WATER POLLUTION CONTROL RESEARCH SERIES • DAST-14
Current Practice
in
Potato Processing Waste Treatment
U.8. DEPARTMENT OP THE INTERIOR • FEDERAL WATER POLLUTION CONTROL ADMINISTRATION
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WATER POLLUTION CONTROL RESEARCH SERIES
The Water Pollution Control Research Reports de-
scribe the results and progress in the control and
abatement of pollution of our Nation's Waters.
They provide a central source of information on the
research, development and demonstration activities
of the Federal Water Pollution Control Administration,
Department of the Interior, through in-house research
and grants and contracts with Federal, State, and
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Triplicate tear-out abstract cards are placed inside
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Space is provided on the card for the user's accession
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utilize the WRSIC system.
Water Pollution Control Research Reports will be
distributed to requesters as supplies permit. Re-
quests should be sent to the publications Office.
Dept. of the Interior, Federal Water Pollution Control
Administration, Washington, D. C. 20242.
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POTATO PROCESSING WASTE TREATMENT
CURRENT PRACTICE
FEDERAL WATER POLLUTION CONTROL ADMINISTRATION
DEPARTMENT OF THE INTERIOR
by
Kristian Guttormsen
Research Engineer
and
Dale A. Carlson
Professor of Civil Engineering
Department of Civil Engineering
University of Washington
Seattle, Washington 98105
Grant No. WP-01486-01
October 1969
EWPfiA
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FWPCA Review Notice
This report has been reviewed by the Federal
Water Pollution Control Administration and
approved for publication. Approval does not
signify that the contents necessarily reflect
the views and policies of the Federal Water
Pollution Control Administration, nor does
mention of trade names or commercial products
constitute endorsement or recommendation for
use.
ii
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ABSTRACT
The continued rapid growth of the potato processing industry represents
a corresponding increase in waste water volume. This paper is a discussion
of potato processing, waste treatment, and current and needed research in
water quality control in this production field, A brief discription is
given of general characteristics of the potato and the effects and im-
portance of cultural and environmental conditions on potato processing.
General descriptions of the production processes have been included and the
literature has been extensively reviewed to present current and proposed
waste treatment technology. The most urgent research needs are discussed
together with suggested methods for meeting these needs. This report was
submitted in fulfillment of Grant Number WP-01486-01 between the Federal
Water Pollution Control Administration and the University of Washington.
iii
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IV
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CONTENTS
SECTION PAGE
Abstract iii
List of Tables vi
List of Figures vii
1 Introduction 1
2 The Potato Processing Industry - Its Growth
and Waste Production 2
3 The Potato 4
General Characteristics of the Potato 5
Variations in Types of Potatoes 6
Cultural and Environmental Conditions 7
4 The Processes 12
General Requirements on Raw Potatoes 12
Handling and Storage 12
Washing of Potatoes Prior to Processing 14
The Peeling Process 14
Potato Chips 20
Frozen French Fries and Other Frozen Potato
Products 22
Dehydrated Diced Potatoes 25
Dehydrated Mashed Potatoes - Potato Granules 27
Potato Flakes 27
Potato Starch 31
Potato Flour 35
Canned Potatoes 36
Pre-Peeled Potatoes 38
Alcohol 38
5 Methods for Reducing the Waste Load 40
Water Re-use and Conservation 40
Counter-Current Flow of Process Water 42
Process Control and In-Plant Treatment 42
Redesign and Modifications of the Process 44
By-Product Recovery from Potato Waste 46
Waste Separation and Combination 49
6 Current Waste Water Treatment Processes 50
Preliminary Treatment 50
Primary Treatment 52
Secondary Treatment 55
Ponds 63
Spray Irrigation 69
Tertiary Treatment 72
7 Disposal of Solids 74
8 Current Research and Development Efforts 79
9 Research Needs 80
Specific Research Needs 81
Suggested Approach to the Problem 85
Appendix A - Bibliography 87
Appendix B - Research Grants on Potato Processing
Wastes 97
Appendix C - Potato Processing Waste Treatment Costs 102
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TABLES
PAGE
I FUTURE PRODUCTION AND CONSUMPTION OF FROZEN POTATO
PRODUCTS 2
II POPULATION EQUIVALENTS PER TON RAW POTATOES 3
III PROXIMATE ANALYSIS OF WHITE POTATOES 5
IV MINERAL CONTENT OF POTATO ASH 6
V DESCRIPTION OF VARIETIES 8
VI RANKING OF THE IMPORTANT POTATO VARIETIES IN THE U.S.
1955 TO 1965 ARRANGED IN ORDER OF POPULARITY IN 1965 9
VII YIELD IN HUNDRED WEIGHTS PER ACRE AND SPECIFIC GRAVITY OF
POTATOES GROWN IN OVER-STATE VARIETY TRIALS IN MICHIGAN IN
1956 9
VIII POTATO PROCESSING WASTE CHARACTERISTICS FOR FRENCH FRIES 24
IX STARCH PLANT WASTE 33
X ORGANIC LOAD FROM STARCH PLANTS 34
XI RAW SCREENED FLOUR PROCESSING WASTE 37
XII LEACHING OF ORGANIC MATERIALS FROM SLICED POTATOES IN WATER 43
XIII EFFECT OF PEELING METHOD ON WASTE DISPOSAL 47
XIV BRUSH PEELING VS. CONVENTIONAL STEAM PEELING 46
XV TRICKLING FILTRATION OF PEACH AND PEAR CANNING WASTE 60
vi
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FIGURES
PAGE
1 TYPICAL POTATO CHIP PLANT 21
2 TYPICAL FRENCH FRY PLANT 26
3 TYPICAL POTATO GRANULE PLANT 28
4 TYPICAL POTATO FLAKE PLANT 30
5 TYPICAL POTATO STARCH PLANT 32
6 TYPICAL POTATO FLOUR PLANT 36
7 ENGINEERING NEWS RECORD INDEX 104
8 MECHANICAL SILT REMOVAL - CAPITAL COST 105
9 PRIMARY TREATMENT CAPITAL COST 105
10 SECONDARY TREATMENT CAPITAL COST 106
11 DISPOSAL BY SPRAY IRRIGATION CAPITAL COST 106
12 OPERATING AND MAINTENANCE COSTS 107
13 STABILIZATION POND CAPITAL COST 107
14 CLARIFIERS CAPITAL COST 108
vii
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viii
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SECTION 1
INTRODUCTION
The potato processing industry in the United States has experienced
tremendous growth during the last decade, and future projections indicate
that this trend will continue. Unfortunately, such marketable products
as French fries and potato chips are not the only products of the industry.
Large quantities of wastes requiring disposal are produced as well. If
discharged untreated or inadequately treated to our waters, these wastes
may create serious pollution problems. Milner Reservoir on the Snake River
in Idaho has experienced four of the nation's largest fish kills since 1960,
due principally to the combined effects of inadequately treated potato waste
and curtailment of the stream flow at the dam.
The predicted future growth of the potato processing industry repre-
sents a corresponding increase in waste water volumes. Since increased
waste discharges to our waters cannot be tolerated, higher and higher
degrees of waste treatment will be required of the potato processing
industry as well as other industries. High degrees of waste treatment with
the methods available today represent large economic burdens on the industry.
More efficient and less costly methods for providing such treatment must,
therefore, be developed.
Industrial wastes often exhibit unique characteristics such as high or
low pH which create unique treatment problems. Troublesome characteristics may
be common to several types of industrial waste, and may therefore have been
thoroughly investigated for purposes of waste treatment. The purpose of
this report is to present waste problems of the potato processing industry
together with current technology and available information. Hopefully this
presentation will serve as an introduction to the field for a larger group
of people involved in waste treatment research and development. By dis-
cussing the capabilities and limitations of the current and proposed
technology, this material should be of value to potato processors and
engineers concerned with potato waste treatment.
The report contains a brief description of the general characteristics
of the potato and the effects and importance of cultural and environmental
conditions. General descriptions of the different processes involved have
been included also. The literature has been extensively reviewed to present
the current and proposed waste treatment technology and pertinent available
information. Finally, the most urgent research needs have been discussed
and methods have been suggested to meet these needs.
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SECTION 2
THE POTATO PROCESSING INDUSTRY - IT'S GROWTH AND WASTE PRODUCTION
The total annual potato production in the United States now is
approximately 15 million tons. This represents an increase of 25 per
cent since 1956. While per capita consumption of potatoes in this
country has remained at about 110 pounds per year during the last
decade, the fraction consumed as processed potatoes has increased rapidly.
In 1956 the annual per capita consumption of processed potatoes was
23.4 pounds, more than twice that in 1949. In 1964 consumption
had increased by almost 54 per cent to 36 pounds. To meet the demand
for processed potatoes about 35 per cent of the total crop is now used
for processing. This is an increase of 147 per cent over the
tonnage processed in 1956. (Talburt and Smith 1967) (Irish Potatoes
1965, 1966).
The growth of the industry is expected to continue in the future.
Results of a computer analysis of the future increase in frozen potato
products are shown in Table I (Kueneman 1968). In 1965 potatoes repre-
sented more than 50 per cent of all frozen vegetables. Projections for
1976 indicate that potatoes will constitute 75 per cent of the vegetables
frozen and will represent about 10 per cent of all frozen foods.
TABLE I
PROJECTED FUTURE PRODUCTION AND CONSUMPTION OF FROZEN POTATO PRODUCTS
Year Poundage Processed Per Capita Consumption
(Million Pounds) (Pounds)
1660 8.35
1880 9.38
2110 10.44
2360 11.53
2610 12.64
2870 13.76
3130 14.88
3400 16.00
3680 17.11
3920 18.20
In a study of the Pacific Northwest by the U. S. Department of the
Interior (1966), a potato production increase of 83 per cent was predicted
during the period from 1965 to 1985. During the same period the pro-
duction of frozen and dehydrated potato products is expected to increase
by approximately 250 per cent.
A significant fraction of the potato is rejected as waste during
processing. The amount wasted depends upon the quality of the potato as
well as the particular type of process, and may vary from as low as
20 per cent to more than 50 per cent. Cooley et al. (1964) analyzed the
waste streams from various types of processing plants and determined
their population equivalents based on biochemical oxygen demand (BOD).
The results are shown in Table II.
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TABLE II
POPULATION EQUIVALENTS PER TON OF RAW POTATOES PROCESSED*
Flakes (Lye Peeling) 420
Chips (No Treatment 171
Chips (With Clarifier) 84
Flour (No Treatment) 318
Flour (With Clarifier) 110
Starch 353
*Based on 0.17 Ib. of 5 day 20°C biochemical oxygen demand (BOD.)
per population equivalent.
The average population equivalent of an untreated waste stream
from Table II is 315 per ton of raw potatoes processed. Thus, the average
daily tonnage of potatoes processed in this country at the present creates
an untreated waste load equivalent to a population of about 5.5 million
people. Based on projections for frozen and dehydrated potato products,
7.4 million tons of raw potatoes will be used in these two processes
alone in 1977 (Kueneman 1968). This represents an untreated waste load
equivalent to a population of almost 8 million people. (In 1966, 56
per cent of all processed potatoes were used for dehydrated and frozen
products.) The magnitude of waste production from potato processing is
indeed immense. The fact that the industry is located primarily in
Idaho, Maine, and the Red River Valley of the North concentrates the
problem in three relatively small areas.
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SECTION 3
THE POTATO
Historical Comments
The white potato, Solatium tuberosum. has been cultivated in the
Andes as far back as 200 A.D. Potatoes were a primary source of food
for the Indians of Peru; they had even developed methods of dehydration
to provide supplies of food for periods between successive crops when
fresh potatoes were not available.
Spanish and English explorers soon recognized the food value of the
potato, and it became an important source of provisions for their ships.
The explorers brought the potato back to their native countries. Records
have shown that a hospital in Seville, Spain, bought potatoes as early as
1573. The potato was introduced to the other European countries, but was
used as food only on a limited scale. In the early years it probably was
regarded a luxury, and later was reputed to cause a number of diseases,
including leprosy. Nevertheless, the potato soon was cultivated extensively.
Although wild ground nuts were used by Indians in the area of the
United States, the white potato was first introduced to this country in
1621, where, as in Europe, it became a major source of food.
Today, the potato is grown in almost every important agricultural
country in the world, and in many countries is still a major contributor
to the average man's diet. In the United States potatoes comprise 7% of
the 1488 pounds of food consumed per capita annually (Mercker 1965).
Development of the Crop Potato
During the early cultivation of the potato by the Peruvian Indians
no conscious efforts were made to develop varieties with specific
characteristics. Natural cross-pollination resulted in new varieties
which may have attracted attention and were thus replanted. In this way a
number of varieties occurred.
After the potato was introduced to Europe and North America, a number
of varieties of varying popularity were cultivated. At that time potatoes
usually were not grown to be sold, and quality control was not important.
The crop was consumed on the farm where it was grown, with low quality
varieties used as livestock feed.
The first great effort to develop varieties with specific characteris-
tics came in the middle of the 19th Century, when the crops in both North
America and Europe had been largely destroyed for several reasons.
Although efforts to develop a disease resistant potato failed, a number of
new varieties with high cooking quality resulted, some of which remained
popular for many years.
Today potatoes are available for specific purposes and environments.
Varieties with characteristics such as resistance to disease, high solids
content, low reducing sugar content, and thick or thin skin have been
developed. New varieties are derived mainly from cross-pollination.
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Research on hybridization of haploid and diploid species is under
way. If successful, diploid varieties may become available, and it may
be possible to add additional characteristics to the varieties while
retaining the varietal characteristics. (Talburt and Smith 1967).
General Characteristics of the Potato
Anatomy of the Tuber
A potato tuber is, morphologically, a modified stem, with its axis
greatly shortened and its lateral members only weakly developed, the
latter forming what are known as the "potato eyes."
The outer layer, the skin, consists of a corky periderm, the purpose
of which is to resist evaporation losses and attack by fungus. In the
event that the potato is cut or wounded, a wound periderm is formed which
apparently is more effective in protecting the tissue than the original
layer. Underlying the periderm is the cortex, a narrow layer of parenchyma
tissue. Between the cortex and the pith, which forms the central core of
the tuber, is the vascular area. This accounts for by far the largest
part of the tuber tissue, and is high in starch content. The vascular
storage parenchyma tissue is divided in two unequal parts by a discontinuous
ring, called the vascular ring, consisting of large polyhedral parenchyma
cells in which small islets of phloem are embedded. The pith, sometimes
called the "water core", is connected to each of the eyes by lateral
branches. It consists primarily of large cells, containing less starch
than the cells in the vascular area and the inner part of the cortex.
The eyes show the relation of the tuber to the stem. Each eye is a
leaf scar, arranged in a spiral around the tuber, with 13 eyes to each
5 turns of the helix.
Composition of the Potato
An accurate description of the composition of the potato is not
possible because of the great variety of potatoes, the area of growth,
cultural practices, maturity at harvest, subsequent storage history and
other factors. Talburt and Smith (1967) presented the following tables,
based on values given by various reviewers.
TABLE III
PROXIMATE ANALYSIS OF WHITE POTATOES
Average Percent Range Percent
Water 77.5 63.2 - 86.9
Total Solids 22.5 13.1 - 36.8
Protein 2.0 0.7 - 4.6
Fat 0.1 0.02 - 0.96
Carbohydrate
Total 19.4 13.3 - 30.53
Crude Fiber 0.6 0.17 - 3.48
1.0 0.44 - 1.9
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TABLE IV
MINERAL CONTENT OF POTATO ASH
Average Percent Range Percent
K20 56 43.95 - 73.61
P205 15 6.83 - 27.14
S03 6 0.44 - 10.69
MgO 4 1.32 - 13.58
Ma 0 3 0.07 - 16.93
CaO 1.5 0.42 - 8.19
SJXL 1 0.16 - 8.11
Starch - Starch is, calorically, the most important nutritional
component of the potato. The starch content, comprising about 65 to 80
percent of the dry weight of the tuber, influences quality parameters
of processed products as well as operational conditions of the processes.
Starch is present in the raw potato as microscopic granules in cells
of the parenchyma tissue, especially in the vascular area. It has been
found that starch content is closely correlated to specific gravity, and
an equation has been derived for the percentage starch based upon specific
gravity. Other factors affecting the starch content are fertilization,
cultural conditions, disease, morphology, and internal distribution.
Sugars - The sugar content of potatoes may vary from trace amounts
to ten percent of the dry weight of the tuber. Different potato varieties
have different sugar contents when harvested, but sugars will easily
accumulate after harvesting. Factors affecting the accumulation of sugars
include variety, storage temperature, maturity when harvested, and different
kinds of treatment during storage.
Potatoes with a high sugar content taste sweet and have poor texture
after cooking. Coloration of potato products, such as French fries,
potato chips, and dehydrated potatoes is closely correlated with the
content of reducing sugar in the raw potato. This results from the non-
enzymatic browning reaction between the aldehyde groups of the reducing
sugars and the free amino groups of the amino acids. Generally, potatoes
with a reducing content above 2 percent are not considered acceptable
for processing.
Variations in Tvpeg_of Potatoes
As mentioned earlier, a wide variety of potatoes is available.
Throughout Europe, 700 varieties are listed; 300 of these are suitable
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for industrial processing (Wiertsema 1968). The varieties in the United
States also are numerous. Many of the species are of little or no
importance, and the majority of the crop consists of a dozen varieties.
Also, new varieties are developed continuously while others are being
discontinued.
Talburt and Smith (1967) presented a general description of the older
varieties which are still popular and the newer varieties which contribute
to most of the present production (Tables V, VI, and VII).
Cultural and Environmental Conditions
The quality of potatoes, as well as the yield, is to a great extent
determined by the cultural and environmental conditions during the growth
period. Factors of influence include (1) date of planting, (2) soil type,
(3) soil reaction, (4) soil moisture, (5) season, (6) location, (7) mineral
nutrition of the plant, (8) cultivation and weed control, (9) spray program
for control of insects and diseases, (10) temperature during the growing
season, (11) time and method of vine killing and (12) time of harvest.
Since different varieties are affected to different degrees by the
above mentioned factors, the choice of variety is of course very important.
Date of Planting
This factor is related to the specific gravity, or solids content,
of the potato. Early planting generally means a longer growing season,
resulting in a potato of greater maturity and with higher solids content
at harvest than potatoes from later plantings.
Soil Type
The soil type in which potatoes are grown also may affect solids
content. Characteristics of the soil such as water holding capacity,
drainage, aeration, structure, temperature and fertility all may affect
the dry weight of the potato. Also, they may balance each other in
effect so that no change occurs. Obviously the possibilities are many.
It has been stated that loam soils generally produce the highest specific
gravity tubers. Probably, this is because loam soils have more nearly
optimal moisture, temperature, and structural relationships for potato
production than the lighter or heavier structured soils. (Talburt and
Smith 1967).
Soil Reaction
Little research has been reported on the effect of pH on potato
production. Smith (1937) found that potatoes grown under slightly acid
conditions had higher specific gravity than tubers from neutral or
slightly alkaline soils.
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TABLE V
DESCRIPTION OF VARIETIES
00
Year Originating Tuber Depth of Skin
Variety Released Agency Maturity1 Shane Eve2 Color
Bounty
Cherokee
Chippewa
Early Gem
Haig
Irish Cobbler
Katahdin
Kennebec
La Rouge
Norgold Russet
Norland
Onaway
Pungo
Red LaSoda
Red McClure
Red Pontiac
Russet Bur bank
Russet Rural
Russet Sebago
Sebago
Superior
Viking
White Rose
1959
1951
1933
1953
1957
1932
1948
1962
1964
1958
1961
1950
1954
. • •
1938
• • *
1903
. . .
1938
1961
1963
1893(?)
Nebraska
Iowa, Indiana and
Dept. of Agr. 3
Dept. of Agriculture3
Dept. of Agr.3 Idaho &
North Dakota
Nebraska
Unknown
Dept. of Agriculture3
Dept. of Agriculture3
Louis iana
North Dakota
North Dakota
Michigan and Dept.
of Agriculture3
Virginia and Dept.
of Agriculture3
Louisiana
• • • •
Dept. of Agr.3
Michigan
Unknown
Michigan
Wisconsin
Dept. of Agr.
Wisconsin
North Dakota
Private
M-L
M-E
M
E
E
E
M-L
L
M
E
E
E
E
M-E
L
M
L
L
L
Round
Round
Elliptical
Long elliptical
Round
Round with
blunt ends
Round
Elliptical
Oval
Oblong
Medium,
oblong
Cubicle
Elliptical,
round
Round-oblong
Round
Round, oblong
Cylindrical
Oval, flattened
Round, elliptical
M
M
S
S
M
D
S
S
D
S
S
M
M
M
S
M
S
S
S
Red
White
White
Russet
White-scaly,
russet
White
White
White
Red
Russet
Red
White
White
Red
Red
Red
Russet
Russet
Russet
Specific
Gravity Disease Resistance
Medium
High
Low
Low
High
High
Medium
High
Low
High
Low
Low
High
Low
Medium
Medium
High
High
Medium
Late blight, scab,
net necrosis
Mild mosaic
Scab
Scab
Mild mosaic
Mild mosaic, net
necrosis
Late blight, net
necrosis
Scab
Scab
Scab
Scab and late
blight
Late blight
....
....
Net necrosis
Scab
Scab
Scab, field resis-
Processing
Rating
Fair
Good
Poor
Poor
Good
Good
Good
Excellent
Poor
Good
Fair
Poor
Fair
Poor
Fair
Poor
Excellent
Fair
Fair
tance to late blight
L
M
M
M-L
Round, elliptical
Oval to long
Oblong-round
Long-elliptical
S
M
S
M
White
White
Red
White
Medium
High
High
Low
Field resistance to
late blight
Scab
Scab
....
Fair
Good
Fair
Poor
^-early; M-medium; L-late.
S-shallow; M-medium; D-deep.
3U.S. Dept. of Agr.
Talburt and Smith, 1967.
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TABLE VI
RANKING OF THE IMPORTANT POTATO VARIETIES IN U.S. 1955 TO 1965 ARRANGED IN ORDER OF POPULARITY IN 1965
Rutiflet Burbank . . .
Red LaSoda. .......
YIELD IN HUNDRED WEIGHTS
1955
.... 2
.... 1
.... 6
.... 3
.... 4
. ... 21
.... 5
.... 7
PER ACRE
1956
2
1
6
3
4
15
5
7
1957
2
1
5
3
4
8
6
7
1958
2
1
5
3
4
20
8
6
7
1959
2
1
5
3
4
10
8
6
7
TABLE VII
AND SPECIFIC GRAVITY OF POTATOES
1960
2
1
4
3
5
9
8
6
7
GROWN IN
1961
2
1
3
4
5
8
7
6
9
1962
2
1
3
4
5
8
7
6
9
1963
2
1
3
4
6
8
5
7
9
OVER-STATE VARIETY TRIALS
1964
2
1
3
4
10
5
7
6
8
12
1965
1
2
3
4
5
6
7
8
9
10
IN MICHIGAN IN 19561
Variatv
Inghaa Co.
Yield Sp. Gr.
Missaukee Co.
Yield Sp. Cr.
Preaque Isle Co.
Yield Sp. Cr.
Bay Co.
Yield Sp. Cr.
Montcalm Co.
Yield Sp. Gr.
Delta Co.
Yield So. Gr.
... 347
. .. 365
,.. 294
,.. 413
. .. 382
, .. 348
, . . 265
, .. 277
, . . 258
, .. 508
... 369
1.083
1.084
1.082
1.075
1.072
1.074
1.072
1.068
1.070
1.072
1.068
1.070
1.068
1.067
234
273
348
279
252
245
257
218
191
223
190
212
299
270
1.082
1.081
1.082
1.077
1.073
1.073
1.074
1.072
1.071
1.073
1.065
1.069
1.068
1.068
212
221
303
200
201
226
174
176
176
196
139
142
268
199
1.086
1.082
1.084
1.075
1.073
1.075
1.072
1.071
1.072
1.071
1.065
1.066
1.068
1.065
131
195
237
83
173
146
126
111
135
60
139
157
219
150
1.077
1.080
1.067
1.067
1.066
1.063
1.064
1.065
1.065
1.063
1.062
1.060
1.059
1.064
254
315
394
245
287
319
294
251
187
180
246
296
334
312
1.090
1.078
1.084
1.075
1.073
1.075
1.075
1.074
1.075
1.068
1.081
1.072
1.069
1.068
373
405
505
301
374
328
317
297
306
308
321
296
503
350
1.082
1.075
1.076
1.076
1.074
1.072
1.072
1.073
1.070
1.067
1.075
1.073
1.071
1.070
Courtesy of D. R. Islleb.
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Soil Moisture
The effect of soil moisture on yield and solids content of potatoes
is a fairly complex matter. In arid regions irrigation is necessary,
while in other areas rainfall may suffice. The amount of water applied
and the time and schedule of application are important factors. Tempera-
ture is another important variable.
Ample soil moisture may result in high yield of potatoes with low
specific gravity. Uniform soil moisture during the growing season to-
gether with the withholding of irrigation prior to harvest has produced
potatoes with high specific gravity. Excessive rainfall or irrigation
late in the season results in crops with low specific gravity.
High moisture content tends to keep the soil temperature cool and
stable, thereby reducing loss by respiration. High moisture content may
thus prove advantageous in high temperature growing areas.
Season
Yield and solids content of the same varieties may differ considerably
from season to season in the same area because of differences in soil
moisture, temperature, and other environmental conditions.
Location
Solids content and reducing sugar content are greatly dependent upon
location, due to differences in environmental conditions. In Sweden a
study was made on the quality of potatoes grown at different latitudes
(Carlson 1968A). It was clearly demonstrated that because of the difference
in temperature and length of growing season, the yield and solids content
were highest and reducing sugar content lowest for potatoes from the
southernmost locations.
Cultivation and Weed Control
Cultivation methods affect primarily the moisture content of the
soil, and thus will have the effects discussed previously. Respiration
of water from leaves Of weeds may reduce the moisture content of the soil
rapidly, and destruction of the weeds when they are small may be important
for retaining sufficient moisture in the soil. A common weed control
chemical is 2, 4 - D, which has been reported to reduce yield as well as
increase it. Increase in specific gravity has been reported to result
from 2, 4 - D application. (Talburt and Smith 1967.)
Mineral Nutrients of the Plants
Several workers have reported that as the fertility of the soil
increases, the specific gravity of the potato decreases. Nitrogen may
increase the yield of potatoes but be detrimental to the quality for
processing. It has been found that starch and solids content decrease
10
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with increasing application of nitrogen. The application of phosphorous
has provided little or no increase in starch and solids content. Potassium,
as muriate of potash (KC1), the most widely used form, reduces the solids
content of potatoes when heavily applied. This is thought to result from
the chloride ion rather than the potassium ion. The sulphate form of
potash usually gives higher starch and solids content than the equivalent
quantity of the chloride form. Magnesium often is not present in sufficient
quantities to give a high yield of potatoes, especially in acid soils.
Addition of magnesium have been found to increase the yield as well as the
starch content of the tubers. (Talburt and Smith 1967.)
Spray Program for Control of Insects and Diseases
Spraying to control insects and diseases is necessary in almost all
potato growing areas, to prevent early death of the plant, reduced yield,
and poor quality. DDT is the most common insecticide used in the United
States. Because of its excellent control of insects, the plants continue
to grow, and do not die or mature naturally, but are killed by frost or by
mechanical or chemical means. This results in poorer chemical composition
of the potato for processing. Specific gravity is lowered and reducing
sugar content increased.
Temperature During Growing Season
The effect of temperature has been mentioned earlier. It determines
to a great extent the length of the growing season and thus the maturity
and specific gravity at harvest.
Time and Method of Vine Killing
As mentioned earlier, because of Insect control the potatoes continue
to grow, and it often is necessary to kill the vines by mechanical or
chemical methods. When the plant is left to die naturally, food in the
form of sugar is transferred from the stem to the tuber, where it is
converted to starch, resulting in higher specific gravity. Artificial
vine killing methods give little opportunity for transfer of food, and
thus a lower quality potato results. Studies have indicated that slow
vine killing, i.e. by chemical means, provides better quality potatoes.
Late killing appears more feasible than early killing. Other studies
indicate that variations in quality during storage are different for
mechanically killed plants and chemically killed plants. (Gustafson 1968).
Time of Harvest
Mature tubers are superior in quality and yield to immature tubers,
and quality of processed products is improved when mature tubers are used.
Therefore, harvest should be as late in the season as possible without
subjecting the potatoes to low temperatures. Potatoes used for processing
should not be exposed to temperatures below 40°F.
11
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SECTION 4
THE PROCESSES
General Requirements on Raw Potatoes
High quality raw potatoes are important to the processor. Potato
quality affects not only the final product, but also the amount of waste
produced. Generally, potatoes with high solids content, low reducing
sugar content, thin peel, and of uniform shape and size are desirable
for processing. Cull potatoes sometimes are sorted for starch and flour
production, but more often low quality potatoes must be wasted and
thereby represent a loss to the processor.
Handling and Storage
As mentioned earlier, potato quality is dependent upon cultural
and environmental conditions. Handling and storage of the crop by the
grower and the processor also affect the quality to a great extent. Thus
efforts to reduce losses and waste loads should include consideration of
these aspects of quality control.
Harvesting is a very important operation. Bruising and other
mechanical injury to potatoes during harvest often result in excessive
rot during subsequent storage. Careful operation and adequate machinery
obviously are very important in maintaining a low level of injury to the
tubers. Numerous types of mechanical harvesters have been developed,
but none has performed satisfactorily under all conditions. Improved
harvesting machinery no doubt would reduce the losses and waste loads.
Transportation of potatoes for processing is another operation where
improper conditions during transit may render potatoes undesirable for
processing. Proper temperature is the most important consideration.
During transit potatoes should be kept at temperatures between 50° and
75°F. If potatoes are held at 40°F or below for several days, reducing
sugars will accumulate resulting in dark color of products such as chips
and French fries. An extended period of temperatures above 75°F may
cause an increase in certain types of storage rot diseases and, in fairly
air-tight areas, may result in blackheart, a discolored breakdown of the
tissue at the center of the tuber. (Talburt and Smith 1967).
Potatoes are shipped in bulk or containers by truck or by rail, and
generally it is necessary to use trucks and railroad cars specifically
designed for potato transport. Temperature must be kept constant
throughout the car, and since outside temperatures may fluctuate con-
siderably, good ventilation must be provided.
A railroad car for bulk transportation of about 90 tons of potatoes
is being developed by ACF Industries (Curry 1968). Tests with outside
temperatures ranging from 9° to 130°F showed that the temperature could
be maintained at 60°F throughout the car.
12
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Loading of trucks and cars must be done with care to prevent mechan-
ical injury. Low outside temperatures during loading may create problems
unless the temperature control in the car performs adequately.
Storage is necessary to provide a constant supply of tubers to the
processing lines during the operating season. In storage, potato quality
may be changed drastically unless adequate conditions are maintained.
The major problems associated with storage are sprout growth, reducing
sugar accumulation, and rotting. Reduction in starch content, specific
gravity and weight also may take place.
Sprouting occurs at temperatures of 50°F and above following a rest
period of several months after harvest. At lower temperatures little or
no sprouting will take place, but reducing sugars will accumulate in the
tubers.
One approach to maintaining high quality potatoes is to treat the
crop with a sprout inhibitor in the field or in storage and then to keep
the storage temperature at 50° to 60°F. A variety of sprout inhibitors
have been used. Maleic hydrazide sprayed on the plants in the field has
given good results. Other chemicals used are tetrachloronitrobenzene,
nonanol, and CIPC, all with various degrees of success. The storage
temperature and especially the storage time appear to be very important.
Gamma irradiation of potatoes at dosages of 10,000 to 15,000 REP has
been found to inhibit sprouting completely for at least one year when the
storage temperature is kept at 50°F.
Reconditioning of potatoes stored at low temperatures over a period
of time by subsequent storage at higher temperatures for a similar length
of time has the effect of reducing the sugar content. Potatoes stored
at 40°F for six weeks and then removed to 70°F for six weeks had sugar
contents similar to the content prior to storage. Potatoes stored at
lower temperatures had higher sugar content after reconditioning.
To prevent large losses by rotting, low quality potatoes should be
sorted out before the crop is placed in storage. Mechanically injured
potatoes are especially susceptible to certain rot diseases and should be
removed prior to storage to avoid rotting of a large portion of the load.
In summary, handling and storage of the raw potatoes prior to pro-
cessing are major factors in maintaining high quality potatoes and re-
ducing losses and waste loads during processing. Careless handling and
storage may well destroy efforts to reduce and treat the waste from the
process line.
13
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Washing of Potatoes Prior to Processing
Raw potatoes must be washed thoroughly to remove sand and dirt
prior to the actual processing steps. Sand and dirt carried over into
the peeling operation can damage or greatly reduce the service life of
the peeling equipment.
Often the incoming potatoes are washed in the water used for trans-
port from the storage or receiving area into the plant. Fluming is an
economical and effective method of transporting potatoes which results
in a minimum of bruising damage. Sand and gravel are removed in stone
traps in which these heavier solids settle out while the potatoes pass
on. Tubers transported into the plant by other means or washed inade-
quately in the flume are passed through washers. A number of different
types of washers are employed. Barrel-type washers are quite common.
Potatoes are tumbled and rubbed against each other and against the sides
of the barrel while immersed or sprayed with water. Other types use
rubber brushes, rolls or paddles to loosen the adhering dirt. Following
the washing operation the potatoes are allowed to drain for a short
period while being carried to the next step which is usually a short
inspection belt where trash and rotten potatoes are removed.
Water consumption for fluming and washing varies considerably from
plant to plant. Wolters (1965) has reported flow rates to vary from
1300 to 2100 gallons per ton of potatoes. Of this volume, 2/3 is used
for fluming and 1/3 for washing. Adler (1965) states that 1000 to 1800
gallons of water are used to wash one ton of potatoes. A study on the
waste waters from five potato starch plants in Idaho, shows a range of
flume water flow rates from 600 to 2700 gallons per ton of raw potatoes
(Ambrose and Reiser 1954). The volumes reported above are based on no
recirculation of the flume and wash water. Today recirculation systems
are used to some extent, and the fresh water input may be reduced
significantly compared to a "straight-through" system.
Depending upon the amount of dirt on the incoming potatoes, the
waste water will contain from 100 to 400 Ibs of solids per ton of potatoes,
Organic degradeable substances are predominately in dissolved or finely
dispersed form, and amount to from 2 to 6 Ibs of BOD,, per ton of potatoes
(Wolters 1965). In a potato starch waste study, an average of 0.4 Ibs of
BOD5 per ton of potatoes was reported (Ambrose and Reiser 1954). This
value naturally depends to a great extent on the quality of the raw
potatoes. Wolters (1965) states that with a recirculation system the
organic matter discharged from the fluming and washing operation will be
from 30 to 50 percent less than with a "straight-through" system.
The Peeling Process
Peeling of potatoes contributes the major portion of the organic
load in potato processing waste. The operation determines to a great
extent the yield of final product and the labor cost for subsequent trim-
ing and inspection.
14
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Many factors must be considered when choosing the peeling method and
establishing the tolerable peeling losses. Peeling requirements vary from
process to process and from plant to plant. Production of potato chips,
for example, requires less complete peel removal than production of French
fries. Thus, disregarding potato quality, peeling losses will be less in
chip factories than in French fry factories.
Potato quality is an important consideration, however. Deep eyes
and thick peel result in high peeling losses if a high degree of peel
removal is required. Other variables which affect peeling efficiency are
age of the crop, size and shape of the tuber. With small potatoes,
peeling losses are generally high because the surface area per unit
weight is large.
Three different peeling methods are used extensively today. These
are abrasion peeling, steam peeling and lye peeling. No one of the
methods will satisfy the requirements of every type of plant. All three
methods may be operated either as a batch process or as a continuous
process. Small plants generally favor batch type operation due to greater
flexibility. In such plants peeling losses and labor costs for trimming
are usually quite high. Large plants use continuous peelers. These are
much more efficient than batch-type peelers, but the capital cost is high
(Talburt and Smith 1967) .
Abrasion Peeling
Abrasion peelers have abrasive discs or rolls which remove peel by
uniform contact with the surface of the potatoes. Peelings and potato
tissue are removed from the abrasive surfaces by water sprays which also
reduce the tendency of potatoes to darken through enzymatic action. The
potatoes must be spun and rotated so that all surfaces are equally exposed
to the abrasive surfaces. Thus it is important that tubers subjected to
abrasion peeling are round. Digger cuts may cause the tuber to slide on
the flat surface thus losing excessive tissue on one side. Uniformly
sized potatoes will result in more evenly peeled potatoes when using this
peeling method. Tubers with deep eyes are not suitable for abrasion
peeling because excessive trimming will be required (Talburt and Smith
1967).
Abrasion peeling is used especially in potato chip plants where
complete removal of the skin is not essential. Sijbring (1968A) said
peeling losses of from 4 to 8 percent are not unusual in chip production.
Smith (1964) made a survey of chip operations in the United States and
found peeling losses ranging from 0 to 25 percent. Abrasion peeling has
been used in the production of pre-peeled potatoes, since the heat ring,
which results from high temperature exposure, does not occur with this
method. High peeling losses, possibly as high as 25 to 30 percent, may
be necessary to produce a satisfactory product, however.
The characteristics of the peeling waste vary with potato quality
and peeling requirements. Gray and Ludwig (1943) reported the following
peeling waste quality in a dehydration plant:
15
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Flow - 600 gal/ton
BOD. • 20 Ib/ton
Suspended solids - 90 Ib/ton
Settleable solids = 15 cu. ft/ton (2 hr settling)
The organic content appears to be directly proportional to the percent
peeling loss, and therefore would be minimized by feeding optimum
quality potatoes. Up to 90 percent of the settleable solids appear to
consist of coarse potato matter, the rest being fine starch particles.
Steam Peeling
Steam peeling yields thoroughly clean potatoes. The entire surface
of the tuber is treated, and size and shape are not important factors as
in abrasion peeling. The potatoes are subjected to high pressure steam
for a short period of time in a pressure vessel. Pressures generally
vary from 3 to 8 atmospheres and the exposure time is between 30 and
90 seconds. While the potatoes are under pressure the surface tissue is
hydrated and cooked so that the peel is softened and loosened from the
underlying tissue. After the tubers are discharged from the pressure
vessel, the softened tissue is removed by brushes and water sprays similar
to the ones used for prewashing. An increase in exposure time causes
larger peeling losses and lower trimming requirements (Talburt and Smith
1967).
Because the gelation point of potato starch is surpassed in steam
peeling, there will always be a heat ring. This heat ring is not always
objectionable, as, for example, in the production of French fries where
it is not noticeable in the finished product. Steam peeling of pre-peeled
potatoes may result in enzymatic darkening under the heat ring. The ring
may harden during storage, seriously affecting the quality of the product
(Talburt and Smith 1967).
One disadvantage with steam peeling is the difficulty with which skin
in the eyes is removed during trimming, particularly when the tubers start
showing sprouts (Sijbring 1968B).
The waste water characteristics from this operation will vary with
potato quality and peeling requirements. Cooley et al. (1964) reported
the following characteristics from a potato flour plant peeling waste:
Flow =625 gal/ton
COD =52.2 Ib/ton - 10,000 ppm
BOD =32.6 Ib/ton - 6,750 ppm
Total solids =53.2 Ib/ton - 10,200 ppm
Volatile solids = 46.8 Ib/ton - 9,000 ppm
Suspended solids =26.8 Ib/ton - 5,150 ppm
pH = 5.3
16
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The peelings and solids usually are removed by screens before the
waste water is treated. These screenings are simply cooked potato
tissue and can be used for cattle feed without additional treatment
except for possibly some drying or mixing with other feed materials.
Because of the relatively high temperature of the waste water, a con-
siderable amount of starch dissolves and cannot be removed by plain
sedimentation.
Lye Peeling
Lye peeling appears to be the most popular peeling method used in
the United States today. The combined effect of chemical attack and
thermal shock softens and loosens the skin, blemishes and eyes so that
they can be removed by brushes and water sprays. Lye concentration,
temperature and immersion time are the variables controlling this peeling
method. Two general procedures are in use. One method uses lye temper-
atures from 190° to 220°F, well above the gelation point for potato
starch. Immersion times from 2 to 6 minutes are required in lye concen-
trations of 15 to 25 percent. The other method is operated at temper-
atures from 120° to 160°F to avoid the formation of a heat ring. Longer
immersion times generally are required. At temperatures below 140°F
minimum immersion times are obtained at lye concentrations between 15
and 20 percent (Talburt and Smith 1967). Lye usage is less at lower
lye concentrations. Sijbring (1968B) reports a usage of 15 kg of lye
per ton of potatoes peeled at a lye concentration of 20 percent, while
at concentrations of 10 to 13 percent the lye usage is 7 to 8 kg per
ton.
If a heat ring remains on the peeled potatoes this can be removed
by immersing the tubers in a second lye bath at lower temperature. It
has been found that a bath at 120°F with a lye concentration of 15 to 20
percent effectively removes the heat ring caused by high temperature
treatment (Harrington 1957).
Preheating of the potatoes in water before the lye bath minimizes
the cooling effect of the tubers on the solution, helps to maintain a
constant temperature, and increases the capacity of the peeler. A
wetting agent or detergent has been found to improve peeling efficiency.
(Lankier and Morgan 1944) (Sijbring 1968B)
If sludge formed in the peeler by the chemical action of lye on the
potato tissue is removed by screening or settling, the service life of
the lye solution can be extended markedly.
The peel, after having been softened and loosened in the lye bath,
is removed by brushes and water sprays as in steam peeling. Sometimes
a short period of time is allowed for the lye to work on the potato tissue
before removing the peel. The tubers then must be thoroughly washed to
remove any lye and lye-affected surface which will harden and cause a
yellowing of the surface.
17
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Lye peeling waste water is the most troublesome potato waste.
Because of the lye, the waste water pH is very high, usually between
11 and 12. Most of the solids are colloidal, and the organic content
is generally higher than for the other peeling methods. The temperature,
usually from 50° to 55eC, results in a high dissolved starch content.
Furthermore, the waste water has a tendency to foam. Cooley et al.
(1964) reported the following waste water characteristics from a lye
peeling installation in a potato flake plant:
Flow • 715 gal/ton
COD =65.7 Ibs/ton - 11,000 ppm
BOD - 40.0 Ibs/ton - 6,730 ppm
Total solids = 118.7 Ibs/ton = 20,000 ppm
Volatile solids - 56.4 Ibs/ton « 9,500 ppm
Suspended solids =49.7 Ibs/ton = 8,350 ppm
pH -12.6
Because this peel is extremely caustic, the pH must be lowered
before the solids can be used for cattle feed. This is accomplished
through microbiological action. In a primary sedimentation tank, for
example, the pH of the settled solids can be lowered by controlling
solids detention time in the tank so that the primary sludge can be
fed directly to cattle after dewatering.
Evaluation of the Peeling Methods
As mentioned earlier no one peeling method will satisfy the
requirements for every type of plant. In choosing the peeling method
the processor must try to achieve the proper balance between peeling and
trimming losses and raw material costs for most efficient operation.
Some larger plants may install more than one type of peeler. Early in
the season, when the potatoes are easy to peel, steam peeling may be
advantageous. Later, when potatoes become difficult to peel, lye
peeling may be more economical.
The waste production should be considered carefully because it may
seriously affect the economic feasibility of a particular peeling
method.
Abrasion peeling wastes do not have the high content of dissolved
starch and fine and colloidal solids associated with wastes from lye and
steam peeling installations, and thus can be treated to a higher degree
by sedimentation. The amount of solids which must be removed from
abrasion peeling waste is large, however, since the peeling losses
generally are high.
In comparing lye and steam peeling wastes, the biggest difference is
the pH of the two wastes. While steam peeling wastes usually are near
18
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neutral, lye peeling wastes have pH values from 11 to 12. This high pH
may cause problems in receiving waters as well as in biological treatment.
Furthermore, the organic content of lye peeling waste is generally higher
than that of steam peeling waste. A study carried out in the Netherlands
on tubers from the same lot clearly shows this (Sijbring 1968B).
Peeling Method
Date
Variety
Peeling loss, percent
Average weight of tubers, grams
Pollution, pop. equivalent/ ton/day
Water consumption, m /ton
Steam
2-27
Bintje
14.6
170
79
2.63
4-4
Bintje
20.8
160
114
3.26
Lye
2-27
Bintje
21.5
170
345
5.48
4-4
Bintje
26.7
140
240
3.82
The study was carried out at a plant processing French fries. Thus
the peeling requirements were quite high. The population equivalent was
based on a BOD of 54 grams discharged per capita per day after one hour
settling of the waste water.
Another study analyzed the combined waste stream from a potato flake
plant in North Dakota prior to and after converting from lye to steam
peeling (Olson et al. 1965):
Total Suspended Solids
Volatile Suspended Solids
Fixed Suspended Solids
Sample date
Caustic
10.8
1297 mg/1
1107 mg/1
190 mg/1
1265 mg/1
2/1/64
Steam
7.1
297 mg/1
201 mg/1
96 mg/1
701 mg/1
9/12/64
Oxygen demand as well as pH and solids content were substantially
reduced. Similar differences in waste quality have been reported by
Talburt and Smith (1967) .
19
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Potato Chips
The processing of potatoes to potato chips involves essentially
the slicing of peeled potatoes, washing the slices in cool water,
rinsing, partially drying, and frying them in fat or oil. White skinned
potatoes with high specific gravity and low reducing sugar content are
desirable for high quality chips. A flow sheet of the process is shown
in Figure 1.
After conventional prewashing, the potatoes are peeled, usually by
the abrasive method, washed and inspected and trimmed prior to slicing.
Losses vary over a wide range. A survey of more than 50 plants in the
U.S. showed that peeling and trimming losses for old potatoes varied
from 2 to 20 percent and for new potatoes from 0.3 to 13 percent.
Another survey showed the losses ranging from 0.5 to 25 percent
and from 0 to 8 percent for old and new potatoes, respectively. Trimming
losses alone may vary from negligible amounts to 10 percent (Smith 1964,
1966). The quality of waste water from the peeling operation has been
discussed earlier. Trimming contributes primarily to the amount of
solid waste.
Slicing yields from 15 to 20 slices per inch. Considerable amounts
of starch are released in the operation and must be washed off to avoid
matting and sticking of the chips during frying (Potato Chip Industry
1960). Most of the starch and slivers are removed in a washer with cool,
fresh water. The combined waste water from slicing and washing has been
reported to have the following characteristics (Cooley et al. 1964):
Flow = 1140 gal/ton raw potatoes
COD - 75.5 Ib/ton
BOD =21.9 Ib/ton
Total solids = 118.5 Ib/ton
Volatile solids = 63.6 Ib/ton
Suspended solids - 53.8 Ib/ton
pH - 7.4
Losses during slicing and washing amounts to 0.05 to 1.0 percent of the
raw potatoes (Talburt and Smith 1967). After washing, the chips are
rinsed in one or two water baths to further remove starch. The waste
from these steps is negligible both in volume and organic content. Drying
of the chips prior to frying reduces the frying time and thus increases
the capacity of the kettle. This is accomplished by a variety of methods
including compressed air and perforated revolving drums. The chips also
may be treated by hot water or chemicals prior to frying to prevent
darkening. Chemicals used include sodium bisulfite, hydrochloric acid,
phosphoric acid and citric acid.
20
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POTATO
1
t
K>
u
CL
PRODUCT CONVBYOR
MAKE-UP WATBR
•^ WA«TK WUATBR
TYPICAL. POTATO CHIP PLANT
-------
Most plants now use continuous friers. Frying oil is circulated
constantly through the kettle, and through a strainer so that small
bits of chips and suspended particles may be removed. Because of the
cost of frying oil, recirculation is essential, and the oil must be
handled carefully to prevent spoilage by overheating or oxidation.
The temperature of the frying oil varies at the heat source, where the
chips enter, from 350° to 375°F and at the finishing end of the kettle
from 320° to 345°F. The temperature is altered to fit the raw material
and the conditions prevailing at the time.
After frying the chips are passed over a shaker screen to remove
free oil, then salted or flavored, and finally cooled and inspected
before packaging.
Cooley et al. (1964) presented the following figures for the
combined waste from a potato chips plant:
BOD - 29.2 Ibs/ton potatoes
COD =78.4 Ibs/ton potatoes
Volatile Solids = 68 Ibs/ton potatoes
Fixed Solids = 115 Ibs/ton potatoes
Suspended Solids =59.8 Ibs/ton potatoes
pH = 7.4
A survey by Forges and Towne (1959) on four chip plants showed an average
of 50 Ibs of BOD and 66 Ibs of suspended solids discharged per ton of
potatoes processed. The average waste flow was 3980 gallons per ton.
New methods for frying chips are being developed. The microwave oven
has been used to dry chips partially fried in oil. It was found that
potatoes of high reducing sugar content could be processed to acceptable
colored chips in this way while complete oil frying produced dark colored
chips.
A vacuum frier for chips has been developed at Wageningen, the
Netherlands. This frier enables the processor to fry the chips at lower
temperatures, thus improving the color of the chips. The vacuum frier
has been tested on a large scale basis with good results (Sijbring 1968C).
Frozen French Fries and Other Frozen Potato Products
Of the 1966 crop, 32 percent of the potatoes processed were used
for frozen French fries. Including other frozen potato products the
figure amounted to 37 percent. (Irish Potatoes 1967) The grade and
quality of potatoes processed into frozen products vary over a wide range.
For French fry production large potatoes of high specific gravity and
low reducing sugar content are most desirable. Large potatoes result in
22
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lower peeling losses and larger yield of long French fry cuts. High
specific gravity insures higher yield per ton of potatoes processed
and low reducing sugar content improves the color of the finished
product.
After prewashing, the potatoes are peeled by the steam or lye
method. The peeling requirements on potatoes for French fry processing
are high, and the abrasion peeling would result in excessive losses.
Peeling and trimming losses vary with potato quality and range from
15 to 40 percent (Talburt and Smith 1967). On the trimming belt low
quality potatoes are diverted from the process line and small tubers
may be removed for processing into co-products like potato patties,
hash brown or mashed potatoes.
The strip cutter produces, besides French fry cuts, slices and
nubbins which must be removed. This is usually accomplished by shaker
screens or rotating reels having slots through which the smaller pieces
pass. These pieces may then be diverted to the co-product processing
lines. The removal of slivers and nubbins may amount to an additional
loss of 10 percent, reducing the overall yield of raw French fry cuts to
within the range of 50 to 75 percent of the tonnage of potatoes processed.
After cutting and sorting, the strips usually are water blanched.
Advantages of blanching include (a) more uniform color of the finished
product, (b) reduction of fat absorption through gelatinization of the
surface layer of starch, (c) reduced frying time because the potato
is partially cooked by blanching, and (d) improved texture of the final
product (Talburt and Smith 1967).
Because the blanching water is relatively warm, its leaching effect
may result in a high dissolved starch content in the waste water.
Surface moisture from the blanching step is removed by hot air
prior to frying. This reduces the frying time and improves the texture
of the strips.
The French fry cuts are carried through the frier by a conveyor.
The temperature of the frying fat usually is maintained within the range
from 350° to 375°F. Frying time is adjusted to meet the requirements of
the consumers. Institutions usually finish frying in deep fat to develop
color and crispness and thus desire a minimum of frying by the processor.
French fries for the home consumer are fried more completely so that
subsequent deep fat frying is unnecessary.
After frying, the free fat is removed on a shaker screen and by hot
air streams. The fries then are frozen and packaged.
Table VIII gives the waste water characteristics from a French fry
plant in Maine (Sproul 1965). This plant used the lye peeling method.
The spray washer, which removes the loosened skin, contributes the bulk
of the pollution load. Of the 22 Ibs of BOD per ton of potatoes
processed, 20 Ibs came from the lye peeler. The table shows also that
23
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N)
TABLE VIII
POTATO PROCESSING WASTE CHARACTERISTICS FOR FRENCH FRIES
(All results in mg/L except pH)
Operation
Spray Washer
Trimming
Cutting
Inspection
Blanching
By-products
& blanching
(combined)
Plant Composite
BOD
1950
30
77
5
1020
500
1150
COD
2830
45
150
32
1470
870
1790
Solids
Total
14900
270
880
260
2283
1310
8100
Suspended
2470
7
16
15
60
140
1310
Alkalinity
Phenol.
2480
_.__
1380
Total
3360
165
220
163
260
1840
Total
P°4
81
27
29
14
160
120
80
pH
11.5
6.9
7.2
6.9
-4.7
5.7
11.1
Total
Nitrogen
as N
60
—
—
—
—
_
20
Notes: Raw potatoes processed - 8.8 tons/hour
Plant BOD - 22#/ton potatoes
Plant suspended solids - 25#/ton potatoes
Water use - 2310 gal/ton potatoes
Data from Sproul (1965)
-------
the by-products contribute a minor part of the waste. This would of
course depend upon the number and kinds of by-products and upon the
fraction of the potatoes diverted to the by-product line. Figure 2 is
a flow diagram of the French fry process.
Dehydrated Diced Potatoes
Dehydrated potato dice are becoming increasingly important in
today's food industry. The major part of the production is used in
processed foods, primarily canned meats.
Potatoes with white flesh color and low reducing sugar content are
desirable for dice production. Exposure of peeled potatoes to the
atmosphere results in increased darkening of the finished product. This
is overcome by using water sprays and dips and by preventing undue delays
along the process line.
After washing and preliminary inspection to remove tubers showing
"light greening", rot, mechanical injury and other defects, the potatoes
are peeled by the steam or lye method. Minimum losses amount to about
10 percent.
The use of electronic sorting machines for removing blemishes and
discolored dried dice has reduced the amount of inspection required at
the trim table. One important factor during trimming is minimizing the
exposure time. The surfaces therefore should be kept wet by water sprays
along the trim table. (Talburt and Smith 1967)
The tubers are cut into different size pieces. Losses in cutting
appear to be directly related to the degree of subdivision. Simon et al.
(1953) report a range of cutting and washing losses from 9 percent for
the larger pieces to 14 percent for the smaller pieces.
After cutting and washing, the dice are blanched with water or steam
at 200° to 212°F. Blanching results in better and more even surface
color and also reduces microbiological contamination. A small solids loss,
up to 1.5 percent, is associated with the blanching operations.
Following blanching a carefully applied rinsing spray removes surface
gelatinized starch to prevent sticking during dehydration.
Sulfite usually is applied at this point as a spray solution of
sodium sulfite, sodium bisulfite or sodium metabisulfite. Sulfiting
protects the product from non-enzymatic browning and scorching during
dehydration and increases the storage life of the product under adverse
temperature conditions.
Calcium chloride often is added concurrently with sodium bisulfite or
sodium metabisulfite. This has the effect of firming the dice and preventing
sloughing. Sodium sulfite and calcium chloride should not be added
concurrently since a precipitate is formed.
25
-------
j L
TRMMNMQ CUTTER
N>
u
IB
rr
i •
Jf
FRYING DE-\MATEmiMO BL.AIMCHHMO
<=> MAKE-UP \AMVTER
••». WASTE \MATER
TYPICAL FRENCH FRY PLANT
FIO.B
-------
Modern continuous belt dehydrators dry the product to the desired
moisture content in 6 to 8 hours. Since storage life has been found
to be closely related to moisture content, it is important to dry the
product to as low moisture content as is economically feasible. Piece
size greatly affects the drying rate. The thicker the pieces, the
slower the rate of drying.
Following drying the potato dice are screened to remove small
pieces and bring the product within size specification limits. Sorting
to remove discolored pieces is done either manually or by electronic
sorters. Finally the dice are packaged in cans or bags.
Dehydrated Mashed Potatoes - Potato Granules
Potato granules are dehydrated single cells or aggregates of cells
of the potato tuber dried to about 6 to 7 percent moisture content. They
can easily be made into mashed potatoes by mixing with hot or boiling
liquid. Because of the increasing popularity of convenience foods,
potato granule production has grown steadily since about 1950.
Since coloration of the finished product is a problem, potatoes of
low reducing sugar content are desirable. Also the low reducing sugar
content minimizes scorching during drying.
A flow diagram of the "add-back" process, which is used in the United
States, is shown in Figure 3. After peeling and trimming, the potatoes
are sliced to obtain more uniform cooking. The slices are cooked in
steam at atmospheric pressure for about 30 to 40 minutes. Cooking usually
is a continuous process where the slices are carried on a moving belt.
After cooking is completed, the slices are mixed with the dry add-back
granules and mashed to produce a moist mix. This mix is cooled and con-
ditioned by holding for about one hour before further mixing and dried to
about 12 to 13 percent moisture content. The powder then is screened,
and granules coarser than 60 to 80 mesh are returned as add-back together
with some of the finer powder. Very coarse material, retained on a 16-mesh
screen, is removed from the process since it does not absorb moisture from
the cooked slices rapidly enough to be helpful. About 12 to 15 percent
of the material is removed for final drying to about 6 percent moisture
content and packaged (Talburt and Smith 1967).
Two very important factors in the process are (1) minimum cell
rupture, and (2) satisfactory granulation. Cell rupture releases excessive
amounts of starch, resulting in a sticky or pasty product. Unsatisfactory
granulation results in a lumpy and grainy finished product.
Potato Flakes
Potato flakes are a form of dehydrated mashed potatoes which have
been dried on a steam-heated roll as a thin sheet and then broken into
small pieces for packaging. Potatoes for flake processing should have
27
-------
POTATO
N>
00
u
MAKE-UP WATSP,
WASTE WATER
TYPICAL. POTATO ORANULE PLANT
-------
the same characteristics as those for potato granule processing. It is
important in this process, also, to keep cell rupture to a minimum.
A flow diagram of the process is shown in Figure 4. After pre-
washing, the potatoes are lye- or steam-peeled. Losses and waste water
from these operations have been described earlier. Following trimming
the tubers are sliced into 0.25 - 0.50 in. slices and washed prior to
precooking in water at 160° to 170°F for about 20 minutes (Cooley et al.,
1964). The water used for precooking may be treated with certain
additives, such as sodium acid pyrophosphate, to prevent graying of the
potatoes. Fresh make-up water is added, and the overflow stream is high
in solids but low in volume. The potatoes are then cooled in fresh water
for about 20 minutes. The purpose of the precook and cooling is to
improve the texture of the finished product. Cooley et al. (1964) have
reported the following characteristics for the combined waste from the
slicer, washer, precooker and cooler:
Flow - 1540 gal/ton potatoes
COD =56.2 Ibs/ton potatoes
BOD =38.4 Ibs/ton potatoes
Total solids - 125.6 Ibs/ton potatoes
Volatile solids * 53.3 Ibs/ton potatoes
Suspended solids =16.4 Ibs/ton potatoes
pH - 5.2
Using steam at atmospheric pressure the cooled potatoes are given a
final cook in a continuous cooker until they are just soft enough for
ricing. This requires about 30 minutes for potatoes of high starch and
solids content and about 40 minutes for varieties of lower solids content.
The only waste stream from the cooker is the steam which condenses on
the potatoes and drains off. This waste water is high in solids but
very low in volume.
After cooking, the potatoes are riced or mashed and the mash is then
dried on a single drum drier. The dried product is in the form of a sheet
a few thousandths of an inch thick. The sheet is broken into flakes of
convenient size for packaging. Olson et al. (1965) analyzed the combined
waste from 3 different flake plants and reported the following values:
PH
Total solids
Volatile solids
Fixed solids
Total suspended solids
Total volatile solids
Total fixed solids
5-day BOD
COD
Nitrogen
(mg/D
(mg/1)
(mg/1)
(mg/1)
(mg/1)
(mg/1)
(mg/1)
(mg/1)
(mg/1)
Plant A
Steam Peeling
7.1
5173
889
4284
297
201
96
701
2142
26.9
Plant B
Lye Peeling
11.4
8746
2543
6203
1055
885
170
1774
3548
86
Plant C
Lye Peeling
11.4
12930
5497
7433
5248
4255
993
3855
7148
105
29
-------
TANK
u
ICT
[=> MAKE-UP WA-
••*• WASTE WATER
TYPICAL POTATO FLAKE PLANT
no. 4
-------
Potato Starch
Potato starch is a superior product for most of the applications for
which starch is used. Because of its high phosphorous content it has
much greater swelling capacity than either tapioca or corn starch. Two
factors which prevent the industry from capitalizing on these advantages
are the unstable supply of raw potatoes and the price paid for starch.
Since the raw material for starch manufacture is primarily cull and
surplus potatoes, starch production is closely tied to fluctuations in the
potato industry, and adequate supplies of low-priced potatoes are often
not available during short crop years. (Douglass 1965) (Harp 1965) The
principal use of potato starch is for paper sizing and coating. Another
important application is textile sizing, and it is used also in the
baking industry, in fine laundering, as a thickening agent, and in adhesives,
The bulk of the starch plants in the United States is located in
Maine and Idaho. Figure 5 shows a flow diagram of a typical Idaho starch
plant. After fluming and washing the potatoes are fed to a grinder or
hammer mill and disintegrated to a slurry which is passed over a screen
to separate the freed starch from the pulp. The pulp is passed to a
second grinder and screened for further recovery of starch. The starch
slurry which passed through the screens is fed to a continuous centrifuge
to remove the protein water which contains solubles extracted from the
potato. Process water is added to the starch, and the slurry is passed
over another screen for further removal of pulp. Settling vats in series
are used to remove remaining fine fibers. The pure starch settles to the
bottom while a layer of impurities, known as "brown starch," forms at the
top. The brown starch is removed to the starch table consisting of a
number of settling troughs for final removal of white starch. The white
starch from the settling tanks and the starch table is dried by filtration
or centrifugation to a moisture content of about 40 percent. Drying is
completed in a series of cyclone driers by contact with hot air. The
starch which now has a moisture content of 17-18 percent is screened and
then packaged. (Ambrose and Reiser 1954) (Talburt and Smith 1967)
Ambrose and Reiser (1954) made a survey of 5 starch plants in Idaho
and found the average values for the waste streams, as shown in Table IX.
The protein water and the pulp accounts for about 95 percent of total
organic load. If the pulp is retained and not wasted, the organic load
is significantly reduced, as shown in Table X. The population equivalent
values are based on 0.167 pounds of 5-day BOD per capita per day.
31
-------
to
10
PLUMB f WASHBR
OBR •CRBBM
STARCH TABLE
c=C> MAKE-UP WATER
••*• WASTE WATER
ORINDER
lUCT
TYPICAL POTATO STARCH PLANT
-------
TABLE IX
STARCH PLANT WASTE CHARACTERISTICS
Flume Water
Protein Water
First Starch Wash Water
Second Starch Wash Water
Brown Starch Water
Starch Water
Pulp (Dry basis)
Flow Rate
Gal /ton
1740a
670
155
135
30
25
BOD
ppm
100
5400
1680
360
640
150
Ib/ton
0.4
30.1
2.2
0.4
0.2
0.0
24.8
COD
ppm
260
7090
2920
670
1520
290
Ib/ton
1.5
40.3
3.3
0.8
0.4
0.0
56.8
Solids Content
% wt.
1.70
0.46
0.81
Protein in
Solids, wt%
38.5
31.1
(a) No recirculation
(b) An average of 55.5 Ibs of pulp (on dry basis) were produced per ton
of potatoes processed.
-------
TABLE X
ORGANIC LOAD FROM STARCH PLANTS
Potatoes processed, tons /day
TOTAL ORGANIC LOAD WITHOUT PULP:
5-day BOD, Ibs/ton
BOD population equivalent /ton
BOD population equivalent of plant
TOTAL ORGANIC LOAD INCLUDING PULP:
5-day BOD, Ibs/ton
BOD population equivalent/ton
BOD population equivalent of plant
Plant
I
200
45.3
271
54,200
70.1
420
84,000
Plant
II
250
27.7
166
41,500
52.5
314
78,500
Plant
III
150
26.2
158
23,700
51.0
305
45,800
Plant
IV
62.5
31.7
190
11,900
56.5
338
21,200
Plant
V
180
35.0
210
25,200
59.8
358
43,000
Average
33.3
200
58.1
348
-------
Potato pulp has proven to be a valuable feed for livestock when
mixed with other Ingredients and thus represents a valuable by-product.
(Dickey et al. 1965)
The protein water is difficult to treat because of the high content
of soluble organic matter.
Potato Flour
Potato flour is the oldest commercial processed potato product.
Although widely used in the baking industry, production growth rates have
not kept pace with most other potato products.
The potato flour process is based on the efficient dehydration of
peeled cooked potatoes on a drum drier and is quite similar to the potato
flake process. The main difference is the cooking step which generally
is one continuous cook in steam at atmospheric pressure rather than the
precook, cooling and final cook in the flake process.
Raw material for potato flour consists primarily of very large
potatoes, small potatoes and potatoes having surface defects.
A flow diagram of the process is shown in Figure 6. After the pre-
wash the potatoes are peeled, usually with steam. Trimming requirements
are not as high as for most potato products due to the "scalping" action
of the applicator rolls on the drum drier. Rot, green end and other
discolorations must be trimmed off, however.
The "flaking" operation requires well cooked potatoes. A cooking
time of 45 to 60 minutes with steam at atmospheric pressure usually is
adequate. (Talburt and Smith 1967) The tubers are conveyed directly
from the cooker to the dryer, where 4 to 5 applicator rolls along one
side of the drum contribute a thin layer of potato mash. The mash is
rapidly dried and scraped off the drum at the opposite side by a doctor
knife.
The dried sheets are passed to the milling system where they are
comminuted by a beater or hammer mill and then screened to separate
granular and fine flour. The moisture content of the final product is
generally from 7 to 9 percent.
The waste water from the peeling operation accounts for the major
part of the organic load. Another source of organic waste is the drum
drier, where peel fragments and other solids tend to accumulate. The
waste water characteristics show much variation from plant to plant as
is the case with all potato processing. The values in Table XI have been
reported by Cooley et al. (1964) and Olson et al. (1965):
35
-------
Ul
u
o o
PRODUCT
i=> MAKE-UP WAT
••^ XA/A8TE VWAT
TYPICAL POTATO FLOUR PLANT
FIO. B
-------
TABLE XI
RAW SCREENED POTATO FLOUR PROCESSING WASTE CHARACTERISTICS
Cooley et al. (1964) Olson et al. (1965)
PH 4.2 6.9
Total Solids* 11792 7493
Volatile Solids 10614 5572
Fixed Solids 1178 1921
Total Suspended Solids 6862 4398
Volatile Suspended Solids 6480 3019
Fixed Suspended Solids 382 1379
5-day BOD 7420 3314
COD 12582 8314
*mg/l except for pH
Canned Potatoes
The production of canned potatoes has increased steadily during the
postwar years as a result of the increasing demand for convenience foods.
Potatoes are canned in several different forms, but whole potatoes account
for the major part of the production.
Potatoes used for canning are primarily the smaller sizes not suitable
for fresh market. An important requirement of canning potatoes is that
they should not slough or disintegrate during processing. Potatoes of
high specific gravity are most likely to slough. Sloughing usually can be
prevented in specific gravity lots of 1.075 to 1.095 by adding calcium
chloride. (Talburt and Smith 1967)
After conventional prewashing the potatoes are peeled. Lye, steam,
and abrasion peeling as well as combinations of these are used in the
canning process. Abrasion peelers sometimes are used rather than lye or
steam peelers to give the potatoes a smoother surface. Because the heat
ring may present a problem, low rather than high temperature lye-peeling
appears to be more suitable for canning.
Since canned potatoes are a low cost product, only a minimum of
trimming is allowed. Some processors prefer to sort out the potatoes
which need trimming and send them through the peeler a second time.
(Talburt and Smith 1967)
If the potatoes have not been size graded previously, this is done
following the trim table inspection. Larger size tubers are usually not
canned whole but cut to make diced, sliced, shoe string or julienne
potatoes.
37
-------
The whole and cut potatoes are then filled in cans, and boiling
water or brine containing 1.5 to 3.0 percent salt is added. A salt
tablet is used with boiling water. The salt, calcium chloride, has
a firming effect on the product.
The cans are closed at a temperature of 160°F or above and then
processed at 240° to 250°F for about 25 to 50 minutes depending upon
the can size. Following processing the cans are water-cooled promptly
to about 100°F.
Pre-Peeled Potatoes
As a result of the demand for convenience foods and the high cost
of hand labor, prepeeled potatoes are becoming increasingly popular.
Restaurant operators generally find it more economical to purchase
pre-peeled potatoes than to invest in labor for hand peeling or in
peeling machinery. Pre-peeled potatoes also have gained popularity in
the household.
Potatoes are pre-peeled for sale as whole potatoes as well as for
French-fry cuts, chips, hash browns and others. The selection of raw
material is to a great extent dependent on the final product and the
same factors discussed earlier must be considered.
The pre-peeling processes do not differ significantly from the pro-
cesses discussed earlier, and the waste streams are consequently similar.
Peeling methods which involve temperatures above 160°F, the gelation
point of potato starch, generally are not feasible in pre-peeling
processes. Abrasion and low-temperature lye peeling are therefore the
most popular peeling methods in use. Trimming and cutting requirements
do not differ from what has been described previously.
Discoloration of pre-peeled potatoes takes two forms. The first
type is the enzymatic formation of melanin, a dark pigment. The second
type is the non-enzymatic "after-cooking darkening". Black-spot or
black-heart may also occur. Microbial spoilage furthermore limits the
shelf-life of pre-peeled potatoes.
To prevent discoloration, addition of chemicals is helpful. The
most common additive is sulphur dioxide. Garrick (1968) reports that
50 ppm of S0? delays browning of peeled potatoes up to 2 days at 20°C
and up to 14 days at 4°C. Microbial deterioration may be controlled
for 10 to 14 days by keeping the peeled potatoes under refrigeration.
(Talburt and Smith 1967)
Alcohol
Alcohol production from potatoes in the United States is small
compared with the volume produced from grain. In Europe potato alcohol
production is important.
38
-------
In fermentation plants, the potatoes are washed, steamed at
about 135-140°C and cooled to 62-65°C. The starch is hydrolyzed by
barley malt or by a mold amylolytic enzyme preparation. The resulting
mash, of 17-20% dry matter, is subjected to alcohol fermentation for 2-3
days. The residue after distillation (120-140 kg/100 kg potatoes, of
4.5% dry matter) is a valuable feed for cattle. Waste water from
distilleries has been reported to have a 5-day BOD of about 530 mg/1
(Szebiotko 1965). Joint production of starch and alcohol is carried
out in Poland, Russia, and Czechoslovakia. The pulp and protein water
from the starch production is used for alcohol fermentation, and the
distillery residue is fed directly to livestock. This allows for
disposal of all wastes. (Szebiotko 1965).
39
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SECTION 5
METHODS FOR REDUCING THE WASTE LOAD
The Importance of in-plant efforts to reduce the total waste load
can hardly be overemphasized. In many cases the reduced losses, improved
product recovery, and reduced water usage have more than offset the cost
of the treatment facilities.
Water Re-use and Conservation
The capital and operational costs of waste treatment facilities are
closely related to the volume of waste that has to be treated. Reduced
waste volumes will significantly reduce the size of the treatment units
and hence the overall cost of treatment. Excessive use of water where
it is not strictly necessary often occurs in processing plants. The
processor, therefore, should examine every point of water use within
the plant to determine where water may be conserved or re-used.
There are several areas in the day-to-day operation where water is
wasted unnecessarily into the waste stream from the processing plant.
The following corrective steps have been suggested by the National Canners
Association:
1. All water hoses should have automatic shut-off valves to prevent
wastage of water when hoses are not in use. A running hose can
discharge up to 300-400 gallons of water per hour.
2. Use low-volume, high-pressure nozzles rather than low-pressure
sprays for clean-up.
3. Avoid unnecessary water overflow from equipment, especially when
not in use. Automatic fresh water make-up valves should be
provided.
4. Avoid using water to flume the product or solid waste where the
material can be moved effectively by dry conveyors.
5. Avoid using water in excess of amount needed to accomplish the
job, e.g., reduce cooling water flow to the minimum needed to
accomplish the necessary product cooling.
6. Divert rain water run-off from buildings away from the factory
and do not allow it to collect inadvertently in the waste
disposal system.
7. Certain water used in the plant which is not re-used and which
meets the purity requirements of the State may be discharged
directly into streams without prior treatment through a waste
disposal system. In some cases this may amount to over 50 percent
of the total water used.
40
-------
Reduced water usage may result not only in reduced waste volumes.
In a vegetable processing plant it was found that the heat loss in the
plant was reduced significantly as a consequence of reduced water use.
(Weckel 1969)
Re-use of process water reduces the waste load as well as the water
usage. In England, biologically treated effluents sometimes must be
partially re-used because of limited water supply and restrictive water
quality criteria. This practice will undoubtedly become more common in
the future. (Gallop 1965)
A large percentage of the process water does not require biological
treatment before re-use. Flume and wash water are low in BOD and dis-
solved solids, and may be reused, in most cases, following treatment by
settling. Water for recirculation must not be allowed to undergo
anaerobic decomposition since, besides being corrosive and odorous, it
may affect the quality of the final product. Thus, the detention time
in the settling tanks should not be excessive, and chlorine should be
added to prevent putrefaction. Welters (1965) suggested that detention
times of about one hour are sufficient, while Dickinson (1965) claimed
two hours of quiescent settling are required to clarify potato wash water.
The constant velocity channel, or grit chamber, designed for water velocities
of one foot per second, is a suitable device for removing sand and
inorganic solids. Mechanical screening should be used to remove larger
organic debris. In two of the largest starch plants in southern Germany,
90 percent of the flume and wash water is re-used after treatment in
sedimentation tanks with continuous sludge removal. The contaminated water
discharged from the system is replenished by fresh water. A dosage of
19 mg of chlorine is added per gallon of wash water. Chlorination requires
close attention, however, since chlorine promotes the formation of the
dark pigment, melanin. (Adler 1965)
Bacterial growth can be controlled by environmental factors. Acidi-
fication of such water with citric acid or other edible acids to pH 3-4
has been found to reduce greatly the growth rate of bacteria. Equally
effective may be reduction of the water temperature. (Rose 1965) Such
precautions permit recirculation of the water until build-up of physical
or chemical components preclude further use. Recirculation may reduce the
organic load from the fluming and washing operation by 30 to 50 percent.
(Wolters 1965)
An example of efficient re-use of cooling water and process water in
a potato granule plant has been described by Berry (1967). Fresh water
is pumped from a well for use in 3 separate systems: (1) sanitary-potable
water system, (2) equipment cooling - potato fluming and washing system,
and (3) process water system. Waste water from the first system is not
reused and is discharged to a sanitary septic tank with a tile drain field.
The equipment cooling water is pumped under high pressure into a rotary
drum washer for removing dirt from the potatoes. The water from the drum
washer then is used for transporting the potatoes by flume to the process
operations. The flume water is passed through a 20 mesh vibrating screen
and piped to a settling pond for silt removal prior to disposal by spray
41
-------
irrigation. Process water, after having been used for steam generation,
cooling, and plant clean-up, is passed through a 40 mesh stationary
screen to remove solid waste and peel which is used as cattle feed.
The screened water is piped to the spray irrigation system for final
disposal.
Others reporting on the effects and importance of re-use of process
water include Ambrose and Reiser (1954), Atkins and Sproul (1964) ,
Eckenfelder (1969), Gallop (1968), Kueneman (1965), and Mercer (1969).
Re-use of a large percentage of the process water will be necessary
in the future as water and waste problems become much more important
factors in the survival and growth of food processing plants. Gallop (1965)
indicated that industry could manage with 10-15 percent of the present
usage of water for processing without loss of product quality. One of the
largest Idaho plants has reduced the water usage to 200-400 gallons per
ton of potatoes by considerable recirculation, and it is expected that
this amount can be reduced by about 75 percent within a few years.
(Kueneman 1965)
Counter-Current Flow of Process Water
Another method for water conservation and waste concentration is
counter-current flow of product and process water. In this system, water
from the last product fluming or washing operation, instead of being
wasted, is collected and passed back in a counter-current manner to be
used in preceding washing and fluming operations. The overall effect is
that the product is moved forward after each washing or fluming operation
water which is cleaner than that used in the preceding operations.
A recent development for final purification of starch employs this
principle. The starch milk is pumped into the first of several solid-
liquid cyclones while clean water is pumped into the last cyclone, and the
two work their way counter-currently through the batteries. The water
emerges from the first unit carrying all the soluble impurities which
had been in the starch milk while the purified starch emerges from the
last unit ready for filtration and drying. (Douglass 1965) In any
process line with successive washes and rinses, counter-current flow
should be considered if water conservation by recirculation is unfeasible.
Process Control and In-Plant Treatment
Proper operation of the process equipment can reduce the waste load
as well as the loss of product. It is therefore important that the
different process steps are adjusted according to the operational
variables so as to reduce the waste volume and/or amount of contaminants
to a minimum under the prevailing conditions. This may involve reduced
solids losses allowed in operations such as peeling, cutting, and screening.
Reduction of water usage should of course be considered. In many cases
such adjustments may require an evaluation of treatment cost versus
trimming cost or product quality. Previous records are helpful in such
42
-------
situations. Examples of steps that may be taken to reduce peeling losses
include better control of the caustic concentration in lye peeling and
use of higher pressure water sprays in washing facilities. (Talburt and
Smith 1967) Maintenance of the process equipment is another important
factor. Efforts to reduce the volume or strength of a waste stream are
easily offset by the effects of inadequate equipment.
Good house-keeping and in-plant treatment, such as screening, can
result in significant waste load reductions. Potato peel and pulp
contain 0.1 mg of BOD per mg of dry solids. (Carlson, 1967) Therefore,
in-plant efforts to separate potato solids from the waste water as early
as possible, or keeping the solids out of the liquid waste altogether,
will markedly reduce the dissolved organic content of the waste stream.
When potato solids are left in contact with water over a period of time,
considerable leaching of organic materials take place. The following table
shows the influence of contact time on soluble BOD. (Sproul, 1968)
TABLE XII
LEACHING OF ORGANIC MATERIALS
FROM SLICED POTATOES IN WATER
Mixing Time
Minutes
2
3.5
5
10
30
Dissolved BOD
mg/L
200
215
225
230
300
In this experiment Maine Russet potatoes were cut into 1/4-inch cubes
and 150 grams were added to 1.5 liters of distilled water. The starch
liberated during cutting vas added also, which accounts for most of the
BOD after 2 minutes of mixing. After 30 minutes the dissolved BOD
had increased by 50 percent with respect to the 2 minute concentration,
and additional mixing would have increased the BOD even more, since 10
percent of the dry weight would give about 2.6 grams of available BOD.
Only 0.45 grams were measured after 30 minutes. Potato pieces with larger
surface area, such as flakes or granules, would leach considerably larger
amounts of organic material per unit weight, since the leaching rate is
proportional to the surface area exposed. The temperature of the water
also influences leaching. Warm water will extract more organics than
will cold water.
Unnecessary spills must be avoided, since spills increase waste loads
as well as product losses. Automatic controls may be used to reduce spills,
and sumps substituted for floor drains will prevent the spilled material
43
-------
from entering, the waste water. Useable materials may be recovered in
this manner. (Black and Forges 1965) Spills during the packing operation
represent a direct loss of finished product as well as solid waste which
often is washed away to the plant waste stream. Wreckel (1969) found a
loss of 1 percent of finished product in the filling operation in a pea
cannery. Similar losses in a plant processing corn were estimated to be
3 percent.
Very few of the persons working on the process line understand the
magnitude of the waste problem and what contributes to it. Efforts to
explain how they, through better house-keeping and consideration, can
reduce this problem, seem well worthwhile.
Redesign and Modifications of the Process
Numerous possibilities exist for redesign and modifications of the
process to reduce the waste load. New and improved equipment and methods
are being developed, but for economical reasons the processor cannot
always take full advantage of the improvements.
Much attention should be given to improving the peeling process,
which contributes the major part of the waste load in potato processing.
Change of peeling method can reduce the waste load considerably.
Conversion from caustic to steam peeling at the Borden's Food Company
processing plant at Grafton, North Dakota, resulted in a BOD reduction
of the combined plant waste of almost 47 percent. The total suspended
solids concentration was reduced by 79 percent and the volatile suspended
solids by 83 percent. Fixed solids were reduced by almost 50 percent.
(Olson et al. 1965)
Presently, two newly developed "dry" peelers are being tested. These
peelers were developed independently by the Western Research Laboratories,
USDA, at Albany, California, and by the Institute for Storage and Pro-
cessing of Agricultural Produce, IBVL, at Wageningen, the Netherlands.
The peeler developed by the Western Research Laboratories is based
on the application of infra-red radiation to caustic treated potatoes
followed by abrasion treatment to remove the peel. The use of water to
remove the peel, as in conventional caustic or steam peeling, is eliminated,
and the peeling waste can be removed from the process as a concentrated
residue.
A pilot plant operation of the process by the Potato Processors of
Idaho Association has been described by Willard (1969). Potatoes were
removed continuously and randomly from the flow to a conventional caustic
peeling line and transported by conveyor to a small conventional ferris-
wheel type caustic peeler. A woven wire mesh conveyor fitted with cleats
transported the potatoes from the caustic peeler to the infra-red treatment
unit. The holding time on the conveyor allowed the caustic solution to
penetrate to the desired depth. The infra-red treatment unit consisted
of a feeder, used to align the potatoes in rows and deliver them
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to a 48 inch roller conveyor, 10 feet long, which conveyed and turned the
potatoes beneath the infra-red source. To provide infra-red radiation
8 rows of 6 porous ceramic burners were used, each rated at 20,000 BTU
per hour, operating on natural gas. The burners provided a temperature
of 1650°F with an output of approximately 50 percent infra-red radiation.
Following the infra-red treatment the softened skin was removed in a
scrubber. The scrubber contains twenty-three 3 inch diameter soft stud
rubber rolls, 6 feet long, rotating in planetary action at adjustable
speeds from 700 to 920 r.p.m. in a continuously rotating cylindrical
cage. An adjustable speed inner screw conveyor controls the residence
time in the scrubber. The peel removed by this vigorous action is thrown
by centrifugal force and collected on the inner surface of a drum sup-
ported to rotate about the rolls. A drag conveyor installed in the drum
continuously wipes the residue to one point for collection. After the
scrubber the potatoes were given a final brush washing. This unit is
similar to the scrubber except that the stud rubber rolls have been
replaced by polypropylene cylinder brushes.
The test conditions used to obtain a "normal" peel were:
Feed rate - 5500 Ibs of raw potatoes per hour.
Caustic treatment - 12.3% concentration, 0.8 minutes contact time,
185°F, holding belt time 9 minutes.
Infra-red treatment - 48 burners operating at 20,000 BTU's per
hour, effective treatment time 1.2 minutes.
Scrubber - 1.32 minutes treatment time with rolls operating at
772 r.p.m.
Brusher - 1.23 minutes residence time with rolls operating at
778 r.p.m., water rate about 4.6 g.p.m.
The process was frequently compared with the conventional caustic peeling
line. Trim loss was taken as an indication of the effectiveness of peel
removal. Following are the results of two tests when the peel removal
on the two lines were approximately equal, as indicated by the identical
trim losses.
Conventional Pilot Conventional
Line Line Line
Trim Loss 5.0% 5.0% 2.5% 2.5%
Peel Loss 12.9% 20.4% 13.1% 22.7%
Caustic Use* 0.18 0.63 0.18 0.63
*Lbs of NaOH used per cwt. of raw potatoes peeled.
These results indicate a substantial reduction in peeling losses and
caustic usage with the infra-red peeler when compared to the conventional
caustic peeler.
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Three separate waste materials were produced in the infra-red process.
These were debris brushed from the conveyor rollers in the radiation unit,
the scrubber sludge, and the concentrated washer effluent. The scrubber
sludge was a heavy viscous paste with a solids content of about 23 percent.
Pump tests demonstrated that the sludge could be pumped, even
at the original solids content. When combined with the brush washer
effluent the solids content was reduced to about 12 to 14 percent, and this
greatly reduced the handling problem.
Successful operation of the infra-red peeling process would reduce
the total waste load significantly. An estimate of the reduction in
waste load to a secondary treatment system using both conventional and
infra-red peeling for two hypothetical operations is shown in Table XIII.
From this table it appears that, based on solids content, infra-red peeling
can reduce the waste load by 70 percent in a French fry plant. Similarly,
in a granule plant the waste load is reduced by 50 percent.
The peeler developed in the Netherlands is quite similar to the
infra-red peeler. The main difference is that no infra-red radiation is
used. The potatoes, after treatment by lye or steam are conveyed directly
into a brushing machine for peel removal. Sijbring (1968B) has reported
operational results on the brush peeler. Two steam peeling lines were
operated in parallel, one using a conventional washer for peel removal,
the other using the brushing unit. The results are shown in Table XIV.
Indications are that, with proper adjustment, water usage for brushing
unit could be reduced to 1 m^ per ton of potatoes.
TABLE XIV
BRUSH PEELING VS. CONVENTIONAL STEAM PEELING
Peel Removal by
Washing Brushing
3
Water consumption, m /ton 21.7 12.1
Pollution, pop. equiv./ton/day 190 48
Peel Loss, percent 17.3 19.0
3
Solids removable by sedimentation, m /ton 0.890 0.130
By-Product Recovery from Potato Waste
Any reduction of the amount of solids entering the waste stream will
aid in the alleviation of the waste problem. Utilization of the recovered
solids in a manner that results in income will reduce the total cost of
waste treatment and eventually reduce the cost of the final product.
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TABLE XIII
EFFECT OF PEELING METHOD ON WASTE DISPOSAL
Type of Plant
Method of Peeling
Input, Ibs/hr
Peel Loss, percent
Peel Loss, Ibs/hr
Peeled Potatoes, Ibs/hr
Peel Waste Solids, Ibs/hr
Non-Peel Waste Solids, Ibs/hr
Total Plant Waste Solids, Ibs/hr
Primary Waste Recovery, Ibs/hr
Total Waste Solids Recovery, Ibs/hr
Waste Solids to Secondary, Ibs/hr
French Fry Manufacturer
Granule Manufacturer
Lye Peel
21,200
18 (a)
3,800
17,400
760
326 (c)
1,086
543 (e)
543
543
Infra-Red
Peel
20,000
13 (a)
2,600
17,400
520
326 (c)
846
163 (e)
683
163
Steam Peel
20,000
10 (b)
2,000
18,000
400
400 (d)
800
400 (e)
400
400
Infra-Red
Peel
20,000
10 (b)
2,000
18 ,000
400
400 (d)
800
200 (e)
600
200
(a) Estimated year-round average, based on pilot plant observations.
(b) Recovery using IR peeling assumed equal until further data available.
(c) Assuming 70 percent total plant loss is peeling loss.
(d) Assuming 50 percent total plant loss is peeling loss.
(e) Assuming 50 percent solids recovery in primary clarifier.
(From Willard 1969)
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All potato processing plants probably use screens to remove large
solids before further treatment or disposal of their waste water. The
degree of removal varies from plant to plant, as do the methods for
handling the solids after removal. In some plants the solids are disposed
of by one of several conventional solid waste disposal methods, while
in others the solids are merely ground to a fine slurry for return to the
waste streams. More and more attention is being directed, however, towards
producing salable by-products from the recovered solids. The feasibility
of by-product recovery depends to a great extent on the size of the plant
and the amount of solids recovered.
The part of the potato which is wasted generally has about the same
high food value as the part which is processed. Shaw (1965) has proposed
utilization of solid waste like pulp and particulate materials for a
number of snack items. Solid waste has been used extensively as feed for
livestock. Depending upon the moisture content, the waste may be dried
or mixed with other feedstuffs or fed directly. Experiments have shown
that the nutritional value of dried potato pulp is equivalent to corn
when fed to beef cattle. (Harp 1965) (Dickey et al. 1965)
Potatoes are a high energy carbohydrate feed with a low protein to
carbohydrate ratio, generally on the order of 1:10 to 1:12. Thus,
excessive use of potatoes for cattle feed results in over-fattening of
the animals and unnecessary wastage of carbohydrate. In Poland, Janicki
et al. (1965) have tried to overcome this problem by growing yeast on
a potato medium to produce a feed material richer in protein. The result-
ing product can be fed to the animals directly or in dehydrated form.
A symbiotic yeast process has been developed and patented by the
Swedish Sugar Corporation. (Wramstedt 1968) Process water is screened
and passed through a desludger, and the supernatant, containing about
2 percent solids, is used to make a growth medium for the yeast, Torula.
The finished product can be used as a feed additive or for human con-
sumption. Pilot plant results have been very promising. Not only is a
valuable by-product produced, but the BOD of the process water is reduced
by 80 to 90 percent.
The protein water, or fruit water, from starch plants is difficult
to treat because of the high concentration of dissolved organics. Recovery
of proteins from this waste stream would result not only in BOD reduction
but also in yield of a valuable by-product.
Protein may be precipitated from the waste stream either by heating
or by acidification. At temperatures above 80°C the protein coagulates
and settles out. At low pH values precipitation takes place as well.
Theoretically, the pH should be adjusted to the iso-electric point, pH 4.7.
Experiments at the University of Idaho showed that most efficient pre-
cipitation took place at pH 3.2. No coagulation took place above pH 5.8.
(Jackson 1962) Heat treatment yields a more easily filterable deposit
than chemical treatment but is more expensive. Acidification, on the
other hand, preserves the valuable ascorbic acid present in the waste,
gives a more desirable product on drying, and inhibits foaming during
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processing. Ascorbic acid and remaining protein can be recovered by
acid and basic ion exchange, respectively. Protein water treated by
coagulation and ion exchange has been found to contain less than 2
percent of the solids originally present, and would not present any
pollution problem. (Jackson 1962) Presently, work is underway to
develop methods for extensive recovery of by-products from starch waste
at the Eastern Utilization Research and Development Division of the
USDA. (Heisler et al. 1969) The proposed treatment process would
consist of five steps: (1) concentration of dilute waste by reverse
osmosis; (2) precipitation and recovery of protein by steam injection
or other suitable method; (3) separation and recovery of potassium
and other inorganic cations by ion exchange; (4) separation and
recovery of amino compounds by ion exchange; and (5) recovery of organic
acids and phosphates by ion exchange. Promising results have been
ob tained.
Deproteinized process water also can be used for yeast production
or alcohol fermentation, and it is more suitable for disposal by spray
irrigation than protein-rich water, since the protein tends to clog
the pores of the soil.
The fuel value of potato wastes has been investigated by Hindin and
Dunstan (1965). They considered anaerobic digestion and combustion and
concluded that because of the capital investments for construction of
such facilities, the use of potato solids as fuel does not appear feasible
at this time. In the future, however, incineration and combustion units
may bring financial return.
Waste Separation and Combination
Waste streams from different process steps in many cases should not
be combined. Large savings in treatment costs may result from keeping
dilute and concentrated waste streams separate. Dilute waste water can
often be re-used or disposed of after little or no treatment. Also, since
the size of treatment units generally is determined by the waste volume
rather than the strength, concentrated wastes will require smaller treat-
ment units at lower capital investments. Waste streams with extreme pH
values should be carefully considered because of their effect on biological
treatment. The combination of acid and basic waste streams may result in
neutralization, and if possible, cooperation between adjacent industries
may be very beneficial.
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SECTION 6
CURRENT WASTE WATER TREATMENT PROCESSES
Preliminary Treatment
Wash Water Silt Removal
Removal of silt and sand resulting from washing the raw potatoes
is important for several reasons. If the wash water is to be reused, the
presence of sand and grit can seriously damage pumps and other equipment
through which the water might pass. The presence of such inorganic
solids in primary sludges is undesirable, since they are not biodegradeable
Where sludges are treated by anaerobic digestion, for example, inorganic
solids can increase the total volume of solids significantly since con-
siderable dirt may be present on raw potatoes. If sand and silt are not
removed prior to disposal by spray irrigation, clogging of pipes and
nozzles is likely to occur.
Stones and gravel in flume water often are removed by sand traps.
These are sections of increased depth in the flume where particles of
high specific gravity settle out. The potatoes are kept from settling
by agitating the water with compressed air or by other means. Stones also
may be caught on riggles, while the potatoes are carried on by rapidly
flowing water. (Talburt and Smith 1967) Regular grit chambers or constant
velocity channels may also be used. Flow velocities of about one foot
per second will allow the heavy inorganic solids to settle out, while
the lighter organic matter is carried on. (Dickinson 1965)
Silt- laden wash water sometimes is treated separately in
shallow settling ponds. Usually, the settled solids do not contain enough
organic matter to cause serious odor problems, and can be removed
mechanically during an off period, when the pond can be drained. (Haas
1968) (Talburt and Smith 1967) The organic content of the effluent
from silt ponds is generally low (BOD of 200-300 mg/1) compared with
overflow from other treatment processes. However, as secondary treatment
plants are installed, the silt pond effluent may contain higher BOD
concentrations than the secondary effluent. Additional treatment of the
silt pond effluents will then probably be required. (Dostal 1968A)
A variety of grit removal and separation equipment is available from
waste treatment equipment manufacturers. One type of degritter is
essentially a centrifuge with no moving parts. This unit is very compact
and requires a minimum of space. Another type combines grit removal,
sedimentation, and surface skimming in a circular tank having an aerated
grit chamber in the middle. Primary sludge and grit are discharged
separately. Aerated grit chambers might prove beneficial when the water
is to be reused.
Disposal of sand and silt presents no problems since the material
is almost completely inert.
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Main Waste Screening
Screening is an effective and extensively used method for removing
larger solids and floating debris. Three types of screens are in use:
fixed or stationary, rotary, and vibratory screens.
The simplest type of stationary screen consists of a number of bars
evenly spaced across the waste channel. The bars usually are installed at
an angle so that material retained on the screen tends to "ride up" on
the bars and thus not restrict the flow of water through the screen. The
simplest type of bar screen is cleaned by periodically raking off the
accumulated material manually. A variety of automatically cleaned bar
screens are available also. The cleaning mechanism consists of a set of
rakes on a motor driven endless chain. Cleaning may be continuous or
programmed to follow an operation schedule. More sophisticated control
and reduced power cost are obtained by having the raking mechanism start
when the head loss across the screen reaches some predetermined value.
Cleaning by rakes limits the bar spacing to a minimum of 1/2 inch, although
3/4 inch is much more common. Bar spacing down to 1/2 inch is possible
when the screen is cleaned by brushes.
Removal of solids smaller than those retained on number 7 mesh is
not practical with fixed screens. Mesh screens with openings of such
size plug easily. Nevertheless, fixed screens, and especially bar screens,
hare proven helpful in affecting further treatment by removing large solids.
This is necessary to protect pumps and finer screens located downstream.
(Ballance 1965)
Rotary screens also are used to a large extent, and a variety of
types are available. The most common type is the drum screen which con-
sists of a revolving mesh drum where waste water is fed into the middle of
the drum, and solids are retained on the peripheral mesh as the water
flows outward. The solids are removed by high-pressure water jets directed
against the outside of the mesh at the top of the drum. The solids fall
into a trough and are removed hydraulically. The smallest practical
opening for screening waste water is about 120 mesh, but more commonly
mesh sizes 20 and 40 are used. (Ballance 1965)
Another type of rotary screen is the disc screen which is a perforated
plate or wire mesh disc set at right angles to the waste stream. The
retained solids are removed at the top of the disc by brushes or water
jets. Mesh sizes smaller than 20 are impractical because of the large
diameter disc necessary to provide enough openings for water passage.
A common disadvantage of rotary screens is the high moisture content
of the screenings. When water jets are used to remove the retained
materials, the moisture content of the screenings may be as high as 99
percent. (Ballance 1965)
Vibratory screens may have reciprocating, orbital or rocking motion,
or a combination of these. The waste water is fed onto the horizontal
surface of the screen, and the water passes through while the retained
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solids are bounced across the screen to a discharge point. Vibratory
screens finer than mesh 40 are uncommon in waste treatment. The main
advantage of this type of screen is the relatively dry screenings
produced. The moisture content is usually about 80 percent.
Removal efficiencies by screening will naturally vary greatly with
the type and number of screens employed and the bar spacing or mesh
sizes of the screens. Ballance (1965) stated that the solids removal by
a 20 mesh screen should not be expected to exceed 35 percent.
The Engineering Committee of the Idaho Potato Processors Association
made a thorough investigation of the standard methods of preliminary treat-
ment of potato wastes. They concluded that self-cleaning rotary or
vibratory screens were effective in removing larger solids which may
cause plugging of pipes and pumps. To prevent plugging and extremely
wet screenings it was recommended that the minimum screen opening should
be 20 mesh. If the screen was to be followed by clarification, it was
felt that it would be better to use larger openings - from 6 mesh to
1/2 inch. Such screens would reduce the BOD by 10 to 15 percent and
the suspended solids by about 25 percent. (Grames and Kueneman 1968)
Talburt and Smith (1967) have summarized waste characteristics from
several operations prior to and after screening. Their data indicate
the following removal efficiencies:
Description of Waste Stream
Chip Plant Waste
French Fries and
Starch Waste
Caustic Peeling Waste
Screenine Removal Efficiency. %
Total
Solids
31
59
Suspended
Solids
44
34
Settleable
Solids
53
BOD
26
23
18
Primary Treatment
Although secondary treatment will be required by many authorities in
the near future, primary treatment will become no less important. Secondary
treatment is more expensive, and the maximum degree of primary treatment
should be obtained to reduce the load on the secondary system. Primary
treatment is used extensively with good results, but much can be done to
improve its performance.
Plain Sedimentation
Because of the high concentration of settleable suspended solids in
potato wastes, sedimentation has been an effective treatment method.
Treatment facilities range from simple settling ponds to rather sophisticated
clarifiers specifically designed for potato waste.
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Settling ponds provide good removal of suspended solids until they
become filled with solids and must be drained and dredged. Dredging
is an expensive and odorous operation which makes the use of clarifiers
seem more desirable.
Conventional clarifiers are either rectangular or circular. The
circular type is available from a number of equipment manufacturers and
is the most common. Many workers have presented design recommendations
and expected removal efficiencies.
Talburt and Smith (1967) report that most clarifiers are designed
for an overflow rate of 800 to 1000 gallons per day per square foot of
surface area and a depth of 10 to 12 feet. Most of the settleable solids
will be removed from the effluent, and COD removals of 50 to 70 percent
may be expected if the plant effluent has been properly screened.
Filbert (1968) recommends similar design parameters. Pilot plant studies
by the Engineering Committee of the Idaho Processors Association indicated
that detention times of 2 to 4 hours with overflow rates of 800 gal/day/sq ft
would give BOD removals of 50 percent. (Kueneman 1965) A deep sludge
blanket gave the highest solids concentration in the underflow. With
caustic peel waste, the underflow would be about 3.5 percent solids, and
by additional conditioning and lowering of the pH, the solids content
could be 5.0 to 8.0 percent. With steam peeling waste the underflow
could be expected to contain 5.0 to 6.0 percent solids.
The results from further pilot plant studies and experience from
early clarifier installations have been reported by Grames and Kueneman
(1968). The maximum desirable overflow rate was found to be 600 gal/day/sq ft
with detention times of 2 1/2 to 3 hours. A deep clarifier with a deep
feed well gave best settling of the fluffy potato solids. Side water
depths of 9 to 12 feet were used successfully, and better solids removal
was obtained when the feed well was provided with anti-turbulence baffles
near the lower lip. Rake mechanisms with sludge-thickening pickets
provided a combined clarifier and thickener and produced an underflow of
maximum solids concentration. This is important for proper sludge
dewatering.
Corrosion protection was found to be another very important consid-
eration. Bacterial decomposition of the settled sludge will lower the
pH, and sometimes it is impossible to prevent the pH from dropping to
4 or even 3, a problem especially for plants using steam peeling, and
sometimes with wastes from caustic peel plants. Two or three heavy coats
of epoxy-tar paint were found effective in protecting both steel and
concrete structures submerged in the clarifier.
Many investigators have reported on the actual performance of primary
clarifiers. Kueneman (1965) reported suspended solids and BOD reductions
of 93 and 70 percent, respectively in an Idaho plant with steam peeling.
A plant with lye peeling was reported to obtain 66 percent COD removal.
Pailthorp and Filbert (1965) reported 58 percent removal of suspended
solids and 44 percent removal of BOD in another lye peeling plant. Olsen
et al. (1965) studied the performance of a clarifier treating waste from
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a chip plant in North Dakota. Suspended solids removal was 92 percent
and BOD removal was 63 percent. Primary clarification of potato flour
processing waste gave 83 percent suspended solids removal and 51 percent
BOD removal. Wastes from the J. R. Simplot Company's plants at Heyburn
and Burley, Idaho, are treated in a 100 ft diameter clarifier with an
overflow rate of about 800 gal/day/sq ft. Dostal (1968B)reported 37
percent BOD reduction for this unit. Both plants are using lye peeling.
Performance data from Simplot's plant at Caldwell, Idaho, has been
presented by Grames and Kueneman (1968). The primary treatment plant
consists of grease removal facilities, three rotary screens with 4-mesh
cloth, and a clarifier 100 ft. in diameter with 12 ft. side water depth.
Based on the reported flow rate the overflow rate is about 730 gal/day/sq ft.
Average removal efficiencies for the 1967-68 operating season were:
COD - 62.2%; suspended solids - 93.5%; and settleable solids - 95.2%.
Flocculation and Sedimentation
Little has been reported on flocculation of potato wastes prior to
sedimentation. Flocculation has been found to increase the removal
efficiency of clarifiers markedly when treating domestic waste as well as
industrial waste.
Mechanical flocculation is accomplished by gently stirring the
waste with rotating paddles, thus causing the finely divided particles
to coalesce into larger floes with improved settling characteristics.
Floes so produced are easily broken up by too rapid stirring, and the
most efficient peripheral speed of the flocculator has been reported to
be 1.4 ft/sec (Klein 1966). Hurley and Lester (1949) obtained 20
percent increase in clarifier removal efficiency by mechanical flocculation
prior to sedimentation. It has been indicated that return of some of
the settled sludge may be beneficial in some cases (Klein 1966).
Chemical flocculation or coagulation is used more extensively in
waste treatment. The addition of certain chemicals to the waste followed
by gentle stirring, results in the formation of an insoluble flocculent
precipitate, which adsorbs and carries down suspended and colloidal
matter. Chemicals commonly used include lime, aluminum sulphate,
copperas, and various ferric salts. The cost of the chemicals makes this
method considerably more expensive than mechanical flocculation, but
higher removal efficiencies are obtained.
In potato processing, coagulation is used to recover protein from
the fruit water of the starch process, as discussed earlier. Heating
of the protein water is also used to coagulate and precipitate protein.
Flocculation prior to sedimentation deserves more attention as a
treatment method for potato wastes than it has received thus far.
Experiments with oxidized lignite and other coagulants have been performed
in North Dakota with some success (Fossum 1965).
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Flotation
Flotation is another solids removal method which has not been used
to any extent in potato waste treatment.
The waste or a portion of the clarified effluent is pressurized to
40 to 60 psi in the presence of sufficient air to approach saturation.
When this air-liquid mixture is released at atmospheric pressure, minute
air bubbles are released from solution. The rising bubbles adhere to
or are trapped by the suspended solids and sludge floes and float them
to the surface where they are skimmed off.
The process is used by a potato processing plant in Presque Isle,
Maine, and the removal efficiency of settleable solids has been reported
to be as high as 86%. However, since the calculations are based on a
volume per unit volume measurement (ml/1) it is difficult to compare this
result with removal efficiencies based on weight per unit volume measure-
ments. (mg/1) (Ballance 1965)
A pilot plant study was carried out by the Potato Products Waste
Disposal Executive Committee for the Red River Valley area of North Dakota
and Minnesota. The flotation unit was a standard Permutit colloidair
unit with a capacity of 80 gallons per minute. Reductions in suspended
solids of from 86 to 94 percent and BOD of from 66 to 75 percent were
obtained. Lye peeling wastes were used. (Francis 1962)
The primary treatment investigations in Idaho considered flotation
as a possible method, but it was concluded that because of the expense
and operational results obtained this method was not feasible. (Grames
and Kueneman 1968)
Centrifugation
Dickinson (1965) pointed out the advantages of treating potato waste,
particularly flume and wash water, by Centrifugation. A centrifuge
conserves space and delivers the solids in a relatively dry state.
Furthermore, any risk of anaerobic decomposition in settling tanks is
avoided.
The investigation carried out in Idaho did not find Centrifugation a
feasible replacement for conventional clarification. (Grames and Kueneman
1968)
Secondary Treatment
Secondary treatment at the present is not being used to any extent
by the potato processing industry. Stricter water quality criteria in the
future will, however, require higher degrees of treatment. Thus, the
Idaho Department of Health has asked that processors now using primary
treatment plants be prepared to supplement these with secondary treatment
in the future. (Cornell, Howland, Hayes and Merryfield 1966)
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Biological Treatment
Since biological treatment depends on the activity of microorganisms,
such treatment can be effective only when the environmental conditions
are favorable to growth. Potato processing wastes
do not always provide a suitable environment for microorganisms. Most
organisms are sensitive to extreme pH values, and wastes from a lye-peeling
plant thus may present problems. Potato wastes also are generally
deficient in two essential nutrients, nitrogen and phosphorous. These
factors must be considered carefully in the design of any biological
treatment facility.
Activated Sludge
No reports on large scale installations of activated sludge treatment
of potato wastes could be found in the technical literature, but several
workers have reported on pilot plant studies.
Anderson (1961) has reported on early activated sludge treatment of wastes
from a plant using lye peeling. The system, which provided for about 4
days aeration time, settling, and sludge return, could not remove more
than 50 to 60 percent COD without nutrient addition. Batch treatment by
aeration and settling with detention times of 2 and 4 days gave COD
reductions of 49 and 82 percent, respectively, when pH was adjusted to
7.0 and nutrients were added. The conclusions from the study were that
pH adjustment of lye peel wastes prior to activated sludge treatment is
not necessary, but addition of nitrogen and phosphorous will increase the
treatment efficiency.
Atkins and Sproul (1964) studied the feasibility of treating the
combined wastes from a processing plant using lye peeling by the complete
mix activated sludge process. The plant produced several types of French
fried products as well as prepeeled uncooked potatoes.
Straight potato processing waste as well as waste adjusted to pH 8
were treated in bench scale units. Treatment of the pH adjusted waste
at a detention time of 8 hours and mixed liquor suspended solids (MLSS)
concentration of 4000 mg/1 gave BOD removals ranging from 85 to 99 percent.
Most of the time the efficiency was above 97 percent. Suspended solids
removal was approximately 90 percent. The organic loading varied from
234 to 413 Ib BOD/1000 cu ft/day. The straight potato waste (no pH
adjustment) was treated at detention times of 6 and 12 hours at a MLSS con-
centration of 4000 mg/1. With organic loadings from 191 to 358 Ib BOD/100 cu
ft/day and 6 hours detention time, BOD removals from 96 to 99 percent were
obtained. The COD removals ranged from 71 to 94 percent. The suspended
solids concentration was generally reduced by more than 90 percent. For the
12 hour detention time, organic loading ranged from 65 to 276 Ib BOD/1000 cu
ft/day. No improvements in removal efficiency over the runs at 6 hours
detention time were observed. It was concluded that pH adjustment of
potato wastes prior to activated sludge treatment is unnecessary, since
56
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the production of carbon dioxide with subsequent formation of carbonic
acid is sufficient to offset the high alkalinity and thus reduce the pH
of the mixed activated sludge to a tolerable level. The unadjusted
influent waste had a pH of 11.5, while the effluent pH had been reduced
to about 9.0.
Based on the results reported above, Sproul (1965) recommended the
following design criteria:
Organic loading: 200-400 Ib BOD/1000 cu ft/day
Mixed liquor suspended solids concentration: 3000-4000 mg/1
Detention time: 8 hours
No pH adjustment is necessary
Cornell, Rowland, Hayes and Merryfield, Consulting Engineers, (1966)
have reported results of a pilot plant study for the Potato Processors
of Idaho Association. It was found that the complete mix activated
sludge system performed best at loadings below 150 Ib BOD/1000 cu ft/day.
At a temperature of 60°F BOD removals above 90 percent were obtained. At
lower temperatures the treatment was less efficient. This is in agreement
with Eckenfelder (1966) who has presented an equation by which a temperature
correction factor can be estimated. Foaming was a problem with loadings
in excess of 150 Ibs BOD/1000 cu ft/day. When operating at this loading,
excess sludge production is high. About one pound of biological solids
will be produced per pound of BOD removed. Because it is difficult to
concentrate activated sludge in a clarifier beyond one percent, a large
volume of excess sludge would result, and present another disposal problem.
Treatment of one million gallons of waste with a BOD concentration of
2000 mg/1 would result in approximately 180,000 gallons of 1 percent
solids excess sludge. This sludge can be concentrated to about 4 percent
solids in a flotation type thickener and, after chemical conditioning,
further concentrated to about 18 percent solids by centrifugation or
vacuum filtration. This would reduce the volume of excess sludge to
10,000 gallons. It was further pointed out in the report that nutrient
addition and chlorination would probably be necessary in a full scale
activated sludge plant.
Bench scale studies on completely mixed continuous flow activated
sludge systems for French fry processing waste and French fry waste in
combination with starch processing waste has been made by the Edward
C. Jordan Company, Engineers and Planners, Maine. (Hunter 1969) With
a mixed liquor concentration of 3000 mg/1 and a detention time of 7 hours,
BOD removals of 90 percent were obtained. The growth rate constant, K ,
was found to be 0.000425. A limited sludge production study indicated
a range of from 0.65 to 1.0 Ibs of volatile solids produced per Ib of
BOD removed. The lower figure was found for the French fry waste, while
the higher value was for the combination of French fry and starch wastes.
The waste from the French fry plant, which used steam peeling, had been
settled for removal of suspended solids and about 40 percent of the BOD.
57
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Buzzel et al (1964) studied the treatment of protein water from
a potato starch plant by the complete mix activated sludge process.
It was found that protein water contains sufficient nitrogen and
phosphorous for biological treatment. The data collected indicated
that whenever the loading intensity was less than 80 Ibs of BOD/day/
1000 Ibs of suspended solids/hour of aeration, the BOD removal would
exceed 90 percent. The loading in terms of BOD/1000 cu ft of aeration
capacity/day would be 420. At higher loadings the removal efficiency
decreased rapidly. Foaming was a problem and was found to increase
with decreased detention time.
Weaver et al. (1953) have reported high removal of COD from protein
water. The waste was aerated vigorously at 30°C with 12 hours detention
time. With an initial COD of 4050 mg/L the removal efficiency was 79
percent.
At the time this report was prepared a full-scale complete mix
activated sludge plant was started up at the Pillsbury Company's processing
plant at Grafton, North Dakota. (Michaelson 1969) The design loading
was 400 Ibs BOD/1000 cu ft/day with a detention time of 5 hours. A
sludge thickener designed for a solids loading of 8 Ibs/sq ft/day was
included. The effluent from the treatment facilities, which was expected
to have a BOD concentration of 200-400 mg/L, was to be discharged to
the Grand Forks municipal sewer for final lagoon treatment before discharge
into the Red River of the North.
Atkins and Sproul (1964) also investigated the possibility of using
the contact stabilization process. With a contact time of one hour and
reaeration time of 6 to 8 hours, 80 percent of the BOD was removed. The
results were obtained in a batch unit at a mixed liquor suspended solids
concentration of 4000 mg/L and with the pH of the waste adjusted to 8.0.
Based on these experiments Sproul (1965) presented the following
tentative design recommendations:
Contact time = 60 min.
Reaeration time = 6-8 hours
Mixed liquor suspended solids = 3000-4000 mg/L
Some pH adjustment by acid may be necessary, but wastes with pH
values of 9.0 to 9.5 could probably be handled successfully.
The pilot plant study by Cornell, Howland, Hayes and Merryfield
(1966) also included contact stabilization. It was found that the
process was capable of about 60 percent BOD removal at loadings up to
480 Ibs BOD/1000 cu ft/day, when operated at a contact time
of one hour and a reaeration time of 10 hours. Reducing the reaeration
time to 6 hours caused a decrease in removal efficiency to about 50
percent. The results were obtained at a temperature of 70°F. Foaming
in the contact basin was a problem. It was stated that nutrient addition
probably would be required in a full scale plant. Excess biological
58
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solids produced by contact stabilization treatment amounted to about
1.3 pounds per pound of BOD removed, and possessed the same characteristics
as sludge produced in the complete mix process.
Kintzel (1964) has reported on laboratory treatment of potato starch
waste water by contact stabilization. Seventy percent BOD removal was
obtained after a contact time of 5 minutes. The removal increased to 90
percent after 30 minutes. The whole process had a combined detention
time of 2.5 hours.
Pasveer (1965) has found the oxidation ditch effective for treating
domestic waste as well as industrial wastes. The oxidation ditch is a
modification of the activated sludge process, similar to the extended
aeration process. The ditch is simple to construct, and the most common
form is a ring-shaped circuit or ditch. Aeration and circulation in the
ditch are provided by one or more partially submerged rotors. The ditch
can be loaded at up to 34 Ibs BOD/1000 cu ft/day and still provide
essentially complete oxidation of the waste.
Biological Filtration
A considerable amount of pilot plant work has been done on the
application of trickling filters for secondary treatment of potato
wastes. The most recent investigations have employed artificial filter
media, which have proven superior to the stone media used earlier.
Buzzel et al. (1964) studied the treatment of protein water by
standard and high rate biological filters using rock media. The standard
filter gave BOD reductions of 90 percent and above at loadings up to 1300
Ibs BOD/acre ft/day (30 Ibs BOD/1000 cu ft/day). The hydraulic loading
rate was rather low because of the high BOD of the protein water. Large
reductions in acidity were obtained at all loadings. The effluent
alkalinity was reduced over the influent but generally increased in
response to the organic loading to values on the order of 200 to 300 mg/1.
The pH of the effluent was generally between 7 and 8.
With the high rate filter, BOD reductions of 90 percent and above
were obtained at organic loadings up to 3000 Ibs BOD/acre ft/day (69 Ibs
BOD/1000 cu ft/day). The recirculation rate was 10. At higher loadings
the filter became clogged with sloughed biological solids. Since the
filter media consisted of rather small rocks, of 3/4 inch diameter, it
was felt that the practical upper limit of organic loading was not
reached in the study. A full scale filter with larger rocks, and thus
larger interstices, would permit the passage of a greater amount of
sloughed material without clogging.
Pailthorp and Filbert (1965) reported results of a pilot plant
study for the Potato Processors of Idaho. The pilot unit used a
synthetic media, Surfpac, which is a polystyrene plastic media made by
the Dow Chemical Company. The unit was classified as a super-rate
filter, and was operated with a recycle ratio of 6. At an organic loading
of 132 Ibs BOD/1000 cu ft/day the BOD reductions were 71 percent with
59
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no settling and 85 percent with settling. No nutrients were added to
the waste before treatment. The influent pH was about 9.0.
Cornell, Howland, Hayes and Merryfield (1966) have reported on
further studies with the same pilot plant. It was found that the Surfpac
unit operated most satisfactorily at a BOD loading of about 400 lbs/1000
cu ft/day; the filter appeared capable of removing 300 Ibs. Although
the recycle ratio was varied during the course of the study, no valid
relationship could be established between percent BOD removal and recycle
rate. It was recommended that full scale installations be designed for
a minimum recycle ratio of 3 with provisions to permit increasing the
ratio to 7. Addition of nutrients was found to be advantageous. It
was not found necessary to adjust the pH of lye peel process water.
Treatment of steam peel wastes may require addition of an alkaline
substance when the loading exceeds 400 Ibs BOD/1000 cu ft/day, to prevent
the pH of the system from dropping below 6.3 to 6.5. Excess solids
production was found to be on the order of 0.6 to 0.8 Ibs per pound of
BOD removed when operating at loadings around 400 Ibs BOD/1000 cu ft/day.
This sludge could be concentrated to about 3 percent solids by gravity
and further concentrated by flotation. One million gallons of waste with
a BOD of 2000 mg/1 would yield 5000 gallons of 18 percent solids excess
sludge. It was further stated that chlorination of the effluent would
most likely be required to meet state requirements on coliform counts.
Mercer et al. (1964) used a Surfpac pilot plant for secondary
treatment of peach and pear canning waste. The influent and effluent
samples were settled for 15 minutes to simulate primary and secondary
clarification. The raw waste had a pH of 10.5, and the effluent pH was
6.2. The results of the study is presented in the following table:
TABLE XV
TRICKLING FILTRATION OF PEACH AND PEAR CANNING WASTE
2 "~ -~— -
Flow, gpm/ft BOD, mg/1 BOD, Ibs/1000ft /day Percent
Raw Recycle Influent Effluent Loading Removal BOD Removal
0.14
0.42
0.72
1.0
1.0
2.0
2.0
2.0
1.0
1.0
4033
3200
2700
3210
2750
580
1395
1800
2040
1515
316
730
1060
1760
1510
273
410
350
630
680
86
56
33
36
451
Nutrients added (20 Ibs diammonium phosphate per 24 hours)
Norman et al. (1965) compared the use of the activated sludge process
and the plastic media trickling filter as roughing treatment for beet
sugar waste. Overloading the activated sludge unit to obtain only 50
60
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percent BOD removal caused the formation of bulking sludge, and it was
concluded that this process was not feasible for such treatment. The
trickling filter gave BOD removals of between 33 and 50 percent on once
through passes at loadings of 400 to 230 Ibs BOD/1000 cu ft/day.
Sak (1967) has reported operating results from full scale installations
as well as pilot plants employing Surfpac media to treat a variety of
industrial wastes.
Hatfield et al. (1956) treated corn processing waste by super rate
biofiltration in a two stage filter system. An artificial filter media,
"Aero Block," consisting of clay blocks with vertical openings of 1 inch
diameter and made by the Red Wing Sewer Pipe Corporation was used in the
filter. The BOD of the waste ranged from 500 to 2000 mg/l with an average
of about 900 mg/l. The pH of the waste, which was predominately acid, was
adjusted to between 6.5 and 8.5 with soda ash. Nitrogen and phosphorous
were added to the waste prior to treatment to give ratios to BOD of 1 to
20 and 1 to 75, respectively. At BOD loadings up to 150 lbs/1000 cu ft/day
and a recycle ratio of 10, BOD removals above 94 percent were obtained.
Similar removals were obtained with BOD loads up to 110 lbs/1000 cu ft/day
when the recycle ratio was 5.
The Anaerobic Filter
The anaerobic filter offers promise as a prospective treatment
facility for certain potato processing wastes. While conventional
anaerobic digestion is limited to wastes of high strength and solids
content at relatively high temperatures, the anaerobic filter has performed
well at nominal temperatures with relatively dilute, soluble wastes.
The anaerobic filter, which is similar to the aerobic trickling filter
in appearance, has upward flow so that the rock media is completely sub-
merged. The anaerobic organisms are attached to the stones as well as
suspended as discrete particles in the interstitial spaces. High solids
retention time (SRT), which is an important operational parameter in
anaerobic treatment, is easily obtained in the anaerobic filter, and is
on the order of hundreds of days (Carlson 1968B). A gradual accumulation
of solids may take place to the point where solids wasting may be
required.
Recent studies have indicated the feasibility of the anaerobic filter.
Young and McCarty (1968) obtained BOD removals ranging from 60 to 99
percent when treating either simple volatile acids or complex protein -
carbohydrate wastes. The BOD concentration of the wastes ranged from
500 to 8000 mg/l, and the filter was loaded up to 150 Ibs BOD/1000 cu ft/day
at a temperature of 25°C. The treatment efficiency was found to be
inversely proportional to the hydraulic detention time, which was varied
from 4.5 to 72 hours. The filter could be operated from several months to
years without requiring solids wasting, and the effluent suspended solids
concentration was sufficiently low so that subsequent settling was not
required. Shock loadings did not appear to have adverse effects, as the
filter recovered very rapidly. Some possible limitations mentioned were:
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(a) The filter is best suited for treating completely soluble wastes,
(b) a significant fraction of carbohydrates in the waste may require
solids wasting, and (c) hydrogen sulfide produced from sulfate reduction
may cause odor nuisances, corrosion problems, and may be toxic to
anaerobic treatment.
Caudill (1968) studied the treatment of dilute wastes by the anaerobic
filter. Soluble, synthetic sewage with a COD of 300 mg/1 was treated at
26 and 37°C, and removal efficiencies of 67 and 80 percent were obtained,
respectively. Potato starch waste with a COD of 300 mg/1 was treated at
37°C. Removal efficiencies of 76 percent was obtained with this waste.
The theoretical hydraulic detention time for these wastes was 1.64 days
and the loading was 5.1 Ibs COD/1000 cu ft/day. Treatment of a more
concentrated starch waste (COD of 1000 mg/1) gave COD reductions of 78
percent at 30°C. It was found that most of the COD removal took place in
the first 10 inches of the 6 inch diameter column used in the study.
Also, most of the microorganisms were found suspended in the liquid
rather than attached to the rock media.
Webster and Carlson (1968) used the anaerobic filter for treatment
of pulp mill sulfite waste liquors. The temperature was held at 110°F
and the initial BOD was about 30,000 mg/1. At detention times of about
4 days and recycle rates of 8:1, BOD reductions up to 90 percent were
obtained. The COD removal was about 25 percent. High gas production
was experienced. The gas consisted mainly of methane and hydrogen sulfide.
Odor control by soil columns was suggested.
Extensive pilot plant studies for the Potato Processors of Idaho
Association on the application of anaerobic filters to potato processing
waste were completed recently by Cornell, Rowland, Hayes and Merryfield
(1969). Two 5-foot diameter filter units were tested, one with a 4-foot
rock media depth and the other with an 8-foot depth. The pilot plant
feed consisted of primary treated process water from the J. R. Simplot
Company's Heyburn and Burley plants. This is a combined waste from lye
peeling operations, potato processing, and potato starch production. The
pH of the primary treated waste varied with the operation of the clarifier
from about 7.5 to about 11.0 with a median value of 10.2. Average
organic removals of almost 70 percent were obtained at loadings of 100 Ibs
COD/1000 cu ft/day. This corresponds to a BOD loading of 57 lbs/1000 cu
ft/day, according to the average COD/BOD ratio determined. Average total
suspended solids removal at this loading was about 60 percent. Almost
identical treatment efficiencies were obtained in both filters. The
average temperature of the filter influent was 25°C, while the effluent
was at a slightly lower temperature. It was estimated that a full-scale
installation would operate at approximately 20°C. Only occasional
additions of alkalinity in the form of sodium bicarbonate were necessary
to adjust the pH in the feed to the filters. It was expected that
alkalinity addition would not be required when operating the filter under
stable conditions on potato processing waste, including wet lye peeler
discharge. The gas produced in the filter had a methane content of more
than 70 percent. This gas is combustible, and, in a full-scale plant,
could be used for energy production.
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The organic removal efficiencies of both filters were found to
increase over the test period without regard to loading, temperature,
or detention time, indicating that the anaerobic bacteria were continuing
to build and becoming further acclimated as the test progressed. It
was expected that the acclimation period, from start-up until efficient
operation is experienced might take two to three weeks. During start-up,
alkalinity should be added to act as a buffer against pH drop from volatile
acids production, and fresh anaerobic seed should be added to provide the
system with methane bacteria. The effluent from an anaerobic filter
should be passed through a short-term, flow-through aeration basin to
provide additional organic removal and render the effluent suitable for
discharge to a receiving stream. With primary treatment, this system
appears capable of 90 percent BOD removal.
Ponds
Pond treatment of domestic sewage as well as industrial wastes is
common around the world, and there are several reports of application of
this treatment method to potato processing wastes on a pilot plant basis
and in full scale ponds. Ponds are often designated by various names,
such as lagoons, oxidation ponds, stabilization ponds, and waste conversion
ponds. Dugan and Oswald (1968) classified the different types of ponds
as follows:
Aerobic ponds - Those ponds in which only the reactions above the
point where dissolved oxygen becomes zero (termed
the oxypause) occur, which provide aerobic
oxidation and photosynthetic oxygenation.
f
Facultative ponds - Ponds in which an aerobic zone exists in the
surface strata and an anaerobic zone exists in
the lower strata.
Anaerobic ponds - Ponds in which the anaerobic reactions below
the oxypause are the predominant ones.
The aerated lagoon is a fourth type, where oxygen is supplied by
diffused or mechanical aeration systems, which also cause sufficient mixing
to induce a significant amount of surface aeration.
Aerobic and Facultative Ponds
Aerobic and facultative ponds depend upon the photosynthetic capa-
bilities of algae to provide the oxygen required to satisfy the BOD
applied. Some surface aeration from wind action also occurs. Since
sunlight is essential for algae, the depth of the ponds is limited. In
aerobic ponds the waste material is stabilized wholly through aerobic
oxidation. The depth is therefore limited to that through which sunlight
will penetrate. For most wastes this will not exceed 18 inches. (Eckenfelder
1966) Extremely large surface areas are therefore required. Most existing
ponds are facultative. In facultative ponds, settled solids undergo
anaerobic decomposition in the bottom layers, while aerobic oxidation
63
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takes place in the upper layers. Serious odor problems will not develop
if adequate depth is maintained and an upper aerobic environment is
predominant. The depth of facultative ponds is seldom greater than
5 feet.
Since both aerobic and facultative ponds are highly dependent upon
algal photosynthesis, the environmental factors affecting the growth
rate of algae must be considered carefully in pond design. Gloyna (1968)
has presented design criteria for the various classifications of ponds.
Cornell, Rowland, Hayes and Merryfield (1966) carried out studies
on 3 foot deep pilot size ponds. It was found that the BOD loading to
the ponds should be kept well below 80 Ibs per acre per day. This is
within the conventional loading range and it was concluded that aerobic
ponds for potato waste be designed according to the criteria used for
domestic sewage ponds.
Forges (1963) made a survey of industrial waste ponds in the United
States in 1962. He reported three ponds treating potato processing
waste. The median loading to these ponds was 111 Ibs BOD/acre/day, and
the median detention time was 105 days. The ponds had an average depth
of 5 feet. No BOD removal efficiencies were reported, but one of the
installations was reported effective while another caused odor nuisances.
Possum et al. (1964) presented data collected over a 40-month period
on the operating characteristics of two ponds for the municipalities of
Park River and Grafton in northern North Dakota. Both ponds had been
heavily overloaded by potato processing wastes during the processing
season. The ponds were ice covered during the winter and acted merely as
storage ponds during this period. The accumulated organic load had to
be stabilized during the summer months. It was found that potato pro-
cessing wastes combined with domestic sewage digest readily in these
ponds, when the organic loading from potato wastes was 15 times or more
the organic loading from domestic sewage. Digestion may be aerobic or
anaerobic. Anaerobic digestion in these shallow ponds caused severe
odors. During summer conditions, potato waste and domestic sewage could
be applied at rates well above the conventional design loading for
northern climates of 20 Ibs BOD/acre/day. Although no specific loading
recommendations could be made from the study because of the "diametrically
opposed" operating season for the processing plant and the pond, it was
indicated that loadings on the order of 50 to 60 Ibs BOD/acre/day might be
possible. The ponds remained aerobic until the BOD in the ponds exceeded
200 mg/1. Once anaerobic conditions were established, the ponds did not
convert back to aerobic operation until the BOD fell below 100 mg/1.
One reason for the extended anaerobic period was found to be the
wave damping effect of potato organics, reducing surface reaeration.
Although the ponds have been subject to serious complaints because of the
odors produced, they carried loadings far above what might have been
expected possible, and certainly much higher than their design loading.
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Olson et al. (1965) have commented further on the over loading of
the Grafton ponds. The increased loading of the ponds presented the
problem of growth of the purple sulphur bacterium, Chromatium. Due to
the extended anaerobic period, the Chromatium was selected out by the
pond. This photosynthetic organism utilizes the hydrogen sulfide
released from anaerobic decomposition in the pond. It was observed that
BOD removal from the pond was about the same during the growth of the
sulphur bacteria as during the later period of algal growth, but the
purple color from the photosynthetic pigments of the bacterium gives
the lagoon a purple color. The pigmentation and anaerobic nature of
the Chromatium prevent the growth of algae. It thus seems that the
growth of purple sulphur bacteria could be a good indicator of an over-
loaded pond.
Voege and Stanley (1963) have reported on the use of industrial
waste stabilization ponds in Canada. A cannery in Vancouver, B.C.,
processing peas and beans, used 4 ponds in series, with depths varying
from 2 to 5 feet. The influent was passed over a 20-step aeration
deck along with recycled effluent. The temperature of the waste varied
between 57 and 72°F, and the pH was controlled between 6.5 and 8 by
adding lime at the aeration deck. Assuming no substantial removal on
the aeration deck, the BOD loading was about 1400 Ibs/acre/day and the
removal efficiency about 87 percent. The effluent had a bright green
color and a BOD of about 100 mgA• It was finally discharged to spray
irrigation fields.
Anaerobic Ponds
Although anaerobic ponds have been used quite extensively for
treatment of food processing waste, they have not been used with much
success by the potato processors. Forges (1963) reported that, in 1962,
3 anaerobic ponds were used in the United States for treatment of
potato wastes. No information was given on the efficiency of these
ponds, but it was reported that odor nuisances were associated with one
of them.
Other industrial wastes have been treated successfully with anaerobic
ponds. Howe and Miller (1963) used an anaerobic pond to treat wastes
from a chemical and fermentation products plant. With a BOD loading of
2.6 lbs/1000 cu ft/day a removal efficiency of 60 percent was obtained
at a temperature of 5°C. At a temperature of 15°C the removal efficiency
increased to 78 percent. To obtain this efficiency it was necessary to
adjust the pH to 6.8 to 7.2. Nitrate was added to prevent formation of
hydrogen sulfide.
\
Mclntosh and McGeorge (1964) had some success with a full scale
anaerobic pond receiving corn processing waste. The pond was loaded at
about 40 Ibs BOD/1000 cu ft/day with sludge recirculation from the end
to the inlet of the pond. After about 40 percent of the surface area of the
pond was covered with a Styrofoam raft, the BOD removal was found to
increase from 32 percent to 40 percent. The pond influent was at a
temperature of 91 to 114°F, and this high temperature undoubtedly improved
65
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the performance of the system. Nitrate was added for odor control, and
the pH was adjusted to between 9 and 11 with caustic soda.
Research efforts on potato waste treatment indicate that anaerobic
ponds can be used advantageously to condition the waste for further
treatment by aerobic means.
Dostal (1968B) has reported results of pilot plant studies at Burley,
Idaho. Two Styrofoam covered anaerobic ponds were first operated in
parallel. Pond 1, with a detention time of 4 days, was loaded at 23 Ibs
BOD/1000 cu ft/day, and gave BOD removals of 17 percent. Pond 2 had
a detention time of 20 days and was loaded at 4.6 Ibs BOD/1000 cu ft/day.
A BOD reduction of 22 percent was obtained. Suspended solids reductions
were 56 and 62 percent for Pond 1 and 2, respectively. The ponds were
not mixed, and the temperature ranged from 60° to 70°F.
During the second period of operation the ponds were operated in
series. The first pond continued to operate as an anaerobic pond, and
a pump was installed to mix the contents. A 5 hp floating surface
aerator was installed in the second pond which consequently operated as
a mechanically aerated pond. The performance of the system under
different operating "conditions has been summarized below.
Detention Time,BOD loadingRemoval - %
Days lbs/1000 cuft/day SS COD BOD
Anaerobic pond 8.8
Aerated pond 8.8
Overall
Anaerobic pond 5
Aerated pond 5
Overall
Anaerobic pond 2.4
Aerated pond 2.4
Overall
11
8
22
20
46
40
82
-230
74
35
-75
66
52
-226
51
33
49
73
15
58
82
15
28
68
25
88
95
12
87
94
12
64
81
These results indicate excellent removals by the combination
anaerobic-aerated ponds. It should be pointed out that the removal
efficiencies were based on effluents with all solids remaining.
Continuing studies on the same pilot plant for the Potato Processors
of Idaho Association have been reported by Cornell, Rowland, Hayes and
Merryfield (1966). The results from the anaerobic ponds were not con-
clusive with respect to design criteria, but valuable information was
obtained. The ponds appeared to take the waste through the first stage
of anaerobic digestion, breaking down large molecules such as starch
and protein into smaller molecules of organic acids, aldehydes, and
66
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alcohols. This results in a rather small BOD reduction, but yields an
effluent which is more amenable to aerobic treatment. Nutrient addition
did not appear necessary. It was indicated that it would not be
advisable to design anaerobic ponds at detention times less than 4 days
due to the high rate of solids buildup. A pond with a 4 day detention
time may possibly be operated for four seasons before cleaning is
necessary, while a pond operating at a one day detention time probably
would have to be cleaned annually.
The effluent from one anaerobic pond was treated in a flow through
aeration basin. When operated at a loading of 130 Ibs BOD/1000 cu ft/day
and a detention time of 22 hours, additional BOD removal of 57.5 percent
was obtained. Limited data was collected at a detention time of 11
hours, which showed similar removal efficiency. Suspended solids in the
effluent were measured in amounts up to 1.2 Ibs per lb of BOD removed,
and consisted of dispersed bacteria, which could not be settled out at
normal detention times. Nutrient addition was not necessary, but foaming
was a problem, and it was recommended that provisions for defoaming agent
addition be included in full scale design.
Results from continued studies on the Burley pilot plant were
reported recently (Cornell, Rowland, Hayes and Merryfield, 1969). The
two covered anaerobic ponds were operated in parallel, one as a straight
flow-through pond, the other as a mixed pond. The effluent from the
mixed pond was passed through the aerated pond. The flow-through pond
obtained BOD removals of about 40 percent at a loading of approximately
7 Ibs BOD/1000 cu ft/day. The effluent volatile acids concentration
was much higher than the influent because of incomplete biological
degradation in the pond. The continuously mixed pond performed much
better than the flow-through pond. Average organic removal efficiencies
of more than 70 percent were obtained at loadings of about 8 Ibs BOD/1000
cu ft/day. The more complete biodegradation also resulted in much lower
volatile acids and suspended solids concentrations in the effluent.
The aerated pond was effective in further reducing the organic
content of the anaerobic process effluent. Organic removals of almost
40 percent were obtained at a loading of about 4 Ibs BOD/1000 cu ft/day.
It was stated that alkalinity in the influent, such as that derived
from the wet lye peel process, would be required in anaerobic pond
applications. The problems associated with inefficient operation
during start-up of the system, offensive odors from the pond unless
covered, and the lack of operational control were emphasized.
Olson et al. (1965) conducted pilot plant studies on combined
anaerobic - aerobic treatment. Two days of anaerobic fermentation gave
solids and BOD reductions of 30 and 22 percent, respectively. When the
effluent was aerated for 4 and 6 days, the combined system yielded BOD
reductions of 85 and 90 percent, respectively. Total solids reductions
through the system were 52 and 54 percent. Future work was proposed
on a bi-level pond, where a suspended air-aqua tube separates the two
zones.
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Aerated Lagoons
Some information on aerated lagoons has already been presented in
the review of the anaerobic - aerated pond systems. However, these
aerated lagoons are treating waste which has already been "conditioned,"
and which appears to be more amenable to aerobic treatment.
Olson and Vennes (1963) reported the results of mechanical aeration
of potato processing waste and domestic sewage at Park River, North
Dakota. A one acre experimental aerated lagoon was constructed to
pretreat the waste prior to treatment in primary and secondary facultative
ponds. During the first 6 months of operation only domestic sewage was
treated. The average BOD loading during this period was approximately
380 Ibs/acre/day with a detention time of 14 days. This gave BOD removals
of 85 percent or more even at temperatures close to 0°C. The average
pH of the sewage was 7.8.
A later operation using equal volumes of potato waste waters and
domestic sewage resulted in a waste mixture with a pH of 11.6. Under this
loading the aerated lagoon pH gradually shifted to 11.3. Neutralization
was not feasible because laboratory studies indicated at least 70 ml of
concentrated sulfuric acid would be needed per 100 ml of waste. While
BOD loadings were almost 3000 Ib/acre/day at a 6 day detention time,
the decrease of BOD removal efficiency to 25% was attributed to the high
pH. It was evident that the aerated lagoon was limited in its ability
to reduce the pH of the mixed waste, and some form of pH control would
be required for this lagoon to be effective as a pretreatment unit. It
was suggested that recirculation from the primary pond might provide the
necessary buffering. In-plant pH control was also suggested. The use
of steam peeling rather than lye peeling will provide a waste with a pH
more suitable for biological treatment.
Olson et al. (1964) also have described the results of installing
an aerator in one of the two ponds at Grafton, North Dakota. These
ponds are ice covered in the winter, and stabilization of the organic
matter takes place in the summer. Anaerobic conditions prevailed
during a large part of the stabilization period, and odors have been a
problem. Aeration was found to shorten the anaerobic period considerably,
and although insufficient oxygen was supplied for complete stabilization
of the organic matter, the purple sulfur bacteria were removed much
easier and an active algal population was restored. It was indicated
that by keeping the pond open during the winter months it might be
possible to maintain the algal population throughout the year.
Other industrial wastes have been treated successfully in aerated
lagoons. Dostal (1968C) reported results from the operation of a lagoon
treating pea processing waste in Washington. The pond which had a surface
area of 1.75 acres, an average depth of 10 feet, and a volume of about
5.6 million gallons, provided a detention time of 5.5 days. Oxygen
was supplied by four 50 horsepower surface aerators. The effluent from
the aeration basin flowed into a smaller polishing pond. Recirculation
of settled solids from the polishing pond back to the aerated pond was
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intended, but this practice was never initiated. According to values
reported the BOD loading to the aerated pond ranged from 3000-4400
Ibs/acre/day (7.0 to 10.3 lbs/1000 cu ft/day). The influent temperature
ranged from 17°C to 30°C with a pH range from 6.7 to 8.2. An average
BOD removal of 76 percent was obtained, while total solids were reduced
by 20 percent. Suspended solids were found to increase by 70 percent
through the lagoon. The polishing pond had little effect on the degree
of treatment as it readily filled with solids. Bulking sludge was
a problem and was thought to be due to the seasonal operation of the
processing plant. Improved operation of the lagoon prior to processing
was expected to better the condition of the sludge. Recirculation of
settled solids would improve the removal efficiencies of the system.
Butler and Burns (1968) presented operational data from a lagoon
treating unbleached kraft pulp mill effluent in Pennsylvania. Two
aeration basins in series, designed for a detention time of 1.5 days
each, were followed by a settling basin with 9 hours detention time.
The design loading was 5 Ibs BOD/1000 cu ft/day. Three 20 horsepower
surface aerators were installed in each aeration basin, and underflow
from the settling pond was recirculated back to the inlet of the aeration
basin. Average BOD removal during the first year of operation was 85
percent. This was obtained with a loading of 4.2 Ibs BOD/1000 cu ft/day
and a detention time of 3.72 days. The effect of seasonal temperature
fluctuations was reported. During the summer, fall, and winter, when
the average temperatures were 30°C, 25°C, and 18°C, respectively, the
BOD removals were 88%, 83.7%, and 81 percent. Nutrients in the form of
30% aqua ammonia and 70% phosphoric acid were added to give BOD:N:P
ratios of 240:3:1. These high ratios made the addition of a defoaming
agent necessary.
Spray Irrigation
Spray irrigation has been used successfully by many processors as
a method of final disposal of waste water from fruit and vegetable
processing. Successful operation of spray irrigation fields is dependent
on the capacity of the receiving site to absorb the waste water. Among
the variables influencing soil receiving capacity are type of soil,
stratification of soil profile, depth to ground water, initial moisture
content, and cover crop. Waste water characteristics also are important.
General design criteria or recommendations cannot be stated for
spray irrigation because of the variables involved, and most systems
must be designed with considerable flexibility. Results and recommendations
from some successful applications of spray irrigation will be presented.
Szebiotko (1965) reported that agricultural use of the effluents
from potato starch plants was found to be the most effective and economical
method of disposal in Poland. It was calculated that one million gallons
of effluent is sufficient to irrigate about 3.5 acres of grassland. The
effluent, which has a very high fertilization value, is free of substances
harmful to soil and plants. Spray irrigation was found most effective
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when used on grassland, and the optimum annual dose was reported to be
from 200 to 500 mm (8 to 20 inches). With high doses (800 to 1000 mm
per year) the grass plants disappeared after 2 to 3 years, and nettles,
which tolerate higher doses of nitrogen, appeared.
Adler (1965) reported spray irrigation to be the best and most
economical method for disposal of potato starch processing waste water
in Germany. One plant was reported to produce from 90 to 130 million
gallons of dilute potato "fruit" water during the 90 days of operation.
The water was sprayed on an area of 620 acres, which corresponds to a
loading of 145,000 to 210,000 gallons per acre. A three-year rotation
program was used, so that a total area of 1860 acres was required. The
importance of soil characteristics and fertilizer value of the waste
stressed.
Successful spray irrigation of effluents from fruit and vegetable
canneries in Britain has been reported by Dickinson (1965). A small
producer of pre-peeled, packed potatoes sprayed a volume of 14,000
gallons per day on an area of 1 acre. The effluent had a BOD of 3600 mg/1
a suspended solids concentration of 1300 mg/1, and a pH of 11.8. A 7-day
rotation program was used, requiring a total land area of 7 acres.
Rose (1965) presented recommendations regarding application rates and
cover crops. For different soil types and drainage conditions the
following application rates were recommended: (from Maryland Processors'
Report, Vol. 11, No. 12, March 1965)
Soil Type Drainage^ Inches per Hour
Galestown S. L. Excessive 1.0
Sassafrass L. S. Well 0.6
Matapeake Silt Well 0.4
Keyport Silt Mod. Well 0.3
Elkton Silt Poorly 0.2
Bayboro Silt Very Poorly 0.2
Without adequate vegetation excessive soil erosion or surface run-
off will occur. It has been reported that, without cover crop, the
amount of liquid taken up by the soil will be only 10 to 15 percent of
the amount which can be absorbed by a field with a cover crop. A cover
crop mixture which has proven to be satisfactory over a wide range of
soils and operating conditions is as follows:
Ladino clover - 1 Ib/acre
Aisike clover - 4 to 6 Ibs/acre
Reed canary - 6 to 8 Ibs/acre
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Haas (1968) reported on successful spray Irrigation of potato
processing wastes at Moses Lake, Washington. A spray field of about
120 acres covered with a mixture of grasses and alfalfa was used. The
cover crop was cut, cured, and baled twice per year, but it was pointed
out that this probably should be done more often. A preliminary survey
showed the soil to be loam with 2 to 4 feet of top soil followed by a
broken layer of caliche and gravel about one foot thick with sand below.
A compacted clay mixture with sand was found 6 to 7 feet below the
surface. The water table was, in one place, found to be 6 to 7 feet
down. The waste consisted of fluming water and primary wash water as well
as process water. Prior to disposal, larger solids were removed on a
20-mesh vibrating screen, and silt was removed in a settling basin. The
total flow to the spray field was about 840 gpm. This corresponds to
an application rate of 0.35 inches per day or 100 inches per year. A
ten-day rotation program was used. The spray field received between
5 and 6 million pounds of organic solids per season.
Drake and Bieri (1951) reported on spray irrigation of vegetable
canning wastes at several plants in Minnesota. One plant, processing
peas and corn, reported successful disposal of an estimated 16 million
gallons to a 72 acre annually cropped field. The waste was passed
through a 20-mesh rotary screen before being pumped to the spray field.
The soil was a silty loam underlain with clay.
Another cannery, also processing peas and corn, experimented with
spray irrigation of lagooned waste mixed with fresh waste. The soil in
this area was a heavy-black loam underlain with clay. The average
application rate was one half inch per day and the rotation cycle took
8 days. When the lagooned wastes were sprayed, objectionable odors
occurred. This was not noticeable when fresh wastes were sprayed.
Similar problems occurred at another plant employing a storage lagoon
during part of the processing season. The odors at this plant did not
appear to be as serious, probably because of the more suitable sandy
soil.
Luley (1963) reported results of an unusual application of spray
irrigation for disposal of tomato, peach and apple processing wastes.
The land area used had a slope varying from 2 to 12 percent. The soil
was a silty clay mixed with shale, underlain with layers of shale at
1 to 2 feet below the surface, so that very little water infiltrated the
ground. The waste which was sprayed on the field trickled slowly over
and through the vegetation on the sloping terrain, which consisted of
honeysuckle and reed canary grass, and flowed down to a creek. It was
found, from average results over one year of operation, that the BOD
of the run-off to the river had been reduced by 97 percent. To prevent
soil erosion, the steepest slopes had been contour-plowed. The spray
system provided at least 2 days rest for the ground between 24-hour spray
applications. The land area used was about 52 acres, and the average
BOD of the raw waste was 1095 mg/1 or 2196 Ibs/day. This corresponds to
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a loading of 4600 gallons/acre/day. The spray field was operated
during the winter as well as during the summer. Some icing of the field
occurred during the winter, but, although the BOD reductions were
somewhat lower, they were quite acceptable.
It should be emphasized again that the results presented above are
valid only under the respective local conditions. Such results may be
helpful when designing new spray irrigation systems, but local conditions
must be considered carefully, and flexibility should be provided.
Tertiary Treatment
As re-use of treated waste water becomes more essential, tertiary
treatment of these waters will become increasingly important. The
biological treatment methods, as presently used, leave significant
residues in the effluents, and several physical and chemical treatment
methods have therefore been investigated as a means for polishing
effluents before re-use. These methods include adsorption, foam separation,
electrodialysis, evaporation, reverse osmosis, coagulation, chemical
oxidation, and freezing.
Adsorption - This process can effectively remove COD-bearing organic
material. Activated carbon has been found to be the most effective
adsorbent for many classes of organic substances. When activated sludge
effluents are passed through beds of granular carbon, or when powdered
carbon is slurried with the effluent and subsequently removed, from 70
to 95 percent of the remaining COD can be removed. The organics which
are not removed are believed to be largely colloidal. Inorganic salts are
not removed by carbon.
Foam separation - The foaming tendancy of secondary effluents is
the basis for this process. Foam generated by deliberately blowing air
through the effluent, at an appropriate rate, will contain 85 to 95
percent of the ABS and up to 35 percent of the remaining organics. The
foam is collected and condensed to a small volume. Foam separation is
especially effective in removing dissolved surface active contaminants
like ABS. Inorganics are not removed unless they are surface active.
Electrodialysis - When a difference in potential is established
across a solution of electrolytes, current will flow as a result of ion
migration toward the electrodes of opposite charge. In electrodialysis,
cation and anion permeable membranes are placed in alternate sequence
across the electric field. The anion permeable membranes will obstruct
the movement of cations toward the cathode, while the cation permeable
membranes will obstruct the migration of anions toward the anode. As a
result, cells are formed in alternate sequence in which the water
becomes either more dilute or more concentrated with respect to the
electrolytes. Electrodialysis reduces the inorganic ion concentration
effectively, with exception of the ammonium ion. Some organics are also
removed, but these will eventually foul the membrane, so that a rather
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difficult regeneration process is required. Power requirements are
estimated to 6 - 10 kwh/1000 gallons of water treated for a removal of
300 to 500 mg/1 of solids, Electrodialysis is already a commercially
proven process.
Evaporation - Although evaporation or distillation of waste water
effluents does not produce drinkable water, the process has attractive
possibilities. The distillate generally contains less than 5-10 mg/1
inorganics and 2-3 mg/1 organic carbon. However, volatiles such as
ammonia and low boiling organics are not removed. The effects of many
of the operational variables are not well known, and further work is
required to evaluate the feasibility of the process.
Reverse osmosis - This process has received less .attention than the
ones above, but nevertheless deserves to be mentioned. Relatively pure
water has been produced by forcing water through semi-permeable membranes
under a pressure of 750 psi. The membranes filter out organics, inorganics,
and even bacteria and viruses. Water with 50 mgA total dissolved solids
and less than 5 mgA organics can be produced.
Coagulation - Coagulation has already been described in connection
with primary treatment. In tertiary treatment coagulation has proven
beneficial as a pretreatment to the processes mentioned above.
Chemical oxidation - Oxidation of organics to carbon dioxide and
water using chemical oxidants would be a very attractive treatment method.
Short detention times and thus small waste treatment facilities would
result. Also, the substances resistant to bacterial oxidation would be
removed. Oxygen, ozone, chlorine, and chlorine dioxide have been tried
as oxidation agents. Active oxygen in the form of free hydroxyl radicals
is also a strong oxidant in aqueous systems and will oxidize organic
compounds containing hydrogen and many other ions such as the halogens.
This radical can be generated using iron salts and hydrogen peroxide.
When this method was used to treat an effluent, refractory organics
were reduced by 50 to 70 percent when the pH was controlled between
3 and 4. ABS removals of 98 percent also were achieved. However,
this method of supplying free hydroxyl radicals is too expensive and
further work is required to produce an economical oxidation agent.
Freezing - Freezing has received much attention as a means of
converting saline water to fresh water. The process also has been
investigated for treating waste water effluents. The ice crystals
formed under proper conditions are relatively pure. The contaminants
adhere to the crystals, and the success of the process depends on
effective washing of the crystals.
Ammonia as a problem - The ammonium ion is difficult to remove from
the effluent by the methods which are capable of removing inorganics.
One solution to this problem is to convert the ammonia to nitrate by
microbial nitrification. This is relatively easily achieved in the
activated sludge process by extending the time of aeration or by operating
at higher mixed liquor suspended solids concentrations. Ammonia also
can be removed by air stripping at high pH.
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SECTION 7
DISPOSAL OF SOLIDS
Solid waste from potato processing operations include sand and grit,
peelings, trimmings, and potato pulp. Solids also are one of the end
products of nearly all waste treatment processes. Effective solid waste
disposal is essential for the waste treatment process to be successful.
Depending upon the method used, solids disposal may result in economic
return or additional treatment cost.
Complete utilization is the ideal solution to the solids disposal
problem, and fortunately a large fraction of the solid waste from potato
processing is suitable for use as animal fodder and even for processing
into by-products of commercial value. (Shaw 1965) (Dickey et al. 1963)
However, large amounts of solid waste are disposed of by other methods
for economic as well as practical reasons. In some areas the demand for
the solid waste products is not sufficient to warrant the capital investment.
Furthermore, pesticide residues and high alkaline content may limit the
usability of raw solid waste. Microbiological spoilage of food wastes
presents another problem, since no economical method of preservation has
been discovered. (Rose 1965)
Disposal to Sewer
Some processing plants discharge solid wastes as well as liquid
wastes directly to a municipal sewer. Generally, larger solids are com-
minuted prior to discharge. From the processor's standpoint this is a
most convenient solids disposal method. The obvious disadvantage is the
greatly increased waste load to the receiving treatment facility or waterway.
In many instances solid waste discharge would not be permitted or would
be economically unsound because of increased treatment cost.
Land Disposal
A widely used method for disposal of solids wastes is by land disposal
Strict control is essential to prevent ground water contamination, fly
breeding, and odor nuisances. An important requirement is that the waste
is covered with a soil layer within 24 hours. (The Cost of Clean Water
1967) Primary and secondary sludges have a very high water content and must
generally be dewatered prior to disposal. The dewatering step can be
omitted by applying the sludge to the land in a thin layer. Liquid sludges
can easily be pumped and sprayed onto the land. The same method may be
applied to the solid waste from the processing operations. This method
provides low cost oxidation of organic matter, providing sufficient low
cost land is available. In many instances agricultural and forest soils
are improved. Odors and fly breeding may cause problems. (The Cost of Clp
Water 1967) n
Composting
Composting processes have long been used as a method of converting
putrescible plant residues to more stable organic materials of value as
fertilizers or soil conditioners. Composting also has had application as
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a method of solid waste disposal. Decomposition of the organic materials
may proceed aerobically or anaerobically, depending upon the availability
of oxygen. Anaerobic processes are slow, and offensive odor production
is difficult to control. Aerobic composting is a much more rapid process
and no offensive odors are produced. The process may be carried out in
outdoor piles or in high-rate mechanical units. (Rich 1963)
Rose (1965) reported results of experiments on fruit waste composting
by the National Canners Association. In early experiments it was found
that efficient aerobic composting would proceed in a pile if the water
content of the material was held below 70 percent by mixing with absorbent
materials. At higher water content slow anaerobic decomposition with
offensive odors was experienced. Grinding the solids greatly improved
the rate of the process by exposing more surface area to microbiological
attack. Fruit acids were found to have an inhibitory effect at pH levels
below 4.5. By adding lime the acids were neutralized and the stabilization
period was shortened. Since composting is a biological process, addition
of urea to the nitrogen deficient waste proved beneficial. Rich (1963)
states that the initial carbon to nitrogen ratio, C/N, should be from 30
to 35 (by weight) for aerobic composting. The C/N ratio of the completed
compost will be within the range from 10 to 20. Further composting
experiments by the NCA compared regular windrows with forced aeration
windrows. Perforated copper pipes were imbedded in the base of the bins,
which were 9 feet wide and 5 to 6 feet deep, containing about 30 cubic
yards of solids. The material was mixed with a windrow turner. Although
the complete results of this experiment were not compiled, all indications
were that forced aeration increased the composting rate and helped
preventing odorous conditions. It was found that raw waste could be added
to the bins at rates up to 86 Ibs/cubic yard/day without adversely
affecting the process. Dried compost together with rice hulls was used as
the absorbant. Automated methods of handling the waste material also were
investigated. A two-sectioned reservoir was built on the site. The first
section was used to hold the waste as received from the cannery. A
bucket elevator was used to convey the solids to a grinder located over
the second section. The pulpy slurry produced by the grinder was pumped
from the second reservoir to the bins or windrows with a diaphragm type
pump. This handling method was found satisfactory.
Composting of primary sludge requires dewatering of the sludge.
Primary sludge is generally from 95 to 98 percent water, and unreasonable
amounts of absorbing material would be required to lower the water content
below 70 percent. Dewatering may be accomplished by air drying, vacuum
filtration, pressure filtration, or centrifugation. (Ballance 1965)
Air drying on sludge drying beds is a method commonly used in
municipal sewage treatment plants. The sludge is applied to a bed of sand
and gravel and the water is drained off. Most of the removal takes
place in one day, after which further removal is primarily by evaporation.
A major disadvantage with sludge drying beds is the land requirement.
Climate is an important factor, and some drying beds are covered with a
glass building similar to a greenhouse.
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Vacuum filtration has been found to be the most favorable method
for dewatering primary sludge from potato processing plants. (Grames and
Kueneman 1968) (Francis 1962, Red River Valley) Studies carried out
by the Engineering Committee of the Potato Processors of Idaho Association
showed that sludge from plants using steam peeling could be dewatered
to a solids content of 12 to 16 percent. The filtrate has a suspended
solids concentration of 1000 to 1200 mg/1, and most of these solids
would settle again when the filtrate was returned to the clarifier.
Dewatering of sludge from plants with caustic peeling at first appeared
impossible. The water would not separate from the solids, and the
gelatinous slurry blinded the filter cloth immediately. It was found that
chemical conditioning of the sludge with ferric sulphate and lime re-
leased the water and flocculated the solids. The cost of chemicals was
high, however. Later it was discovered that ageing of the sludge in the
clarifier improved the filterability due to bacterial action. If the
solids were held too long, the bacteria would decompose the solids and
filterability was greatly reduced. Also, reduced clarifier efficiency
was observed.
The optimum time of ageing has been found to vary from plant to
plant. While 4 to 5 hours may be sufficient in one installation, 24
hours may be required in another.
The filtration rate is dependent upon sludge concentration and con-
ditioning and may vary considerably. Experience indicates that it is
safe to size filters on the basis of 5 Ibs of dry solids per square foot
per hour, although rates as high as 15 Ibs/sq ft/hr have been obtained
when the sludge characteristics were favorable. (Grames and Kueneman 1968)
Pressure filtration is a batch process and does not find much
application, since it has the major disadvantage of requiring hand labor
to remove the sludge cake. (Ballance 1965)
Continuous centrifugation of primary sludge can be used successfully.
The solids content of the dewatered sludge is in the range of 16 to 20
percent. (Kueneman 1965) A problem associated with centrifugation is
removal of the finer solids discharged with the centrate. The solid
particles are broken down by the centrifugal force so that they exibit
poor settling characteristics when returned to the clarifier. (Grames
and Kueneman 1968)
Incineration and Wet-Oxidation
Incinerators currently are used in municipal treatment plants to
burn solid organic wastes. (Hindin and Dunstan 1965) (Cost of Clean
Water 1967) To avoid objectionable odors from the volatile organic
acids, temperatures of about 1400°F must be maintained. Two basic types
of open-air sludge incinerators are in use. These are the flash drier-
incinerator and the multiple hearth incinerator.
By incinerating solid waste the fuel value of the solids can be
utilized. The recovered heat energy may be used to generate steam for
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general plant use. Uindin and Dunstan (1965) found that screenable
potato waste solids had a fuel value of about 6650 BTU per pound of
dry solids. The heat energy obtained from a wet waste depends on the
amount of organic matter present in terms of COD or volatile solids
content and the degree of completion of the combustion.
In recent years, wet oxidation or pressure burning of industrial
waste as well as municipal waste has been practiced. The Zimpro process
has been used to oxidize various kinds of sewage sludges and waste pulp
liquors. The waterborne organic matter is oxidized, under pressure,
with air. Operational results of the process have been reported by
Hurwitz et al. (1959). A sewage sludge containing 5.24 percent total
solids, 3.47 percent volatile solids, and 64400 mg/1 COD was fed to the
reactor at a rate of 229 gallons per hour. With an average reactor
temperature of 506°F and an average pressure of 1200 psi, 7058 BTU
were produced per pound of dry solids when 2.34 Ibs of air were added
per gallon of sludge. The effluent contained 13700 mg/1 COD, 1.74 percent
total solids, and 0.4 percent volatile solids. The steam produced was
used to heat the incoming sludge.
A more recent development is the Dorr-Oliver FS-System. In this
process a preheated fluidized bed is used to dry and incinerate the wet
organic waste. Thermal oxidation occurs at a pressure of about 2 psi
and a temperature of 1500 - 1700°F. The process has been found self-
sustaining if the water content of the wet waste does not exceed 65
percent. If the water content is higher or the waste has a low organic
content, fuel as propane or fuel oil is added directly to the fluidized
bed. (Hindin and Dunstan 1965)
It is important to note that dewatering of solid wastes with high
water content is necessary for efficient use of any of the combustion
methods described above.
Anaerobic Digestion
Anaerobic digestion of solid waste decomposes the organic liquids
and solids to inorganic matter and organic gases. Methane is the
principle organic gas formed.
Hindin and Dunstan (1963) studied digestion of varying mixtures of
potato waste solids and sewage sludge. The potato waste solids are
deficient in nitrogen and phosphorous, essential nutrients for bacteria,
and the sewage served as a source of these nutrients. Also the sludge
provided the mixture with an inocculum of methanogenie microorganisms,
responsible for the methane fermentation process. Using conventional
rate sewage sludge digestion, satisfactory digester performance was
obtained with a mixture containing equal amounts of potato waste solids
and sewage sludge. Signs of digester distress were observed when the
mixture contained 75 percent potato waste solids. It was recommended
that in actual large scale operation the digester feed should not
contain more than 25 percent potato waste solids. Although it was found
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that the digester destroyed the solid organic matter efficiently, the
supernatant had a BOD in excess of 1000 mg/1. Disposal of this highly
organic liquid may present problems.
Much research is needed towards efficient utilization of the fuel
value of potato waste solids through anaerobic digestion. Other areas
which require further research are supernatant disposal, nutrient
supplementation, and application of the high rate and contact digestion
processes.
Animal Feeding
Utilization of potato pulp and peelings for cattle feed already has
been discussed. Sludge from primary clarification of potato processing
waste water also has been used successfully for cattle feed. All the
sludge recovered from the clarifiers of the J. R. Simplot Company is fed
to cattle. The sludge is dewatered to about 14 percent solids content by
vacuum filtration. Caustic peel sludge is stored until the pH falls to
neutral or below through fermentation. At the beginning of the feeding
period, the mixture contains about 45 percent potato solids (by weight).
The rest of the feed is mainly chopped hay with some grain. After 14 days
the potato solids content is increased to about 70 percent, and this
mixture is used for the remainder of the feeding period. The potato
solids have been found to be at least equivalent to barley in nutritional
value, and reports indicate that there has been an accelerated weight
gain of about 1/2 Ib/animal/day after the potato solids were included in
the diet of the cattle. At the present the total weight gain of the
Simplot cattle ranges from 2.6 to 4.1 Ibs/animal/day with an average of
about 3,0 Ibs. Livestock feeders were long reluctant to use filtered
sludge. Since its value was proven through experience, the filtered
sludge has been in demand, and many processors are selling the sludge
along with their screened solids at a price of about $3.00 per ton of
waste at about 14 percent solids content. This price is sufficient to
recover capital costs of primary treatment in two to four years. (Grames
and Kueneman 1968)
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SECTION 8
CURRENT RESEARCH AND DEVELOPMENT EFFORTS
At the present time a considerable amount of research and develop-
mental work is under way on potato processing waste treatment in this
country. The Pacific Northwest Water Laboratory of the Federal Water
Pollution Control Administration in Corvallis, Oregon, has been assigned
national responsibility for food processing wastes. In each of the
major food processing areas, such as potato, the waste treatment research
needs will be developed and these needs will be assigned priorities. The
total problem will be attacked systematically from three directions.
First, the FWPCA will do some in-house research. Second, research grants,
contracts, and demonstration grants will be awarded to various universities,
industries, and other groups to work on designated problems. Third, and
not least, work will be done by industries and groups .such as the Potato
Processors of Idaho Association.
Research grants directly involved with potato processing wastes are
described in Appendix B. The projects are those given in the Water
Resources Research Catalog (1967, 1968). These projects cover aspects of
biological waste treatment processes, by-product recovery, in-plant
modifications, chemical process application, peeling processes, odor
control and other process and treatment modifications. In addition to
the projects described in Appendix B, many smaller projects are conducted
by industry and other institutions.
Many studies on process waste water disposal for other related
industries are under way and constitute a large potential source of
research information which may be applicable to the potato processing
industry. The concern for environmental quality control is international
and is focused on preventing further deterioration of the environment.
The effects of this growing concern, no doubt, will be to provide further
stimulus for research and further requirements for waste water control.
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SECTION 9
RESEARCH NEEDS
With the existing waste treatment technology any reasonable effluent
quality requirement imposed on the potato processing industry can be met.
In England, where effluent requirements are considerably more restrictive
than in the United States, potato waste treatment facilities capable of
producing effluents with BOD and suspended solids concentrations below
20 mg/1 are in operation. In one such plant, primary sedimentation is
followed by two stages of biofiltration and activated sludge treatment.
Final polishing on sand filters enables re-use of a large fraction of the
effluent in the processing operations without detrimental effects on the
quality of the final product. Up to 75 percent of the effluent may be
re-used. A treatment scheme such as this is of course costly, and cost
is the main treatment problem facing most potato processors. Capital as
well as operating costs are high, with little or no possibility for
return on the investments. This is true now for conventional
secondary treatment and will be a continuing problem as federal and
state requirements on effluent quality become more restrictive, and a
higher degree of treatment becomes necessary.
Cornell, Rowland, Hayes and Merryfield (1969) have presented average
capital and operating costs for potato waste treatment and compared these
with similar costs for municipal waste treatment presented by Smith (1968)
The costs for primary potato waste treatment were based on facilities
constructed in the Pacific Northwest, while the costs for secondary
treatment were based on engineering estimates from demonstration projects
and from pilot plant systems studied by the Potato Processors of Idaho
Association. The curves presented are shown in Appendix C. Because of
the rapid change in construction costs, all figures were adjusted to a
common base of June 1967 by using the Engineering News-Record building
cost index. The history of the building cost index and a projection of
the index into the future also is shown in Appendix C.
A survey of many potato processing plants was made in connection
with this report. Limited treatment cost information was obtained.
Primary treatment was reported to cost from $0.02 to $0.064 per pound of
BOD removed. In terms of raw product input a treatment cost of $0.50 per
ton of potatoes was given. A starch plant reported operation and main-
tenance cost of $0.04 per pound of BOD removed. Protein water was
treated by anaerobic fermentation and diffused aeration and combined with
flume water for sedimentation and disposal to a municipal sewerage system.
The survey showed that a large percentage of the potato processors
do not know the cost of treating their own waste. Capital cost of the
facilities is of course known, but operational cost is not determined.
For efficient operation and control of the waste treatment facilities
and to evaluate the effects of in-plant changes and procedures, cost
information is essential in most cases. Large sums of money may be
wasted unnecessarily unless consideration is given to cost of treatment
versus the operational variables in the processing plant as well as in
the treatment plant.
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Proper considerations on the part of the processor also will result
in considerable savings in capital costs. Efforts to reduce waste
production must start with the operations prior to processing, i.e.,
harvesting, handling and storage. The in-plant efforts have been dis-
cussed earlier. Finally, good engineering knowledge must be used in
designing and constructing the waste treatment facilities.
Although much can be done to reduce the cost of waste treatment
with the knowledge and means available today, the future will bring more
restrictive waste treatment requirements, and we must prepare to meet
these requirements with economically feasible methods.
Specific Research and/or Demonstration Needs
Many possibilities exist for reducing the amount of waste from
potato processing and improving the waste treatment technology; a great
deal of work has already been done to alleviate the potato waste problem.
However, with all due respect to previous and present efforts, there
is always room for further improvements.
Harvesting. Handling, and Storage
Improvements in the operations prior to processing may reduce the
total waste load significantly.
Harvesting. Mechanical injury to the tubers during harvesting
greatly increases the chance of tuber disease and discoloration during
storage. Rejection of injured tubers during processing increases the
amount of solid waste and represents a direct loss to the processor.
Improved mechanical harvesting equipment therefore should be developed.
Dirt Removal. Removal of dirt from the potatoes in the field would
reduce the amount of water used for washing in the processing plant.
Although wash and flume water does not require a high degree of treat-
ment at the present time, secondary treatment will undoubtedly be re-
quired in the future. Therefore, reduction of wash water volume is
important.
Transportation. Potato quality is affected by temperature during
transit, and improvements in the environmental control systems in rail-
road cars and trucks would reduce the amount of potatoes wasted due to
high reducing sugar content.
Storage. Temperature control is equally important during storage.
Research also is needed in the field of sprout inhibition and in pre-
venting diseases like rotting. Mechanically injured tubers should be
sorted out before the crop is placed in storage.
Processing Operations
In-plant changes and modifications are considered by many to be the
most important for waste reduction and prevention. In general, processing
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equipment and techniques need be improved to reduce the amount of waste
water produced and the amount of solids entering the waste streams.
Several possibilities and practices have been discussed earlier.
Peeling. The peeling operation, which contributes from 50 to 75
percent of the total plant waste load must be improved in order to
reduce the waste load significantly. Very promising results have been
obtained with the dry caustic peeler previously described. However,
more work is required to perfect this process. Handling, disposal and
utilization of the slurry produced from the peel and waste water must be
investigated. The economics of the process compared to other peeling
methods also must be demonstrated.
Other possible methods of peeling with minimal water usage should
be investigated.
Other Processing Operations. The rest of the processing operations
should be considered as well. Solids losses and watet usage must be
reduced, since these increase the waste load as well as the total loss
from the process. Improved equipment and methods for slicing, blanching,
cooking, etc. should be developed. In the same respect, firm guide lines
for good housekeeping should be established, and process line personnel
should be educated in waste prevention.
Solids Removal. A certain loss of solids will always occur. Pre-
ferably these solids should not be allowed to enter the waste stream. If
they do enter the waste water, then as much as possible of these solids
should be removed from the waste water immediately in the processing
plant before considerable leaching of organics take place. Removal may
be achieved by screening, filtration, or centrifugation. In this respect,
research is needed on suspended solids particle size in relation to
screening. Fragmentation of the particles on the screen may increase the
apparent BOD. A similar phenomenon may take place in the centrifuge. The
solid particles may be broken down by the centrifugal force and thus
remain in the centrate. It has been reported that this indeed happens
when primary potato sludge is dewatered by centrifugation. The small
particles discharged with the centrate have poor settling characteristics
and thus are not removed easily by sedimentation.
Re-use of Process Water. Re-use of process water has been discussed
earlier. Besides removal of suspended solids, quality control of the
water must be investigated. Various methods of microbial control should
be evaluated to control deterioration of the recirculated water. The
tolerance limits for different pollutants should be established for
various steps in the process on a health hazard basis as well as on a
product quality basis.
Separation and Concentration. As mentioned earlier, separation
of various waste streams may be advantageous for subsequent treatment in
different systems. Waste concentration also may prove very advantageous,
since concentrated waste can be treated more efficiently than dilute
waste. Concentration and separation would be necessary for efficient
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by-product recovery in many cases. Concentration and separation by
reverse osmosis is one possibility which presently is being investigated.
The concentrated portion of the waste stream may be subjected to recovery
of various valuable constituents while the separated dilute portion may
be re-used in the processing operations. The present research efforts
are directed towards potato starch plant waste. Feasible application of
this or similar processes to other types of potato waste water should
be investigated.
By-Product Recovery. A variety of salable by-products can be re-
covered from the various waste streams, and considerable research has
been conducted in this field. Few large scale economically feasible
processes have been developed, however.
Some of the compounds which may be recovered from potato waste
include amino acids, protein, organic acids, potassium, phosphates and
other inorganic ions. All these compounds have been recovered by physical
or chemical processes.
Potato pulp and waste water may also be used as growth media for
yeasts and molds for production of protein and antibiotics. Promising
results have been obtained with the yeast Torula.
A number of edible products for human consumption have been proposed
from larger potato solids. Utilization of potato solids for livestock
feed has found wide acceptance.
In order to take advantage of these possible by-products from
potato wastes, feasible processes and a market must be developed. The
present efforts on by-product recovery are concentrated mainly on starch
plant waste, since the potato starch industry is a rather marginal industry.
More emphasis should be directed towards recovery of salable products
from other types of potato processing waste.
Waste Treatment
The ultimate solution to the waste treatment problem would be to
produce an effluent which could be completely re-used in the processing
operations. Although such a goal is rather impractical at the present
time, the possibility of effluent re-use nevertheless should be kept
in mind. In order to solve the more contemporary problems facing the
potato processors, existing and proposed technology must be improved
and modified to give more efficient, less costly waste treatment. The
most pressing problem at present is secondary treatment, a requirement
which is facing most of the processors across the nation. However,
continued efforts to improve primary treatment methods should not be
ignored since primary treatment can reduce the load on the secondary
treatment facilities significantly.
Primary Treatment. Primary treatment has been adopted by a large
part of the potato processing industry, and design criteria have been
established through experience from pilot plants and full scale operations.
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Methods for improving the removal of colloidal and dissolved matter
should be improved.
Flotation. Solids removal by flotation has been tried to some
extent in potato waste treatment. Promising results have been obtained,
but high costs also have been reported. Further research on the
applicability of the process to potato waste is needed.
Coagulation. Some research has been conducted on chemical coagula-
tion of primary treated potato waste. Although the results obtained
did not show appreciable improvement in the overall removal efficiencies,
work in this area should be continued. The large variety of coagulants,
coagulant-aids, and polyelectrolytes available should be tested at various
points in the waste treatment process and for different types of potato
waste.
Flocculation by pH Control. Recent investigations have shown that
additional removal of solids from primary effluent can be accomplished
by holding the effluent for a period of time until the pH is lowered
by microbiological action. When the pH was lowered, the solids tended
to flocculate and settle or float to the surface. Up to 50 percent
additional removal was obtained. (Gates 1969) The feasibility of pH
control for additional solids removal should be further investigated.
The effects of coagulant aids, temperature and density should be established,
Secondary Treatment. Potato processing wastes have been found
easily degradable by biological treatment processes, and considerable
progress has been made in the application of different processes to
potato waste treatment. A significant amount of pilot plant work has
been done, but operational results and experience from full scale in-
stallations are limited.
Biological Processes. Research needs for biological treatment pro-
cesses are not unique to potato processing wastes but apply to most
industrial wastes. In general, better prediction models for the different
processes must be developed. The values of the model factors, i.e.,
removal rate constants, growth rate constants, etc., and their variations
with waste quality parameters, should be determined more precisely. More
specifically, the availability of the essential nutrients, such as
nitrogen and phosphorous, for adequate treatment should be investigated.
The amount of nutrients in potato waste is generally sufficient for
effective biological treatment, but the nutrients may not be readily
available for cell incorporation. The effects of conditions or compounds
directly inhibitory to biological treatment, such as high pH, antifoaming
agents and cleaning compounds, should be studied further.
Anaerobic Processes. Promising results have been obtained with the
anaerobic filter and the anaerobic contact process in potato waste treat-
ment, and work on these processes should be continued. Special attention
should be given to start-up characteristics, duration of start-up period,
optimum operating conditions, and solids-liquid separation. Solids
disposal also should be considered.
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Spray Irrigation. Successful applications of spray irrigation have
been reported. Research is needed to determine the effect of sodium on
the soil used for spray irrigation, and on proper soil conditions and
operating conditions for maintaining adequate growth and soil drainage.
Chemical-Physical Processes. High-rate chemical oxidation processes
have not been found economically feasible at the present. Further research
on these and other chemical and physical processes should be conducted,
especially with regard to more complete re-use of treated effluents.
Solids Handling and Disposal. Conventional primary treatment and
biological secondary treatment produce excessive solids. Primary sludge
has been used successfully for cattle feed. The possibility of utilizing
secondary sludge in a similar way should be investigated. The economics
of other solids disposal methods should be evaluated, since little is
known about the feasibility of secondary sludge for cattle feed, and
since there may not be a market for this product. Efficient and economical
methods for dewatering dilute sludges should be developed, along with
methods for handling sludge with high solids content.
Tertiary Treatment Processes. Although enforcement of tertiary
treatment may be some years in the future, several of the processes
developed for polishing effluents may soon be applicable in potato waste
treatment for extensive effluent re-use and by-product recovery. The
feasibility of these advanced treatment processes for potato waste should
therefore be investigated.
Suggested Approach to the Problem
Current research in the specific area of potato processing waste
waters involves about two million dollars per year. This expenditure
includes demonstration grants. The research thus far has made in-roads
on the pressing problems of applying secondary treatment and more
satisfactory peeling methods to field installations. Further development
is yet needed on anaerobic and non-conventional treatment.
Major emphasis needs to be given to reuse, recycle, recovery and
good housekeeping as techniques to reduce waste loads. Research in
these aspects of process modification may provide mechanisms which will
offset much of the research investment. The salvage, saving and use of
waste soil, potato material, and process chemicals involved in utilization
of the potato can represent monetary gain to the producer as well as
relieve some of the waste burden on the environment. The use of pollution
control awareness programs for employees helps spread the appreciation for
waste control and its beneficial aspects throughout the operation and
will, if properly handled, produce significant waste load reductions.
With proper direction toward evaluation of newer experimental process
control techniques and with a proportional investment in good research
aimed toward applying new and imaginative processes to potato processing
and potato processing wastes, the present dollar research expenditure and
more could be well spent in the future in developing the production and
waste control processes toward the continued further alleviation of waste
load insults to the environment. At least 10% of the total monies spent
on research and development should be reserved for innovative laboratory
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research. Of the remaining monies, care should be taken to avoid spending
major fractions of the available research dollars on construction and
maintenance of conventional facilities which have already been investigated
in some detail. The research supported should be able to provide meaning-
ful results which can be of significant value in solving the waste control
problems of the industry. Enthusiastic monetary support is difficult to
sustain when applicable fruitful results are not forthcoming for the projects
supported. However, the problems in potato processing are real and require
attention. With imagination, persistence, diligence and adequate support,
competent researchers can provide the information needed to maintain the
quality of the environment.
Environmental Impact
The impact of the potato processing industry on the total environment
will be an area of vital concern in the seventies. It is not sufficient to
consider only the growth and production of the product and the treatment of
emanating waste streams. Concern must be directed as well to the chemicals,
materials, energy and ecological balances involved in the production
system and perhaps the most important research will deal with the effect of
production on these balances. While the problems are not unique to the
potato processing industry they are part of the total responsibility of
mankind in maintaining the quality of the environment.
The loads of salts, pesticides, and herbicides dumped into the en-
vironment should be carefully evaluated in terms of their insult capacity
to the environment and alternative methods should be considered for growing
and processing where the method used is not compatible with maintaining
the quality of the environment. Other methods of growing, harvesting and
processing should be under study to explore mechanisms for providing greater
amenability with the use of preservation of resources. Increases in re-
ceiving water temperature resulting from waste discharges can disrupt bio-
spheres and create system imbalances which may have perturbations in other
industries and water uses.
Cultivation and processing of food products encumber the growers and
processors with the responsibility for proper management of the unused and
wasted portions of the materials applied in the process as well as with
the sale of satisfactory products. The use of the environment and its
growing potential entails with that use the care and preservation of the
environmental components which make life possible. Thus conservation of
energy and material as well as proper use of those commodities and proper
stabilization of components returned to the environment are all part of the
total production process. Future research should deal effectively with the
individual processing industry not only as an entity but also as part of the
total environmental picture. While every productive consumptive use of
material involves the destruction and wastage of some environmental component,
it is necessary, for the future, to consider resources in terms of their
highest and best use.
It is incumbent on workers in this field to be cogniant of their
societal impact and research may well be involved with the legal and
regulatory aspects of the process including incentive systems, planning
and agricultural basin development. The future for research in potato
processing involves technological assessment and improvement. Future
research should expand also into the role of the industry in relationship
to man's needs and the maintenance of a quality environment.
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APPENDIX A
BIBLIOGRAPHY
87
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APPENDIX A
BIBLIOGRAPHY
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Carlson, D. A., 1968B. "Recent Developments in Anaerobic Waste Treatment,"
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California," Journal of the American Society of Sugar Beet
Technologists. 13. 5, (April 1965).
Gates, J. H., 1969. Personal Communications, (September 1969).
Olson, 0. 0., Van Heuvelen, W., and Vennes, J. W., 1964. "Aeration of
Potato Waste," Proceedings of the 19th Industrial Waste Conference.
Purdue University, (1964).
Olson, 0. 0., Van Heuvelen, W., and Vennes, J. W., 1965. "Experimental
Treatment of Potato Wastes in North Dakota, U. S. A.," Proceedings
International Symposium. Utilization and Disposal of Potato Wastes.
New Brunswick Research and Productivity Council, N. B., Canada,
(1965) .
Olson, 0. 0., and Vennes, J. W., 1963. "Mechanical Aeration of Potato
Processing and Domestic Sewage." Park River Study, Federal Water
Pollution Control Administration, (1963).
Pailthorp, R. E., and Filbert, J. W., 1965. "Potato Waste Treatment in
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93
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Pasveer, A., 1965. "The Use of the Oxidation Ditch for the Purification
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Forges, R. , 1963. "Industrial Waste Stabilization Ponds in the United
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(1963).
Forges, R., and Towne, W. W. , 1959. "Wastes from the Potato Chip Industry,1
Sewage and Indus trial Was tes, _31_, 1, (January 1959).
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Rich, L. G., 1963. Unit Processes of Sanitary Engineering. John Wiley
and Sons, New York, (1963).
Rose, W. W., 1965. "Treatment and Disposal of Potato Wastes," Proceeding^
International Symposium. Utilization and Disposal of Potato
Was tes, New Brunswick Research and Productivity Council, N. B.,
Canada, (1965).
Sak, J. G., 1967. "Plastic Biological Oxidation Media for Industrial
Waste Treatment Needs," Paper Presented at the 14th Ontario
Industrial Waste Conference, Niagara Falls, Canada, (June 1967).
Shaw, R., 1965. "Potato Specialties from Edible Potato Wastes - A Review,"
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Sijbring, P. H., 1968A. Personal Communications, (September, 1968).
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presented at the Utilization Section Meeting, European Association
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Sijbring, P. H., 1968C. "Principles of Vacuum Frying and Results of
Practice," Proceedings of the 18th National Potato Utilization
Conference, Corvallis, Oregon, (1968).
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"Influence of Piece Size on Production and Quality of Dehydrated
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Smith, 0., 1966. "Report of PC11 Director of Research," Proc. Prod, and
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(September 1968).
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Water and Sewage Works. 2., 93, (February 1968).
Szebiotko, K., 1965. "Total Utilization of Potatoes Including the Disposal
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R. H., Howerton, W. W., and Cordon, T. C., 1953. "Aerobic
Microbiological Treatment of Potato Starch Factory Wastes,"
Bureau of Agriculture and Industrial Chemistry, Eastern Regional
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Webster, G., and Carlson, D. A., 1968. Laboratory Studies at the
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Wiertsema, P., 1968. "Special Problems of the Potato Chip Industry in
Western Europe," Proceedings of the 18th National Potato
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APPENDIX B
RESEARCH GRANTS ON POTATO PROCESSING WASTES
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APPENDIX B
RESEARCH GRANTS ON POTATO PROCESSING WASTES
The following is a list of research work directly involved with
potato processing wastes, as described in the Water Resources Research
Catalog (1967, 1968).
Treatment of Protein Water Waste from the Manufacture of Potato
Starch by Anaerobic Fermentation - Aerobic Stabilization Process
W. Van Heuvelen
North Dakota Department of Health
State Capitol Building
Bismark, North Dakota 58501
The microbiological treatment of protein water waste from the man-
ufacture of potato starch will be evaluated. A treatment of
anaerobic fermentation and aerobic stabilization will be used.
Supporting Agency: Federal Water Pollution Control Administration
Treatment of Alkaline Wastes from Potato Processing
C. Bruce
Vahlsing, Inc.
Easton, Maine 04740
The objectives of this project are to demonstrate the feasibility
of: Treating potato processing waste using the activated sludge
system; combining potato processing waste with sugar beet refining
waste; and the feasibility of three in-plant closed waste water
systems in the sugar beet plant. The project will provide extremely
valuable data to both the potato processing and beet sugar industry.
The aim is also to determine if a $30 million industrial complex,
composed of potato and sugar beet processing and a residential com-
munity, can exist on a small stream, as is proposed, and have clean
waters.
Supporting Agency: Federal Water Pollution Control Administration
Aerobic Secondary Treatment of Potato Processing Wastes with
Mechanical Aeration
W. M. Swanson
R. T. French Company
Drawer AA
Shelly, Idaho
The objective of this project is to demonstrate the aerobic biological
treatment for potato processing wastes, to establish design criteria
and to develop construction and operating costs. The following
systems will be studied: 1) Extended aeration with sludge return;
2) Flow through aeration with sludge return; 3) Intermittant aeration
with intermittant effluent withdrawal.
Supporting Agency: Federal Water Pollution Control Administration
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Operation of Potato Processing Plants to Reduce Waste and Stream
Pollution
M. L. Weaver
U. S. Department of Agriculture
Albany, California
Object: To help alleviate the growing problem of disposing
of wastes from plants processing potatoes into food products,
without polluting streams or the air, through the development of new
or modified in-plant operations to reduce the quantity of wastes
discharged and/or to convert them to a form more readily adaptable
to available methods of waste treatment.
Plan of Work: Investigations will be made to determine the basic
nature of the waste material, i.e., amount and kind of both mineral
and organic solid particles, amount and kinds of soluble materials,
pH, biochemical oxygen demand, chemical oxygen demand, etc.,
associated with different types of processed potato food products.
The most economical and efficient means of removing suspended solids
from aqueous plant wastes will be sought. Also, how to separate the
mineral matter from insoluble organic solids. Possible uses for the
suspended organic solids will be explored. Investigations will be
made of ways to reduce the total quantity of soluble solids to be
disposed of and to concentrate these for more efficient secondary
treatment. Special attention will be given to the peeling operation
in order to reduce the disposable waste.
Supporting Agency: U. S. Department of Agriculture
Pilot Plant Development of the Ion-Exchange Process for Recovery of
Amino Compounds from Potato Starch Factory Effluents
W. L. Porter
U. S. Department of Agriculture
Chesnut Hill
Philadelphia, Pennsylvania 19118
Object: To alleviate the problem of disposal of secondary wastes
from potato starch factory effluents and reduce stream and air
pollution; to obtain a cost estimate for the process; and to produce
crude amino acid mixtures.
Plan of Work: An evaluation will be made by pilot plant scale of
the methods of recovery of free amino acids from potato starch plant
effluent by ion-exchange treatment. The investigation will include:
Effect on process of variation in concentration of in-put solids
from 0.5-3.0% solution; applicability of Dutch process for recovery
of protein before ion-exchange treatment of effluent liquor; degree
of clarification required before ion-exchange processing; disposal
of solutions from regeneration of columns and selection of regenera-
tion acid from this viewpoint; methods for stabilizing the amino
acid product; and determination of composition, BOD and COD of
effluent stream before and after processing. Cost estimates will
be provided based on the data and final process lay-out, for a full-
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scale plant to recover nitrogen-containing materials from the 'protein
water' effluent of a 10 ton per day and a 30 ton per day potato
starch factory. A minimum of 500 pounds of dry crude amino acids will
be delivered representing the typical product of the process for use
in utilization studies and market development.
Supporting Agency: U. S. Department of Agriculture
Two grants have been awarded recently by the Federal Water Pollution
Control Administration.
Western Potato Service, Inc., at Presque Isle, Maine, and Grand
Forks, North Dakota, has been awarded a grant for "Full Scale Demonstration
and Evaluation of Potato Dry and Wet Caustic Peeling Processes." It is
proposed to install three dry caustic peeling lines in the Grand Forks
processing plant. Conventional wet caustic peeling, existing in the
Presque Isle plant, will be studied as a control. At both facilities
will be installed equivalent primary waste treatment equipment for the
purpose of comparative analysis.
The project objectives are as follows:
1. To determine total capital expenditures and operational and
maintenance costs of dry caustic process and the conventional
caustic process.
2. To compare the quantity and quality of the waste generated
by the two systems.
3. To compare the treatment efficiency of silt removal systems
and final clarifier and primary treatment systems at both
plant locations.
4. To determine whether the dry caustic sludge would be accepted
or rejected during cattle feeding operations.
The City of Grand Forks, North Dakota, was awarded a grant to study
"Controlled Treatment of Combined Potato Processing - Municipal Wastes
by Anaerobic Fermentation, Aerobic Stabilization Process." Project
Objectives: Demonstrate, develop, and evaluate joint treatment of potato
processing - municipal wastes by use of stabilization pond pretreatment
methods consisting of (1) anaerobic - aerated combination, (2) anaerobic,
or (3) aeration treatment. Study the effects of the treatment methods
on the stabilization ponds. Determine any special procedures related to
most efficient operation of the anaerobic and aerated units, factors
most responsible for waste removal, and development, and control of odors.
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APPENDIX C
POTATO PROCESSING WASTE TREATMENT COSTS
101
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APPENDIX C
POTATO PROCESSING WASTE TREATMENT COSTS
The cost curves presented in the following figures are taken from a
report to the Potato Processors of Idaho Association by Cornell, Rowland
Hayes, and Merryfield (1969). The costs for domestic systems were
presented by Smith (1968).
The costs for primary treatment of potato waste are based on systems
which have been designed and constructed in the Pacific Northwest. The
costs for secondary treatment of potato waste are based on engineering
estimates which have been made for demonstration projects and preliminary
estimates based on pilot plant systems studied by the Potato Processors
of Idaho Association. All costs have been adjusted to a common base of
June 1967 by using the Engineering News-Record building index. (See
Figure 7) The costs, which include the contractor's overhead and profit
and engineering, are averages, and should be used only for general
guidance and comparison.
Silt Removal. Figure 8 is a presentation of the capital cost for
silt removal. The costs are based on a mechanically-cleaned clarifier,
and include solids pumps, electrical, piping and a building to house pumps
and electrical gear. It is assumed that the unit would be adjacent to
and integral with either primary or secondary treatment units.
Primary Treatment. The capital costs for primary treatment are shown
in Figure 9. The costs include screen, clarifier, solids pumps, vacuum
filter, solids bin, flow measurement, and a building to house pumps,
screen, vacuum filter, and electrical gear.
Secondary Treatment. Figure 10 shows the capital costs for secondary
treatment. The costs include primary treatment and solids handling
equipment. It is assumed that the cost of land for stabilization ponds
would be $500 per acre, that the cost for construction would be $2000 per
acre, and that stabilization ponds would be loaded at about 50 pounds of
BOD per acre per day.
Irrigation. The costs for irrigation systems are shown in Figure
11. The costs include a pump station, a self-cleaning screen, and a
solids grinder. An allowance of $500 per acre of land has been made. The
costs do not include primary treatment which would precede irrigation.
An application rate of 1/2-inch per day has been assumed.
Operation and Maintenance Costs. The operation and maintenance costs
for primary and secondary treatment systems are presented in Figure 12.
The costs for potato waste treatment are based on very limited field
information and are, for the most part, estimates. No allowance has been
made for return from sale of the reclaimed solids.
Stabilization Ponds. The capital costs for stabilization ponds are
shown in Figure 13. The costs are based on construction costs for municipal
102
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ponds and do not include allowance for land.
Clarifiers. Figure 14 shows the costs for clarifiers. The costs
include the clarifier mechanism, concrete structure, piping, and foundation
gravel. Normal excavation for a unit which sits 4 feet into the ground
is included. No unusual foundation problems are included.
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o
FIO. 7
NEWS RECOUP COST INDEX
CONSTRUCT ION
COST INDEX
-------
I-
a
a
u
o.i o.a 0.3
FI_O\A/- MOO
MECHANICAL. «ILT MMOVAL.-CAPITAL
DCVIOIM CAPACITY - MOO
PMIMAMY TMBATMBNT CAPITAL
ElBil
105
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TEM, AE
SYSTEMS
ACTIVATED
SLUDOE
ANAEROBIC CONTACT
O.B
i a a
DESIQN CAPACITY - MOD
SECONDARY TREATMENT CAPITAL COST
FIG. 1O
^
APPL. PIATB
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••JIMAPJY
INCLUDED
DESION CAPACITY - MOO
DISPOSAL BY
IAY IRRIOATIOIM CAPITAL
FID. 11
106
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8
i:
DMION CAPACITY - MOD
TINO & MAIIMTBNAIMCK
FIO. 18
"1 • 3 4 B I 7 ' "• "" •
10
•TABILIZATION POIMO CAPITAL COST
FIB. 13
107
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0
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i •
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INO
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108
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