Pollution Abatement in the Fruit and
       Vegetable Industry
           WASHINGTON. D. C.

Pollution Abatement  in the Fruit  and Vegetable  Industry
                       Volume  1
              Office of Technology Transfer
                   Washington,  D. C.

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.

                          TABLE OF CONTENTS
List of Figures                                                iv

      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

      Materials Balance                                      II - 1
      Management and Pollution  Controls                      II - 3
      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

      Grab Samples                                          IV - 1
      Composite Samples                                     IV - 1
      Sample Storage                                         IV - 3

      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

                         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

                            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.

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.

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.

                                                      WATER DISTRIBUTION
 "&; 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.

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.

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.

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

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.

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
waste discharge
                             r e oxy g ena tion
                               Time  of flow, days
                   Figure 2.  A hypothetical oxygen-sag curve.

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.

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

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

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.


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.

 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.


 Raw Commodities
- $

I  Principal Products
I  By-products
  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.

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.

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

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.


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 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.

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 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
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.

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,

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

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

                                              2nd stage
1st stage
                      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:

      Ibs BOD =   BOD (mg/1) x total flow (gallons) x 8. 34
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 (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

standard method for COD is designed to remove interferences at low chloride
concentrations and can be used for analyzing processing wastewaters.

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-

                                    2. Evaporating dish
                                       placed in drying oven
                                       for one hour at 103°C.
1. Evaporate sample
  to dryness on
  steam table.
                            Total fixed
                            solids de-
                            termined by
                            weighing re-
                            sidue after
                Cool combusted
                                 dishes trans-
                                 ferred to
                                 for 45 min-
                                 utes to cool.
                                                  4. Total solids
                                                     determined by
                                                     weighing dried
            5« Sample heated in muffle
              furnace for 20 minutes
              at 600° C to burn the or-
              ganic material.
         Volatile Solids  =
Total Solids  -
Fixed Solids
 Figure 6. Steps in the determination of total and fixed solids.
                             in - 7

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.

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.

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.

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.

           14  T
            11  • •
            9  •
            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

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

Aside from carbonaceous organic matter which are measured largely  as BOD,
nutrients of primary concern are organic nitrogen and phosphorus-containing

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.

                          -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.

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.

As previously indicated,  laboratory results from numerous grab samples  taken
within a  period  of time can be used to calculate meaningful averages for that

°.   1000
                                                               Tf Vv
                                                               Tf Vv
                    12N           6P
                             Time of day
     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

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.

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

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.

                    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.

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.

          Figure 9.  Bar rack with automatic rake.
Figure 10.  Vibrating screen for separation of solid particles.
                            V - 2

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 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
                                           /ONONEWftLV    SC^ER-,
        Figure 12.  Sectional diagram of a circular clarifier.

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 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

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.

   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).

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.

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

               AIR PRESSURE
                              PRESSURE  AIR-LIQUID
                              TANK     DISSOLVING
                                                  FLOTATION SYSTEM
               1st. STAGE
     • — ' RETENTION
                  FLOATABLE    SETTLED
                     SOLIDS    COARSE SOLIDS
                                              SOLIDS TO DISPOSAL
 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.

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.

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.

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.

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)


 Definition of Selected Terms
          used in
Water and Waste Management

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

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

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

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

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.
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

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.
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

      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

      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.

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.
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

land disposal -- (1) Disposal of wastewater onto land by spray or surface
      irrigation.  (2)  Disposal of solid waste materials by incorporating

      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.
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).

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
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

      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.

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

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

      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

      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

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

      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.

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

      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.

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

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

      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

sludge conditioning -- Treatment of liquid sludge before dewatering to
      facilitate dewatering and enhance drainability, usually by the add-
      ition of chemicals.

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

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
      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.

 step aeration -- A procedure for adding increments of settled wastewater
      along  the line of flow in the aeration tanks of an activated sludge

 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.

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.

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.
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

      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.

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.