DAIRY WASTE

TREATMENT

by aeration

^ ^ R ^

THEORY

DESIGN

CONSTRUCTION

OPERATION

AGRICULTURE HANDBOOK NO. 176

AGRICULTURAL RESEARCH SERVICE

UNITED STATES DEPARTMENT OF AGRICULTURE
Acknowledgments

Members of the Dairy Research and Marketing Advisory Committee of the U.S. Department of Agriculture have offered many

suggestions throughout the course of the investigations. The

work of the members of the group currently known as the Dairy

Industry Committee Subcommittee on Dairy Waste, of which

E. C. Thompson is chairman, has been outstanding. H. A.

Trebler, former member of the subcommittee, followed the work

critically and gave worthwhile suggestions, as did A. J. Steffen

and C. W. Watson, Jr.

The pilot plant stud^^ at the Pennsylvania State University

was under the supervision of R. R. Kountz, Professor of Sanitary

Engineering, who also designed industrial units from which practical information became available.

The continual interchange of ideas with W. W. Eckenfelder,

Jr., of Manhattan College, was valuable, as he was one of the

ill'st sanitär}^ engineers to apply these studies to other wastes.

Precaution

Dahy plant management should become acquainted with the

requirements of the laws governing pollution control that pertain

to the locality. The requirements usually specify that a registered

professional engineer be retained to evaluate the problem, design

the waste treatment plant, and obtain the proper approvals before

construction begins.

Foreknowledge of special requirements may save considerable

time and money and assure good relations between the dairy plant

and the pollution control agency.

Good housekeeping and pollution

Essential information

Batch treatment plant

Sample calculations

Tank size

Selection of aeration device

Number of ejectors

Design of plant

Operation of single-tank batch

method

Use of air under pressure

Continuous-process treatment plant_

Pumps and piping

Construction of treatment plant

Cost estimates

Washington, B.C.

CONTENTS

Page

1

1

2

3

4

4

5

5

7

9

9

11

13

14

Conclusions

Literature cited

EURDD publications

Appendix

The COD method

Whey wastes

Ejectors as aeration devices

Oxygen content of the atmosphere

Excessive foaming

Heating the dairy waste

Waste treatment systems using

ejector aeration

Index

Issued July 1960

For sale by the Superintendent of Documents, Government Printing Office, Washington 25, D.C. Price SO cents
DAIRY WASTE

TREATMENT by aeration

THEORY, DESIGN,

CONSTRUCTION, OPERATION

By NANDOR PORGES, THOMAS S. MICHENER, JR., LENORE JASEWICZ, and SAM R. HOOVER, Eastern Utilization Research

and Developfnent Division, Agricultural Research Service

Waste water disposal is an important consideration in every dairy plant. The direct discharge of

untreated waste waters into streams, public sewer

systems, or onto land is frequently not possible or

permissible. In such instances, it is necessary for

dairy wastes to undergo treatment before disposal.

Information available from investigations conducted at the Eastern Utilization Research Laboratory shows the technical possibility of providing

adequate treatment for any quantity or concentration of dairy waste material. This Agriculture

Handbook presents laborator}^ and pilot plant data

of value to dairy plant personnel and sanitary

engineers and gives details for planning and installing treatment systems using aeration.

GOOD HOUSEKEEPING AND POLLUTION

Wastes produced in operating a dairy plant vary

greatly according to the products made and to

housekeeping practices. The approximate quantities of waste present in various dairy process

waters are listed in a guide, the ''Manual for Milk

Plant Operators" of the Milk Industry Foundation {16}} Losses range from less than 1 percent

to more than 3 percent of the milk received, depending on the complexit}^ of operation. Wide

variation occurs in the amount of water used for

washing and cooling. Well-operated dairy plants

may use a gallon or less of water for each quart of

milk received, whereas others may use more.

However, when the cost of treatment is considered,

dairy operators will find good reasons for makmg

every effort toward waste elimination and good

housekeeping.

A small dairy plant that receives 10,000 pounds

of milk per day may produce each working day

about 1,250 gallons of waste with a milk solids

concentration of approximately 0.1 percent, or

1,000 parts per million (p.p.m.). This is the same

as mixing 100 poimds of fluid milk with 1,237 gallons of water. The polluting effect will be at least

4 and possibly 8 times as great as the same amount

of municipal sewage, and the dairy waste will require as much treatment as the waste from 40 to

60 persons. If wastes equal to 100 pomids of milk

were dumped into a lake, the resultmg bacterial

action on this amount of food would require all the

oxygen dissolved in approximately 200,000 gallons

of saturated lake water for complete oxidation of

the food material. Until the bacterial demands

for ox^^gen are satisfied, no oxygen would be available in this part of the lake for fish or plant life.

It is this tremendous polluting effect that makes

treatment necessary for such high oxygen-demanding waste before it is drained into natural

water coiuses.

ESSENTIAL INFORMATION

Extensive investigation on the bio-oxidation

of dairy wastes established the amount of oxygen

required and the rate at which oxygen must be

supplied to treat dairy wastes successfully (17).

Treatment consisted of two major phases. During

the first, or assimilation, phase, sludge bacteria

rapidl}^ consumed the food in the milk waste and

required oxygen at a high rate (8). During the

second, or endogenous, phase, because these

bacteria received no new food supph^, they

digested themselves and used considerably less

1 Italic numbers in parentheses refer to Literature Cited,

p. 15.

ox^^gen (6). Endogenous respiration also occurred during the assimilation process. The successful application of these biological principles

to the treatment of dairy waste is dependent on

the following information, which is based on

laborator}^ and pilot-plant investigations.

(1) Each pound (dry weight) of the organic

matter in dairy waste (equivalent to about 10

pounds of wasted fat-free fluid milk) requires

about 1.2 pounds of ox^^gen for complete oxidation. This oxygen requirement is termed the

''chemical oxygen demand'' (COD) and can be

determined by a rapid method (19) described on
AGR. HANDBOOK 176, U.S. DEPT. OF AGRICULTURE

p. 18. Of tlie total solids present in dry nonfat

milk, about 83 percent are organic; tlius, a unit

weight of dry nonfat milk requires a unit weight

of ox3^gen.

(2) During the rapid assimilation of food,

bacteria need about 37.5 percent of the total

oxygen requirement, or 1.2X0.375 =0.45 pound

of oxygen per pound of organic matter.

(3) About 0.52 pound of new bacterial cell

material is formed from each pound of waste in

the assimilation phase.

(4) Nitrogen is often needed in the treatment

of cheese plant wastes and may be added in an

available form, such as ammonium salts, ammonia,

urea, or casein. Nitrogen resulting from the

breakdown of self-digesting sludge is also available

for re-use.

(5) Rapidity of oxygen utilization and sludge

formation in the assimilation phase depends on

the quantity of seed bacteria present. Good

results were obtained by using the sludge itself as

bacterial seed for later additions of dairy waste.

When the dry weight of sludge cells equaled the

dry weight of the incoming waste solids in a

single-dose feeding, assimilation was completed

within 3 hours at 90° F. If the seed sludge was

doubled, assimilation time was halved; if sludge

was halved, the time required for waste assimilation was doubled (7).

(6) Sludge respiration requires the remainder

of the total oxygen (COD) to oxidize the newly

formed sludge: 1.2 — 0.45 =0.75 pound of oxygen

for each 0.52 pound of sludge produced, or 1.44

pounds of ox^^gen required for oxidation of each

pound of ash-free sludge.

(7) During endogenous respiration at 90° F.,

the sludge will normally consume itself at approximatel}^ 1 percent per hour. The hourly rate

of oxygen demand of the sludge during selfdigestion is, therefore, 1.44X0.01 =0.0144 pound

of oxygen per pound of sludge in the tank. The

rate may be much lower at times (6", 14)-

(8) A pound of well-aerated dairy waste sludge

usually occupies a volume of 0.8 cubic feet, or 6

gallons, after it is allowed to settle for 30 minutes

Itis apparent, then, that the effluent of the dairy

must be studied and measured before a practical

treatment plant can be designed. The maximum

volume of waste must be known to establish the

proper tank size. The characteristics of the rate

of flow are needed to establish the rate and duration of supply of ox3^gen. The volume and rate

are readily obtained by metering or collecting the

waste in a calibratecl tank. The temperature

should be observed to insure that the waste is not

too hot or too cold for bacterial activity.

The oxygen demand or strength of the waste

must also be determined. The oflnicial chemical

test or the rapid one described on p. 18 may be

used. The chemical oxygen demand (COD) is

the amount of oxygen required for complete oxidation of the organic substances and is usually

reported in parts per million (p.p.m.). It is

practicallv equal to the ultimate biochemical oxygen demand (BOD) for milk wastes.

Formula (1) may be used to obtain the actual

pounds of oxygen for the total milk waste:

Total oxygen (lb.) =

COD (p.p.m.)Xtotal waste (lb.)

1,000,000 (1)

Calculations from the above information will

determine the capacitv of the aeration tank, the

quantity of seed sludge, the production of new

sludge, and the oxygen requirements for the entire

process. At this point, a decision to select a filland-draw (batch) system or a continuous operation process must be made. The fiU-and-draw

system is simple to construct and to operate and

will be covered first in this Handbook. FiU-anddraw units that handle up to 40,000 gallons of

waste daily are now in operation, and larger sizes

are feasible. These units work well for dairy

plants that confine their operations to an 8- to

10-hour workday. When round-the-clock operations are necessary, continuous treatment units

that can process any quantity of wastes are probably more suitable. Both systems can be completely automated by the installation of timers,

switches, and power-operated valves.

BATCH TREATMENT PLANT

Simplicity of operation makes a batch, or filland-chaw, treatment of milk waste an attractive

process for plants running on an 8- to 10-hour

workday schedule. The designs suggested here

are based upon operating conditions used in the

pilot-plant studies made at the Pennsylvania

State University, as sponsored by the Eastern

Utilization Research and Development Laboratory

{11)'^ Similar plants have been constructed,

utilizing the same method of operation. It is

believed that any treatment unit designed accordingly and properly maintained and operated should

also perform satisfactorih^

2 Numbers in parentheses at right refer to formula designation.
DAIRY WASTE TREATMENT BY AERATION

SAMPLE CALCULATIONS

To demonstrate the Ccilculations used to design

a batch-type waste treatment phmt, consider for

example, a dairy that produces a maximum daily

waste volume of 10,000 gallons containing 1,500

p.p.m. COD.

{a) TOTAL OXYGEX REQUIREMEXT from formula (1) :

Total oxygen (lb.) =

1,500 X 10,000X8.34

1,000,000

= 125 pounds

(6) OxYGEX FOR ASSIMILATION (37.5 pct.

COD):

Oxygen (lb.) = 125 X 0.375

=46.9 pounds

{c) WASTE ORGANIC MATTER, ash-free, drv basis

(83.3 pct. of COD):

Organic matter (lb./day) = 125 X 0.833

= 104.2 pounds per da}'

{(i) NEW SLUDGE, ash-free, dry basis (52 pct. of

organic matter):

New sludge (lb./day) = 104.2 x 0.52

= 54.2 pounds per day

The second phase of the treatment, endogenous

respiration, depends not only on the supply of

oxygen but also on the total quantity of seed

sludge present in the tank. Theoretically, excesssludge disposal facilities would be mmecessary if

endogenous respiration could be used to burn up

the exact amount of sludge formed in the system

from new waste. In practice, this means that

conditions may be established to minimize excess

sludge accumulation and yet retain sufficient seed

for proper operation of the process.

Since it is possible to provide conditions in

which the sludge will consume itself at a rate of 1

percent per hour, or about l^S percent for 20

hours of aeration, the new sludge formed is used

to represent l-S percent of the seed sludge in the

tank.

(e) EQUILIBRIUM SLUDGE WEIGHT

/lOO

V 18 X new sludge j:

54 2

Total sludge Ob.) = Q-Yg

=300 pounds

(J) HOURLY OXYGEN REQUIREMENT—

ENDOC;ENOUS PHASE (seed shKkc x 1 pct. X

1.44 1b.):

Oxygen (lb./hour) = 300 X 0.01 X 1.44

=4.32 pounds per hour

xlsSIMILATION PHASE

a of total for 8-lu\ influcnt j:

Oxygen (lb./hr.)=^

= 5.86 pounds per hour

TOTAL OXYGEN (sum of two results):

Oxygen (Ib./hr.) =4.32+ 5.86

= 10.18 pounds per hour

This hourly oxygen requirement is needed

during the assimilation of the raw waste to maintain aerobic conditions. The oxygen required

during the rest of the 20-hour aeration period

will be the amount needed for endogenous resphation only, 4.32 pounds per hour.

Figure 1 shows the pounds of oxygen required

per hour for different amounts of waste solids

treated per day over a total aeration period of 20

hours while the wastes are received for 8 hours.

a:

UJ

o

UJ

o:

3

o

lAJ

a:

UJ

o

X

o

400

Fir.UKE 1.—Relation between waste received i)er day and

oxygen required per hour. Waste received tor »

hours; aeration continued 20 hours.
AGR. HANDBOOK 176, U.S. DEPT. OF AGRICULTURE

TANK SIZE

When the fiU-and-draw method of treatment

is used, the size of the tank must be large enough

to hold the anticipated waste volume with adequate freeboard, the settled sludge volume, and

an additional liquid layer at least 2 feet in

depth above the sludge to allow removal of the

clear, treated effluent with minimum entrainment

of sludge. In practice, a total liquid depth of

about 8 feet has given good results. The freeboard above the waterline recommended for a

tank of this kind is usually 1 foot or more, so

that an emergency overflow drain can be installed

to control the liquid in case of accidental flooding

or excessive foaming.

The first step in determining the size of the

tank is calculating the volume of the seed sludge

and the working volume of the tank.

(a) SEED SLUDGE VOLUME (dry weight X 6

gal./lb.):

Sludge volume (gal.) = 300X6

= 1,800 gallons

or=240 cubic feet

(b) WORKING VOLUME (sum of waste+sludge) :

Volume (gal.) = 10,000+1,800

= 11,800 gaUons

Volume (cu. ft.) = 1,333 +240

= 1,573 cubic feet

The working volume does not include the 2

feet vertical distance between the top of the

settled sludge and the clear effluent drain required to prevent discharging slower settling

sludge particles. The working depth is obtained

by subtracting the 2 feet distance from the

total liquid depth. ,. . , , ^ i •

(c) AREA OF TANK (volume divided by working

depth) :

Area (sq. lt.j=—^

=262 square feet

A cylindrical tank of 18.3 feet diameter, or a

rectangular tank 12 feet by 21.9 feet, would be

satisfactory. The shape of the tank is not

critical, but the tank and equipment must be

adapted to each other.

Figure 2 shows the space required in the tank.

U967 GAL. FREEB0AR.2 ii? Z.TL.

10,000 GAL. MILK WASTE 5.1 FT.

3,933 GAL. SETTLING SPACE

"I,SQOALT "^ETTCED"^LDDÛ"

2.0 FT.

"5.9"Ff"

^'/;y^^^yyy/^^^y^^yyyy/y^^^^y^y//y}/y^//^'777'A

9.0

FT

FIGURE 2.—Diagram of a tank to treat 10,000 gallons of

waste per day by fill-and-draw method.

The settled sludge volume of 1,800 gallons will

occupy 0.9 foot of the 2.9 feet settling space,

allowing the 2 feet distance required to prevent

discharge of sludge particles; and the 10,000

gallons waste will take 5.1 feet. The total

liquid height of 8 feet is equal in this case to a

total liquid volume of 15,733 gallons. Allowing

1 foot freeboard, the minimum tank capacityshould be 17,700 gallons. It is advisable to use a

tank of 20,000-gallon capacity as this allows a

safety margin of approximately 25 percent.

SELECTION OF AERATION DEVICE

The next problem is to make oxygen available

in the sludge-waste mixture at the rates required

by the bacteria. Experimental studies showed

that the amounts of oxygen dissolved in water

solutions from the atmosphere varied greatly for

different aeration devices (13). A pipe with rows

of holes allowing air to be bubbled through the

liquid gave 1 to 2 percent transfer efñciency. An

efficiency of 25 percent was obtained for an ejector

(Penberthy,^ model XL-96 design, size 7A,

steam) with a pump that forced the waste liquid

through it at a rate of 60 gallons per minute.

Atmospheric ah' entered the liquid via the suction

connection of the ejector by means of pipe extend3 It is not implied the U.S. Department of Agriculture

recommends the above company or its product to the

possible exclusion of others in the same business.

ing above the liquid level. Under these conditions,

1.6 pounds of oxygen were dissolved per hour.

When air was delivered under a pressure of 6

pounds per square inch (p.s.i.) to the ejector air

intake, oxygen went into solution at the rate of

2.4 pounds per hour.

All possible aeration methods and devices have

not been investigated. Under the conditions

studied, the ejector described was consistently

capable of dissolving oxygen rapidly enough for

the bacterial demand with an excess concentration

of 0.3 to 0.5 part per million. These ejectors can

maintain sludge in suspension despite variations

in the depth of submergence. The ejectors also

break up bacterial clumps thoroughly and expose

more bacterial surface to the oxygen supply. (See

Appendix, ''Ejectors as Aeration Devices.'^
DAIRY WASTE TREATMENT BY AERATION

NUMBER OF EJECTORS

To assist ill rapidly deterniiiiing the luiinber of

size 7A ejectors and other essential factors for a

dairy waste treatment unit, the calculations have

been condensed hito tabular form (table 1).

The hourly oxygen requirements of the seed

sludge have been added to the assimilation needs

to give the maximum oxygen demand (col 7).

This has been converted to the number of ejectors

by dividing by the factor of 1.6 pounds per hour

per ejector and rounded to the next hio-her unit

(col. 8).

In the example treating a dailv waste load of

10,000 gallons (125 pounds COD), the 10.2 pounds

of oxygen can be readily supplied by 7 ejectors.

The 4.3 pounds of oxygen per hour tx) satisfy the

seed sludge can be supplied by 3 ejectors operating

at full pressure. However, the same requirements

can be fulfilled by using all 7 ejectors at reduced

pressure. (See Appendix, p. 19.)

TABLE 1.—The numhr of (jedors {size 7A)

needed^ the oxygen required, the sludge produced,

and the seed sludge necessary for various waste

loads in a batch operation that operates 8 hours a

day

Waste,

COD

Oxygen for

assimilation New

sludge

Seed

sludííe

required

Oxygen

for seed

sludge

Maximum

oxygen

Ejectors

needed

Total Per hour

(1) (2) (3) (4) (5) (6) (7) (8)

Lb./(lay

25

Lb.

9. 4

Lb.

1. 2

Lb.I(hill

10. 9

Lb.

60. 5

Lb./hr.

0.8

Lb./hr.

2. 0

Number

50 18. 8 2.3 21. 7 120. 6 1. 6 3. 9 3

100 37. 5 4. 7 43. 4 241. 1 3. 1 7. 8 0

150 56. 3 7. 0 65. 1 361. 7 4. 6 11. 6 8

200 75. 0 9. 4 86. 8 482. 2 6. 3 15. 7 10

300 112. 5 14. 1 130. 2 723. 3 9.4 23. 5 15

400 150. 0 18. 8 173. 6 964. 4 12. 5 31. 3 20

DESIGN OF PLANT

The information developed by following the

calculations in the preceding sections should now

be used to design the treatment unit. Preliminary

sketches should be made to help \dsualize the size

and location of tlie tank, the arrangement of

ejectors, piping, pumps, and influent and effluent

lines. These sketches should be developed to the

point where construction costs, simplicity of operation, and maintenance costs can be estimated.

Several schemes should be evaluated before the

final plan is adopted.

For instance, it will be assumed that the example of 10,000 gallons is to be treated by a batch

process. It has also been assumed that the two

rates of oxidation are to be provided by separate

pumps, one for the high rate and one for the low

rate. In cases wliere ample area and slope of

terrain are available, a design such as shown in

figure 3 would fit the treatment needs. The illustration shows eight ejectors to allow for plant

expansion, although only seven are needed for the

example. It also contains only one pump, whereas

the text recommends two. Several other details

have been omitted for the sake of clarity, such as a

catwalk for servicing the ejectors, safety handrails,

and screens on the ejector air inlets. Conditions

at the building site will frequently suggest modifications of the design shown in figure 3.

The principal aim of the waste treatment plant

design is to coordinate the shape of the tank with

the arrangement of the ejectors. The discharge

of the ejectors should give a sweeping action to the

entire contents of the tank to prevent dead pockets and to maintain the sludge in suspension.

Pump inlets should be placed to avoid ''short

circuits'' within the tank.

Other factors related to the overall design of tlie

plant should include a consideration of materials

or equipment readily available at the dairy and

exclude the use of construction items difficult to

procure. The designer will find the sections on

"Operation of Single-Tank Batch Method,"

'Tumps and Piping," and "Construction" of interest. Visiting existing installations will be

extremely helpful.

One practical item should not be overlooked.

This is the need for screening the waste just before

it enters the treatment tank to remove bottle

caps, wires, or other objects tliat may damage the

pumps or clog the ejectors. Screening should be

one-fourth-inch mesh and liave ample area. The

screen is usually placed at the entrance to tlu^ tank

adjacent to a small sump where sand and grit are

settled out of the waste.

A second item that is beneficial is a small pond

for receiving the treated effluent and holding it

for final polishing. The pond may be stocked with

fisli, whicli will show good growth as testimony

to the purity of the discharged effluent. The

pond will also trap any sludge that may occasionally become entrained in the effluent.

in the case of a dairy that discharges a small

quantity of waste, it is possible to use simple

equipment and procedures and yet provide proper

waste treatment. The plant sliown in figure 4,

which was designed for 5,000 gallons daily, uses

four ejectors operated l)y a single pump. Here

economy of construction and simplicity of operation led to tlie choice of a single pump witli a

10-horsepowei- motor, which is adequate ior

assimilation. The same pump is USCHI duringendogenous respiration, because a (wo-punip
6

pumpAGR. HANDBOOK 176, U.S. DEPT. OF AGRICULTURE

.dairy waste inlet

FIGURE 3.—Typical batch-type dairy waste treatment plant.

-dairy waste inlet

punnp motor

steel support

for pump

reinforcing bars

%"diam.J6"centej::s

concrete slab

water line

—tank built of

cinder block

or concrete

emergency drain

size 7A,model XL-96 ejectors^ -clear effluent drain

FIGURE 4.—Arrangement for a small dairy waste treatment plant that handles 5,000 gallons daily.
DAIRY WASTE TREATMENT BY AERATION

system would have been more expensive to

install. The simplicity of this design, however,

has led to difficulty in maintaining the ejectors

and pump, since repairs must be made after

draining the tank. The arrangement would be

better if, along with other improvements, a hoist

could be provided to lift the pump and ejectors

clear of the tank.

In larger aeration units, it is desirable to use at

least two pumps. One pump can be in continual

operation and supply the relatively small quantity

of air required for sludge burnup. The second

pump would also be running during assimilation,

so that the two pumps together would provide

the maximum amount of oxygen. Or the second

pump may be used to furnish the entire amount

of air needed during the assimilation phase.

In the disposal unit shown in figure 5, two

pumps each deliver 900 gallons of hquid per minute

for tlie assimilation phase. Then for the endogenous phase, only one pump is used to supply

tlie 24 ejectors by means of the cross-connection

at the far end of the manifolds. This is shown on

the right in figure 5.

Another detail of interest in this figure is the

design of the two cylindrical screens that protect

the pump suction. The extension of the top of

these screens to a level higher than the waterhne

not only increases their area but makes them

easy to inspect and clean.

The protection of the air intakes for the ejectors

at this treatment plant should also be mentioned.

The location of each ejector can be identified by

the two pipes connected to it (fig. 5). One pipe

IS connected to the larger pipe manifold; this is

the liquid connection to the ejector. The other

pipe of eacli group of two connects the air intake

of the submerged ejector witli the atmosphere.

The entrance of these air intakes is filled with a

screen of one-half-inch mesh hardware cloth.

The suction created here is powerful enough to

draw small birds, leaves, and other debris into

the pipe and to cause clogging of the piping or

ejectors. The notch in the cinderblock wall at

the far side of the tank is used to control accidental

flooding by directing the overflow into a small

lagoon.

Not discernible in the photograph is the healthy

color of the aerated sludge and waste. A properly

operating plant will usually develop a light-brown

or pinkish-colored sludge.

OPERATION OF SINGLE-TANK BATCH METHOD

The operation of a treatment plant can be quite

simple when the equipment and sludge bed are in

good condition. As the waste from the dairy

begins to enter the tank, the full aeration system

is turned on. To insure that all fresh organic

matter is assimilated, aeration continues while the

waste is being received and for an additional hour

or two. When the waste has been assimilated,

the pump is shut off, and the sludge is allowed to

settle. In a normally operating treatment unit,

settling is usually complete within 2 hours. The

clarified water above the sludge can then be

discharged through the clear effluent drain. In

the drawing in figure 2, this drain was placed 2.9

feet above the tank bottom, or 2 feet above the

settled layer of sludge. After draining has been

completed, the drain valve is closed. The aeration

system is again started and run for the remainder

of the 24 hours at a rate adequate for endogenous

respiration. The cycle of daily operation is again

initiated at the start of the next workday by

raising the aeration rate to fuU capacity as soon as

wastes enter from the dairy.

It can be seen from the above outline that a

normally operating plant would require only four

short periods of attention. It is suggested that

the cost of automatic operation for all or part of

the system be investigated.

In starting a new waste treatment plant, time is

required to accumulate the calculated equilibrium

sludge quantity. A severe lack of seed sludge

will slow down the assimilation rate, making

longer aeration necessary. Some operators have

added a quantity of sludge from another aeration

system or washings from a rich garden soil to

accelerate sludge buildup. This is probably unnecessary, because the average treatment system

offers excellent food and environment for bacterial

multiplication.

Some control can be exercised over the size of

the seedbed by varying the time and rate of

aeration for endogenous respiration. The success

of the treatment, however, depends on providing

the correct environment for the sludge. Careful

measurements in the pilot plant verified the possibility of a rate as high as 1.25 percent per hour

for seed sludge burnup. Average conditions easily

produced a burnup rate of 1 percent per hour.

Keports of plants in operation tell of total daily

rates as low as 5 percent and as high as 25 percent.

A type of treatment described as total oxidation

is based entirely on successful endogenous respiration {15,21),

If excessive sludge accumulates in the system

despite the operator's efforts, it will require

removal. As the sludge from this type system is

well aerated, it is practically odorless, but because

it is a mixture of bacterial cells, some care should

be exercised in its disposal. In its diluted state,

the sludge may be readily pumped and safely

spread on an uncultivated field. In a solid or

semisolid state, it is more difficult to handle, but

can be transported, dried, and disposed of by

methods simüar to those used in municipal plants.

538411—60-
8 AGR. HANDBOOK 176, U.S. DEPT. OF AGRICULTURE
DAIRY WASTE TREATMENT BY AERATIOX 9

If insufficient sludge is present and less aeration

is needed, it is suggested that a program of short

aeration periods alternating with long resting

periods be followed. Sludge in good condition

can rest 6 hours without deleterious effects if it

is then aerated for approximately ji hour. It is

not known how much longer sludge in this type

system can remain aerobic without a fresh o\\ygen

supply.

Operating difficulties will eventually be encountered as with all mechanical contraptions.

Pump impellers and ejector water jets will show

signs of wear when the waste contains much gritty

material. Measuring the velocity of the air flowing into the ejector intakes can be used as a check

on the performance of the ejectors and pumps.

Precise measurement in terms of the volume of

air is not so important in this case as employing

a measmdng device that will give repeatable results with which later measurements can be compared. When low entrance-air velocity is discovered, the cause should be investigated and corrected if the plant is to be kept in top condition.

The correction of other difficuhies, such as excessive foaming and low tempérâtlue wastes, have

been discussed in separate sections.

USE OF AIR UNDER PRESSURE

When the quantity or strength of waste is high,

it may be advantageous to supply air under slight

pressure to assist the ejectors. À fewer number of

ejectors and a smaller recirculating pump would

then be needed. The stud}^ showed that when

compressed air was supplied to the air intake of

the ejector (size 7A) at 6 pounds per square inch,

the rate of dissolving oxygen was increased b}^ 50

percent. Under such conditions, even though

more oxygen was forced into solution, the efficiency of the ejector is not so high as when it is

drawing ah' at atmospheric pressure. The quantity of ah' passing through the device was doubled

in order to dissolve 50 percent more oxygen.

Fm'ther increases in air pressure gave insignificant

increase in oxygen-dissolving ability.

By using air under pressure, the increased

oxygen-dissolving capacity of ejectors ma}^ be

used to improve existing plants where dairy operations have expanded and treatment for additional waste is needed.

CONTINUOUS-PROCESS TREATMENT PLANT

The biological principles of continuous treatment are identical with those of a batch process,

but the continuous process poses design problems

not encountered in batch treatment (5). These

include necessary settling space and time to give

a clear effluent; sufficient aeration for proper

assimilation ; space for endogenous respiration ; and

means of returning seed sludge to the assimilation

area. Each problem must be successfully solved

for the continuous treatment plant to work satisfactorily. Figure 6 presents a schematic diagram

in which air is suppKed under pressure for a

theoretical continuous process. If a continuousprocess treatment plant is contemplated, a competent sanitary engineer should be employed

who understands the biochemistry of milk waste

disposal.

Many arrangements have been used for continuous-flow milk waste treatment. One type

combines all aeration with flow equalization in the

first tank. A second tank is used for setthng.

This type of operation returns all sludge to the

first tank, and flow rates are adjusted to provide

for assimilation and sludge burnup concurrently

(9). Variations of this arrangement have used a

separate flow equalization tank, or provided for

occasional or regular sludge removal. Where the

treatment plant depended on regular removal,

the sludge was directed to a sandbed or digester

or was spread on a field. A different treatment

approach is mentioned (5), wherein the sludge is

separated from the water inmiediately after assimilation and is oxidized in the form of a concentrate.

Theoretically, the ideal system provides adequate sludge for rapid assimilation, limits the

quantity to be settled, and provides sufficient return sludge for endogenous respiration to destroy

the exact weight of sludge produced from the incoming waste. Removal of excess sludge would

be minimized, and yet an adequate seeding would

be assured. The following general discussion

shows steps in designing a unit.

Again, the first step is to know the quantity of

waste and its concentration. In order to give a

concrete example, a rate of flow of 1,200 gallons

per hour and a concentration of 1,600 p.p.m.

COD will be assumed.

(a) TOTAL OXYGEN REQUIRED:

Total oxygen (lb.)

1,200 gal.Air.X8.34 Ib./gal.X 1,600 p.p.m.

~ 1,000,000

= 16 pounds oxygen per hour

Following the example of batch treatment calculations, it will be seen that 6 pounds per liour

(37.5 percent) of oxygen are needed for assimilation. This can be suppHed by 4 ejectors, each

dissolving 1.6 pounds of oxygen per hour.

The problem of endogenous respiration can yield
10 AGR. HANDBOOK 176, U.S. DEPT. OF AGRICULTURE

^dairy waste inlet

water air water

pumps

.baffles

assi milat ion

area

^

endogenous

r espi ration

area

<f clear effluent

to natural

drainage

settling

area

V

J). sludge return

pump suction

FIGURE 6.—Schematic diagram of continuous-process dair}^ waste treatment.

to a wide latitude of treatment plant designs.

Where space is limited, the tank area for endogenous respiration may be made quite small by

selecting a short retention time. In such cases,

an enormous quantity of seed sludge must be

continually settled, returned, and mixed with the

influent. The limiting factors for long periods of

retention are the large tank size and insufíicient

sludge to satisfy rapid assimilation. (See par. (5),

p. 2.)

To select a reasonable retention time, the new

sludge production must be known. The hourly

production of sludge is obtained by taking 52 percent of the incoming waste solids (equal to the

total COD divided by 1.2).

(&) NEW SLUDGE:

New sludge (lb./hr.) =

16X0.52

1.2

=6.92 pounds sludge per hour

The period of retention will undoubtedly be

governed by local circumstances and the personal

preference of the designer. The calculations will

be here demonstrated for 12 hours. At the established rate of 1 percent per hour, 12-hour retention will consume approximately 10 percent of the

seed sludge, which means that 10 times the weight

of sludge to be oxidized must be present at the

entrance. The minimum quantity of sludge to be

settled and returned to the entrance of the endogenous area will be the difference between the total

required and the new sludge production.

(c) RETURNED

sludge) :

Returned sludge (lb./hr.) =69.2

SLUDGE (total sludge—new

6.9

62.3 pounds per hour

V The volume of this sludge will not be subject

to exact prediction because of variation in nature

of the sludge and the operation of the settling

tank. Equipment for returnmg sludge to the head

of the endogenous chamber should handle at least

double the ^'well-settled^' volume (see par. (8)

p. 2) of this amount of sludge.

Air requirements for the endogenous phase may

be calculated in the same way as for a batch treatment unit. In the continuous operation plant,

however, some excess air should be provided to

insure that the sludge is well aerated when it

enters the settlement tank.

{d) OXYGEN FOR SLUDGE BURNUP (total sludge

weightXl pet. per hr.Xl.44):

Oxygen (lb./hr.) =69.2X0.01X1.44

=0.996 pound per hour

In this example it was shown above that the

immediate assimilation of waste required 6 pounds

of oxygen per hour. To this figure is added the

oxygen needed for burning up the recirculating

sludge at a rate producing equilibrium. The total

requirement then is 7 pounds per hour.

Two properties of the continuous system should

be pointed out. The controlled return of a large

amount of sludge makes the assimilation of a new
DAIRY WASTE TREATMENT BY AERATIO:; 11

waste material practically instantaneous; as a re-

^It, a separate tank for this phase is unnecessary.

The second property of the process is that the

endogenous activity of sludge continues during

settlement. The rate of activity mav not be as

high as 1 percent per hour, since no^ aeration is

used during settlement.

The remaining step in the continuous treatment

is that of clarification of the effluent in a settling

chamber. Design of this chamber mav be based

on measurements taken during the experimental

studies, which showed that bacterial cells from

milk waste settled at a rate of 2 to 8 feet per hour,

depending on the concentration. This is equal to

a surface loading of 15 to 60 gallons per hour per

square foot of surface (360 to 1,440 gallons per

day per square foot). An empirical formula was

developed from the pilot plant data relating the

settlmg rate (7?, as feet per hour) with the sludge

cell concentration (parts per million).

^_10,240-p.p.m.

950 (2)

The sludge concentration in the continuous

process example is calculated in parts per million

from the weight of sludge divided by the weight of

liquid entering the settling tank on an hourly basis

according to the following formula :

n ^ ^- / ^ ^X1,000,000 ,^, Concentration (p.p.m.)^^^^^,^^^^^^ (3)

^4=weight of sludge (lb.)

5=influent volume (gal.)

6 —return sludge volume (gal.)

(weight of sludge, lb.X6 gal./lb.)

(e) SLUDGE CONCENTRATION (b}^ formula 3):

62.3X1,000,000 Concentration (p .p .m. ) =

(1,200 +374) X8.34

= 4,746 parts per million

In this example the theoretical figure for return

sludge volume has been given. In practice, the

capacity of the sludge return equipment should

be used.

(/) SETTLING RATE (by formula 2):

p_ 10,240-4,746

950

= 5.8 feet per hour

=43.35 gallons per hour per square foot

(g) SETTLING AREA (total gallons^rate) :

=36.33 square feet

This is the theoretically correct value, subject

to increase by the engineer in light of his experience

with settlement tanks.

Attention must also be given to the inlet and

outlet of the settlement basin. The velocity of

the liquid at the entrance must not exceed 1 foot

per second, or the liquid will have a tendency to

remain in a solid stream, disturb the settling,,

and cause turbulence in the chamber.

At the outlet of the settlement basin the usual

practice is to provide a baffle under which aU

water must flow, then a weir over which the clear

water flows into a trough for collecting and discharging. The present accepted practice in the

design of outlet weirs is to limit the discharge to

5 gallons per minute (or 300 gallons per hour) for

each foot of weir length. The rate of overflow

will be the same as the rate at which the waste

enters the treatment plant, and, in this case, will

require 4 lineal feet of overflow weir. Many

designers retard the liquid movement at the

entrance and exit by means of baffles, divider

partitions, or piping, but areas occupied b}^ these

devices should not be considered part of the

settling area.

One further detail is necessary. In the experimental work, cells forming the sludge have a

tendency to cling together and become difficult

to move once the}^ become compacted. For this

reason, some mechanical means should be provided

to scrape the sludge slowly toward the sludge

return pump suction if the settling tank has a flat

bottom.

PUMPS AND PIPING

As the waste treatment system will be an

essential and continuing part of dair}^ plant operations, reliability is a most important factor to

consider when planning the system. For instance,

the pumping requirements may be provided by

using two pumps. This may not be feasible for

a small system, but a spare pump is desirable.

The plans may provide for the future addition of

a second pump by the proper placement of tees or

other fittings. After a year or two of operation,

a review of the waste treatment program may

show that a somewhat larger capacity is needed.

At this time, a larger pump may be instaUed

and the original pump reserved as a spare. The
12 AGR. HANDBOOK 176, U.S. DEPT. OF AGRICULTURE

new pump may be designed to operate the same

size and number of ejectors at a higher operating

pressure and higher rate of flow, in order to satisfy

the increased oxygen requirements. Other alternatives may be to use the new pump for the assimilation phase and the old pump for the endogenous phase ; or the two pumps may be used together

for assimilation, with only one used for the endogenous phase.

The first step in selecting a pump is to sketch

out a piping diagram, such as figure 7, to fit the

size and shape of the tank that has been selected.

Figure 7 provides branches for 8 ejectors instead

of the 7 calculated to be necessary for the 10,000-

gallon example. This illustrates the suggestion

that the original layout should provide definite

steps for future expansion.

A good pipe layout is as simple and direct as

possible. It provides a system that may be

completely drained, and it has enougli valves for

isolation of any unit that may need repairs while

the rest of the system continues to operate.

Unions on small pipes and bolted flanges on larger

pipes should also be used to facilitate necessary

repairs.

Once the general idea of the piping is sketched,

showing the proposed dimensions, sizes, and flows,

the frictional pressure losses are determined.

This is done with the aid of information and tables

usually found in the general catalog of plumbing

supply companies or in standard engineering

handbooks, (^dculations need be made only for

the ejector that is farthest from the pump.

A summary of typical pipe friction losses is

given in table 2, based on the arrangement shown

in figure 7, for the treatment plant. The fittings

have been converted to equivalent lengths of

straight pipe, using the factors from the chart in

the catalog of Crane and Company (4). Velocities

and losses per 100 feet are from the same source.

The equivalent length method is suggested because

it is widely available and easy to follow. For the

more exact determination of pressure losses in

large complicated systems, it is recommended that

the method using losses as a percentage of velocity

pressure be followed. Tliis is available in standard

mechanical engineering texts. The resistance to

flow is the sum of all the effects in the series of

pipes, fittings, and devices that the pump must

overcome in the system to produce the desired flow

O

^.-¿ «><^^ •e'!;¡odi«> "^

0.¡«^

^screen

,6" diam.

suction pipe

6x6x6 tee

8 ejectors

60 g.p.m. each

vs- 34 p.s.lPump selection:

480 gpm vs 39psi.

(90 feet of head)

FIGURE 7.—Sketch of piping diagram for a treatment^plant'to handle 10,000 gallons of waste per day.
DAIRY WASTE TREATMENT BY AERATION 13

TABLE 2.~GalcuLation of pipe friction for a plant handling 10,000 gallons of dairy waste per day

Description

Suction piping

Entrance loss (abrupt)

6-inch pipe, 14 feet long

Elbows, 3, total

Valve, open

Tee, run

Flow

Discharge piping

4-inch pipe nipple

4-inch gate valve, open

4x6 increaser

6-inch pipe, 17 feet long

6-inch elbows, 2, total

6-inch run of tee

6-inch pipe, 5 feet long

Cross

6-inch pipe, 5 feet long

Cross

6-inch pipe, 5 feet long

Cross

2-inch side outlet, cross

2-inch pipe, 10 feet long

2-inch els, 2, total

2-inch gate valve, open

G.p.m.

480

480

480

480

480

480

480

480

480

480

480

360

360

240

240

120

120

60

60

60

60

Velocity

Equivalent length

Part

Ff.fsec.

5.

5.

5.

5.

5. 3

12. 0

12. 0

12. 0

5. 3

5. 3

5. 3

4. 3

4. 3

2.

2.

1.

1.

5.

5. 7

5. 7

5. 7

Feet

Total

Feet

Pressure losses

Per 100 feet Per ite

61

17

17

17

30

P.s.i.

0. 66

. 66

5. 17 !

. 66

.384

. 182

. 036

2. 96

P.s.i.

0. 059

Total '

0. 059

.515 .574

. 310 .310

. 403 . 713

. 065 . 778

. 031 .809

. 006 . 815

. 888 1. 703

1 Discharge, total 1 703

Suction, total .574

2. 277

Pressure used at ejector 34, 0

Total pumping head, p.s.i 36 277

Feet of head = 36.277X2.311 = 83.84 feet.

of liquid through the last ejector. As the routes

to the other ejectors are shorter, they offer slightly

less resistance. During operation, slight throttling

at the 2-inch valves in the lines to the ejectors

with shorter runs mav be necessary if perfect

balance of output is to be achieved.

Once the frictional losses are determined and

the design of the s^^stem is found satisfactory,

the pump is selected. With each of the size 7A

ejectors delivering 60 gallons of flow per minute

at 34 pounds per square inch pressure at the

nozzle, the pump selected from data obtained

in table 2 should delivery 480 gallons per minute

against a head of 90 feet. Preferably, it should

be a ball-bearing type with a speed of not more

than 1,750 r.p.m. It should be a double-suction

type with a stainless steel shaft and split glands,

if it is to have a long life and be easy to maintain.

The pump should also be set low enough to keep

the suction piping flooded at all times. Further

details, advantages, and economies of pump

selection should be discussed with the representative of the pump manufacturer.

One thing should be categorically stated: the

electric motor driving the pump should be

guaranteed not to be overloaded under normal

operating conditions. Good pump and motor

installation requires that the electric motors be

operated at the highest usable voltage at the

plant, be properly protected by overload devices,

and that 3-phase current be used on motors of

1 horsepower or larger. The motors should be

rated for continuous duty and preferably be

totally enclosed.

CONSTRUCTION OF TREATMENT PLANT

A desirable site for the treatment plant must be

selected and surveyed to assure enough difference

of elevation from the dairy to the treatment plant

and from the treatment plant to the receiving

stream. Most State regulations requh^e a minimum fall in drain piping of 0.4 foot per 100 feet.

If sufficient drop to the tank from the drain outlet

is not available for gravity drainage, the waste

can run into a sump pit and be pumped into the

treatment tank.

The cvlindrical tank shown in figure 4 for handling 5,000 gallons of waste may be constructed
14 AGR. HANDBOOK 17 6, U.S. DEPT. OF AGRICULTURE

economically of cinder-concrete blocks. It would

be desirable, though not necessary, to allow 6 feet

of the tank to be below ground with about 3 feet

above ground. This would provide lateral support, allow for easy observation of the tank contents, provide insulation against low temperatures,

permit ready cleaning of the inlet strainer, allow

accessibility to the effluent drain, and create less

difficulty in raising the motor.

Specifications for such a cinder-block tank

should give finished dimensions and type of reinforcing, define mortar used (2)^ parts sand; 1 part

cement; no lime), and require cement dashing and

hot asphalt waterproofing on the inside surfaces.

Worlnnanship, material for electric wiring, plumbing, and any special conditions should also be

specified. Attention must be given to details of

good construction. Those outlined here may not

apply to tanks of other sizes or shapes, but are

included to indicate that a high level of workmanship quality should be incorporated in building the

system to provide a long trouble-free life.

The base slab of concrete should extend beyond

the walls of the tank to serve as a footing. A

concrete slab that has a wall resting on its edge

should be reinforced. The round tank selected

as an example would have a bottom slab 7 inches

thick and be strengthened with reinforcing bars,

Yo inch in diameter, placed 6 inches on centers.

Two complete sets of bars would be installed

perpendicular to each other and protected by 3

inches of concrete above, below, and at the edge.

In constructing tank walls, the pressure of liquid

must be taken into consideration. The greatest

pressure on the finished wall is at the bottom;

hence, vertical bars for the walls must be well

anchored in the base slab. The use of separate

pieces of rod 4 feet long, bent at right angles in

the middle, is recommended. These are wired to

the slab reinforcing before the slab is poured, with

half the bar placed upright at the correct location

to fit the cinder-block courses. The vertical rods

for the wall are securely wired to the short rods

with a 15-inch lap. Although many details concerning concrete are found in the ''Building Code

Requirements for Reinforced Concrete'' (i), expert engineering advice should be obtained for all

but the simplest structures.

The wall should be as heavy as possible to assure the greatest stability when subjected to

var3âng horizontal pressures as in a dairy waste

treatment tank. Weight is provided by using as

many solid cement blocks as possible in constructing the tank. Alternate courses could be made of

solid and hollow blocks. The vertical rods may

pass between the ends of solid blocks in one set

of courses and through the center of hollow

blocks on the alternate courses, which are then

filled with well-tamped mortar. Filling the

cells bonds the rods and cement work together

and adds to the stabilit}^ of the wall by making

it heavier.

Rectangular tanks may also be built of cinderconcrete blocks, if ample buttressing is provided.

Thus, a typical block wall, 8 inches thick, may be

used if distances between buttresses or piers are

short; i.e., not over 10 feet. Piers must be heavy

and the wall must be weU reinforced to withstand

the water pressure acting horizontally when the

tank is full and the earth pressure when the tank

is empty.

Flexibility must be provided at the joints where

pipes pass tlirough the wall of the tank. A separate sleeve of cast iron or asbestos-cement pipe

should be placed in the waU as the masonry is

laid. This should allow at least one-fourth inch

all around the futm^e pipe to be installed. After

the wall is waterproofed, the piping is installed

through the sleeve and packed with oakum and

flexible calking compound.

COST ESTIMATES

Costs of installing dairy waste treatment plants

vary widely. Installation of the rapid-aeration

units have cost about one-third of the more

elaborate multiple-unit methods of waste treatment (^S). Tanks and equipment available at

the site have also been used to reduce the cost of

small units.

The batch process, in which a single tank is

used for the entire process, is the least costly.

If the dairy is in operation 15 hours or longer,

continuous sedimentation is necessary and an

additional tank or a separate compartment in

the same tank is needed. A chlorinator may be

needed if disinfection is required by the health

authorities. The following construction cost

items are to be considered: (1) Land for the treatment plant; (2) property easements for sewer

lines; (3) electrical power line; (4) pmnping

station; (5) excavation; (6) tank construction;

(7) pump, ejectors, and piping; and, if needed,

(8) sedimentation tank and (9) disinfection tank.

If sufficient land with suitable slope is on hand,

then the bare minimum for cost will be that for

electric power lines, tank construction, pump,

ejectors, and piping, including the repiping of

nonpoUuted waters.

In 1959, the method for the treatment or disposal of milk wastes had not been standardized.

In 1953, a 5-year appraisal of 20 milk products

plants reported wide differences in methods of

treatnaent {23). Some plants took advantage of

municipal sewerage systems and paid rental

charges that amounted to 0.02 to 0.11 cents per

quart of milk handled. In some cases, additional

expenditures for pretreatment were required.

Two elaborate waste-treatment plants using
DAIRY WASTE TREATMENT BY AERATION 15

triclding filters were described later {24), One

was constructed at a cost of $100,000 to treat

500 pounds of BOD daily and operated at an

annual cost of $4,000. Construction costs of the

second plant, treating 325 pounds of BOD, was

$70,000 with an annual operating cost of $2,500.

Several small milk-waste disposal plants of

varied design are in use {9), A simple one-tank

batch method {12) of 25,000-gallon capacity

treats 220 pounds of BOD daily and cost $6,000

in 1954, according to the owner. The engineering

estimate on this plant was $14,000, but the owner

used existing equipment and plant personnel

on the installation and thus effected savings.

An estimate made at the same time for a dairy

receiving 150,000 pounds of milk per day was

$11,000 for installation of a treatment plant, and

power costs were estimated at $16 per da}^ for

the unit.

These 1954 estimates i-epresented minimal costs

at that time and may not have inchided cost of

land, easement rights, and engineering. Estimates

for 1960 will undoubtedly be liigher and will vary

according to local costs of labor and materials.

The 1954 estimates calculate to $70 to $80 per

pound of BOD treated daily, but actual construction costs of $140 per pound of BOD were found

to be the case in the north-central area of this

country the same year.

Although the cost of construction generally increases with the size of the plant, the cost per

pound of waste to be treated shows a decrease. In

very small plants the cost is not proportional to the

smaller quantity of milk handled. A greater allowance is usuall}^ made for future expansion in the

small plant, and thus the treatment plant may be

twice the size necessary for immediate needs. This

may make the initial construction cost high.

CONCLUSIONS

Treatment of dairy waste is being recognized as

an integral part of dairy plant operation. Disposal

of dairy waste by aerobic treatment must follow

recognized principles and proven practices. Treatment costs money. Good housekeeping and elimination of wasteful practices will reduce the waste

and reduce the cost of treatment. This handbook

gives facts, figures, and suggestions that the plant

operator and the sanitary engineer can use. Aeration units that are in operation should be visited

before designing a new plant. The dairy plant

operator should check on the work of the engineer,

know the equipment, and adequately understand

the operation of the treatment plant. He should

also be familiar with the requirements of the local

sanitation code.

LITERATURE CITED

(1) AMERICAN CONCRETE INSTITUTE COMMITTEE 318. (8)

1956. BUILDING CODE REQUIREMENTS FOR REINFORCED CONCRETE (ACI-318-56J. Amer.

Inst. Jour. 27 (Proc. 52): 913-986, illus.

(Title 52-57).

(2) AMERICAN PUBLIC HEALTH ASSOCIATION, INC.

1955. STANDARD METHODS FOR THE EXAMINATION

OF WATER SEWAGE AND INDUSTRIAL WASTES.

Ed. 10. Waverley Press. Baltimore, Md.

(3) CoRMAN, J., TSUCHIYA, H. ÀI., KoEPSELL, H. J., and

others.

1957. OXYGEN ABSORPTION RATES IN LABORATORY

AND PILOT PLANT EQUIPMENT. Appl.

Microbiol. 5: 313-318, illus.

(4) CRANE AND COMPANY.

1949. VALVES, FITTINGS, PIPE, LUBRICATED PIPING.

Catalog 49.

(5) EcKENFELDER, W. W., JR., and O'CONNOR, D. J.

1959. BIO-OXIDATION OF ORGANIC WASTES

THEORY AND DESIGN. Civil Engin. Dept.,

Manhattan College, N. Y. 127 pp., illus.

(6) HOOVER, S. R., JASEWICZ, L., and PORGES, N.

1952. BIOCHEMICAL OXIDATION OF DAIRY WASTES.

IV. ENDOGENOUS RESPIRATION AND STABILITY OF AERATED DAIRY-WASTE SLUDGE.

Sewage and Indus. Wastes 24: 1144-1149.

(7) JASEWICZ, L., and PORGES, N.

1954. BIOCHEMICAL OXIDATION OF DAIRY WASTES.

VI. RELATIONSHIP BETWEEN THE RATE OF

PURIFICATION AND RATE OF OXIDATION AND (14)

GRAPHICAL ESTIMATION OF FIRST ORDER

VELOCITY CONSTANTS. Purdue Univ. Indus.

Waste Conf. Proc. 9: 71-79.

and PORGES, N.

1952. ASSIMILATION OF DAIRY WASTES BY ACTIVATED SLUDGE. II. THE EQUATION OF SYNTHESIS AND RATE OF OXYGEN UTILIZATION.

Sewage and Indus. Wastes 24: 306-312.

(9) HoRTON, J. P., and TREBLER, H. A.

1953. RECENT DEVELOPMENTS IN DESIGN OF SMALL

MILK WASTE DISPOSAL PLANTS. Sewage

and Indus. Wastes 25: 941-949.

(10) JASEWICZ, L., and PORGES, N.

1958. AERATIOiSr OF WHEY WASTES. I. NITROGEN

SUPPLEMENTATION AND SLUDGE OXIDATION.

Sewage and Indus. Wastes 30: 555-561.

(11) KouNTZ, R. R.

1953. DAIRY WASTE TREATMENT PILOT PLANT.

Purdue Univ. Indus. Waste Conf. Proc.

8: 382-386.

(12)

1954. BIG PROBLEM: DAIRY WASTES, STRIKING

SOLUTION: BIO-QXIDATION. Food Engin.

26: 89-90.

(13)

1956. EVALUATING PROPRIETARY AERATIQ^í DEVICES, hi Biological Treatment of Sewage

and Industrial Waste. Aerobic Oxidation.

(McCabe and Eckenfelder, eds.). v. 1,

pp. 212-214. Reinhold Publ. Corp., N. \.

and FORNEY, C., JR.

1958. ACTIVATED SLUDGE TOTAL OXIDATION METABOLISM. Purdue Univ. Indus.

Conf. Proc. 13: 313-320

Waste
16 AGR. HANDBOOK 176, U.S. DEPT. OF AGRICULTURE

(15) McKiNNEY, R. E., SYMONS, J. M., SHIFRIN, W. G.,

and VEZINA, M.

1958. DESIGN AND OPERATION 0,F A COMPLETE

MIXING ACTIVATED SLUDGE SYSTEM. Sewage and Indus. Wastes 30: 287-295.

(16) MILK INDUSTRY FOUNDATION.

1957. MANUAL FOR MILK OPERATORS. Ed. 2.

686 pp., illus. Washington, D.C.

(17) FORGES, N.

1956. WASTE TREATMENT BY OPTIMAL AERATIONTHEORY AND PRACTICE IN DAIRY WASTE

DISPOSAL. Milk and Food Technol. Jour.

19: 34-38.

(18) JASEWICZ, L., and HOOVER, S. R.

1956. SIMPLE METHOD FOR ESTIMATING OXYGEN

VALUE OF WASTES. ludus, Wastes 1:

95-98.

(19) PEPINSKY, J. B., HENDLER, N. C, and

HOOVER, S. R.

1950. BIOCHEMICAL OXIDATION OF DAIRY WASTES.

I. METHODS OF STUDY. Sewage and Indus.

Wastes 22: 318-325.

(20)

(21)

(22)

(23)

(24)

POWERS, T. J. /TT o TD + + A-r.

1949 TREATING SEWAGE. (U.b. latent INO.

2,479,403.) (Aug. 16, 1949).

TAPLESHAY, J. A.

1958 TOTAL OXIDATION OF ORGANIC W^ASTES.

Sewage and Indus. Wastes 30: 652-661,

illus.

TREBLER, H. A., and HARDING, H. G.

1955. EXPERIENCES AND QUESTIONS CONCERNING

AERATION METHODS AS APPLIED TO DAIRY

WASTES. Purdue Univ. Indus. Waste Conf.

Proc. 10: 1-13.

ZACK, S. I.

1953. TREATMENT AND DISPOSAL OF MILK WASTES.

Sewage and Indus. Wastes 25: 177-187,

illus.

1956. TRICKLING FILTER TREATMENT OF WASTES

AT TWO MILK PROCESSING PLANTS. SewagC

and Indus. Wastes 28: 1009-1019.

EURDD PUBLICATIONS

The following publications were published in the course

of laboratory and pilot plant investigations on the biological oxidation of dairy waste by the Eastern Utilization

Research and Development Division.

1949

HOOVER, S. R., and PORGES, N.

TREATMENT OF DAIRY WASTE BY AERATION. II.

CONTINUOUS AERATIO?; STUDIES. Purdue Univ. Indus.

Waste Conf. Proc. 5: 137-144.

PORGES, N., and HOOVER, S. R.

TREATMENT OF DAIRY WASTE BY AERATION. 1.

METHODS OF STUDY. Purdue Univ. Indus. Waste

Conf. Proc. 5: 130-136.

1950

PORGES, N., PEPINSKY, J. B., HENDLER, X. C, and

HOOVER, S. R.

BIOCHEMICAL OXIDATION OF DAIRY WASTES. I.

METHODS OF STUDY. Sewage and Indus. Wastes 22:

318-325, illus.

PEPINSKY, J. B., HENDLER, N. C, and HOOVER,

S. R.

BIOCHEMICAL OXIDATION OF DAIRY WASTES. II.

COMPARATIVE STUDY OF YEASTS. Sewage and Indus.

Wastes 22: 888-892, illus.

1951

HOOVER, S. R., JASEWICZ, L., PEPINSKY, J. B., and

PORGES, N.

ASSIMILATION OF DAIRY WASTE BY ACTIVATED SLUDGE.

Sewage and Indus. Wastes 23: 167-173.

JASEWICZ, L. B., and PORGES, K.

VITAMIN Bi2 IN ACTIVATED SEWAGE SLUDGE. ScieilCe

114: 213.

PEPINSKY, J. B., JASEWICZ, L. and PORGES, K.

AERATION AS A PARTIAL TREATMENT FOR DAIRY

WASTES. Purdue Univ. Indus. Waste Conf. Proc. 6:

313-319.

PEPINSKY, J. B., PORGES, X., and HOOVER, S. R.

APPLICATION OF RAPID CHEMICAL OXYGEN DEMAND

TEST FOR DETERMINING ORGANIC POLLUTIONS. Purdue

Univ. Indus. Waste Conf. Proc. 6: 367-374.

PoRGES, N., PEPINSKY, J. B., and JASEWICZ, L.

FEED YEASTS FROM DAIRY BY-PRODUCTS. Jour. Dairy

Science 34: 615-621.

1952

HOOVER, S. R., JASEWICZ, L., PEPINSKY, J. B., and

PORGES, N.

ACTIVATED SLUDGE AS A SOURCE OF VITAMIN B12 FOR

ANIMAL FEEDS. Scwage and Indus. Wastes 24: 38-44.

JASEWICZ, L., and PORGES, N.

BIOCHEMICAL OXIDATION OF DAIRY WASTES. IV.

ENDOGENOUS RESPIRATION AND STABILITY OF AERATED

DAIRY WASTE SLUDGE. Sewage and Indus. Wastes

24: 1144-1149, Also Purdue Univ. Indus. Waste

Conf. Proc. 7: 541-548.

and PORGES, N.

ASSIMILATION OF DAIRY WASTES BY ACTIVATED

SLUDGE. II. IHE EQUATION OF SYNTHESIS AND RATE

OF OXYGEN UTILIZATION. Sewage and Indus. Wastes

24: 306-312.

and PORGES, X.

TREATMENT OF DAIRY WASTE BY AERATION. U.S. Bur.

Agr. Indus. Chem. AIC 332, 7 pp.

PORGES, X"., JASEWICZ, L., and HOOVER, S. R.

MEASUREMENTS OF CARBON DIOXIDE EVOLUTION

FROM AERATED SLUDGE. SeWage and Indus. W^astes

24: 1091-1097.

PEPINSKY, J. B., JASEWICZ, L., and HOOVER, S. R.

BIOCHEMICAL OXIDATION OF DAIRY WASTES. III.

FAILURE OF SODIUM NITRATE AS A SOURCE OF OXYGEN.

Sewage and Indus. Wastes 24: 874-881. Also

Purdue Univ. Indus. W^aste Conf. Proc. 7: 33-43.

195S

HOOVER, S. R.

BIOCHEMICAL OXIDATION OF DAIRY WASTES. SewagC

and Indus. Wastes 25: 201-206, illus.

— JASEWICZ, L., and PORGES, X"^.

AN INTERPRETATION OF THE B.O.D. TEST IN TERMS

OF ENDOCENOUS RESPIRATION OF BACTERIA. SewagC

and Indus. Wastes 25: 1163-1173.

JASEWICZ, L., PORCES, X"^., and HOOVER, S. R.

BORAX AS A PRESERVATIVE OF DAIRY WAS E FOR THE

B.O.D. TEST. Purdue Univ. Indus. Waste Conf.

Proc. 8: 387-392.

KouNTz, R. R.

DAIRY WASTE TREATMENT PILOT PLANT. Purdue UlliV.

Indus. Waste Conf. Proc. 8: 382-386.

PORGES, X^., JASEWICZ, L., and HOOVER, S. R.

A MICROBIOLOGICAL PROCESS REPORT. AEROBIC

TREATMENT OF DAIRY WASTES. Appl. Microbiol. 1:

262-270.
DAIRY WASTE TREATMENT BY AERATION 17

1954

HOOVER, S. R., JASEWICZ, L., and PORGES, N.

BIOCHEMICAL OXIDATION OF DAIRY WASTES. VI. RELATIONSHIP BETWEEN THE RATE OF PURIFICATION

AND THE RATE OF OXIDATION AND GRAPHICAL ESTIMATION OF FIRST ORDER VELOCITY CONSTANTS. Pui'due

Univ. Indus. Waste Conf. Proc. 9: 71-79.

JASEWICZ, L., and PORGES, N.

THE MAGNETIC OXYGEN ANALYZER IN STUDIES OF

OXYGEN UPTAKE. Water and Sewage Works 101:

81-83.

JASEWICZ, L., and PORGES, N.

MEASUREMENT OF OXYGEN TRANSFER. Instruments

and Automation 27: 774-775.

KouNTZ, R. R.

BIG PROBLEM: DAIRY WASTES. STRIKING SOLUTION:

BIO-OXIDATION. Food Engin. 26: 89-90.

and ViLLFORTH, J. C.

BIOLOGICAL OXIDATION AERATORS. Purdue Unlv.

Indus. Waste Conf. Proc. 9: 53-63.

ViLLFORTH, J. C.

THE VENTURI INJECTOR AS AN AIR DISPERSION DEVICE.

M. S. Thesis, Pa. State University. Dept. Civil

Engin., 46 pp., illus.

1955

KouNTZ, R. R.

DAIRY WASTE TREATMENT. jNIilk and Food Technol.

Jour. 18: 243-245.

PORGES, N.

BIO-OXIDATIVE TREATMENT OF DAIRY WASTES. 3D

Ontario Indus. Waste Conf., 55-61.

SIMPLIFIED DAIRY WASTE. Milk Prod. Jour. 46:

10-11, 54.

PORGES, N.

RAPID BIO-OXIDATION METHOD OF WASTE DISPOSAL.

Amer. Soc. Brewing Chemists Proc. 1955: 56-64,

illus.

JASEWICZ, L., and HOOVER, S. R.

BIOCHEMICAL OXIDATION OF DAIRY WASTES. VII.

PURIFICATION, OXIDATION, SYNTHESIS AND STORAGE.

Purdue Univ. Indus. Waste Conf. Proc. 10: 135-146.

1956

HOOVER, S. R.

TRANSFORMATIONS OF CARBON BY MICRO-ORGANISMS.

Indus, and Engin. Chem. 48: 1419-1420.

JASEWICZ, L., and PORGES, N.

AEROBIC PROCESS FOR TREATMENT OF DAIRY WASTES.

Internatl. Dairy Cong. Proc. 14 (v. 2, pt. 2): 238-242.

JASEWICZ, L., and PORGES, N.

BIOCHEMICAL OXIDATION OF DAIRY WASTES. VI.

ISOLATION AND STUDY OF SLUDGE MICRO-ORGANISMS.

Sewage and Indus. Wastes 28: 1130-1136.

KouNTZ, R. R.

DAIRY WASTE TREATMENT PLANT DESIGN. In Biological Treatment of Sewage and Industrial Wastes.

Aerobic Oxidation (McCabe and Eckenfelder, eds.),

V. 1, pp. 356-359.

EVALUATING PROPRIETARY AERATION DEVICES. In

Biological Treatment of Sewage and Industrial

Wastes. Aerobic Oxidation (McCabe and Eckenfelder, eds.), v. 1, pp. 212-214. Reinhold Publ.

Corp., N.Y.

TOTAL OXIDATION TREATMENT. Purdue Uuiv. InduS.

Waste Conf. Proc. 11: 157-159.

and PoRGES, N. TT a T^ +

DAIRY WASTE TREATMENT BY AERATION. U.b. Uept.

Agr. ARS (EURDD), Agr. Res. Ssrv. 73-16, 8 pp., illus.

WASTE TREATMENT BY OPTIMAL AERATION THEORY

AND PRACTICE IN DAIRY WASTE DISPOSAL. Milk and

Food Technol. Jour. 19: 34-38.

— JASEWICZ, L., and HOOVER, 8. R.

PRINCIPLES OF BIOLOGICAL OXIDATION. In Biological

Treatment of Sewage and Industrial Wastes. Aerobic

Oxidation (McCabe and Eckenfelder, eds.), v. 1, pp.

35-48. Reinhold Publ. Corp., N.Y.

—- JASEWICZ, L., and HOOVER, S. R.

SIMPLE METHOD FOR ESTIMATING OXYGEN VALUE OF

WASTES. Indus. Wastes 1: 95-98, illus.

1957

BEST, C. N.

AIR-DISPERSION SOLUTION IN A VENTURI INJECTOR.

M. S. Thesis. Pa. State Univ. Dept. Civil Engin.,

33 pp. illus.

ECKENFELDER, W. W., JR., and PORGES, N.

MICROBIOLOGICAL PROCESS REPORT. ACTIVITY OF

MICRO-ORGANISMS IN ORGANIC WASTE DISPOSAL. IV.

BIO-CALCULATIONS. Appl. Microbiol. 5: 180-187,

illus.

PORGES, N.

CURRENT STUDIES ON DISPOSAL AND UTILIZATION OF

WHEY. Wash. State Col. Ann. Pacific Northwest

Indus. Waste Conf. Proc. 8: 153-156.

MICROBIOLOGICAL PROCESS REPORT. ACTIVITY OF

MICRO-ORfîANISMS IN ORGANIC WASTE DISPOSAL. I.

INTRODUCTION. Appl. Microbiol. 5: 166.

and JASEWICZ, L.

APPLICATION OF BIOCHEMICAL STUDIES TO DAIRY

WASTE TREATMENT. Wash. State Col. Ann. Pacific

Northwest Indus. Waste Conf. Proc. 8: 51-61, illus.

1958

JASEWICZ, L., and PORGES, N.

AERATION OF WHEY WASTES. I. NITROGEN SUPPLEMENTATION AND SLUDGE OXIDATION. Scwagc and

Indus. Wastes 30: 555-561, illus.

PORGES, N.

DAIRY WASTES: DISPOSAL BY BALANCED BIOCHEMICAL

BIO-OXIDATION. PART 1. Dairv Engineering (London) 75: 255-258, 294-297, illus.

DEVELOPMENTS IN DAIRY WASTE DISPOSAL. Mich.

State Univ., Dairy Engin. Conf. Proc. 6: 92-99.

PRACTICAL APPLICATION OF LABORATORY DATA TO

DAIRY WASTE TREATMENT. Food Techuol. 12: 78-80.

— WASSERMAN, A. E., HOPKINS, W. J., and JASEWICZ,

OXIDATION OF RADIOACTIVE GLUCOSE BY AERATED

SLUDGE. Sewage and Indus. Wastes 30: 776-782,

illus.

1959

PORGES, N.

NEW ASPECTS OF WASTE TREATMENT. Appl. MicrObiol. [In press.]

and JASEWICZ, L.

AERATION OF WHEY WASTES. II. A C.O.D. AND SOLIDS

BALANCE. [In press.]

and JASEWICZ, L.

DAIRY WASTE CAN BE TREATED. [In prCSS.]
18 AGR. HANDBOOK 176, U.S. DEPT. OF AGRICULTURE

APPENDIX

THE COD METHOD

The ox3^gen demand of a waste may be determined by a chemical procediu'e such as given in the

^'Standard Methods" (2) or by other methods.

This chemical oxygen demand (COD) approximates the 20-day or ultimate biological oxygen

demand (BOD) of dairy waste. By use of appropriate factors determined b}^ experimentation, the

5-day BOD of tlie waste can be approximated.

The method is not used to replace the standard

5-da3^ BOD test, but it is of inestimable value in

planl control of waste, as results are obtained in

about 20 minutes. A rapid procedure was used in

these studies made with dairy wastes. Details of

the technique are given here.

Reagents used in the rapid chemical oxidation

method are as follows:

1. Oxidizing agent prepared by adding 2.5

grams of KgCrsOy to a mixture of 500 milliliters of

concentrated H2SO4 and 500 milliliters 85 percent

H3PO4. It is advisable to triturate the dichromate

to a fine powder. Let stand a few days with

occasional shaking until the dichromate is in solution. Filter through glass wool or decant with

care, in order to obtain a clear oxidizing reagent

free of particles.

2. Potassium iodide solution made by dissolving

55.3 grams KI in 200 milliliters water.

3. Standard 0.05 normal sodium thiosulfate

titrating solution prepared by dissolving exactly

12.41 giams Na2S205.5H20 and making up to 1

liter, or by diluting a more concentrated solution to

the desired strength.

4. Starch indicator solution made by dispersing

1 gram of starch in about 25 milliliters water and

adding 75 milliliters boiling water.

The procedure follows:

1. Place exactly 50 milliliters of the dichromate

oxidizing solution in a 500-milliliter Phillips

beaker or Erlenmeyer flask. Twenty-five-milliliter solution has been used also, with proportional

reduction of other reagents and at reduced costs.

2. Add exactly 5 milliliters of the waste sample

to the oxidizing solution. The strength of the

waste should be between 50 and 1,500 p.p.m. If

of more than 1,500 p.p.m., dilute the sample, or

add less and make up with water to give 5

milliliters.

3. Place on hot plate and heat uniformly so that

oxiciizing solution reaches a temperature of 165°

to 170"^ C. in 6 minutes.

4. Remove immediately from heat, place in

water bath, and cool to room temperature.

5. Add 200 milliUters of distilled water and cool

again in water bath.

6. Add 10 milliUters of the potassium iodide

solution and titrate immediately with the standard

0.05 normal thiosulfate solution, adding starch

near the end point. The color change is from dark

blue to pale blue green. Ferroin may also serve as

an indicator {18).

7. Make a blank determination, using 5 milliliters water.

8. The total oxygen demand in parts per million

or milhgrams per liter is equal to 80 times the

difference in titration in milliliters between the

water blank and the sample. If the original waste

was diluted for testing, this must also be taken into

consideration. The calculation follows:

ÖX0.05X8 X1,000=DX80 (4)

D =difference in titration between the blank

and sample ;

0.05 =normality of the thiosulfate;

8 =milligram-oxygen equivalent to 1 milUliter

normal thiosulfate;

5 =volume taken for oxidation;

1,000=conversion value to obtain milligrams

per liter or parts per million.

The result approximates the total or ultimate

amount of oxygen required for the oxidation of the

waste or sample. The proportion of the oxygen

requirement due to sugar or casein can be ascertained by determining the amount of sugar or protein and converting to oxygen demand. Thus, 1

gram of lactose anhydride requires 1.123 grams of

oxygen, while a gram of protein requires about 1.44

grams of oxygen for total oxidation. Likewise, an

estimate of the total sludge weight may be obtained

by multiplying the COD of the sludge by 0.8, as 1

gram of sludge has a COD of about 1.25.

WHEY WASTES

Dairies that produce large quantities of cheese

will find that excess whey in the dairy waste can

cause trouble in the treatment unit. The whey,

which may contain 5 percent solids, can be treated

by biochemical oxidation if a nutrient balance and

aerobic conditions are maintained, but the enormous oxygen demand makes the process costly.

The possibility of returning whey to the farm for

livestock feeding or of converting whey to useful

products should be investigated.

Infrequent inclusion of whey will not harm the

normal dairy waste process, especially when the

quantity of whey solids is small compared to milk

solids. If the rate of whey discharge is not rapid,
DAIRY WASTE TREATMENT BY AERATION 19

there will be enough nitrogen in the whole milk

waste and in the seed sludge for bacteria to dispose

of the w hey.

Although ejector aeration units recover rapidly,

shock loadhig by dumping large quantities of wdiey

is not a recommended practice. In one case, the

weekly discharge of the equivalent of 700 pounds

of whey solids to a treatment plant designed for

300 pounds of milk solids per day did not appear

to interfere with the aeration process. The most

noticeable effect was an accumulation of sludge.

During the pilot plant study, a large quantity of

whey was accidentally discharged into the treatment unit designed for 10,000 gallons of dairy

waste per day. This caused excessive foaming

and incomplete purification. Chemical analysis

revealed a nitrogen deficiency caused by the high

lactose content of the wlie\. The condition was

corrected by adding 100 pounds of ammonium

sulfate to balance approximately 5,000 gallons

of whey.

Nitrogen is essential for the proper grow^th of

micro-organisms. Ordinary dairy waste is an ideal

food for bacteria because it has much the same

composition as milk. Its COD to nitrogen ratio

is approximately 25 to 1. The ratio for whey is

much higher, 50 to 1, because the cheese process

removes the principle nitrogen-containing compound, casein. This leaves a material of liigh

sugar and low nitrogen contient. If whey or

similar materials are to be consumed by barterial

oxidation, nitrogen must be added to maintain a

level suitable for the bacteria.

Each 1,000 pounds of liquid whey contains about

50 pounds of solids, which is about equal to 50

pounds COD. To maintain a 25 to 1 COD to

nitrogen ratio requires 2 pounds of nitrogen.

Adding this amount would never be necessary,

because the analysis of ^^'hey shows 2 percent

soluble nitrogen. The maximum nitrogen addition to ^\'llev would be 1 pound, whicíi can be

supplied by 5 pounds ammonium sulfate.

Part of the nitrogen content of the seed sludge

may also be utilized to reduce the cost of nitrogen

supplementation. A well-aeiated stabilized sludge

contains 11.25 percent nitrogen and has a COD to

nitrogen ratio of 12 to 1 on a chy-weight basis (10).

Sludge-waste mixtures need at least 7 percent

nitrogen to effect adequate treatment. The difference is available for bacteria during whey consumption. Each pound of sludge solids in the

unit can give up enough nitrogen for the bacteria

to utilize 1 pound of whey solids. If the proportion of whey to sludge exceeds this, nitrogen in a

readily soluble form must be furnished.

EJECTORS AS AERATION DEVICES

Of the many devices available, the ejector was

originally selected for studying large-scale aeration

of dairy wastes because it liad separate pipe connections for air and liquid inlets as well as a

discharge outlet. It was known as an eflVctive

mixer of two inlet streams. As designed, the two

streams, air and water, were to be controlled by

separate pumps. Tests soon showed that an air

pressure pump was unnecessary, because the

ejector could readily dissolve oxygen at the high

rates required. The ejector is simple to operate,

contains no moving parts, and is low in initial

cost and upkeep. The use of ejectors or mixing

jets for waste treatment has been reviewed {22).

They were suggested for this purpose as early as

1905. Their use at a commercial installation for

treating chemical wastes was later patented (20).

Some installations that use small-size ejectors in

treating dairy waste w^re reported and discussed

(22).

Ejectors operate on the principle of creatmg a

high velocitv stream that is directed into the

throat of a venturi tube. Figure 8 shows a crosssection through the type reconnnended. The

waste is pumped through the device and enters at

the left, where the reduced size of tlie tip of tlu^

jet increases the stream velocity. This fastmoving liquid enters the venturi tube mixing with

the air that is drawn in through the an' mtake.

The velocitv and turbulence of the mixture gives

recirculating

vraste

• g^fiazzzzzzzzzzzzzzzs^ venturi

FIGURE S.—Cross section through model XL-96 ejector.

the device its tremendous oxygen-dissolving ability.

The ejector used in the investigations reported

in this Handbook w^as selected after three sizes

and two styles were studied. Comparison of the

efiiciencv of the three sizes is illustrated in figure 9.

The largest of the three, model XL-96, size 7A

(steam type), is recommended for dairy waste

aeration.* It will do tlie work of two units of the

next smaller size (5A) and six units of the smallest

size studied (3A). Its large physical dimensions

almost completelv prevent clogging by debris

normallv found in the w^astes. Clogging has

caused serious maintenance problems at treatment

plants where small ejectors have been installed.

Closer mesh screens at the pump suction for small

ejectors have only partially alleviated the problem,

because tlie screens must l)e cleaned more Irequently.
20

2.0| r

AGR. HANDBOOK 17 6, U.S. DEPT. OF AGRICULTURE

120

20 30 40 50 60

WATER FLOW, GAL. PER MIN.

FIGURE 9.—Oxygen transfer to a sulfite solution through

three sizes of ejectors at varying rates of water flow, j^

u

Q 2-1

_L I

CALCULATED FOR:

2500 FT ALTITUDE

90» F.TEMPERATURE

60 •/. REL. HUMIDITY

, 20V. OF OXYGEN DISSOLVE*

35 40 45 50 55 60

WATER FLOW RATE, GAL. PER MIN.^

FIGURE 10.—Relation of oxygen dissolved and calculated

aspirated-air volume to water flow for one ejector

size 7A, steam type, immersed 4 feet. '

-^ 100

UJ

a.

< 80

o

o 60

o.

I 40

O

20

<

,/

^ ^y ^

^'^!í> y^

y^

.^.

vî^k^r

\>Af

.1.^. r/^r

y

^

/

À

/

/

/

/

f

/

/

/

/

o 20 40 60 80 ÍOO

OPERATING PRESSURE, LB. PER SQ. IN.

FIGURE 11.—Flow versus pressure for one ejector.

15

^ 10

Q:

lij

X

Q.

(O

O

O

o:

<

t

A

V

\

V<^ t 1^*>

\

' t>

V 1 \

fe V

\

V

\

hk.'<>

\

V

1

^ \ k.

\

^^s-

•<

^

A'._

\

s^^

N

1—

1—^ ^

^

>12^

- '^

5 10

IMMERSION DEPTH, FEET

15

FIGURE 12.—Variation of air flow with immersion depth

for one type ejector under constant nozzle pressure.
DAIRY WASTE TREATMENT BY AERATION 21

A formula was developed relating the oxygen

dissolving ability of this specific ejector to the flow

of liquid through its nozzle.

Oxygen dissolved (Ib./hr.)=0.165 T^'-^^ (5)

1 T-_ riozzle flow (c.f.s.)

nozzle diameter (ft.)

The performance of the recommended ejector is

summarized in figure 10 for water rates ranging

from 34 to 64 gallons per minute. These rates

were determined from the oxidation of a solution

of sodium sulfite (3), Tlie curve may be used to

determine if suflftcient oxygen is being supplied at

reduced pressures.

Figure 11 is introduced to show the approximate

water pressure needed to force var^ang amounts of

liquid through the same ejector. The chart has

been prepared from the manufacturer's published

data.

The depth of immersion of the ejector influences

the amount of oxygen that can be dissolved at a

given nozzle pressure. In figure 12, data for a

similar ejector (same size, different style) have

been plotted to show how the amount of air

aspirated will vary with the depth of immersion

of the device. No data are presentlv available

on this aspect of the performance of steam-type

ejectors. Furthermore, tlie data presented should

not be confused with figures given elsewhere for

dissolved oxygen. However, the conclusion that

the performance of these ejectors is improved

when operating at shallow depths appears inescapable. This is in addition to evidence

assembled during tlic study that the overall

efficiency of a pump and ejector system is greatest

at the lowest rate of water flow consistent with

proper functioning of the ejector.

The manufacturer states that au will be aspirated and the device work efficiently at a minimum

of 20 p.s.i. nozzle pressiu-e. This must be at

least fom^ times tlie pressure against which the

device is aimed. Careful testing of all systems is

recommended, particularly those designed with

low nozzle pressures, to insm*e some allowance

for wear on pump impellers and enlargement of

ejector nozzles.

To make the data available from the study

complete, the following formula is presented. The

volume of air aspirated during the test with sulfite

solution was also related to the nozzle streamsurface velocity.

Vohune of air aspii^ated (c.f.m.) =2.30Xl^^'^^ (6)

T ^r_volume of stream (c.f.s.)

~ nozzle diameter (ft.)

OXYGEN CONTENT OF THE ATMOSPHERE

In applying aeration devices to dairy waste

treatment, some difficulty may be encountered

90 80 70 60%

3

Ü

o

X

o

<

Io

o

o:

<

2

3

O

>

in hot, humid regions. Most air equipment is

rated for the standard conditions of 70° F., 50

percent relative humidity, and a barometric pressure of 29.92 inches of mercury. Figm^e 13 has

been included to demonstrate the increased air

50%

407o>

2

3

30 7o

20 7o

10 7o

UJ

oc

80

BULB TEMP.,

90 100

DEGREES F.

FIGURE 13.—Chart for relating volume of air containing

one pound of oxygen to temperature and relative

humidity.

1.25

1.20 -

1.15 -

1.10 —

1.05 —

1.00.

0 1,000 2,000 3,000 4,000 5,000

ELEVATION ABOVE SEA LEVEL, FT.

FicuRE 14.—Factors for correcting air volume for altitudes

above sea level.

O

<

z

o

hu

UJ

(r

o

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22 AGR. HANDBOOK 176, U.S. DEPT. OF AGRICULTURE

voliune required to contain a pound of oxygen at

nonstandard conditions. Values to be obtained

from this chart will apply only at a constant

barometric pressure equivalent to sea level. A

separate chart (fig. 14) is used to correct for higher

elevations. By multiplying the factor taken from

figm^e 14 with the value for temperature and

relative humidity from figiu-e 13, the correct

quantity of air to contain 1 pound of oxygen can

be closely estimated. In the worst cases, the

correction may amount to as much as 25 percent.

The information noted in this section makes no

reference to the efficiency of the apparatus introducing the oxygen into solution. Calculations to

determine volumes of supply air for all devices

must include a factor for the percentage of oxygen

dissolved by the device subject to the corrections

described above.

EXCESSIVE FOAMING

Excessive foaming has been troublesome at

times. In this type of treatment system foaming

does not usually occur while the waste is being

added and assimilated by the sludge. It tends

to occm' toward the end of the assimilation period

and at the start of the endogenous phase. Overflow of the foam may be avoided at any time by

interrupting the air supply. This may safely be

done only if the aeration system has the abilit}^

to quicldy replenish dissolved oxygen. If necessary, assimilation may also be interrupted by a

period of settlement and draining to lower the

water level when foaminp; occurs.

Foaming may also be caused by overaeration.

As the plant must be designed to care for the waste

produced during the highest seasonal flow of

milk, it may prove to have too large a capacity

at other times. This happens more frequently

when equipment of low ox^^gen transfer efficiency

has been used. In such cases a large quantity of

air must flow through the liquid to provide the

required oxygen. Barring conditions caused by

the presence of unnatural materials in the waste,

foaming will usually subside when aeration is

stopped or substantially reduced.

HEATING THE DAIRY WASTE

As with other biological processes, the rates of

assimilation of the waste and respiration of the

sludge vary with the temperature of the solution.

Fortunately, many dairies discharge wastes at a

temperature favorable for biological treatment.

Although the process is fairly hardy, some retardation may be expected if the temperature in the

tank falls much below 70° F.

The use of hot water and steam in the dairy

produces a waste with an average temperature of

85° to 90° F. This is ideal for the bacteria that

purify dairy waste. If the temperature in the

aeration tank were to drop to 55° or 60°, many

forms of bacteria could not survive or reproduce

and treatment would be retarded or incomplete.

Some dairies may find it advisable to heat the

waste.

Heating the dairy waste by means of steam coils

is unsatisfactory, because the waste cooks onto the

pipes and seriously impairs heat transfer. Waste

hot water or steam that is allowed to discharge

elsewhere can be repiped to be included with the

waste to be treated. A simple solution is the use

of hotter water in dairy plant cleaning operations,

but this may be too costly. Other piping changes

may be possible that will prevent large flows of

cold water from diluting and cooling the warm

waste. Direct addition of waste steam to the

tank is probably the most practical method of

heating dairy waste.

If piping modifications do not bring the waste

to a desirable temperature for satisfactory operation of the waste plant, then steam heating may

have to be applied. The dairy plant operator

would tlien need to know the size of pipe and the

amount of steam required. The chances are excellent that only a small pipe would be actually

needed, but the factors in determining the size of

the pipe are explained.

The fhst step is to find the quantity of heat

necessary to correct the temperatm^e of the waste.

The general formula for this for unit time would be:

Q=Wc (U-t,)

where

(7)

Q=quantity of heat (B.t.u. (British thermal

units)/hr.)

Tr= total weight of material (lb.)

c=specific heat of the substance, which in

this case will be 1, the same as water

^2—^1=initial temperature subtracted from the

final temperature (° F.)

If it is assumed that the average waste temperature, 65° F., should be 85° and 1,200 gallons per

hour are to be treated, the following would be the

calculation:

(a) QUANTITY OF HEAT (by formula 7):

Heat (B.t.u./hr.) = l,200 X 8.34 X 1 X (85°-65°)

-200,160 B.t.u. per hour

The number of pounds of steam required to

supply this much heat depends on the steam près-
DAIRY WASTE TREATMENT BY AERATION 23

sure available. For a low pressiu'e sourco, the

following calculations can be made to determine

the size of pipe and quantity of steam to be used.

The amount of heat given up by each pound of

steam is first determmed. This is the difference

between the total heat in the steam as it enters

the tank and its final condition after reaching the

temperature of the surrounding mass of liciuid.

The example below is for steam at 1.3 pounds

per square inch, gage:

(b) HEAT PER POUND OF STEAM:

Heat of Latent Total

liquid heat of heat

evaporation

P.tM. P.t.U. P.t.ll.

Entering steam 184.4 967.6 1,152.0

Final (at 85° F.) 53. 0 0 53. 0

Heat available per pound ], 099. 0

(c) STEAM NEEDED EACH HOUR:

200,160 B.t.u

1,099 182 pounds

In order to determine the size of pipe necessary

to supply this amount of steam, its density must

be known in cubic feet per pound. The constants

of steam are available in any standard table of

properties of saturated steam. A reasonable yelocity for low-pressure steam of 6,000 feet per

minute would be used in the standard velocity

formula for determining the size of pipe needed:

.4Xi^Xl,728 V=- rx60X12 (8)

Where T"= velocity in feet per minute;

.Impounds of steam per hour;

5=volume of steam in cubic feet per pound

at tlie stated pressure (24.75 cubic feet

at 1.3 pounds pressure);

i'=area of pipe in square inches;

1,728 =cubic inches per cubic foot;

12=inches per linear foot;

60=minutes per hour.

Transposing and simplifying, formula (8) becomes

C= AXBX2A

V

(9)

(d) AREA OF PIPE (by formula 9) :

C= 182X24.75X2.4

6,000

= 1.8 square inches

Next, convert this cross section area to internal

diameter of pipe. A standard table shows that a

pipe 2 inches in diameter has ample cross-section

area to deliver the desired amount of steam.

However, if the length of the run from the steam

som-ce to the assimilation tank were very long,

the recommended steam line should be increased

one size to 2l2-inch pipe.

WASTE TREATMENT SYSTEMS USING EJECTOR AERATION

A number of dairy plants now treat waste

successfully by using ejectors for rapid aeration.

Some treatment units use as few as 4 ejectors,

whereas others use as many as 26.

This Handbook recommends that operating installations should be inspected prior to the design

and construction of a new waste disposal system.

More than 125 successful plants were in operation

in 1958. A partial list of these plants may be obtained from the Eastern Utilization Research and

Development Division, 600 East ^Mermaid Lane,

Wyndmoor, Pa.

INDEX

Page

Aeration device 4^ 0

Aerobic conditions 3^ 9

Aeration tank. See Tank size and depth.

Assimilation 1, 2, 5

Time ' 2

Bacteria. See Sludge.

Batch treatment 2

Calculations 3

Cost estimates 14

Designs 5

Operation 7

Biological oxygen demand (BOD) 1, 15, 18

Chemical oxygen demand (COD):

Definition 2, 18

Of whey 18

Rapid method 18

Clear effluent drain 4, 7

Continuous treatment 2, 9

Depth of tank 4

Ejectors 4

Depth of immersion 20

Efficiency i)

Number of 5

( )xygen transfer (formula) 21

Performance check 9

Table 1 5

Volume of air aspirated 21

Water now 20

Endogenous respiration 1, 2, 3, 5, 7, 9

Equilibrium sludge weight 3, 9, 10

Calculations 3, 10

Estimated costs 14

Fill-and-draw systems. See Batch treatment.

Foaming 22

Freeboard 4

Friction in piping 12

Calculations 13

Inlet baffles 11

Interrupted aeration 9, 22

^'Manual for Milk Plant Operators" 1

New sludge formation 2, 3, 5, 10

Calculations 3, 10

Nitrogen supplementation 2, 18

Nonfat milk solids 2

Organic matter in waste 1,3, 10

Calculations 3, 10

Overñow, control -1

Outlet weir 11

Oxygen demand. See Br)D and COD.

Oxygen dissolved by ejector (formula) 21

Page

Oxygen requirement 1, 5^ 12, 18

Calculations for batch process 3

Calculations for continuous process 9

Pilot plant studies 11,2, 11

On ^^'hey 19

Piping 7, 11

Friction 12

Pond 5

Pump 5

Performance check 9

Selection n

Mot ors 13

Reinforcing bar 14

Respiration. See Endogenous respiration.

Retention time 10

Returned sludge (calculations) 10

Screens 5, 7

Seed. See Sludge.

Settling 2, 5, 7

Area calculations 11

Rate calculations 11

Tank H

Short circuit 5

Site 13

Size of tank. See Tank size and depth.

Sludge:

Burnup, batch process 2, 7

Burnup, continuous process 10

Color 7

Concentrate 9

Concentration, continuous process 11

Insufficiency 9

In whey treatment 18

Removal 7, 9

Return 9

Seed 3, 9, 10

\"olume 2

Weight 2

Solids, nonfat milk 2

Sump pit 5

Surface loading 11

Tank area (calculations) 4

Tank size and depth 4, 10

Temperature 2, 22

Total oxidation 7

Transfer efficiency 4, 21

Volume of air aspirated by ejector (formula)___— 21

Water used in dairy 2

Water pressure vs. flow 20

Waste, strength of 2

Waste, organic matter (calculations) 3

Whev wastes 18

U.S. GOVERNr.-ENT PRINTING OFFICE: I960