Pollution Abatement
625377007C in the Fruit and
Vegetable Industry
Wastewater Treatment
PATechndogy Transfer Seminar Publication
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EPA625/3-77-!
POLLUTION ABATEMENT IN THE
FRUIT AND VEGETABLE INDUSTRY
Wastewater Treatment
IJ.S. Envircnmerita! Protection
Region 5, Library (PL-12J)
7/ West Jackson Boulevard 12th
Chicago, It 60604-3590
ENVIRONMENTAL PROTECTION AGENCY
Environmental Research Information Center* Technology Transfer
July 1977
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ACKNOWLEDGMENT
This seminar publication contains materials prepared for the
United States Environmental Protection Agency Technology Trans-
fer Program and presented at industrial pollution-control seminars
for the fruit and vegetable processing industry.
The Technology Transfer Program extends its appreciation to the
Food Processors Institute and CH2M Hill, Inc. for their work in
preparing the publication.
NOTICE
The mention of trade names or commercial products in this publication is for
illustration purposes, and does not constitute endorsement or recommendation for use
by the U.S. Environmental Protection Agency.
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CONTENTS
Page
Chapter I. Introduction/Background 1
Introduction 1
Background 1
Chapter II. Pretreatment 15
Introduction 15
Pretreatment Processes 16
Further Pretreatment 25
Chapter III. Primary, Secondary and Advanced Treatment 26
Introduction 26
Requirements for Treatment 27
Primary Treatment 29
Biological Secondary Treatment 33
Tertiary (Advanced) Waste Treatment 51
Operation And Maintenance 57
Chapter IV. Land Treatment and Disposal 59
Introduction 59
Processes 59
Operation and Management 67
Costs of Alternative Application Methods 68
Chapter V. Solids Disposal 70
Sources And Nature Of Solids 70
Sludge Handling 73
Methods Of Solids Disposal 78
References 82
LIST OF FIGURES
II-l Circular center-feed vibratory screen 17
II-2 Rectangular end-feed vibratory screen 18
II-3 Rotary drum screen 19
II-4 Tangential screen (45°) 19
II-5 Slotted drum screen 20
II-6 Silt clarifier '.'.'.'.'.'.'. 25
III-l Effect of treatment on solids and BOD 28
III-2 Clarifier '.'.'.'.'.'.'.'. 31
III-3 Dissolved air flotation clarifier 32
III-4 Primary treatment plant 32
III-5 Floating mechanical aerator (high speed) 40
III-6 Activated sludge plant 43
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LIST OF FIGURES (Continued)
Page
III-7 Activated sludge plant 46
III-8 Activated sludge plant 46
III-9 Package activated sludge plant 47
111-10 Activated biological filter tower 49
III-ll Activated biological filter activated sludge plant 49
111-12 Trickling filter plant 50
111-13 Pressure filter 53
IV-1 Land treatment processes 60
IV-2 Spray irrigation system 62
V-l Vacuum filter 76
V-2 Solid bowl centrifuge 76
V-3 Disc nozzle centrifuge 77
V-4 Basket centrifuge 78
LIST OF TABLES
1-1 Common wastewater parameters for fruit and vegetable processing 3
1-2 Typical raw wastewater characteristics for canned and preserved
fruits and vegetables 6
1-3 Factors contributing to raw-waste load variabilities 7
1-4 Federal effluent limitation guidelines 8
1-5 Summary of estimated costs for fruit and vegetable processing 14
II-l Cost summary for flow measurement and screening 22
II-2 Cost summary of neutralization (for acid waste) 24
III-l Treatment unit processes for fruit and vegetable processors 26
III-2 Primary treatment design criteria for fruit and
vegetable wastewaters 30
III-3 Secondary treatment design criteria for fruit and
vegetable wastewaters 37
III-4 Available nutrients for fruit and vegetable wastewaters 39
III-5 Cost summary for aerated lagoon system 42
III-6 Cost summary for activated sludge system 44
III-7 Cost summary for activated sludge with aerobic digestion
and dewatering 45
III-8 Tertiary waste treatment applications 51
III-9 Cost summary for filtration 54
111-10 Cost summary chlorination system 58
IV
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LIST OF TABLES (Continued)
Page
IV-1 Land treatment and disposal processes 61
IV-2 Estimated maximum hydraulic loading of wastewater effluent
for various soil textures (ideal conditions) 65
IV-3 BOD loading rates 66
IV-4 Recommended maximum limits of inorganic constituents for
irrigation water 67
IV-5 Comparison of capital and operating costs for 1-mgd systems 69
V-l Percentage of solid waste produced in fruit and vegetable
processing 71
V-2 Treatment plant solids characteristics for fruit and
vegetable wastewaters 71
V-3 Solids handling options 73
V-4 Design criteria for solids handling devices for fruit and
vegetable wastewaters 75
V-5 Cost ranges of hauling and disposal 81
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Chapter I
INTRODUCTION/BACKGROUND
INTRODUCTION
This publication offers to fruit and vegetable processors a general understanding of waste-
water treatment technology that will enable processors to deal more effectively with regulatory
agencies and their own waste disposal situations. The material will give an understanding of the
following topics:
1. Important Waste Characteristics
2. EPA and State Regulations
3. Sewer Ordinances
4. Pretreatment Technology
5. Treatment Technology Required to Meet Present and Future Effluent Requirements
6. Land Treatment Disposal Methods
7. General Costs of Pollution Control
8. Sludge and Solid Residuals Disposal Methods
The information presented is based on general engineering practice in the fruit and vegetable
processing industry. More detailed and specific information for the theory of treatment processes
and design systems can be found in textbooks and other EPA publications. Current reviews can
be found in publications from state agencies and associations such as the National Gartners'
Association (NCA). An annual review of literature on fruit and vegetable processing waste is
found in the Journal of the Water Pollution Control Federation.
For reference purposes, general design criteria are presented in task form throughout the
text. This information can help processors determine the adequacy of proposed systems to han-
dle waste, or to develop preliminary sizes for treatment units, but it should not be used for design.
Cost summaries are also given for the more significant treatment processes discussed. The costs
were developed for a hypothetical fruit and vegetable processing plant, producing one million
gallons per day (mgd) of wastewater, and operating for 90 days each year. The estimates are
presented to illustrate the relative magnitude of various treatment processes, and should not be
used to project actual construction costs.
BACKGROUND
GENERAL
The first step of a pollution control program is to characterize the wastewater. In this
chapter we present typical wastewater characteristics for various products and common param-
eters used to characterize wastewater. These characteristics and the reduction quantity required
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determine the type and cost of pollution control. Chapters II through V give the methods for
treating wastes associated with the fruit and vegetable industry. The current federal effluent
requirements for this industry are given in this chapter.
Fruit and vegetable processing wastewater has as one of its characteristics a seasonal variation
which causes major problems in treatment. Each raw product has a processing season that may
vary from year to year, from field to field, and from beginning to end of the pack. Processors
with treatment systems are aware of these variations.
Each processing plant is unique. Plants operated by the same corporation and producing the
same product can have significantly different wastewater characteristics. Therefore, wastewater
quality data must be developed for each plant. Waste quantities for new plants, or for expansions
of existing plants, are usually estimated by assuming a proportional (on the basis of production
capacity) waste from similar plants or processes. Possible expansion and product changes must be
considered when determining waste loads.
WASTE CHARACTERISTICS
Scientists and engineers have developed many parameters to characterize wastewater. Com-
mon parameters are as follows:
Biochemical oxygen demand (BOD) -
BOD is used to size treatment systems or to determine sewer service charges when an
industry is discharging to a public treatment system. The acclimated seed used for the
BOD test should not contain nitrifying bacteria. If it does, the tests will yield high
results because nitrogenous BOD as well as carbonaceous BOD will be measured.
Special test procedures can be applied to avoid the problem.
Chemical oxygen demand (COD) -
COD can be used as a fast way to estimate the BOD for most food processing waste by
empirically determining a ratio of BOD to COD. A few cities use COD to assess sewer
service charges. For a majority of cannery wastes, the BOD is 60 to 80 percent of the
COD. For many wastes it is also possible to develop a useful correlation of volatile
solids to BOD.
Total suspended solids (TSS) -
TSS is used to calculate the amount of waste solids resulting from treatment. TSS is
also used to determine sewer service charges.
Volatile suspended solids (VSS) -
The volatile fraction of total suspended solids is needed to help determine the volume
of biodegradable waste solids.
Nutrients -
A balance of nitrogen and phosphorus is needed for successful biological treatment. In
unusual cases, other trace elements (Mg, Fe, etc.) may also be critical nutrients. Many
food processing wastewaters are deficient in nutrients for biological treatment. If a
deficiency exists, nutrients can be added. Adequate nutrients are often present in a
joint treatment system with a city because domestic waste contains excess nutrients.
pH-
Local sewer ordinances usually limit the allowable pH range. The city may also require
that waste be neutralized before treatment or land application.
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Alkalinity and acidity -
Alkalinity and acidity are measured to determine the resistance of wastewater to pH
changes. This information is used to design neutralization systems or to determine the
stability of pH during biological treatment.
Temperature -
Wastewater temperature is important in sizing biological treatment units. Process
stability, even in physical-chemical systems, can be adversely affected by wide ranges
in waste temperature. Municipal ordinances usually limit maximum waste temperature.
Toxicity -
Food processing waste usually is not toxic, but some discharge requirements include
toxicity limits. The most common causes of wastewater toxicity are excessive amounts
of free ammonia, residual chlorine from disinfection, discharges of detergents (from
cleanup) or other toxic materials such as paint, solvents, and biocides.
In the future, the following tests may be required: chlorinated hydrocarbons; chlorine
residual; color; heavy metals; and phenolic compounds. Table 1-1 shows common wastewater
parameters that will be required for the three possible waste disposal methods.
Table 1-1.Common wastewater parameters for fruit & vegetable processing
Characteristics
Flow
pH
Temperature
Dissolved oxygen
BOD
COD (use as a check or
guide for BOD)
Total suspended solids
Volatile suspended solids
Oil and grease
Total dissolved solids
Nitrogen
Phosphorus
Settleable solids
Specific ionsb
Discharge
to sewer3
X
X
X
X
X
X
X
X
Discharge
to own
treatment
plant
X
X
X
X
X
X
X
X
X
X
X
X
Discharge
to land
X
X
X
X
X
X
X
X
X
X
X
X
X
aTypical requirements are set forth in sewer-use ordinances.
bSeetablelV-4.
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Sampling, Testing, and Flow Measurement
A program for sampling, testing, and measuring flow is important to waste characterization.
It provides basic information to calculate sewer service charges, to compare the economics of in-
plant waste reduction versus "end of pipe" treatment, and to help select and size treatment
processes.
The EPA's Monitoring of Industrial Wastewater1 is a good reference on the practicalities of
waste characterization and on methods of sampling and analysis. The reader should also utilize
the EPA's Methods for Chemical Analysis of Water and Wastes2 as a reference on analytical pro-
cedures and preservation of samples.
Building, staffing, and maintaining a wastewater analysis laboratory is costly. The use of an
outside laboratory for wastewater testing may be less costly, particularly for difficult tests. Many
states require that data submitted to regulatory agencies be analyzed by a state-certified or
approved laboratory. The EPA and the states require the use of the latest edition of standard
methods3.
The single most important wastewater characteristic is flow. Flow is the primary criterion
used to size many treatment units. Several different wastewater flows must be known for effi-
cient treatment design: (1) average flow, (2) maximum instantaneous flow, and (3) peak daily
flow. Other wastewater characteristics are measured only in concentration. The mass (pounds
per day) for these characteristics can only be determined if flow is known. Concentration alone
is of little value.
Selection of a point and method of measuring flow is important. The following factors
should be considered:
Reliability of automatic flow-measurement equipment
Nonclogging characteristics of flow-measurement equipment
Accuracy required
Maintenance required
Costs
Accessibility of the flow-measurement station
Sampling points must be carefully selected to obtain representative samples. As a result of
solids separation, the waste strength may vary from the top to the bottom of the flow in a large
sewer. Sampling points should be selected where the waste is thoroughly mixed.
Variations in processing activities will change wastewater characteristics. Therefore, samples
should be taken during each operating shift and during different stages of the finished-product
and raw-product runs. Flows should be monitored continuously, even during cleanup and on
weekends.
The amount of testing varies according to plant operation and the purpose of testing. Re-
quirements are difficult to generalize, but if the purpose of testing is to establish the waste load
for a product, reasonable accuracy should be achieved by taking flow proportion composite sam-
ples daily for 8 to 20 days.
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The sampling program should include monitoring waste during the peak processing period.
The remainder of the sampling will probably be done on two 2-week periods. The first 2-week
period could be in the first half of the processing season, and the second during the latter half of
the season. Flow measurements should include instantaneous flow and peak daily flow during the
periods of monitoring. Flows for these two-week periods should be measured and recorded con-
tinuously; samples should be taken at least hourly for each day (24 hours) and composited in
proportion to flow.
Typical Wastewater Characteristics
Table 1-2 summarizes typical wastewater characteristics for many fruits and vegetables. The
range between minimum and maximum values is large. These numbers are combinations of data
from EPA and NCA. The sources do not indicate if the values are for raw or screened waste. The
characteristics in table 1-2 are given in unit loadings such as thousand gallons (or pounds) per ton
of raw product. Typical concentrations (mg/1) for BOD and suspended solids can be calculated
from these relationships:
concentration (mg/1) = mass (Ibs/day)
v 8/ ' flow (million gal/day) x 8.34
or
... , ... mass (Ib/ton) x 120
concentration (mg/1) = -z /\ Ann i /+r
v & ' flow (1,000 gal/ton)
Changes in Waste Strength
Many factors cause changes in waste strength (table 1-3). Length of season affects wastewater
characteristics. If a crop is harvested over a long period of time (potatoes, for example), the waste-
water quality and quantity may differ significantly from beginning to end of season. Changes in
waste strength may also occur from shift to shift. For example, waste flows during a cleanup
shift will be different than those coming from a processing shift.
Daily or seasonal shutdown and startup of a processing plant usually causes wastewater char-
acteristics to vary greatly. This variation often causes problems in a treatment system. Biological
treatment systems perform best on a uniform supply of a given source of food (BOD). If the food
supply changes greatly, the biological process may not be able to adjust to the change. The impact
of frequent shutdowns and startups on a treatment system should be carefully evaluated.
REGULATIONS
Fruit and vegetable processors must meet the discharge requirements of one or more govern-
mental agencies: (1) federal, (2) state, and (3) local. Each industry discharging to a receiving
waterway must have a permit under the National Pollutant Discharge Elimination System (NPDES
permit). Industries discharging to land or to municipal sewers may require additional discharge
permits from the EPA, state or city. Although the EPA guidelines focus on process wastes, per-
mits set restrictions on all discharges cooling water, sanitary waste and storm drainage.
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Table 1-2.Typical raw wastewater characteristics for canned and preserved fruits and vegetables*'
Crop
Apples
Apricots
Asparagus
Dry beans
Lima beans
Snap beans
Beets
Broccoli
Brussels sprouts
Berries
Carrots
Cauliflower
Cherries
Citrus
Corn
Grapes
Mushrooms
Olives
Onions
Peaches
Pears
Peas
Peppers
Pickles
Pimentos
Pineapples
Plums
Potato chips
Potatoes, sweet
Potatoes, white
Pumpkin
Sauerkraut
Spinach
Squash
Tomatoes, peeled
Tomatoes, product
Turnips
Flow
1,000 gal /ton
raw product
Min. Mean Max.
0.2 2.4 1 3
2.5 5.6 14
1.9 8.5 29
2.5 8.8 33
2.4 7.7 22
1.3 4.2 11.2
0.3 2.7 6.7
4.1 9.2 21
5.7 8.2 12
1.8 3.5 9.1
1.2 3.3 7.1
12 17 24
1.2 3.9 14
0.3 3.0 9.3
0.4 1.8 7.6
0.6 1.5 5.1
1.8 7.8 28
8.1
2.5 5.5 10
1.4 3.0 6.3
1.6 3.6 7.7
1.9 5.4 14
0.9 4.6 16
1.4 3.5 11
5.8 6.9 8.2
2.6 2.7 3.8
0.6 2.3 8.7
1.2 1.6 2.2
0.4 2.2 9.7
1.9 3.6 6.6
0.4 2.9 11
0.5 0.9 3.0
3.2 8.8 23
1.1 6.0 22
1.3 2.2 3.7
1.1 1.6 2.4
2.4 7.3 18
BOD
Ib/ton
raw product
Min. Mean Max.
3.9 18 44
18 40 80
0.9 4.9 22
15 60 182
9.3 48 175
1.6 15 81
28 53 127
5.8 20 61
4.2 7.5 14
11 19 40
17 30 53
5.5 16 36
21 38 78
0.9 9.6 26
12 27 64
6.4 9.0 13
7.7 15 28
27
57 57 58
17 35 70
19 50 126
16 38 87
5 32 50
26 42 75
39 55 76
13 25 45
6.5 10 14
17 25 38
39 93 217
42 84 1 67
9.2 32 87
4.6 5.6 15
5.7 14 31
20
6.3 9.3 14
2.2 4.7 9.7
- - -
TSS
Ib/ton
raw product
Min. Mean Max.
0.4 4.5 21
5 9.9 19
4.3 7.5 13
2.6 43 99
4.6 39 231
0.8 6.1 46
7.3 22 64
4.6 17 61
2.9 15 79
1.4 7.1 22
4.5 17 53
2.8 7.8 22
1.0 2.0 3.8
0.7 3.7 14
3.6 10 27
1.5 1.7 2.0
5.1 7.3 12
27 -
5.3 17 55
3.4 8.6 21
3.6 12 33
3.8 1 1 38
1 58 1 70
3.0 8.2 23
4.1 5.8 8.1
5.2 9.1 17
0.6 2.1 4.3
22 32 48
40 57 117
39 128 423
2 67 12
1 .0 2.6
1.8 6.1 21
- 14
5.8 1 2 26
5.6 10 19
_ _ _
NOTE.These figures represent two different types of samples: screened and unscreened. This increases the range of
values shown.
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Table 1-3.Factors contributing to raw-waste load variabilities
Fruit or vegetable processed
Product mix
Raw-product condition (ripeness, damage)
Product-conveying systems (countercurrent vs. single pass fluming, dry conveying,
pneumatic conveying)
Process methods (blanching, peeling)
Cleanup methods (dry vs. wet, detergent, disinfectant)
Batch dump frequency (brine, caustic)
Frequency, duration of shutdowns
Type and condition of equipment
People
Federal Requirements
The Federal Water Pollution Control Act Amendments of 1972 (PL 92-500) reqvured EPA
to establish guidelines for all industrial wastewater discharged to receiving waters. "Phase I" and
"Phase II" guidelines have been completed.4-5 The guidelines originally covered the following
characteristics: fecal coliform count; BOD; Total Suspended Solids (TSS); pH; and grease and oil.
However, the fecal coliform limitation has been deleted. 7>8 Processors and government agencies
should refer to the Code of Federal Regulations for effluent guidelines and standards.9
Table 1-4 gives the allowable mass emissions of BOD and TSS. The effluent pH limit is 6 to
9.5 for both 1977 and 1983 for all fruit and vegetable processing.
An additional oil and grease limitation of 20 mg/1 for 1977 and 10 mg/1 for 1983 has been
set for the following products:
Added ingredients
Baby foods
Chips (potato, corn, tortilla)
Ethnic foods
Jams/jellies
Mayonnaise and dressings
Soups
Tomato-starch-cheese canned specialties
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Table 1 -^.-Federal effluent limitation guidelines^
[pounds allowed per ton raw product]
Commodity
Added ingredients3
Apple juice
Apple products (except juice)
Apricots
Asparagus
Baby food3
Beets
Broccoli
Brussels sprout
Caneberries
Carrots
Cauliflower3-13
Cherries (sweet)
Cherries (sour)
Cherries (brined)
Chips (potato)8
1977
Daily max 30-day avg Annual avg
BOD TSS BOD TSS BOD TSS
1.90 0.00 1.10 0.00 0.72 0.00
1.20 1.60 0.60 0.80
2.20 2.80 1.10 1.40
6.00 10.72 3.62 7.48 2.52 4.66
...
2.46 4.46 1.46 3.10 1.02 1.90
2.02 3.76 1.42 2.94 1.14 2.24
7.66 13.56 4.42 9.14 2.94 5.30
...
1.54 2.76 0.92 1.90 0.64 1.16
3.52 6.38 2.22 4.60 1.64 3.08
2.24 4.02 1.38 2.86 0.98 1.84
3.54 6.40 2.22 4.60 1.62 3.04
5.74 10.36 3.56 7.36 2.56 4.76
6.92 12.50 4.34 8.98 3.16 5.94
1983
Daily max 30-day avg Annual avg
BOD TSS BOD TSS BOD TSS
M 1.560 - 1.100 - 0.460 -
L 1.560 - 1.100 - 0.460 -
0.40 0.40 0.20 0.20
0.40 0.40 0.20 0.20
M 2.522 4.556 1.876 2.618 0.970 1.972
L 2.522 2.522 1.876 1.876 0.970 0.970
M 1.678 3.002 1.222 1.630 0.580 1.172
L 1.678 1.678 1.222 1.222 0.580 0.580
M 1.364 2.484 1.096 1.704 0.722 1.444
L 1.364 1.364 1.096 1.096 0.722 0.722
M 3.788 6.684 2.674 3.342 1.114 2.228
L 3.788 3.788 2.674 2.674 1.114 1.114
M 0.364 0.656 0.268 0.368 0.134 0.274
L 0.364 0.364 0.268 0.268 0.134 0.134
M 1.932 3.512 1.458 2.092 0.794 1.618
L 1.932 1.932 1.458 1.458 0.794 0.794
M 0.896 1.626 0.674 0.958 0.362 0.736
L 0.896 0.896 0.674 0.674 0.362 0.362
M 2.204 4.026 1.678 2.450 0.944 1.924
L 2.204 2.204 1.678 1.678 0.944 0.944
M 1.526 2.876 1.242 2.026 0.846 1.744
L 1.526 1.526 1.242 1.242 0.846 0.846
M 3.366 6.064 2.488 3.428 1.258 2.548
L 3.366 3.366 2.488 2.488 1.258 1.258
00
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Table 1-4. Federal effluent limitation guidelines^ Continued
[pounds allowed per ton raw product]
Commodity
Chips (corn)6
Chips (tortilla)8
Citrus
Corn (canned)
Corn (frozen)
Cranberries
Dehydrated onion/garlic
Dehydrated vegetables
Dried fruit
Dry beans
Ethnic foods3
Grape juice (canning)
Grape juice (pressing)
Jams/jellies8
Lima beans
1977
Daily max 30-day avg Annual avg
BOD TSS BOD TSS BOD TSS
3.16 5.80 2.80 4.34 1.60 3.06
4.82 8.68 3.00 6.22 2.18 4.08
1.60 2.40 0.80 1.70
1.42 2.64 0.96 2.00 0.76 1.46
2.90 6.26 1.68 4.60 1.12 3.14
3.42 6.12 2.06 4.28 1.46 2.68
4.90 8.86 2.92 6.04 1.96 3.52
5.96 10.60 3.52 7.30 2.42 4.42
3.72 6.68 2.26 4.68 1.60 2.96
5.00 8.96 3.02 6.26 2.14 3.94
4.78 8.46 2.82 5.82 1.92 3.46
2.20 3.98 1.38 2.88 1.02 1.92
0.44 0.80 0.28 0.58 0.20 0.36
0.84 1.52 0.52 1.08 0.38 0.72
7.36 13.12 4.38 9.06 3.02 5.52
1983
Daily max 30-day avg Annual avg
BOD TSS BOD TSS BOD TSS
M 2.284 4.234 1.796 2.772 1.714 2.286
L 2.284 2.284 1.796 1.796 1.114 1.114
M 3.330 6.050 2.506 3.578 1.352 2.754
L 3.330 3.330 2.506 2.506 1.352 1.352
0.28 0.40 0.14 0.20
M 0.892 1.674 0.720 1.760 0.480 0.988
L 0.892 0.892 0.720 0.720 0.480 0.480
M 1.974 3.664 1.556 2.408 0.970 1.988
L 1.974 1.974 1.556 1.556 0.970 0.970
M 1.240 2.248 0.930 1.320 0.496 1.010
L 1.240 1.240 0.930 0.930 0.496 0.496
M 2.318 4.134 1.674 2.204 0.774 1.562
L 2.318 2.318 1.674 1.674 0.774 0.774
M 3.562 6.356 2.576 3.398 1.196 2.412
L 3.562 3.562 2.576 2.576 1.196 1.196
M 1.466 2.674 1.112 1.610 0.616 1.254
L 1.466 1.466 1.112 1.112 0.616 0.616
M 2.806 5.018 2.042 2.726 0.972 1.962
L 2.806 2.806 2.042 2.042 0.972 0.972
M 3.176 5.652 2.286 2.982 1.040 2.092
L 3.176 3.176 2.286 2.286 1.040 1.040
M 1.532 2.798 1.166 1.698 0.652 1.332
L 1.532 1.532 1.166 1.166 0.652 0.652
M 0.222 0.406 0.170 0.246 0.094 0.194
L 0.222 0.222 0.170 0.170 0.094 0.094
M 0.374 0.684 0.284 0.416 0.160 0.328
L 0.374 0.374 0.284 0.284 0.160 0.160
M 3.506 6.234 2.516 3.266 1.132 2.276
L 3.506 3.506 2.516 2.516 1.132 1.132
<£>
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Table 14.-Federal effluent limitation guidelines^ Continued
[pounds allowed per ton raw product]
Commodity
Mayonnaise and dressings3
Mushrooms
Olives
Onions (canned)
Peaches
Pears
Peas
Pickles (fresh pack)
Pickles (process pack)
Pickles (salt stations)
Pimentos'5
Pineapples
Plums
Raisins
Sauerkraut (canning)
1977
Daily max 30-day avg Annual avg
BOD TSS BOD TSS BOD TSS
0.74 1.34 0.48 0.98 0.34 0.66
6.02 10.72 3.56 7.36 2.44 4.44
10.88 19.58 6.68 13.84 4.78 8.88
6.18 11.02 3.66 7.56 2.50 4.56
3.02 5.44 1.86 3.86 1.34 2.52
3.54 6.42 2.24 4.64 1.66 3.10
4.84 8.72 3.00 6.22 2.16 4.04
2.44 4.38 1.50 3.08 1.06 1.98
2.90 5.26 1.84 3.82 1.36 2.56
0.36 0.66 0.24 0.50 0.18 0.36
...
4.26 7.70 2.66 5.52 1.92 3.62
1.38 2.48 0.84 1.74 0.58 1.08
0.86 1.56 0.56 1.14 0.42 0.78
1.00 1.78 0.60 1.26 0.42 0.80
1983
Daily max 30-day avg Annual avg
BOD TSS BOD TSS BOD TSS
M 0.420 0.772 0.326 0.490 0.194 0.396
L 0.420 0.420 0.326 0.326 0.194 0.194
M 2.376 4.244 1.724 2.292 0.812 1.640
L 2.376 2.376 1.724 1.724 0.812 0.812
M 4.570 7.852 3.212 4.382 1.592 3.226
L 4.570 4.570 3.212 3.212 1.592 1.592
M 3.438 6.270 2.610 3.786 1.452 2.960
L 3.438 3.438 2.610 2.610 1.452 1.452
M 1.532 2.794 1.166 1.688 0.648 1.320
L 1.532 1.532 1.166 1.166 0.648 0.648
M 1.710 3.150 1.328 2.006 0.794 1.624
L 1.710 1.710 1.328 1.328 0.794 0.794
M 1.990 3.636 1.516 2.216 0.854 1.742
L 1.990 1.990 1.516 1.516 0.854 0.854
M 1.278 2.278 0.922 1.212 0.426 0.858
L 1.278 1.278 0.922 0.922 0.426 0.426
M 1.304 2.416 1.022 1.568 0.626 1.286
L 1.304 1.304 1.022 1.022 0.626 0.626
M 0.168 0.326 0.144 0.250 0.108 0.226
L 0.168 0.168 0.144 0.144 0.108 0.108
...
M 2.952 5.362 2.222 3.170 1.198 2.440
L 2.952 2.952 2.222 2.222 1.198 1.198
M 0.566 1.008 0.408 0.540 0.190 0.382
L 0.566 0.566 0.408 0.408 6.190 0.190
M 0.408 0.760 0.326 0.514 0.210 0.434
L 0.408 0.408 0.326 0.326 0.210 0.210
M 0.520 0.940 0.388 0.540 0.200 0.408
L 0.520 0.520 0.388 0.388 0.200 0.200
-------
Table 1 -4. Federal effluent limitation guidelines^ Continued
[pounds allowed per ton raw product]
Commodity
Sauerkraut (cutting)
Snap beans
Soupsc
Spinach
Squash
Strawberries
Sweet and white potatoes
Tomatoes
Tomato-starch -cheese
specialties3
1977
Daily max 30-day avg Annual avg
BOD TSS BOD TSS BOD TSS
0.16 0.28 0.10 0.22 0.08 0.16
3.02 5.34 1.74 3.60 1.16 2.08
8.28 14.76 4.92 10.18 3.38 6.20
4.74 8.38 2.72 5.62 1.82 3.28
1.80 3.28 1.18 2.46 0.92 1.74
3.56 6.38 2.12 4.40 1.48 2.70
1.80 3.38 1.32 2.74 1.10 2.18
2.42 4.30 1.42 2.96 0.98 1.80
2.74 6.62 2.16 4.46 1.44 2.60
1983
Daily max 30-day avg Annual avg
BOD TSS BOD TSS BOD TSS
M 0.092 0.174 0.076 0.128 0.054 0.112
L 0.092 0.092 0.076 0.076 0.054 0.054
M 2.096 3.716 1.494 1.910 0.652 1.306
L 2.096 2.096 1.494 1.494 0.652 0.652
M 5.532 9.868 4.000 5.276 1.858 3.744
L 5.532 5.532 4.000 4.000 1.858 1.858
M 2.352 4.150 1.660 2.076 0.692 1.222
L 2.352 2.352 1.660 1.660 0.692 0.692
M 0.590 1.068 0.440 0.614 0.228 0.464
L 0.590 0.590 0.440 0.440 0.228 0.228
M 1.238 2.210 0.898 1.188 0.420 0.846
L 1.238 1.238 0.898 0.898 0.420 0.420
M 1.144 2.180 0.952 1.606 0.684 1.414
L 1.144 1.144 0.952 0.952 0.684 0.684
M 1.048 1.866 0.756 0.990 0.346 0.698
L 1.048 1.048 0.756 0.756 0.346 0.346
M 1.962 3.490 1.410 1.836 0.638 1.286
L 1.962 1.962 1.410 1.410 0.638 0.638
aLb/ton final product
Guidelines have not been established as of April 1976
cLb/ton raw ingredients
NOTES Medium (M) and large (L) food processing plants have the same guidelines for 1977, but they are separated for 1983. Small processing plants are
not subject to these guidelines.
Large is defined as a plant that processes more than 10,000 tons per year.
Medium is defined as a plant that processes between 2,000 and 10,000 tons per year.
Small is defined as a plant that processes less than 2,000 tons per year.
-------
The guidelines for 1983 have been divided according to size of plant (medium (M) or large
(L), as shown in table 1-4). The Federal Register of April 16,1976, stated that, "Industry plants
with less than 2,000 tons per year production remain excluded from the regulation. While these
plant groups are not covered by these effluent limitations due to potential economic impacts,
permitting authorities have sufficient information in the Development Document to regulate the
discharges from these excluded plants on a case-by-case basis."8 A "medium" plant is one that
processes between 2,000 tons and 10,000 tons per year. "Large" is defined as greater than 10,000
tons per year.
The EPA guidelines are based on what is attainable with current treatment processes, not on
what is required to protect water quality. For 1977, the effluent standards are based on what is
defined as the "Best Practicable Control Technology Currently Available (BPCTA)." By 1983,
the effluents are to conform to limits that are achievable by the "Best Available Technology
Economically Achievable (BATEA)."
Although the EPA guidelines are written for waste discharged into receiving waters, they also
affect processors discharging into a municipal sewer. The law requires that all industries meet the
guidelines. Fruit and vegetable processors discharging to a sewer meet their treatment obligations
through the use of the joint city-industry treatment plant operated by the city. If the city's treat-
ment plant does not adequately treat the waste, processors may be forced to provide treatment
facilities to make up the difference.
State Requirements
Each state with an EPA-certified pollution control program issues NPDES permits. The EPA
issues permits in states without a certified program under guidelines that represent the minimum
standard or the maximum permissible discharge. The states must consider water quality of receiv-
ing waters when establishing additional limits; therefore, many state requirements are more restric-
tive than EPA guidelines. Some states require a state discharge permit even for industries discharg-
ing to publically owned treatment works.
Local Requirements
Local requirements are primarily in the form of sewer ordinances that apply to sewer users.
These ordinances are intended to prevent blockages and damage of the collection system, hazards
to workers in the sewers and at the treatment plant, or interferences with the treatment process.
They contain specific limits on heavy metals, toxic compounds, oil and grease, temperature, pH,
and other characteristics. Ordinances set the basis for sewer user charges and requirements for
flow measurement, sampling, sample storage, and testing. Copies of sewer ordinances are always
available to industrial users.
Processors discharging to municipal systems are subject to local sewer service charges. Gen-
erally, cities charge for the use of their sewers and treatment plants. The base and amounts of
charges do (and will for some time to come) vary greatly from city to city. The largest contribut-
ing factor to this variation is the body of regulations set by EPA for federally assisted treatment
construction projects. If a city is not receiving federal funds, then the sewer charge can be
nominal, perhaps covering only a fraction of the operation and maintenance of the treatment
plant. Charges vary from a flat rate to a charge proportional to the flow or floor area of the plant.
However, if a facility is receiving federal funds for treatment plant construction, service
charges usually rise. EPA requires that industry pay its "fair share" of the operation and main-
tenance, and the capital cost of the treatment plant. Industry's "fair share" is calculated in pro-
portion to the amount of waste loading (usually flow, BOD, and suspended solids) it contributes
to the treatment plant. Processors must understand the city's ordinance and determine the effect
of EPA grant regulations (if any) on charges.
12
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TREATMENT
There are two basic reasons for treating waste: one, to reduce sewer user charges, and two,
to comply with an effluent standard set by EPA, the state, or the city.
Once the treatment need is established, three possible options can be used:
Install pretreatment; discharge to city sewer.
Install full treatment; discharge to stream.
Discharge to land.
Unless the processor is building a new plant, all of these options are not usually available.
The remainder of this text is devoted to discussion of the various techniques available under each
option. Each is discussed separately in its own chapter. The techniques of meeting a treatment
need are listed along with general design and operational considerations.
COSTS
In each cost estimate, the cost of capital was based on an amortization period of 10 years
and an interest rate of 12 percent. This results in a cost of 17.7 percent of the capital per year.
The costs are for October 1975 and assume competitive bids by contractors. The estimates
are "order of magnitude" estimates. It was assumed that significant site grading would not be
required and that good soil conditions existed. Costs were not included for site acquisition or for
separate fencing, yard lighting, access roads, and laboratories. In the examples, a plant producing
1 mgd of wastewater and operating 90 days per year has been assumed. The costs associated with
startup and shutdown have not been included.
The cost range from $0.18 per 1,000 gallons to $3.21 per 1,000 gallons is for systems which
operate 90 days per year. A total system will likely cost more since the financing of screening,
primary treatment, and secondary treatment, if required, would be additive.
Table 1-5 summarizes the costs from the text, and gives costs for 180 and 360 days of oper-
ation, as well as 90 days. Other assumptions for each example are either listed on the tables or
given in the text. The operating and maintenance costs, as presented, are only major direct costs.
They do not include any general or corporate overhead or equipment replacement costs.
Generalized cost curves are also given in the two EPA effluent guideline development docu-
ments for the fruit and vegetable industries. These are good references for comparative system
costs.4'5
COMMUNICATIONS
Communications between the processing plant staff and municipal treatment plant operators
cannot be over-emphasized. Good communications will improve public relations and assist the
treatment plant operators in handling occasional upsets or unusual conditions. Treatment plant
operators need to know, as much in advance as possible, when the plants will start up or when the
product mix will be changed. Early notification of planned wastewater "dumps" of an unusual
nature, or immediate notification of accidental spills, can be invaluable to treatment plant oper-
ators. Make an effort to know the people and system that serve your plant.
13
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Table \-5.-Summary of estimated costs for fruit and vegetable processing
£>
11-1 Flow measurement
and screening
II-2 Neutralization
alll-3 Aerated lagoon
III-5 Activated sludge
without sludge
concentration
III-6 Activated sludge
with sludge
concentration
III-9 Filtration
111-10 Chlorination
Number of operating days per season
90 Days
.
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Chapter II
PRETREATMENT
INTRODUCTION
Most fruit and vegetable processing plants discharging to a city sewer system use some method
of pretreatment. In the broadest sense, pretreatment is the treatment applied before discharge to a
treatment system. However, pretreatment usually refers to gross solids removal, soil removal, or
neutralization. Common pretreatment steps are screening, neutralization, and flow equalization.
Frequently, more extensive treatment, such as gravity sedimentation or dissolved air flotation, is
used.
The reasons for pretreatment are as follows:
Meet municipal ordinance requirements.
Reduce costs.
Accommodate production increases.
ORDINANCE REQUIREMENTS
Pretreatment is often required by city ordinance, of which screening is almost always a
requirement. Neutralization, flow equalization, and soil removal are also usually required.
REDUCE COSTS
Despite the apparent high rates charged by some cities for using their sewers, it is usually
difficult to economically justify treatment for sewer charge reduction. The main reason for this
difficulty is the high cost of solids disposal and the high cost of building and operating small treat-
ment systems. Because of the high cost of industrial capital, the short processing season, and other
factors, the cost for comparable treatment by fruit and vegetable processors alone is considerably
higher. Because of the federal grant program regulations, industries participating in joint treat-
ment essentially receive a 30-year, interest-free loan for the EPA-funded share of the joint treat-
ment facilities, and a low-interest (7%±), long-period (20 to 30 years) loan for the remaining share,
which is financed by state or local bonds.
A decision to provide extensive pretreatment or separate treatment should be based on a
thorough, after-tax analysis of the costs. If a processor can irrigate part or all of the plant effluent
onto nearby land, the cost can be favorable when compared to treatment by a municipality in a
mechanized plant.
Presently, recovery of fruit and vegetable processing by-products is usually less than a
"break-even" proposition. For this reason, recovery is usually only practical if it responds to other
requirements for pretreatment or helps to defray some of the pretreatment operating costs. For
certain products in live-stock-producing areas, screenings and treatment sludges can be recovered
and used in animal (cattle, poultry, hogs) feeding operations. If by-product recovery is to be
practiced, all sanitary waste must be separated.
15
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PRODUCTION INCREASES
Extensive pretreatment is often required as a result of plant expansions. Plants discharging to
public systems frequently reach their allocated treatment capacity as a result of increasing waste
loads. Presently, the time required to expand a public treatment plant is about 5 years. The
ability of the municipal plant to meet its own discharge limitations might prevent additional waste
discharge from increased production. Few processors can wait for a city to provide additional
capacity. One option is to pretreat the waste so that the processor's contribution to the public
system does not increase as a result of the expansion.
PRETREATMENT PROCESSES
SCREENING
In almost all canning plants, discrete waste solids (such as trimmings, rejects, and pits) are
effectively and economically separated from liquid wastes by screening. Screening has several
objectives including recovery of useful solid by-products; a first stage primary treatment opera-
tion; or pretreatment for discharge to a municipal waste water treatment system.
Screens are often characterized by the size of the openings. There are several methods of
designating the open area in a screen. Wire screen openings are usually measured in meshes per
inch, and are available in increments of the Tyler Standard Sieve sizes. For example, the popular
20-mesh screen has a standard wire diameter which is woven in a rectangular grid with 20 wires
per linear inch. A second method of screen size measurement describes the clear opening between
screening elements (usually flat or wedgewire in shape), either in millimeters or mils. For example,
a 0.76 mm opening is equal to 30 mils (0.030 in) and approximately equivalent to a 40-mesh screen.
Bar screens, because of their very large openings, are measured by their clear opening, usually in
centimeters.
The following are typical examples of screens:
Manufacturer Remarks
SWECO 135-mesh are possible; 50-or 60-mesh
are more common. Few blinding
problems with cannery waste.
Link Belt Some blinding on 20-mesh screens.
Recommended 6-to 10-mesh for
canning waste.
Dorr Oliver No blinding with equivalent 20-mesh
(1.5 millimeters).
Screening prevents the spray nozzle from plugging. Removal of grease or neutralization may
be required to prevent soil or crop damage. Certain ions may have to be removed to prevent soil
or crop damage or ground-water contamination.
Screens should be located as close as possible to the process producing the waste. The longer
the solids are in contact with water and the rougher the flow is handled, the more material will
pass through the screens and the more solids will be dissolved. Keep the contact time and agitation
to a minimum before and during screening.
16
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The following are often considerations in purchasing screens:
Initial cost
Hydraulic capacity
Hydraulic head required
Solids captured
Blinding potential
Moisture of screenings
Operating and maintenance costs
Space required.
Four types of screens are commonly used in the fruit and vegetable industry. Vibratory
screens are very common. Two variations are the circular center-feed units (in which solids may be
discharged in a spiral toward the center or periphery) and the rectangular, end-feed variation (in
which solids are discharged along the screen toward the lower end). These units are shown on
figures II-l and II-2.
Figure 11-1. Circular center-feed vibratory screen. (Courtesy of SWECO, Inc.)
17
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Figure 11-2. Rectangular end-feed vibratory screen. (Courtesy of CH2M Hill)
The rotary drum screen is also common. These screens may be designed so that the flow is
from the inside of the drum toward the outside, or the reverse. If the flow is from the inside, then
the solids are collected inside the screen and removed by augers, or a trough. In units where the
flow is from the outside to the center, the solids are retained on the outer surface of the drum and
are removed by a doctor (or scraper) blade. A drum screen is shown on figure II-3.
Tangential screens (figure II-4) are also commonly used. The water flows down and through a
parabolic screen, but the solids are retained on the surface of the screen and discharged from its lower em
A recent derivation of the tangential and drum screens is illustrated in figure II-5. The waste-
water is introduced behind the slotted drum, which rotates forward at the top. Solids are retained
on the surface of the drum and scrapped off by a blade. The screened waste falls through the drum
and backwashes the underside before being discharged.
Rotating centrifugal or collar screens can be used when high-solids capture is required. The
screens can be very fine, up to 400 mesh. The waste is sprayed under pressure onto the inside of
the rotating drum. The water passes through the screen and the solids are collected on the inside of
the collar. The solids typically have a high-moisture content.
Successful application of screens depends on many variables. Screens ordinarily achieve a high
removal of settleable and floatable solids, but variable amounts (up to 70 percent) of the suspended
solids. Proportional amounts of BOD are ordinarily removed with the solids.
18
-------
Figure 11-3. Rotary drum screen. (Courtesy of CH2M Hill)
Feed
Screened waste
Screenings
Figure 11-4. Tangential screen (45°). (Courtesy of Dorr Oliver)
19
-------
Figure 11-5. Slotted drum screen. (Courtesy of Hydro Cyclonics Corp.)
Location of the waste screen is very important. One option is to collect wastewater in a sump
below the floor level of the plant, and then pump the wastewater to the screen. Many screens are
located above the solids hopper. These require pumping, but usually avoid the need for a solids
conveyor. Pumping may reduce screening efficiency by reducing the particle size of suspended
solids. Pumps, valves, and piping should be designed to minimize agitation. Another option is to
place the screens below the level of the plant drains (if the elevations permit). After screening,
the solid waste can be conveyed up to the waste hopper.
Screening is an inexpensive method for removing large solids (greater than about 60 mesh)
from wastewater. A good screen may remove the same amount of solids at less cost than in-plant
dry cleanup. Compared to other pretreatment methods, screens require only a small space, and
they can usually be installed in an existing plant.
Screening efficiency is affected by the following:
1. Mechanical features
Wastewater flow rate
Area of screen
20
-------
Screen inlet and outlet locations
Screen motion
Screen opening size
Screen fabric (wedgewire, flat, or round).
2. Wastewater properties
Discrete particle dimensions
Concentration of discrete materials
Shape of discrete material (irregular, round, fibrous)
Consistency of discrete material (hard, soft, sticky).
An estimate of the costs for screening is given in table II-l. These costs are for October 1975
and assume a 20-mesh tangential screen. The estimate assumes that the plant floor drains will
not have to be modified to collect all waste at one point.
NEUTRALIZATION
It is sometimes necessary to install pH control systems to treat wastes from the fruit and
vegetable processing industry. Typically, municipal ordinances require wastes discharged to its
sewers to be between pH 6 and 9, and many biological treatment systems cannot tolerate wide
ranges in raw waste pH. Wastes with low pH result from processing of acidic fruits, e.g. plums, and
wastes with high pH result from the use of lye during peeling such as typical peach peeling operations.
Depending on the daily operating mode of the processing plant, variations in instantaneous
flow can be from very small to very great (a maximum of four times the minimum). Each plant
is obviously different, but large variations in flow may be smoothed with a surge tank of about
10 to 20 percent of the total daily flow volume. Settling of solids will be a significant problem in
a tank of this size; so the tank must either be mixed or some means provided for solids removal.
If solids accumulate, odor will result.
SOIL REMOVAL
Root crops (potatoes, carrots and beets) and machine harvested crops (tomatoes) introduce,
along with the raw product, large amounts of field soil to a food processor's waste stream. Since
the present incentive for field cleaning is slight, each processor has to handle and/or remove the
soil. Municipal plants usually are not built to deal with large quantities of soil. The abrasive
material accelerates equipment wear, settles in pipelines and accumulates in the treatment plant's
solids handling system (i.e., the sludge digester).
Some city ordinances are now being written to require fruit and vegetable processors to
remove a majority of the soil from their waste. Soil may also have to be removed from waste
before it is irrigated.
21
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Table 11-1. Cosf summary for flow measurement and screening
to
to
Criteria
Flow:
BOD:
TSS:
pH:
Season:
Amortization:
1 mgd average
2 mgd peak
1000mg/l
IOOOmg/1
4.5
90 days
10 years at 12%
Engineering, legal and contingency costs included at
25% of construction cost
Labor at 7.00 (including overhead) ~ 1 hr/day
October 1977 dollars
Schematic
Process piping
Existing
wastewater
collection
system
Receiving sump
Screens
Solids storage
hopper
Flow measurement
Process flow to
downstream
treatment
Truck disposal
Assumptions
Solids hauling and disposal at 4 dollars/cy
(approximately 700 Ibs/day at $80/ton)
Use of 20-mesh screen (tangential)
Costs
Capital
$71,600
Operation and maintenance
Labor
Disposal
Total
Amortized capital plus O&M
unit cost
$ 700/yr
2,500/yr
$3,200/yr
$15,900/yr
17.7«!/1000gal
-------
Settling lagoons have and can be used for soil removal. Provisions must be made for draining
the ponds to remove the solids. Odor is a potential problem if organic suspended matter is present;
however, the extent of odor production cannot be forecast. In general, it is better to have fewer
organics, a higher pH and a snorter detention time. The effluent from settling ponds is often high
in BOD and suspended solids.
A reliable neutralization system has two or three mixed tanks, in series, in which an acid or
base is added. The acid or base is automatically added, using a metering system controlled from
effluent pH readings.
A consistently alkaline waste can be neutralized by using carbon dioxide (CO2). Boiler stack
gas may be a source of CO2.
A cost estimate for a neutralization system is given in table II-2. The costs are for October
1975 and include two mixed tanks, an instrumentation and control system, and chemical storage.
It was assumed that tomato processing waste is acidic and is neutralized with caustic. Facilities
for neutralization with lime or sulfuric acid will differ only in chemical storage and delivery.
Rarely will a fruit and vegetable processing plant produce a waste that exceeds both alkaline
and acid limits. In cases where limits are exceeded, the storage, feed and control system must pro-
vide for either an acid or base addition. This system is both more complicated and expensive.
If it is necessary for the individual plant to install a pH control system, it will generally be
found that the automatic control of pH for the neutralization of waste streams can present
problems including:
1. The relationships between the amount of reagent needed and the controlled variable
(pH being non-linear).
2. The pH of the wastewater can vary rapidly over a range of several units in a short period
of time.
3. The flow will change while the pH is changing since the two variables are not related.
4. The change of pH at neutrality can be sensitive to the addition of a reagent so that even
slight excesses can cause large deviations in pH from the initial setpoint.
5. Measurement of the primary variable, pH, can be affected by materials which coat the
measuring electrodes.
6. The buffer capacity of the waste has a profound effect on the relation between reagent
feed and pH and may not remain constant.
7. A relatively small amount of reagent must be thoroughly mixed with a large volume of
liquid in a short period of time.
FLOW CONTROL
Control of surges in effluent flow is usually not required as a pretreatment measure. However,
if flow variations can be smoothed out and accidental spills contained and controlled, screens can
be smaller, and effluent pH control will be simpler.
23
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Table 11-2.Cosf summary of neutralization (for acid waste)
to
Criteria
Flow:
pH:
Season:
Amortization:
1 mgd average
2 mgd peak
4,5
90 days
10 years at 12%
Engineering, legal and contingency costs included at
25% of construction cost
October, 1975 dollars
Labor at $7.00/hr (including overhead)
Schematic
NaOH storage &
dilution tanks
Mixer
Chemical feed
pumps
Process flow to
downstream
treatment
Process
flow
Neutralization tanks
Assumptions
Neutralization with 20% NaOH at 200 mg/l NaOH
average application rate (216 gal 50% NaOH per day)
« NaOH cost at 165 dollars per anhydrous ton (.08^/lb)
Tank truck shipping cost at 3 cents/100 Ib liquid/mile
with 100-mile shipping distance ($60.00/ton)
Two neutralization tanks in series with 15-minute
average retention
Costs
Capital
$100,000
Amortized capital plus O&M
unit cost
Operation and maintenance
Labor $ 1,000/yr
Caustic
(50%)/day 22,600/yr
Total $23,600/yr
$41,300/yr
45.9«5/1000gal
-------
Where space and disposal of solids is a problem, circular clarifiers (figure II-6) can be used to
settle and thicken the soil. Typically, circular clarifiers will produce a mud two or three times
thicker than could be obtained in plain settling ponds. This means that the amount of mud to be
disposed of is proportionally less.
Grit-removing cyclones have also been tried at some plants. The units are relatively inexpensive,
but they must be run at a constant flow to achieve their design efficiency. Cyclones are not as
efficient as a well-designed clarifier, and they tend to produce a dilute mud. The system must be
designed to withstand abrasion.
Fine screens (to 400 mesh) have also been applied to remove soil. The application is similar
to screening. Several screens can be used in series to concentrate the solids. These units approach
the efficiency of clarifiers, but are considerably more difficult to operate and maintain, and are
usually more expensive.
FURTHER PREIREATMENT
If additional removal of suspended solids or BOD is needed, more complex process units must
be used. These processes and others are discussed in complete detail in Chapter III.
Influent screen
Underflow or mud
to dewatenng
Influent silt stream
from flumes P"
Figure 11-6. Silt clarifier. (courtesy of CH2M Hill)
25
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Chapter III
PRIMARY, SECONDARY&ADVANCEDTREATMENT
INTRODUCTION
Discharge to public waters (streams, lakes) requires treatment beyond pretreatment. Moreover,
additional treatment may be required for land disposal or discharge to a city sewer.
Treatment processes are divided into three broad categories, based on their ability to remove
increasing amounts of pollutants: (1) primary treatment, (2) secondary treatment, and (3) advanced
waste treatment (tertiary treatment). The processes commonly thought of as being under each of
these three categories are listed in table III-l. For the treatment of fruit and vegetable processing
waste, primary treatment is used to remove a portion of the suspended solids in the wastewater;
secondary treatment is used to remove a portion of the dissolved and suspended solids material;
and advanced, or tertiary, treatment is used to remove additional amounts of these constituents
as well as other constituents not removed by the secondary treatment. These same processes are
used to treat domestic sewage.
Table 111-1 .Treatment unit processes for fruit and vegetable processors
Primary treatment
Grit removal
Silt removal
Plain sedimentation
Dissolved air flotation
Chemical treatment
Secondary treatment
Stabilization ponds
Aerated lagoons
Activated sludge
Anaerobic systems
Anaerobic ponds
Anaerobic contact process
Anaerobic filters
ABF/activated sludge
Trickling filters
Rotating biological contactors (RBC)
Tertiary treatment
Chemical clarification
Filtration (mixed bed
of sand)
Reverse osmosis
Carbon adsorption
Ion exchange
26
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Figure III-l is a graphical representation of how BOD and suspended solids are removed in
various treatment processes. The length of the bars in the figure is semi-quantitative. The sum of a
pair of bars represents the total amount of solids (or BOD) in the waste. The length of the BOD
bars should not be compared with the length of the solids bars. BOD is an effect, or demand,
exerted by the solids, and may not be in proportion to the mass of solids.
It should be noted, however, that figure III-l is not correct in all cases. The dissolved solids
would decrease in activated sludge aeration and sedimentation. The dissolved solids may be either
increased or decreased in chemical clarification depending on the coagulant used and the method
of operation. The most common chemicals used are lime, alum, and iron salts. Before choosing a
coagulant, a thorough study of both clarification and solids dewatering is essential.
Treatment is accomplished by the removal or conversion of solids. All treatment processes
result in sludge which must be disposed. Treatment of this sludge is discussed in Chapter V.
REQUIREMENTS FOR TREATMENT
In nearly every case the amount of treatment is established by local, state, or federal effluent
standards. However, treatment in excess of governmental regulations could be required as a result
of law suits brought by people who claim to be adversely affected by the discharge or operation of
a treatment system. Common causes for litigation are odor (air pollution), noise, and ground-water
contamination.
EPA GUIDELINES
The Environmental Protection Agency has established discharge guidelines for fruit and vege-
table processors who have their own discharge to public waters. Secondary treatment is required
for all plants that discharge into the nation's waterways by mid-1977. By mid-1983, the EPA guide-
lines may mandate advanced treatment. The guidelines are given in table 1-4.
The 1977 guidelines for the apple, citrus and potato processing industries are to be met with
secondary treatment. Exemplary secondary treatment plants studied by EPA included the following
processes: activated sludge, trickling filter and aerated ponds, multiple aerated ponds, and
anaerobicaerobic ponds. The potato processors that were studied used primary clarifiers ahead of
secondary treatment.4 The 1983 guidelines are assumed to be met through the use of in-plant con-
trols, the addition of more aerated lagoons or a sand filter, and chlorination.
The effluent guidelines5 assume that processors of all products other than apple, citrus and
potato products will meet the 1977 requirements with one of two kinds of secondary treatment,
i.e., either aerated ponds or activated sludge. The 1983 guidelines are assumed to be met by reducing
the load on the treatment plants through in-plant processing changes. However, large plants may
have to add multi-media filtration.
Thus, for the future, primary treatment alone will probably be used only for discharge to some
kind of land treatment system or for pretreatment. Primary treatment can be used as a first step in
secondary treatment installations if the influent waste is high in settleable suspended solids (tomatoes,
carrots, potatoes, etc.).
OTHER CONSIDERATIONS
Treatment may be needed to allow in-plant water re-use, ground-water recharge, or to extend
the life of a land treatment system. The State of California, for example, is setting standards for
waste applied to land.
27
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Total Solids
A
99.9
NOTE: Bars indicate relative magnitude (percent) removal for each additional step in the treatment process chain.
Figure 111-1. Effect of treatment on solids & BOD.
28
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Water used for irrigation has to meet the quality requirements outlined in Chapter IV. Treat-
ment prior to agricultural use may be required. Minerals such as boron, sodium, and calcium play an
important role in determining the feasibility of agricultural re-use. These constituents are seldom
restricted in discharges to receiving waters.
If a fruit and vegetable processing plant discharges to a city sewer system, the plant manager
should understand the workings of treatment processes, even though the plant may only be required
to perform pretreatment. The opening of the processing season is usually a significant day for the
operators of a city treatment plant. If a plant manager understands the effect wastewater has on the
operation and performance of the city treatment plant, he is in a better position to communicate
with the city staff and maintain good relations.
A basic understanding of the treatment processes will make it possible for fruit and vegetable
processors to judge the adequacy of proposed municipal systems which are intended to treat their
processing wastes.
PRIMARY TREATMENT
Primary treatment is used to remove both inorganic and organic solids. Solids removal can be by
gravity (or by skimming, in the case of flotables) and may be assisted by chemicals (lime, alum or
polymer) to make the particles settle faster. Removal can also be accomplished by mixing the waste
with dissolved air and chemicals to make the solids float to the top.
Primary treatment of domestic sewage usually removes 40 to 60 percent of the influent sus-
pended solids and 30 to 35 percent of the BOD. These removals are usually not achieved in fruit and
vegetable processing waste. Typically, much of the BOD in these wastes is in a dissolved form that
will not settle or float. Potato waste is an exception because 40 to 60 percent of BOD is removed
with primary treatment.
Suspended solids reductions that are achievable in primary treatment vary widely with raw and
finished products. Significant suspended soils reductions are attainable with primary treatment in
products like potatoes, tomatoes, beets, or carrots. Little reduction is achieved in products like corn,
peas, peaches, or pears. Primary treatment is seldom used for apple juice waste because there are
few settleable solids. The waste consists primarily of dissolved fruit sugars. Tomato processing waste
is typically high in settleable solids from field soil, so primary treatment is effective. Primary treat-
ment of potato waste can remove up to 75 percent of the suspended solids.
SEDIMENTATION
Primary treatment systems using gravity sedimentation are sized on the theoretical settling or
falling rate of the slowest particles to be removed. This settling rate is expressed as gallons treated
per day divided by the surface area in square feet of the clarifier (gpd/sf). Typical values are between
300 and 1000 gpd/sf, which is equivalent to settling rates of 0.33 and 1.11 inches per minute, re-
spectively (see table III-2). These settling rates can be determined by special laboratory tests.
Clarifiers are usually at least 10 feet deep to allow for uneven flow distribution, sludge storage, and
flow surges. In addition, primary clarifiers can also thicken these solids. The solids loading on a
clarifier determines the degree of sludge thickening. Solids loading is the total pounds of solids
settled divided by the surface area of the clarifier. High solids loadings can also hinder the settling
rate of solids. Typical values for solids loadings are given in table III-2.
Chemicals such as lime, alum or polymers may be added to the primary sedimentation tanks.
This increases the rate of settling of the suspended particles by coagulating smaller particles together
into larger particles. Because of fluctuations in chemical requirements, chemical coagulation systems
can be extremely difficult to operate on food processing waste effluents, especially if consistently
high removals are required.
29
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Table 111-2. Primary treatment design criteria of fruit and vegetable wastewaters
Sedimentation
Clarif ier type
Bottom slope
Circular or rectangular with width equal
to 1/4 to 1/3 of length.
1-2 inches per foot for light sludge.
3-4 for heavy sludge.
Overflow rate
Common municipal waste
Silt and clay
Lime floe
Alum floe
800 gal Ions/day/sq ft (gpd/sf)
300 gpd/sf
900-1,000 gpd/sf
600 gpd/sf
Side-water depth
10 feet minimum; 12 feet best.
Rake speeds
Rectangular tanks: 2-4 fpm
Circular tanks: 2-4 fpm at the tip,
but should be 10-15 fpm for silt and clay.
Scum removal
Should be on all clarifiers. Scum trough should
be on downwind side of clarifier.
Solids loading
10-30 Ibs/sf/day for light organics.
80-100 Ibs/sf/day for silt and clay.
Sludge piping
Preferably 6 inches in diameter. Flow
velocity should be about 2-5 fps.
Dissolved air flotation
Overflow
Air-to-sol ids ratio
Recycle ratio
Solids loading
Pressure
1,000-5,000 gpd/sf
0.01-0.1 Ibs air/lbs solids
30-100 percent
0.3-1.3lbs/hr/sf
50-60 psi
Figure III-2 is a cross section of a typical circular gravity clarifier. Common loadings for gravity
clarifiers are given in table III-2.
FLOTATION
For certain wastes, dissolved air flotation clarifiers can be used effectively. Removal of sus-
pended solids depends on the fine air bubbles that attach to each solids particle, thereby providing
buoyancy. The buoyant solids are then skimmed off after they rise and form a blanket, or float, on
the top of the clarifier. Solids that settle are removed by either an auger or rake.
The most common type of air flotation is dissolved air flotation. A portion of the waste, usually
the effluent, is pressurized and air is injected. When the air and solids mixture is released into the
open tank, the air comes out of solution in small bubbles, which attach to the solids and cause the
solids to float.
30
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Weir Scum box
Influent feed well
Drive motor
Surface skimmer
Scum baffle
Effluent
launder
Solids withdrawal
Hopper
Scrapers thicken and
move solids to hopper
Rotating clarif ier
rake arm
Figure 111-2. Clarif ier.
Dissolved air flotation units must be designed empirically from pilot experiments for a given
waste. Several criteria must be examined in the pilot studies. These criteria are hydraulic loading,
solids loading, air-to-solids ratio, and chemical dose requirements (if used).
Figure III-3 shows a typical, rectangular, dissolved air flotation clarifier. This clarifier is
equipped to remove solids from both the top and bottom. Common loadings in dissolved air flota-
tion units are given in table III-2.
COMPLETE PRIMARY SYSTEMS
Figure III-4 is a schematic of a complete primary system. In addition to the criteria that must
be met in the design of the clarifier, it is vitally important that the sludge handling and treatment
systems be well matched.
The clarifier must be sized to store sludge until it can be accepted by the dewatering equipment
(a vacuum filter or centrifuge). If the vacuum filter or centrifuge is undersized, the clarifier will fill
with sludge. Some sludge becomes septic when stored. This usually causes a reduced dewaterability
of the sludge, requiring more chemical additions, and can also cause process failure and odors. De-
watering equipment is discussed in Chapter V. Systems having a dewatering unit must be designed
to accept the recycled flow and solids from the unit as well as any wash or seal water used on the
unit. These flows can be from 10 to 20% of the influent flow to the primary treatment system, and
the solids from 5 to 20% of the influent solids.
Primary treatment systems operating on waste from root crops, (or other wastes, like tomato)
may have special problems with field soil (mud). Some clays and silts are thixotropic, which means
that they will solidify unless constantly agitated. If the sludge does solidify, it must be manually
removed from the clarifier. Most mud will settle and thicken in clarifiers to 30 to 40% total solids
(by weight), depending on the fractions of sand, silt and clay. At these concentrations, the head loss
in pump-suction pipelines is so great that special pumping provisions must be made. The sludge
pump can be located beneath the clarifier near the center, or dilution water can be added to the
sludge at the center hopper of the clarifier.
31
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H opper to
collect float
Auger to
remove float
Influent
Surface skimming
mechanism
Effluent
Recycle pump
Pressurization tank
Heavy solids
Recycle line with
dissolved air
Auger to remove
heavy solids
Figure 111-3. Dissolved air flotation clarif ier.
Plant effluent
Clarif ier
Treated flow
Vacuum filter
Filter cake: 8% to
50% total solids
Scum
Sludge: 4% to
15% total solids
Figure III-4. Primary treatment plant.
32
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BIOLOGICAL SECONDARY TREATMENT
While primary treatment is used to remove settleable solids, secondary treatment removes
soluble organic material (BOD) and settleable solids (figure III-l). Biological secondary treatment
may be (1) aerobic, which means that the biochemical reactions are carried out in the presence of
oxygen, or (2) anaerobic, in which case different biochemical reactions are carried out in the
absence of oxygen.
ANAEROBIC SYSTEMS
Principles
Anaerobic treatment is most commonly used in city treatment plants to digest sludges. A
generalized equation for the biochemical reaction characterizing anaerobic treatment is:
food (BOD) + nutrients (N, P, etc.) -* cells + methane gas
The mass, or yield of cells generated per pound of BOD stabilized, is from 0.04 to 0.06 which
is considerably less than in aerobic treatment. Much of the carbon in the food source (BOD) is con-
verted to methane gas. Anaerobic digestion requires little power. The process reduces the sludge
weight and stabilizes it for disposal.
Reaction rates of anaerobic treatment increase with temperature. Sludge digesters are often
heated to about 90 degrees Fahrenheit. The methane gas generated by the digestion is often used
for this purpose. The anaerobic process is not often used to treat total industrial effluent. How-
ever, anaerobic ponds and anaerobic filters are of use for processing fruit and vegetable wastes.
Ponds
Anaerobic ponds followed by some kind of aerobic process (like an aerated pond) are common
in the meat packing industry and achieve high removals. Processors of potatoes, corns, and apples
have also used anaerobic ponds.
Anaerobic ponds are typically deep (15 to 20 feet) and have a retention time of 2 to 20 days.
COD removals of 75 to 80% have been reported in the potato industry.10 However, anaerobic
processes often produce odorous gasses. Consequently, if a natural floating cover of grease and
solids does not form, an artificial cover may have to be constructed.
Filters
A recent innovation is the anaerobic filter. Physically, the filters are covered tanks filled with
large rock or other open media. The waste is passed through the tanks and the generated methane
gas collected. The methane gas can be used to heat the incoming waste or it can be burned. These
filters have been used as a pretreatment device for a wheat starch waste. Removals of COD have
been high (up to 80%) with a net retention time of 2 days in the tanks.
Once the anaerobic growth is fully developed and attached to the rock, if the filter can be
shut down for a period of months and restarted with only minor losses in efficiency, it is a sub-
stantial advantage for fruit and vegetable processors. Filters can be used as a pretreatment unit on
selected waste (containing high dissolved organics, and low suspended solids) before discharging
to a municipal system.
33
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AEROBIC SYSTEMS
Principles
Aerobic systems are the most common type used for waste treatment. The general relation
characterizing the biochemical reaction is:
food (BOD) + O2 + nutrients (N, P, etc.) -» cells + CC>2 + H2O
As opposed to anaerobic treatment, typical cell yields range from 0.3 to 0.6 pounds per pound
of BOD oxidized. Depending on how the treatment system is operated, the requirements for applied
oxygen will vary from 0.5 to 1.14 times the amount of BOD removed. Methods of getting this
oxygen to the cells are discussed later.
Nutrients, especially nitrogen and phosphorus, can be critical in the performance of aerobic
systems. The exact point at which nutrients become critical depends on the type of treatment
process, and how it is operated. More discussion on this is found in the section on nutrients.
The basic treatment unit in aerobic systems is a biological reactor (aerated basin, pond,
trickling filter). This reactor provides an environment for the conversion of soluble organic ma-
terial into insoluble micro organism cells. The subsequent unit is a secondary clarifier or pond
where the cells are allowed to settle. The settled cells, or sludge, may be either returned to the
biological reactor cell mass (the mixed liquor), wasted from the system (waste sludge), or stored.
As the result of biological growth, large volumes of organic solids are generated in secondary treat-
ment processes. These solids are typically very wet (0.5 to 1.0 percent solids by weight), voluminous,
and are difficult to dewater. In addition to the sludge resulting from biological growth, sludge also
results from the removal of suspended solids that are not biodegraded.
Several different biological systems are used to provide secondary treatment. In all cases, the
secondary treatment units must provide an environment suitable for the growth of biological
organisms. These treatment units depend on having enough oxygen to support aerobic decomposi-
tion of the organic matter. Most removals are given in terms of 5-day BOD removal which will range
from 80- to 99-percent removal depending on a great range of variables, including waste character-
istics, treatment flow pattern, treatment environment, system loading, and operating conditions.
A summary of design factors for each process discussed is included in table III-3.
The following characterizes the aerobic conversion of waste (including a generalized scheme
of this conversion):
BOD5 is a measure of oxygen required.
BOD5 is not a direct measure of O2 required to treat waste.
BOD5 does not measure the total amount of O2 required to treat a waste.
BOD 5 x 1.4 is about equal to the total O2 needed to treat a waste.
BOD 5 is a way to measure the O2 required to stabilize a mixture of organic compounds.
Organic Compounds + Oxygen + Nutrients -> End Products
34
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Sludge Production
CO2 + H2O
Synthesis 1 Endogenous 1 ^ i
1 Ib BODc 1 » =T n fi lh VSS 1 ^ -J
D
°2
2 Equivalent
1.4 Ibs O2
f
0.5 Ibs O2
(cells) 02 ""I
^ 0.1 5 Ibs VSS
A 0.4 5 Ibs
0.9 Ibs 02
cells
I
0.67 Ibs O2
portion of
cells not easily
degraded
0.23 Ibs O2
Minimum O2 theoretical = 0.5 # O2/3 BOD5
Maximum O2 theoretical = 0.5 + 0.67 = 1.17 #O2/#BOD5
Minimum sludge production = 0.15 #/#BOD5
Maximum sludge production = 0.6 #/#BOD5
Non-biodegradable solids in the waste add directly to the amounts produced by biodeg-
radation of organics.
Aeration Methods
An artificial aeration system is required for nearly all aerobic treatment systems. These aera-
tion systems can be classified according to two approaches: (I) bubbling compressed air into the
waste through the use of diffusers (diffused aeration), and (2) entrainment of air in the waste through
agitation of the surface (mechanical aeration).
The following aerators are used in these systems:
Types of aerators Description
Mechanical surface
Low speed Rotor, gear box drive
High speed Propeller, direct drive from motor
Diffused air
Fine bubble Socks, stones
Large bubble Holes in pipe
Sparge air Combines mechanical and diffused
Hinde tubes Small tubes with slits
35
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Types of aerators Description
Helical Spirial static diffuser
Brush Rotating brush
Aspirator (Penberthy) Venturi aspirator
Inka grid Low pressure system
Aeration equipment is rated at standard conditions: 20 degrees centigrade, zero dissolved
oxygen in water being aerated, transfer rates and solubilities for tap water (clean water), at sea
level.
Actual operating conditions will likely be: 4 degrees to 30 degrees centigrade, 0.5 to 2.0 mg/1
dissolved oxygen, reduced transfer rates and solubility for wastewater above sea level.
The actual net transfer under field conditions for all types of aeration systems will range from
45 to 60 percent of the rated condition.
Blowers in diffused-air systems compress air to about 8 psi. The compressed air then enters
the waste through diffusers, which are mounted close to the bottom of the aeration basin. Many
methods exist to diffuse air into solution with an efficiency of only about seven percent. Diffusers
clog easily from particles in the waste or from deposits that build up on the diffuser pores. Diffusers
should be mounted so they can be easily removed for cleaning. As a rule, to maintain complete
mixing, 20 to 30 cfm (cubic feet per minute) should be applied to each 1,000 cubic feet of basin
volume. Diffused-air systems deliver around 1.0 pound of oxygen per horsepower hour at field
conditions. There are a great variety of diffused air systems which have differing transfers.
A typical mechanical aerator is shown on figure III-5. These aerators may be either rigidly
mounted in a tank or installed with floats, so they can rise and fall with the water level, as illustrated.
The amount of power to maintain complete mixing with these units is one-half to one horsepower
per 1,000 cubic feet of basin volume.
Nutrient Requirements
In addition to air and waste, a biological system needs nutrients to maintain a healthy state.
Microorganisms need about the same trace minerals that humans do, but the lack of these is rarely
a serious problem in waste treatment. The most common deficiencies in fruit and vegetable
processing wastes are nitrogen and phosphorus. The amount of these nutrients required for a given
microorganism depends on its age. However, the amount of nutrients required for a treatment
process depends both on the age of the organisms and the numbers of cells generated during the
reduction of BOD. A BOD/nitrogen/phosphorus ratio of 100:5:1 is usually adequate. However,
high-rate systems with no available nitrogen or phosphorus in the waste could require a ratio of
100:10:2. As seen in table III-4 most fruit and vegetable processing wastes have a nutrient
deficiency. Ratios lower than 100:5:1 may be adequate for aerated ponds and systems with a very
long sludge age. In rare cases, nutrients such as iron and magnesium must be added. All nutrients
need to be in a soluble form to be used by the microorganisms.
36
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Table 111 -3.Secondary treatment design criteria for fruit and vegetable wastewaters
Conventional activated sludge
Aeration basin
Mixed liquor suspended solids (MLSS)
Food/micro-organism ratio (F/M)
Sludge age (days)
Aeration time
Depth
Aeration type
Returned sludge
Secondary clarifiers
2,000 - 4,000 mg/l
0.1 - 0.5 Ib BOD removed/lb MLSS
3- 10days
16 48 hours, but controlled by sludge age,
F/M, and MLSS concentration
10-20 feet
Floating mechanical aerators or diffused aeration
25 100% of incoming plant flow
Typical overflow rate is 400 gpd/sf.
Solids or floor loading 1525 Ib/sf/day
based on influent plus recycle flow
Most secondary clarifiers are circular
Pure oxygen activated sludge aeration basin
Aeration basin
Mixed-liquor concentration (MLSS)
Food/micro-organism ratio (F/M)
Sludge age (days)
Aeration time
Depth
Aeration type
Returned sludge
Secondary clarifiers
3,000 - 5,000 mg/l
0.5 - 0.7 Ib BOD removed/lb MLSS
6- 10 days
824 hours, but controlled by sludge age,
F/M, and MLSS concentration
15 feet
Diffused, high-purity oxygen in mechanically agitated
covered tanks
25 100% of incoming plant flow
Same as conventional activated sludge except floor
loading 25 - 40 Ib/sf/day
Aerated ponds
Depth
Hydraulic retention time
Aeration
Mixing
7- 15 feet
20 - 45 days
1.1 - 1.3 lbO2/lb BOD applied (~40lbO2 per
hp/dayj
Minimum 8 10 hp/mg
Maximum - 14 - 20 hp/mg
37
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Table 111-3.Secondary treatment design criteria for fruit and vegetable wastewatersCon't.
Activated biofilter
Filter tower
Height
Configuration
Hydraulic loading
BOD loading
Media type
Aeration basin
Clarifier
20 feet
Circular with rotating waste distributors, or
rectangular with stationary distributor
1 2 gpm/sf of tower area including recycle
0.15 - 0.3 Ib BOD per cubic foot of filter
media
Redwood slats or various plastic shapes
Same criteria as an activated sludge aeration basin.
Assume that 40 - 60% of the influent BOD has
been removed by the tower
Same criteria as an activated sludge clarifier.
Sludge can be returned to both the aeration basin
and the filter tower. Floor loading 15 to 25
Ib/sf/day
Trickling filter (high rate)
Filter
Depth
Configuration
Hydraulic loadings
BOD loading
Recirculation
Media type
Clarifier
3-8 feet
Circular with rotating distributor
20-90gallons/sf/day
20-50 Ibs BOD/1,000 cf
100 - 400% of influent flow
Rock media: 1 3 inches diam.
Plastic media now being used
Overflow rate 400 - 600 gpd/sf
Floor loading of 20 - 35 Ib/sf/day
Rotating biological contactor
Contactor
Clarifier
Size to be determined by pilot testing
Overflow rate 400 600 gpd/sf
Floor loading 20- 35 Ib
NOTE:Clarifiers for trickling filters and RBS units are usually controlled by the overflow rate rather than floor
loading because these systems do not use mix liquor as a part of the process. Overflow rates of 400 to
600 gpd/sf are common.
38
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Table 111-4. Available nutrients for fruit and vegetable wastewaters5
Commodity
Apricots
Artichokes
Asparagus
Beans
Beets
Blueberries
Broccoli
Brussels sprouts
Caneberries
Carrots
Cauliflower
Cherries
Corn
Cranberries
Dry beans
Dehydrated onions
Figs
Grapes
Jams & jellies
Lima beans
Mushrooms
Okra
Olives
BOD/N/P ratio
100/1. 67.23
100/4.4/.8
100/6.5/1
100/4.4/.8
100/3.1/3.9
100/.9/.1
100/7.2/1
100/7.2/.7
100/1.8/.2
100/2.3/.5
100/6.8/.9
100/1.7/.2
100/2.8/.5
100/.7/.1
100/5.4/.6
100/2.1/.004
100/1.3/.2
100/1.6/.1
100/.1/.01
100/5.4/.6
100/7/1.9
100/5/.6
100/1.2/.1
Commodity
Onions
Peaches
Pears
Peas
Pickles (avg.
sweet & dill)
Pimentoes
Pineapples
Plums
Potato chips
Potatoes
Prunes
Raisins
Rhubarb
Sauerkraut
Spinach
Squash
Strawberries
Sweet potatoes
Tomatoes
Zucchini
BOD/N/P ratio
100/3.1/.5
100/1.4/.3
100/1/.01
100/6/.7
100/1/.2
100/2.8/.3
100/.6/.1
100/.6/.1
100/1. 1/.2
100/2.4/.4
100/.7/.2
100/.7/.2
100/3.0/.5
100/4/.5
100/7.7/.6
100/3.7/.7
100/1.6/.3
100/1.3/.2
100/4/.6
100/5/.8
NOTE:Domestic waste ratio is 100/20/2
The values in table III-4 are taken from the EPA effluent guidelines report5 and presumably
were developed from analyses for total nitrogen and phosphorus. Because most of the nitrogen
found in fruit and vegetable processing wastes is in the form of insoluble organic nitrogen, it is not
readily available for microorganism use. Thus a greater amount of supplemental nitrogen is needed
than table III-4 would indicate.
39
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Motor (TEFC)
Water lubricated shaft
bearing
Metallic pumping chamber
deflector and draft core
> t \
\ ^ Ceramic coated shaft
Figure 111-5. Floating mechanical aerator (high speed)
Stabilization Ponds
Stabilization ponds are large, usually 3 to 6 feet deep, and retain the wastewater for a
period of 60 days or longer. Oxygen needed for biological action comes primarily from the
action of photosynthetic algae, although some oxygenation occurs as a result of the contact be-
tween the pond surface and the atmosphere (wind action). Depending on the degree of treatment
desired, waste stabilization ponds may be designed to be operated in a variety of ways, including
series and parallel operations. In some cases, treatment may include tertiary ponds for algae re-
moval prior to effluent discharge.
Because of the high strength of fruit and vegetable processing wastes, BOD loadings deter-
mine the necessary size of the ponds. The loading should be kept at 20 to 40 pounds BOD per
acre per day. A lagoon area of about 300 acres would be required for a 1-mgd flow with a BOD
of 1,000 mg/1. Stabilization ponds can cause several problems that result in their being abandoned:
Growth of algae (resulting in high effluent suspended solids and BOD).
Odors, especially during startup.
Several algae removal systems are under study and some are under construction; however,
there is no full-scale, long-term operating experience.11
40
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Aerated Lagoons
Aerated lagoons are similar to stabilization ponds except that oxygen is artificially added
either by compressed-air diffusion or by mechanical agitation (figure III-5). Supplemental aeration
allows the pond volume to be greatly decreased and the depth increased, although ponds are seldom
deeper than 12 feet with special provisions for mixing. They can thus reduce surface area and heat
loss. The biological life in an aerated lagoon will contain limited numbers of algae and will be
similar to that found in activated sludge.
Adequate mixing must be provided in aerated lagoons to distribute oxygen (8 to 15 horse-
power per million gallons). However, the mixing should not be over 15 horsepower per million
gallons or sludge will be suspended. The exact limits depend on the type of aeration as well as
the depth and configuration of the lagoon. At least 0.2 pounds of sludge are produced for
each pound of BOD removed. These solids will accumulate and must be removed or they will
discharge in the effluent. Lagoons in series are often used for solids separation. The second
lagoon serves as a polishing pond.
Table III-5 is an estimated cost of an aerated lagoon for a 1-million gallon-per-day waste-
water flow. In addition to the assumptions given in table III-5, the following should be noted:
Lagoon depth is 10 feet.
Inside slope 3:1; outside 2:1.
Mechanical aerators: 12 at 40 HP each, and one at 20 HP; all moored to the bottom.
Total land for both lagoons is 11 to 12 acres.
Material used in dike construction comes from the lagoon excavation.
It was assumed that the 30 mg aerated pond would have to be excavated below the ground.
This results in 150,000 yards of excavation. Assuming a cost of $4 per yard for excavation and if
the pond could be constructed with a balance of cut and fill, the excavation cost would be about
$144,000. It is assumed the settling pond would be lined with concrete. The estimated liner cost
is $7,500.
The liner assumed is 30 mil hypolon, 440,000 ft2 at $.44/ft2 = $178.800.
If the pond could be constructed without a liner and with balanced cut and fill, the estimated
cost would be $517,700.
This would reduce the amortized capital cost of $91,600.
Activated Sludge
In activated sludge, waste is discharged into an aerated basin. The presence of abundant
organic food, nutrients, and oxygen is favorable to sustaining a large concentration of micro-
organisms. Ordinarily, dissolved-oxygen levels are kept at 1 to 2 mg/1. The combination of the
waste flow and microorganisms is called mixed liquor. The mixed liquor flows from the aeration
basin to clarifiers where the microorganisms settle from the liquid. The settled microorganisms
(activated sludge) are returned to the aeration tank to maintain the mixed-liquor concentration.
The excess microorganisms produced and non-biodegraded materials removed in secondary treat-
ment are wasted from the system (waste activated sludge). A schematic of an activated sludge
plant is given in figure III-6. Design criteria for activated sludge processes are given in table III-3.
Figures III-7 and III-8 are photographs of activated sludge plants treating potato wastes.
41
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Table 111-5. Cost summary for aerated lagoon system
Criteria
Flow:
Season:
Amortization:
1 mgd average
2 mgd peak
90 days
10 years at 12%
Engineering, legal and contingency costs
included at 25% of construction cost
Excavation and disposal cost at $4/cy
October 1975 dollars
Schematic
Aerated
lagoon
Aerators
Settling
pond
to
Assumptions
Costs
Both aerated lagoon and settling pond
are lined earthen basins
30-day detention time in aerated lagoon
400 gpd/SF overflow rate in settling pond
No nutrient addition for this example.
(However, practice may require nutrient
addition. See table 111-6.)
Power cost at 2 cents/kW-hr
Labor at $7.00 (including overhead)
Capital
$517,700
Operation and maintenance
Labor 4,500/yr
Power (500 hp) 16,000/yr
Total $20,500/yr
Amortized capital plus O&M
Unit cost
$112,100/yr
125rf/1 OOOgal
-------
Floating mechanical aerator
Effluent
From primary clarifier
or cannery
/
Return solids pump
Waste solids
Figure 111-6. Activated sludge plant.
An operational problem with activated sludge plants is bulking. Sludge bulking is the in-
ability of the activated sludge to settle or thicken in the secondary clarifier. This occurs com-
monly in plants treating wastewater containing a high percentage of carbohydrates (corn,
apples, etc.) because of the formation of filamentous, or stringy, bacteria. Unless carefully
designed and operated, plants will develop filamentous growth and consequently not perform
efficiently.
There are many variations of activated sludge processes; however, all operate basically the
same. Unit arrangements and methods of introducing air and waste into the aeration basin ac-
count for the variations. A small, compact, prefabricated activated sludge plant is shown in
figure III-9.
Tables III-6 and III-7 give cost estimates for an activated sludge plant (1.0 mgd), both with,
and without, sludge digestion and dewatering. In addition to the assumptions listed in the tables,
the following should be noted:
Activated sludge food to micro-organism ratio (F/M) is 0.2, where:
F = pounds BOD in influent per day, and
M = pounds of mixed liquor under aeration
Aeration basin sludge age: 6.5 days
Aeration basin mechanical aerators: 10 to 50 HP each
Two 40-foot diameter clarifiers
Area requirements for activated sludge alone: about 2 acres
Area requirements with digestion, dewatering: about 3 acres
Aerobic digester sludge age: 15 days
Two gravity dewatering units for waste sludge concentration
Raw-waste activated sludge to truck: 95,000 gal/day at 0.8% solids
43
-------
Table 111-6.Cost summary for activated sludge system
Criteria
2 mgd peak
Season: 90 days
Amortization: 10 years at 12%
Engineering, legal and contingency costs
included at 25% of construction cost
October 1975 dollars
Assumptions
Lined earthen aeration basin with 2-day
detention time F/M = 0.2
Two conventional secondary clarifiers with
400 gpd/sf overflow rate
Cost of NH4OH at $184/ton (100% basis)
cost of H3P04 at $0.21 5/lb SOL'N.
Power cost at 2 cents/kW-hr
WAS disposal cost at 1.5 cents/gal for
20-mile haul
Labor at 9 hrs/day at $7.00/hr.
Schematic x< NH^OH & H3PO4
/Y Nutrient addition
Secondary clarifiers
r-^ /
Vj /
' Waste activated
sludge
basi n \
/^ Process flow to 1
Aerators / downstream J
- f fji i ~ LJ rtment /
-U*; vv^-L/ ** rt**r~f
f A Ts\* / V r*-ir
/ »fgf; I L JLj
/ »" TJ TT IT
^ Process I \^r
flow >. Return sludge
Costs
Capital Operation and maintenance
$645,000 Labor $5,000/yr
Nitrogen 2,900/yr
Phosphorous 5,000/yr
Power (500 HP) 16,000/yr
Waste sludge8 disposal 130,000/yr
Miscellaneous 16,100/yr
Total $175,000/yr
Amortized capital plus O&M $289,1 50/yr
Unit cost 321^/1 000 gal
aNormally, the sludge from the clarifier is further thickened and then dewatered. See table III-7.
-------
Table 111-7.-Cost summary for activated sludge with aerobic digestion and dewatering
CJl
Criteria
Flow:
Season:
Amortization:
1 mgd average
2 mgd peak
90 days
10 years at 12%
Engineering, legal and contingency costs
included at 25% of construction cost
October 1975 dollars
Schematic
Aeration basin
Secondary clarifiers
Nutrient addition [NH4OH & H-POJ
Sludge
dewatering
units
Polymer I
Return sludge
Waste activated sludge
Aerobic digesters
Conveyor
Dewatered sludge to storage hopper
Assumptions
See assumptions for activated sludge
system (table 111-6)
Dewatered sludge trucking costs at
$3.70/ton dry solids/mile (Approximately
30 mile haul at 20% solids)
Polymer addition at 6 Ib/ton solids
Polymer cost at $2.25/lb
Unit dewatering rate at 1000 gph for
digested sludge
Labor at 10hrs/day @ 7.00/hr.
Costs
Capital
$1,115,000
Operation and maintenance
Labor
Nitrogen
Phosphorous
Polymer for sludge
Power (575 H.P.)
Dewatered sludge disposal
Miscellaneous
Total
Amortized capital plus O&M
Unit cost
$6,300/yr
2,900/yr
5,000/yr
3,000/yr
18,500/yr
17,000/yr
5,800/yr
$58,500/yr
$255,850/yr
284/1 OOOgal
-------
S3..
'94.
Figure 111-7. Activated sludge plant. (Courtesy of CH2M HILL)
Figure II1-8. Activated sludge plant. (Courtesy of CH2M HILL)
46
-------
Aerobic digester section '
Figure II1-9. Package activated sludge plant. (Courtesy of Cantex)
Digested, dewatered, waste activated sludge to truck: 35 cubic yards/day at 9% solids
Small building for motor control center and pumps
Small building to house dewatering units.
Oxygen Activated Sludge
The activated sludge process that uses high-purity oxygen (HPO) merits discussion. This system
uses covered multi-stage (3 to 5 stage) aeration basins into which oxygen-rich gas is fed. Oxygen
utilization is approximately 90 percent. Oxygen concentration varies from above 90 percent in the
inlet gas to about 50 percent in the exhaust gas. Mechanical mixers project through the roof to mix
the basin contents and entrain the oxygen. Dissolved oxygen concentrations can be maintained at
high levels (1 to 15 mg/1, versus 1 to 2 mg/1 in conventional plants) in the wastewater flow. The
basin effluent is clarified in standard secondary clarifiers and sludge is returned to the first stage
aeration basin. Excess sludge is wasted as it is in a conventional activated sludge plant.
Current knowledge of fruit and vegetable processing waste and the high-purity oxygen, activated-
sludge process suggests that when compared with more conventional activated sludge systems, this
modified process results in the following advantages:
47
-------
A sludge more settleable in secondary clarifiers, resulting in lower secondary effluent
suspended solids and BOD levels. This has been observed in the treatment of other
high-strength carbohydrate wastewaters. It is believed to be related to the high dissolved
oxygen concentration within the system.
Retention of wastewater heat necessary for effective treatment in cold climates.
Less land area.
The capital cost of a high-purity oxygen system is usually greater than conventional systems,
but it should be considered where the need for biological secondary treatment is indicated. Com-
monly used design criteria for HPO processes are given in table III-3.
Activated Biological Filter (ABF)/Activated Sludge
Activated bio-filtration (ABF) was developed in recent years to take maximum advantage of
artificial filter media characteristics. Plastic and redwood biological filter media have high void-to-
total-volume ratios and high surface-to-total-volume ratios. These characteristics make high organic
loadings possible.
In the original ABF system, secondary clarifier underflow is combined with the secondary
plant influent and pumped to the bio-filter. Bacteria grow on the filter media and in the waste-
water flow. Portions of the bacterial mass, which continuously slough from the media, join the
bacteria growing in the wastewater and settle out in the secondary clarifier. Most of the bacterial
mass settled in the secondary clarifier is returned to the filter influent to maintain a high concentra-
tion of bacteria in the flow through the filter. The flow scheme has the appearance of activated
sludge, which gives rise to the name of activated bio-filtration.
A recent modification of the ABF process has been the insertion of an activated sludge aeration
tank between the ABF tower and the final clarifier. The effluent from the tower is sent through the
aeration basin for further treatment. The aeration basin is designed to assimilate 40 to 60 percent
of the organic loading to the tower. The return sludge from the final clarifier is usually returned to
the tower. At least one of the suppliers of plastic media has recently indicated that there will be
better performance if the sludge is not returned to the tower. In this case, the filter would simply
be a roughing filter ahead of the activated sludge units.
This ABF-activated sludge process has shown great promise in successfully treating high carbo-
hydrate wastewaters (potatoes) without developing the sludge bulking problems of activated sludge.
The process is also resistant to shock loadings. Figure 111-10 shows a circular ABF tower operating
on combined domestic and potato waste. The towers (about 20 feet high) may also be square or
rectangular. Figure III-ll is a schematic of the ABF-activated sludge process. Design criteria for
ABF-activated sludge plants are given in table III-3.
Rotating Biological Contactors (RBC's)
This system has many large diameter, lightweight discs mounted on a horizontal shaft in a
semi-circular shaped tank. The discs are rotated slowly with the lower half of their surfaces sub-
merged in the wastewater. Bacteria and other micro organisms grow on the disc surfaces and in the
tank. In rotating, the discs carry a film of wastewater into the air where it absorbs oxygen. The
mixing created by the disc rotation also transfers oxygen to the tank contents. Shearing forces
cause excess bacterial growth to slough from the discs and into the wastewater. The sloughed solids
flow out with the treated waste to the secondary clarifier for separation and disposal.
48
-------
Figure 111-10. Activated biological filter tower. (Courtesy of CH2M HILL)
Waste from
primary
treatment
1
Return
solids
Distributor
Filter
Recycle
Waste solids
to disposal
Aeration
basin
Figure 111-11. Activated biological filter activated sludge plant.
49
-------
Rotating biological contactors have been successfully applied to municipal and some industrial
waste. Operation is simple and power requirements are low, but the capital costs of the discs are
high. Before this system is applied to the treatment of fruit and vegetable processing waste, pilot
plant testing and economic analysis should be done to answer the following questions:
(1) Effect of wastewater pH.
(2) Effect of wastewater strength.
(3) Temperature of waste.
(4) BOD and suspended solids removal efficiency related to BOD and suspended solids unit
loadings.
(5) Capital and total costs compared to alternative systems.
Trickling Filters
One of the oldest biological treatment systems is the trickling filter. Typically, the filter is a
6-foot deep bed of 2-1/2 to 4 inch rock over which the wastewater is distributed. Atmospheric oxygen
moves naturally through the void spaces in the rock. In the environment thus created, biological
slimes (consisting mainly of bacteria) flourish and colonize on the rock surfaces. As the waste
trickles over the surface of the growths, organic matter is removed. As the growths become more
and more concentrated, their attachment to the media surface is weakened and they are washed
from the filter. The solids are then removed by sedimentation as in other high-rate processes. See
figure 111-12 for a diagram of this process.
There are a number of variations of the biological filter process, depending on the waste load-
ings applied to the filters, the arrangement of the units, and the number of filters employed. Trick-
ling filters are very stable and easier to operate than activated sludge plants. Removals of BOD
seldom exceed 80 percent, and the effluent contains a higher level of suspended solids than the
activated sludge process. For this reason, no new trickling filter plants are now being designed to
meet the new EPA requirements. Common design parameters for trickling filters are given on
table III-3.
Distributor
Filter media
Influent
Effluent
Recycle
Waste
solids
Figure 111-12. Trickling filter plant.
50
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TERTIARY (ADVANCED) WASTE TREATMENT
With the exception of two or three rapid-sand filter installations, tertiary treatment is not
being practiced by the fruit and vegetable processing industry4'5. Only those processes with the
greatest possible applicability are discussed here (table III-8). These processes are: chemical'
precipitation, filtration, carbon absorption, ion exchange, and reverse osmosis. In this discussion,
it is assumed that any advanced waste treatment process is treating effluent from a secondary
treatment plant.
CHEMICAL PRECIPITATION AND SEDIMENTATION
The primary application for this step as a tertiary process is the removal of suspended solids
that escape secondary treatment. The process involves the use of a coagulant to (1) form a
precipitate with the waste that settles out, and (2) form a metal precipitate which "sweeps"
out other colloidal matter. The coagulants commonly used are lime, alum, or ferric chloride.
Polymers are sometimes used as a primary coagulant, but most often as an aid.
Simplified chemical reactions illustrating the action of these coagulants are given below:
Lime
Ca(OH)2 + Ca(HCO3)2 -» 2CaCO3 (4) + 2H2O
Alum
A12(SO4)3 + 6HCO3 -» 3SO4 + 2A1 (OH)3 (j) + 6CO2
Ferric Chloride
FeCl3 + 3H2O -» Fe (OH)3 (|) + 3H + 3d"
( (-J.) indicates a solid material or precipitate that settles out.)
Table 111-8.-Tertiary waste treatment applications
Process
Carbon adsorption
Chemical precipitation
Filtration
Ion exchange
Reverse osmosis
COD
X
X
X
X
X
BOD
X
X
X
X
X
Pollutant to be
Suspended
solids
X
X
X
emoved
Dissolved
salts
X
X
X
X
Refractory
organics
X
May remove
some refractory
compounds
X
X
51
-------
The overflow rate on the chemical clarifier can be from 500 to 2,000 gpd/sf, depending
on the coagulant used. Expected solids concentration in the sludge varies from 3 to 7 percent.
If lime is used as a coagulant, the floe is very dense and settles easily. The use of alum increases
sulfates in the water, and this floe is more difficult to settle and dewater than lime. The use of
iron increases the chloride concentration in the water and can cause low pH problems. Chemical
precipitation, however, is the most efficient way to prevent deterioration of effluent during
biological plant upsets.
FILTRATION
Filtration reduces suspended solids of colloidal sizethose that will not settle out.
Historically, a single media was used with a filtration rate of 0.05 to 0.13 gpm/sf, and has been
termed slow-sand filtration. Rapid-sand filtration, now in use, has a filtration rate of 1 to 5
gpm/sf. In addition to single-media filters, dual- and tri-media filters are also used.
Filters may be classified by five parameters as follows:
(1) Direction of flow
(2) Type of media
(3) Flow rate
(4) Gravity or pressure
(5) Cleaning method.
Today the filters used most successfully on wastewater are downflow filters using dual-
or tri-media. A filtration rate of 2-1/2 to 5 gpm/sf is common. Cleaning is by hydraulic
backwash, commonly at a rate of 15 gpm/sf. This backwash may be preceded by air backwash
and assisted by surface wash. Often a filtration aid like polymer or alum is added to the feed
to strengthen floe and improve solids removal. Figure 111-13 shows a small package mixed-media
pressure filter installation.
Single-media filters can achieve high removals but ordinarily remove only 70 percent of the
influent solids under ideal conditions. Seventy-five to ninety percent of the head loss occurs in the
first inch of this media, which indicates that filtration is really a surface phenomenon. In addi-
tion, single-media filters tend to "blind off" at the surface, reducing filter runtime, and thus
necessitating more frequent backwashing.
Mixed-media (dual- or tri-media) filters generally give longer runs and better removals, even
though the media is slightly more expensive. The idea behind mixed-media is to provide a con-
stant gradation of pore size in the filter from coarse on the surface to fine on the bottom. The
gradation in pore size allows filtration and storage of solids throughout the depth of the bed,
as opposed to a single-media bed in which filtration takes place in the top.
As a rule, filters cannot be used when the influent suspended solids exceeds 100 mg/1 or
when the size distribution of solids changes rapidly so that selection of media type or mix is im-
possible. It is usually uneconomical to use filters if the required backwash volume exceeds 10 per-
cent of the incoming flow. A better choice would be a chemical clarifier. A key to successful
operation of filters is adequate backwash. There must be provisions to break up surface slime
and caking.
52
-------
r T --
«*«
i +
Effluent
Backwash
Filter tanks containing
mixed media
Figure 111-13. Pressure filter. (Courtesy of Neptune Microfloc)
Table III-9 gives a cost estimate for mixed-media filtration of 1 mgd of secondary effluent.
It is assumed that filtration is a workable option for additional removal of suspended solids, al-
though this is not always the case. Secondary effluent suspended solids may be high enough to
"blind off" filters after a short-run time (less than 6 hours). When this happens, filter backwash
volumes become so large that the secondary plant capacity must be significantly increased to
handle the backwash return flow.
In addition to those shown on table III-9, the following assumptions in the development
of the estimates should be noted:
2 horizontal pressure filters
Filter rate: 2.5 gpm/sf
150,000 gal lined earthen surge pond ahead of filters
60,000 gal concrete clearwell
60,000 gal backwash return surge pond
Polymer dose: 1 mg/1.
53
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Table 111-9. Cost summary for filtration
Criteria
Flow:
Season:
Amortization:
1 mgd average
2 mgd peak
90 days
10 years at 12%
Engineering, legal and contingency costs
included at 25% of construction cost
October 1975 dollars
Schematic
Backwash storage
pond
Surge
pond.
Backwash
water to
plant
head works
Clearwell
To downstream
treatment
Assumptions
n
Two pressure filters with 2.5 gpm/ft
application rate
18 gpm/ft backwash rate
Lined earthen surge pond
Concrete clear well
Labor 3 hrs/day at 7.00/hr
Chemicals: 1 ppm poly at $2.25/lb.
Costs
Capital
$271,000
Operation and maintenance
Labor
Polymer
Miscellaneous
Total
Amortized capital plus O&M
Unit cost
$2,000/yr
1,700/yr
300/yr
$4,000/yr
$51,960/yr
57.7^/1000 gal
-------
CARBON ADSORPTION
Carbon adsorption removes refractory organic compounds like those causing taste and
odor (tannins, lignins, and ethers). It also removes residual COD, BOD, insecticides, herbicides,
and related components. However, few tests have been run with activated carbon treating fruit
and vegetable processing wastewater.
Carbon adsorption can be accomplished either by granular or powdered activated carbon.
Powdered carbon still has many problems, not the least of which is its recovery for reuse.
However, the technology of granular activated carbon in columnar beds is well developed.
The influent to a granular carbon process must be low in BOD, COD, and suspended solids.
The effluent from carbon adsorption can go to ion exchange, or reverse osmosis, and/or dis-
infection.
A design criterion is to use upflow expanded bed columns with a contact time of 20 minutes.
The hydraulic rate should be between 6 to 7 gpm/sf and the granular carbon used should be an 8 x 30
mesh.
Carbon adsorption is the only method to remove refractory organics, with the exceptions of
reverse osmosis, distillation, or freezing (but these are not competitive).
As a rule, activated carbon cannot be expected to remove reducing sugars from fruit and
vegetable processing wastes. However, some organic acids can be removed.
If the influent contains high concentrations of BOD and COD, the column can become anaer-
obic and produce hydrogen sulfide. This is generally not a problem with filtered secondary effluent.
The problem can be solved by frequent backwashing, chlorination, or the addition of sodium nitrate.
ION EXCHANGE
There are many applications of ion exchange, ranging from the selective removal of specific
substances such as ammonia, phosphates, or nitrates, to the complete demineralization of water.
Ion exchange to remove calcium and magnesium is currently practiced by many processors for
boiler water treatment. The regenerant for these softeners is sodium chloride.
The simplified equations below show the action of a typical cationic ion exchange resin, during
both use and regeneration. R indicates the resin.
Use: RN&2 + Ca++ -» RCa + 2Na+
Regeneration: .RCa + 2NaCl -> RN&2 + CaCl 2
Demineralization of wastewater requires both cationic and anionic resins to remove cations
(like sodium) and anions (like phosphates), respectively. These can be mixed in a single bed, but
more often, they are set up in a series of separate beds. Since 1965, pilot tests on ion exchange have
been run in Pomona, California, where carbon column effluent is used as the feed water. The system
contains four resin beds in series: two cationic and two anionic. The cationic resins are regenerated
with sulfuric acid and the anionic with ammonia. Historically, removals have been as follows:
COD 63.0%
Total dissolved solids 86.7%
Thirteen percent of the volume treated becomes a waste brine.
55
-------
Pilot work by Rohm and Haas, Inc., using their modified Desal ion exchange process on dis-
infected secondary effluent, gave the following removals:
COD 83.3%
TDS approximately 90%
No full-scale, long-term installations of ion exchange for dissolved solids reduction have been
operated on wastewater. Little work has been done on a pilot scale to test dissolved solids removal
in food processing wastewater.
Three of the largest problems in the use of ion exchange are (1) in achieving efficient regen-
eration of the resin, (2) the disposal or recovery of the waste regenerant solution, and (3) the length
of the resin life.
REVERSE OSMOSIS
The natural process of osmosis has been known since the middle of the eighteenth century, but
it was not until the 1950's that experiments were conducted in reverse osmosis. If fresh and saline
water are separated by a semipermeable membrane, the natural tendency is for the fresh water to
migrate through the membrane into the saline water until the concentrations of the salts on both
sides of the membrane are equal. The driving force to accomplish this appears as a pressure differen-
tial called osmotic pressure. In reverse osmosis, this osmotic pressure is overcome by pumping to
reverse the process, which leaves the salts behind and makes fresh water from saline water.
The semipermeable membrane is now commercially made of a cellulose acetate. While reverse
osmosis is applied in the reclamation of sea water and brackish water, its use on wastewaters has
fouled the membrane. In theory, reverse osmosis has the capacity to remove more than 90 percent
of inorganic ions, and most organic matter.
The most extensive experience in reverse osmosis has been gained from pilot plants in Pomona,
California. These plants achieved the following removals from domestic activated sludge effluent:
COD 88.5%
TDS 92.1%
Twenty-five percent of the volume treated went to waste as brine, but this fraction can be re-
duced to 15 percent. The flux, or flow rate, through the membrane is about 10 gpd/sf. Pressure used
was 750 psi.
Some low-molecular weight organic compounds like amines, alcohols, and acids are not re-
moved by reverse osmosis. Reverse osmosis has the greatest potential for technological improvement
of any process for removing dissolved solids. Currently, however, reverse osmosis is costly. Work is
continuing to increase the flux and the product-to-waste ratio, and to develop methods of disposal
of the highly concentrated brine.
CHLORINATION
Disinfection by chlorination is often practiced in domestic water and waste treatment. Disin-
fection is required because disease carrying organisms, or pathogens, are present in the water or
waste. Chlorination is also used in the fruit and vegetable processing industries for odor and slime-
growth control in flumes and process units.
56
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As long as sanitary or domestic waste is kept separate from processing wastewater, there will
be no need for final disinfection for pathogen removal, except where it is required to meet water
quality standards. However, some fruit and vegetable processors are disinfecting the effluent from
their secondary treatment plants.
If a local requirement is based on total coliforms then disinfection will be required. A cost
estimate for chlorination of 1.0 mgd of secondary effluent is given in table 111-10. The critical
assumptions in the estimate are given in the table.
Chlorine also oxidizes BOD and some organic compounds. The additional chlorine demand of
these compounds must be satisfied before adequate disinfection can occur. This has proved to be a
major problem in stabilization pond effluent, where the algae exerts a high-chlorine demand.
OPERATION AND MAINTENANCE
Every treatment system requires regular care and attention, regardless of the skill of the de-
signer and the nature of the treatment process. Adequate operation and maintenance are paramount
in achieving the greatest possible efficiency from a treatment system. The person responsible for the
operation must have a thorough understanding of the basic theory of waste treatment. A complete
and current operation and maintenance manual is a must for any system. Monitoring and testing
must be adequate to give the operator all needed data to determine system performance and to judge
the need for changes in operation.
The staff responsible for operating treatment systems should receive special training. Training
is available from the state and also from many community colleges. Membership in the Water Pollu-
tion Control Federation also offers valuable exposure to operating information through literature
and local meetings.
Regulatory agencies increasingly recognize the need for proper operation and maintenance. A
requirement in the future may be that every industrial treatment plant operator be certified by a
state agency. Some states now require certification. In addition, laboratories performing tests to be
submitted to regulatory agencies may also require state certification.
An aid to determining staffing requirements is the EPA's Estimating Staffing for Municipal
Wastewater Treatment Facilities.12 As stated in the title, this manual is oriented toward municipal
treatment facilities. Frequently, in an industrial setting, fewer operating man hours are required,
because the plant can be operated as one portion of the total processing plant. The industrial plant
can usually share maintenance crews, cleanup crews, supplies, office and laboratory space, technical
staff and other items.
Finding adequate qualified staff can be particularly difficult in the seasonal fruit and vegetable
processing industry. Two options to staffing your own plant are:
Use an outside consultant with operating staff.
Contract the local public agency for operation of your treatment facility.
57
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Table 11 \-10.-Cost summary chlorination system
01
oo
Criteria
Flow:
Season:
Amortization:
1 mgd average
2 mgd peak
90 days
10 years at 12%
Engineering, legal and contingency costs
included at 25% of construction cost
October 1975 dollars
Schematic
Chlorine
solution
Process
flow
Chlorinator
Process flow
to final
disposal
Assumptions
Costs
Concrete chlorine contact chamber
with 1 hour detention time at average
flow
Chlorine dosage at 10 mg/l
Chlorine cost at 27.5 cents/pound
Small chlorination building included
Labor at $7.00/hr 1 hr/day
Operation and maintenance
Labor
Chlorine
$ 600/yr
2,200/yr
Total
Amortized capital plus O/M
Unit cost
$2,800/yr
$9,530/yr
10.64/1 OOOgal
-------
Chapter IV
LAND TREATMENT AND DISPOSAL
INTRODUCTION
Land disposal or treatment is the application of wastewater onto land by a conventional irriga-
tion procedure. Treatment is provided by natural processes (chemical, physical and biological) as the
effluent moves through the "filter" provided by the cover crop and soil mantle. Part of the water is
lost to the atmosphere through evapotranspiration, part to surface water by overland flow, and the
remainder percolates to the ground water system. The method of application, the site, and the load-
ing rate determine the percentage of flow to each destination.
Land treatment is deceptively simple. Although there are successful systems, there are
many which have, and will fail as a result of, misapplications and increasing restrictions on ground-
water quality, surface runoff, air quality, and other environmental factors.
System failures do not usually occur in the first few years. Failure is more likely to occur after
five years or more. The common symptoms and causes of failure are:
Symptom
Runoff resulting from decreased
soil permeability
Runoff resulting from organic
overload
Increase in ground water nitrate
Decreases in cover crop quality
Mounding of water under the site
resulting in cover crop loss
Salt build-up in soil resulting in
in crop loss
Cause
Solids build-up on or in soil. Physical and
chemical changes in soil.
Slime layer forms on surface of ground.
Root zone becomes anaerobic.
Accumulation of nitrogen in soil and
percolation to ground water.
Nutrient imbalance.
Horizontal movement of water in soil not
adequate to keep ground water below root zone.
Salts from waste flow concentrated in soil as
result of evaporation and transpiration.
These problems can be avoided or corrected with good engineering and system management.
PROCESSES
Land treatment is done in several ways (see figure IV-1). For discussion, these have been divided
into four processes: overland flow, irrigation, high-rate irrigation, and infiltration-percolation (see
table IV-1). Most fruit and vegetable processors use some kind of high-rate irrigation by spray nozzles.
The objectives and characteristics of each of the four processes are distinctly different. The
most suitable process depends on the characteristics of the site, the type of waste to be applied, and
environmental regulations. Overland flow is especially suited to the treatment of wastewaters high
in BOD and suspended solids, such as from tomato processing. Removal efficiencies greater than
90 percent have been reported for processing plants using overland flow.
The infiltration-percolation process is least suited to treatment and disposal of high BOD and
suspended solids wastes because most of the wastewater, with its pollutants, may enter the ground
water untreated.
59
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Evapotranspiration
Tailwater ditch
or receiving
stream
Percolation (slight or none)
OVERLAND FLOW
Evapotranspiration
I !
Slight
or no
Tailwater
ditch for
runoff
/ ^" Sf** runoff
±1x U Ww*
* flrtion - * . * . -
\i \ \ \
XX"
/ 77> V
4^
Percolation
IRRIGATION
Evapotranspiration
Tailwater
ditch for
runoff if any
"ZLT .vlT,...
Slight runoff
Evapotranspiration
Infiltration
f T T
Infiltration
f I
[^rT^r^f
J)?^»^^\^222p±±j
Percolation
HIGH-RATE IRRIGATION
Percolation
INFILTRATION-PERCOLATION
Fig. IV-1. Land treatment processes
60
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Table IV-1.Land treatment and disposal processes
Process
Overland
flow
Irrigation
High-rate
irrigation
Infiltration-
percolation
Objective
Maximize waste
treatment. Crop is
incidental. Allow
runoff.
Maximize agricultural
production.
Maximize waste treat-
ment by evapotranspira-
tion and percolation
without runoff crop
production a side
benefit.
Recharge ground
water or filter water;
crop may be grown
with little or no benefit.
Suitable
soils
Low permeability
and/or high-water
table.
Suitable for irrigated
agriculture.
More permeable soils
suitable for irrigated
agriculture; may use
marginal soils if coarse
texture.
Highly permeable
sands and gravels.
Typical
annual
application
60-300"
12-60"
24-120"
240-6000"
Dispersal
of applied
water
Most to surface runoff.
Some to evapotranspiration
and ground water.
Most to evapotranspiration.
Some to ground water; little
or no runoff.
Evapotranspiration and ground
water; little or no runoff.
To ground water some
evapotranspiration; no runoff.
Impact on
quality of
applied waste
BOD and SS greatly
reduced. Nutrients re-
duced by fixation and
crop growth. TDS
increased in runoff.
BOD and SS removed.
Most nutrients consumed
in crop or fixed. TDS
greatly increased in
percolated water.
BOD and SS mostly
removed. Nutrients
reduced. TDS sub-
stantially increased
in percolated water.
BOD and SS reduced.
Little change in TDS
of percolated water.
-------
Some nutrients are used by crops in overland flow, but most will be carried away in the runoff
water. Most of the nutrients are carried into the pound water or subsurface drainage system in the
infiltration-percolation process. Few, if any, plants are grown on the site for nutrient uptake.
The irrigation process is most effective for removing the nutrients in wastewater. The applica-
tion rate is limited so the nutrient loading does not exceed the crop nutrient requirement. The
nutrients are removed from the site by crop harvest.
PRETREATMEIMT REQUIREMENTS
Some pretreatment of wastewater is necessary before land application. The waste is usually
screened to avoid plugging the distribution system. Screens (10 to 20 mesh) are necessary to pre-
vent clogging of the sprinkler nozzle. Silt and other suspended particles that may hinder operation
of the distribution and application system should be removed. The pH of the wastewater must be
controlled for application on land because pH outside the range of 6.4 to 8.4 may render some
nutrients inaccessible to plants.
Design modification may be needed to remove oil and grease, avoid soil sealing, remove specific
ions (such as sodium) and avoid loss of infiltration capacity or poisoning of plants.
APPLICATION METHODS
Three methods are commonly used for application of wastewater: (1) sprinkler irrigation,
(2) surface irrigation, and (3) drip (or trickle) irrigation. In sprinkler irrigation, water is sprinkled
onto the land to simulate rainfall (figure IV-2). Sprinkler and surface irrigation are most commonly
used for wastewater application. Water is distributed in furrows or small channels, or by flooding
in surface irrigation. With drip irrigation, water is applied through small holes (emitters), spaced
along the supply line. Drip irrigation is impractical for use with fruit and vegetable process
wastewater because suspended material can clog the holes.
Figure IV-2. Spray irrigation system. (Courtesy of Ch^M HILL)
62
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The selection of an irrigation method depends on soil characteristics, crop, operation, main-
tenance, topography, costs, water supply, weather, and need for control of runoff. Each method
has distinct advantages.
Distribution of water by sprinkler irrigation is controlled by the selection and design of the
equipment used. Surface irrigation depends on soil permeability and soil uniformity for an even
distribution of wastewater. If soil conditions are suitable, surface irrigation normally offers
economic advantages in power and hardware requirements. Both sprinkler and surface methods
have been used in freezing conditions.
SYSTEM SELECTION
The various processes and application methods are not necessarily interchangeable. The
process selected will depend on the specific waste, site, and discharge limits. Some waste charac-
teristics influencing the selection are solids, BOD, nutrients, salts, and pH.
Location
Site characteristics that will influence selection are as follows:
Soil and topography must be suitable for the disposal process (overland flow,
sprinkling, ponding).
Areas with continual winds (greater than 10 mph) cannot be used without
great allowances for sprinkler droplet drift.
Slopes must not exceed 15 percent.
The site must not have shallow ground-water depths (less than 4 to 5 feet)
The site should be a short distance from the processing plant, and it must be
easily accessible.
The site should allow for buffer zones, sight screens, roads, etc.
The site preparation requirements must not be prohibitive.
The site must be properly zoned.
The site should be situated to allow for expansion.
Discharge limits that will influence selection are as follows:
Permissible nitrate in ground water
Limits on runoff
Limits on constituents in applied waste or harvested crop.
Loadings
The amount of liquid that can be applied depends upon the infiltration and percolation capacity
of the soil. Quality discharge limits placed on deep percolation to ground water or return flow to
63
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surface streams may require a limited loading rate or extensive pretreatment. A soil-crop system has
a finite capacity for removal of various pollutants. If this capacity is exceeded, the system will
eventually fail, odor will develop, and pollution of ground water or a nearby stream can result.
The various constraints on loading may be classified as hydraulic, treatment, and chemical
as follows:
Hydraulic constraints:
Infiltration capacity of the soil
Permeability of the root zone
Permeability of the underlying soil
Treatment constraints:
Capacity of the soil to remove and oxidize BOD
Capacity of the soil to filter and assimilate suspended solids
Chemical constraints:
Capacity of the soil to remove major plant nutrients (nitrogen, phosphorus and
potassium)
Sensitivity of the soil to other wastewater characteristics such as salt content,
sodium-adsorption ratio, and pH.
Hydraulic Constraints
The infiltration capacity of a soil is the rate at which water can be applied without runoff.
Previous erosion or lack of a dense vegetative cover will reduce infiltration capacity and require a
reduction in application rates. The infiltration capacity of the soil will influence the choice of
irrigation methods. Infiltration rates limit the instantaneous (daily or hourly) rate of application,
but rarely will it limit the total seasonal application.
Permeability of the soil determines the allowable percolation rate. It will establish the total
effluent and precipitation that can be applied. In a year with high rainfall, the amount of effluent
which can be applied must be reduced.
Three to five feet of aerated soil are required in the root zone to provide sufficient treatment
of the applied effluent. If the permeability of the site is not adequate for the amount of waste
applied, the ground water will rise into a root zone and drown the cover crop, causing treatment
failure.
If no runoff is allowed, the maximum hydraulic loading is the sum of the soil moisture de-
pleted by evapotranspiration, plus the quantity of waste that can be transmitted through the root
zone. Maximum hydraulic loadings, less evapotranspiration under ideal conditions for different
soils, are given in table IV-2. Daily loadings should not exceed the rates given in the first column
in inches per day. The average loading throughout the season should not exceed the rates given in
the right-hand column. One inch is approximately equal to 27,000 gallons per acre.
64
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Table IV-2. Estimated maximum hydraulic loading of
wastewater effluent for various soil textures (ideal conditions)
Soil root zone
Fine sandy
Sandy loam
Silt loam
Clay loam
Clay
Movement through
Infiltration rate
inches/day15
15.0
7.5
3.5
1.5
0.5
the soil root zone3
Percolation rate
inches/year0
300
180
90
40
10
aOoes not include evapotranspiration
"Rate not to be exceeded on any one day.
Reduce if site is sloped
cRate not to be exceeded in a growing season (or year)
To avoid runoff, or ponding on the surface, the instantaneous sprinkler-application rate should
not exceed the infiltration rate (measured in inches per hour). The following are typical infiltration
rates for these soil types:
Fine sand
Sandy loam
Silt loam
Clay loam
Clay
1.0 + inches/hour
0.5-1.0
0.3-0.7
0.2 - 0.4
0.1 - 0.2
The allowable loading rate for infiltration-ground-water recharge depends on the soil and surface
geology. Recharging a water-bearing aquifer also depends on the permeability of the aquifer itself.
Treatment Constraints
BOD is associated with both suspended solids and dissolved organic material. The BOD asso-
ciated with suspended solids will remain close to the surface where the soil organisms have access
to atmospheric oxygen to break the material down. The BOD in the dissolved organic material will
percolate through the unsaturated zone of the soil and, under aerobic conditions, be removed during
percolation. If the loading is too great, the soil will become anaerobic, and the crop and treatment
process will fail. Table IV-3 lists typical BOD loading rates of various soil conditions for processes
that rely on an aerobic root zone for BOD removal. Experience indicates that higher loadings are
possible if the site is irrigated for only a few weeks each year and is well maintained.
Clogging of soil is most often due to incomplete biological breakdown of organics in an
anaerobic environment. Aerobic conditions can be maintained by intermittent application of the
allowable amount of waste. A day of application followed by several days of rest is typical.
65
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Table IV-3.BOD loading rates
Process
Irrigation and high-rate irrigation
Fallow soil with no fresh organics
Fallow soil following addition of
organic residues
Soil with growing plants
Estimated recommended maximum
BOD load to be added on well
aerated soil 13
Overland flow
Infiltration/percolation
Lbs/acre/hr
1-2
2-4
3-6
-
-
-
Average summer
summer season
Ibs/acre/day
36
72
108
100
40-100
600
If the soil becomes sealed with inert suspended solids, such as silt, it can usually be opened
by harrowing or disking. The amount of silt which can be accepted without a loss of permeability
can be estimated from an analysis of the soil and the inert solids.
Suspended solids of up to 200 Ibs/acre/day14 have been applied. However, a loading limit of
about 70 pounds per acre per day is more typical.
Chemical Constraints
Typically, the total nitrogen found in fruit and vegetable wastewaters is mostly organic nitrogen.
All of this nitrogen is not immediately available for plant use. The "mineralization rate" of organic
nitrogen to nitrate is such that 20 to 30% of it becomes available for plant use in the first year, 5%
in the second, 2% in the third, and so on. These figures were developed from domestic sewage sludge
(primary and secondary), but recent information indicates that up to 40 per cent of the nitrogen in
fruit and vegetable processing waste will mineralize in the first year.13
Nitrate is the only form of nitrogen used by crops. Removing the grown crops is a major
method of removing nitrate from the soil.
Irrigation systems that allow no runoff or percolation to the ground water should have an
applied rate of total nitrogen controlled to match the nitrogen removed in the crop. The nitrogen
removed is 100 to 300 pounds per acre per year, depending on the extent of irrigation, climate, crop,
soil, temperature, etc., plus the amount lost through nitrification-denitrification.
If nitrogen application is not controlled, the excess nitrogen (beyond that removed by the crop,
nitrified-denitrified) will enter the ground water or receiving stream as nitrate. The nitrification-
denitrification mechanism will only work if an anaerobic soil layer is present below the aerobic
surface layers (a condition which is not controllable).
Caustic peeling processes used for commodities such as potatoes and peaches may result in
high sodium wastes. If the sodium content is high compared to the calcium and magnesium content,
it will be absorbed by the soil and replace the calcium and magnesium salts present. As the ex-
changeable sodium increases, the soil becomes more alkaline, and adverse growing conditions will
occur. These can reduce permeability in some clay bearing soils. The potential effect of sodium on
the soil is measured by the sodium-adsorption ratio, SAR, of the waste.
66
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SAR =
where Na, Ca, and Mg, are measured in equivalents per liter.
Generally, the SAR must not exceed 6.0 to 9.0, depending on the soil. Gypsum (CaSC>4) can
sometimes be applied to the soil to increase the amount of sodium that can be applied. If the SAR
of the waste is high, additional soil analysis will be necessary to determine if the waste can be applied
directly, or if the sodium should be eliminated from the wastewater.
Some wastewater may contain certain constituents that retard plant growth or present poten-
tial health hazards. Table IV-4 lists recommended concentration limits of these constituents for
continuous irrigation on all soils. These limits are for non-sandy, non-acidic soils.
Table IV-4.-Recommended maximum limits of inorganic constituents for irrigation wafer15
Inorganic
constituents
Recommended limit
for irrigation on all
soils
Aluminum, mg/l
Arsenic, mg/l
Beryllium, mg/l
Boron, mg/l
Cadmium, mg/l
Chloride, mg/l
Chromium, mg/l
Cobalt, mg/l
Copper, mg/l
Fluoride, mg/l
Iron, mg/l
Lead, mg/l
Lithium, mg/l
Manganese, mg/l
Molybdenum, mg/l
Nickel, mg/l
Selenium, mg/l
Vanadium, mg/l
Zinc, mg/l
Sodium-adsorption ratio
pH
5.0
0.10
0.10
0.50
0.01
70.0
0.10
0.05
0.20
1.0
5.0
5.0
2.5
0.20
0.01
0.20
0.02
0.10
2.0
6.0 - 9.0
6.4 - 8.4
OPERATION AND MANAGEMENT
The major tasks involved in operating a land treatment system include: (1) maintaining the
proper application rate and frequency, (2) managing the soil and cover crop, and (3) monitoring the
performance of the system. Scheduling wastewater applications will depend on the weather. During
wet months, the amount that can be applied will depend on daily precipitation. Applications will
also have to be coordinated with harvest. For the most efficient operation of the system during wet
months, irrigation should be scheduled on a daily basis to incorporate the daily measurement of
precipitation and not exceed the application criteria. Thus, a storage pond is often required to hold
the wastewater during times when it cannot be disposed. This pond must be adequately aerated to
prevent odors.
67
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Experience with potato wastewaters has shown that spray irrigation facilities can be operated
during winter months when the field ices. Ice accumulates during the winter and melts in the spring.
The thaw is usually gradual enough that BOD loading rates are not greatly exceeded and odors do
not occur. If the thaw is too fast, ground water pollution and odor can result.10
Proper soil management is required to maintain the infiltration rate and prevent erosion. To
accomplish this, a healthy cover crop should be established and general soil conservation practiced.
Grasses and other crops keep the infiltration rate high by preventing droplets from sprinkler
irrigation from puddling and sealing the surface. A good cover crop is also necessary to remove
nutrients from the soil treatment system. The crops must be periodically harvested and removed
from the site. Monitoring the wastewater characteristics, soil, crop, ground water and runoff are
very important for successful operation of a land treatment system. Monitoring also gives advance
warning of developing problems. Failure in any part of the system, in wastewater quality, soil infil-
tration, crop growth, or ground water drainage can eventually cause failure of the whole treatment
and disposal system.
COSTS OF ALTERNATIVE APPLICATION METHODS
Costs for different land wastewater treatment systems are compared in table IV-5. This table
is an update of table 28 in the EPA's Wastewater Treatment and Re-Use by Land Application}-6
In that EPA report, several assumptions were made which are not consistent with those made for
the cost summaries in this report. Thus, the costs in table IV-5 are only useful in illustrating the com-
parative costs of the three land treatment systems. They should not be compared with the other cost
estimates in this report.
68
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Table IV-5. Comparison of capital and operating costs for 1-mgd systems^
-------
Chapter V
SOLIDS DISPOSAL
SOURCES AND NATURE OF SOLIDS
Because of the nature of fruits and vegetables, a great many solids are generated during process-
ing. These solids, or residuals, may exceed the mass of solids generated by treatment of the effluent.
The handling and disposal of in-plant and waste treatment solids or sludges varies not only with
the characteristic of each, but also with the governmental classification of the solids. Currently,
transportation and final disposal of waste solids from treatment plants are more closely regulated
than waste solids from fruit and vegetable processing.
IN-PLANT SOLIDS (RESIDUALS)
Only about 20 to 30 percent of many vegetables are finally used for human consumption. Some
of this residue is left in the field during harvest, but a large portion is generated in processing. Table
V-l lists estimates, developed in 1971, of the percentages of raw products that show up as solid
waste, or residuals, in fruit and vegetable processing. The table also shows the amount of total solid
waste that is used as a by-product and the amount that is finally handled and disposed of as a waste.
By-product utilization is primarily for animal feed. None of the waste is reprocessed and used for
human consumption.
The use of residuals in livestock feed is not possible for most fruit and vegetable processors.
Most of the residuals used for feed come from citrus, corn, pineapple and potato processors. These
four alone produce about 75 percent of the nation's waste used for animal feed.
It is worth noting why the processors of these four items can use these residuals in livestock
operations:
1. The residuals are generated over a long season (up to a year). The exception is corn, but
corn can be stored for later use. Most other commodities are processed over a very short
season, and the waste cannot be stored for any reasonable length of time without de-
composing.
2. The products are processed in cattle raising areas.
3. With the exception of potatoes, all the wastes from these four commodities are produced
dry. Potato screenings and primary clarifier sludge are used as cattle feed in some areas.
In the Salinas Valley of California, trimmings from local vegetables are used as cattle feed.
Such items as asparagus, broccoli, lettuce, and artichoke trimmings and process screenings are used.
However, most food processors must resort to some type of land disposal for their residuals.
70
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Table V-1 .Percentage of solid waste produced in fruit and vegetable processing
17
Product
Apples
Beans, green
Beets, carrots
Citrus
Corn
Olives
Peaches
Pears
Peas
Potatoes (white)
Tomatoes
Vegetables (misc.)
Percent
total waste
produced
28
21
41
39
66
14
27
29
12
33
8
22
Percent
utilized as
by-product
19
10
21
38
62
12
9
9
8
29
2
9
Percent
handled as
solid waste
9
11
20
1
4
2
18
20
4
4
6
13
NOTE - These are average percentages of total incoming raw products.
TREATMENT PLANT
Depending on the processes used and the extent of treatment, solids generated in waste treat-
ment can be quite significant. Table V-2 lists the types of treatment and the characteristics of the
general types of solids produced. Two main categories are screenings and sludges. Sludges are
generated in primary, secondary, and, to a minor extent, tertiary treatment processes.
Table V'-2.- Treatment plant solids characteristics for fruit and vegetable wastewaters.
Type of treatment
Primary
Biological sludge
Pure-oxygen activated sludge
Lime clarifier sludge (Tertiary)
Sludge characteristic
Percent solids: 1-5%. A higher percentage of
silt in the sludge can raise the percentage of
solids to 20 - 40%.
0.5 - 1% solids from the clarifier underflow.
1 -2% solids.
7% sol ids.
Screenings
The amount of screenings varies according to the nature of the waste and screen mesh size.
Screenings are wet and will drain if allowed to stand. Draining the water does not reduce the
volume of screenings to be hauled away, but makes them easier to handle and more acceptable by
landfill sites.
71
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Primary Treatment Sludge
Primary treatment wastes are in the forms of sludge from the bottom of the clarifier, scum
from the top of the clarifier, and float from the top of dissolved-air flotation units.
Dissolved-air flotation float commonly has a total solids concentration of about four to six
percent, and is not difficult to pump. Sludge from the bottom of clarifiers can be very difficult to
pump, depending on the product being run. For example, field dirt from tomatoes and potatoes
can be thickened to about 40 percent solids, which can then be pumped with only positive dis-
placement pumps. This same mud will only settle and concentrate to about 20 percent solids in
a tank or pond without a thickening rake. An organic sludge from a primary clarifier will prob-
ably not exceed a concentration of three to five percent solids.
The actual mass (pounds per day) of sludge or float from primary treatment will be a func-
tion of the raw product. The volume (gallons per day) will be a function of both the product
run and the primary treatment process used.
Secondary Treatment Sludge
The masses of sludges from the secondary treatment processes are a result of the process
used, the BOD load, and the inert suspended solids load. The biological processes used in
secondary treatment all produce sludge. In biological treatment, dissolved BOD is transformed
into microorganism cellular matter, which then settles in the final or secondary clarifier. The
largest sludge producing processes are the high-rate processes described in Chapter III. Of these,
the activated sludge process produces the most sludge. Stabilization ponds and aerated ponds
accumulate sludge on the bottom of the ponds.
An activated sludge plant, operating at a high rate (or low sludge age) will produce 0.5 to
1.0 pounds of microorganisms for each pound of BOD treated. In addition to the production
of up to 0.5 pounds of microorganisms per pound of BOD removed, added sludge results from
the non-biodegradable suspended solids, both volatile and nonvolatile, in the influent to secondary
treatment. Consequently, it is not uncommon for the total secondary sludge production to be
0.8 to 1.0 pounds per pound of BOD removed. Sludge from secondary treatment systems is
still biologically active and will putrefy. This can cause an intolerable odor. If the sludge contains
no domestic wastes, it may be possible to spread and dry the sludge quickly on a disposal site
or agricultural land, and then plow it into the soil.
Secondary sludge is difficult to dewater. Raw, undigested secondary sludge has a total
solids content of only one-half to one percent. In addition, the cellular matter in the sludge is
only fifteen percent solids.6 Unless the cell membranes are ruptured, microorganisms cannot
be dewatered to greater than ten percent solids. Cells can be ruptured by heating or slow freez-
ing although natural freezing can be used in some climates. Commercially available heat treat-
ment systems which have been used for municipal waste activated sludge are costly and have
not been used in the fruit and vegetable processing industry.
Tertiary Treatment Sludges and Concentrates
With the exception of chemical clarification, none of the tertiary treatment processes dis-
cussed earlier generates a solid waste. Reverse osmosis and ion exchange produce a waste brine
or concentrate, which is probably best handled by evaporation and disposal in a landfill. Spent
carbon in columns, if not regenerated, becomes a solid waste that is usually acceptable for dis-
posal in a sanitary landfill. Backwash water from filters is usually stored and pumped at a con-
stant rate back to the treatment plant headworks.
72
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Sludge from tertiary chemical clarifiers varies in handling ability according to the coagulants
used in the treatment process. Lime sludge is quite dense (about seven percent solids) and can
be dewatered rather well with vacuum filters or centrifuges. Lime sludge lines should be over-
sized to allow for scaling in the lines and cleaning. Alum sludge, however, is quite light,
gelatinous, and difficult to dewater. Ferric chloride sludges are usually not difficult to dewater,
but they are messy. Vacuum filters are usually used on ferric sludges. Unless a secondary plant is
upset, tertiary chemical clarifier sludge will contain few organics and does not require further
stabilizing the sludge to prevent putrefaction.
SLUDGE HANDLING
Table V-3 lists the available options most commonly used in handling waste treatment
sludges. Treatment and disposal of waste treatment solids require a substantial portion of the
cost of treatment (tables III-6 and III-7).
DIGESTION
There are two types of biological sludge digestion processes: anaerobic and aerobic. Anaerobic
digestion has been practiced for many years at municipal treatment plants across the country.
Anaerobic systems are prone to upset and must be heated to 90° F for good operation. The
tanks must be covered to collect the generated gas, which usually contains about 65 percent
methane and can be used as a fuel.
A well-operating anaerobic digester will destroy about 50 to 60 percent of the volatile, or
organic fraction, in the sludge. It operates well on domestic primary sludge alone, although few
process sludges have been digested alone. The required retention time of sludge in a digester is
20 to 80 days when maintained at 90° F.
Aerobic digestion is more practical than anaerobic digestion for seasonally operated plants
treating only food processing waste. Aerobic digestion allows the metabolic processes of the
microorganisms used in treatment to continue, but in the absence of food (BOD). The organ-
isms continue metabolizing at decreasing rates (termed "endogenous respiration") in the digester.
Aerobic digestion will reduce the organic content of sludge up to 40 percent. Detention time
of the sludge in aerobic digestion is 10 to 20 days. Enough air is supplied in the open digester,
either by diffusion or mechanical means, to satisfy the oxygen requirements of the organisms.
Regardless of the method of digestion chosen, the digester must be kept operating after
the end of the processing season to stabilize the remaining sludge.
Table V-3.Solids handling options
Digestion
Anaerobic
Aerobic
Thickening
Gravity
Dissolved air flotation
Centrifuge
Dewatering
Vacuum filter
Centrifuge
Pressure filter
Dewatering belts
Drying beds
Disposal
Sanitary landfill
Disposal on soil
AnimaJ feeding3
Composting
Use of waste activated sludge for animal feeding operation is not approved by the U.S. Food and Drug
Administration.
73
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THICKENING AND DEWATERING
Thickening is used to reduce the volume of sludge to enable the use of a smaller dewatering
device or to control sludge solids concentration for optimal operation of the dewatering devices.
Three units are commonly used for thickening sludge: gravity thickeners, flotation thick-
eners, and centrifuges. Flotation thickeners are the same as air-flotation clarifiers, but operated
at higher solids loading rates. Gravity thickeners look like ordinary clarifiers, except the clarifier
rake is rotated faster to convey and agitate the sludge blanket. Representative design criteria for
thickeners are given in table V-4.
Dewatering lowers water content of sludges to facilitate disposal, whether by landfill or by
incineration. Before sludge can be hauled in open trucks, it should be dewatered so that it does
not flow. Several kinds of dewatering units are available. The most common are vacuum filters and
centrifuges; however, filter presses and capillary action devices may also be used.
Vacuum Filters
A common type of vacuum filter is shown in figure V-l. The sludge is pumped into a vat
or pan at the base of the filter. The sludge level is usually high enough to submerge the filter
drum to about 30 to 40 percent of the diameter of the drum. A vacuum applied to the drum
(about 10 to 20 inches of mercury) picks up the sludge and forms a cake during the time the
drum is submerged. As the drum rotates out of the sludge, air is pulled through the sludge cake,
drying it so it falls or can be scraped from filter cloth. The yield, or rate of sludge dewatering
by this method, is about one to ten pounds of dry sludge per hour for each square foot of filter
drum area.
Many sludges must be conditioned with chemicals before they can be filtered. The addi-
tion of chemicals will usually increase the filter yield. A key to good filter operation is the
solids concentration in the filter feed.
Vacuum filters have a high capital cost and are difficult to operate. Sometimes they re-
quire a full-time operator.
Centrifuges
Three types of centrifuges are now commercially available. The solid bowl centrifuge
(figure V-2) is more suitable for the dewatering of inorganic sludges. Disc nozzle (figure V-3) and
basket centrifuges (figure V-4) work better on organic sludges, but the disc nozzle type tends
to clog at high concentrations of sludge, or when proper sludge pretreatment (grit removal,
screening) is not provided. Several basket centrifuges installations are now operating on
secondary sludge.
Other Methods
Filter presses or pressure filters work well on some sludges. They are, however, quite ex-
pensive and can be difficult to operate and maintain.
About three different units on the market use a combination gravity and capillary action
to dewater sludge. These units rely on a porous cloth to suck water from the sludge as it is
squeezed between rollers. These units are easy to operate but have a low capacity. They cannot
be universally applied to different sludges, and appear to work best on waste activated sludges
from domestic treatment plants.
74
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Table V-4. Design criteria for solids handling devices for fruit and vegetable wastewaters
Digestion
Anaerobic
Retention time
Ideal temperature
Volatile solids reduction
Methane production
Solids loading
Aerobic
Retention time
Solids loading
Oxygen requirement
Volatile solids reduction
20 - 30 days, depending on whether the digester is heated
90 - 100°F
50 - 60%
8-12 cf/lb volatile solids destroyed
Standard Rate: 0.03 - 0.10 Ib volatile solids/cf/day
High rate: 0.1 - 0.4 Ib volatile solids/cf/day
10-20 days, depending on the sludge age of the activated
sludge system and the ambient temperature
0.1 - 2.0 Ib volatile solids/cf/day
1.5 - 20 Ibs/lb of volatile solids destroyed
Up to 40%
Thickening
Gravity
Solids loading
Overflow rates
Dissolved-air flotation
Solids loading
Overflow rates
Unox sludge
Air-to-sol ids ratio
Recycle rate
Pressure
4 - 15 Ibs solids/sf/day, depending on the concentration
of the incoming sludge
400 - 900 gpd/sf
1.5-2 Ibs/sf/hour
1,400 - 5,000 gpd/sf
3 Ibs/sf/hour
0.01 - 0.1 Ib/lb
50 - 800%
60 - 70 psi
Dewatering
Vacuum filters
Common yields
Cake total solids content
Solids capture
Centrifuges
Cake total solids content
Solids capture
Common capacities
1 - 4 Ibs of dry solids/hour per sq ft of drum area for
organic primary sludge
8 - 10 Ibs/hr/sf for properly conditioned silt and clay
11 - 13% for primary sludge
20 - 70% for silt or clay. Not applicable for biological
sludges
85 - 95%
For primary sludges 4 - 25%, depending on the use of
chemicals and type of centrifuge. For waste activated
sludge
Solid bowl type: 6 - 10%, w/poly
Disk nozzle type: 4 - 5%, w/o poly
Basket type: 7 - 10%, w/o poly; 9-12%, w/poly
60 - 70% without chemicals
Up to 95% with chemicals
10 - 300 gpm
75
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Vat or pan
containing sludge
Filter cake hopper
Figure V-1. Vacuum filter. (Courtesy of Envirex)
Gear box
. . Adjustable
Inspection p|aJtedam
Pillow block plate
bearing
Conveyor
Impellers
Torque
Control
Feed tube
Drive pulley
/ Feed
4
i_j ;_T'r"
> 'f "*V Ft "r
Torque
overload
switch
Oil feed
to bearings
Oil discharge Frame
from bearings
Vibration switch
Conveyor discharge
nozzles
Figure V-2. Solid bowl centrifuge. (Courtesy of Sharpies)
76
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Centrate
Solids
Figure V-3. Disc nozzle centrifuge. (Courtesy of Sharpies)
Sludge Drying Beds and Lagoons
In areas with dry weather during the processing season, sludge drying beds and sludge lagoons
may be effectively used to dewater digested sludge for disposal. Drying beds are constructed with
sand bottoms and an underdrain system to capture water that percolates down through the
sludge. Digested sludge is pumped to each bed until the depth reaches about 18 inches; then
new sludge is pumped to another bed. Water evaporates from the sludge surface and also perco-
lates down through the bed. The drained water is returned to the treatment plant headworks
and when the sludge is sufficiently dry, it is taken out with a skip loader. Drying beds will have
only a slight musty odor, provided the sludge is adequately digested.
Sludge lagoons differ from beds in that they are deeper (about two or three feet), and do
not have a sand blanket with underdrains. If sufficiently dry, the sludge may be taken out with
a skip loader; otherwise it must be removed with a drag-line or dredge.
77
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Feed
Cake knife
Figure V-4. Basket centrifuge. (Courtesy of Sharpies)
METHODS OF SOLIDS DISPOSAL
The ultimate disposal of solids is becoming quite a problem. Most municipal treatment
plants are now disposing dewatered digested sludge in landfills. In-plant residuals from most
fruit and vegetable processing plants are disposed in landfills, usually owned by a public agency.
As these sites are filled, the processors are often asked to go elsewhere with their residuals,
screenings, and sludge. Some fruit and vegetable processors are now operating their own
land disposal system for residuals and treatment plant sludges.
78
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Many processors are able to dispose of some portion of the solid wastes, usually screenings,
to animal feeding operations. Due to the relatively low food value of screenings, they must be
mixed with grains or other common feed to provide a balanced diet for animals. Because of the
specific dietary requirements of many animals and the variability of goals of feeding (egg versus
meat production for poultry, for example), feeding requirements should be studied before starting
such a program. As a rule, the lack of nutrients in fruit and vegetable processing waste, coupled
with the seasonality of waste production, does not make the program attractive to animal feeders.
Transportation costs also make this option unattractive. Year-round operations (like potato pro-
cessing, for example) have been successful in setting up operations with local feed lots to accept
screenings and primary sludge.
LAND DISPOSAL OF WASTE SOLIDS
Residuals that are not converted to a by-product or animal feed are a major problem. Some
form of land disposal is usually the only option. Local regulations on land disposal are becom-
ing more stringent. Present practices should be carefully reviewed to avoid problems. In the
future, land disposal sites will have to be selected and operated with greater care. The follow-
ing is a general discussion of the factors to consider.
Silt, screenings, primary treatment sludges, and other dry waste can usually be incorporated
in a landfill or tilled into the soil. However, sludges from secondary and advanced waste treat-
ment would not be allowed in a landfill unless they were concentrated to a semi-solid. This
conversion is usually too costly to be practical. Therefore, the usual option for disposal of
dilute sludge is land spreading as a fertilizer. The limits for application of fruit and vegetable
waste solids to land are much less defined than for irrigation of liquids.
Land application of waste solids can be grouped into two methods: (1) fertilizer and (2)
disposal. The fertilizer method maximizes crop production while using the waste solids for nutri-
ents and soil conditioning. The loading rates are relatively low when compared to the disposal
method. Any soils suitable for high-production agriculture will generally be suitable for applica-
tion of waste solids. Clay soils or other soils with low-organic matter will receive special benefit
from residuals. Loading rates are about three to ten tons of dry solids per acre per year.
The disposal method maximizes disposal by incorporating large amounts of the solids into
the soil. This process is essentially a sanitary landfill, and most are now publically owned and
operated. A crop is maintained mainly to enhance site appearance, minimize wind erosion, take
up moisture, or use some of the nutrients in the residuals. Loading rates are about 5 to 50 tons
per acre per year. The leachate from landfills is a substantial problem because it is odorous,
high strength, and must be irrigated or treated for discharge.
Pretreatment Requirements
Waste solids vary greatly in character and pretreatment requirements, depending on the food
being processed, method of processing and method of treatment. Adjustment of the pH will be
required before land application if it is below 6.4 or above 8.4. These limits will vary, depend-
ing on the texture and buffering capacity of the soil and the loading rate. The solids may need
to be stabilized by biological treatment so that rapid degradation and odor do not result when
they are applied to land. The solids may need to be ground to allow better incorporation into
the soil and better operation of application equipment. Dewatering of solids may be advantageous
to a land disposal system. It will result in less volume and a smaller disposal site.
79
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Application and Incorporation Methods
Waste solids can be applied to land by several methods. As a liquid, they can be injected
or plowed under the surface, spread by truck or tractor, or sprayed. As a solid, they can be
spread by equipment such as manure spreaders. The selection of the suitable method depends upon
soil characteristics, crop, labor requirements, maintenance, topography, and costs.
In general, the solids must not be allowed to remain on the soil surface for a long time
because of odor, insect, wind, and water erosion problems which often result. Insect problems
may develop even when liquid waste solids are immediately incorporated into the soil. This
has been prevented by spreading the solids in a thin layer and allowing them to remain on the
surface just long enough to dry before tilling into the soil.
Site Selection Criteria
The criteria for site selection are generally the same as those listed for a waste effluent
irrigation site with the following exceptions:
Hydraulic loading will not be as great; therefore, the subsurface permeability is not
as important.
Because of the appearance of solids and the nature of the operation, a remote or
concealable site should be selected.
Application Rate Constraints
The application rate will be limited by several constraints.
Nutrient balances
BOD
Nitrogen
Solids loading rate
SAR
pH
All of the above-mentioned factors vary greatly between types of food processed and the
method of processing and waste treatment. The loading rate must be studied carefully in each
case. The hydraulic loading limits, infiltration capacity, root-zone permeability, and geologic
permeability are not usually limiting because only small amounts of water will be applied with
the solids. Solids must be incorporated into the soil as applied, or very shortly thereafter.
Limits exist on how much organic solids can be physically incorporated into the soil, and on
the soil's ability to decompose solids without causing plant toxicity problems. Limits on BOD,
nitrogen, SAR, dissolved salts, etc. are approached the same as for irrigation of effluent.
Management and Operation
Proper management and operation of a solids disposal system is as important as for a waste
effluent treatment and disposal system. A major factor for successful operation is the timing of
land application.
80
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In a fertilizer application system, where crop production is optimized, waste solids cannot
be applied and tilled into the soil while the crop is growing. Tillage would kill most crops.
Cropping areas and disposal areas can be alternated. The method of disposal usedeither
fertilizer or disposalwill depend greatly on who owns the site and who operates the system.
A farmer will want to maximize crop production, and a food processor will want to maximize
residual disposal. Other practices, such as crop and soil management and monitoring, are also
important as noted in the discussion of waste effluent treatment and disposal.
Cost of Residuals Delivery and Application
The cost of disposing of residuals onto land can vary greatly depending on the amount of
liquid in the residuals, the distance to be transported, and the method of delivery and applica-
tion. Some typical recent costs for hauling are given in table V-5. Actual costs vary consider-
ably due to differences in disposal sites, government regulations, availability of trucking firms,
and pretreatment requirements. The costs given in the table do not include pretreatment or site
preparation costs.
Table V-5.Cost ranges of hauling and disposal
Hauling of liquid sludge (4-15% TS) to
ponding site (20 mi haul)
Hauling of liquid sludge (4% TS) to farm
land (35 mi haul)
Hauling of screenings, mud to land fill
Hauling, spreading of dewatered sludge to
disposal site (5 mi haul)
Hauling, spreading of liquid sludge to dis-
posal site (5 mi haul)
Hauling of hazardous waste (acid, caustic)
to evaporation ponds
4 - 5 cents/gallon includes disposal fee of
3-1/2 cents/gallon
2 cents/gallon or $3.70/ton-mile
$4.00/cubic yard includes disposal
fee of $1.00/cubic yard
$1 - $2/ton-mile
$3 - $4/ton-mile
8 - 10 cents/gallon includes disposal
fee
81
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1 Handbook for Monitoring Industrial Wastewater, U.S. Environmental Protection Agency,
Cincinatti, Ohio, Aug. 1973.
"^Methods for Chemical Analysis of Water and Wastes, U.S. Environmental Protection Agency,
EPA-625/16-74-003, Cincinnati, Ohio, 1976.
^Standard Methods for the Examination of Water and Wastewater, (14th ed.), American Pub-
lic Health Association, New York, N.Y., 1976.
^Development Document for Effluent Limitations Guidelines and New Source Performance
Standards for the Apple, Citrus and Potato Processing Segment of the Canned and Preserved Fruits
and Vegetables Point Source Category, U.S. Environmental Protection Agency, Office of Air and
Water Programs, Washington, D.C., Mar. 1974.
^Development Document for Interim Final and Proposed Effluent Limitations Guidelines and
New Source Performance Standards for the Fruits, Vegetables and Specialties Segment of the Canned
and Preserved Fruits and Vegetables Point Source Category, U.S. Environmental Protection Agency,
Office of Water and Hazardous Materials, Washington, B.C., Oct. 1975.
6"Management of Solid Residuals," Proceedings, 1971 Research Highlights Meeting, National
Canners Association, Berkeley, Calif., Nov. 1971.
7 "Effluent Guidelines and Standards for Canned and Preserved Fruits and Vegetables Process-
ing Point Source Category, Apple, Citrus, and Potato Subcategories," Federal Register, Vol. 39,
No. 56, Mar. 21,1974.
8 "Effluent Guidelines and Standards for Canned and Preserved Fruits and Vegetables Point
Source Category," Federal Register, Vol. 41, No. 75, Apr. 16, 1976.
9 "Effluent Guidelines and Standards, Environmental Protection Agency," Code of Federal
Regulations, Title 40, Chapter 1, Subchapter N.
10 "Waste Disposal," Potato Processing, Chapter 21, AVI Publishing Company, Inc., 1975.
11 Proceedings, Fourth National Symposium on Food Processing Wastes, U.S. Environmental
Protection Agency, EPA-660/2-73-031, Dec. 1973.
12 Estimating Staffing for Municipal Wastewater Treatment Facilities, U.S. Environmental
Protection Agency, Mar. 1973.
13 Irrigation of Agriculture Lands, American Society of Agronomy, Agronomy Series No. 11,
Madison, Wis., 1967.
14 Survey of Facilities Using Land Application of Wastewater, American Public Works Associa-
tion, July 1973.
82
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15 Guidelines for Interpretation of Water Quality for Agriculture, University of California
Extension, January 15,1975.
16 Wastewater Treatment and Re-Use by Land Application, U.S. Environmental Protection
Agency, Office of Research and Development, Aug. 1973.
17 Waste Disposal Control in the Fruit and Vegetable Industry, Noyes Data Corporation, 1973.
83
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METRIC CONVERSION TABLES
Description
Length
Area
Volume
Mass
Force
Moment or
torque
Flow (volumetric)
Description
Precipitation,
run-off,
evaporation
Flow
Discharges or
abstractions.
yields
Usage of water
Untt
meter
kilometer
millimeter
micrometer or
micron
square meter
square kilometer
square millimeter
hectare
cubic meter
litre
kilogram
gram
milligram
tonne
newton
newton meter
cubic meter
per second
liter per second
Unit
millimeter
cubic meter
per second
liter per second
cubic meter
per day
cubic meter
per year
liter per person
per day
Recommended Units
Symbol Comments
m Basic SI unit
km
mm
^m or^i
m2
km2
mm2
ha The hectare (10,000
m2) is a recognized
multiple unit and will
remain in interna-
tional use
m3
t
kg Basic SI unit
9
mg
t 1 tonne = 1,000 kg
N The newton is that
force that produces
art acceleration of
1 m/s2 in a mass
of 1 kg.
N m The meter is mea-
sured perpendicular
to the line of action
of the force N
Not a joule
m3/s
l/s
Application of Units
Symbol Comments
mm For meteorological
purposes, it may be
convenient to meas-
sure precipitation in
terms of mass/unit
area (kg/m2).
1 mm of ram =
1 kg/m2
m3/s
l/s
m3/d 1 l/s = 864m3/d
m3/year
I/person/
day
Recommended Units
Customary
Equivalents"
3937m = 3281ft^
1.094yd
0.6214 mi
0.03937 m
3.937 X 105m= 1 X 104 A
1076sqft= 1 196 sq yd
0 3861 sqm. = 2471 acres
0 001550 sq m
2 471 acres
35.31 cuft = t.308cuyd
1. 057 qt = 02642 gal =
0.8107 X10-4 acre ft
2 205 Ib
0 03527 oz = 1543gr
0 01543 gr
09842 ton (long) -
1 102 ton (short)
0.2248 Ib
= 7 233 poundals
0.7375 Ib-ft
23 73 poundal-ft
15850gpm =
2,119cfm
1585gpm
Description
Velocity
linear
angular
Viscosity
Pressure or
stress
Temperature
Work, energy,
quantity of heat
Power
Unit
meter per
second
millimeter
per second
kilometers
per second
radians per
second
pascal second
centipoise
newton per
square meter
or pascal
kilo new ton per
square meter
or kilopascal
bar
Celsius (centigrade)
Kelvin (abs.)
joule
kilojoule
watt
kilowatt
joule per second
Symbol
m/s
mm/s
km/s
rad/s
Pa-s
Z
N/m2
or
Pa
kN/m2
or
kPa
bar
°C
°K
J
kJ
W
kW
J/s
Comments
1 joule = 1 N-m
where meters are
measured along
the line of action
of force N
1 watt = 1 J/s
Customary
Equivalents*
3281 fps
0003281 fps
2,237 mph
9 549 rpm
06722poundal{s)/sqft
1450 X 10 7 Reyn(M)
00001450 Ib/sq m
0 14507 Ib/sq in
14 50 Ib/sq in
(°F-32)/1 8
°C + 2732
2778X 10 7
kw-hr =
3.725 X 10 7
hphr- 07376
fMb - 9.478 X
10 Btu
2778X 10-"kwhr
44 25 ft-lbs/mm
1.341 hp
3.412 Btu/hr
Application of Units
Customary
Equivalents*
35 31 cfs
1585gpm
0.1835gpm
264 2 gal/year
0 2642 gcpd
Description
Density
Concentration
BOD loading
Hydraulic load
per unit area.
e g., filtration
rates
Air supply
Optical units
Unit
kilogram per
cubic meter
milligram per
liter (water)
kilogram per
cubic meter
per day
cubic meter
per square meter
per day
cubic meter or
liter of free air
per second
lumen per
square meter
Symbol
kg/m3
mg/l
kg/m3/d
m3/m2/d
m3/s
l/s
lumen/m2
Comments
The density of water
under standard
conditions is 1,000
kg/m3 or 1,000g/l
If this is converted
to a velocity, it
should be expressed
in mm/s (Imm/s -
864m3/m2/day)
Customary
Equivalents*
0 06242 Ib/cu ft
1 ppm
0 06242 Ib/cu ft/day
3 281 cu ft/sq ft/day
0 09294 ft candle/sq ft
"Miles are U S statute, qt and gal are U.S liquid, and oz and Ib are avoirdupois
-U S GOVERNMENT PRINTING OFFICE- 1977-757-056/6460 Region No. 5-11
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U S ENVIRONMENTAL PROTECTION AGENCY
ENVIRONMENTAL RESEARCH INFORMATION CENTER TECHNOLOGY TRANSFER
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