of Poultry
                      Upgrading Poultry-Processing
                       Facilities to Reduce Pollution
FATechnotogy lansfer Seminar Publication

                               PRETREATMENT OF

                                   Upgrading Existing
                            Poultry-Processing Facilities
                                   to Reduce Pollution
                        July 1973

     This seminar publication contains materials prepared for the
U.S. Environmental Protection Agency Technology Transfer Program
and presented at industrial pollution-control seminars for the
poultry-processing industry.

     The basic publication was prepared by A. J. Steffen, Consulting
Environmental Engineer, West Lafayette, Ind., with the assistance of
Dan Lindenmeyer, FMC Corporation, Chicago, HI.; M. E. Ginaven,
Bauer Bros. Company (subsidiary of Combustion Engineering, Inc.),
Springfield, Ohio; Robert Johnson, FMC Corporation, Atlanta, Ga.;
and Charles Grimes, Rex Chainbelt, Inc., Waukesha, Wis.
     The mention of trade names or commercial products in this publication is
for illustration purposes, and does not constitute endorsement or recommenda-
tion for use by the U.S. Environmental Protection Agency.

     Since most poultry plants are now using flowaway systems, the subject matter relates largely to
this type of waste-handling system. The customary screens used in flowaway systems to remove offal
and feathers are intended to improve the wastewater for reuse in the processing plant and for recovery
of byproducts. They are therefore not considered as part of pretreatment for discharge to a municipal
system, although it is recognized that effluent may often be improved by improvements in flowaway

     Pretreatment does not include treatment of sanitary wastes (normally discharged directly to the
city sewer), storm water, cooling water, or condenser water.

     Disposal of the recovered screenings, floatables, and settled solids is beyond the scope of this
study, but concentration of the floatables and settled solids by screening to reduce liquid content is



Preface	iii

Part I. Introduction	   1
    WhyPretreat?	   1
    When to Pretreat	   2
    How to Pretreat	   3
    Costs	   3
    Summary	   4

Part II.  Screening	   7
    Introduction	   7
    Vibrating Screens	   7
    Static Screens	10
    Other Screening Devices	13

Part III. Separation of Grease and Suspended Solids	21
    Gravity Grease Recovery and Separation	22
    Dissolved Air Flotation	25
    Other Systems	28

Part IV. Municipal Ordinances	45
    Limitations on Quality of Poultry Plant Waste water	45
    Surcharges	46

PartV.  Summary	49

Bibliography	50

Appendix A.  List of Equipment Manufacturers	51



                                     WHY PRETREAT?
     This paper is concerned with the treatment of poultry wastes after the customary screening in
flowaway systems and prior to discharge to a municipal sewer. The term "pretreatment" will be
used to cover all physical, chemical, or biological treatment provided for this purpose.

     The majority of poultry plants discharge to municipal sewers. In a 1971 Department of Agri-
culture survey [8] of 386 poultry plants, almost two-thirds were connected to some type of public
sewer system.  The survey did not show how many had pretreatment. Whether pretreatment is
required at a poultry plant depends most frequently upon municipal regulations regarding some of
the ingredients in the poultry wastes.  Ingredients such as feathers may be prohibited because they
cannot be efficiently removed and disposed of in conventional municipal sewage treatment plants,
whereas other ingredients, such as solids, may be  subject to special charges to defray the expense of
their removal and disposal in the municipal system.

     Federal regulations covering grants-in-aid to municipalities touch on pretreatment of industrial

     The Federal Water Pollution Control Act Amendments of 1972  require that before any grant
approval to a municipality the Environmental Protection Agency must be assured that provisions
are made to prevent the municipal system from receiving pollutants that would inhibit the operation
of the municipal treatment works, or that would  pass through the system untreated. In addition
any municipality that will receive industrial wastes must have a system of surcharges such that  the
industrial discharger repays an equitable portion of the full cost of construction and operation of
the system.

     Thus, if the municipality receives a Federal grant, the poultry plant may be required to provide
pretreatment  if the waste would be detrimental to the system of municipal treatment.  Note also
that the cost of treating the poultry wastes must be recovered in "an  equitable system of cost
recovery."  In some  cases, municipal treatment requirements can be reduced by pretreatment at the
poultry plant, which may produce overall savings to the poultry plant operator if a cost recovery
charge is to be levied.

     There are many other instances in which pretreatment may become an economic advantage.
Suppose, for example, that the municipal plant is overloaded and a plant expansion is contemplated.
A study shows that pretreatment at the poultry plant will eliminate the overload. The decision
whether to pretreat or to go along with the municipal plant expansion program depends upon the
relative annual cost of the two alternatives to the poultry plant operator.

     As another example, suppose that excessive  discharges of grease, feathers, or suspended matter
are causing special problems in operating primary clarifiers and anaerobic sludge digestion at the
municipal plant. The first step for correction of such problems is waste conservation at the poultry
plant and attention to the flowaway system (a check for escape of solids in the flowaway screen and

offal area). If these elements are all in order and good waste conservation is being practiced in the
plant, pretreatment may be the next step.

     As a further example, suppose that the poultry plant management is considering an increase in
poultry production or some additional processing. The added sewage-treatment load resulting from
such changes can be calculated, to compare the sewage service charges for municipal plant expansion
made necessary by the added load with the cost of pretreatment to produce the same results.
                                  WHEN TOPRETREAT?
Prohibitory and Restrictive Limits May Make Pretreatment Necessary

     The discharge of some ingredients such as feathers, entrails, and the like into the municipal sys-
tem may be completely prohibited.  If the best in-plant conservation practices and careful operation
of efficient flowaway equipment do not eliminate these materials to the municipality's satisfaction,
some form of pretreatment will be necessary.

     On the other hand, restrictive limits (that is, limits of concentration of biochemical oxygen
demand (BOD), solids, and grease, for example, in milligrams per liter) may vary with the type of
municipal treatment. For example, emulsified fats from poultry-cooking operations are amenable
to activated sludge treatment, whereas they may be troublesome in a trickling-filter-type plant. A
municipality with activated-sludge treatment could then recognize that emulsified fats would be
paid for under BOD charges, with grease restrictions applying only to floatable grease.

Pretreatment May Reduce a Poultry Processor's Overall Waste-Treatment Cost When a Municipal
Surcharge System Is Contemplated

     Surcharge systems vary, and no one can predict whether pretreatment can be justified econom-
ically until costs are evaluated.  A surcharge system should be based upon an evaluation,  by the city's
consulting engineer, of the cost of the elements of the municipal treatment plant necessary to
accommodate the flow, remove the suspended matter, and treat the other ingredients of  the indus-
trial wastewater to the required levels, all on a unit basis (cost per pound of ingredient).

     Many surcharge systems start with a flow base rate and apply multipliers for concentrations of
any or all such ingredients as BOD, suspended solids, and grease. As an example, the flow base rate
charged to all sewer users may be 50 percent of the water bill, including flow from private water
supplies. Then, taking BOD as an example, assume that 250 mg/1 has been established as a bottom
base for surcharges. Then a multiplier might be applied for BOD between 250 and 500 mg/1, and a
higher multiplier between 500 and 1,000 mg/1.  Another set of multipliers might be applied for sus-
pended solids, another for grease, others for other factors.  These multipliers are then added together
to establish a single multiplier to be applied to the flow base charge to arrive at the total  bill.

     In other surcharge systems charges for the  pounds per month, above a base quantity, of BOD,
suspended solids, and other ingredients are added to the flow charges based on gallons.

     Except for compulsory action to remove materials prohibited from entering the city sewers,
the degree of pretreatment is generally an economic decision.  However, since plants differ and

surcharges differ, no simple set of parameters can be established. Each case must be evaluated
individually, not only to establish present practices but also to prepare for the future.
                                   HOW TO PRETREAT?
     Pretreatment can cover a broad range of wastewater processing elements, including screening,
gravity separation of solids and floatables, pressurized air flotation, chemical treatment as an adjunct
to gravity separation or flotation, and biological treatment such as aerated or unaerated lagoons or
some other form of aerobic treatment.

     Before any pretreatment is considered, an adequate survey should be made, including flow
measurement, composite sampling, and chemical analysis, to determine the extent of the problem
and the possibilities for pretreatment.  Analyses may include BOD, suspended solids, suspended
volatile solids, settleable solids, pH, temperature, and oils and grease. A permanent flow-measuring
and composite-sampling arrangement is warranted if sampling is done regularly to determine
municipal surcharges.

     Most commonly, pretreatment will consist of separation of floatables and settleable solids.  In
some instances lime and alum, ferric chloride, or a polymer may be added to enhance separation.
Paddle flocculation  may follow alum and lime or ferric chloride additions to assist in coagulation of
the suspended solids. Separation may be accomplished by gravity or by air flotation. Screening
may precede the separation process and may also be used to concentrate the separated floatables
and settled solids. These various systems will be discussed under separate headings.

     Removal of floatables and suspended matter will also accomplish some reduction in BOD.
Frequently this degree of treatment will satisfy municipal requirements.  If additional BOD removal
is required, a study of biological processes for pretreatment may be instituted, possibly in pilot
scale. Several biological treatment systems have been successfully adapted to the treatment of
poultry wastes.  Lagoon treatment is discussed in the section on Direct Discharge to a Watercourse
of the paper entitled "Waste Treatment."  Other BOD removal systems may be suitable.  The so-
called "Dutch Ditch," which utilizes an aeration device in an oval-shaped shallow "race-track" ditch
to recycle the flow,  has been applied to meat-waste treatment and may be suited to poultry wastes
as well. High-rate aeration, with clarification and sludge return (activated sludge), is available in
many configurations.

     A rotating biological contactor (fig. 1-1) treats the effluent from an air flotation tank in a pre-
treatment system at a poultry plant in Illinois.  In the contactor, wastewater flows through a tank
in which a series of half-submerged disks, about 12 feet in diameter, rotate slowly on a horizontal
shaft.  As the shaft turns, a film of biological growth forms  on the rotating surfaces. Rotation of
the disks passes the  biomass alternately through the wastewater where the biomass absorbs organic
matter, then through the air where it obtains oxygen for biological metabolism.  Excess biomass
sloughs off and  is separated in a clarification step. The plant in Illinois treats 130,000 gallons per
day and is reported to remove 90 percent  of the BOD in the wastewater leaving the flotation tank
(influent at 2,000 mg/1, effluent at 200 mg/1).

     Costs of pretreatment depend on many factors, such as size of poultry plant, type of processing,
space available for pretreatment, quality of in-house waste conservation, pumping requirements,

municipal requirements regarding quality of effluent, local labor costs, construction costs, and
Federal and State tax incentives for industrial waste treatment.

     However, approximate costs of equipment are given wherever possible, as well as approximate
costs of any chemicals required. Installation costs of prefabricated systems may be generally esti-
mated at about 30 to 40 percent of equipment cost.  Processors often prefer prefabricated units for
convenience in installation.

     Variations in loading due to changes in processing should not be overlooked in making rough
approximations for sizing pretreatment. For example, cut-up and packaging can produce 15 percent
greater BOD than processing to the eviscerating stage only, and fowl can increase grease content
from the usual 1.0 to 1.5 pound per 1,000 birds to 1.5 to 2.0 pounds.

     In spite of the wide divergence of costs, some examples of costs of plants, as built, may be
useful. In one recent instance in Arkansas, in a plant processing 5,000 broilers an hour, with partial
cut-up and packaging and some deep fat frying, a 20 X 20 mesh vibrating secondary screen (4 feet X
10 feet) cost $20,000 installed, including a 200-gpm pump. Installation of dual pumps, which is
advisable, would probably add from $1,000 to $2,000 to this figure.  Another plant in Arkansas,
killing and eviscerating birds and preparing frozen dinners, installed pretreatment in 1969, treating
1,250,000 gallons of wastewater daily. Secondary screening cost $19,500, a vacuator for grease
removal (see part III) cost $45,000, and buildings, flumes, piping, and controls cost $259,000, for a
total of $323,500.

     A pretreatment plant under design for a Georgia processor will cost $80,000 to $100,000,
including pumping and pretreatment to produce an effluent of 300 mg/1 BOD and suspended solids
and 100 mg/1 fats and grease. The plant processes 6,000  birds per hour, including eviscerating,
cut-up, and packaging.

     A screen plus a gravity grease separator treating 330,000 gallons per day from a killing and
eviscerating plant in Canada cost $85,500 installed, excluding the cost of the building.

     A pretreatment facility in South Carolina which handles offal and blood in addition to
2,800,000 gallons of daily flow for a plant killing and eviscerating birds and preparing frozen dinners
cost $278,000 for screening and a vacuator in 1965.  The building cost an additional $125,000.

     The plant in Illinois, described in an earlier paragraph, with air flotation and revolving-disk con-
tactor system, cost $80,000.  The contactor alone cost $22,000.
     The following outline suggests procedures for developing a decision matrix for pretreatment:

     • Select a project manager. He may be a company engineer or a consulting engineer, depend-
       ing upon the extent of the study and the capability of company personnel to produce the
       necessary information.

     • Measure flow and collect and analyze composite samples over a period of days sufficient to
       develop maximum as well as average data.

     • Make an in-plant waste conservation survey.  The annual cost for each possible change
       should include:

     —Amortized cost of improvements, installed

     —Power costs (heating, cooling, pumping)

     —Chemical costs

     —Labor cost (maintenance and operation)

• Make a study of possible pretreatment systems, with annual costs developed from the in-
  plant waste conservation survey.

• Determine the annual cost of municipal surcharges and compare with costs already

• Select the elements of the conservation survey and possible pretreatment systems that are
  economically justified.

• Design necessary improvements considering:

     —Portability of system

     —Flexibility for alteration and expansion

     —Operating skills required

     —Cost of disposal of residual solids and grease

                                                   SCRAPER DRIVE MOTOR

                                                           SLUDGE SCRAPER
                     Figure 1-1.  Rotating disk contactor.

                                          Part II


     In pretreatment, secondary screens may serve for final polishing with no further pretreatment
after flowaway, or they may precede air flotation systems and gravity separation basins to reduce
the bulk of solids that would otherwise have to be removed in the subsequent units.

     Screens vary widely both in mechanical action and in mesh size, which ranges from 0.5-inch
openings in stationary screens to 200 mesh in high-speed circular vibratory polishing screens. In
some cases the efficiency of screening in the flowaway systems may be sufficient to circumvent
secondary screening; in others, secondary or polishing screening may be warranted. Floor drains not
connected to the flowaway systems are usually then discharged to this polishing screen.  With no
secondary screening, the floor drains in the offal room and those adjacent to the flowaway screens
and offal conveyors should be pumped back to the flowaway screen influent. These floor drains
are frequently the source of serious problems when difficulties arise in the flowaway screen systems
or conveyors.

     In some plants "followup" stationary screens, consisting of two, three, or four units placed
vertically in the effluent sewer before discharge to the municipal sewer, have successfully prevented
escape of feathers and solids from the drains in the flowaway screen room and other drains on the
premises.  These stationary "channel" screens are framed and are usually  constructed of mesh or
perforated stainless steel with 1A- to Vi-inch openings. The series arrangement permits removal of a
single screen for cleaning and improves efficiency.
                                  VIBRATING SCREENS
     The vibrating screen is a structure with means for producing a rapid motion with one or more
perforated or meshed surfaces for separating material according to size.  The effectiveness of a
vibrating screen depends on a rapid motion. Vibrating screens normally operate at speeds of 1,000
to 2,000 rpm in a motion of 1/32 to 1/8 inch.

     A successfully operating screen of any type must accomplish a combination of the following

     • Conveyance of material retained on the screen surface to uncover the opening, so that the
       cloth can pass the undersize material or liquid.

     • Agitation of the bed of material on the screen surface. Agitation and stratification are re-
       quired to open the bed so that the fine particles or liquids can work their way down through
       the large particles and pass the opening.

     • Dislodgment of particles that stick or wedge in the opening.  Particles of nearly the same
       dimension as the opening will clog.  Motion of the screen must dislodge the particles.

     • Distribution of the material in order to take full advantage of the area of the screen. The
       material must be distributed over the surface to insure efficient screening. The motion of
       the deck should distribute the material over the deck evenly.

     • Retention before discharge. For high efficiency, sizing, or removing water from the solids,
       it is desirable to retain the oversize as long as possible. The material must be moved faster
       at the feed end to obtain quick distribution and a shallow bed where the volume is the
       greatest. At the discharge end where the volume is least, the rate of travel should be slowed
       to allow the remaining fines or liquids to be removed.

     Following are some of the advantages of the vibrating screen over the rotary in handling poul-
try plant waste:

     • The vibrating screen requires  less floor space and less horsepower for operation.

     • Spray water is usually not needed to wash particles from the screen cloth.

     • The screen cloth required to resurface a vibrating screen is less than one-third the amount
       needed for a revolving screen  and much easier to install.

     • The initial cost of a vibrating screen is lower in most cases.

     • The vibrating screen produces drier tailings owing to its motion.

     The vibrating screen is driven by a shaft turning in a pair of bearings.  The shaft carries un-
balanced weights, either machined into or keyed to the shaft. This assembly is usually driven by a
V-belt drive.

     When the unbalanced weights are rotated the screen follows the weights through a path. When
a vibrator is placed on the top of the  box, a slight rocking action will take place, resulting in ellipti-
cal motion with the ellipse leaning toward the vibrator. This motion tends to move the material
away from the feed end and retard it at the discharge end. The screen box is mounted on springs to
keep vibration from being transmitted to the supports.

     On most vibrating screens the cloth is pulled tightly across longitudinal steel members equipped
with rubber caps. The cloth may be changed easily by loosening the tension bolts and sliding it out
at either end.

     Of prime importance in the selection of a proper vibrating screen is the application of the
proper cloth.  The capacities on liquid vibrating screens are based on the percent open area of the
cloth. With this in mind, cloth should be selected with the proper combination of strength of wire
and percent of open area.  If the waste solids to be handled are heavy and abrasive, wire of a greater
thickness and diameter should be used to insure long life.  However, if the material is light or sticky
in nature the durability of the screening surface may be the smallest consideration. In such a case,
a light wire may be necessary to provide an increased percent of open area and more free screen-
cloth conditions.

     Screen cloth is woven in a variety of materials, such as black steel, spring steel, all types of
stainless steel,  Monel, and brass wire.  Normally, on liquid waste applications, a type No. 304 stain-
less steel wire is used.  However, when conditions require other types of metal, special wire cloths
can be supplied.

     In our discussion of various installations the term "mesh" will be used frequently to designate
the opening.  Where mesh is referred to as a number, the reference is to the number of openings to
the linear inch. The mesh is counted by starting from the center of one wire and counting the num-
ber of openings to a 1-inch distance. If the count does not work out to an even number, the frac-
tional part of the opening should be specified.

     The actual opening between the wires is known as "space." Thus, M-ineh space, .135 wire
implies that the wires are Vt inch apart and the diameter of the wire is 0.135 inch. We have standard-
ized on a 20-mesh screen for offal, a 36 X 40-mesh screen cloth for feathers, and a 36 X 40-mesh
for pretreatment. On most applications a double-crimped square-weave cloth is used.  Double-
crimped wire is woven in such a manner as to arch the shoot wire over the warp and then the warp
wire over the shoot.  Each wire then forms a support for the other, keeping both wires tight and
rigid, thus eliminating shifting or slipping.

     We will now see how a liquid dewatering vibrating screen can be used effectively in the pre-
treatment of poultry plant waste for discharge to a municipal system.

     There are many vibrating screens  in service in poultry plants throughout the United States—too
many to list.  They are installed as feather screens, as offal screens, and as pretreatment screens for
discharge to municipal systems.

     The following cost data are necessarily limited to screens manufactured by FMC Corporation.

     The liquid vibrating screen is manufactured in sizes that vary from 2 feet 0 inches wide X 4 feet
0 inches long to 4 feet 0 inches wide X 10 feet 0 inches long. The most common unit supplied is an
NRM-148 liquid dewatering screen (fig. II-l). This screen is 4 feet 0 inches wide  X 8 feet 0 inches
long, and as a pretreatment screen is equipped with a 36-mesh X 40-mesh 304 stainless steel screen
cloth.  The unit will handle approximately 600 gpm of wastewater.  An NRM open screen complete
with stainless steel screen cloth and drive will cost slightly less than $2,000.  An NRM-148 liquid
dewatering screen complete with screen cloth, drive, and  feed flume and tank will cost slightly more
than $3,000.

     The NRM-148 screen, as a feather screen, will handle feathers from about 8,000 birds per hour.
As an offal screen, it will handle the viscera from about 10,000  birds per hour.

     The influent to the pretreatment  screen has had most of the feathers and viscera removed.  The
screen's primary function is to remove most of the remaining solids from the plant wastewater be-
fore it goes to the sewage-treatment plant. The ideal way to feed a vibrating screen is directly by
gravity from the flowaway system.  The velocity of the water must be fed over the screen to reduce
screen blinding.  The screen is installed at a 10° downslope; as the pretreatment screen is subjected
to wastewater with a high fat content,  the less pumping that is done, the longer the screen cloth
will operate without blinding. Pumping breaks  down fat  in the  water, and the smaller particles
cause blinding. Emulsified fats from cooking can also have the same effect.  In some plants where a
high percentage of the fats is emulsified, either the screen cloths must be sprayed intermittently
with hot water or steam to remove the fat or an automatic spray system may be installed.

     Good efficiency in feather removal is reported. In fact, a plant engineer at a poultry plant in
Athens, Ga., states that a 4 X 8 vibrating screen  operating as a pretreatment screen showed only one
feather in the effluent in a 24-hour test.

     The normal maintenance on a liquid dewatering screen consists of greasing the bearings at
regular intervals and maintaining the proper spring tension on the screen cloth. If the screen cloth
breaks and the break is parallel to the longitudinal members of the screen deck, the screen is too

     The operating cost of an NRM-148 liquid dewatering screen is the cost of the current required
to operate a 2-hp motor.
                                     STATIC SCREENS
     During the past several years, a substantial number of so-called static screens have been installed
in many process industries to recover suspended matter from plant effluents or liquid flows within
a plant. Highly successful screening operations have been achieved in the meat packing, tanning,
canning, textile, and paper and board products industries,  as well as in domestic sewage-treatment
operations.  Interesting new developments are underway, such as the treatment of wastes from
animal-producing farms and poultry-processing plants.

     In most instances, the installed equipment represents new functions or concepts in recovery
and generally involves recycling or some other use of the recovered solids.  In many cases, stationary
screens are installed as replacements for screens that require  moving parts to make a suitable separa-
tion of solids from a process stream.

Basic Design Concepts

     The primary function of a static screen is to remove "free" or transporting fluids.  This can be
accomplished in several ways; in most older concepts, only gravity drainage is involved. A concavely
curved screen design using high-velocity pressure feeding developed and patented in the 1950's for
mineral classification has been adapted to other uses in the process industries.  This design employs
bar interference to the slurry which knives off thin layers of the flow over the curved surface.

     Beginning in 1969, U.S. and foreign patents were allowed on a three-slope static screen made
of specially coined curved wires. This concept used the Coanda or wall attachment phenomenon to
withdraw the fluid from the underlayer of a slurry stratified by controlled velocity over the screen.
This method has been found to be highly effective in handling slurries containing fatty or sticky
fibrous suspended matter.

     Since the field tests to be reported were conducted on the later design of stationary screen,
details of this unit are presented here. The device is known commercially as a Hydrasieve. A typical
installation of a single screen operating on industrial wastewater is illustrated in figure II-2.

Method of Operation

     The slurry to be screened or thickened is pumped or may flow by gravity  into the headbox of
the machine. As shown in figure II-3(a), the incoming fluid  overflows the weir above the screen
area and is accelerated in velocity and thinned in depth as  it  approaches the screen. A lightweight
hinged baffle is incorporated into the assembly in such a position that it reduces turbulence in the
flow.  Turbulence is reduced by the shape of the foil, which  causes the fluid to respond to Bernoulli's
theorem through  the wedge-shaped entrance.  The increasing velocity of fluid draws the baffle
toward the surface of the screen.

     Suspended solids tend to stratify in the thin stream, and fibrous materials align themselves
lengthwise with the direction of flow. Figure II-3(b) shows a segmental section of the screen wires
and the slurry as it contacts the upper end of the Hydrasieve screen. Note that the wall attachment
of the  fluid to the metal bars or wires draws or bends an underportion of the flow through the

openings. Part of the underflow also moves along the arcuate surfaces of the wires and is primarily
concentrated at the apex of the downward curve. Here it falls by gravity from the screen back or
flows in streams attached to the underside of the wire assembly in a central path between the sup-
ports.  The screen pattern permits a maximum of fluid extraction based on the limit of flow rate
and screen area.  Figure II-3(c) illustrates the screen design, which is registered under the trademark

     On the first (top) slope of the screen most of the fluid is extracted from the bottom of the
stream traveling at 25° from the vertical. When the angle of the screen changes to 35° some addi-
tional fluid is withdrawn, and usually the massing solids begin to roll on the surface, owing to the
residual kinetic energy.  This action compacts the solids very slightly.  On the final slope of the
screen, the solids tend to hesitate for simple drainage action but are always moved off the flat sur-
face by displacement with oncoming material.  The effluent is aerated as it passes through the
screen in ultrathin ribbons completely exposed to a natural or controlled atmosphere.

Unique Features

     The arrangement of transverse wires with unique singular flow curves provides a relatively non-
clogging surface for dewatering or screening. The screens are precisely made  of No. 316 stainless
steel and are extremely rugged. Harder, wear-resistant stainless alloys may also be used for special

     Openings of 0.010 to 0.060 inch meet normal screening needs. The essential features of the
Hydrasieve are covered in U.S. Letters Patents  No. 3,452,876 and No. 3,751,555. Other U.S.
patents are pending. Patents are also issued and pending in foreign countries.

     The Hydrasieve has a number of advantages over vibrating and rotary screens, including:

     • Initial cost is low.

     • It is compact and inexpensive to install.

     • There are no motor, no wires, no moving parts, no noise, no safety problems.

     • It requires little, if any, attention.

     • Construction is stainless steel. Fiberglass frame is optional.

     • There are no screens to puncture, warp, or blind.

     • Wide  variation in flow rate or loading does not seriously affect performance.

     • Uniform terminal solids moisture can be maintained.

     • Units can be readily combined with secondary and tertiary biological treatment systems.

     • Assemblies of units are readily constructed to meet high-capacity flow needs.

In-Plant Testing Results

     A series of tests were conducted with small Hydrasieve screens in an Ohio poultry-processing
plant in the autumn of 1972.  A simplified drawing of the wastewater flow is shown in figure II-4.

     It was found that some suspended solids could be removed immediately following screening for
viscera (rotary 20-mesh screen), as well as after a treatment of the water with lime and alum.  How-
ever, the continuous operation of the unit required steam sprays to prevent an accumulation of
fatty film on the V-bars, which interfered with the establishment of a good fluid wall attachment on
the screen.

     No problems were encountered when the effluent was screened from the flotation system. The
principal testing was done with a Hydrasieve located on the flow to the sewer as indicated in figure
II-4 at position 4. A secondary advantage for using a screen in this location is that it rescreens all
effluent water prior to its discharge to the city sewage system.

     An adequate evaluation period on full flow volume has not been achieved, but test results show
a worthwhile removal of fine suspended solids, along with a small drop in BOD levels.  Some improve-
ment in BOD is credited to the aeration provided by the Hydrasieve.  Some minor improvements in
color have been observed; the pH is also raised slightly.

     The brief specifications in table II-l are suitable for preliminary planning of an installation of
effluent screen.

     While the screening device described is now widely accepted for solids removsil from effluents
in many processing plants, it is not yet well established in the poultry industry, owing primarily to
the manufacturer's brief experience with this industry's operations and problems.  However, the
exploratory work done within the past several months has indicated that improvements in effluent
quality can be made economically.
Table 11-1 .—Typical design information for chicken processing plant effluent based on use of 0.020-inch slot opening
No 552-18" 	
No 552-36" 	
No 552-48" 	
No 552-60" 	
No. 552-72" 	
No 552-72-2 	
No. 552-72-4 	
No 552-72-6 	
No 552-72-8 	
No 552-72-10 	

Overall dimensions, feet
Price for
estimating, dollars

                               OTHER SCREENING DEVICES

Rotary Screen (Revolving, Trommel, Scrubber, or Barrel Screens)

     Rotary and vibrating screens are the most popular types in poultry wastewater processing.

     One type of barrel or rotary screen (see fig. II-6(a)), driven by external rollers, receives the
wastewater at one open end and discharges the solids at the other open end. The liquid passes out-
ward through the screen, usually stainless steel screen cloth or perforated metal, to a receiving box
and effluent sewer mounted below the screen. The screen is usually sprayed continuously by means
of a line of external spray nozzles.  The screen is usually inclined toward the solids exit end. This
type is popular as an offal screen, but has not been used to any great extent in secondary screening.

     The other most common type of rotary screen, used to some extent in secondary screening, is
driven by an external pinion gear. The influent is discharged into the interior of the screen below
center, and solids are removed in a trough and screw conveyor mounted lengthwise at the center line
of the barrel (see fig. II-6(b) and fig. II-6(c)). The liquid exits outward through the screen into a
box in which the screen is partially submerged. Perforated lift paddles mounted lengthwise on the
inside surface of the  screen  assist in lifting the solids to the conveyor trough.  This type of screen is
also generally sprayed externally to reduce blinding. Four  of these screens (5 feet in diameter by
12 feet long with 10 X 10 mesh cloth) were installed at the municipal sewage-treatment plant in
Gainesville, Ga.,  in 1964 to polish the raw wastewater. Operating at 4 rpm, each treats 2 million
gallons per day.  In 1964 there were seven poultry-processing plants in Gainesville. The central sys-
tem solved maintenance and operating problems at the municipal plant resulting from residual
feathers and offal not captured by offal and feather screens at the processing plants.

Other Mechanical Screens

     Several other types of mechanical screens have had limited application in this field.

     One is a rotating disk that is partially submerged in the wastewater flow.  As it rotates, particles
partially adhere and are scalped off above the flow.  The screen disk is placed vertically or at a slight

     Another mechanical type is a circular spring-mounted horizontal screen, driven by a motor
located under the screen and equipped with variable eccentric v/eights. As the motor rotates, the
eccentric weights impart multiplaned vibrations to the spring-mounted screen. These units are
usually centrally fed at the top, the liquid discharging through the screen to a pan above the motor
and sludge discharging from a port at the periphery (see fig. II-7). Small units (18 inches diameter)
are available on loan for testing.

     There are many other ingenious mechanical screens, but they have not been tested on poultry
wastewaters.  Some,  such as a vertical spinning drum, have  successfully screened red meat waste
solids. Under the impetus of need to improve effluents, testing such devices on poultry waste may
be accelerated.

High-speed vibrator
                                  Figure 11-1.  NRM-148 liquid dewatering screen.

Figure 11-2.  Single Hydrasieve screen operating on industrial

                  Gravity feed
                  of liquids/solids
 Self cleaning,
 non clogging stainless
 steel screen for
 continuous dewatering
 Removed or
                                            feed inlet
 Figure 11-3.  (a) Diagram showing path of slurry screened by Hydrasieve. (b) Segmented section of screen
   wires with slurry contacting upper end of Hydrasieve screen, (c) Screen design of Marvel' Hydrasieve.

                                    Recycled and prescreened
                                    feather effluent

             Timed control
             valve      \.
                          * ' !
     Rotary screen,
     20 mesh
           tank, Solids
To city sewer,
estimated  175 gpm
Miscellaneous process

     (position 4)

_f f f 't *J> f



\ -
                         200 gpm
                                                                                            To disposal
   Figure 11-4.  Wastewater flow system in chicken-turkey processing plant using small Hydrasieve screens.

                                                                                                                                        ¥   O D ("FOR USE W\TH DKESSEI?
                                                                                                                                            T-fPE COUPUNSO
                                                                                                                                                              DIA, - 12 HOLES
                                                                                                                                                           EQUALLY SPACED
                                               Figure !!-5.  Diagram for model 552-36 Hydrasieve.  (Courtesy of the Bauer Bros. Co.).

                                                         -aafff spraypipe mff> /et nozzles
                                                                              precision cut gporteeth

                                                                               -filtering tare -14 separate
                                                                                sections around cylinder
                                                                                   *—channel iron hoMng WH
                                                                                    mesh onto square ear
                                                                                              driving prwn
                                                                                              receiving tank
      Figure 11-6.  Rotary screens for poultry wastewater processing1  (a) rotary screen driven by external rollers;

         (b)  rotary screen driven by external pinion gear, (c) cross section of rotary screen driven by piston gear.

Figure 11-7. Influx and discharge from spring-mounted motor-driven screen.

                                          Part III




     This section considers the requirements for design, guidance for design, available equipment,
and the capability and limitations of four schemes of equipment arrangement for gravity grease
recovery and separation. A hypothetical case was designed to establish a size parameter for discus-
sion of the various tanks and mechanical equipment schemes. The approximate prices for the tanks
and the mechanical equipment as enumerated are based on the sizing for the hypothetical case.
These prices should be considered as "order-of-magnitude" rather than as fixed costs for specific
applications. Such applications require specific estimates for equipment and construction costs;
modifying the following information to accommodate a particular situation could produce very
misleading results.

Design Criteria:  Influent Characteristics

     Rate of Flow. Hydraulically, this is the most important single criterion for design of the grease-
separation unit.  Rate of flow should be considered with respect to overall rate, total variations in
rate, the magnitude of variations in rate, and the duration of variations in rate.  The average flow
from most poultry plants is on the order of 8 to 10 gallons per bird processed.  Reports indicate
that 75 percent of the flow can be expected during the processing day, the balance appearing during
the cleanup period.

     Temperature of Water.  The  temperature of water has some effect on gravity and grease separa-
tion ; the variation of temperature may have a more detrimental effect than a uniform high or low
temperature. Wide swings in temperature variation in gravity separation basins can result in temper-
ature -gradients and contribute to  short circuiting in the basin. There are considerable supporting
data to indicate that higher temperatures of water contribute to settling characteristics of solid
heavy particles.  Conversely, it would be in order to assume that lower water temperatures would
contribute to greater grease separation.

     BOD. BOD reduction may not be an objective of pretreatment; however, it is usually a side
benefit of grease removal, since a  large portion of the BOD contribution is from grease itself.  BOD
can vary from  1,200 ppm to approximately 400 ppm. Most municipal criteria limit the contribu-
tion to a 300-ppm level; hence, it may be desirable to use a grease recovery unit as a primary sedi-
mentation basis in an effort to  achieve BOD removal by the withdrawal of settleable solids.

     Grease. Grease loads normally run in a range of 200 ppm, but they can vary to as high as 1,300
ppm. Most municipal plants require a grease loading not to exceed 100 ppm.

     Settleable Solids. Most data indicate  that settleable solids run on the order of 150 ppm in the
effluent from poultry-processing plants. In any low-velocity or detention-type basin settleable
solids will settle out.  It may be desirable to remove the settleable solids and attempt to achieve a
BOD reduction, or these solids may be returned to the flow going to the municipal treatment plant;
in any event, there will be a certain amount of solids settling out in the basin.


Design Criteria:  Factors Affecting Design

     Detention Period.  Usually this period is governed by other design parameters of the grease re-
covery basin. However, in some States where the basins are to be utilized as primary sedimentation
basins in addition to grease removal, 1 to 2 hours of detention time may be required on the

     Tank Depth.  Theoretically, the more shallow a tank the faster either floating or settleable
solids will separate; however, from data obtained in the field it has been found that depths of less
than 6 feet are usually impractical. Hence, most State requirements will be on the order of 6 to 7
feet of tank depth.  There are tanks of shallower depth in operation, no doubt operating satisfac-
torily. However, the shallower depth is not recommended because of the probability of upset by
scouring or velocity currents.

     Surface Area.  Normally called "overflow rate," and probably  the most commonly considered
parameter of tank design, surface area is a combination of the horizontal velocity through the basin
and the vertical velocity of  the particle.  A number of grease removal applications have indicated
satisfactory removal with rates on the order of 1,440 gallons per day per square foot and even
greater; however, if the separation unit is being applied as a primary separation, basin rates of 700
gallons per  day per square foot or less should be applied. Many States will require rates not to ex-
ceed 700 gallons per day per square foot.

     Particle Size.  Basically, for particles with like specific gravity,  the larger the particle size, the
easier the separation will be. Hence the larger the  grease particle the more rapidly it will float and
the easier it will be to remove; the larger the particles of settleable solids, the more easily they can
be settled out.

     Density of Particles. Grease removal by gravity separation depends upon the density of the
grease being lesser than the  density of the water, so that the grease floats to the top.

     Removal  Facilities. May be either manual or mechanical; the mechanical mechanisms will be
discussed in the following pages.

     Flow Fluctuations. This is usually regarded as an undesirable effect, since it contributes to
short circuiting and resuspension of particles; however, within certain ranges flow fluctuation can
enhance the flocculation and agglomeration and, hence, the  separation.

     Pretreatment.  There are several forms of pretreatment that may be considered, for instance
grit removal, preaeration, flocculation anoVor screening; however, these pretreatment processes and
their effects should be considered independently for each particular application.

Hypothetical Case

     Sizing Parameters.  Let us assume

     • 40,000 birds per day

     • 10 gallons of processing water per bird

     • 75 percent of flow occurring during 10-hour killing day

     • 150 ppm grease load

     • 450ppmBOD

     • State requirements dictating overflow rate of 700 gallons per day per square foot and IVi
       hours minimum detention time

     Selection of Type of Tank (Circular Versus Rectangular).  Engineers are sharply divided as to
the merits of rectangular versus circular separators for various purposes. Many engineers prefer rec-
tangular to circular gravity grease recovery tanks; they believe that because of the increasing surface
area traversed by the scum on a circular tank as it proceeds outward in a radial direction to the
peripheral weir, the grease loses its cohesiveness. Others claim that the gradually reducing velocity
of the flow as it  moves radially outward  improves grease separation as well as solids separation (a
majority of engineers prefer circular tanks for settling flocculent solids).  However, it is safe to say
that, for gravity recovery of grease, the majority favor rectangular basins. In dissolved air flotation
systems (see succeeding section), the two factions are about evenly divided, a slightly greater number
favoring rectangular basins.  Circular dissolved air flotation systems are described and illustrated in
the last section of this part. In the preference of clarifiers following biological treatment systems,
the circular clarifiers have a decided majority.

     With the above sizing parameters, this example will utilize a pair of rectangular tanks with a
common wall, 59.0 feet in length, each 10 feet in width and 6.0 feet average water depth.

     Tank Construction—Concrete. Concrete tanks have the inherent advantages of lower overall
maintenance and more permanent structure. However, some owners prefer to be able to modify
their operation for future expansion or alterations or even relocation. The approximate cost for a
pair of concrete tanks of the above sizing, assuming approximately 12-inch-thick walls, above grade,
and nominal footings, and installed concrete costs of approximately $150 per cubic yard in place,
would be $25,550.

     Tank Construction—All Steel. All-steel tanks have the advantage of being semiportable, more
easily erected in field, and more easily modified than the concrete  tanks. The all-steel tanks require
additional maintenance as a result of wear in areas of abrasion and corrosion or rusting in other areas.
The approximate price for a pair of tanks of the above configuration in all-steel construction would
be $26,800; a rough price for installation would be $2,900.

     Tank Construction—Steel Walls. The tank utilizing all-steel walls and concrete bottom is prob-
ably the best compromise between the all-steel tank and the all-concrete tank. The advantages are
the same as for steel; however, the all-steel tank requires footing underneath the supporting members,
whereas with the steel-wall tank the concrete bottom forms the floor and supporting footings for the
tank. The disadvantage is that this tank is not as readily movable as the all-steel tank.  The approxi-
mate price for a pair of this nature, assuming a concrete pad approximately 18 inches thick and in-
stalled concrete cost of approximately $150 per cubic yard, would be $30,900, with an erection cost
of approximately $1,900.

Four Possible Equipment Schemes for Grease Recovery: Functional and Cost Comparison

     Four-Sprocket Collector with Scum Pipe. This unit is shown in figure III-l. Its advantages are
that the scum is conveyed by  the return run of the flights on the chain and the flight collector's con-
tinually pushing  the scum toward the scum pipe. The sludge is conveyed at the same time  by the
same collecting mechanism to the sludge hopper for withdrawal to some other point. The disad-
vantage of this type of unit is that an operator is still required to operate the lever-type scum trough
to admit the floating grease.  The quality of operation depends upon the ability of the scum pipe
operator to select the proper timing interval and tilt of the tube to obtain the best concentration

of grease.  Frequently the scum accumulates too rapidly to permit the operator to remove it often
enough. Another disadvantage is the possibility that grease can adhere to the flights on the return
run; when carried beneath the scum trough and baffle it may eventually float up and go over the
weirs into the effluent. The approximate price for this unit, including the complete sludge collector
drive and the scum trough, would be approximately $12,5001 with an approximate installation cost
of $3,000.!

     Four-Sprocket Collector With Flight-Type Skimmer. This collector consists of the four-
sprocket arrangement as discussed above with the addition of a flight skimmer as shown in figure
III-2.  This unit has basically the same advantages as those listed above, with the added advantage  of
a flight-type collector that conveys the dewatered grease to the horizontal trough to flow into the
scum pit.  Basically, the only disadvantage to this unit is that the return flights of the horizontal
sludge collector can again carry grease down behind the scum skimmer, from which it may eventually
float up and over the weirs. The  approximate price for this arrangement would be $23,000;! the
approximate price for the installation of this equipment in one of the above tanks would be $3,600.l

    Three-Sprocket Collector  with Flight Skimmer Full  Length and Cross Screw Conveyor.  This
equipment arrangement, shown in figure III-3, is probably the best possible assemblage of gravity
grease removal equipment.  The advantages are that the three-sprocket collector conveys the sludge
and therefore circumvents the problem of grease adhering to the flights.  Another advantage is that
the skimmer travels the full length of the surface of the tank, bringing the grease up over the beaching
plate and into the cross scum trough; the utilization of a ribbon-type screw conveyor in the cross
trough permits the positive  conveyance of the grease to the collecting pit.  The additional  advantage
of this unit is the low requirement for operator attention; these units can either be placed on a timer
or operated continuously, the operator checking them only occasionally and utilizing normal main-
tenance and housekeeping procedures. The approximate1 price for these units is $32,500  and the
approximate installation cost is $5,700.1

    Helical Scum Skimmer. This type of mechanized skimmer, shown in figure III-4, is a com-
promise with the flight-type skimmer mentioned above. The unit is slightly less expensive and slightly
more economical to maintain than the flight skimmer; however, it does not have the volumetric
capacity of the flight-type skimmer.

Maintenance and Operation Requirements

    Overall Arrangement of System Elements. Most gravity grease recovery units use no  additional
chemicals, flocculants, or polymers to achieve the grease separation. Therefore, there is no require-
ment for design or maintenance of a chemical feeding system.  The gravity grease recovery unit is
quite simple in construction and operation, alleviating the need for sophisticated or highly trained

    In gravity grease recovery  and separation, as with any system of wastewater treatment, the over-
all system must be considered in addition to the individual elements.  Particular attention  should be
given to maintaining low turbulence in the flow and minimizing pumping.

    Housekeeping. Each gravity grease  recovery system requires a certain amount of housekeeping.
After operating for a few months, the equipment becomes coated with grease. It is difficult, if not
impossible, to ascertain the need  for maintenance when the parts are not visible.  Hence, there is a
need for scraping, scrubbing, steam cleaning, and in some cases high-pressure hosing, to assist the
          Design Criteria: Factors Affecting Design."

people responsible for maintenance in keeping the units operational.  Cleanliness also helps in the
reduction of odors and elimination of odor-producing bacteria.

     Mechanical Maintenance. The day-to-day observation and the periodic checking of alignment,
grease levels in speed reducers, and greasing of bearings are natural requirements of any wastewater
operation. Eventually the chains will wear and require replacement.  The replacement interval can
be lengthened considerably by utilization of timers. This equipment basically has a wear life
proportional to the hours of use; hence, if a unit is placed on a timer, a longer wear life can be
expected. A high percentage of grit in the wastewater may accelerate the wearing of the components;
the grease will tend to hold the grit in the wearing part of the unit, acting as a lapping compound and
accelerating the wear.
Pilot Plants

     The use of pilot plants for grease recovery and/or other wastewater treatment design cannot be
overemphasized.  The most important information obtained from pilot plant studies is that the plant
must be operated with a flow representative of that for which the ultimate plant will be designed.
One of the most frequent errors in the use of pilot plants for design purposes is the application of
the pilot plant data to a flow different from that ultimately intended to be treated.

     Most major manufacturers have pilot plant equipment available on rental terms.
                                DISSOLVED AIR FLOTATION
     Dissolved air flotation is a waste-treatment process in which oil, grease, and other suspended
matter are removed from a waste stream. This treatment process has been in use for over 15 years
and has been most successful in removing oil from waste streams.  Its principal early use was, as it
still is, the removal of oil from petroleum refinery wastewater. Another natural area for application
of this treatment system has been the removal of contaminants from the food-processing-plant
waste streams. One of the very first applications of this treatment system was for this purpose.

     Basically, dissolved air flotation is a process for removing suspended matter from wastewater
that uses minute air bubbles, which upon attachment to a discrete particle reduce the effective spe-
cific gravity of the aggregate particle  to less than that of water. Reduction of the specific gravity for
the aggregate particle causes separation from the carrying liquid in an upward direction.  As figure
III-5 suggests, the particle to be removed may have a natural tendency  either to rise or to settle.
Attachment of the air bubble to the particle induces a vertical rate of rise noted as VT.

     Figure III-6  illustrates the basic  design considerations of the flotation unit. The measurement
of the parameter  VT will be  discussed later. Since the waste flow must pass through a treatment
unit, the particle  to be removed will have a horizontal velocity. Certain criteria have been estab-
lished for limits of the parameter VH, which sets the width and depth of the treatment unit.  There-
fore, as figure III-6 suggests, the effective length of the treatment unit is directly proportional to
the horizontal velocity and depth and inversely proportional to the vertical rate of rise of the par-
ticle to be removed.

     The mechanics of operation for a dissolved air flotation unit are illustrated in figure III-7. It
can be noted that a portion of the clarified effluent is pressurized by a recycle pump. This recycled
flow is pumped to a pressure tank into which  air is injected. In the pressure tank at approximately
40 psig, the recycle flow is almost completely saturated with air.  The pressurized recycle flow,

containing the dissolved air, leaves the air saturation tank and flows through a pressure reduction

     A 40-psig pressure drop occurs at the pressure reduction valve, causing the pressurized flow
stream to relinquish its dissolved air in the form of tiny air bubbles. This air-charged recycle flow
is then blended with the raw process flow to effect attachment of the air bubbles to the oil and
other suspended solids to be removed. The combined flow stream (raw flow plus recycle flow con-
taining the air bubbles) is mixed and uniformly distributed over the cross section of the basin.

     As the incoming flow travels to the effluent end of the basin, separation of the oil and solids
from the associated liquid occurs.  Solids accumulate at the water surface and form an oily sludge
blanket. Clarified liquid flows over the  effluent weir and into a wet well. From the effluent wet
well, a portion of the effluent is recirculated. The remainder of the effluent is remo>ved from the
basin for subsequent treatment or discharge.  The floated scum blanket of separated solids can be
removed from the basin by skimmer flights traveling between two endless strands of chain. Since
the influent stream may also contain small amounts of heavy solids, such as grit, which are not
amenable to flotation, provision must also be made for solids removal from the bottom of the unit.

     The foregoing discussion illustrates the recycle method  of injecting the air bubbles into the
waste stream. Figure III-8 shows all three methods of dissolved air injection currently used. Total
pressurization, as the name implies, occurs when the total waste flow is pressurized before entering
the treatment unit.  Partial pressurization is a method whereby a portion of the waste flow is pres-
surized and mixed with the remaining raw flow before entering the treatment unit.

     To obtain optimum treatment with some wastes, it has  been necessary to use chemical pretreat-
ment before dissolved air flotation. The necessity for use of chemical conditioning is normally
associated with a high degree of emulsification of the oil or grease matter in waste stream  flow. It is,
therefore, a requirement to break the emulsion and form a floe to abborb the oil or grease. It has
been shown (fig. III-9) that increasing the particle size increases the rate of separation. Flocculation
as a means of promoting particle growth preceding flotation  contributes to the effectiveness of the
flotation process where chemical conditioning is used. The points of chemical injection and the pos-
sible use of flocculation associated with the three methods of air injection are shown in figure 111-10.

     The use of steel-package dissolved air flotation units lends itself to application in the poultry-
processing industry. This arrangement provides an economical, flexible design that requires minimal
construction cost and  area investment (fig. III-ll). Most manufacturers of dissolved air flotation
units have a complete  line of steel tank units to meet a wide  variety of flow conditions.

     The use of steel-package units lends itself equally well to those applications requiring flash
mixing and flocculation as a part of chemical pretreatment.

     In the following discussion, a steel-package Model No. 6020 with flash mix and flocculation
compartments has been used to illustrate the costs associated with this type of unit.  The  capital cost
of this unit would be approximately $37,500, which would include the following equipment:

     • Flash mixer and drive

     • Flocculator and drive

     • Two-shaft surface skimmer and drive

     • Screw conveyor, sludge collector, and drive

     • Complete steel tank

     • Pressure tank and associated air central system

     • Recycle pump

     • Compressor

     • Recycle piping

     Table III-l lists the operating horsepower included in the above-described unit. Based upon a
10-hour-day, 5-day-week operation, costs of running Model No. 6020 for 52 weeks are shown for
electrical costs at 1 cent per kW-h and 1.5 cents per kW-h.

     Table III-2 illustrates typical results from the treatment of poultry-processing wastes by dis-
solved air flotation with and without chemical treatment.  The raw waste characteristics and treat-
ment results shown are for grab samples from a unit in Alabama. The characteristics of this waste
somewhat exceed those of waste normally encountered in this application; the necessity of chemical
treatment is therefore evident for this particular application.  The raw flow to this unit is 150 gpm;
based upon a lime dosage of 100 mg/1, the total lime use in a single 10-hour working day would be
76 pounds.  Extending this use to a continuous operation of 5 days per week, 52 weeks per year,
the yearly lime use would be approximately 20,000 pounds. The cost of this amount of lime would
be about $1,000 per year; capital cost of a simple lime feed system would be between $6,000 and

     As is the case with most industrial waste, treatability studies should be conducted not only to
determine the design parameters for a flotation unit, but also  to determine whether chemical treat-
ment is necessary to meet treatment objectives.

     Pilot dissolved air flotation units are available from most manufacturers for treatability studies.
The rental cost varies, but the normal rate is approximately $500 per month.

     A laboratory bench scale test procedure developed to simulate the dissolved air flotation process
has been used most successfully in the determination of design parameters for an air flotation unit.

     This flotation test (fig. 111-12) is used to determine the suspended particle rise rate (VT), which
is the most critical design parameter in the design of the flotation unit.  The rate is determined by
filling the pressure cell with liquid to simulate closely the recirculation of the unit effluent of pres-
surization in a full size unit; this recycle water should be developed by several previous flotation runs.
                    Table I\\-~\-Operating horsepower for Rex Chainbelt Model 6020
Flash mixer 	
Flocculator ....
Skimmer .... . . .
Bottom screw .... ....
Recycle pump 	 	



11 0

                       Note.—Based on a 10-hour-day, 5-day-week operation, yearly operating
                      ists equal: $214,at1 cent per kW-h; and $321, at 1.5 cents per kW-h.

Table 111-2.—Typical operational results from treatment of poultry-processing wastes by dissolved air flotation with
                                  and without chemical treatment
                                    Raw waste
Suspended solids
Oil and grease  .
Run number

Lime, 100 mg/l.
Alum, 300 mg/l.
Percent removal
This liquid is then injected with air until a pressure of over 40 psi is obtained; the cell is then shaken
vigorously to insure that the air is put into the solution.  The pressurized liquid is then introduced
into the waste. The exact amount of pressurized liquid is determined by trial and error for best
results.  As the minute bubbles are released from solution, they attach to the suspended particle and
oil and rise to the surface.  After flotation is complete, a sample of the effluent is taken and analyzed.
During the test, observation of the rise rate of the major portion of the solid material with respect to
time is recorded.  From a graphic plot of these data a rise rate can be calculated.  This rise rate,
along with factors for turbulence and short circuiting, is used in the selection of the basic size neces-
sary to accomplish treatment required.
                                      OTHER SYSTEMS
     Whereas the preceding section was limited to a discussion of rectangular dissolved air flotation
systems, it should be noted that the same principle is applied to circular-shaped tanks by a number
of equipment manufacturers.  These tanks are similar to conventional clarifiers with center baffled
inlet, peripheral weir, bottom sludge removal scrapers, and surface skimmer arms discharging to a
surface scum trough.  The pressurized air recjrcle arrangements are the same as those used in rectan-
gular tank systems. The first accompanying flow diagram (fig. 111-13) shows a small poultry plant
pretreatment system at Allentown, Pa., using a circular flotation tank. In this instance a portion of
the effluent of the flotation tank is pressurized, aerated, and returned directly to the flotation tank.
In the  second instance, at Fayetteville, N.C. (fig. 111-14), a portion of the effluent is again recycled,
but in  this instance the recycle is not pressurized and aerated. Rather, the recycled effluent is
recycled to the screened raw waste; the entire screened raw waste plus recycle are then pressurized,
aerated, and discharged to  the flotation cell.  This is similar to the "total" pressurization illustrated
at the top of figure 111-10,  with the addition of recycle from effluent to influent. The costs shown
include the flotation tank complete with pump, air saturation tank, and mixing tank, and mixer
but do not include the screen or the cost of erection.

     In some cases, vacuators have been used to separate floatables in pretreating poultry plant
wastewater. Vacuators are basically completely enclosed concrete tanks where a vacuum is applied
as the wastewater passes through the tank. The vacuum enhances flotation in a three-product separa-
tion similar to air-pressurized flotation. The need for complete enclosure limits observation of
operating characteristics. Designs range from 300 gpm to 2,000 gpm per unit.  As stated in "Costs" in
part I,  a vacuator installed in Arkansas to treat 1,250,000 gallons daily cost $45,000 in 1969.

                       '"nl,**™ it
                       JiX^ruw^ ~**



o«,~~  ~s\

GUAKD    '
                                      ~d=——tf	=^ -y
                                      ^Tl^f                "^

                               Figure 111-1.  Four-sprocket collector with scum pipe for grease recovery. (Courtesy of the Link-Belt Company.)

                                                                                                                                          -SCUM TROUGH FLUSHING

                                                                                                                                            WATER VALVE « HIGH

                                                                                                                                            END OF SCUM TROUGH
                                                                                                                                               ( HIQH KATEI LEVEL
                                                                                                                                                 IK PIPE
                                                                        KITH 13 TOOTH'SF-rt
                                                                        WID 2U FLIGHTS , ^s .
                                  Figure 111-2. Four-sprocket collector with flight-type skimmer for grease recovery.  (Courtesy of the Link-Belt

•_ 3


^ UL™_ 	
wti&s aart*. jaaf

n , P 	 	 ,H
"^ /.j

. R

                                                                                 X_ PIVOT FLIGHTS
                                                                                   ARE PMLI.EC -5;
                                                                                                            FLOOR SLOPCS APPROX
                      Figure lil-3.  Three-sprocket collector with flight skimmer full length and cross screw conveyor.  {Courtesy of the Link-Belt Company.)

Figure II1-4.  Helical scum skimmer.  (Courtesy of the Link-Belt Company.)

                        Figure 111-5. Separation of particle
                         from wastewater by dissolved air
                          flotation  (VT = vertical rate of
Figure 111-6.  Basic design considerations of flotation unit.  (Vj- = vertical rate of rise;
              V/_f = horizontal velocity; L = length of treatment unit.)

      Figure 111-7.  Dissolved air flotation unit: mechanics of operation.
   Figure 111-8.  Injecting air bubbles into the waste stream: recycling, total
                 pressunzation, and partial pressurization.

w 0.40
JS- 0.30







0.40 0.50 0.60 0.70 0.80
Figure 111-9.  Effect of average particle size on rate of rise: 100 ppm lime;
                 20 ppm bentonite; 20 percent recycle.
           WASTE _
            FLOCCULATING     TANK
            (IF REQUIRED)

WASTE _/-\


1 I l_^J I «_» 1—1—

•fl-Vc t LAT
| L«i IIP R


O t Q—

      Figure 111-10. Points of chemical injection and use of floccula-
         tion associated with total and partial pressurization and

                                                                                                 THROTTLING VALVE
                   PRESSURE TANK

                                                                                                                fTuMP SELECTED ON BASIS OF MAXIMUM
                                                                                                               <[  REQUIRED PRESSURIZED FLOW DELIVERED TO
                                                                                            PRESSURIZING PUMP ^PRESSURE TANK 6> 40 I? 5.1.
                                                                                                 SEE PRESSURE  TANK SIZE
                                                                                                                    !g-	PLUG VALVE

                                                                                                                  	JF2	K
                                                                                                                              EFFLUENT ^.
            FOR TANK 6-0'TO 9-6"WIDE

- '
^^' -_-. -



"WTi^-~— ^
..._":__,' "^..\^__
                                                                                          CONVEYOR  TRAVEL
4  DIA PIPE ->t-- -^	.
                                                                                             SEE TABLE FOR      /SCREW CONVEYOR
                                                                                             NUMBER OF LEGS    \ DRIVE UNIT
                                   Figure 111-11. Steel tank with skimmer and sludge-removal facilities.  (Courtesy of Rex Chambelt Inc.)

             Component parts—Rex Flot-Aire Kit
Flot-Aire pressure cell with clarified effluent
Glass cylinder with raw waste
Clarified effluent in Flot-Aire pressure cell pressurized to 40 psi
                                                                         Pressurized effluent introduced to raw waste
Figure 111-12. Laboratory bench scale test to simulate dissolved a.r flotation process.  (Courtesy Rex Chainbelt Inc.

Minute air bubbles floating waste material to surface of cylinder
 Flotation complete m cylinder
    Clarified waste sample being withdrawn from cylinder
Analysis made of clarified waste
               Figure 111-12.  Laboratory bench scale test to simulate air flotation  process —Continued

    See Figure 2 - Data Sheet 315-10. 804 for Rex Float-Treat Test Kit.

A.  Assume that a recirculation ratio of 0. 33/1 is to be tried.

    1.   Place 750 ml of a representative sample of the waste in a one liter
        graduated glass cylinder. (See Figure 3, Data Sheet 315-10. 804. )

    2.   Fill the Float-Treat Pressure Cell approximately three-fourths full
        with liquid.  (See  Figure  3, Data  Sheet 315-10. 804. )
              (It is desirable that the operation of the Float-Treat
              Pressure Cell closely  similate the recirculation of
              effluent as  used in the  Float-Treat Flotation System.
              The returned effluent (recycle water) may be developed
              by repeated flotation of several different portions of raw
              waste.  After the recycle water has been developed and
              used in the flotation tests,  samples may then be withdrawn
              for chemical analyses. )

    3.   Secure the cover gasket and  cover of the Float-Treat Cell,  making
        certain  all the valves are closed.

    4.   Inject air into the cell until a pressure of 40 psi is attained  and
        maintained during testing.  (See Figure 4,  Data Sheet 315-10. 804. )

    5.   Shake the cell vigorously for thirty seconds.

    6.   Release 250  ml of the liquid which has been pressurized into the
        graduated cylinder.  (See Figure 5, Data Sheet 315-10. 804. )  The
        volume  of liquid in the graduated cylinder then totals 1000 ml
        (750 ml raw  and 250 ml pressurized).   The ratio  of volumes of
        recycle water to  the raw waste is termed  the recycle ratio.  This
        ratio is expressed in percent and is termed the recycle rate.  Thus,
        the recycle rate used in this  test is 33%.   The most  suitable recycle
        rate can be determined by repeated tests at varying  rates of recycle
        and  usually is  not less than 20% and no more than 50%.  To  facilitate
        the introduction of the air-charged recycle water to  the graduated
        cylinder, a rubber tube may  be connected to the petcock on  the
        pressure cell.  After clearing the rubber  tube of  air, (Allow some
        liquid to escape through the tube  by opening petcock.   Sufficient
        liquid  should be removed until it  has a milky appearance) the air-
        charged recycle water is introduced through the rubber tube into the
        graduated cylinder.  The end  of tube should be placed near bottom of
        the cylinder.   (See Figure 5,  Data Sheet 315-10.804.)
       Figure 111-12. Laboratory bench scale test to simulate air flotation process.—Continued


     The air bubbles rise through liquid in a manner similar to that in
     the Float-Treat flotation system.

7.   Allow the contents of the graduated cylinder to come to rest and
     observe the flotation. (See Figure 6,  Data Sheet 315-10. 805.)
     Allow sufficient time for the rising solids to come to the surface
     of the liquid.   Usually ten minutes will be sufficient time for the
     flotation to be completed.  (See Figure 7, Data Sheet 315-10. 805. )

8.   After the flotation is completed, a sample of the raw waste and
     treated waste should be taken for analysis. (See Figures 8 and 9,
     Data Sheet 315-10. 805. ) The treated waste  should be carefully
     withdrawn from the graduated cylinder either through the use of
     a petcock installed in the side and near the bottom of the cylinder
     or through the use of a siphon inserted in the cylinder.  Sufficient
     liquid should be withdrawn to complete the desired analysis, how-
     ever,  care should be taken to avoid the break up of the  skum blanket.

9.   Should chemical flocculation with flotation be desired,  the  chemical
     may be added into the raw waste after step "l" is completed, floc-
     culation may be  carried out, for convenience, in another  vessel.
     Care should be taken not to break up the floe when transferring  the
     waste to the  cylinder. Enough time for flocculation should be allowed
     before introducing the air-charged recycle water.  Under appropriate
     conditions, a floe may  be  formed  by gentle agitation  of the waste
     after the chemical is added.  The procedure described above also
     applies when chemical  flocculation is used.  When using  chemical
     flocculation, care should be exercised not to break up the floe par-
     ticles in handling  the flocculated waste.

     Because of the peculiarities of some floe formations, they will break
     up readily upon any excessive agitation after being formed.  This is
     most readily noticed when a liquid with a preformed floe is transferred
     from the cylinder used in the jar mixing test to the cylinder used  in
     the flocculation test.  If the floe does break up and does not re-form
     immediately,  it is suggested that the  transfer to the flotation cell not
    be made and  that  flotation  be accomplished  in  the  vessel  where the
     floe was formed.   The procedure for running this test  are  the  same.
     However, withdrawing of the clarified liquid, as described in step  "8",
    will probably be  through a  siphon.
     Figure 111-12. Laboratory bench scale test to simulate air flotation process.—Continued


In flotation of a particular waste,  it is quite possible that the test using
the recirculation ratio of 0. 33/1 may not yield  the best results.  It
may be that some other recirculation ratio  would yield the results
needed to work in with the economy of a final plant design and effluent
requirements.   Therefore, the tests  described above may be repeated
with other recirculation ratios until the optimum ratio is obtained.  In
these tests the values shown in steps "l"  and  "6"  will be  changed

When running flotation tests in the Rex Float-Treat demonstration kit,
the observed rate of  rise of the major portion of the solid  material
should be recorded.  This value can be recorded in terms of inches per
minute and will be used in determining the full scale plant requirements.

In order to insure the validity of results obtained,  care should be taken
that representative samples of waste are obtained before running tests.
When results have been obtained, they should  be  recorded on Question-
naire for Design Data  Sheets 315-10. 101 and 315-10.102.  These
completed sheets  should be returned  to CHAIN Belt Company.
    Figure 111-12. Laboratory bench scale test to simulate air flotation process.—Concluded

       ALLENTOWN.   PA.
                   100,000 GPD
                   RAW WASTE
1250 GAL
                                      APPROXIMATE EQUIPMENT
                                      COST - $30,000
                                                    100 GPM
            EFFLUENT TO
Figure 111-13. Poultry-plant pretreatment system at Allentown, Pa., using circular flotation tank.

        CAPE  FEAR  FEED CO.
   20HP EACH
                      125 GPM
                      RAW WASTE
                             FLOAT VALVE
                                      0-65 GPM
                 5000 gal
               SURGE  TANK
              12  -6 DIAMETER
COST-  $25,000
        CITY  SEWER
Figure 111-14. Poultry-plant pretreatment system at Fayetteville, N.C., using total pressurization
                   with recycle from effluent to influent.

                                       Part IV

                            MUNICIPAL ORDINANCES

Limitations of Two Types

     Prohibition of Objectionable Matter.  Various minerals, toxic materials, and waste characteris-
tics and materials that are difficult to treat are excluded.  The following examples are typical.

     The Metropolitan Sanitary District of Greater Chicago includes the following exclusions on
ingredients that may affect poultry plant effluents:

     • Noxious or malodorous liquids, gases, or substances which either singly or by interaction
       with other wastes are sufficient to create a public nuisance or hazard to life or are sufficient
       to prevent entry into the sewers for their maintenance and repair

     • Solid or viscous wastes which cause obstruction to the flow in sewers or other interference
       with the proper operation of the sewerage system or sewage-treatment works, such as grease,
       uncomminuted garbage, animal guts or tissues, paunch manure, bone, hair, hides, fleshings,
       entrails, and feathers

     • Waters or waste containing substances which are not amenable to treatment or reduction by
       the sewage-treatment process employed or are amenable to treatment only to such degree
       that the sewage-treatment-plant effluent cannot meet the requirements of other agencies
       having jurisdiction over discharge to the receiving waters

     • Excessive discoloration

     Other cities use similar limiting clauses in their ordinances, often copied from the manual [9],
from which the Chicago wording was adapted in part.

     Concentration of Pollutional Characteristics. The ordinance of the Metropolitan Sanitary
District of Greater Chicago provides no top limits for BOD or suspended solids but does include
"surcharges" for these items (see "Surcharges," below). It does, however, limit temperature to a maxi-
mum of 150° F (65° C) and fats, oils, or greases (hexane solubles) to a maximum of 100 mg/1.
These limits  are frequently  included in municipal ordinances.

     A small suburb of Louisville limits BOD to 300 mg/1 and suspended solids to 350 mg/1. Its
ordinances state: "The Town Board of Trustees is authorized to prohibit the dumping of wastes
into the Town's sewage system which, in its discretion, are deemed harmful to the operation of the
sewage works of said Town."

Source Information on "Limitations"

     A large number of cities use, as a guide, the so-called Model Ordinance published as part of
Water Pollution Control Federation Manual of Practice No. 3 [9]. Article V of the Model Ordinance
contains an extensive list of limiting characteristics applicable to poultry plant wastewaters dis-
charged to public sewers.  The background material, along with Article V, are too voluminous to
reproduce here.  The "Regulation of Sewer Use" (Manual of Practice No. 3) is available at $1.50
($1 to Federation members) from:  Water Pollution Control Federation, 3900 Wisconsin Ave.,
Washington, B.C. 20016.  A 15-percent quantity discount is available in lots of 12 or more copies.
     The Metropolitan Sanitary District of Greater Chicago charges 2.1 cents per 1,000 gallons, 1.4
cents per pound of BOD, and 2.4 cents per pound of suspended solids, after deducting the first
10,000 gallons per day and the BOD and suspended solids it would contain. Also deducted are the
sewer district tax (a property -type tax) plus 4 mills per day per employee, an allowance for sanitary
sewage discharged during the working day.

     Most of the simpler sewage billing systems are based on the water use, ranging from about
50 percent to as high as 125 percent of the water billing, with maximums for BOD, suspended
solids, grease, and sometimes other ingredients. These are basic sewer charges applicable to all
users— domestic, commercial, and industrial— and are not classified as surcharges unless they include
escalation for BOD, suspended solids, grease, etc., and possibly flows, in excess of a "domestic"
base.  Thus the surcharge portion of the ordinance might be similar in structure to the Chicago
ordinance, but with a charge for flow in excess of a  base, and a charge per pound of ingredients
above a base represented by discharge from a single residence.

     As a guide to municipalities developing charges to industrial users, the Environmental Protec-
tion Agency has published Federal Guidelines— Equitable Recovery of Industrial Waste Treatment
Costs in Municipal Systems [13] , from which the following is excerpted:

     Quantity or quality formulas based on total cost or average unit costs:  This method of cost
allocation or derivation of industrial charge is computed by several forms of the generalized formula:
where C;. = charge to industrial users, dollars per year

      VQ = average unit cost of transport and treatment chargeable to volume, dollars per gallon

      b  = average unit cost of treatment chargeable to BOD, dollars per pound

      SQ = average unit cost of treatment (including sludge treatment) chargeable to suspended
          solids, dollars per pound

      y. = volume of wastewater from industrial users, gallons per year

      Bi = weight of BOD from industrial users, pounds per year

      Sf = weight of suspended  solids from industrial users, pounds per year

     Note: The principle applies equally well with additional terms (e.g., chlorine feed rates) or
fewer terms (e.g., VQ Vf only).

     The terms b  and SQ may include charges (surcharges) for concentrated wastes above an estab-
lished minimum based on normal load criteria.

     Inasmuch as it is an objective of the Guidelines to encourage the initiation and use of user
charges, this general method of allocation is both preferable and acceptable.


     Pretreatment of poultry-processing wastewater, prior to discharge to a municipal system, is a

     • When constituents prohibited by municipal regulations are present in the wastewater.
       Feathers, whole blood, and entrails are typical of such prohibited materials.

     • When maximum concentrations have been established for certain constituents and the waste-
       water contains such constituents in excess of those limits.  BOD, grease and oils, and sus-
       pended solids are examples of such constituents.

     • When the poultry processor is paying or anticipates paying for municipal treatment through
       a surcharge system and can effect economies by pretreatment.  Examples of constituents for
       which surcharge rates may be established are BOD, suspended solids, and possibly grease and

     Decisions regarding the last item are the most difficult.  To save surcharge dollars by pretreat-
ment, the poultry-plant operator must determine the degree of pretreatment that represents the
economic breakpoint. He must also weigh other factors such as the probability that the surcharge
rates may change, that the municipal treatment plant may need expansion in the near future and
may seek a Federal grant which will introduce requirements previously discussed, and that the State
may establish regulations both as to degree of pretreatment and to operation of the facilities (such
a law was recently passed in New Jersey). The processor must also consider his own future business
plans, such as changes in processing, additional processing, overall expansion, or possibly reduction
in operations.

     Considering these  often elusive variables, the poultry processor must select the type of pretreat-
ment, such as:

     • No pretreatment at all

     • Secondary screening only

     • Secondary screening and separation of floatable and settleable solids by gravity, pressurized
       air flotation, or other means

     • Separation of floatable and settleable solids, as above, but without secondary screening

     • Secondary screening and separation of floatable and settleable solids, plus biological or
       chemical treatment for further BOD removal

     The pretreatment  processes and the capacities selected depend upon the size of the processing
plant, efficiency of the selected process, facilities for handling the materials removed from the
wastewater, and related engineering and cost factors, as well as the three regulatory considerations
set forth above.

 1.  W. M. Crosswhite, R. E. Carawan, and J. A. Macon, "Water and Waste Management in Poultry
    Processing," Proceedings, Second Food Wastes Symposium (Continuing Education Publications,
    Waldo Hall 100, Corvallis, Oreg. 97331, pp. 323-335, Mar. 1971.
 2.  W. J. Camp, "Waste Treatment and Control at Live Oak Poultry Processing Plant," Proceedings
    18th Southern Water Resources and Pollution Control Conference, North CEirolina State
    University, Raleigh, N.C., Apr. 1969.
 3.  "Wastes from the Poultry Processing Industry," Technical Report T. R. W62-3, U.S. Depart-
    ment of Health, Education, and Welfare, Public Health Service, R. A. Taft Sanitary Engineering
    Center, 1962.
 4.  "Industrial Waste Profile No. 8, Meat Products," The Cost of Clean Water Series, U.S. Depart-
    ment of the Interior, Washington, D.C., 1967.
 5.  "Waste 'Treatment Lagoons—State of the Art," Water Pollution Control Research Series, 17090
    EHXO 7 U.S. Environmental Protection Agency, Washington, D.C., July 1971.
 6.  Chas. T. Decker, "Rate Surcharges:  Friend or Foe?" Water and Wastes Engineering 8(11),
    F2-F4, Nov. 1971.
 7.  Y. Maystre and J. C. Geyer, "Charges for Treating Industrial Wastewater in Municipal Plants,"
    Journal of the Water Pollution Control Federation, 42(7), 1277-1291, July 1970.
 8.  "The Poultry Processing Industry—A Study of the  Impact of Water Pollution Control Costs,"
    U.S. Department of Agriculture Economic Research Service, Marketing Research Report No.
    965, Prepared for Office of Water Programs, Environmental Protection Agency, June  1972.
 9.  "Regulation of Sewer Use," Water Pollution Control Federation Manual of Practice No. 3,
    Washington, D.C., 1963.
10.  John M. Bolton, "Wastes From Poultry Processing Plants," Proceedings of the 13th Industrial
    Waste Conference, Purdue University, Lafayette, Ind., May 1958.
11.  Nelson Leonard Nemerow, Theories and Practices of Industrial Waste Treatment, Syracuse,
    N.Y., Addison-Wesley Publishing Co., Inc., 1963.
12.  A. J. Steffen, "The Control and Treatment of Poultry Processing Wastes," Second Annual
    Meeting of the Mississippi Sewage and Industrial Waste Association, Mar. 1959.
13.  Federal Guidelines—Equitable Recovery of Industrial Waste Treatment Costs in Municipal
    Systems, Environmental Protection Agency, Washington, D.C., Oct. 1971.

                                    Appendix A
     Following is a list of manufacturers of equipment discussed in this study. Any mention of
products or services here or elsewhere in the study is for information only, is not selective unless it
is used to illustrate a point, and is not to be construed as an endorsement of the product or service
by the Environmental Protection Agency or the authors.

     Although the list is intended to be complete, there may be some oversights. Such over-
sights are not to be construed as reflecting on the merits of the product or service.

     The authors will appreciate being advised of errata, in order to improve subsequent editions of
this list.
Rotating Biological Contactor:
    Hormel Rotating Disc
Vibrating Screens:
    "Selectro," "Gyroset," "Kelly"
    Other models
Static Screens (Wedge Bar):
     Static Sieves   .  .  .
Autotrol Corporation, Bio Systems Division
  5855 North Glen Park Road
  Milwaukee, Wis.  53209
G. A. Hormel & Co.
  Environmental Pollution Control Division
  Austin, Minn.  55912

Productive Equipment Corporation
  2924 W. Lake Street
  Chicago, 111.  60612
Allis-Chalmers Manufacturing Company
  1126 S. 70th Street
  Milwaukee, Wis.  53214
DeLaval Separator Company
  Poughkeepsie, N.Y. 12600
Link Belt, Materials Handling Division
  FMC Corporation
  300 Pershing Road
  Chicago, 111.  60609
Rex Chainbelt, Inc., Environmental Control Group
  1901 S. Prairie
  Waukesha, Wis. 53186
Simplicity Engineering Company
  Durand, Mich.  48429
    Bauer Hydrasieve
F. J. Clawson & Associates, Inc.
  6956 Highway 100
  Nashville, Tenn. 37205
Bauer Bros. Company
  Subsidiary of Combustion Engineering, Inc.
  P.O. Box 968
  Springfield, Ohio 45501

Static Screens (Wedge Bar)—Continued:
    Wedge-shaped screen with bars in
       direction of flow	
    Other models
Enclosed Vacuum Tanks: Vacuator
Rotary Barrel Screens:
    North Green Bay Screen
    Other models
Rotating Disk Screens
Eccentric-Weighted Horizontal Disk Screens:
    Aero Vibe	
    Other models
Gravity Grease Recovery and Separation:
Hendricks Manufacturing Company
  Carbondale, Pa. 18407
Dorr-Oliver, Inc.
  Havemeyer Lane
  Stamford, Conn. 06904
Hydrocyclonics Corporation
  968 North Shore Drive
  Lake Bluff, 111.  60044
Peabody Welles
  Roscoe, 111. 61073
Dorr-Oliver, Inc.
  Havemeyer Lane
  Stamford, Conn. 06904

Green Bay Foundry and Machine Works
  Box 2328
  Green Bay, Wis. 54306
Dorr-Oliver, Inc.
  Havemeyer Lane
  Stamford, Conn. 06904
Link Belt Material Handling Division
  FMC Corporation
  300 Pershing Road
  Chicago, 111. 60609
Rex Chainbelt, Inc., Environmental Control Group
  1901 S. Prairie
  Waukesha, Wis.  53186
Link Belt
Rex Chainbelt

Allis Chalmers
Eriez Syncro-Matic
  1401 Magnet Drive
  Erie, Pa.  16512
Sweco, Inc.
  6033 E. Bandine Boulevard
  Los Angeles, Calif.  90054
DeLaval Separator Company
  Poughkeepsie, N.Y.  12600
Hydrocyclonics Corporation
  968 North Shore Drive
  Lake Bluff, 111.  60044
Kason Corporation
  231 Johnson Avenue
  Newark, N.J.  07108

Infilco Division, Westinghouse Electric Company
  901 S. Campbell Street
  Tucson, Ariz. 85719
Koppers Co., Metal Products Division
  Hardinge Operation
  York, Pa.  17405

Gravity Grease Recovery and Separation—Continued:
    Other models	Chicago Pump Division, FMC Corporation
                                               622 Diversey Parkway
                                               Chicago, 111.  60614
                                             Clow Corporation, Waste Treatment Division
                                               1999 N. Ruby Street
                                               Melrose Park, 111.  60160
                                             Crane Company, Environmental Systems Division
                                               Box 191
                                               King of Prussia, Pa. 19406
                                             Dorr-Oliver, Inc.
                                               Havemeyer Lane
                                               Stamford, Conn.  06904
                                             Dravo Corporation
                                               One Oliver Plaza
                                               Pittsburgh, Pa.  15222
                                             Environmental Services, Inc.
                                               1319 Mt. Rose Avenue
                                               York, Pa. 17403
                                             Envirotech Corporation
                                               Municipal Equipment Division
                                               100 Valley Drive
                                               Brisbane, Calif. 95005
                                             Graver, Division of Ecodyne Corporation
                                               U.S. Highway 22
                                               Union,  N.J.  07083
                                             Jeffrey Manufacturing Company
                                               961 N.  Fourth Street
                                               Columbus, Ohio 43216
                                             Keene Corporation, Fluid Handling Division
                                               Cookeville, Tenn.  38501
                                             Lakeside Equipment Company
                                               1022 E. Devon Avenue
                                               Bartlett, 111. 60103
                                             Link Belt  Environmental Equipment
                                               FMC Corporation
                                               Prudential Plaza
                                               Chicago, 111.  60601
                                             Ralph B. Carter Company
                                               192 Atlantic Street
                                               Hackensack, N.J.  07601
                                             Rex Chainbelt, Inc., Environmental Control Group
                                               1901 S. Prairie
                                               Waukesha, Wis. 53186
                                             Walker Process Equipment, Inc.
                                               Division of Chicago Bridge & Iron Company
                                               Box 266
                                               Aurora, 111.  60507
                                             Zurn Industries, Inc.
                                               1422 East Avenue
                                               Erie, Pa.  16503

Dissolved Air Flotation:
     Graver "Aeroflotor"	Graver, Division of Ecodyne Corporation
                                               U.S. Highway 22
                                               Union, N.J.  07083
     Other models	Beloit-Passavant Corporation
                                               Middletown, Ohio 45042
                                             Black Clawson Company
                                               Middletown, Ohio 45042
                                             The Carborundum Co.-"Pacific"
                                               Buffalo Avenue
                                               Niagara FaUs, N.Y. 14302
                                             Environmental Systems
                                               Division of Litton Industries, Inc.
                                               354 Dawson Drive
                                               Camarillo, Calif. 93010
                                             Envirotech Corporation
                                               Municipal Equipment Division
                                               100 Valley Drive
                                               Brisbane, Calif. 95005
                                             Infilco Division, Westinghouse Electric Company
                                               901 S. Campbell Street
                                               Tucson, Ariz.  85719
                                             Keene Corporation, Fluid Handling Division
                                               Cookeville, Tenn.  38501
                                             Komline-Sanderson Engineering Corporation
                                               Peapack, N.J.  07977
                                             Rex Chainbelt