THESI-

 

This is to certify that the

thesis entitled

WATER CONSERVATION AND POLLUTION REDUCTION

DURING POTATO PROCESSING

presented by
Ahmad Shirazi

has been accepted towards fulfillment
of the requirements for

MS Food Science &

d .
egreel Human Nufrition

Major professor

Date October 31, 1979

 

0-7639

 

 

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25¢ per dey per it.

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charge froe circulation records

 

 

 

 

_ WATER CONSERVATION AND POLLUTION REDUCTION

DURING POTATO PROCESSING

By

Ahmad Shirazi

A THESIS

Submitted to
Michigan State University
in nartial fulfillment of the requirements

for the degree of

MASTER OF SCIENCE

Department of Food Science and Human Nutrition

1979

ABSTRACT

WATER CONSERVATION AND POLLUTION REDUCTION

DURING POTATO PROCESSING

By

Ahmad Shirazi

This study was designed to examine water usage and
waste production in a commercial, frozen French fry pro-
cessing operation.

Existing plant layout and water/product flow patterns
were studied, including measurement of water usage in
virtually all of the plant's unit operations. Effluent
measurements included in the study utilized Total Non-
filtrable Residue (Total Suspended Matter, TSM), Biochemical
Oxygen Demand (BOD), Chemical Oxygen Demand (COD), pH, and
grease and oil content as the principal indices of pollu-
tion and included temperature measurement as well.

Based on data collected during the study, a number of
possibilities for improved water conservation and waste
reduction have been discussed. These suggested changes
include by-product recovery, water reuse and recycling,

as well as various process and equipment modifications.

Dedicated to

The Toiling People of Iran

11

ACKNOWLEDGMENTS

’The author wishes to express his sincere appreciation
and fondest regards to his advisor, Dr. T. Wishnetsky,
whose help and guidance made the completion of this work
possible.

Appreciation is also extended to Professors Alvin L.
Rippen, P. Markakis and Steven L. Gyeszly for their critical
evaluation of this Thesis. Thanks are also due to the
management and other personnel of Mid-America Potato Com—
pany for their cooperation during the period of the plant
survey.

Finally, the author is particularly grateful to his
wife, Homa, for her patience, understanding and support

throughout this study.

111

TABLE OF CONTENTS

Chapter Page

LIST OF TABLES. . . . . . . . . . . . . . . . . . . Vi

LIST OF FIGURES . . . . . . . . . . . . . . . . . . viii
INTRODUCTION. . . . . . . . . . . . . . . . . . . . 1
LITERATURE REVIEW . . . . . . . . . . . . . . . . . 3

Waste Characterization. . . . . . . . . . . . . 27
Selecting Indices of Pollution. . . . . . . . . 30
Analytical Procedures . . . . . . . . . . . . . 31

Interpretation of Data. . . . . . . . . . . . . 31
EXPERIMENTAL. . . . . . . . . . . . . . . . . . . . 32
Process Description . . . . . . . . . . . . . . 32

Receiving/Cleaning. . . . . . . . . . . . . 32
Fluming/Transportation. . . . . . . . . . . 32
Lye Peeling/Trimming. . . . . . . . . . . . 33
Surface Darkening Control . . . . . . . . . 33
Cutting . . . . . . . . . . . . . . . . . . 3A
Sizing. . . . . . . . . . . . . . . . . . . _3A
Blanching . . . . . . . . . . . . . . . . . 3A
Coloring/Sugar Dip. . . . . . . . . . . . . 35
Surface Drying. . . . . . . . . . . . . . . 35
Frying and Defatting. . . . . . . . . . . . 35
Precooling and Freezing . . . . . . . . . . 35
Packaging and Storing . . . . . . . . . . . 36

Water Use in the Plant. . . . . . . . . . . . . 36

Solvents and Chemicals. , , , , , . . . . . . . 36

iv

Chapter Page

Sampling. . . . . . . . . . . . . . . . . . . . 37

Sample Handling and Preservation. . . . . . 38

,Analytical Methods. . . . . . . . . . . . . . . 39
Sample Preparation. . . . . . . . . . . . . 39
pH Determination. . . . . . . . . . . . . . 39
Temperature Measurement . . . . . . . . . . 39

Total Nonfiltrable Residue
(Total Suspended Matter, TSM) . . . . . . . A0

Chemical Oxygen Demand (COD). . . . . . . . A0
Biochemical Oxygen Demand (BOD) . . . . . . A2
Grease and Oil Determination. . . . . . . . A5

Flow Measurement and Water Usage
Determination . . . . . . . . . . . . . . . . . U7

RESULTS AND DISCUSSION. . . . . . . . . . . . . . . 50

Plant Layout and Water Flow

Pattern . . . . 50
Water Usage . . . . . . . . . . . . . . . . . . 5“
Waste Generation. . . . . . . . . . . . . . . . 59

BOD-to-COD Ratio. . . . . . . . . . . . . . . . 71

Comparison of the Obtained Results
with Those From Other Studies . . . . . . . . . 73

Potential for Improved Water Conserva-
tion and Waste Reduction. . . . . . . . . . . . 7H

SUMMARY AND CONCLUSIONS . . . . . . . . . . . . . . 82
LITERATURE CITED. . . . . . . . . . . . . . . . . . 85

APPENDIX. . . . . . . . . . . . . . . . . . . . . . 9A

Table

10

LIST OF TABLES

Page
Potato Production and Processing
in the U.s. 1968-1975 . . . . . . . . . . . A
Effect of Peeling Methods on
Quantity of Waste . . . . . . . . . . . . . 22
Suspended Solids and Total
Solids in Potato Blanching
Effluent. . . . . . . . . . . . . . . . . . 2A
Pollution Load in Effluent
from Water Blanching. . . . . . . . . . . . 25
Pressure Gauge Readings
(Water Pressure) for Unit
Operations. . . . . . . . . . . . . . . . . A8
Gallons of Water Used by
Specific Operation. . . . . . . . . . . . . 55
Total Nonfiltrable Residue
Dried at lO3-lOS°C (Total
Suspended Matter) . . . . . . . . . . . . . 6O
Biochemical Oxygen Demand,
BOD (5 Days, 20°C). . . . . . . . . . . . . 61
Chemical Oxygen Demand,
COD . . . . . . . . . . . . . . . . . . . . 62
Grease and Oil Content of
the Total Plant Effluent. . . . . . . . . . 63

vi

Table

11

12_

13

II

III

IV

VI

VII

VIII

Temperature and pH of the
Effluents . . . .

Total Pollutants Discharged
Per Operating Day

BOD-to—COD Ratio.
Manufacturers' Designation
for Spray Nozzles in Unit
Operations Under Study.
Water Usage in Specific Unit
Operation

Water Usage and Waste Generation
in Specific Process Steps
Finished French Fries Hourly
Production Rate

TSM Values for Different
Sources, mg/£..

COD Values for Different
Sources . . .

BOD Values for Different
Sources . .

Grease and Oil Content of
the Total Plant Effluent.
Statistical Comparison of
the Calculated Means of the

Waste Indices . . . . . .

vii

Page

66

68

72

9A

95

111

112

113

117

120

122

12A

Figure

LIST OF FIGURES

General Sketch of the Plant
Scaled—up Sketch of the

Processing Area
Water/Product Flow

Pattern

viii

Page

51

52

53

INTRODUCTION

’Continued increase in demand for processed convenience
potato products has led to rapid expansion of the potato
processing industry. Consumption of frozen French fries
has ranked above all other potato products. These increases
in production resulted in more water usage. It also faced
this industry with the problem of increasing waste that
had to be either: (1) utilized; (2) treated and disposed
of privately by the plant; or (3) transferred to a munici-
pal system for treatment and disposal.

The increasing pollution problem prompted governmental
bodies to promulgate and enforce stringent water quality
standards and restrictive requirements for industry. There-
fore, each industrial unit must attempt to minimize pollu-
tion, either through in-plant changes, end-of-pipe treat-
ment or both.

Between the stated alternatives, in-plant changes as
preventive measures have usually been less costly (27).

They include process modification, use of special machinery
which use a minimum amount of water, in-plant reuse/recycling
of water, and waste segregation and utilization. On this
basis, the present study was undertaken to investigate:

(1) Pattern and quantity of water usage, (2) character

and quantity of the plant waste, and (3) methods of
water conservation and waste utilization/minimization in
a frozen French fry plant, the Mid-America Potato Company
plant in Grand Rapids, Michigan.

- Cost analysis was considered beyond the scope of this
investigation, though it is recognized that water-saving
and waste-reducing changes would not normally be imple—
mented in commercial situations without a thorough review

of cost factors.

LITERATURE REVIEW

.The frozen potato products industry is reported to have
begun in l9A5 with the commercial freezing of French fries
(7A). Since then, there has been a phenomenal increase in
the consumption of such processed potato products as frozen
French fries, hash brown, potato puffs, etc. in the United
States. Based on data given by USDA (77), annual per capita
consumption of frozen potato products was 0.1 pound in 1950.
This was increased to 2.7, 5.7, 11.1, and 13.7 pounds in
1960, 1965, 1970, and 1975, respectively. To satisfy the
demand for these items, more and more potatoes were grown
and processed, as indicated by the data in Table 1.

Population growth and convenience in consumption
of frozen foods are probably two major reasons for this
increase. The frozen product is a decided convenience
for both home and food service use because it needs only
to be removed from the package and heated in an oven or
briefly deep fat fried before serving.

Among the frozen potato products, frozen French fries
are consumed the most. Amount of raw potatoes processed

7 cwt

into frozen French fries increased from 3.8 x 10
in 1968 to 6.9 x 107 cwt in 197A. These figures represent

8A.62 percent and 88.25 percent of the potatoes used for

 

 

 

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production of frozen potato products in the stated years,
respectively.

Increase in production of processed potatoes, like
other segments of the food industry, has resulted in a
corresponding increased volume of waste with potentially
the same increase in water pollution (21). The fact that
the food industry used 6.16 x 109 gallons in 195A and
8.0A x 109 gallons of fresh water in 1963 shows this
increasing trend (78).

Processing of fruits and vegetables necessitates
the use of large quantities of water and generates enormous
volumes of liquid wastes and solid residuals (A2,56,83).
In other words, the food industry is a major producer of
"waste" with the usual intended product being the minor
output. For example, the average cannery until recently
used to produce ten times as much waste water as canned
product (28). Root vegetables, in particular, require
large volumes of water in processing operations, and sub—
stantial amounts of organic materials are introduced into
processing plant waste water (A8,A9).

In the processing of potatoes, 20 to 50 percent of the
processed raw potato is discharged as waste. Several
values have been reported for waste water flow in potato
processing. Most of the values fall within the range of
8A0 to 5,000 gallons per ton of raw potato processed,

depending on the desired product (21,A2). A wider range

cited in the literature is 813 (22) to 12,000 (56) gallons
per ton of raw potatoes. Average values of 3,A20 - with
standard deviation of 1,590—(30), 2,700 (2A), and 3,600
(83) gallons of waste flow per ton of raw potatoes pro-
cessed have also been reported.

Faced with a general rise in the potential solid and
liquid waste load that ultimately must be treated, utilized,
or transferred to the water environment and the realiza-
tion that water supplies are not unlimited, governmental
bodies at both state and federal levels have promulgated
and enforced more stringent water quality standards (30,63,
91). Above all, it is Public Law 92—500, established by
the U.S. Congress on October 18, 1972, which sets limita-
tions on the quality of effluent. PL 92-500 necessitates
the application of the "best practical control technology
currently available" by July 1, 1977, the "best available
technology economically achievable" by July 1, 1983 for
the present sources, and the "best available demonstrated
technology" for all the new sources (83). The industry
should also meet the aim of "zero discharge" by 1985
(A1). Due to this law, all waste water dischargers should
obtain a permit known as the National Pollutant Discharge
Elimination System (NPDES) which assures that effluent
limitations are being met and that designated water quality
standards are maintained. Furthermore, there are state

and local requirements that are usually more restrictive

than EPA guidelines (83) which industry must comply with.
On the other hand, it is well realized that both water
supply and waste disposal influence industrial growth,
operation and product cost (91).

. Based on the above, concern over water usage and pol-
lution has touched the food processing industry at least
as deeply as other sectors of the economy (A3,A8). Con-
siderable effort has been made and extensive research is
still going on to minimize pollution loads. These gen-
erally involve in-plant process changes and/or end-of-
pipe waste water treatment (30,83).

Focussing on the end-of—pipe treatment alternatives
for handling liquid waste from food processing operations
are discussed in several references (A2,59,79,83). Waste
treatment is accomplished to reduce sewer user charges
and to comply with effluent standards set federally, by
state, or city. There are three possible options used
for waste treatment (83):

1. Pretreatment of the waste and discharge to city
sewer. This option includes common treatment like screen-
ing, neutralization, flow equalization or more exten-
sive treatments such as gravity sedimentation or air
flotation for soil and solids removal or neutralization.
It is often required by city ordinance and is done to meet
municipal ordinance requirements (63), reduce cost (37,83),

and accommodate production increases. Efficiency of

pretreatment processes are reported in the literatures
(21,A2,81,91).

Processors discharging to municipal systems are
subject to local sewer service charges varying from a
flat rate to a charge proportional to the flow or floor
area of the plant. Charges usually are higher when the
industry uses a facility that has received federal funds
for treatment plant construction. Such charges are
called industry's "fair share" and are calculated in
proportion to the amount of waste load discharged by the
industry. Pretreatment is used in cyclic processes.

2. Complete treatment of waste and discharge to
stream. Potato wastes are organic in nature (A2,7A)
with an average BOD of about 10 to 30 times greater
than domestic sewage (39,A6). Waste water from the
French fry industry and similar effluents can be treated
quite successfully by conventional biological treatment
plants which treat domestic sewage, providing there are
suitable modifications to compensate for the waste water
characteristic differences (15,30).

This option, preceded by in-plant management and
pretreatment and followed by chlorination and filtra-
tion, can meet "zero discharge" requirements (79).
Biological treatment systems for potato waste, as shown
in the literature, are able to reduce BOD by 71 to 98

percent (21).

Installation and operation of complete treatment
facilities is very expensive. A thorough study of costs
of treatment to meet effluent requirements is found in
EPA publication number AAO/l—7A-027-a (79).

‘ 3. Discharge to land. Land treatment systems such

as spray or flood irrigation are effective and relatively
economical alternatives for waste treatment. This option
is one of the oldest methods of treatment which has been
used successfully for the disposal of cannery wastes (15).
When feasible, it is generally the most economical end-of-
pipe treatment technique that will meet EPA standards
scheduled to go into effect in 1983 as well as EPA
standards for new source performance (55,79). Aside

from unavailability of extensive areas of land, there

are other factors which limit the use of land for dis—
posal of wastes. Such factors are climatic conditions,
soil texture, contamination of underground waters when
operated improperly and runoff problem (15,59). Costs of
using land as the ultimate disposal method have been
estimated (79). The financial burden of such operations
can be minimized by a modest revenue obtained from the
sites, as when crops are grown on the irrigated land.

No doubt that high level technology exists for complete
end-of—pipe waste treatment, but the application is very
costly. This is obvious and can be fully understood by

’1

scanning several references (27,28,37,79).

10

Conversion of raw food materials into processed
products inherently requires the use of water. Since
water comes in direct contact with the raw materials
during processing, significant amounts of organic and in-
organic materials in the suitable colloidal, or particulate
form are generated as "waste". Waste is normal, but
allowing it to cause pollution - which is a resource out
of place — is abnormal. It shows a serious lack of proper
management of two major resources, namely food solids and
water (26). Dumping the wastes requires setting up sludge
plants, which are expensive bacterial cafeterias. One
should develop other industries utilizing wastes from the
first stage of industry for the production of by—products
(27). As stated by Gallop et a1. (1976), "In effect, the
individual discharges from process units become the in-
gredients of a large, manufactured, inedible, almost ir-
reversible, worthless "omelette" in drains." The processor
is faced with a problem to solve promptly at great cost.
The effluent must be treated to satisfy EPA with regard to
protection of fish, the public, and the environment as a
whole. The problem is that of separating the solutes and
suspended matter from the carrier before discharging and
then buying some more water to repeat this foolish exercise.
Therefore, it would be wiser to prevent this problem
from occurring because prevention is always preferable

to an attempted cure later. In this connection, one can

ll

reduce the organic load in the discharge by minimizing
product-waste contact whenever possible. In more specific
terms, we must manage 100 percent of our minimal water
input so as to minimize our wasteful output. Waste streams
should be monitored at their source and kept concentrated
and isolated prior to conditioning for re—use within or
beyond the plant or for discharge under good control with
negligible environmental damage.

Based on the above, reduction of product-water contact
is the other way of pollution minimization as previously
stated in contrast with end-of—pipe treatment of wastes.
It can be achieved by varying operational practices and
by use of improved food processing equipment (83). These
together could generally be called in-plant modifications
every effort of which somehow aims toward conservation
of water.

Among the beneficial results stemming from water
conservation are: (1) assurance that limited resources
of fresh water will keep pace with the growing population
and expanding industries (89); (2) savings in the purchase
and disposal of water (3A,38); (3) reductions in the
volume and increases in the concentration of leached material
in process water plus reduction in leaching because of the
reduced concentration gradient all contribute to greater
economy and efficiency of treatment (50,51,56); (A) en-

hanced potential for recovery and utilization of by-products

12

(83); and (5) conservation of heat energy when reused at
the elevated temperatures of the discharging unit opera-
tions (29,A7).

_ There has been much controversy concerning the safety
of water reuse in the food industry in order to achieve
the above-described benefits. The National Canners
Association presented data supporting a continuation of
those water conservation practices now in use which have
been shown to have no adverse effect on the quality and
wholesomeness of the finished product (83). Efforts
toward water conservation have been tackled in several
ways.

Employment of low—volume, high-pressure systems for
washing the product and for clean up reduces water use and
waste generation (A5). It was reported that increasing
nozzle pressure from A0 psi (2.7 atmospheres) to 250 psi
(17 atmospheres) reduced water use by approximately 65
percent.

Other changes in operational practices such as elimina-
tion of excess running water, prevention of unnecessary
overflows, spillages, and dumps, dry handling and dis-
posal of solid wastes from floors, machines, and other work
areas instead of fluming-to-waste will reduce water
usage and waste generation (A2,A5). Conveying product

and solid wastes in water instead of "dry" increases both

13

the waste flow and BOD more often than not (56).

The handling of crops containing much soil may cause
problems during processing, such as plugging of flows,
conveyors, and sewer lines due to settling of soil.
Precleaning of raw potatoes by dry method - agitating
on screens or roller conveyors - removes adhering soil
which may amount to 1.87 percent (53) and reduce water
usage.

Being concerned primarily with the product quality
improvement, food processing industries have been using
too much water through the employment of the absurd,
expensive, linear process "once-use" system (19,28).
Such a practice has caused most of the industry's pollu-
tion problems and turned it into the world's largest
effluent-producing industry (27). This has probably
resulted from the historical belief that water is the
cheapest commodity available in comparison with pro-
cessing equipment and labor (30).

Among the approaches used to solve pollution and
economic problems resulting from extravagant water
usage is water reuse. This does not necessarily change
the manner of use by industry, only the source. It
deals only with the recovered water fraction of the
waste water. Such a case is reported (5) for a potato
processing plant in England where strict water pollution

regulation and high cost of process water Justified

1A

the reuse of the reclaimed waste water. The waste water,
having a BOD of 1,918 mg/t, was subjected to primary
settling, biological treatment, sand filtration and
chlorination before reuse.

- -Immediate reuse (before treatment) may also be
practiced. In a case confirming such practices, an
overall possible reduction in excess of AA percent
for the total daily water needs of a potato processing
plant was reported (38). As stated in the report, 18.8
percent of total plant water intake per day - from the
refrigeration compressors and condensors — could be
reused with little or no further treatment in any process-
ing operation. An additional 10 percent of reusable
water (part of the 29.1 percent of total daily plant
intake that is used by the Allen grader, the conveyor
flume for by-products and the potato cutters) is suitable
for immediate reuse in fluming of raw potatoes. The
rest - 19.1 percent - could be reused after treatment
to remove suspended solids and reduce bacteria to an
acceptable level for other purposes.

Use of waste water from any process line as the
make up water in the fluming of potatoes has also been
suggested by Hindin (1970). He studied water use and
waste water reuse at three processing plants whose
major product was frozen French fried items and pro-

posed a scheme for reuse of waste water in processing

15

based on the in-plant investigations.

Reuse of water in processing may effect consider—
able reduction in overall usage, but waste separation
- separation of low and high strength waste streams -
which is an essential practice (15,30,60) must precede
any effort toward water reuse. Kueneman (1965) reported
that waste flow of 3,650 to A,200 gallons per ton of
raw potatoes could be reduced to 200 to A00 gallons per
ton with considerable water reuse. Dornbush et al.
(1975) showed that water usage dropped from 3,500 to
815 gallons per ton of raw potatoes processed through
extensive in-plant water conservation along with utiliza-
tion of a dry-caustic peeling process.

In the course of reuse, the quality of the water
that comes in contact with the product is of extreme
importance (30). On the other hand, water used in some
unit operations need not necessarily be of the same
sanitary quality (83). For example, the quality of
water used to remove potato peels is the least critical
in regard to quality of all the process operations (39).
Therefore, from a practical standpoint, the same water can
be used for a number of successive purposes, each less
demanding of quality than the preceding, with or without
purification (5A,60). In such a "retrograde" manner
of water reuse - which is called counterflow water

system - most of the fresh water is used in the final

16

operation. This water is then collected and reused in
previous operations. Since the water always passes counter
to the flow of the product, the product comes into con-
tact with successively cleaner water (83,89) and is
finally washed or rinsed with fresh water. Such water
reuse reduces the (fresh) water usage and minimizes
the volume of waste water discharges.

The amount of water saved by a counterflow system
varies within each plant. Under average conditions
this is estimated to be about 50 percent of the total
water usage (83). A study (79) showed that one—third
less water was used and there was less danger of bac—
terial growth in a once-through counterflow system than
in the recirculation system with which it was compared.
Bruce §£._l- (1977) reported over 30 percent reduction
in water usage in a few frozen potato plants through the
use of a counterflow water system. They found the major
problem in retrograde water reuse to be in controlling
microbial growth within the water system and prevent—
ing product contamination to the next unit process.
The problem was controlled by use of chlorine dioxide
as the primary microbial control agent in the
system.

Another approach toward water conservation and waste

minimization is recycling of waste water which could be

l7

done in either limited or complete form. When a closed
system is not practical, limited recycling - recircula-
tion of waste water for a limited number of cycles -
would save some water. For example, according to Hindin
(1970), the trim table waste water can be recycled for
at least seven hours before disposal.

Complete or continuous recycling of waste water (also
called a closed loop system) eliminates most pollution
problems through monitoring of wastes at their sources.
In such a reliable, cheap and adaptable process, the ef-
fluents from each step of the line are used in a systematic
counter flow pattern, with each one being cyclically
used for one operation. This system requires only make-
up volumes of water and permits solids accumulation to,
and maintenance at, an acceptable "background" level
and only excesses above these need be removed between
each reuse by simple means like screening, flocculation,
settling, filtration, cycloning, cooling, chlorination
and other cited treatment methods (81). Most of the
problems are also controlled this way. For example,
color, foam, bacteria and the like problems during re-
circulation of wash water at the potato rinse stage can
be solved by a combination treatment of pH and activated
carbon (A1). Such minor purifications by in-line "cart-
ridge purifiers" is bound to be cheaper and more de-

sirable than purifying similar volumes to a much greater

18

degree in a large external treatment plant, discharging
it out,then buying more fresh water. Furthermore, this
"creaming-off" of the excess percentage of nuisance
factors follows the fact that reuse of the pollutant
fraction should be an integrated part of the water reuse
planning (16). It brings about the potential for recovery
or by-product utilization which not only saves water,
minimizes pollution, and expands product usefulness (5A),
but can also sometimes be implemented at a profit (28,6A,75).
Therefore, waste treatment could turn into a money making
proposition. For example, the starch in cutter water
causes extremely high BOD and suspended solids concentra—
tion, the removal of which by centrifugal hydrocyclones
reduces the total effluent BOD and makes a slight profit
when it is sold (37). Taylor (1973) reported that use
of hydrasieves and cyclones in potato processing reduce
BOD and suspended solids by more than 50 percent,
resulting in lower treatment costs and saving $A39 per
day on recovered products. In several European potato
processing plants the suspended starch grains are
separated by sedimentation followed by vacuum filtra-
tion. The recovered starch is washed, dried and sold, and
the starch-free water is reused (15).

Another complete recycling is in the closed system
for fluming of raw potatoes, the required in-line treat-

ment for which is sedimentation. In one case (37),

l9

fluming used 50 percent recycled water and discharged

75 gallons per minute of effluent having an average
suspended solids (silt) of 7,000 mg/l and a BOD of

110 mg/A. Addition of one mg/£ of anionic polymer caused
quick gravity settling of silt which was dewatered and
used as topsoil replenisher.

The recovery of potato protein, which is a remark-
ably nutritive protein and contains all the essential
aminoacids (57), can be achieved directly from the waste
stream or indirectly by fermentation (75). In the
direct method (25), reverse osmosis and ultrafiltration
membrane processes are employed. With the indirect
method, waste starch and other carbohydrates may be
converted into yeast cells (protein). The first com-
mercial Symba-yeast plant to purify potato waste was
built in Sweden. It was able to achieve 90 percent
purification of input material (68). Preparation of an
organic cleaning compound from potato processing waste
has also been reported (8).

Conservation of water and reduction of wastes through
equipment and/or process modification is of paramount im-
portance in potato processing. This is because 20 to 50
percent of raw potatoes become waste during processing.

To utilize slivers and nubbins, that part of the waste

20

resulting from cutting, by—products such as patties,
puffs, hash-brown and mashed potatoes may be produced.
This reduction in waste represents about 10 percent (7A)
of the raw potatoes processed. A considerable amount

of loss still remains; namely that which occurs during
other processing operations.

Peeling of potatoes is one of the major waste-pro-
ducing processes. It represents 20 percent of the water
flow, over 50 percent of BOD, and over 60 percent of
suspended solids of the total processing effluents (79).
This considerable waste stems from the large quantities
of water usage along with the high losses from the raw
potatoes which (when trimming is included) usually falls
within the range of 15 to A0 percent of raw product
weight (7A). This is because the amount of loss varies
with size and shape of potatoes, depth of eyes, length
of storage time of the tubers, and type of peeling.

Use of large potatoes, which have less peeling losses
(7A), or certain tuber varieties the deep eyes of which
are bred out, can reduce wastage (26) during peeling.
Newly harvested potatoes have less loss than older
potatoes from storage. Burton (1963) stated that, over
long periods of storage, potatoes become increasingly

unacceptable until, at 10 percent weight loss (based on

21

original weight going into storage), the potatoes are
wrinkled, spongy and very difficult to peel.

Caustic and steam peel treatment are the generally
accepted methods (79) of peeling in the potato process—
ing industry - except for potato chip manufacture,
which usually utilizes abrasion peeling. Table 2 pro-
vides a summary of estimated quantities of peel in
waste in potato generated by different methods of peel-
ing.

The dry caustic or infrared caustic process which was
developed by the USDA Western Regional Laboratory as a
modification of the conventional or wet caustic peeling
process has proved to be very efficient from a pollution-
control point of view. This process reduces water usage
by 75 percent, BOD by 67 to 78 percent and solids by 73
percent. Improvements in the dry peeling process such
as double-dip caustic peeling (A0) or recirculation of
water from the washer to the scrubber (18) can save more
caustic or water, respectively.

Change of equipment can also serve the purpose of
pollution control. For example, by installation of dry
brushing equipment such as the Dutch I.B.V.L. brushing
machine (85) right after the lye or steam peeler, the
treated potato skin will be brushed off clean without
the use of water. By keeping the dry peel waste generated

by the dry process out of the plant waste water, a reduction

22

 

 

 

Table 2. Effect of Peeling Methods on Quantity of Waste.
BOD
' Peel Wastes lb/ton of (1)
Peeling Method % of Raw Wt. Raw Potatoes Ref.
Abrasion 3-12 —-— 32
Abrasion 25 —-- 33
Abrasion 1A-25 --- 23
Infrared 13 260 87
Infrared 10 200 87
Lye (Wet Caustic) 18 --- 87
Lye (Wet Caustic) 12-30 --— 52
Lye (Wet Caustic) 22 -—- 33
Lye (Wet Caustic) 11-23 --- 23
Lye (Wet Caustic) -- 186 86
Dry Caustic -- 26 31
Mechanical<2> 7—31 --- 90
Lye/steam 15 --- 2
Steam 10 260 87
Steam 11-19 ——— 23
Steam l8 --- 33

 

 

(1) Numbers correspond to listing in Literature Cited.

(2) The author did not specify type of mechanical system
The term may have signified abrasion peeling.

used.

23

of approximately 75 percent (69) can be achieved in the

amount of solids in the effluent of a French fry plant.
Production of a uniformly-colored final product is

of notable importance in French fry processing. Hot

water blanching, in addition to its other functions (as

detailed under Experimental), is the process which deals

with this purpose. The process has a leaching effect

on reducing sugars which, when coupled with amino

acids, cause brown color in potato cuts during heat treat—

ment (7A). Meanwhile gelatinized starch is released and

other desirable low molecular weight compounds (15),

e.g., flavor constituents (7A), are also leached out into

the blanching liquor. A considerable amount of liquid

waste is generated during water blanching, which con-

tributes significantly to overall plant effluent. It

is reported (79) that blanching of potatoes may contribute

over 20 percent of the BOD in the plant waste load and,

in the case of frozen products, the rate of water usage

is 250 gallons per ton of raw potatoes processed. It

has been reported (86) that blanching, when coupled with

peeling, will account for about AA percent of the total

plant effluent, 89 percent of the total BOD, 86 percent

of the total COD, and 37 percent of the total suspended

solids generated during processing of potatoes. Tables

3 and A present blanching data.

The alternate low-waste producing blanch processes

2A

Table 3. Suspended Solids and Total Solids in Potato
Blanching Effluent.

 

 

 

Effluent
% of SS”) TS(2) (5)
_Process Step gal/min Total. :mg/R mg/k RGf.
"Hot Blanch" (steam) 3O -- 3300 -—-- 6
"Wet Blanch" (water) 90 —- 195 -——— 6
Blancher and Peeler 153.5 AA ---- 3330 86

 

 

Source: EPA Report 12060 EDK 08/71.

(1) Suspended Solids. (2) Total Solids. (3) Numbers
correspond to listing in Literature cited.

25

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26

like hot gas, microwave, steam, and individual quick
blanch (IQB) methods which are discussed in several ref-
erences (10,12,17,A9,6l,62) are not applicable (15) to
French fry processing at the present time. This is because
there are normally large amounts of the leachables which
must be removed during this process step in order to
prevent development of brown color on the surface of

the cuts in later heat treatments.

The effluent, generated in the blanching process, is
separable from the total waste stream and can be treated
to reduce pollution loads significantly in the total
process waste flow (63). As a preventive measure, use
of potato varieties which are poor sugar formers and
processing of stored tubers at periods during which
they are at the desired sugar level plus the use of re-
conditioning (1,7A) may leave no necessity for the use of
water blanching to leach unwanted reducing sugars. This
will enable processors to substitute low-waste producing
methods (such as those referred to above) to conserve
water. It is also possible to minimize pollution from
blanching by recirculating the blanch water to build up
the concentration of extracted soluble constituents so
as to restore some of the soluble material extracted by
passage of the potatoes through the blancher (7A). It
is said (79) that this procedure will decrease the

product loss, but it can also adversely affect the

27

removal of undesirable leachables from the product.

In the defatting operation, surplus oil is removed
from the French fries by passing the product over vibrat-
ing screens (15,7A). Oil recovery can be enhanced by a
variety of methods. Hot water may be sprayed on the
fried cuts during the vibrating process. It is also
possible to use specially designed equipment (7A) in
which the French fries are shaken and subjected to a high
velocity stream of hot air to aid the removal of excess
fat.

The most ideal solution (3) to water and waste manage-
ment in the food industry - and naturally, potato proces-
sing - is a total system approach such as that proposed
by Gallop gt a1, (1976). In such a system, one must view
the entire plant as a "total system" with the waste element
being as important as (or in some cases, more important

than)the product being put out for commercial sale.

Waste Characterization

The reduction of pollution in the processing of fruits
and vegetables depends on the identification of sources
and characteristics of the waste water (30). This enables
a researcher to find large water-use, waste-producing
areas in the processing operation and to determine methods
of reducing their effect on total pollution load. There-

fore, the first step of a pollution control program is

28

to characterize the waste water so as to determine (A,83,91)
the quantity and the treatability of organic compounds
involved. This also provides information (91) relating
to possible in-plant separation of the most significant
waste streams for separate handling at the processing
plant.

After initial studies (80,91), including the estab—
lishment of a complete picture of the entire production
process, showing of all raw materials, additives, and
products, by-products, and liquid and solid wastes and
also locating the process piping and waste drains, one
can proceed with flow measurement and determine points
of sample collection.

Collection of flow data is an essential part of the
waste water survey on which any pollution control measure
is dependent. Selection of the proper measuring method
or device should be done with consideration given to such
factors as cost, type and accessibility of the conduit,
hydraulic head available and type and character of the
waste. ’A thorough description of flow measurement -
methods is given in the EPA Handbook for Monitoring In-
dustrial Waste Water (80).

Sampling is of paramount importance in waste survey
programs. The information obtained by sampling provides
the basis for any plant pollution abatement program. The
type of information desired will dictate the method

29

utilized for obtaining waste water samples (83). The
choice between grab and composite samples should be made
on the basis of the stability of the constituent to be
measured, and the degree of accuracy desired in the
results. Although composite samples have the advantage
of being less sensitive to fluctuations in waste charac-
teristics which occur during the sampling period (83),

a grab sample may be preferred over a composite sample
when the waste characteristics are relatively constant
(80). For wastes in the latter category a complex sampling
is not necessary since an occasional grab sample may be
entirely adequate to establish waste characteristics.

In other words, the data collected by grab samples, while
not as precise, would still be exceptionally valuable in
terms of definingtfluaprocess from a waste-generating
standpoint. For in-plant surveys, grab samples should

be taken several times per shift (83) but, in deciding

on the frequency of sampling, one must always strike a
balance between reliability and cost (66).

In situations where analysis of waste water samples
will be unavoidably delayed, the samples may be pre-
served. In the case of freezing, samples should be placed
in flexible containers with sufficient space left in the
containers to allow ice expansion (83). The subject of
sample collection and care of sample is treated adequately

in references (7) and (80).

3O

Selecting Indices of Pollution

Determination of the volume and composition of the
wastes permits the assessment of locations at which the
greatest pollution load problems occur in the course of
processing (63). For this purpose, significant indices
of waste water composition should be evaluated.

For potato processing, a thorough analysis of the
literature (15) shows that Biochemical Oxygen Demand
(5-day, 20°C, BOD5), Total Suspended Solids (TSM), and pH
are the measures having major pollutional significance.

Determination of Chemical Oxygen Demand (COD) of the
waste is also useful from any of the following stand-
points: (1) serving as a quick check or guide for BOD
(83); (2) measuring the oxygen equivalent of the portion
of the organic matter in the effluent that is susceptible
to oxidation by a strong chemical oxidant (but not neces-
sarily biodegradable) and, last but not least; (3) being
the only method for determining the organic load in
certain wastes containing toxic substances (7).

Settleable solids is another major waste water index
(83) which would be included in the determination of
total nonfilterable residue — previously referred to as

Total Suspended Solids or Total Suspended Matter (7).

31

Analytical Procedures

Many researches (38,71,91) follow the methods des-
cribed in "Standard Methods for the Examination of Water
and_Waste Water" (7). The test procedures described in
the Standard Methods are approved by the U.S. Environ-
mental Protection Agency (83). Other EPA approved test
procedures (82) are basically the same as those given in
the Standard Methods.

The BOD test can be done on either prepared dilu-
tions of the sample or the undiluted sample. The Stan-
dard Dilution Method, though long used, has never been
completely satisfactory. The Hach Manometric BOD Ap-
paratus, using undiluted sample and producing equivalent
results in terms of both accuracy and precision, has

several advantages over the Standard Dilution method

(35).

Interpretation of Data

The Q-Test (20) can be used as the criterion for
rejection of an observation in the measurement of desired
waste water indices.

Once the data are obtained, a proper statistical
technique should be used to interpret the results. The
four recommended techniques (91) are: (1) Testing the

difference between means, (2) Analysis of runs, (3) Re-

gression, and (A) Chi-square test.

EXPERIMENTAL

Process Description

Raw product quality and uniformity are the predominant
factors which determine the rate of water usage and waste
generation. Ideally, potatoes received at the processing
plant should have high solids content, low reducing sugars
content, thin peels and uniform size and shape. The pro-

cessing steps are as follows:

Receiving/Cleaning: Potatoes purchased and used during
the period of these tests were of the Kennebec variety.
Delivery was by truck and rail car. Potatoes received at
the plant may have soil loads of 3-5% of their weight (Lutz
33 El. 1967). Soil removal and elimination of some foreign
materials are achieved by passing the raw product on roller
conveyors and upward—inclined belt conveyors. The potatoes

are then stored in piles for processing.

Fluming/Transportation: The potatoes are washed away
from the leading edge of selected storage piles into a
flume by recycled water and conducted to a settling basin
for gravel and silt removal. Intermittent discharge of

silt calls for making up the water of the closed fluming

32

33

system. Fluming acts as a dual purpose step, transporting
and washing the raw product. Potatoes are pumped from the
settling basin to the elevated dewatering screens from
which they are dropped down into successive hoppers and
conveyors for better cleaning and foreign matter removal.
The relatively clean product is next taken to the peeling

operation by a vertical pump-referred to as a pump/flume.

Lye Peeling/Trimming: The tubers are dipped in a 20

 

percent lye bath at 160°F for a few minutes (depending on
the thickness of the peel) to loosen their skins and then
conveyed to the scrubber. The conveyor is sprayed with
fresh water through a perforated pipe. In the scrubber,
abrasive rolls, revolving in opposite directions, and fresh
water spray remove most of the peel from the potatoes as
they roll along the unit down to the washer. This unit
is identical to the scrubber and is employed for better
peel and caustic removal.

The trimming operation completes the peel removal.
In this operation the eyes, blemishes, and remaining peel
are removed manually. A spray of chlorinated water at the

end of trimming conveyor improves sanitation.

Surface Darkening Control: A pump, similar to that
before the lye peeler, takes the trimmed potatoes into an
elevated surge tank containing 802 solution to prevent

brown color develOpment.

3A

Cutting: The peeled-trimmed potatoes are cut into
smaller pieces having the desired shape. During cutting,
a number of potato cells are ruptured and a considerable
amount of starch is released. Some water is used to remove
this starch and facilitate the operation in the cutters.
The starch-rich-effluent is then discharged into the waste

stream.

Sizing: Potato cuts are directed onto a multiple-
1ayer vibrating screen with water sprays on the top to
eliminate remaining starch and the undersized cuts called

slivers and nubbins.

Blanching: A two-step, hot water blanch (160°F, 8—20

 

min.) is employed to achieve the following:

1. Inactivation of enzymes to prevent color and flavor
changes.

2. Partial cooking to reduce frying time and also fat
absorption through gelatinization of the surface
layer of starch.

3. Reduction of bacterial count.

A. Elimination of excessive reducing sugars to obtain
the desired color in the final product.

5. Improvement of the texture of final product.

This step is one of the biggest water users in the plant.

35

ColoringLSugar Dip: Since virtually all of the sugar
has been removed from the potato cut during blanching, a
small, controlled amount must be added back during the
coloring/sugar dip stage. This :hs done by fluming of the
blanched cuts in a solution containing dextrose, sodium
acid pyrophosphate, and food color to establish the desired

color in the finished product.

Surface Dgying: Surface moisture is removed by hot

air blast to prevent high oil pick up during frying.

Egying,and Defatting: The cuts are par-fried to
facilitate later preparation by the consumer or the
institutional user. Some heat inactivation of micro-
organisms is also accomplished during this step.

Surface oil of the fries is washed off by hot water
spray on a vibratory screen conveyor. The waste water,
containing considerable oil, goes to an oil recovery system,

then to a grease trap, and finally to the sewer.

Precooling and Freezing: After cooling by a cold air
blast, the cuts are quickly frozen in a tunnel freezer,
which is the bottleneck unit operation in the plant. The
coils of the cooler and the freezer should be defrosted
at intervals during the operation. Fresh water is used

for this purpose.

36

Packaging and Storing:” The frozen cuts are packedin

 

the desired size containers and stored at freezing tempera—

tures.

Water Use in the Plant

 

Water is used in different processing steps and achieves

the following purposes:

1. Transportation: Fluming of raw potatoes, water

 

conveying of the colored cuts.

2. Washing/Cleaning: Washer, trimming belt, cutter,

 

sizer, and fluming of raw potatoes.

3. Removal or Separation of Unwanted Materials:

 

Scrubber, cutter, sizer, defatter, liquid/solid
waste separator, and blanchers.

A. Heating or Cooling: Ammonia or air compressors,

 

boilers, blanchers, and defrosting of freezer and

cooler coils.

Solvents and Chemicals

All solvents, chemicals and reagents were of analytical
grade. Distilled, deionized water was used for labora-

tory analyses throughout the study.

37

Sampling

Selection of unit processes for which the effluent
would be surveyed, was based on several factors, namely:
volume and/or pollutional strength of effluent, possibility
of by-product recovery, possibility of effluent being re—
used or recycled with little or no treatment, and feasibility
of sample collection.

Based on the above mentioned factors, the chosen unit
processes were the washer, cutter, sizer, and each of the
two blanchers. The final plant effluent and the mixture
prior to addition of defatting and sanitary effluent were
also sampled.

Samples were collected for determination of Biochemical
Oxygen Demand (BOD), Total Nonfiltrable Residue (Total
Suspended Matter, TSM), Chemical Oxygen Demand (COD),
Grease and Oil (for final plant effluent), pH, and tempera-
ture from the selected unit processes.

Grab sampling was chosen over composite sampling for

the following reasons:

1. Remote location of the plant necessitated longer
time between taking and freezing of the samples.

2. Composite sampling needs costly equipment, espec-
ially when there are more sampling points.

3. Continuous operation of the plant with a relatively

stable production rate (11A hours per week and

38

about 9,000 lb of processed potatoes per hour)
gave reasonable assurance that the strength of

the waste waters should be relatively constant.

However, for improved accuracy, the samples were manually
composited. That is, several (three) grab samples taken
from the same point at different times, were combined to
form representative samples of each unit operation.
Samples taken for grease and oil determination, however,
were not composited before testing.

Plastic containers were used for all samples to
withstand freezing. Approximately 1,500 m1 samples
were collected in half-gallon milk bottles for BOD and
TSM tests, 500 ml samples were collected in freezer boxes
for COD measurement at each discharge point, and 1,000
m1 samples were obtained for grease and oil determina—
tion from the final plant effluent for each sampling

date.

Sample Handling and Preservation - The samples were
kept in styrofoam chests over ice soon after they were
taken and during transportation. Samples taken for COD
and grease and oil analysis were acidified at the sampling
site. Acidification was done by gradual addition of
concentrated H280” to the sample under continued stirring

until a pH of :_2 was attained.

39

Representative portions (each of about 300 ml) were
taken from the larger samples and kept at +A°C for at
most a few days before TSM determination. All other samples
were placed in the freezer (-15°F or -26°C) where they were
held until time of analysis - a time lapse of about two
months. There is no indication in the literature that the

freezing/thawing process has any effect on test results.

Analytical Methods

Sample Preparation - The frozen samples were placed in
warm water until completely thawed. In the case of BOD and
COD samples, the containers were shaken occasionally for
rapid thawing. Tests were run on the thawed samples (BOD,

COD, and Grease and Oil) immediately.

pH Determination - The pH was measured immediately after

 

taking the sample at the sampling site, using a Corning

pH Meter, Model 7.

Temperature Measurement - A portable digital readout
thermocouple and a bimetallic strip thermometer were used
alternately to measure the temperature of the effluent at

each discharge point.

A0

Total Nonfiltrable Residue (Total Suspended Matter,
TSM) - Method number 208D, page 9A, of the Standard
Methods for the Examination of Water and Waste water, lAth

edition, 1976 (7) was used to determine TSM of the ef-
fluents. The sample was kept well mixed by a magnetic
stirrer. An aliquot (at least 10 ml) was transferred slowly
by pipet to a pre-washed, dried, and tared glass fiber disk
filter set on a Gelman A7 mm magnetic filter funnel and
vacuum filtered. The interior of the funnel was then
washed with three successive 10 ml portions of distilled
water. After breaking the vacuum, the filter and its
contents were transferred into a tared aluminum planchette,
dried for at least one hour at 103° to 105°C, cooled in

a desiccatorenuiweighed. The drying cycle was repeated
until weight loss was less than 5.0 mg. Total Suspended
Matter was calculated as shown in Footnote (1), Appendix

Table V.

Chemical Oxygen Demand (COD) - Method number 508, page
550, of the Standard Methods for the Examination of Water
and Waste Water, lAth edition, 1976 (7), was employed to
determine chemically oxidizable matter in the effluents.

The strong effluent was diluted with distilled deionized
water, using a dilution factor of 1/20. A combination of
reagents was selected, as detailed in Table 508.1, page 553,

of the "Standard Methods . . ." in which 0.A g of crystalline

A1

HgSOu was added to 20.0 ml of diluted sample to complex
chlorides that would otherwise interfere with the results.
After addition of 5 m1 of H280” reagent and cooling of the
flask content, 10.0 ml of the standard K2Cr207 solution

was added. The glass was attached to a condenser, cooling
water started, and the remaining H280“ (25 ml) added through
the open end of the condenser. At the same time, flask
contents were mixed well to prevent localized overheating.
The mixture was refluxed for at least 2 hours. Then the
condenser was washed down, the mixture was cooled and diluted
to about twice its volume and, using 2-3 drops of ferrion
indicator, the excess dichromate was titrated with standard
ferrous ammonium sulfate to a sharp color change from blue-
green to reddish brown.

A blank sample consisting of reagents and distilled
water equal in volume to that of the sample was refluxed
and titrated in the same way.

The reactions involved in chemical oxidation and titra-
tion may be represented, respectively, in a general way as
follows (66):

= + A 8+8C 3+
CnHaOb + cCr207 + 80H + nC02 + '7?_'H20 + 2cCr

-2 81-2
Where C - 3 n + 6' 3

6Fe++ + Cr o= + 11m+ + 6Fe3+ + 201-3+ + 7H20

2

A2

To evaluate the technique and quality of reagents, a
standard solution was made by dissolving A25.1 mg of
potassium acid phthalate in distilled water and diluting
to 1,000 ml. This solution has a theoretical COD of 500
mg/1. The analysis of this solution showed 98.AA percent
recovery of the theoretical oxygen demand which fell within
the range given by the "Standard Methods . . .".

Normality of the standard ferrous ammonium sulfate was
checked daily and the COD of samples were calculated as

shown in Footnote (1), Appendix Table VI.

Biochemical Oxygen Demand (BOD) - Hach Manometric BOD
apparatus (Model 2173A; Hach Chemical Co., Ames, Iowa)
was used to determine the quantity of oxygen required
during stabilization of decomposable organic matter by
aerobic biochemical action. Aside from the simplicity of
BOD measurement by Manometric Method, the results have been
proven to be equivalent in terms of both accuracy and pre-

cision to those obtained by the Standard Dilution Method

(35).

Preparation of Dilution Water: The desired volume
of distilled water was placed in plastic milk bottles and
then 1 m1 of each BOD reagent listed in the "Standard
Methods . . ." namely, MgSOu, CaCl2, and FeCl3 solutions
was added per liter of water. The bottles were cotton-

plugged and kept in an incubator at 20i1°C until needed

A3

(maximum Of 35 hours). One ml of phosphate buffer was added
per liter of dilution water just prior to using it to dilute

the effluent sample, as described below under Procedure.

Preparation of Seed: The supernatant liquor from raw
domestic sewage - primary effluent - was taken from the
East Lansing Waste Water Treatment Plant in plastic milk
bottles, settled for 2A-36 hours at 20°C - in an incubator -

and was used as the standard seed material.

Procedure: To determine the BOD of the effluents, a
representative portion - 100 ml - was taken from each
sample. After adjusting its pH with l N H2804 or NaOH
to bring it within the range of pH 6.5-7.5, the volume
was increased to 1,000 ml by dilution water (dilution factor
of 1/10) to bring the final BOD within the working range
of the apparatus (maximum of 700 mg/l). For the cutters
and sizer effluents a different dilution factor (1/20)
was used. Consulting the Table of Volume-Scale Relations
(35), 95 m1 of the prepared sample was placed in the bottle
of the apparatus. One ml of seed material was added to each
BOD sample and a magnetic stirring bar was placed in each
bottle.

300 ml of the diluted seeding (dilution factor of 1/2)
was also prepared to be used both as a control and a cor-
rection basis for the results. Seal cups, each containing

3 pellets of KOH and with seal lips greased with mineral

AA

oil, were placed in the necks of the sample bottles.
When_putting the sample bottles on the apparatus and
starting the motor, the bottle caps were screwed in place
lo sely while the manometer caps were open. After running
the apparatus for 30 minutes to reach the thermal equilibrium
in the incubator, the previously greased manometer and
bottle caps were tightened, the scales were adjusted to
zero, and the time was recorded.

Manometer readings were obtained each 12 or 2A hours
for any possible later use of the data. The BOD of the
samples was calculated as indicated in Footnote (1), Ap-

pendix Table VII.

Prgparation of BOD Standard Samples: Standard samples

 

were run periodically to check the accuracy of the data
obtained. For this purpose, a solution was prepared con-
taining 150 mg/l glucose and 150 mg/A glutamic acid, each
of which had been previously dried in an oven at 103°C
for one hour. One hundred eighty ml of this standard
solution was seeded with 20 ml of the seed. Then 160 ml
of this seeded standard was used for determination of the
BOD. The corrected BOD of the standard solution fell
within the recommended range of 220:11 mg/A which indi-

cated that the apparatus was performing properly.

A5

Grease and Oil Determination - Method number 502A,
page_515 of lAth edition of the "Standard Methods . . ." (7)
was used for measurement of grease and oil content of the
final plant effluent. A deviation from the method was
necessary to evaporate liquids other than oil. For this
purpose, in addition to the use of recommended evaporat—
ing technique, the extract was vacuum dried at 70°C until
its weight loss became less than 5.0 mg per one hour.

The level of the thawed sample in the container was
marked for later sample volume determination. The whole
sample then was transferred into a 2,000 m1 separatory
funnel. The sample container was carefully rinsed with
30 m1 of Freon-113 (1,1,2-trichloro—l,2,2-trif1uoroethane).
The rinse liquid was added to the separatory funnel, the
contents of which were then shaken vigorously for 2 minutes.
After separation of layers, the Freon layer was drained
through a funnel containing solvent-moistened filter paper
(Whatman No. A0) into a clean, tared distilling flask.

The extraction was repeated two more times and then the
filter paper was washed with 10 ml of Freon. The flask
containing the combined extracts was placed in a water bath
at 70°C to remove most of the Freon by evaporation and

then on a steam bath for 15 minutes to remove the last
traces of Freon. During the final one minute, air was
drawn through the flask by means of an applied vacuum.

Since the standard procedure did not remove the non-oil

A6

liquids, the mixture was vacuum dried as stated previously.
Scorching occurred during vacuum drying which indicated that
scorchable, non—oil organic materials were extracted by
Freon along with the desired grease and oil, during the
eXtraction process. It is felt that the scorching and
accompanying weight loss minimized the possible error from
non-oil nutrients in the Freon extract.

To determine the solvent residue, 50 ml of Freon was
placed in a tared clean distilling flask and underwent the
same drying procedures. The gain in weight of the flask,
which corresponded to the residue weight from 50 ml of
solvent, was converted to that of 110 m1 of Freon and used
as weight of solvent residue in the calculation of grease
and oil content of the sample, as shown in Footnote (1),

Appendix Table VIII.

Standard Sample Preparation: Standard sample was made
by mixing one gram of the frying oil used in the processing
plant with water to a total volume of one liter. The con-
tainer used for this purpose was the same as those used for
the final plant effluent samples taken for grease and oil
determination. The standard sample was handled and analyzed
the same way as the effluent samples. The results of the
standard sample analysis was used as a correction basis
for reporting the data (See Footnote (1), Appendix Table
VIII).

A7

Flow Measurement and Water Usage Determination

A total water usage of 300,000 gallons per day by the
plant was used as a basis for calculations in these studies.
This value had previously been determined from water usage
data by the plant personnel.

The flow rates for specific operations in the plant
were determined in several ways. The method(s) in each
instance, being chosen on the basis of reliability and
practicability under plant conditions, are cited in Ap-
pendix Table II along with the flow rate data. The methods
used were: 1) Meter readings on specific water lines;

2) Measurement of water quantities in measured periods of
time, representing influents or effluents of various unit
processes at average operating pressure. During periods of
water collection, operating pressures were adjusted to the
average operating pressures given in Table 5. These, in
turn, had been determined previously by installation and
monitoring for a two-week period of pressure gauges on the
water pipes leading to each of the listed unit operations.
In a few of the Operations listed in the Appendix Table II,
pressure readings could not be obtained but flow rates in
each of these unit operations were insensitive to variations
in line pressure (based on previous determinations by plant
personnel); and 3) Calculation of water usage by formula,

using manufacturer's specifications for nozzle output as

A8

 

 

 

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A9

a function of line pressure. Appendix Table I provides
information relating to the spray nozzles used in each
unit operation. Footnote (3-b) to Appendix Table II

indicates the method used to calculate nozzle flow rate.

RESULTS AND DISCUSSION

Plant Layout and Water Flow Pattern

The general sketch of the plant at the time of these
studies (1976-77) is shown in Figure 1 and a scaled-up
sketch of the processing area is displayed in Figure 2.
Preparation of these figures resulted in better assess-
ment of the drains and water flow in the plant.

The water flow pattern is shown in Figure 3. The
product flow plus both solid and liquid waste flows are
also shown in this figure. It is evident that water
conservation in terms of water reuse or recycling is
being practiced just in three unit operations. The first
area of conservation involves fluming of raw potatoes
in which water is recycled continuously with occasional
discharge of mud. Some of the water is lost during each
mud discharge. The make up for this loss comes from the
fresh water which is used to lubricate the pumps or to
obtain the required level in the pumping and destoning
unit through an automatic level controller. The second
area of water conservation is the first blanching unit
which reuses cooling water from the water—cooled ammonia
compressors. The third area is the sugar dip or coloring
operation in which the coloring solution is used for

fluming of the treated potato cuts to the vibratory screen

50

51

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Figure 3. Water/Product Flow Pattern.

 

5A

(also called shaker) located just before the dryer. There-
by, the solution is recycled continuously and only a small
portion of it is lost during each cycle. This small loss
is made up from a reservoir containing fresh coloring solu—
tion. Another thing shown in Figure 3 is that, other than
the pumping, defatting and sanitary waste waters, all
the effluents from different processing steps enter into
the gutters which, being continuously flushed with re-
cycled waste water, constitute a part of a waste water
recycling loop within the plant. The solids, washed off
the floor or directly dumped into the gutters, are sepa-
rated from the recyclable liquid portion by a screen/
shaker-type separator and then passed on to the solid
waste reservoir (referred to by plant personnel as a
"cyclone").

The three practices described above, along with the
use of cooling towers, constitute the total water conserva-

tion effort in the plant.

Water Usage

 

The total flow rates for all streams in the plant are
listed in Table 6. (Table II in the Appendix gives the
original weight per time measurements and other details
as well as sample calculations.)

The Miscellaneous category in Table 6 includes daily

Table 6.

55

Gallons of Water Used by Specific Operations.(l)

 

 

Water Usage

 

 

 

 

Water Using Gal/ Gal/ Gal
No.. Operation Min. Day3 Ton %
- Fluming of Raw
Potatoes .5 9360 3A.7 3.1
5 Pump/Flume .9 A176 15.5 l.A
7 Post-Peeler
Conveyor 17.3 2A912 92.3 .3
8 Scrubber 16.5 23760 88.0 .9
9 Washer 22.6 325AA 120.5 10.8
10 Trimming Belt .9 2736 10.1 0.9
11 Pump/Flume 3.0 A320 16.0 l.A
13 Cutter 8.7 12528 A5.9 A.2
1A Sizer 8.8 12672 A7.A A.2
16 Blancher I 22.2 31968 118.A 10.7
17 Blancher II 31.6 A550A 168.5 15.2
18 Coloring System 0.1 1AA 0.5 0.0
22 Defatter 22.7 32688 121.1 10.9
-- Defrosting 2.8 A032 1A.9 1.3
35 Liquid/Solid Waste
Separater 8.2 11808 A3.7 3.9
37 Air Compressor 5.3 7632 28.3 2.5
33 Boilers 1.1 158A 5.9 0.5
-- Cooling Towers 0.5 720 2.7 0.2
-- Ammonia Compressors 2.7 3888 lA.A 1.3
-- Weekly Clean—up 13.2 19008 70.A 6.3
Subtotal 195.9 282096 10AA.8 9A.
Miscellaneous? 12.u 17856 66.1 6.
Tota18 208.3 299952 1110.9 100.0

 

 

(1) Data were taken all from Appendix Table II.

56

Table 6. Continued.

 

Footnotes:

(2) Numbers correspond to those in Figure 2.

(3) Based on 2A hours per day.

(A) Based on 270 tons of raw potatoes processed per day.

(5) Based on the average daily water usage of 300,000 gallons
which had been calculated from water bill data by the
plant personnel.

(6) Included in Blancher I.

(7) Includes daily housekeeping, sanitary, laboratory, and

(8)

other non-processing uses.

See Footnote (5) of this Table.

57

housekeeping, sanitary, laboratory, and other non-processing
uses.. One minor usage of water during processing is also
included in this Miscellaneous category because of its
negligible nature, namely water to fill the surge tank
between trimming belt and cutters. The Miscellaneous
category may be somewhat larger or smaller than the true
total value for the various miscellaneous water uses that
are listed since it reflects the unavoidable errors in-
volved in measuring water usage in each of the other
categories.

The conversion of gallons per minute into gallons
per day has been done by a factor of 1AAO (minutes per
2A hours). For example, in the case of fluming of raw

potatoes, it is done as follows:

(6.5 gallons)(l,AAO minutes)
(minute) (day)

= 9,360 gallons per day

Although the most meaningful unit of water flow is in
terms of volume per time (89), most researchers have chosen
the unit of volume (of water) per ton of raw product
processed. On this basis and for ease of comparison, at
an average hourly production rate of 9,000 pounds of
finished French fries (see Appendix Table IV) and an

average yield of A0 percent(15,7A,8A), the daily tonnage

58

of raw potatoes processed was calculated. Flow rates
were then converted into gallons of water per ton of raw
potatoes processed. The calculation of raw product ton-

nage is shown below:

lb finished fries (2“ hours)

9’000 hour day

Raw Potatoes Used
A0 lb finished fries (2 000 1b )
I100 1b raw potatoes ’ ton

270 Tons/Day

As in the case of fluming of raw potatoes, a sample cal-
culation of flow rates in terms of gallons per ton of

raw potatoes processed would be as follows:

9,360 gallons/day

27o tons/day = 34.7 gallons/ton of raw potatoes

Considering the fact that a negligible amount of water
is consumed through evaporation in the plant, it seems
reasonable - for the purpose of simplified calculation -
to assume that all influent water turns into waste water.
Thereby, comparison of total water used in the plant per
ton of raw potatoes processed (1,111 gal/ton) with the

reported range (21,22,2A,30,A2,56,83) of waste water flow

59

in potato processing (813 to 12,000 gallons per ton)
reveals that this plant could be classified as an effic-
ient water conserving establishment. (A more detailed
comparison of literature values with those obtained in
theSe studies of water usage for specific stages of
processing is shown in Appendix Table III.)

A more careful examination of Table 6 reveals that
lye-peeling (comprised of post—peeler conveyor, scrubber
and washer), blanching (including both blanchers), de-
fatting, sizing, and cutting are the major water users
in the plant using 27.0, 25.9, 10.9, A.2, and A.2 percent

of total water intake, respectively.

Waste Generation

Values for Total Nonfiltrable Residue (Total Sus—
pended Matter, TSM), Biological Oxygen Demand (BOD) and
Chemical Oxygen Demand (COD) of the measured effluent
streams, including the final plant effluent plus grease
and oil content of the final plant effluent are shown in
Tables 7, 8, 9, and 10, respectively. (More detailed
data may be found in Appendix Tables V, VI, VII, and VIII,
respectively. Relevant sample calculations are included
with the respective tables.)

As indicated in the above-mentioned tables, the same

seven sampling points were used throughout the study,

60

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63

Table 10. Grease and Oil Content of the Total Plant

 

 

 

 

Effluent.
Grease and 011 Content
Sample mg per liter of Sample
6/9/77 571.8
6/1u/77 557.8
6/16/77 582.9
6/20/77 “No.9
6/23/77 569.7
6/27/77 581.u
6/29/77 808.3
Average(1) 5h6.5
C.V., Percent(2) 11.0

 

 

(1) Average amount (mg) of grease and oil per liter of
sample calculated for the samples dated 6/1M/77 to
6/27/77. Discussion of reasons for exclusion of
6/9/77 and 6/29/77 data from calculated mean can be
found under Results and Discussion.

(2) See Footnote (6), Table 7.

6U

thereby providing sets of seven samples for each of the
times and dates on which measurements were made. Since

a trial sampling was conducted on 6/9/77 to find any
obstacle associated with the sample handling, results
obtained on that date will not be discussed here. Like-
wise, data from 6/29/79 have not been averaged with the
other results because of the dissimilarity between cottage
fries (which were processed on that date) and the types

of cuts normally produced by the plant. In addition,

these potatoes were atypical with respect to quality (small,
somewhat dehydrated, and shriveled). Data from both of
these dates are, however, included in the tables for reasons
of general interest and completeness of data.

Therefore, attention will be focussed on the mean
values calculated for the period of 6/lh/77 to 6/27/77.
Although the magnitude of the coefficients of variation
associated with the mean values for unit operations shown
in Tables 7 through 10 for this period indicates a highly
variable effluent discharge, the mean values for the period
(based on both steak cut and shoestring French fries)
are believed to be valid. The Justification for combining
the data for the steak- and shoestring-cut potatoes in
Tables 7 through 10 has been detailed in Appendix Table
IX.

Factors contributing to variation of the results

presented in Tables 7 through 10 may include raw product

65

composition (e.g., sugar content), process variations
(e.g;, water usage), sampling errors, and the inherent
error of the method of analysis.

, The results of the grease and oil content of the final
plant effluent (Table 10) may be higher than the true
values. This stems from the fact that Freon, like other
solvents, has the ability to dissolve not only grease
and oil, but also other organic substances. Such a
theoretical consideration was supported by the scorching
of unknown organic materials which occurred on the inside
surface of the sample containers during the vacuum drying
that followed extraction.

Temperature and pH values of the effluents are listed in
Table 11. These values remained fairly stable over a

long period of time, hence the average of two separate
measurements was chosen to provide a reliable estimate of
those in the plant. Monitoring of the pH of an effluent
that is to be reused or recycled can be useful in pre-
venting adverse effects on equipment or product. pH
measurements are also of value in determining the degree
of neutralization required by plant effluent. Temperature
is important both from the standpoint of product quality
and heat recovery (or thermal pollution which is the other
side of the coin).

To draw any inference from the obtained data or to use

it for comparison with those reported in the literature

Table 11. Temperature and pH of the Effluents.

66

 

 

 

Temperature

Source °C °F pH
Post-Peeler Conveyor 2M 75 11.3
Washer 22 71 9.7
Cutter 18 6A 6.8
Sizer 19 66 6.8
Blancher I 69 156 6.2
Blancher II 69 156 6.“
Defatter 56 13H 7.6
Recycled Waste Water 28 82 12.3
Air Compressor 38 100 7.H
Plant Effluent 1(1) 28 82 12.2
Plant Effluent 11(1) 30 85 12.2
City Water 15 59 7.U

 

 

(1) See Table 7 for descriptions.

67

it should be arranged in a more expressive way through
which the totality of each waste stream could be regarded.
Such an arrangement can be found in Table 12. To con-

struct this table, the following equation was used:

Daily Pollutant, lb/day =

.1.

gal)(Waste Produced, %§)

a1
(Water Usage, %E§)(3.785

5 m
(u.536 x 10 T8)

For example, total suspended matter for the washer was

calculated as follows:

a1 1 mg
(32,1400 gfimws ga—lmauu t) =

n.536 x 105 ¥§

Washer, TSM =

63A lb/day

Percentage of total pollutant attributable to each source

is also shown in Table 12, as calculated from the lb/day

figures.

68

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70

Based on the Table 12 results, the cutter effluent,
though relatively low in volume, holds a large share of
the total daily waste production (10 to 20 percent, de-
pending on which index of pollution is used). The sizer,
using almost the same amount of water as the cutter, pro-
duces only 5 to 7 percent of the daily waste. Blanchers
are large water users, but small TSM producers. However,
blanching effluents are very strong both from BOD and COD
standpoints.

The main contribution of the defatter to the total
waste production is the grease and oil found in the final
plant effluent. The washer, as a part of the peeling
operation, generates higher TSM than BOD or COD. This
might be ascribed to the incorporation of parts of the
skin into the effluent which includes a layer of corky
periderm. Other phases of the overall peeling Operation
are included as part of the Miscellaneous category in
Table 12. This Miscellaneous category is made up of all
effluent sources not Specifically listed in the table,
namely: flume for raw potatoes, lye-peeler, post-peeler
conveyor, scrubber, trimming belt, surge tank, and water
handling of solid wastes generated all over the plant
plus other minor waste producing sources.

Among the above sources contributing to the Miscel-
laneous category in Table 12, the scrubber is the major

source of pollution, but meaningful measurements could

71

not be made because of the extremely wide variation in
rate-of solid discharge from this unit. Hosing of solid
wastes into the gutters brings about more contact time
between solids and water both within the gutters and during
passage through the liquid/solid waste separator, result-
ing in increased leaching of pollutants. Fluming of raw
potatoes is another significant source of pollution,
consisting primarily of insoluble solids such as silt

from the potato surface. Some indication of the quantity
of pollutants derived from the other Miscellaneous sources

mentioned above can be found in the literature (38,39).

BOD—to-COD Ratio

The BOD-to-COD ratio for each of the effluent streams
under consideration was calculated. These ratios, which
are listed in Table 13, provide an indication of the
probable effectiveness of biological treatment. The
higher the ratio, the more effective the biological treat-
ment would be. Thus, the final (or total) plant ef-
fluent, having the highest ratio, would be the most
responsive and the cutter effluent, with the lowest ratio,
would be the most refractory waste water with regard to

biological treatment.

72

 

 

 

 

 

Table 13. BOD-to—COD Ratio.
BOD-to-COD Ratio
Bffluent (1) Literature Values(2)

Source Exp. Value Plant A Plant B Plant
Washer .561 _-__ __-- _-__
Cutter .u96 .132 .157 ---_
Sizer .679 __-_ _-__ . -___
Blancher I .860 .858 .76l(3) .500
Blancher II .823 .u7u ---- ___-
Plant Effluent 1(a) .839 -__- -___ _-__
Plant Effluent II(”) .863 .627 —-—— .596

 

 

(1) Based on experimentally-obtained (mean) values in Tables

8 and 9.

(2) Calculated from the BOD and COD values reported by

Hindin (1970) in his studies on three potato processing

plants.

(3) Values for both Blanchers (I and II) are included.

(A) See Table 7 for description.

73

Comparison of the Obtained Results with Those From Other

Studies

The comparison of test results obtained in these
studies with those of other studies taken from the litera-
ture is shown in Appendix Table III. Focussing on total
plant effluent, one can see that the plants reported upon
in the literature used substantially more water per ton
of potatoes than the one under study here. As might
logically be expected, the high water-using plants
exhibited lower concentration of pollutants in the ef-
fluent. This dilution effect is apparent in the compara—
tive figures for TSM, BOD and COD of total plant effluent
as well as in the TSM, BOD and COD values for those
process steps for which comparative values are given.
Based on data shown in Appendix Table III, less water is
being used in Just about every process step mentioned in
the table with the exception of blanching and defatting.
The biggest water saving processes are primary wash flume
(fluming of raw potatoes), cutting and trimming.

The slightly higher pH of the total plant effluent in
these studies might be attributable to lower water usage
or possibly to higher initial alkalinity of the water
supply. The higher pH of both blanching effluent and
cutting effluent in these studies, as compared with Table
III literature values may likewise have resulted from

higher pH of the fresh water supply. Other factors such

7A
as potato variety and condition, size and type of cut,
and time and temperature of contact between water and
potato cuts may have also contributed to the pH variations
shown in Table III, but there appears to be no direct
evidence to support this belief.

Although the quantity of waste generated by the peeling
operation in the plant under study is not fully reflected
in the Appendix Table III, data for peeling and washing
(since they do not include waste emanating from the scrubber),
earlier reports (79) indicate that peeling is invariably
one of the major waste-producing operations in the overall
manufacturing process. This has been discussed in more
detail in the Literature Review.

According to Table 13, the BOD-to—COD ratios obtained
in these studies are higher than those calculated from
the studies done by Hindin (1970). This difference may
be ascribed to storage time and variety of potatoes and/or

to processing conditions.

Potential for Improved Water Conservation and Waste Reduc-

tion

 

The results of these studies indicate possible prac-
tices the implementation of which will culminate in
conservation of water and/or reduction of waste. Each

of these possibilities, discussed hereunder, has certain

75

advantages and drawbacks the balancing of which determines
its feasibility.

The most feasible practice deals with the reuse of
air compressor cooling water. This warm water has a normal
pH (as it is shown in Table 11) and is, at least, as clean
as the cooling water from the ammonia compressors, but is
being discharged directly as waste water. Some piping
may make its reuse possible in any unit operation - pref-
erably those using heated water such as blanching - with-
out further purification and, thereby, a saving of 2.5
percent could be achieved in the total plant daily water
use. Added to this, is the recovery of heat energy of this
effluent.

As it was discussed in Literature Review, slivers and
nubbins constitute about 10 percent of the raw potatoes
(7“). Processing of these cuts into some sort of by-
products seems to be promising from several standpoints.
As a water saving technique, it eliminates the practices
of hosing these potato cuts into gutters and rinsing them
at the liquid/solid separator later. This can, at least,
save 3.9 percent of total plant water use which is ap—
plied in the separator. However,1fiu3elimination of the
abovementioned rinsing may necessitate the dry handling
of other solid wastes (namely, potato cuts spilled on the
floor or tubers rejected by trimming operation). As a

waste reducing measure, it avoids leaching of solubles

76

off the usable pieces of potatoes (slivers and nubbins)
during fluming. Finally, it not only prevents a notice-
able portion of raw product from ending up as waste,

but also brings about more marketable by-products. On
the other hand, its accomplishment requires more new
equipment and manpower.

Other possible practices involve water reuse or re-
cycling and/or process modification. In defatting
operations hot water is sprayed upon the fried cuts at
a rate of 22.7 gpm. The effluent goes through a partial
oil recovery system and discharged still hot (13U°F) and
containing some oil (see Table 11 and Footnote lO, Appen-
dix Table II). If a more efficient oil recovery system
is maintained, the hot and relatively oil free effluent
can be recycled with some make-up water. This can save
a considerable percentage of total plant water use that
is now being utilized for this purpose (Table 6). It
also can save the considerable energy being used to heat
this water. In contrast with the stated advantages, the
implementation of this practice requires new equipment
and may cause less oil recovery from the cuts. In another
development, a completely mechanical defatting process
requiring no water can be used. Oil recovery in this
operation can be improved by employment of hot air stream.
Conservation of water (10.9 percent of the total plant

water use) and reduction of oil content of final plant

77

effluent are the advantages of this system. However, cost
of new equipment is expected to be the main drawback.
Product weight loss might occur due to the drying effect
of the hot air though it might be negligible because the
oil layer around the cuts may work as a barrier to moisture
loss. Operating cost may range above that of the present
system.

Blanching was shown to be one of the biggest water
using operations in the plant. The major reason for
using water blanching in French fries processing has been
discussed to be the undesirable leachables, mainly reduc-
ing sugars (15,7U). Hot water serves to even out varia-
tions of sugar concentration at or near the surfaces of
French-fry strips. Therefore, use of potatoes that are
"reconditioned" to reduce sugar level and/or varieties
resistant to sugar build up during storage can reduce
water use and waste generation in the blanching opera-
tion.

Another way of water conservation and waste minimiza-
tion in blanching involves a counterflow water system.

An experiment was performed on 5/5/77, in which the
effluent from blancher II was reused in blancher I.
Focussing on the amount of fresh water used in blancher
I, unlike the usual average usage rate of 20 gpm, the
counterflow system reduced the fresh water use to 7.3

gpm (see Appendix Table II). This reduction corresponds

78

to 6.1 percent of the total plant water use.

The above counterflow water system could be extended
to the upstream unit operations namely, peeling operation
units on one hand and all pump flumes on the other hand.

To do so, the blanching effluent may undergo a purification
process started with a heat exchange step to yield its

heat energy. The effluent, depending on the reuse require-
ments, can go through further purification, which may
involve fine-screening to leave its large floating or
suspended particles, an air flotation step to give up its
fine suspended matter, and a disinfection step for sani-
tary purposes.

Twelve gpm of the treated blanching effluent, corres—
ponding to 5.8 percent of the total plant water use, can
satisfy the requirement of the four pump flumes,two of
which operate in the Pumping and Destoning Section and the
other two are numbered 3 and 7 in Figure 2 or Table 6.

The remainder (about 28 gpm) can be reused in a retro-
grade manner in washer, scrubber, and post-peeler conveyor.
Reuse of washer effluent in the scrubber and that of
scrubber on post-peeler conveyor have to be preceded by
screening and/or settling. Such a counterflow use of
water starting from blanching can save 38.9 percent of the
total plant water use. This saving includes 6.1, 5.8,
10.8, 7.9 and 8.3 percent of total plant water use which

corresponds to blanching and pump flumes (as mentioned in

79

the above), washer, scrubber, and post—peeler conveyor,
respectively. However, cost of the equipment and the
effort needed for practicing this water use pattern
(including operation supervision and maintenance) may
discourage its complete implementation.

In connection with peeling, the desirable practice
might be the Dry-Caustic or Infrared peeling proved to
reduce water usage and waste generation to 25 percent or
less of that normally associated with the wet caustic
process. This can result in a saving of more than 20
percent of the total daily water usage shown in Table 6.
Another aspect of it is the potential advantage of separate
(dry) handling of peeling waste. Nevertheless, the invest-
ment required and the increasing cost of energy (which
escalates the operating costs) are the two major disad-
vantages associated with this practice.

Partial modification of present peeling system is also
worthy to note. Installation of a dry brushing equip—
ment (85) directly after the lye-peeler will brush clean
the lye-treated potatoes without use of water. In order
to remove the adhering starch, however, the potatoes are
said (85) to require after-washing with about one cubic
meter of water per ton of potatoes. If true, the 270
tons of potato processed per day would use “9.5 gpm of
water rather than the 56.“ gpm used presently in the washer,

scrubber and post-peeler conveyor (see Table 6). Therefore,

80

a saving of at least 3.3 percent in total plant water use
can be achieved. Another advantage is the separate (dry)
handling of peeling wastes. In contrast with these ad-
vantages, the equipment and operating costs should be
considered for further evaluation.

Starch recovery in cutting and sizing operations is
another promising practice. As it is shown in Table 12,
the rough daily discharge of total suspended matter (TSM)
from cutting and sizing is 2,500 pounds. This conforms
to 27.6 percent of the daily TSM discharged by the plant
and most of it is the starch washed off the surface of
potato cuts in these two operations. Therefore, if the
effluent from sizer is reused in cutters, almost all the
washed starch can then be recovered from cutters ef-
fluent by means of hydrasieve cyclones or settling. Such
a system can reduce 27.6 percent of total TSM, 15.“ per-
cent of total BOD, and 2“.“ percent of total COD discharged
from the plant each day. A marketable product can be
made from the starch and saving of at least “.2 percent
can be achieved in the total daily water usage in the
plant. In addition, the clean effluent from the starch
recovery system is reusable in any upstream unit operation.
This practice calls for new investment and would change
the operating cost, but would probably result in increased
earnings (15,37,76) for the company.

The suggested water conservation and waste reduction

81

plans in these studies do not change the pattern, source
and/or amount of water use in other unit operations.
These are, namely; boilers, cooling towers, ammonia and
air compressors, defrosting, trimming belt, surge tank,

coloring, weekly clean up, and sanitary and laboratory

USES .

SUMMARY AND CONCLUSIONS

The studies reported herein were designed to ascer-
tain the water usage, waste generation and ways of pollu-
tion reduction in a potato processing plant through water
conservation and waste utilization.

The study of plant as well as water and waste flow
patterns reveal possibilities for water conservation and
waste reduction. Water usage measurement and calculated
values show that the major water using Operations are lye
peeling (including the units immediately following lye
immersion-the post-peeler conveyor, scrubber, and washer),
blanching, defatting, sizing, and cutting with 27.0. 25.8,
10.8, “.2 and “.2 percent of the total daily plant water
use, respectively.

Results of the present studies, when considered in
conjunction with previously-reported findings, suggest some
process and/or equipment modifications as well as conserva-
tion practices to minimize water use and waste genera-
tion. These possibilities, discussed in Results and Dis-
cussion, are briefly stated in the following.

The most easily implementable change, representing a
saving of about 2.5 percent of total water usage, would
involve the reuse of air compressor cooling water without
treatment in the blanching operation.

Production of by-products from slivers and nubbins

82

83

coupled with dry handling of solid wastes will minimize
pollution and curtail total water usage at least 3.9
percent. A new product would also be offered for sale.

Use of modified defatting systems which employ either
recycled water or a mechanical method can reduce the
amount of oil in the final plant effluent and save up to
10.9 percent of the total water usage.

Using low sugar varieties or reconditioned potatoes
helps in waste reduction and water conservation in blanch-
ing. Reuse of second blancher effluent in the first
blancher achieves a 6.1 percent reduction in total water
usage. An additional 32.8 percent saving can be achieved
through the reuse of blanching effluent in pump flumes
and, in a retrograde manner, the peeling operation.

Setting up a dry caustic peeling process can be
expected to save about 20 percent or more of the plant's
present total water usage. This will also take most of
the peeling waste out of the plant effluent stream. The
installation of dry brushing equipment can reduce water
consumption by at least 3.3 percent.

Finally, a starch recovery system can reduce total
plant waste 15.“ to 27.6 percent and water usage by “.2
percent, at the same time yielding a considerable amount
of marketable starch. Other operations requiring water
would not be affected.

Despite the stated benefits of the changes suggested

8“

above, a thorough cost analysis would be required before
commercial implementation of each such change. Cost
analyses, however, were considered to be beyond the scope

of this investigation.

LITERATURE C ITED

10.

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Rosenau, J. R., Whitney, L. F., and Haight, J. R.
1978. Upgrading potato starch manufacturing wastes.
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Soderquist, M. R., Blanton, G. I., Jr. and Taylor,

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7“.

75.

76.

77.

78.

79.

80.

81.

82.

83.

8“.

85.

92

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8'6.

87.

88.

89.

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91.

93

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J. H., 1968. Vegetable canning process wastes.
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tion; Dramatic changes taking place. Food Engineering

“2(6):79.

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uses of water in Michigan. Graduate School of Business
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. 1968. In-plant treatment of cannery
wastes, A Guide for Cannery Waste Treatment, Utiliza-
tion and Disposal. Publication No. 38. State Water
Resources Control Board, Sacramento, CA.

 

APPENDIX

9“

Table 1. Manufacturers' Designation for Spray Nozzles in

Unit Operations Under Study.

 

 

 

 

Nozzles
Unit Operation Number
in Use Type and Number

Pumping and H 1/8 VV “00“
Destoning Unit 1 Spraying Systems Co.
Scrubber “ 81-3 SC 15

Delavan Co.
Washer 8 81-3 SC 15

Delavan Co.
Trimming Belt 6 H 1/8 VV “003

Spraying Systems Co.
Sizer 12 l/“ GG Flat Jet 6.5

Pat. #310“829

Spraying Systems Co.
Liquid/Solid l/“ P3520 Flat Jet
Waste Separator “ Pat. #2530571

Spraying Systems Co.
Defatter 13 l/“ GG Flat Jet 6.5

Pat. #310“829
Spraying Systems Co.

 

 

95

 

 

 

 

 

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112

Table IV. Finished French Fries Hourly Production Rate.

 

 

(1)

Production Rate

 

 

Date lbs/hr
6/9/77 9200
6/1h/77 9000
6/16/77 8500
6/20/77 8590
6/23/77 9780
6/27/77 9750
6/29/77 8000

Mean 897u(2)

 

 

(1) Data obtained from plant production records.

(2) Rounded out to 9000 lbs/hr.

113

Table V. TSM values(l) for Different Sources, mg/l.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Source
Sample Blancher Plant Effluent
Date No. washer Cutter Sizer I II I II
1 5210 ---- ---- 160 --- 3920 4530
2 5980 —--- ---- 130 ---- 3350 4370
6/9/77 3 6250 ---- ---- 120 ---- 3700 4600
4 5760 ---- ---- 150 ---- 3590 4100
mean 5800 140 3640 4400
v2 7.61 10.71 6.51 5.04
Adjustgd 5674 137 3561 4304
mean
1 41640 ---- 4810 730 170 2760 3020
2 1560 ---- 4490 900 190 1980 2610
6/14/77 3 1940 ---- 4930 1040 140 2150 2400
4 1820 ---- 4570 690 240 2470 3130
mean 1740 4700 8404 185 2340 2740
v 9.88 5.19 19.23' 22.72 14.78 12.29
Adjusted
mean 1740 4700 840 185 2340 2740
1 3210 15240 21145 295 60 3980 3720
2 2100 21050 5270 310 275 2850 3980
6/16/77 3 2710 22440 4990 335 215 3010 4390
4 2900 13750 5790 260 200 2120 3160
mean 2730 18120 5350 300 230 2990 3800
v 17.14 23.55 7.59 10.45 17.25 25.59 13.07
Adjusted
mean 2891 19186 5665 318 244 3166 4024
1 1720 9630 6900 350 290 1620 3230
2 1290 164206 7010 375 265 2600 2330
6/20/77 3 2090 270 8550 320 215 22906 2750
4 1540 14600 7900 295 230 350 2490
mean 1660 13550 7590 335 250 2170 2700
v 20.27 25.94 10.29 10.41 13.65 23.08 14.57
Adjusted
mean 1739 14197 7952 351 262 2274 2829
1 3520 19900 9240 380 105 4770 67205
2 2660 26930 8490 465 120 4130 4640
6/23/77 3 3010 24120 8230 450 100 5190 5120
4 3690 15330 9740 305 135 3990 4730
mean 3220 21570 8925 400 115 4520 4830
v 14.66 23.48 7.78 18.34 13.75 12.41 5.28
Adjusted
mean 2963 19850 8213 368 106 4160 4445

 

 

114

 

 

 

 

 

 

 

 

Table V. Continued.
Source

Sample . Blancher Plant Effluent

Date No. Washer Cutter Sizer I II I II
1 2700 18310 5310 295 110 4260 5360
2 2420 23540 5040 370 100 4730 5300
6/27/77 3 2330 15080 4670 350 90 4010 4090
4 2890 24870 4500 305 120 4040 4530
mean 2585 20450 4880 330 105 4410 4820
v 9.95 22.32 7:47 10.86 12.29 7.61 12.78

Adjusted
mean 2386 18877 4505 305 97 4071 4449
1 23106 4130 6120 210 100 4370 6800
2 6450 3700 7060 235 80 6030 5070
6/29/77 3 5640 4050 7810 230 95 5480 5740
4 5340 3480 5330 45 85 4900 7110
mean 5810 3840 6280 225 90 5195 6180
v 9.88 7.92 16.46 5.88 10.14 13.82 15.28
Adjusted

mean 6536 4320 7065 253 101 5844 6952

 

 

(1) a) Calculation of total suspended matters (TSM):

(B—A) 1000 %§-
TSM; mg/liter of effluent =

m1 sample

 

.__&___
1000 m1

= B'A x 106
51 sample

where: A weight of filter and planchette, g;

00
II

weight of filter and planchette after filtration and
drying the sample, g.

For example, calculating the TSM of the sizer on 6/16/77:

For sample No. 1, 14 m2 was filtered, A and B turned out to
be 1.5285 and 1.5581, respectively. Thus, TSM would be:

(1.5581-1.5285) x 106

14 = 2114 mg/IL.

Table V.

(1) a).

115

Continued.

Continued.

Doing the same thing for the other samples, we get:

Sample No. A, g B, g (B—A), g Sample Filtered, m£ TSM, mg/i

15me

1.5285 1.5581 .0296 14 2114
1.5137 1.5664 .0527 10 5270
1.5014 1.6012 .0998 20 4990
1.5080 1.5659 .0579 10 5790

b) Rejection of suspected results:

One of the calculated TSM values (2114) seems to be out of line
with the others. Using the Q-Test (20) for rejection:

4990-2114 :

5790-2114 ‘ '78 VS' Q0.90 = '76

Since Q > .76, this observation is discarded.

0) Mean (E) and coefficient of variation (v) is calculated as

8)

follows:

x = 4990 + 5270 + 5790 = 5350 mg/z

and the standard deviation is calculated to be 406 mg/2
Thus,
Standard Deviation

v = Mean 1: 100

= 406 x 100

5350 = 7.59%

Adjusting the Mean:

The mean value is adjusted on the basis of 9000 pounds per hour
for ease of comparison: '

5350 mg/R x 9000 1b§1hr _
Respective Production Rate, 8500 lbs/hr ' 5665 mg/2

The value of 9000 lbs/hr was chosen because it represents the
average production rate over the period of 6/9/77 to 6/29/77
(See Appendix Table IV).

116

Table V. Continued.

(2)
(3)
(4)

(5)

(6)

For calculation of coefficient of variation (v) see Footnote (l-c).

Adjustment of the mean is shown in Footnote (l-d).

.The mean value of 840 is actually the summation of Blancher I

and Blancher II mean TSM values. This is because the effluent
from Blancher II was being reused in Blancher I. Therefore, the
actual mean TSM value for Blancher I is:

840-(mean TSM value of Blancher II) = 840 - 185 = 655 mg/2.

Rejected by Q-Test (see Footnote (l-b), this table) and therefore
not used in calculation of mean.

Considered as determinate error. That is, the error which can, at
least in principle, be ascribed to definite causes and is generally
unidirectional with respect to the true value, in contrast to
indeterminate errors which lead to both high and low results with
equal probability.

117

Table VI. COD Values(l) for Different Sources.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Source
Sample Blancher Plant Effluent
Date‘ No. washer Cutter Sizer I II I II
1 7305 ---- ---- 5042 ---- 5121 5439
6/9/77 2 7305 ---- ---- 4962 -—-- 5161 5518
mean 7305 5002 5141 5479
Adjusted
mean 7146 4893 5029 5360
1 2293 ---- 8094 8880 2829 4112 4586
6/14/77 2 2333 ---- 8252 8920 2829 4112 4507
mean 2313 ———- 8173 89002 2829 4112 4547
Adjusted
mean 2313 8173 8900 2829 4112 4547
1 3542 24809 7357 5948 3326 4480 5691
6/16/77 2 3502 24653 7043 5909 3404 4441 5770
mean 3522 24731 7200 5928 3365 4460 5730
Adjusted
mean 3729 26186 7624 6277 3563 4722 6067
1 2499 18220 10532 6378 3717 3947 4330
6/20/77 2 2537 18144 10609 6340 43717 3947 4445
mean 2518 18182 10571 6359 3717 3947 4387
Adjusted
mean 2638 19050 11076 6663 3894 4135 4596
1 3986 28888 11089 6884 2279 6886 7876
6/23/77 2 3906 28964 11013 6963 2279 6926 7757
mean 3946 28926 11051 6924 2279 69067* 7816
Adjusted
mean 3631 26619 10170 6372 2097 6355 7193
1 2832 27316 6413 6039 1216 5467 6293
6/27/77 2 2714 27552 6491 5960 1255 5546 6372
mean 2773 27434 6452 6000 1235 5507 36333
Adjusted
mean 2560 25324 5956 5538 1140 5083 5846
l 7022 4144 8209 4340 568 6826 8153
6/29/77 2 7100 3987 8365 4184 490 6748 8231
mean 7061 4066 8287 4262’ 529 6787’ 8192
Adjusted
mean 7944 4574 9323 4795 595 7635 9216

 

 

 

118

Table VI. Continued.

(1) Calculation of Chemical Oxygen Demand (COD):

COD, mg/liter of effluent = (a—b) N x 8000
(m2 sample)(dilution factor)

 

where,

a = m8 of ferrous ammonium sulfate titrant, Fe(NH4)2 (30 )2,
used for blank. 4

b = m1 titrant used for sample.

N = Normality of the titrant determined by daily standardiza-
tion and calculated as follows:

N = mi dichromate x 0.25
ml titrant

For example, calculating the COD values on 6/9/77:

Standardization of the titrant: Using two lobmi-portions of
the standard dichromate solution (0.25 N), each of which took
25.6 m4 of the titrant to complete reduction. The average
volume of titrant required for the reduction of 10.0 ml of
0.25 N dichromate solution is:

25.6 + 25.6

12, = 25.6 ml

 

Therefore, the normality of the titrant would be:

N = (10.0)(0.250) = 2

25.6 9.77 x 10

Taking the Blancher I, two 20-m£-portions of the 20-fold diluted
original effluent were reduced by 18.45 and 18.55 ml of the titrant
after digestion. On the other hand, the average volume of the
titrant used for two blank samples (control samples) turned out

to be 24.80 mi. Thus, the corresponding CODs are calculated as
follows:

-2
(24.80-18.45) m4 (9.77 x 10 ) (8000) _
20 1112. (*1/20, - 4963 mg/g,

-2
(24.80-18.55) m1 £9.77 x 10 ) (8000) _
20 m2 (1/20) ' 4885 mg/“

119

Table VI. Continued.

As the standard solution of potassium acid phthalate, having a
theoretical COD of 500 mg/8, showed an average COD of 492.2 mg/fi,
the percent recovery is:

égéég-x 100 = 98.44%

Correcting for the percent recovery:

4963/0.9844
4885/0.9844

5042 mgr/2
4982 mg/R

Taking the average:

5042 g 4962 = 5002 mg/Q.

 

The calculated value (5002 mg/i) was finally adjusted to 4893
mg/i. Description of the method of adjustment is given in Foot-
note (1-d), Table V.

(2) The value of 8900 is the summation of COD values for both blan-
chers. This refers to the reuse of the effluent from Blancher
II in the first blancher. The actual COD of Blancher I is cal-
culated as follows:

8900 - (COD value of Blancher II) = 8900 - 2829 = 6071 mg/R.

120

Table VII. BOD Values(1) for Different Sources.

 

 

 

 

 

 

 

 

 

 

 

Source
Sample Blancher Plant Effluent

Date No. Washer Cutter Sizer I II I II

Measured 5984 -—-- —--- 4484 ---- 4834 5134

Adjusted 5854 ---- ---- 4387 --—- 4729 5022

Measured 1388 ---- 7277 72323 2382 3632 4082
6/14/77

Adjusted 1388 ---- 7277 7232 2382 3632 4082

iMeasured 2088 14477 5080 5387 2737 3487 5237
6/16/77 -

Adjusted 2211 15329 _5379 5704 2898 3692 5545

Measured 1340 8380 6180 5490 2840 3090 3940
6/20/77

Adjusted 1404 8780 6475 5752 2976 3237 4128

IMeasured 1990 13176 6376 6338 2138 6238 6438
6/23/77

Adjusted 1831 12125 5867 5833 1967 5740 5925

Measured 1638 12976 4576 4830 980 4530 5080
6/27/77

Adjusted 1512 11978 4224 4458 905 4182 4689

IMeasured 4230 2460 5960 3280 330 5934 6884
6/29/77

Adjusted 4759 2768 6705 3690 371 6676 7744

 

 

(1) Calculation of BOD values:

The BOD values can, unlike the Standard Dilution Method, be read

directly from the scale when the Manometric Method is used.

Only

very simple calculations are needed to correct the reading for
A standard sample, con-
taining glucose and glutamic acid and having a theoretical BOD
of 220 mg/1, was used periodically to see if the apparatus was

the seeding or the dilutions (if any).

functioning properly. An apparatus is said to be performing

properly if the corrected BOD of the standard solution is with-

.pin the range of_220:11 mg/z. As an example, results for some of

J. the samples from 6/9/77 and a standard solution are shown below:

121

Table VII. Continued.

 

 

 

 

 

Readings

Dilu. Seeding, Days BOD5’ mg/l

Source Factor Percent O 1 2 3 4 5 Cor. Adj.

washer 1/10 1 0 160 490 600 600 600 5984 5854

Blancher I 1/10 1 O 240 450 450 450 450 4484 4387
Plant Ef-

fluent II 1/10 1 O 235 445 510 515 515 5134 5022

Standard soln. - 10 O 175 235 235 235 235 219 ----

Seeding 1/2 — 0 6O 80 80 80 80 1608 ----

 

(a) No correction needed. To get the BOD5, the 5th day's reading is

(2)

(3)

divided by the respective dilution factor.

To calculate the BOD5, the 5th day reading was taken, corrected
for seeding and then divided by the dilution factor. For example,
the calculations for the washer would be as follows:

BOD = X'th day's Reading ~ (seeding percent)(BODx of the seeding)
X Dilution Factor

 

Thus,

_ 600 - (1/100) (160) _
BOD5 - 1/10 - 5984 mg/£

 

Finally, this calculated value was adjusted to 5854 mg/£ (see
Footnote (2)).

Method of adjustment of the data is shown in Footnote (1-d),
Table V.

Due to the reuse of the effluent of Blancher II in blancher I,
the BOD of the Blancher II should be subtracted from the value of
7232, to get that of blancher I:

7232 - 2382 = 4850 mg/R.

.122

Table VIII. Grease and Oil Content(1) of the Total Plant Effluent.

 

 

Grease and

 

 

Weight Oil, mg_

V01ume Tare weight Final Gross Difference per liter

Sample m2 g Weight, g g of sample
6/9/77 952 115.1058 115.5327 0.4269 571.8
6/14/77 1017 116.2840 116.7332 0.4492 557.8
6/16/77 1085 117.6510 118.1470 0.4960 582.9
6/20/77 1080 114.6020 114.9755 0.3735 440.9
6/23/77 1083 115.0415 115.5254 0.4839 569.7
6/27/77 918 115.4173 115.8359 0.4186 581.4
6/29/77 970 116.1612 116.7761 0.6149 808.3
Standard(2) 1000 116.6165 117.4153 0.7988 784.3
Solvent(3) 5O 115.8840 115.8906 0.0066 -----
Average(4) 546.5
Total Average(5) 587.5

 

 

(1) Calculation method:

a) Solvent Residue, SR:

SR =

weight of residue, g

0.0066 g

50 ml

0.0145 g

x 110 mt

m2 solvent used for residue test

m2 solvent used to

extract grease

123

Table VIII. Continued.

(1) b) Percent Recovery, PR:

= (weight Difference of the Standard Sample) - SR

PR Weight of Grease Used to Make the Standard

x 100

= (0.7988 - 0.0145) g x 1

1 g 00

78.43%

c) To calculate grease and oil (0&0) content of each sample,
the following formula was used:

G&O,mg/

(ml of sample)(Perceniggecovery)

Taking the sample dated 6/9/77 as an example:

6
c & 0 = 094269 I 10 = 571.8 mg 0 & 0 per liter of effluent
78.43 sample.
952 x 'ICKT'

 

mg_ ml
2 = (Weight Difference of the Sample, g)(103 g )(103 T)

(2) Preparation, handling and analysis of the standard sample is dis-

cussed under Experimental.
(3) See Experimental and Footnote (1-a) of this Table.

(4) Average amount (mg) of grease and oil per liter of sample cal-
culated for the samples dated 6/14/79 to 6/27/77.

(5) Average amount (mg) of grease and oil per liter of sample cal-
culated for all the samples.

124

 

 

 

 

 

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