation of
reduced sulfur compounds such as sulfides in a putrefaction activity.
(2) Living or taking place in the absence of molecular oxygen.
anaerobic digestion -- The degradation of organic matter brought about
through the action of microorganisms in the absence of elemental oxygen.
assimilative capacity -- The capacity of a natural body of water to receive:
(a) wastewaters, without deleterious effects; (b) toxic materials,
without damage to aquatic life or humans who consume the water;
(c) BOD, within prescribed dissolved oxygen limits.
available chlorine -- A measure of the total oxidizing power of chlorinated
lime and hypochlorites.
-------
» B
biochemical oxygen demand (BOD) -- The quantity of oxygen used in the
biochemical oxidation of organic matter in a specified time, at a
specified temperature, and under specifiedconditions. (2) A standard
test used in assessing wastewater strength.
biological oxidation -- The process whereby living organisms in the
presence of oxygen convert the organic matter contained in
wastewater into a more stable or a mineral form.
BOD load -- The BOD content, usually expressed in pounds per unit of
time, of wastewater passing into a waste treatment system or to
a body of water.
BOD:N:P ratio -- The ratio based upon analysis of wastewater passing
into a waste treatment system, of the BOD to total nitrogen
to total phosphorus contained in the waste stream. To assure a
nutrient balance within a biological treatment system, a ratio
of 100:5:1 is generally recommended.
brackish water -- Water having a mineral content in the general range
between fresh water and seawater. Water containing from 1,000
to 10,000 mg/1 of dissolved solids.
breakpoint chlorination -- Addition of chlorine to water or wastewater
until the chlorine demand has been satisfied and further additions
result in a residual that is directly proportional to the amount added
beyond the breakpoint.
buffer action -- The action exhibited by certain chemicals that resist a.
change in the effective acidity or hydrated H+ ion content of a solution.
In surface water the primary buffer action is related to carbon
dioxide, bicarbonate and carbonate equilibria.
-------
bulking sludge --An activated sludge that settles poorly because of a floe
of low density.
chemical oxygen demand (COD) -- A measure of the oxygen -consuming
capacity of inorganic and organic matter present in water or waste-
water. It is expressed as the amount of oxygen consumed from a
chemical oxidant in a specific test. It does not differentiate between
stable and unstable organic matter and thus does not necessarily
correlate with biochemical oxygen demand. Also known as OC and
DOC, oxygen consumed and dichr ornate oxygen consumed, respectively.
chloramines -- Compounds of organic or inorganic nitrogen and chlorine.
chlorine demand -- The difference between applied chlorine and residual
available chlorine in aqueous media under specified conditions and
contact time. Chlorine demand varies vrith dosage, time, tem-
perature and nature of the water impurities.
clarification -- Any process or combination of processes the primary
purpose of which is to reduce the concentration of suspended
matter in a liquid.
C/N ratio -- The weight ratio of carbon to nitrogen.
coagulation -- The process of modifying chemical, physical or biological
conditions to cause flocculation or agglomeration of particles.
coliform group -- A group of bacteria predominantly inhabiting the
intestines of man or animal, but also occasionally found elsewhere.
It includes all aerobic and facultative anaerobic, Gram-negative,
non-spore forming bacilli that ferment lactose with production of
-------
gas. Also included are all bacteria that produce a dark, purplish-
green colony with metallic sheen by the membrane-filter technique
used for coliform identification. The two groups are not always
identical, but they are generally of equal sanitary significance. Their
presence in water is presumptive evidence of contamination by fecal
material.
colloids -- (1) Finely divided solids which will not settle but may be removed
by coagulation or biochemical action or membrane filtration; they
are intermediate between true solutions and suspensions. (2) In
soil physics, discrete mineral particles less than two microns in
diameter. (3) Finely divided dispersions of one material, called
the dispersed phase with another, called the dispersion medium.
(4) In general, particles of colloidal dimensions are approximately
10 A to lu in size. Colloidal particles are distinguished from
ordinary molecules by their inability to diffuse through membranes
that allow ordinary molecules and ions to pass freely.
combined available chlorine -- The concentration of chlorine which is
combined with ammonia as chloramine or as other chloro derivitives,
yet is still available to oxidize organic matter.
composite wastewater sample -- A combination of individual samples of
water or wastewater taken at selected intervals, generally hourly
for some specified period, to minimize the effect of the variability
of the individual sample. Individual samples may have equal volume
or may be roughly proportioned to flow at time of sampling.
contact stabilization process -- A modification of the activated sludge
process in which raw wastewater is aerated with a high concentration
of activated sludge for a short period, usually less than 60 min, to
obtain BOD removal by absorption. The solids are subsequently
removed by sedimentation and transferred to a stabilization tank
-------
where aeration is continued further to oxidize and condition them
before their reintr eduction to the raw wastewater flow.
denitrification -- (1) The conversion of oxidized nitrogen (nitrate and
nitrite -N) to nitrogen gas by contact wth septic wastewater solids
or other reducing chemicals. (2) A reduction process with respect
to oxidized nitrogen.
detritus -- (1) The coarse debris carried by wastewater. (2) The heavier
mineral debris moved by natural watercourses, usually in bed-load
form.
diatomaceous earth, diatomite -- A fine, siliceous earth consisting mainly
of the skeletal remains of diatoms (unicellular organisms).
diffuser -- A porous plate, tube, or other device through which air is
forced and divided into minute bubbles for diffusion in liquids.
Commonly made of carborundum, alundum, metal, or plastic
materials.
digested sludge -- Sludge digested under either aerobic or anaerobic condi-
tions until the volatile content has been reduced to the point at which
the solids are relatively nonputrescible and inoffensive.
dispersed growth -- Non-flocculating micro- prganisms whose presence in
treated wastewater results in a turbid effluent.
dissolved oxygen (DO) -- The oxygen dissolved in water, wastewater, or
other liquid, usually expressed in milligrams per liter, parts per
million, or percent of saturation. Abbreviated DO. In unpolluted
water, oxygen is usually present in amounts of up to 10 ppm. Adequate
-------
dissolved oxygen is necessary for the life of fish and other aquatic
organisms. About 3-5 ppm is the lowest limit for support of fish
life over a long period of time.
dissolved-oxygen sag curve -- A curve that represents the profile of dis-
solved oxygen content along the course of a stream resulting from
deoxygenation associated with biochemical oxidation of organic
matter and reoxygenation through the absorption of atmospheric
oxygen and biological photosynthesis. Also called oxygen-sag curve.
dissolved soilds -- The total amount of dissolved material, organic and
inorganic, contained in water or wastes. Excessive dissolved solids
can make water unsuitable for industrial uses, unpalatable for drinking,
and even cathartic. Potable water supplies may have dissolved solid
content from 20 to 1000 mg/1, but sources which have more than
500 mg/1 are not recommended by the U.S. Public Health Service.
drinking water standards -- (1) Standards prescribed by the U.S. Public
Health Service for the quality of drinking water supplied to interstate
carriers. (Z) Standards prescribed by state or local jurisdictions for
the quality of drinking water supplied from surface-water, ground-
water or bottled-water sources.
JL
E. coli -- Abbreviation of Escherichia coli, a species of bacteria in
the coliform group and normal inhabitants of the intestine of man
and animals. Its presence of considered indicative of fresh fecal
contamination.
effluent -- (1) A liquid which flows out of a containing space. (2) Waste-
water or other liquid, partially or completely treated, or in its
natural state, flowing out of a reservoir, basin, treatment plant,
or part thereof. (3) An outflowing branch of a main stream or lake.
-------
estuary -- The mouth of a river, where tidal effects are evident and where
fresh water and sea water mix.
eutrophication -- The normally slow aging process by which a lake evolves
into marsh and ultimately becomes completely filled with detritus and
disappears. In the course of this process the lake becomes overly rich
in dissolved nutrients (for example, nitrogen and phosphorus), so that
an excessive development of algae results. First the water becomes
murky, the noxious odors and unsightly scums appear. In the lower
layers dissolved oxygen levels become depressed, and bottom-dwelling
fauna change from clean-water forms to pollution-tolerant forms.
evapotranspiration -- Water withdrawn from soil by evaporation and/or
plant transpiration.
extended aeration -- A modification of the activated sludge process which
provides for aerobic sludge digestion within the aeration system.
The concept envisages the stabilization of organic matter under
aerobic conditions and disposal of the end products into the air as
gases and with the plant effluent as finely divided suspended matter
and soluble matter.
_F
facultative bacteria -- Bacteria that can adapt themselves to growth and
metabolism under aerobic or anaerobic conditions. Many organisms
of interest in wastewater stabilization are among this group.
fats -- Triglyceride esters of fatty acids. Naturally occuring compounds
functioning as storage products in the living organism. Generally
semi-solid or oily at normal temperatures. Erroneously used as
synonymous with grease.
-------
filter -- A device or structure for removing solid or colloidal material,
usually of a type that cannot be removed by sedimentation, from
water, wastewater, or other liquid. The liquid is passed through
a filtering medium, usually a granular material but sometimes
finely waven cloth, unglazed porcelain, or specially prepared paper.
There are many types of filters used in water or wastewater treat-
ment. See trickling filter filtration .
filtrate -- The liquid which has passed through a filter.
filtration -- The process of passing a liquid through a porous medium
for the removal of suspended or colloidal material contained in the
influent liquid by a physical straining action. The trickling filter
process used in wastewater treatment is a method of contacting
dissolved and suspended organic matter with biologically active
aerobic slime growths, and hence is not a true filtration process.
five-day BOD -- The part of oxygen demand associated with biochemical
oxidation of carbonaceous, as distinct from nitrogenous, material.
It is determined by allowing biochemical oxidation to proceed, under
conditions specified in standard methods, for 5 days.
fixed solids -- The residue remaining after ignition of suspended or dis-
solved matter according to standard methods.
floe -- Gelatinous or amorphous solids formed by chemical, biological, or
physical agglomeration of fine materials into large masses that are
more readily separated from the liquid.
floe culat ion --In water and wastewater treatment, the agglomeration of
colloidal and finely divided suspended matter after coagulation by
gentle stirring by either mechanical or hydraulic means. In biological
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wastewater treatment where coagulation is not used, agglomeration
may be accomplished biologically.
flotation -- The raising of suspended matter to the surface of the liquid in a
tank as scum -- by aeration, the evolution of gas, chemicals, elec-
trolysis, heat, or bacterial decomposition -- and the subsequent
removal of the scum by skimming.
F/M ratio -- Food to microorgams ism ratio: the weight ratio of BOD (food)
in wastewater to suspended solids (microorganisms) within an acti-
vated sludge treatment system. This value is used as an operational
control criterion for activated sludge processes.
fouling -- A gelatinous, slimy accumulation on the waterway of a conduit,
resulting from the activity of organisms in the waters. Fouling
is more easily removable than tuberculation. Fouling may be found
on concrete, masonry, and metal surfaces, but tuberculation is
found only on metal surfaces.
free available chlorine -- Generally includes that chlorine existing in water
as the hypochlorous acid. Characterized by rapid color formation
with orthotolidine, can be titrated in a neutral solution with phenyl
arsene oxide and produces a rapid organism kill in low concentrations.
free residual chlorination -- The application of chlorine or chlorine com-
pounds to water or wastewater to produce a free available chlorine
residual directly or through the destruction of ammonia or certain
organic nitrogenous compounds.
grease -- In wastewater, a group of substances including fats, waxes,
free fatty acids, calcium and magnesium soaps, mineral oils, and
certain other nonfatty materials. The type of solvent and method used
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for extraction should be stated for quantitation.
grit -- The heavy suspended mineral matter present in water or wastewater,
such as sand, gravel, cinders.
hardness -- A characteristic of water, imparted by salts of calcium,
magnesium, and iron such as bicarbonates, carbonates, sulfates,
chlorides and nitrates, that causes curdling of soap and increased
consumption of soap, deposition of scale in boilers, damage in some
industrial processes, and sometimes objectionable taste. It may be
determined by a standard laboratory procedure or computed from
the amounts of calcium and magnesium as well as iron, aluminun,
manganese, barium, strontium, and zinc, and is expressed as
equivalent calcium carbonate. Soft water is that with less than 60
ppm of salts, temporary water, 60 to 120 ppm, permanent water, in
excess of 120 ppm.
hydrolysis -- (1) The reaction of a solute with water in aqueous solution.
(2) A change in the chemical composition of matter produced by
combination with water. Sometimes loosely applied in wastewater
practice to the liquefaction of solid matter in a tank as a result of
biochemical activity.
infiltration -- (1) The penetration of water through the soil from surface
precipitation, stream or impoundment boundaries. (2) The entrance
of groundwater into a sewer through breaks, defective joints or
porous walls.
influent -- Water, wastewater, or other liquid flowing into a reservoir,
basin, or treatment plant, or any unit thereof.
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integrator -- A device for indicating the total quantity of flow through a
measuring device, such as a Parshall flume or weir.
intermediate treatment -- Wastewater treatment such as aeration or
chemical treatment, supplementary to primary treatment. Such
treatment removes substantial percentages of very finely divided
particulate matter, in addition to the suspended solids removed by
primary treatment. Supplementary processing improves the efficiency
of treatment so that about 60 percent of both BOD and suspended solids
are removed.
iodophor -- A germicide consisting of a mixture of iodine and a carrier.
The carrier is a surfactant which stabilizes the iodine. Reaction of
iodophors is similar to chlorine.
ion-exchange -- (1) A chemical process involving reversible interchange
of ions between a liquid and a solid but no radical change in structure
of the solid. (2) A chemical process in which ions from two different
molecules are exchanged. (3) Ion-exchange treatment of water or
wastewater involves the use of ion-exchange materials such as resin
or zeolites to remove undesirable ions from a liquid and substitute
acceptable ions.
K_
Kraus process A modification of the activated sludge process in which
aerobically conditioned supernatant liquor from anaerobic digesters is
added to activated sludge aeration tanks to improve the settling charac-
teristics of the sludge and to add an oxygen resource in the form of
nitrates.
L
land disposal -- (1) Disposal of wastewater onto land by spray or surface
irrigation. (2) Disposal of solid waste materials by incorporating
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the solid waste into the soil by cut-and-fill techniques or by sanitary
land-fill operations.
leaching -- (1) The removal of soluble constituents from soils or other
material by percolating water. (2) The removal of salts and alkali
from soils by abundant irrigation combined with drainage. (3) The
disposal of a liquid through a non-watertight artificial structure,
conduit, or porous material by downward or lateral drainage or
both , into the surrounding permeable soil. (4) The loss of soluble
constituents from fruits, vegetables, or other material into water
or other liquid in which the material is immersed. (5) The escap-
ing of free moisture from a solid waste land disposal site into the
surrounding environment, frequently causing odors and other nuisance
conditions of public health significance.
loading -- The quantity of waste, expressed in gallons (hydraulic load) or
in pounds of BOD, COD, suspended or volatile solids (organic load)
which is discharged to a wastewater treatment facility.
M
membrane filtration -- A method of quantitative or qualitative analysis of
bacterial or particulate matter in a water sample by filtration through
a membrane capable of retaining bacteria.
mesh -- One of the openings or spaces in a screen. The value of the mesh
is usually given as the number of openings per linear inch. This gives
no recognition to the diameter of the wire, and thus the mesh number
does not always have a definite relation to the size of the hole.
mesophilic range -- Operationally, that temperature range most conducive
to the maintenance of optimum digestion by mesophilic bacteria, general-
ly accepted as between 27° and 32° C (80° and 90° F).
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mgd -- Abbreviation for million gallons per day.
mg/1 -- Abbreviation for milligrams per liter. A unit of the concentration of
water or wastewater constituent. It is 0. 001 g of the constituent
in 1, 000 ml of water. It has replaced the unit formerly used commonly,
parts per million, to which it is approximately equivalent, in reporting
the results of water and wastewater analysis.
mixed liquor -- A mixture of activated sludge and organic matter undergoing
activated sludge treatment in the aeration tank.
MLVSS -- Abbreviation for mixed liquor volatile suspended solids, the
quantity of solids contained in the mixed liquor of an activated sludge
treatment system which is lost on ignition of the dry solids at 600 C.
This value is an index of the active biological mass within the treatment
system.
modified aeration -- A modification of the activated sludge process in
which a shortened period of aeration is used with a reduced quantity
of suspended solids in the mixed liquor.
most probable number (MPN) -- That number or organisms per unit volume
that, in accordance with statistical theory, would be more likely
than any other number to yield the observed test result or that would
yield the observed test result with the greatest frequency. Expressed
as density of organisms per 100 ml. Results are computed from the
number of positive findings of coliform-group organisms resulting from
multiple-portion decimal-dilution plantings.
natural purification -- Natural processes occurring in a stream or other
body of water that result in the reduction of bacteria, satisfaction of
the BOD, stabilization of organic consituents, replacement of
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depleted dissolved oxygen, and the return of the stream biota to nor-
mal. Also called self-purification.
navigable water -- Any stream, lake, arm of the sea, or other natural
body of water that is actually navigable and that, by itself or by
its connections with other waters, is of sufficient capacity to float
watercraft for the purposes of commerce, trade, transportation or
even pleasure for a period long enough to be of commercial value;
or any waters that have been declared navigable by the Congress of
the United States.
nitrification -- (1) The conversion of nitrogenous matter into nitrates by
bacteria. (2) The treatment of a material with nitric acid.
nitrogen cycle -- A graphical presentation of the conservation of matter in
nature, from living animal matter through dead organic matter,
various stages of decomposition, plant life, and the return of living
animal matter, showing changes which occur in course of the cycle.
It is used to illustrate biological action and also aerobic and anaerobic
acceleration of the transformation of this element by wastewater
and sludge treatment.
nitrogenous wastes -- Wastes of animal or plant origin that contain a sig-
nificant concentration of nitrogen.
nutrient -- A chemical substance (an element or a chemical compound)
absorbed by living organisms and used in organic synthesis. The
major nutrients include carbon, hydrogen, oxygen, nitrogen, sul-
fur, and phosphorus. Nitrogen and phosphorus are of major concern
because they tend to recycle and are difficult to remove from water
due to their solubility.
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o
oils -- (1) Liquid fats of animal or vegetable origin. (2) Oily or waxy
mineral oils.
outfall -- (1) The point, location, or structure where wastewater or
drainage discharges from a sewer, drain, or other conduit. (2)
The conduit leading to the ultimate disposal area.
overturning -- The phenomenon of vertical circulation which occurs in
large bodies of water. It is due to the increase in density of
water above and below 39. 2 F, the temperature of maximum
density. In the spring, as the surface of the water warms above
the freezing point, the water increases in density, becomes
heavier, and tends to sink, producing vertical currents, while
in the fall, as the surface water becomes colder and therefore
heavier, it also tends to sink. Wind may also create such vertical
currents.
oxidation process (treatment) -- Any method of wastewater treatment for
the oxidation of the putrescible organic matter. The usual methods
are biological filtration and the activated sludge process. Living
organisms in the presence of air are utilized to convert the organic
matter into more stable or mineral form.
oxygenation capacity -- In treatment processes, a measure of the ability
of an aerator to supply oxygen to a liquid.
oxygen demand -- (1) The quanitty of oxygen utilized in the biochemical
oxidation of organic matter in a specified time, at a specified
temperature, and under specified conditions. See BOD.
oxygen-sag curve -- A curve that represents the profile of dissolved
oxygen content along the course of a stream, resulting from
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deoxygenation associated with biochemical oxidation of organic
matter and reoxygenation through the absorption of atmospheric
oxygen and through biological photosynthesis. Also called dissolved
oxygen-sag curve.
ozone -- Oxygen in molecular form with three atoms of oxygen forming
each molecule (O-).
Parshall flume -- A calibrated device developed by Parshall for measuring
the flow of liquid in an open conduit. It consists essentially of a
contracting length, a throat, and an expanding length. Flows through
the device are determined by measuring the head of water at a speci-
fic distance from a sill over which water passes.
particulate matter -- Refers to detectable solid materials dispersed in
a gas or liquid. Small sized particulates may produce a smoky
or hazy appearance in a gas, milky or turbid appearance in a
liquid. Larger particulates are more readily detected and
separated by sedimentation or filtration.
parts per million (ppm) -- The number of weight or volume of units of a
minor constituent present with each one million units of the major
constituent of a solution or mixture. Formerly used to express the
results of most water and wastewater analyses, but more recently
replaced by the ratio milligrams per liter.
percolation -- (1) The flow or trickling of a liquid downward through
a contact or filtering medium. The liquid may or may not fill the
pores of the medium. Also called filtration. (2) The movement
or flow of water through the interstices or the pores of a
soil or other porous medium. (3) The water lost from an unlined
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conduit through its sides and bed.
permeability -- (1) The property of a material that permits appreciable
movement of water through it when it is saturated and the move-
ment is actuated by hydrostatic pressure of the magnitude normally
encountered in natural subsurface water. Perviousness is some-
times used in the same sense as permeability. (2) The capability
of a rock or rock material to transmit a fluid.
pH -- The reciprocal of the logarithm of the hydrogen-ion concentration.
The concentration is the weight of hydrogen-ions, in grams, per
liter of solution. pH values reflect the balance between acids and
alkalies. The extreme readings are 0 and 14. The pH of most natural
waters falls within the range 4 to 9. Neutral water, for example, has
a pH value of 7. 0 and a hydrogen-ion concentration of 10"? . Slight
decrease in pH may greatly increase the toxicity of substances such
as cyanides, sulfides, and most metals. Slight increase may greatly
increase the toxicity of pollutants such as ammonia. Alkaline water
will tend to form a scale, acid water is corrosive.
pollutional load -- (1) The quantity of material in a waste stream that re-
quires treatment or exerts an adverse effect on the receiving
system. (2) The quantity of material carried in a body of water
that exerts a detrimental effect on some subsequent use of that
water.
polymer -- Any one of several commercially available high-molecular-
weight, water-soluble polymeric flooculation agents. When added
to water, these substances form a flocculent precipitate which will
agglomerate or coagulate suspended matter and expedite sedimentation.
population equivalent -- A means of expressing the strength of organic
material in wastewater. Domestic wastewater consumes, on an
average, 0.17 Ib of oxygen per capita per day, as measured by the
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standard BOD test. This figure has been used to measure the strength
of organic industrial waste in terms of an equivalent number of persons,
For example, if an industry discharges 1, 000 pounds of BOD per day,
its waste is equivalent to the domestic wastewater from 6, 000 persons
(1,000 *- 0.17 = 6,000).
potable water -- Water that does not contain objectionable pollution, contami-
nation, minerals, or infective agents and is considered satisfactory
for domestic consumption.
precipitate -- The formation of solid particles in a solution, or the solids
that settle as a result of chemical or physical action that caused
solids separation.
preliminary treatment -- (1) The conditioning of a waste at its source
before discharge, to remove or to neutralize substances injurious
to sewers and treatment processes or to effect a partial reduction
in load on the treatment process. (2) In the treatment process,
unit operations, such as screening and comminution, that prepare
the liquor for subsequent major operations.
primary settling tank -- The first settling tank for the removal of settle-
able solids through which wastewater is passed in a treatment works.
primary treatment -- (1) The first major (sometimes the only treatment
in a wastewater treatment works. Commonly considered to include
bar racks, grit chambers, comminution, sedimentation and sludge
digestion treatment operations, may include flocculation or disin-
fection. (2) The removal of a substantial amount of suspended matter
but little or no colloidal and dissolved matter.
process water -- Water (liquid or vapor) that comes in contact with an end
product or with materials incorporated in an end product.
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proportional composite sample -- A combination of individual samples of
water or wastewater taken at selected intervals, generally hourly
for some specified period, to minimize the effect of the variability of
the individual sample. Prior to combination, each individual sample
is roughly proportioned to the flow at time of sampling.
rapid sand filter -- A filter for the purification of water, in which water
that has been previously treated, usually by coagulation and sed-
imentation, is passed downward through a filtering medium. The
medium consists of a layer of sand, prepared anthracite, coal, or
other suitable material, usually 24-30 in. thick, resting on a
supporting bed of gravel or a porous medium such as carborundum.
The filtrate is removed by an underdrainage system which also
distributes the wash water. The filter is cleaned periodically by
reversing the flow of the water upward through the filtering medium,
sometimes supplementing by mechanical or air agitation
during washing, to remove mud and other impurities which have
lodged in the sand. It is characterized by a rapid rate of filtration,
commonly from two to three gallons per minute per square foot
of filter area.
receiving waters -- A natural watercourse, lake, or ocean into which treated
or untreated wastewater is discharged.
residual chlorine -- Chlorine remaining in.water or wastewater at the
end of a specified contact period as combined or free chlorine.
reverse osmosis -- A process in which, if pressure is put on the con-
centrated side of a liquid system in which liquids with different
concentrations of mineral salts are separated by a semipermeable
membrane, molecules of pure water pass out of the concentrated
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solution to the weak or fresh-water side (contrary to the case of
normal osmosis).
riprap -- Broken stone or boulders placed compactly or irregularly on
dams, levees, dikes, or similar embankments for protection of
earth surfaces against the action of waves or currents.
roughing filter -- In wastewater treatment, a trickling filter containing
coarse material or plastic medium operated at a high rate to afford
partial treatment preliminary to a secondary treatment operation.
By using a roughing filter, the organic loading imposed on the
subsequent biological system is significantly reduced.
runoff -- (1) That portion of rainfall or melted snow which runs off the
surface of a drainage area and reaches a stream or other body of
water or a drain or sewer. Runoff is faster and greater during
heavy rain than during protracted drizzle, on clay soils than on
sandy soils, on frozen soils than on frostless soils, in treeless
areas than in forests. The ratio between runoff and rainfall varies
considerably with climatic conditions. (2) Total quantity of runoff
water during a specified time. (3) In the general sense, that por-
tion of the precipitation which is not absorbed by the deep strata,
but finds its way into the streams after meeting the persistent de-
mands of evapotranspiration, including interception and other losses.
(4) The discharge of water in surface streams, usually expressed
in inches depth on the drainage area, or as volume in such terms as
cubic feet or acre-feet.
saline water -- Water containing dissolved salts -- usually from 10,000 to
33,000 mg/1.
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sand filter -- A filter in which sand is used as a filtering medium. Also
see rapid sand filter, slow sand filter.
scum baffle -- A verticle baffle dipping below the surface of wastewater in
a tank to prevent the passage of floating matter. Also called scum
board.
secondary wastewater treatment -- The treatment of wastewater by
biological methods after primary treatment by sedimentation.
Common methods of treatment include trickling filtration, act-
ivated sludge processes, and oxidation.
sedimentation -- The process of subsidence and deposition of suspended
matter carried by water, wastewater, or other liquids, by gravity.
It is usually accomplished by reducing the velocity of the liquid be-
low the point at which it can transport the suspended material. Also
called settling.
s elf-cleans ing velocity -- The minimum velocity in sewers necessary to
keep solids in suspension, thus preventing their deposition and sub-
sequent nuisance from stoppages and odors of decomposition.
self-purification -- The natural processes occuring in a stream or other
body of water that result in the reduction of bacteria, satisfaction
of the BOD, stabilization of organic constituents, replacement of
depleted dissolved oxygen, and the return of the stream biota to
normal. Also called natural purification.
settleable solids -- (1) That matter in wastewater which will not stay in
suspension during a preselected settling period, such as one hour,
but either1 settles to the bottom or floats to the top. (2) In the
Imhoff cone test, the volume of matter that settles to the bottom
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of the cone in one hour.
skimming tank -- A tank so designed that floating matter will rise and
remain on the surface of the wastewater until removed, while the
liquid discharges continuously under curtain walls or scum boards.
slimes -- Substances of viscous organic nature, usually formed from micro-
biological growth.
sloughing -- A phenomenon associated with trickling filters and contact
aeration units where slimes build up to a varying degree and then
slip off into the discharged flow.
slow sand filter -- A filter for the purification of water in which water with-
out previous treatment is passed downward through a filtering med-
ium consisting of a layer of sand or other suitable material, usually
finer than for a rapid sand filter and from 24 to 40 in. thick. The
filtrate is removed by an underdrainage system and the filter is
cleaned by scraping off and replacing the clogged layer. It is char-
acterized by a slow rate of filtration, commonly 3-6 mgd/acre of
filter area.
sludge -- (1) The accumulated solids separated from liquids, such as water
or wastewater, during processing, or deposits on bottoms of streams
or other bodies of water. (2) The precipitate resulting from chem-
ical treatment, coagulation, or sedimentation of water or wastewater.
sludge bulking -- A phenomenon that occurs in activated sludge plants
whereby the sludge occupies excessive volumes and will not concentrate
readily.
sludge conditioning -- Treatment of liquid sludge before dewatering to
facilitate dewatering and enhance drainability, usually by the add-
ition of chemicals.
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sludge density index -- The reciprocal of the sludge volume index
multiplied by 100.
sludge digestion -- The process by which organic or volatile matter in
sludge is gasified, liquified, mineralized, or converted into more
stable organic matter through the activities of either anaerobic or
aerobic organisms.
sludge treatment -- The processing of wastewater sludges to render them
innocuous. This may be done by aerobic or anaerobic digestion
followed by drying on sand beds, filtering, and incineration, filter-
ing and drying, or wet air oxidation.
sludge volume index (SVI) -- The ratio of the volume in milliliters of sludge
settled from a 1, 000-ml sample in 30 min. to the concentration of
mixed liquor in milligrams per liter multiplied by 1, 000.
solids-contact clarifier -- A unit in which liquid passes upward through a
solids blanket and discharges at or near the surface.
solute -- The substance dissolved in a solution. A solution is made up of
the solvent and the solute.
solvent -- Liquid used to dissolve a substance.
sparger -- An air diffuser designed to give large bubbles, used singly or
in combination with mechanical aeration devices.
specific conductance -- Measure of a water's capacity to convey an electric
current. This property is related to the total concentration of the
ionized substances in the water and the temperature of the water.
Most inorganic acids, which dissociate readily in aqueous solution,
will conduct an electric current'well, while organic compounds
(such as sucrose and benzene), which do not dissociate in aqueous
-------
solution will conduct a current poorly if at all.
Sphaerotilus -- A filamentous, sheath-forming bacterium, often considered
the organism responsible for bulking sludge. In polluted streams
the presence of this bacterium is evidenced by fibrous growths ad-
hering to rocks and plants along the stream bed.
stabilization -- (1) Maintenance at a relatively nonfluctuating level, quanti-
ty, flow, or condition. (2) In lime-soda water softening, any pro-
cess that will minimize or eliminate scale-forming tendencies.
(3) In waste treatment, a process used to equalize wastewater flow
composition prior to regulated discharge. (4) In erosion control^
treatment of dikes or shorelines with riprap, sod, penetrations,
or similar protective devices. (5) In corrosion control, pH adjust-
ment of water to maintain carbonate equilibrium at the saturation
point.
stage aeration -- Division of activated sludge treatment into stages with
intermediate settling tanks and return of sludge in each stage.
standard methods -- (1) Methods for the Examination of Water and Waste-
water published jointly by the American Public Health Association,
the American Water Works Association, and the Water Pollution
Control Federation. (2) Methods published by professional organ-
izations and agencies covering specific fields. These include,
among others: American Public Health Association, American
i
Public Works Association, American Society of Civil Engineers,
American Society of Mechanical Engineers, American Society for
Testing and Materials, American Water Works Association, United
States Bureau of Standards, United States of America Standards
Institute (formerly American Standards Association), United States
Public Health Service, Water Pollution Control Federation.
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step aeration -- A procedure for adding increments of settled wastewater
along the line of flow in the aeration tanks of an activated sludge
plant.
substrate -- (1) The substances used by organisms in liquid suspension.
(2) The liquor in which activated sludge or other matter is kept
in suspension.
supernatant liquor -- (1) The liquor overlying deposited solids. (2) The
liquid in a sludge-digestion tank that lies between sludge at the
bottom and floating scum at the top.
suspended solids (SS) -- (1} Solids that either float on the surface of, or are in
suspension in, water, wastewater, or other liquids, and which are
largely removable by laboratory filtering. (2) The quantity
• of material removed from wastewater in a laboratory test, as pre-
scribed in "Standard Methods for the Examination of Water and
Wastewater" and referred to as nonfilterable residue.
tapered aeration -- The method of supplying varying amounts of air into
the different parts of an aeration tank in the activated sludge pro-
cess, more at the inlet, less near the outlet, in approximate pro-
portion to the oxygen demand of the mixed liquor under aeration.
tertiary treatment -- Treatment beyond normal or conventional second-
ary methods for the purpose of increasing water re-use potential.
thermal pollution -- Impairment of water through temperature change due
to geothermal, industrial', or other causes.
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thermophilic range -- That temperature range most conducive to main-
tenance of optimum digestion by thermophilic bacteria, generally
accepted as between 120° and 135° F.
total dissolved solids (TDS) -- See dissolved solids.
totalizer -- A device for indicating the total quantity of flow through a
measuring device. Also called integrator.
total organic carbon (TOC) -- A test expressing wastewater contaminant
concentration in terms of the organic carbon content.
total solids (TS) -- Refers to the solids contained in dissolved and suspended
form in water. Commonly determined on a weight basis by evapora-
tion to dryness and expressed as milligrams per liter (mg/1).
toxic substance -- A substance that either directly poisons living things
or alters their environment so that they die. Examples are cya-
nides found in plating and steel mill wastes, phenols from coke
and chemical operations, pesticides and herbicides, and heavy metal
salts. Another broad group includes oxygen-consuming substances
that upset the balance of nature, such as organic matter from food
plants, pulp and paper mills, chemical plants, and textile plants. Still
another group are sulfides, produced by oil refineries, smelters, and
chemical plants.
transpiration -- (1) The process by which water vapor is lost to the atmos-
phere from living plants. (2) The quantity of water thus dissipated.
trickling filter -- A structure containing an artificial bed of coarse mate-
rial, such as broken stone, clinkers, slate, slats, or plastic
materials, over which wastewater is distributed or applied in
drops, films, or spray from troughs, drippers, moving distri-
butors, or fixed nozzles, and through which the wastewater trickles
-------
to the underdrains, giving opportunity for the formation of
zoogleal slimes which clarify and oxidize the wastewater. See
filter filtration.
turbidity -- (1) A condition in water or wastewater caused by the presence
of suspended matter, resulting in the scattering and absorption of
light rays. (2) A measure of fine suspended matter in liquids.
(3) An analytical quantity usually reported in arbitrary turbidity
units determined by measurements of light diffraction.
turnover -- A phenomenon usually occur ing in spring and fall because of
the increase in density of water above and below the temperature
of maximum density. In the spring, as the surface of the water
warms above the freezing point, the water increases in density,
becomes heavier, and tends to sink, producing vertical currents,
while in the fall, as the surface water becomes colder and there-
fore heavier, it also tends to sink. Also see overturning.
ultimate biochemical oxygen demand -- (1) Commonly, the total quantity
of oxygen required to satisfy completely the first-stage biochem-
ical oxygen demand. (2) More strictly, the quantity of oxygen
required to satisfy completely both the first-stage and the second-
stage biochemical oxygen demands.
undigested slutige -- Settled sludge promptly removed from sedimentation tanks
before decomposition has much advanced. Also called raw sludge.
unloading -- The periodic or continuous sloughing of the biological film
from the medium on which it has been growing.
upflow contact clarifier -- A unit in which water enters the bottom and is
discharged at or near the surface. See solids contact clarifier.
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USPHS drinking water standards -- Standards prescribed by the U.S.
Public Health Service for the quality of drinking water supplied
to interstate carriers and prescribed as standards by most state
and local jurisdictions for all public water supplies.
vacuum filter -- A filter consisting of a cylindrical drum mounted on a
horizontal axis, covered with a filter cloth, and revolving with a
partial submergence in liquid. A vacuum is maintained under the
cloth for the larger part of a revolution to extract moisture. The
cake is scraped off continuously.
venturi meter -- A differential meter for measuring flow of water or
other fluid through closed conduits or pipes, consisting of a
venturi tube and one of several proprietary forms of flow-registering
devices. The difference in velocity heads between the entrance and the
contracted throat is an indication of the rate of flow.
volatile acids -- Fatty acids containing six or less carbon atoms, which
are soluble in water and which can be steam-distilled at atmospheric
pressure. Volatile acids are commonly reported as equivalent to
acetic acid.
volatile solids -- Apparent loss of matter from a residue ignited at 550 C
for a period of time sufficient to reach constant weight of residue,
usually 10-15 min.
W
watercourse -- (1) A natural or artificial channel for passage of water.
(2) A running stream of water. (3) A natural stream fed from permanent
or natural sources, including rivers, creeks, runs, and rivulets. There
must be a stream, usually flowing in a particular direction (though
it need not flow continuously) in a definite channel, having a bed
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or banks and usually discharging into some other stream or body
of water.
water cycle -- The circuit of water movement from the atmosphere to the
earth and return to the atmosphere through various stages or
processes such as precipitation, interception, runoff, infiltration,
percolation, storage, evaporation, and transpiration. Also called
hydrologic cycle.
water quality standards -- Limits set by authority on the basis of water
quality criteria required for beneficial uses. Limits are imposed
on the physical and chemical characteristics required for specific
beneficial use.
water softening -- The process of removing from water, in whole or in
part, those cations which produce hardness.
weir •-- (1) A diversion dam. (2) A device that has a crest and some side
containment of known geometric shape, such as a V, a trapezoid,
or rectangle, and is used to measure flow of liquid. The liquid
surface is exposed to the atmosphere. Flow is related to upstream
height of water above the crest, to position of crest with respect to
downstream water surface, and to geometry of the weir opening.
wet oxidation process -- A method of sludge disposal that involves the
oxidation of sludge solids in water suspension and under increased
pressure and temperature.
zeolite -- A group of hydrated aluminum complex silicates, either natural
or synthetic, with cation-exchange properties. Also see ion ex-
change, zeolite process.
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zeolite process -- The process of softening water by passing it through a
substance known in general as a zeolite, which exchanges sodium
ions for hardness constituents in the water.
zooglea -- A jelly-like matrix developed by bacteria. A major part of
activated sludge floe and of trickling filter slimes.
a U.S. GOVERNMENT PRINTING OFFICE: W75-2104M:57
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