SINGLE CELL PROTEIN
AND OTHER FOOD RECOVERY
TECHNOLOGIES FROM WASTES
Municipal Environmental Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
EPA-600/8-77-007
May 1977
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development. U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
This report has been assigned to the ENVIRONMENTAL PROTECTION TECH-
NOLOGY series. This series describes research performed to develop and dem-
onstrate instrumentation, equipment, and methodology to repair or prevent en-
vironmental degradation from point and non-point sources of pollution. This work
provides the new or improved technology required for the control and treatment
of pollution sources to meet environmental quality standards.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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EPA-600/8-77-007
May 1977
SINGLE CELL PROTEIN AND OTHER
POOD RECOVERY TECHNOLOGIES PROM WASTE
by
Sylvia A. Ware
Ebon Research Systems
Silver Spring, Maryland 20901
Contract No. CI-76-0088
Project Officer
Clarence A. demons
Solid and Hazardous Waste Research Division
Municipal Environmental Research Laboratory
Cincinnati, Ohio 45268
MUNICIPAL ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATT, OHIO 45268
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DISCLAIMER
Ihis report has been reviewed by the Municipal Environmental Research Labora-
tory, U.S. Environmental Protection Agency, and approved for publication.
Approval does not signify that the contents necessarily reflect the views and
policies of the U.S. Ehvlronnental Protection Agency, nor does mention of
trade names or coranercial products constitute endorsement or reccranendation
for use.
ii
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FOREWORD
The Environmental Protection Agency was created because of
increasing public and government concern about the dangers of pollu-
tion to the health and welfare of the American people. Noxious air,
foul water, and spoiled land are tragic testimony to the deterioration
of our natural environment. The complexity of that environment and
the interplay between its components require a concentrated and
integrated attack on the problem.
Research and development is that necessary first step in problem
solution and it involves defining the problem, measuring its impact,
and searching for solutions. The Municipal Environmental Research
Laboratory develops new and improved technology and systems for the
prevention, treatment, and management of wastewater and solid and
hazardous waste pollutant discharges from municipal and community
sources, for the preservation and treatment of public drinking water
supplies, and to minimize the adverse economic, social, health, and
aesthetic effects of pollution. This publication is one of the
products of that research; a most vital communication link between
the researcher and the user community.
This study presents a comprehensive review of the techniques
available for the bioconversion of waste materials to single cell
protein or other animal feed, feed supplements, and human food.
Francis T. Mayo
Director
Municipal Environmental
Research Laboratory
iii
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ABSTRACT
In the field of waste management, much research has focused on the stabiliza-
tion of wastes with formation of a marketable product to defray the costs of
treatment before land disposal. Some wastes are already being commercially
exploited for their energy potential. It is also possible to produce a human
food or an animal feed through a number of biological waste management tech-
nologies .
Very few of the methods of producing proteins or edible carbohydrates from
wastes have been explored beyond the pilot plant stage. Mich of the research
now underway is still at the bench-top scale.
Growth of single cell protein (SCP) on non-wastes is entering commercial ex-
ploitation, and companies are now testing and developing markets for raLcro-
bial products. There are a number of technological refinements necessary to
produce SCP acceptable for human consumption. Growth of feed-protein on
waste cellulose while technologically feasible, because of incomplete utili-
zation of the waste and poor yields of product, is not now economically
competitive with more conventional proteins. Growth of protein on various
food-processing wastes appears economically and technically feasible at
present. SCP production on any substrate generally consumes more energy than
production of vegetable proteins, but less that animal proteins when compared
in terms of energy input per gram of protein produced.
Enzyme hydrolysis of cellulose to produce glucose, while an environmental1y
acceptable method of stabilizing wastes is currently more costly than acid
hydrolysis of cellulose to glucose. The process is not energy Intensive.
Anaerobic digestion of cellulose produces methane and a sludge with potential
as a fertilizer or feed. Extensive nutritional and toxicological testing of
the feed-potential of the sludge has yet to take place. If the sludge proves
valuable as a feed or feed-supplement, this process is especially valuable,
as it also produces energy in the form of methane.
In addition to the technological and economic problems associated with treat-
ing and recycling wastes for their nutritional value, there is also the prob-
lem of sociological acceptance, especially with human consumption of SCP.
This report was submitted in fulfillment of Contract No. CI-76-0088 by Ebon
Research Systems under sponsorship of the U.S. Environmental Protection
Agency. This report covers the literature available up to July 1, 1976 and
work was completed as of September 19, 1976.
iv
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CONTENTS
Foreword [[[ ill
Abstract [[[ Iv
Figures [[[ vl
Tables [[[ vii
Abbreviations and Symbols ..................................... ix
Metric Equivalents ............................................ x
Acknowledgments ............................................... xi
1. Introduction ......................................... 1
2. Conclusions .......................................... 9
3. Recommendations ...................................... 10
4. Single Cell Protein- Overview ........................ 11
5. The Nutritive Potential of Wastes .................... 33
Cellulose ...................................... 33
Non-Cellulosic Carbohydrates ................... 86
Whey ........................................... 96
References [[[ 103
Appendices
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FIGURES
Number Fags
1 Protein Intake, 1970 5
2 Cost of Selected Feedstuffs in the U.S., 1962-1975 6
3 Land Use Efficiency of Several Protein Sources 8
4 Protein Efficiency Ratios of a Number of Protein Sources 26
5 Alternative Products from Salvage of Cellulosic Wastes 34
6 Structural Formula of Cellulose .35
7 Possible Pood/Peed Recovery Systems from Cellulosic Wastes 42
8 Possible Whey Utilization and Salvage Schemes 99
vi
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TABLES
Number Page
1 Estimates of Organic Wastes Generated In the U.S 2
2 Characteristics of Selected Pood Industry Wastes 3
3 Efficiency of Protein Production of Several Protein
Sources in 24 Hours 8
4 Peed Grade SCP Plants 12
5 Food Grade SCP Plants 13
6 Other SCP Systems Under Consideration 13
7 Factors Influencing the Choice of a Substrate 17
8 Summary of Desirable Characteristics and Problem
Areas Associated with Single Cell Proteins 20
9 Mass Doubling Times 24
10 Forecast of Animal Feed Consumption in the
United States, 1960-1990 32
11 Cellulose Content of Various Materials 36
12 Various Methods of Pre-treating Cellulosic Wastes
so as to Improve Their Biodegradability 38
13 Approximate Protein Content of Selected Organisms
Grown on Waste Materials 46
14 Amino Acid Profile of Selected Organisms Grown on
Cellulosic Wastes 47
15 Number of Animals Required to Economically Support
Methane Generation Treatment of Animal Wastes 50
16 Estimated Excreta N from U.S. Livestock in 1972 53
17 In Vitro Dry-Matter Digestibility of Various Woods
and Their Bark 55
18 Composition and Cellu1a.se Digestion of Various Woods
Before and After S02 Treatment 57
19 Effect of Fermentation on Composition and .In Vitro
Digestibility of Municipal Wastes 59
20 Composition and Digestibility of Papers 59
21 Effects of Dilution Rate on Mean Algal Yield In
Two Locations 63
22 Cost of Cellulose Wastes , 67
23 Value of Products Obtained from Cellulose • 68
24 Costs of Nutritional Protein 69
25 Current Truckload Prices F.O.B. for "Torutein",
Hutchinson Plant, 1976 70
26 Costs of Nutritional Carbohydrates 72
27 Costs of Various Waste Processing Technologies 74
28 On Farm and Food Processing Industry Energy Usage in
the U.S. Food System, 1970 78
vii
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TABLES (continued)
Number Page
29 A Rough Approximation of Energy Consumption for a
Number of Pood Production Systems including SCP 82
30 Energy Production Per Ton Input for Anaerobic Digestion
to Methane 83
31 Composition of a Spent Spruce Sulfite Liquor 8?
32 Chemical Composition of Pekilo Protein 88
33 BOD-7 of a Spent Sulfite Liquor before and after
continuous Pekilo Fermentation 88
3^ Comparison of Various Treatment and Disposal Methods
for Pood Industry Wastes 91
35 General Efficiency of Fungi Imperfect! Process 92
36 Efficiency of Reducing Sugar Utilization by
MoickeZAa. kototentxiA 92
37 Reducing Sugar Utilization and Yields of Organisms
Grown on Selected Brewery Wastes 9^
38 Typical Composition of Sauerkraut Brine 95
39 Dry Solids in Cheese Whey 98
viii
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LIST OF ABBREVIATIONS AND SYMBOLS
ADF — acid detergent fibre
ATCC — American Type Culture Collection
BOD — biochemical oxygen demand
BODc — 5 day biochemical oxygen demand
Btu — British thermal unit
COD — chemical oxygen demand
cm — centimeter
OG — degrees Celsius
oc — degrees Fahrenheit
FPU — filter paper unit
FSL — fermented sludge liquor(brewing)
g — gram
GPL — grain press liquor(brewing)
IVRD — in vitro rumen digestibility
K cal — kilocalorie
kg — kilogram
K — saturation constant
BP — British Petroleum
EPA — Environmental Protection Agency
ERGO — Energy Resources Company
ERDA — Energy Research and Development
Administration
FAQ — Food and Agriculture Organiz-
ation, United Nations
ICI — Imperial Chemical Industries
IFP — Ihstitut Francais du Petrole
kw — kilowatt
kwhr — kilowatt hour
1 — liter
M — molar (solution)
mg — milligram
ml — milliliter
MMBtu — Btu x 10b
MSW — municipal solid waste
NDM — nonfat dry milk
NPU — net protein utilization
PER — protein efficiency ratio
ppm — parts per million
— specific oxygen demand
scf — standard cubic feet
SCP — single cell protein
TPL — trub press liquor
WPG — whey protein concentrate
MIT — Massachusetts Institute
of Technology
NASA — National Aeronautics and
Space Administration
PAG — Protein Advisory Group,
United Nations
RHM — Ranks Hovis McDougall
SHWRD — Solid and Hazardous
Waste Research Division,
EPA
SHWRL — Solid and Hazardous
Waste Research Laboratory
UN — United Nations
ix
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METRIC EQUIVALENTS
OP U.S. CUSTOMARY UNITS
1
1
1
1
1
1
1
1
1
short ton
long ton
short cwt
Ib.
cubic foot
gallon
acre
bushel
Btu
0.907 metric ton
1.016 metric tons
45.4 kilograms
0.454 kilogram
0.028 cubic metre
3.79 litres
0.405 hectare
35.24 litres
252 calories
Note: U.S. customary units are used throughout the text where their use is
most familiar. This was done for ease of comprehension of certain
data.
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ACKNOWLEDGMENTS
Ebon Research Systems gratefully acknowledges the contributions of Dr. Gilbert
Jackson, Genesis Ltd., to the comparative energy usage section of this report;
and of Dr. David Kidder, University of Lowell, to the comparative economics
section.
Special thanks go to Dr. Don Crawford, University of Idaho; Dr. Bruce Sharfstein,
City University of New York; Dr. K. Spurgeon, South Dakota State University;
and Dr. Tom Abeles, University of Wisconsin, who reviewed the subject matter
of this report.
We are also indebted to Dr. Charles Dunlap, University of Missouri, and Dr.
Prank McDonough, U.S. Department of Agriculture, for their suggestions and
comments. Most of the paper's referred to or directly quoted in this report
were provided by the authors. We are very grateful to all contributors for
permission to use their material.
We wish to acknowledge the work of Virna Mills and Susie Schafer who typed
the report.
The following tables and figures were reprinted with permission of the
copyright owners:
Material contained in Figure 4 reproduced from the Encyclopedia of Pood
Technology, Avi Publishing Company, Connecticut, p. 4, 1974, with permission
of the author, Dr. Martin S.Peterson.
Table 2 reprinted from Chemical Engineering Symposium Series, Vol.67, No. 108,
p.l64, 1974, with permission of the American Institute of Chemical Engineers.
Table 8 reprinted from Chemical Processing, September 1974, with permission of
Chemical Processing, London,England. Copyright^) IPC Business Press Limited.
Table 15 reprinted from Paper No. NA74-107,p.l9, by W.J.Jewell et al presented
at the 1974 Regional Meeting of the American Society of Agricultural Engineers,
August 1974.
Tables 17 and 18 reprinted from Cellulose Technology Research, ACS Symposium
Series, Vol. 10, p. 78 and 90 , 1975, with permission of the American Chemical
Society.
xi
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Tables 19 and 20 reprinted from Federation Proceedings, Vol. 33, No.8, pp.
1942-1944, 1973, with permission of the Federation of American Societies
for Experimental Biology.
Table 21 reprinted from Nature, Vol. 254, p. 594, 1975, with permission of
Nature and the senior author, Dr. J.C.Goldman.
Material contained in Tables 22, 24 and 26 reprinted from Food Technology,
December 1975, pp.62-67. Copyright ©by Institute of Food Technologists.
Tables 22 and 23 reprinted from Biotechnology and Bioengineering Symposium
No. 5, pp.73-75, 1975, with permission of John Wiley and Sons, Inc.
Table 28 derived from Energy Sources, Use and Role in Human Affairs by C.E.
Steinhart and J.S. Steinhart, Duxbury Press, Massachusetts, p.334, 1974.
Reprinted with permission of copyright owner.
Material quoted from Pimental et al, Food Production and the Energy Crisis,
Science, November 1973, pp.443-448, reproduced by permission of the author
and the publisher. Copyright 1973 by the American Association for the
Advancement of Science.
Tables 32 and 33 reprinted from a paper presented by Kaj Forss at the Symp-
osium on Wood Chemistry, Pure and Applied, ACS National Meeting, Los Angeles,
March 1974, with permission of the American Chemical Society.
Table 34 reprinted from Chemical Engineering Symposium Series, Vol. 67, No.
108, p. 165, with permission of the American Institute of Chemical Engineers.
Table 35 reprinted from Developments in Industrial Microbiology, Vol.13, p.43,
1972, with permission of the American Institute of Biological Sciences.
Table 36 reprinted from Proceedings of the 1st International Congress of Food
Science and Technology, Vol. 2, 1975, with permission of the author, Dr. John
Litchfield, and the publishers, Gordon and Breach Science Pub.,Inc.
Table'37 reprinted from the Journal of Food Science, Vol. 40, p.827, 1975.
Copyright ©by the Institute of Food Technologists.
Table 38 reprinted from Applied Microbiology, Vol. 27, No.4, p.807, 1974,
with permission of the American Society for Microbiology.
Material from Single Cell Protein I and Single Cell Protein II with permission
of the Massachusetts Institute of Technology Press, Cambridge, Mass. Copyright
1968 and 1975 respectively.
xii
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Material from Pace, G.W., and D.J. Goldstein, "Economic Analysis of Ultra-
filtratlon-Fermentation Plants Producing Whey Protein and SCP from Cheese
Whey," In: Single Cell Protein II, by S.R. Tannenbaum and D.I.C. Wang (eds),
reproduced with special permission of the Massachusetts Institute of Technol-
ogy Press, Copyright MIT 1975-
Material from Chemical Engineering, December 9, 1974, excerpted by special
permission. Copyright © 197^ by McGraw-Hill, Inc.,New York, N.Y. 10020.
xiii
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SECTION 1
INTRODUCTION
Purpose
The management of solid wastes in che USA is complicated by increasing quan-
tities of wastes, rising energy costs for disposal and treatment prior to
disposal, limited land available for fills and lagoons, and stringent en-
forcement of environmental legislation. The estimated quantities of wastes
from various sources is given in Table 1. Cellulosic residues are the most
plentiful and available of all solid wastes. Large amounts of cellulose are
found in crop residues, the forest industries, manures, industrial wastes,
sewage solids and urban refuse. Hence, much research has focused on sta-
bilizing wastes through utilization of the cellulose content, both to prevent
pollution and to offset the costs of disposal through production of market-
able goods. These products include methane from anaerobic digestion of
organic wastes, ethanol from acid and enzyme hydrolysis of cellulose, various
chemicals from corncobs, animal feed pellets from pea vines, etc.
Not only are cellulosic wastes a continuing and increasing disposal problem,
but other organic wastes, from the food-processing industries in particular,
have an extremely high biochemical oxygen demand (BOD) and therefore place a
very heavy burden on the environment if discharged into rivers and streams
(see Table 2).
The Solid and Hazardous Waste Research Division (SHWRD), U.S. Environmental
Protection Agency, has encouraged and sponsored many research efforts de-
signed to handle all waste materials in a more efficient, economic and re-
sponsible fashion. As alternative technologies develop, they are potentially
in competition for available wastes. It becomes necessary to establish which
processes are the most technologically and economically viable as well as the
most environmentally acceptable. It is the purpose of this report to provide
the Solid and Hazardous Waste Research Division with an intensive review of
the techniques available for the bioconversion of waste materials to single
cell protein (SCP) or other animal feed, feed supplements, or human food.
Both cellulosic and other organic wastes will be discussed with an emphasis
on the former, because in terms of volume, they present the greatest disposal
problem, and in terms of resource recovery, they hold the greatest promise.
As cellulosic wastes are already being exploited commercially for their energy
potential, it is important to compare and contrast food/feed production from
cellulosic wastes with energy production from the same wastes. Although the
general public in this country is well aware of the depletion of fossil fuel
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TABLE 1
ESTIMATES OP ORGANIC WASTES GENERATED IN THE U.S.
(MILLIONS OF DRY TONS fFER YEAR) (1)
Source
Manure
Urban refuse
Uncovered logging and
wood manufacturing residues
Agricultural crops and
food wastes*
Industrial wastes t
Municipal sewage solids
Miscellaneous organic wastes
1971
200
129
55
390
M
12
50
1980
266
222
59
390
50
14
60
* Assuming JQ% dry organic solids in major agricultural crop waste
solids.
t Based on 110 million tons of industrial wastes per year in 1971,
of which 40/£ were organics.
^ Short ton. U.S. weights and measures are used throughout this report
where still customary. Metric equivalents may be found listed
on page x.
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CHARACOERISTICS OP
TABLE 2
POOD INDUSTRY WASTES (2)
Type of Waste
Packing house and
stockyards
Meat products
Rendering
Dairies and milk
products
Soft drinks
Cannery
Asparagus
Beans, green or wax
Beets
Corn, whole kernel
Corn, cream style
Cherries, sour
Grapefruit
Peaches
Pears
Peas
Potatoes, sweet
Potatoes, white
Pumpkin
Tomatoes, whole
Tomatoes, juice
rvr> rynnrinrvhs
5 day BOD
(ppm)
595
1,141
1,180
674
430
100
160 to 600
1,580 to 5,480
1,123 to 6,025
623
700 to 2,100
310 to 2,000
1,350
2,250 to 4,700
380 to 4,700
295
200 to 2,900
2,850 to 6,875
570 to 4,000
i7ft t-.n ^ ftnn
Suspended solids
(ppm) Reference
Hurwitz &
606 Jonas
820 - ^ •
fi^ji ,
Ujf — —
387
ppn «
Sanborn
30
60 to 85
7'IO to ? 188
•300 to Jl 000
?02
20 to 60R
170 to 287
600
1 POO tn 6 700
070 to JIQO
610
QQO to 1 l80
yftc 4-0 "3 ^00
ion 1-n ? nnn _
170 f-.n 1 _lfift
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resources and perceives the energy crisis as more inminent, the 'Impending1
global protein shortage is already a reality in many Third World countries
(see Figure 1). Ultimately, it is possible that a choice will have to be
made between energy and food production, based on survival priorities rather
than technological and economic data. Meanwhile, it is important for
officials in decision making positions and the general public to appreciate
the many factors that will hasten or impede the utilization of organic
wastes for their potential nutritive value.
Need
Protein-calorie malnutrition is the most serious and the most common cause
of infant mortality and morbidity in the emergent nations, as well as among
lower socio-economic groups in the industrialized countries. KwashiorkDr
and marasmus may directly cause the death of an infant, or indirectly result
in fatality upon infection, when the body's meager protein reserves are
depleted further. Long term effects of protein-calorie deficiency in utero
or in early infancy may include retarded physical and mental development.
Malnutrition and starvation are facts of life to countless millions in the
Third World. Even in parts of the United States, a recent nutritional sur-
vey has found evidence of- inadequate nutrition. Despite development of new
genetic strains of wheat and rice with double or triple yields of grain and
improved amino acid profiles, the protein gap between the developed nations
and the Third World remains as wide as ever. This is partly a result of the
continuing geometric increase in population. Also a factor is the increased
demand for more and better quality protein as income rises in the industrialized
nations. In the United States alone, per capita beef consumption has more than
doubled since 19^0 (4).
World supplies of high quality protein are not meeting the rising demand.
Fishing was once considered an ever plentiful source of protein. Due to
overfishing and coastal pollution, world fish catches are well down. The
failure of the anchoveta catch off Peru in 1972, not only caused a rapid esca-
lation of fish meal prices, but also drove up prices for all alternative feeds
(see Figure 2).
A decrease in world production of legumes in favor of high yield cereals has
also contributed to the world-wide need for more protein. However, there is
a limit to the amount of land suitable for soy bean production in the United
States. A shortage of protein for feeding to domestic animals causes slow
growth and low productivity of farm animals and thus contributes to the poor
diet of the human populace.
In the United States, as can be seen in Figure 1, the majority of essential
protein consumed comes from animal sources. The feeding of grains to live-
stock to produce animal protein is not an efficient way to produce high
quality protein. In terms of efficiency of protein production, Thaysen (6)
demonstrated that a 1,000 Ibs. bullock can synthesize 0.9 lb. of protein
every 24 hours, whereas 1,000 Ibs. of soybeans synthesize 82 Ibs. of protein
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North America
Western Europe
Japan
latin America
Near East
East Africa
West Africa
North Africa
India
Central Africa
_L
animal protein
^ other proteins
protein required
20 40 60 80 100
Grans of protein per capita per day
Figure 1. Protein Intake, 1970 (3)
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350 -,
o\
to
o
•i
c
•H
w
I
8
u
I
300 4
250
200 1
150 1
100 J
50
1962
* provisional figures
meal
60% protein
Angeles
1976
protein
*May 1976*
April 1976
Cottonseed meal, 41% protein
Menphis
1965
1975
1970
Year beginning October
Figure 2. Cost of Selected Feedstuffs in the U.S., 1962-1975 (5)
1980
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in the same time, and in theory, 1,000 Ib. of yeast could produce more than
50 tons of protein in a day. In terms of quantity, the amount of feed con-
centrates' fed per animal unit in the United States has risen from a value
of 1.98 tons in 1959 to 2.4l tons in 1973 (5). The quantity of feed pur-
chased represented 17*5% of total farm production expenses in this country
in 1959 and slightly over 20% of expenses in 1973 (5)• It is obvious that
not only is the feeding of high quality grains to farm animals an ineffic-
ient method of producing protein, but it is also costly in both human and
economic terms.
The primary resource ultimately limiting expansion of agriculture is avail-
ability of suitable land. In terms of land utilization, Gray (7) calculated
that an acre of corn could produce 26l Ibs. of corn gluten protein, 280 Ibs.
of fungal protein and only 72 Ibs. of beef (see Figure 3). Meadows and
Meadows vt at (8) estimated that even if all possible land available is
utilized for farming, there will be a desparate land shortage before the
turn of the century, if per capita land requirements and population growth
rates remain as they are today.
Modern agriculture is an extremely energy intensive industry (see Comparative
Energy Usage section of this report). Not only are our available energy re-
sources rapidly dwindling, but the cost of unregulated fuels has skyrocketed
since the advent of the political energy crisis of 1973. A recent report
prepared for the National Science Foundation illustrates the impact of energy
costs on the total variable costs of crop production in this country. The
report stated that for every crop (14 field crops throughout the continental
United States) the energy component of production costs has risen between
50 and 7556 from 1970 to 1974 (9).
The need and concern for more efficient and economic means of producing high
quality protein has stimulated research into unconventional sources of pro-
tein (including microbial protein) in the past twenty years. New protein
sources will not replace the more traditional methods of protein production,
but will be compared to modern farming practices and prices. In the case of
protein production from waste materials, the technologies available must
prove more viable than alternative waste management systems.
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corn gluten
protein
fungal
protein
beef protein
Ibs production
Figure 3. Land Use Efficiency of Several Protein Sources,
Quantities for One Acre (7)
TABLE 3
EFFICIENCY OF PROTEIN PRODUCTION OF SEVERAL PROTEIN SOURCES IN 24 HOURS (5)
Organism
(1,000 Ibs)
Amount of
Protein
Bullock
Soybeans
Yeast
0.9 Ib
82.0 Ibs
50 tons
8
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SECTION 2
CONCLUSIONS
Much of the research into food/feed production from solid wastes is still at
the bench-top scale. A few pilot plant projects have confirmed the need for
more research and development. Therefore, it is not possible to fully eval-
uate these technologies as methods for solid waste management at present.
Recycling waste cellulose for its nutritive potential is an environmentally
acceptable method of stabilizing wastes. Effluents generated by any of the
processes discussed are easier to treat than large volumes of solid waste.
Pood/feed production from waste cellulose does not appear to be economically
competitive with fuel production from the same wastes, at least in the near
future. In the long run, the situation could well be reversed. Processes
for producing energy from wastes are now entering comnercial exploitation,
and are now economically and technically practicable.
Pilot plant studies with food industry wastes have indicated the technical
and economic feasibility of SCP production on wastes such as whey, potatoes,
citrus and other fruit wastes, corn and pea-canning residues, etc.
Anaerobic digestion of agricultural wastes, especially manures, is a very
promising waste management technique. Methane is generated and the sludge
has potential value as either a fertilizer or a feed. However, there is a
need to determine the safety, digestibility and palatability of the sludge
to livestock. Several ongoing studies should clarify all possible uses of
this sludge.
Not only will protein products derived from wastes have to compete with con-
ventional food sources for potential markets, but with other "unconventional"
protein sources now under development. A comparison of the status of re-
search into all protein resources will prove useful.
Finally, while reclamation of the nutritive potential of wastes is not an
Immediate possibility, it does appear that such a reclamation will take
place, perhaps within 10 years. Funding of research in this area should be
considered an investment in the future. While the Gn.e.en Revolution con-
tinues, the Garbage. Revolution has Just begun.
9
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SECTION 3
RECOMMEM)ATTONS
There are a number of research areas requiring attention before full-scale
exploitation of the nutritive potential of solid wastes is possible:
(1) Pilot plant studies are needed, especially for SCP processes and
enzyme hydrolysis. Only larger scale projects will provide the
raw data necessary to solve technological problems and to clarify
the economic future for these processes.
(2) Computer simulations are needed to Identify areas of economic sen-
sitivity. Economic data must include variables associated with
collection and transportation of wastes and the seasonality of some
crop residues.
(3) An In-depth energy analysis should be performed based on at least
pilot plant experience.
(4) The sludge of anaerobic digestion of manures has potential as a feed
or fertilizer. There is a need to determine the safety, acceptability
and digestibility of this sludge to livestock.
(5) Research into pre-treatment of wastes to improve their digestibility
should continue and expand. Genetic engineering approaches to improve
yields and composition of protein products should receive attention.
(6) All food or feed products derived from wastes (or any other unconven-
tional food source) must undergo stringent and exhaustive safety eval-
uations before reaching the market place.
(7) Methods for Improving the digestibility and functionality of single
cell protein for human consumption need more investigation.
Though much research is still to be accomplished, and the economic future of
some of the processes described is unclear, it does appear that commercial
exploitation of the nutritive potential of wastes will become a reality.
financial tuppovL jjo/t &uc.h an undertaking, howeveA, mu&t come, friom 40otce6
po&&eA&inQ vi&ion in tke, ^utwie., patie.nce. in the. px.eAe.nt, and undeJi&tanding
OfJ the, e.xpesiim£nta£ e^ot£4 o£ the. pott.
Nylri and Tarmen, 1975.
10
-------
SECTION H
SINGLE CELL PROTEIN — OVERVIEW
Introduction
Single cell protein Is the name given to the non-viable dried cells of micro-
organisms such as yeasts, mycelial fungi bacteria and microalgae grown on
various carbon sources. The name was coined by Professor Caroll Wilson of
Massachusetts Institute of Technology in May 1966, to present a neutral
image of the product to a general public which might react unfavorably to the
idea of a "mtcrobial" or "bacterial" protein source.
In addition to a source of carbon, the substrate, microorganisms require added
nutrients, principally nitrogen, phosphorus, calcium, magnesium and Iron in
order to maintain growth. Algae with few exceptions require light as a
nutrient.
While the composition of different single cell proteins varies depending on
the choice of organism, substrate selected and conditions of growth, single
cell proteins generally contain more than 50/S high quality protein, together
with smaller amounts of nucleic acids, carbohydrates, fats, ash, calcium,
phosphorus and water.
Various companies, institutions and universities throughout the world have
widely researched most aspects of SCP production, particularly in the last
twenty years. However, man has a familiarity with the food and feed usage
of microorganisms stretching back for centuries. Yeasts have been utilized
in the brewing and baking Industries since antiquity. Bacteria are eaten in
products as diverse as sauerkraut, sausages and yoghurt. Haylage and silage
are prepared through the activities of anaerobic bacteria and have proved a
very satisfactory energy source for ruminants. A blue-green algae, SpiAuLina.
mcutima., has been eaten by nationals of the Republic of Chad for centuries,
and various species of marine algae have been used to prepare soups and to
make glac£ cherries. Higher fungi have been widely used for food purposes,
as well as finding a place in religious ritual. According to Robert Graves,
the mythological "ambrosia of the gods" was probably a species of mushroom.
The first modem effort to grow microorganisms for food/feed purposes was in
Germany during the First World War. Over 15,000 tons of Torula yeast was
added to human foods per year up to the mid thirties. The yeast was grown on
beet molasses > wood sugar hydrolyzates, and later, following development of
the process by Heljkenskjold in Scandinavia in 1925-1928, on spent sulfite
liquor (10).
11
-------
TABLE 4
GRADE SCP PLANTS (12)
Type of plant Country Substrate Organism Tons/year
Demonstration
BP U.K. n-Paraffin Yeast 4,000
Chinese Petroleum Taiwan n-Paraffin Yeast 1,000
Dianippon Japan n-Paraffin Yeast
ICI U.K. Methanol Bacteria 1,000
Kanegafuchi Japan n-Paraffin Yeast 5,000
Kohjin Japan Yeast 2,400
Kyowa Hakko Japan n-Paraffin Yeast 1,500
Milbrew U.S. Whey Yeast 5,000
Shell Holland Methane Bacteria 1,000
Svenka-Socker Sweden Potato Starch Yeast 2,000
Semi-Commercial
BP Prance Gas Oil Yeast 20,000
United Paper Mills Finland Sulfite Waste Yeast 10,000
USSR USSR n-Paraffln Yeast 20,000
Commercial
BP Italy n-Paraffin Yeast 100,000
Liquichimica Italy n-Paraffin Yeast 100,000
12
-------
TABLE 5
POOD GRADE SCP PLANTS (12)
Plant Country Substrate Organism Tons/year
Amoco Poods
Boise Cascade
St. Regis Paper
Slovnaft-Kb j etin
U.S.
U.S.
U.S.
Czech.
Ethanol
Sulfite Waste
Sulflte Waste
Ethanol
Yeast
Yeast
Yeast
Yeast
5,000
6,000
5,000
1,000
TABLE 6
OTHER SCP SYSTEMS UNDER CONSIDERATION (12)
Substrate Organism Corporation
Animal Feed
Cellulose Waste Bacteria LSU-Bechtel
Citric Acid Waste Fungi Tate & Lyle
Coffee Waste Fungi ICAITI (Guatamala)
C02-Sunlight Algae IFF
Feed Lot Waste Actinomyoete General Electric
Methanol Yeast Mitsubishi
Paper Pulp Waste Fungi Finnish Pulp & Paper
Human Food
Ethanol Bacteria Exxon-Nestle
Molasses Yeast Dianippon
Starch & Carbohydrates Fungi RHM - Dupont
Whey Yeast Kraftco
13
-------
In 1920, Prlngsheim and Lichtenstein (11) reported feeding animals with the
fungal mycelium, tepviQiJUiuA fiimlgcutuA, grown on straw with added inorganic
nitrogen as a nutrient. After World War n, growth of fungi in submerged
cultures for production of antibiotics, led to an investigation of the
potential of microfungi as flavor additives to replace mushrooms.
In the fifties, the petroleum industry began experiments on the biological
removal of wax and sulfur containing fractions from crude oil. Ihe micro-
organisms used were found to contain over 50% protein, and became of primary
interest themselves as either an animal feed or a human food.
Today, many demonstration and semi-commercial plants for SCP production are
found throughout the world, as well as several full-scale commercial plants
(see Tables *», 5 and 6). As can be seen from these tables, the majority of
producers are growing yeasts on a variety of petro-chemical based substrates.
An understanding of the status of SCP growth on any substrate is a necessary
background to understanding the additional problems associated with use of
a cellulose substrate.
Further details of the market status of food and feed grade SCP appear
towards the end of this section.
General Overview of the Process
With the exception of algal protein, SCP is grown in a fermenter which con-
tains the culture, the carbon substrate, air to supply oxygen, water, added
nutrients and ammonia to supply nitrogen and to adjust the pH. All Inputs
to the fermenter must be sterilized to prevent contamination of the culture,
which is a particular problem with the slower growing fungi (13).
The fermentation is continuous, that is, a volume of broth and suspended
cells is continually removed from the fermenter as fresh medium is added to
keep the volume constant. A steady state growth rate of the microorganisms
can be made to approach maximum values by adjusting the limiting nutrient
input (flow rate). The productivity of a continuous culture expressed in
grams of cells/unit volume per unit time, is higher than in a similar batch
culture. Continuous cultivation of microorganisms has been limited on a
large scale because of problems of maintaining sterility, changes due to
harmful mutation and a lack of knowledge of mLcrobial behavior (14). Know-
ledge advances in both biochemistry and engineering have made the design of
large scale continuous plants feasible. Computer-coupled systems provide an
immediate ongoing analysis of environmental conditions within the fermenter.
The limiting step in the growth of the organism is the rate of oxygen uptake
from the airstream. Aerobic organisms require oxygen for respiration and
growth up to a certain critical concentration of oxygen, which ranges from
0.1 to 1.0 ppm. for homogeneous cultures grown at 20-50° C (14). Oxygen
utilization is related to growth and/or cell concentration. At a steady
state, the oxygen transfer rate is equal to the oxygen uptake rate, which
-------
varies depending on the organism and substrate. For example, bacteria, be-
cause of their lower lipid and higher nitrogen content require less oxygen
than yeasts. The cost of oxygen enrichment can add significantly to the
cost of the process.
The design of the fermenter has a considerable effect on the rate of oxygen
transfer (15). Different types of fermenter include conventional stirred,
draft-tube and air lift. An important new concept in fermenter design has
come from Imperial Chemical Industries (ICI) in England. Their pressure
cycle fermenter has operated on a continuous basis accepting runs of 2,000
tons of broth per hour, for periods up to eight weeks. The design of the
fermenter optimizes the rate of oxygen transfer by forcing air bubbles
through the vessel from the base without the problem of foaming. It is also
designed to minimize heat shock of the organisms as they pass through the
heat exchangers (16).
As previously implied, the reaction is exothermic and therefore heat exchang-
ers are required to remove excess heat. Heat removal is especially costly
for mesophilic organisms grown in hot climates where ambient water temperat-
ures are high and refrigeration is required. Hence in warmeg climates,
microbes with temperature optima greater than or equal to 40 C would prove
economically useful. Optimal temperatures for operation of fermenters will
depend on whether the specific organisms involved are thermophilic or meso-
philic in nature (v-ccte. -twjj/m). Departures from the optimal temperature for
a particular organism will result in reduced rates of growth according to
the Arrhenius equation (17):
k = A exp (u/RT)
where k is the rate of reaction
R is the caloric Gas Constant
T is the absolute temperature
y is the temperature characteristic of the organism
A is a constant
The pH of the fermenting broth is also an important factor in the yield and
crude protein content of the harvested cells. The product is removed from
the broth by centrifuging or filtering, perhaps after an initial dewater or
with addition of a flocculent. The supernatant may be recycled to the ferm-
enter to reduce sterilization costs, to utilize substrate and nutrients more
efficiently, and to lower the biochemical oxygen demand of the effluent (12).
Harvesting can be a problem depending on the size of the cells and their
concentration in the broth. Microalgae, for example, are so small and present
in such dilute suspensions that they cannot be removed by sedimentation or
flotation (18). Exceptions include some blue green algae which float to the
top of the fermenter and may be removed by skimming. If the biomass is to be
used as an animal feed, it is washed and roller or spray dried. If the pro-
tein is to be incorporated into a human food, then it is likely that further
15
-------
treatment is required to remove nucleic acids which could cause kidney damage.
Also, it may be necessary to treat the SCP to rupture the cell wall to improve
digestibility and to texturize the protein. After treatment, the product is
washed, centrifuged and spray dried (12).
Ihe recovery of cells from n-alkane substrates presents a particular problem
in that residual hydrocarbons adhere to the cells. Ihe techniques for har-
vesting from n-paraffins are therefore modified to remove contaminants from
the SCP.
Choice of a Substrate
As can be seen in Table 7, there are many factors to be considered when
choosing a substrate for SCP growth. Historically, as previously mentioned,
the major oil companies began their research as part of a program to dewax
fractions of crude oil. Hence in Europe and Japan, where oil companies were
in the vanguard of research into single cell proteins and are now marketing
feed grade SCP, gas-oil and n-alkanes are favored substrates. Ihe cost of
these substrates has escalated considerably since 1973, so that the advan-
tage of high yields, which reduce production costs, has been offset by the
cost of the substrate. This cost has delayed the further expansion plans of
British Petroleum and LLquichimica (19).
There are a number of technological disadvantages to the use of a paraffin
substrate. The oxygen requirements of the system are greater than for a
partially oxidized substrate, the heat generated is greater and hence heat
transfer more costly (12). The possibility of absorption of the substrate
into the cell wall caused a furor in Japan where organized consumer groups
forced the postponement of plans for production of feed-grade SCP (20). The
fear was that carcinogenic polycyclic aromatic compounds, present in ap-
parently harmless concentrations in Japanese "petroprotein" samples, might
accumulate in livestock tissue.
The lower alcohols have several advantages as substrates. Apart from their
free availability in a very pure form, their partially oxidized state means
that less oxygen is required for growth of the microorganisms and less heat
is generated, thus lowering heat transfer requirements and hence cost (21).
Methanol and methane are currently considered the most economically attrac-
tive of the petro-chemical substrates (22) (see Comparative Economics section
of this report). ICI has chosen methanol as a substrate partly for the
reasons listed in Table 7 but also because the Corporation is a big producer
of methanol from methane. Similarly, the Mitsubishi Gas Chemical Company
which has also chosen methanol as a substrate, is a major producer of meth-
anol for world markets. Amoco Foods which is currently selling food grade
yeast to about 50 food companies in the United States (23) chose methanol
partly because of its availability in a pure form, but also because of its
psychological acceptability to the general public.
In Scandinavia, where forest industries are of major importance, sulfite
waste liquors of the paper and pulping Industry have been well utilized.
16
-------
TABLE 7
FACTORS INFLUENCING THE CHOICE OF A SUBSTRATE
Item
Methanol
Ethanol
Methane
Higher paraffins
Cellulosic wastes
Availability widely available from
many hydrocarbon sources
Cost
Versatility
Properties
available from petro-
chemicals or sugar
fermentation
available at high purity available at high purity
lowest cost petrochem-
ical available
restricted use by micro-
organisms, hence low
possibility of contami-
nation
completely miscible w.
water
explosion hazard less
than methane
easy to store & handle
relatively high cost
versatile substrate, can
be used by many organ-
isms, contamination
problems
completely miscible w,
water
explosion hazard low
well-head gas now flar-
ed could be used to
grow SCP at low cost
could be easily manu-
factured should natural
resources run short
costs low but likely to
rise, shortage of nat-
ural gas
no known yeast will
grow on methane, thus
eliminating one source
of contamination
gas, insoluble in water
danger of explosion w.
concentrations of 00
easy to store & handle as above
freely available in the
petroleum producing
countries
requires purification
before use
cost of substrate ris-
ing, only economic for
oil producing nations
versatile substrate,
thus contamination
problems
Insoluble in fermenta-
tion media
possible explosion
problems
as above
plentiful and renew-
able resource
some wastes are easily
collectable
sane wastes only avail-
able seasonally
low or negative cost
of wastes
fungi and bacteria
fermentation slow as
llgnln shields the
cellulose, problems w.
solubillzing substrate
storage of some wastes
not feasible
-------
TABLE 7 (continued)
Item
tfethanol
Ethanol
Methane
Rtgher paraffins
Celluloslc wastes
oo
Properties partially oxidized,
therefore reduced ox-
ygen requirement
Tbxlclty more toxic than ethan-
ol
Status semi-coamercial plant
partially oxidized,
therefore reduced ox-
ygen requirement
less toxic than raethan-
ol, most psychologic-
ally acceptable because
of long use as a bever-
ccmnerclal plant
contains no oxygen,
therefore added oxygen
requirement
as a gas unlikely to
contaminate substrate
demonstration plant
contains no oxygen,
therefore added oxygen
requirement
greater heat of ferm-
entation, needs more
cooling
need to purify sub-
strate & product-fear
of carcinogenic cmpds.
conmercial, historical
development on paraff-
ins
contains oxygen, re-
duced 02 requirement
conversion to SCP re-
duces BOD of waste
In themselves never
toxic, but many contain
pesticides, heavy metals
other materials harm-
ful to microorganisms
sane pilot plant scale,
most bench scale, some
R & D still to complete
Yields
acceptable yields
acceptable yields
acceptable yields
especially high yields low yields
-------
In the U.S., Boise Cascade and the St. Regis Paper Company are each producing
5,000 to 6,000 tons of food grade yeast per year, and are likely to expand
their facilities.
In countries with a strong agricultural base such as the United States, all
forms of agricultural waste are being examined as substrates for SCP growth.
The Louisiana State University pilot plant used bagasse as a substrate for
bacterial SCP growth. The process is applicable to most cellulosic wastes
and Bechtel has shown interest in promotion of the process. General Electric
has investigated growth of thermophilic actinomycetes on feed lot wastes in
a demonstration plant at Casa Grande in Arizona. For a variety of technical
reasons Including heavy metal contamination of the substrate, animal feeding
trials were stopped, and the plant ceased operation. It has not reopened
for economic reasons (24).
In terms of large scale development, growth of SCP on cellulosic and non-
cellulosic carbohydrate wastes is several years behind petrochemical sub-
strates. The renewable nature of these wastes, together with escalating
prices for non-renewable petroleum derived substrates, makes the future
appear promising for SCP growth on wastes, though a number of technical
difficulties must be overcome (vu.cfe. Unfauti*
While the choice of a carbon source depends very largely on availability and
cost of substrate, other factors, including psychological acceptance of the
product at the market place, are also important.
Choice of an Organism
The choice of an organism is based on several selection criteria. The most
important factor is the safety of the organism. It must be non-pathogenic
and must not produce toxins. If the product is to be incorporated into
human food, it must be acceptable to the palate, both in taste, texture and
form, and it must not alter the functional properties of the food to which
it is added.
The growth rate and the maintenance requirements should permit maximum cell
yield, lower operating costs and reduced contamination potential. As most
continuous fermentations are limited by the oxygen transfer rate, maximum
yields can be achieved by either high cell density at low growth rate or a
low cell density at a high growth rate (25).
Another factor of importance when choosing an organism is the efficiency with
which it converts the raw materials into protein, and the stability of the
culture as it grows.
The ease with which the protein can be processed is also an important cri-
terion in choice of an organism. Table 8 summarizes the advantages and
disadvantages of the four classes of organism commonly used. Table 9 com-
pares the mass doubling times of different organisms, illustrating one of
the important advantages of SCP production over other protein sources.
-------
TABLE 8
SUMMARY OP DESIRABLE CHARACTERISTICS AND PROBLEM AREAS
ASSOCIATED WITH SINGLE CELL PROTEINS (2?)
Desirable characteristics
Problem areas
Comments
growth in outdoor ponds
simple nutrient requirements
possibility of utilizing
sewage or industrial wastes
ro
o
ALGAE
illumination
C02 limitation
contamination
harvesting
nutritional value
product quality
sensory quality
costs
Artificial illumination is too costly.
Outdoor cultivation is practical only
below 35° latitude.
COg must be supplied. Sometimes simple
aeration will supply an adequate quan-
tity of C02.
Pathogenic bacteria and viruses may
contaminate algae growth in sewage
oxidation ponds.
Cells settle at slow rate, centrifuga-
tion too costly, flocculants contaminate
product.
Poor digestibility in man and non-ruminants,
Without pre-treatment cells tend to be
deficient in methionine: algae toxins
might be present.
Bitter flavor is not acceptable to man or
some animals: may require special treatment,
Estimated production cost of $0.24 per
kilo make algal protein non competitive.
-------
TABLE 8 (continued)
long history of human and
animal use
possibility of utilizing
low cost hydrocarbons or
waste carbohydrates as
substrates
YEASTS
substrate
concentration
oxygen
requirements
contaminants
Low concentration of carbohydrates must be
used to avoid carbon losses.
Large amounts of oxygen are required es-
pecially with hydrocarbons.
Aseptic conditions may be required es-
pecially in tropical regions.
ro
favorable protein and
araino acid contents
- good nutritional value
cooling
harvesting
waste
nutritional
value and
product quality
cost
Large amounts of heat released during growth,
especially with hydrocarbons: refrigeration
required.
Separation of trace residues of hydrocarbons
from cells may be troublesome.
Spent growth medium may have high BOD which
must be treated.
Hydrocarbons may depress growth, methionine
limiting; only limited amounts can be added
to human diets without imparting adverse
flavor.
Production costs using hydrocarbon substrates
would make product uncompetitive in animal
feed markets in U.S.A.
-------
TABLE 8 (continued)
Mushrooms have long
history of human
consumption
Possibility of uti-
lizing waste carbo-
hydrates as substrates
Mycelium may be
harvested by filtra-
tion
FUNGI
growth rate
contaminants
cooling
fU
PO
wastes
nutritional value
and product
quality
cost
Growth rates are lower than bacteria or yeast;
poorer productivity.
Contaminants may have higher growth rates and
take over. Aseptic conditions are required.
Fungi, of interest as protein sources, do not
grow well above 35°C, refrigeration may be
required. However, many potentially useful
fungi which have not been examined closely
will grow optimally at + 35°C.
Spent growth medium may have high BOD
which must be treated.
Toxins may be produced by some fungi, Mycelium
tends to be deficient in methionine. Nutri-
tional value for mycelia for domestic animals
and man have not been established.
Slow growth rates-and requirements for aseptic
conditions and cooling make fungal protein non-
competitive in U.S. for use in animal feed.
May be useful as flavoring additive.
-------
TABLE 8 (continued)
BACTERIA
- rapid growth rates
oxygen
requirements
ro
LO
ability to utilize low
cost- substrates such as
methane, paraffins,
methanol, cellulose
generally good yields-
protein contents (70-oOSK)
and aralno acid profile
genetic
stability
cooling
harvesting
nutritional
value
cost
Large quantities of oxygen are required
especially with hydrocarbons. Sterility
must be maintained since pathogenic
bacteria may grow under same conditions
as desired.
May vary widely among different species.
Large amounts of heat released during
growth. Refrigeration may be required.
Small size of bacterial cells makes
centrifugation too costly.
Endotoxins may be present in cells,
acceptability to humans and animals yet
to be established.
Achieving production costs of less than
$0.20 per kilo will require improved
oxygen transfer system and product separa-
tion techniques.
-------
TABLE 9
MASS DOUBLING TIMES (19)
Time for one
Organism mass doubling
Bacteria and yeast 10-120 min.
Mold and algae 2-6 hours
Grass and some plants 1-2 wks.
Chickens 2-4 wks.
Pigs 4-6 wks.
Cattle 1-2 mo.
People 0.2-0.5 yrs.
Other advantages of SCP production include:
- Genetic experimentation to improve protein quality is possible.
- Production of SCP is not limited by land surface or sunlight ex-
cept for algae.
- Microorganisms not dependent upon agriculture or climatic condi-
tions (except algal growth in ponds) (14).
The microorganisms available for growth to single cell protein are convenient-
ly classified according to the temperature range for optimum growth. Mesc-
philic organisms grow well between 20-45° C and thermophilic organisms grow
best between 45-60° C. They are all aerobic microorganisms, i.e., they re-
quire oxygen for growth. Temperature control of the fermenter using ground
water at ambient temperatures is more easily accomplished with thermophiles
(26).
when utilizing cellulosic wastes as a substrate, there are additional ad-
vantages in using thermophilic organisms (26):
24
-------
(a) Therraophiles have a higher rate of cellulose and lignin
digestion than mesophiles;
(b) Thermophiles grow at pasteurization tenperatures, thus
eliminating pathogens present in the wastes.
Further Treatment for Human Consumption
As previously mentioned, single cell proteins contain percentages of nucleic
acids ranging from 6 to 25% depending on conditions of growth and species of
microorganism (28). Ruminants possess enzymes which metabolize nucleic acids
to the soluble excretable allantoln. Man lacks these enzymes and metabolizes
nucleic acids to the sparingly soluble uric acid, which increases In concen-
tration in the urine and plasma (28). Increased plasma levels of uric acid
result in deposition of uriate crystals in the joints, as in gout. The Pro-
tein Advisory Group of the United States (PAG) has established an upper
limit of 2 grams of nucleic acid per day for the healthy adult (29). This
figure is based on research by Waslein vt aJL at Berkeley (3Q) and Edozien
e£ aJL at the Massachusetts Institute of Technology (31). Individuals on a
low purine diet cannot tolerate this high a level of nucleic acids.
Therefore, if SCP is to be marketed as a human food, it must be processed to
remove the nucleic acids, or at least to reduce their percentage to an ac-
ceptable level. Several methods are under investigation for modifying the
nucleic acid content of single cell proteins. They Include(28):
(a) Control of growth rate - the RNA content of cells is
dependent on growth rate;
(b) Base-catalysed hydrolysis - treatment with sodium
hydroxide or potassium hydroxide has been proposed for
microalgae;
(c) Chemical extraction - hot sodium chloride reportedly
removes nucleic acids from yeast;
(d) Cell disruption - physical, chemical and biological
(enzymatic) treatments have been described as methods
for cell disruption when the protein isolate is de-
sired. High pressure homogenization has been proposed
by Sucher e£ aJL (32) as a means of producing protein,
a glycan and a yeast extract from bakers' yeast.
Ultrasonic techniques have successfully solubilized
the protein from heat-treated soybean products (33),
and cottonseed products (3*0 and could be applicable
to release of protein from SCP cells.
(e) Treatment with exogenous or endogenous enzymes - Castro
&t o£ (35) used exogenous pancreatic RNase to reduce
the nucleic acid content of yeasts, and found that the
efficacy of the process was independent of either the
25
-------
whole egg 11
3.5
whey protein
concentrate
fish protein
concentrate
whole milk
beef
SOP bacteria
(cone./isolate)
SCP yeasts
(isolate)
SCP yeasts
(whole cell)
soy
SCP bacteria
(whole cell)
cooked Lima
beans
peanut butter
3-3.2
3.0
Illlllllllllllllllllll
2.7
II
2.6
,'2.5
2.4
Illllllllllllll
2.0
•Illlllllllll
1.8
1.7
whole wheat
Illlllllllll
Illllllll"
1.5
I
• 11 conventional
protein source
SCP
protein source
1234
protein efficiency ratio (PER)
Figure 4. Protein Efficiency Ratios of a Number of Protein Sources (40), (12)
26
-------
age or species of yeast.
Following either heat or chemical shock, activated
endogenous RNase will reduce the RNA content of
Candida, utttca from 7 to Q% to 1 to 2%.
The effectiveness of these treatments in removing nucleic acids must be bal-
anced against the cost of each treatment and its effect on the functional
properties of the SCP. Much research and development work is still under-
way both to reduce the nucleic acid content and/or to release the protein
from the cells. Sinskey and Tannenbaum (28) are looking into the possibil-
ities of genetic engineering to produce temperature sensitive mutants which
stop nucleic acid synthesis above a certain temperature.
In man and mono-gastric mammals, the digestibility of single cell protein is
thought to be hindered by the cell wall (36). The production of protein con-
centrates from whole cells is known to improve the biological availability of
the protein (37).
The manner in which the SCP is treated and dried also alters its functional
properties, such as gel formation, whipping and foaming abilities and water
and fat absorption characteristics (38). More research is required into
the functional properties of variously processed single cell proteins. This
requirement applies to SCP grown on any substrate including solid wastes.
i
Protein Quality and Amino Acid Composition
The protein content of a product as measured from a nitrogen assay (Kjeldahl
nitrogen X 6.25) is inaccurate because of the non-protein nitrogen in the
cell. Amino acid analysis provides a more accurate indication of the nutri-
tive value of the SCP. If the protein has an amino acid composition corres-
ponding to the ideal pattern required by the body, it may be well utilized.
The Pood and Agriculture Organization (FAO) has established a reference pro-
tein with a particular percentage of essential amino acids, to which other
proteins are compared. The value of a particular protein source is limited
by the amino acid present in the lowest proportion. For example, in the case
of wheat gluten, lysine is the limiting amino acid, reducing the utilization
of wheat protein to 33% that of an ideal protein. The amino acid distribu-
tion in single cell proteins varies, depending on the microorganism and the
substrate, as well as the environmental factors of production. Some single
cell proteins have been found deficient in the sulfur-containing amino acids,
methionine and cystine.
Empirically, the quality of a given protein is established through nutrition-
al trials to establish how much weight gain results per gram of protein con-
sumed. This figure may be expressed as protein efficiency ratio (PER); as a
biological value (BV) or as net protein utilization (NPU). Figure 4 compares
the protein efficiency ratio of yeast and bacterial SCP, with the PER values
for more conventional protein sources.
27
-------
Certain amino acids which cannot be synthesized by the human body are con-
sidered essential in the diet. They are isoleucine, leucine, lyslne, meth-
ionine, phenylalanine, threonine, tryptophan and valine (39). Histidine
is essential for growth in infants.
Nutritional Studies
However favorably the amino a'cid analysis compares with the FAO reference
protein, the true digestibility or acceptability of the SCP can only be es-
tablished by short and long-term nutritional trials of laboratory animals.
Every single cell protein must undergo stringent toxicological and nutri-
tional trials before marketing can be considered. In 1972, PAG reissued
updated guidelines in a series relating to the clinical testing of all novel
proteins as potential animal feeds or as human food (29), (4l). These
guidelines are extremely comprehensive and are adhered to in principle in
laboratories throughout the world.
SCP for Human Consumption
Various researchers have reported adverse gastrointestinal effects on human
consumption of even small quantities of yeast, though at least a dozen re-
ports have indicated a human tolerance of up to 100 grams/day (g/day) (4).
Similarly, according to some reports, algae have been tolerated up to 100
g/day without gastrointestinal disturbance, while other nutritional trials
have demonstrated a poor tolerance of microalgae even in small amounts (4).
Galloway aJL at at Berkeley, found that small quantities of several bacterial
proteins produced stomach cramps, nausea and vomiting in human volunteers,
when larger doses have indicated no adverse effects in a variety of experi-
mental animals. Researchers at MIT have similarly noted gastrointestinal
problems and the development of sensitivity among two groups of fifty human
volunteers ingesting 12 g of a bacterial SCP or 20 g of a yeast. Both or-
ganisms were grown on food-grade ethanol. A MIT study feeding fungal pro-
tein to human volunteers at the rate of 40 g/day for one week also reported
abdominal discomfort (4).
Though published results of nutritional trials with human subjects have been
limited, the mixed results so far reported are discouraging. The reasons for
the poor human tolerance of single cell proteins are not clearly understood,
though a number of possibilities exist. It is clear that there is a need for
more basic research into the acceptability of single cell products as human
food. Because a product has successfully completed a series of animal feed-
ing trials, no assumptions can be made with regard to human acceptability.
In spite of these general difficulties, Amoco Foods is now marketing a food-
grade yeast, "Torutein". "Toruteln" is Torula yeast grown on ethanol and
spray dried. This yeast has long been established and accepted as a food
ingredient and Amoco Foods has already obtained government clearances to
market "Torutein" in Canada and Sweden as well as in the United States (23).
28
-------
The yeast is about 52JK protein and due to Its relatively low methionine level
has a PER value of about 1.7. The yeast has a high lysine content and as
little as 9% added to wheat will improve the PER value of wheat from 1.1
to 2.0. "Torutein" is being marketed as a flavor enhancer of high nutrition-
al value, with very acceptable functional properties. Three grades of "Tor-
utein" are available:
(a) "Torutein" - especially well suited for addition to
meat products;
(b) '*rorutein-LF" - low flavor "Torutein" especially ac-
ceptable where a low yeast flavor is desirable, and
valuable as a replacement for nonfat dry milk;
(c) "Toruteln-94" - which can replace 20 to 100? of whole
egg or egg yolks in salad dressings, bakery goods, etc. (23).
Other major firms interested in manufacturing food-grade SCP include Exxon/
Nestle and Ranks Hovis McDougall/Du Pont. Exxon Enterprises has looked into
growth of both bacteria and yeasts on food-grade ethanol. They are investi-
gating strains of the bacterium, A
-------
has been a special emphasis on nutritional trials with pigs, poultry and
calves though other animals (fish, quails, etc.) have also taken part in the
testing program C46). The BP Cap Lavera plant is on-line at 20,000 tons/year.
A 100,000 tons/year plant is under construction in Sardinia.
"Pruteen", the ICI feed-grade protein, analyses as 72% crude protein at nor-
mal moisture levels. It will be marketed as a source of energy, vitamins and
minerals as well as a highly balanced protein source. The methionine and
lysine content of "Pruteen" (1.8 and 4.9/S respectively) compare very favorably
with white fish meal. Extensive feeding trials have indicated that "Pruteen"
is better than fish meal in many diets. A commercial plant of capacity
100,000 tons/year is in the final stages of design (47).
The construction of a 100,000 tons/year plant by Liquichimica Company of Milan
in Calabria, Italy, was delayed by financial problems. A special feature
of their process is the sea-water cooling system using DeLaval titanium plate
heat exchangers of special surface design (48).
In the next ten years, it is anticipated that there will be many feed-grade
SCP plants of at least 100,000 tons/year capacity in Czechoslovakia, Prance
Great Britain, Japan, Italy and the USSR.
Future Prospects.
There is a difference of opinion as to future directions for single cell pro-
tein manufacture. While the technology for production of food-grade SCP
is not as advanced as that for feed-grade protein, some experts believe that
the potential of SCP as a food is greater than its potential as, a feed for
economic reasons (12). The marketing of "Torutein" by Amoco as a food ad-
ditive is seen as an attempt to test and develop markets for food-grade SCP.
Many companies have expressed an interest in "Torutein", and Amoco is "en-
couraged" bu the response of its marketing efforts (23). Marketing a new
product in well-established markets is the preceding stage to development of
new markets and uses for the product.
The acceptability of a bacterial, fungal or algal protein for human consump-
tion probably suffers more psychological constraints than does consumption
of yeasts. Certain agricultural wastes are also likely to be "unacceptable"
substrates for growth of food-grade SCP, e.g., manures. A number of cultural,
religious and sociological taboos limit the consumption of a new food even
though it has an acceptable taste and "mouth-feel".
Some experts believe that consumer resistance to products considered "arti-
ficial or imitation" food will delay acceptance of SCP products in sophisti-
cated markets, at least until vegetable-based proteins are more widely ac-
cepted by the general public (49).
European markets are currently more promising outlets for feed-grade SCP than
the U.S., as Europe has to Import the bulk of its oil-seeds while the United
States is the world's leading exporter of soy products. In this country,
long term prospects for marketing of feed-grade SCP from low cost cellulosic
30
-------
wastes are very attractive. Table 10 projects the U.S. demand for high pro-
tein feed-grains to 1990 (50).
Government regulations relating to usage of SCP in animal feed or as a human
food vary from country to country. As previously mentioned, most companies
are adhering in principle to the PAG guidelines for clinical testing of novel
proteins. In Europe, the European Association of Single Cell Protein Pro-
ducers (UNICELPE) was inaugurated on November 27, 1974. Che of the functions
of UNICELPE is to develop a common policy toward testing and regulation of
single cell proteins In Common Market countries.
The future for SCP in sophisticated markets looks promising both as a food or
feed. Whether food-grade SCP will solve problems of the hungry in Third
World Countries is another question. All processes so far mentioned are high
technology, high investment projects. Tate and lyle believe that a low cost,
"village-level" technology is needed for the emergent nations. They are
building a pilot-plant in Belize, Central America, to examine the feasibility
of utilizing citrus industry wastes to produce fungal protein for feeding to
pigs and poultry. They have investigated growth of AApe/uj.ct£u6 nigesi (Ml)
and a Fuao^uun 4p. on carbohydrates (especially carob pods and spoiled pa-
paya) in the laboratory for some years (51). Their calculations indicate that
a low technology plant in a country with cheap labor could be economic on the
scale of 100 tons of SCP product/year. The citrus industry in Belize pro-
duces about 2300 tons/annum of a high BOD waste, most of which is dumped (52).
Whether a "village-level" technology, manufacturing a relatively expensive
feed-grade SCP to support an expanding livestock Industry, will in fact solve
the food problems of the very poor, is also questioned by many.
It is clear that though many problems of technology, economics and acceptabil-
ity are not solved, that a new industry has been born which will continue to
work towards production of high quality, inexpensive protein for human and
animal consumption.
31
-------
TABLE 10
FORECAST OP ANIMAL PEED CONSUMPTION
IN THE UNITED STATES, 1960-1990
(Millions of Tons) (50) *
Item I960 1970 1980 1990
Peed Grains 121.80 144.90 176.00 200.00
High-Protein Supplements:
Soybean Meal 8.84 13.46 17.80 22.85
Other Oilseed, Animal
and Grain
Total High Protein
Other Processed Feeds
Total Feed
7.95
16.79
11.24
149.83
7.81
21.27
13-31
179-48
8.95
26.75
15.85
218.60
8.55
31.40
17.80
249.20
* 1980 and 1990 estimated. I960 and 1970 derived from USDA Economic Research
Bulletin No. 410, Feed Statistics through 1966, as supplemented through
1969, Feed Situation, November 1971 and certain unpublished data.
32
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SECTION 5
THE NUTRITIVE POTENTIAL OP WASTES
CELLULOSE
Cellulose is a major component of the municipal, industrial and agricultural
waste streams both in terms of volume and weight. Prom 1.4 to 2.0 billion
tons of cellulose are discarded each year (53). Traditional methods of
disposal of solid wastes, principally landfill and incineration, are not
strictly controlled by environmental legislation, and are becoming increasingly
expensive. In order to defray cost of treatment and disposal of cellulosic
wastes, attention has focused on the reuse of these materials. Products of
commercial value which could be obtained from cellulosic wastes include various
chemicals, energy, animal feed or human food (see Figure 5).
However the waste is to be commercially exploited, there are problems connected
with the collection and seasonality of certain wastes, notably the agricul-
tural field residues which are generated in the largest quantities. Certain
agricultural wastes are found in large enough volumes in specific locations
to make collection a simple and relatively economic proposition. These wastes
include sugar cane bagasse, com cobs and stalks, milling wastes from wheat,
rice and other grains, and prunings from orchards and vineyards. Large volumes
of manures concentrated at feedlots are a pollution problem, and because of
market limitations on the use of manure as a fertilizer, are negative cost
wastes for resource recovery systems. Logging slash and the wastes of the
pulping industries are also readily available at certain locations.
An extensive state-by-state inventory of all agricultural wastes was under-
taken by Stanford Research Institute. Their findings are the most complete
and accurate record of the nature, magnitude, distribution and availability
of agricultural wastes across the United States (115).
Municipal solid waste (MSW) is of course generated dally and is collected
regularly for disposal. A number of cities are operating or planning energy
recovery systems using MSW as a fuel source, either through co-firing, water-
wall Incineration or pyrolysis (St. Louis, Missouri; Ames, Iowa; Wilmington,
Delaware; Seattle, Washington, etc.)
Since cellulose-containing materials are naturally biodegradable by a variety
of microorganisms, much of current research into stabilization of organic
wastes has focused on biological methods for decomposing cellulose to useful
products. Biological attack of cellulose is impeded by impurities in the
33
-------
Figure 5. Alternative Products from Salvage of Cellulosic Wastes
-------
wastes, heavy metal contamination, high salt content, herbicides and pesti-
cides (5*0. Variable composition wastes are also a problem when establishing
optimal reaction conditions and concentrations for a commercial process.
Table 11 gives the cellulose content of various wastes (55)•
What is Cellulose?
Cellulose is an Insoluble linear polymer of anhydroglucose which exists as
both an amorphous and a crystalline solid. The composition of cellulose is
Illustrated in Figure 6. In nature, cellulose Is associated with heml-
celluloses and lignin. The ease with which the cellulose is attacked by
microorganisms is limited by the percentage of lignin In the sample (56).
H
Figure 6. Structural Fbrmula of Cellulose
35
-------
TABLE 11
CELLULOSE CONTENT OP VARIOUS MATERIALS (55)
Material Cellulose, % dry weight
Filter paper 98+
Newsprint 85
Sugar cane bagasse 51
Rice straw 3^
Corn cobs 37
Prairie grass 37
Cotton linters 90
Cottonseed hulls 50
Paper-pulp bagasse 96+
Cellulolytic organisms manufacture enzymes called cellulases which attack
either or both cellulose and hemicellulose to form mono- or di- saccharides
which are then used as food by the microorganisms (50). The rate of reaction
of the cellulases depends on the surface available for attack. A decrease
in crystallinity of the cellulose, which increases its surface area, will
increase the rate of reaction (56). Lignin is a three dimensional polymer
formed by condensation of radicals of cinnamyl alcohol. Various forms of
lignin are recognized and while the nature of the lignin-cellulose complex
is not fully explained, the lignin appears to form a "cage-like" structure
around the cellulose which reduces its availability to cellulase attack (26)-.
36
-------
Whether the cellulosic waste is attacked by anaerobic organisms to produce
methane and carbon dioxide, or by various aerobic organisms to grow SCP,
rates and yields of reaction are limited by the crystallinity of the cellu-
lose, but more especially by the lignin "net". Also, the lignin content
of several field residues makes for poor digestibility by ruminants and
hence limits the possibilities of directly refeeding certain straws and
grasses to cattle (57).
Various chemical and physical methods to strip the lignin or in some way
modify the structure of the lignocellulose add significantly to the cost
of all biological resource recovery systems from cellulosic wastes.
Pre-treatment of the Wastes
Table 12 summarizes some of .the pre-treatments tested and found acceptable
by investigators currently active in nutrient recovery from wastes. Chem-
ical and physical methods have received more attention, but biological
methods for pre-treatment of cellulosic wastes to improve biodegradability
are also possible. As research is ongoing into various forms of pre-treat-
ment, newer methods may prove more technologically and economically feasible
than the methods presented in Table 12. It should also be noted that there
will probably never be just one most effective method, but that the most
feasible treatment will continue to vary depending on the nature of the
wastes.
Another approach to improving the utilization of the cellulose by the micro-
organisms is to select an organism better adapted for growth on lignocellu-
lose. The cellulolytic thermophilic filamentous actinomycete, Tk&unomono-
ApoM, tfu6ca has been found capable of significantly degrading substrates
with up to 18$ lignin (58). An additional possibility is to find an organ--
ism which will attack the lignin prior to attack of cellulose by cellulo-
lytic organisms. Crawford and co-workers at the University of Idaho are
beginning systematically to screen various white-rot fungi and bacteria
(expecially the actinomycetes) for their ability to attack lignin (59). Pre-
liminary to this screening, it was necessary to develop a new and more ac-
curate procedure for determining the degree of lignin biodegradation than
the commonly used KLason procedure.
An organism known to be a lignin degrader (PotypottuA vWApon&. jjttdco.) grew off the lignocellulose without evolving CC^. Natural
lignocelluloses (twigs) fed l^C-tagged phenylalanine incorporated the 1^C
only into their lignin components. The percentage of radioactive carbon
dioxide evolved was taken as a measure of the lignin-degrading activity of
the organism. A minimum value of approximately 2% conversion to ^CCv? is
considered acceptable as identifying lignolytic activity (63).
There are a number of other problems connected with commercial exploitation
of bioconversion processes to stabilize wastes and exploit their nutrient
37
-------
TABLE 12
VARIOUS METHODS OP PRETREATING CELLOLOSIC WASTES
SO AS TO IMPROVE BIODEGRADABILriY
Substrate
Organism
Treatment
Results
Reference
Sugar cane
bagasse
Peed lot
wastes
U)
CD
Newspaper
(Boston Globe)
virude.
alkaline swelling at
moderate saturated
stream pressure, uv
Irradiation, severe
mining, partial acid
hydrolysis
acid treatment, alkali
treatment, oxidation
with HNO^n
enzymes for 15 hrs.
@ 80°C
ball milling, pot
milling, cupranmonlum,
alkali, viscose, soak
in water, boil in
water, shredding,
hydropulping
alkaline swelling Dunlap
at moderate satu- (54)
rated steam pressure
most effective at
lowest cost
NaOH. 0.05M § 23°C Bellamy
for 4 hrs. 7^-81* (60)
degradation
NaOH, 0.05M 6 23°C
for 20 hrs. 76-80*
anhy. NH? @ 10 ats
& 23°C 72-80*
enzymes, acid & oxi-
dations relatively
ineffective
ball milling very Spano
effective, pot (6l)
milling acceptable
too, preliminary
hydropulping would
cut costs
-------
TABLE 12 (continued)
Substrate
Organism
Treatment
Results
Reference
oo
vo
Various pure
cellulose sub- VAJu.de.
strates
Agricultural
wastes:
Rice hulls
Bagasse
Manures, etc.
Paper:
Computer print-
outs
Milk cartons
Corrugated
flbreboard
etc.
MSW:
Black Clawson
Bureau of Mines
Ground refuse, various
wood pulp, water- mycelial
pulped refuse fungi
pot and ball
milling
ball milling
effective In Im-
proving % of
sacchariflcation
Spano
(61)
high temperature
hydrolysis, electron
irradiation, nitrate
photochemical treat-
ment, alkali oxida-
tion
nitrite photochemi- Rogers
cal treatment superior (53)
to others tested
alkali oxidation also
Improved rate of degra-
dation
others not effective
-------
TABIE 12 (continued)
Substrate
Organism
Treatment
Results
Reference
Waste paper
(Newsprint
without Ink,
newspaper)
Pulped wood
(3, 8 & 18%
lignin)
ball milling
dried and ground
(40 mesh)
% cellulose utilized Ubdegraff
varied from $\% to (62)
Bl% depending on
paper, reaction
conditions
total cellulose loss Crawford
after 5 days: (58)
3% lignin - 9256
8% lignin -
18% lignin -
-------
value. The handling of an Insoluble solid substrate presents engineering
difficulties, but the technology exists to overcome these problems. How-
ever, more experience of large scale fermentation is required.
Alternative Food/Peed Production Systems
As indicated in Figure 7, there are a number of alternative processes for
food/feed production from cellulosic wastes. The aerobic fermentation of
wastes to produce SCP is but one possibility. Another feasible system is
anaerobic fermentation of the wastes to produce methane and a sludge with
potential value as an animal feed. Certain agricultural wastes could be
fed to ruminants without further treatment (manures) or with treatment to
improve digestibility (grasses, straws, and manures). A brief overview of
each possibility follows.
Aerobic Fermentation of Wastes to SCP
Although the commercial growth of SCP on cellulosic wastes is not as advanced
as SCP growth on other substrates, partly for historical reasons, and partly
because of the special limitations mentioned above, there is much active re-
search ongoing in the field.
The growth of a symbiotic culture of the mesophilic bacteria, C&l£u£omoncu>
4p. (ATCC #21399) and A£ca£c0ene6 rfaeco&ta (ATCC #21400), on sugar cane
bagasses has been studied at Louisiana State University. The process is
applicable to a variety of wastes.
The bagasse was treated with a.i-T
-------
ro
WOOD WASTES
aexobic fermentation
untreated manure
growth of fly pupae
sludge as feed
fermentation
anaerobic digestion
of sludge
methane as
treatment of field
residues to improve
digestibility
crops - ensilage,haylage
growth of water
hyacinths on sewage
enzyme hydrolysis
growth of algae
KEY
MSW — Municipal
Solid Waste
SCP - Single Cell
Protein
Figure 7. Possible Food/teed Recovery Systems from Cellulosic Wastes
-------
study by the Western Regional Research Laboratory, U.S. Department of Agricul-
ture. As the burning of rice straw is now limited by pollution legislation,
efforts are being made to find an economic use for the millions of tons of
rice straw generated each year (an estimated 7.6 million metric tons in 1970
In the United States (57)).
As generated, rice straw is a low-quality feed, poorly digested by ruminants
with only 4.556 crude protein (57). Both the lignin and the high silica con-
tent of rice straw (up to 155? dry weight) limit the digestibility of rice
straw (30% digestibility, c.f. alfalfa 5056).
At the Western Regional Research Laboratory, after pre-treatment with either
soda or aqueous ammonia, the rice straw was fermented with both mixed and
individual cultures of CeJUMomon&& &p. and McaJUgweA ^ae.caLi&. The mixed
cultures utilized 7556 of the substrate and produced 18.61 of total substrate
weight as nrLcroblal protein. The cells were 385? crude protein and the resi-
due contained 1256 protein (64). In vitro rumen digestibility (IVRD) of the
cellulose residue increased to 5256, while the digestibility of the cell was
41.2$ to 5556. Both the cells and the residue had a high ash content, 2556
and 2156 respectively. Data indicated that the residues could be used as a
high protein feed for ruminants, and the nrLcroblal cell fraction could be
fed to nonruminants.
The Western Regional Research Laboratory has also investigated the semisolid
fermentation of Candida utitU, Aufre.obaA
-------
The General Electric Company has studied growth of a series of thermophilic
actinoraycetes on feedlot wastes. Several hundred species of microorganism
collected from a number of sources were screened for growth on cellulose and
lignocellulose. The organisms chosen grew optimally at 55° C and pH 7.5 -
7-8. The Casa Grande demonstration plant was built recognizing the need to
investigate high solids fermentation on a larger scale than the bench-top
fermenter. feeding trials were stopped because of problems including
culture stability and variability. Experience with large-scale high solids
or "solid-state" fermentation is still very limited.
At the University of Pennsylvania, Humphrey and co-workers have investigated
growth of a Th.&woa.c£Lnomyc.oA &p. obtained from General Electric. The ini-
tial substrates chosen were feedlot wastes, cryogenically ground Oregon
grass, seed hay and bagasse. The high solids concentration of the wastes
caused problems with mixing, sampling and line plugging.
Because of problems in obtaining uniform feedlot samples for laboratory study
and because of the variability of data obtained from the wastes, it was decided
to concentrate on growth of TkeJunoavtuiomyceA on pure cellulose. Though the
substrate under study (AVICEL/FMC PEL02) is highly crystalline, rates of
degradation as high as 5-10 g/litre-hour were recorded (66). Both batch and
continuous runs were studied. Pew of the runs produced total cell yields
higher than 25/6 with complete cellulose digestion. Economic analysis indicated
35% yields as the break even point.
Both oxygen transfer and glucose concentration limited growth of the cells.
Preliminary results have indicated that yields of 0.45 g. cell/g. cellulose
utilized and cell growth rates of 0.45 hr-1 are possible. The key problem
was identified as optimizing cell productivity and yield as well as achiev-
ing high cellulose digestion.
The Northern Regional Research Laboratory, U.S. Department of Agriculture,
has investigated growth of "Pudiode^mo. vVvLde. on feedlot wastes. They found
that not only did the fungus produce high yields of cellulases but that
after rapid growth of the fungus for four days, the unpleasant odor of the
wastes was replaced by an earthy odor (67). After seven days, the cellulase
activity of the fungus approached its highest value and the wastes were
stabilized. It was found that 66% of the carbohydrates were utilized.
The fermented waste retained its nitrogen and improved its amino acid pro-
file, increasing the percentage of tysine and retaining the sulfur-contain-
ing amino acids. Crude protein content of the fermented solids increased
from 18.8# in the undigested manure to 22.6$ (67). The highest cellulase
activity coincided with a final pH of 5 and an Initial substrate concentra-
tion of 2.5$. Tween 80 (polyoxyethylene sorbitan monooleate) and oleic acid
(0.1$) were added to stimulate cellulase production. The stabilized
enriched wastes are being considered for refeeding as a protein supplement.
The Solid and Hazardous Waste Research Laboratory (SHWRL), Environmental
Protection Agency, has studied growth of fungi on waste cellulosics, in-
cluding ground or water pulped municipal refuse. A summary of pre-treatments
investigated by SHWRL is found in Table 12.
44
-------
The Laboratory has also looked at ways to luprove the quantity of protein
synthesized by the fungus, by adding various agents to the cultures which
might stimulate the metabolism of nitrogenous compounds. A number of auxins
and herbicides were added to fungal cultures, individually or with zinc
sulfate. The effect of zinc sulfate alone was also evaluated. After three
days incubation, each flask was analyzed (Kjeldahl nitrogen) for increased
protein synthesis. The results were statistically compared using Dunnet's
t-statistic test (68).
The results indicated that for the fungi evaluated {ftuicSwdwma.
Aape/U}.t&fcu6 fiumigatuA, tepesigMZuA oixiwonJCi, grown on glucose or whey as a
substrate, zinc sulfate in combination with growth regulators increased both
mycelial mass and fungal protein content over both the control and growth
stimulators alone. The improvement was more noticeable for fungi grown on
the glucose than on the whey (68).
As the economics for production of SCP from cellulosic wastes are marginal,
any improvement in protein quality and quantity would increase the economic
feasibility of the process.
Updegraff at the Denver Research Institute has studied growth of
vesiAwxuuja. on ball-milled newspaper. The maximum rate of cell growth recorded
was 0.3 grams /litre/day (g/l/day) and the maximum protein yield was 1.42 g/1
(62). Urea (0.3 g/1) and yeast autolysate (1.0 g/1) stimulated growth rate
and protein production. It does not appear that this process is economically
feasible because of the low yields and growth rates.
Pulp and paper industry sludge presents a definite disposal problem. The
sludge is difficult to dewater as the pulp fibers retain water to form a
gel-like structure. Incineration of the sludge cake and landfill are both
increasingly expensive and are associated with various pollution problems .
Growth of Th&unomono&poML fa&ca. on pulp and paper mill sludge could be a
process which would not only stabilize the wastes, but also defray the
costs of disposal by production of a marketable product.
(For an approximate protein content of selected organisms grown on waste
materials, see Table 13).
The University of Wisconsin has investigated growth of T. rfuaco. on a number
of sludges. Growth of the bacteria on aspen sulfite fines for six days gave
a 30 - 4056 yield of a product containing 30 - 35% protein. The araino acid
profile is good (see Table 14), and preliminary feeding trials with test
and control groups of chicks indicated that replacement of 2555 of their feed
with T. j{u6ca was well accepted. In three weeks, the average weight gain
for the test group was 123g and for the control, 125g (70). Growth of bac-
teria reduced the BODjj by 9Q%. Effluents from the process would require
some treatment prior to disposal, perhaps in aiereated lagoons (59) .
The aim of the Swedish Forest Products Research Laboratory is to develop a
process based on solid lignocellulose waste in which hydrolysis and protein
production are carried out simultaneously. They are investigating conver-
-------
TABLE 13
APPROXIMATE PROTEIN CONTENT OF
GROWN ON WASTE MATERIALS
ORGANISMS
Organism
Substrate
% Protein Source
Fungi
Fu&o/tuun
Ttiichod&ma.
Pae.oJJtomyc.eA
Bacteria
CeJUtu&omonoA
Candida.
Ge.o&Uckum candidum
Sac.chanomyQ.eA
maxJuna.
Eugtena.
newsprint 30
glucose 31
ag. carbohydrates 25-35
ag. carbohydrates 41-51
glucose 34
rye-grass straw 10.9
glucose
sulfite waste liquor 55-60
bagasse 50-55
rice straw 38
feedlot waste 50
woodpulp fines 30-35
(carboxymethyl-
eellulose) 5^-59
(cellobiose) 59
sulfite waste liquor 50
rye grass straw 12.4
acid food wastes 45-46
brewery wastes 46
acid food wastes 39-3
cheese whey 54-56
secondary waste water 50
sewage or swine manure
digest 60-70
Updegraff (62)
Rogers
-------
TABIE 14
AMEND ACID PROFHE OP SELECTED ORGANISMS
GROWN ON CELLULOSIC WASTES
Organisms
Andno acid
isoleucine
leucine
lysine
methionlne
phenylalanine
threonine
tryptcphan
valine
histidlne
tyrosine
alanine
arginine
aspartic acid
cystine (1/2}
glutamic acid
glycine
proline
serine
Key:
QrEpnl "HI
1
4.74
11.20
6.84
1.86
4.36
5.37
10.71
2.30
2.67
9.21
1 - CeMu&omonoA 4p.
2 - Tke/unocLctinomye.eA
3 - Thexmoa
e£tnom(/ae6
2
7.76
9.15
3.29
0.62
5.45
4.88
6.38
4.16
1.13
3.55
7.71
3.19
9.51
2.06
15.89
4.47
1.68
4.27
(ATCC
# 26
# 24
3
4.2
7.3
12.3
1.5
5.15
2.1
16.2
3.4
4.3
4.1
3.6
3.0
4.9
6.8
2.4
2.2
1.8
#21399)
4 - The/unomono&poJw. fiu&ca
5 - AapeAg>t££tt6 AumigatuA
# 3
6 - TtujchodesuncL vinAde. # 9
4 5
3.20 7-30
6.10 8.80
3.63 4.40
2.06 7.30
2.64 6.10
4.00 7.00
12.97 2.60
1.96 2.20
1.87 3.90
13,92 5-90
5.62 3.70
6.74 8.80
0.41
18.03 11.00
4.42 5-30
6.10 2.90
2.57 5.50
substrate
. bagasse
- feedlot waste
- feedlot waste
- fines
- waste paper
- waste paper
6
4.00
5.10
4.40
2.00
5.50
4.40
4.80
1.60
3.70
5.10
4.00
7.70
9.90
5.90
3.70
2.60
reference
- (7*U
- (26)
- (26)
- (70)
- (53)
- (53)
PAD
reference
4.2
4.8
4.2
2.2
2.8
2.8
4.2
2.8
-------
sion of waste fibers from a sulfite mill to protein using the white rot
fungi, Spofijo#u.clum puut.vesiute.ntum. The cultivation starts on glucose and
continues on cellulose. Unlike Wilke it oJL In California (q.v.), the
Swedish group found that the change in substrate did not result in a long
induction period (1.5 hours) (75).
The mycelium contains only 25 - 30/6 protein when grown batch-wise on waste
fibers. It grows In pellets (0.2-0.torn.) which are easy to filter. In
order to improve the protein content, the Laboratory has investigated a
symbiotic process with C. wti£ti. It is felt that symbiotic cultures on
water-soluble olJgomeric materials are more feasible while utilizing Im-
mobilized enzymes.
Erikson and co-workers have also mutated white rot fungi into cellulase-
free mutants. These fungi produce enzymes which attack lignin in wood chips
to permit deflbration of the wood with less energy expenditure (76).
Enzymatic Hydrolysis of Cellulosic Wastes
Researchers at Natick have developed a mutant strain of the fungus, THJicho-
d&una v
-------
as well as the quality of the enzyme. Milled cotton was 6% hydrolyzed com-
pared to over 90% sacchariflcation for milled pulp, SWECO 270 (6l).
The pre-pilot plant operating at Natick is interfaced with a computer for
rapid data analysis and process estimation. Capacity will increase steadily
from 1,000 Ibs/month to 4,000 Ibs/month.
Continuous cellulase production is under study at the University of Califor-
nia at Berkeley. In the first stage of a multi-stage operation, TJu.ckod&una
vjjildi (QJV19414) utilized glucose for growth and in the second stage grew on
pure spruce wood cellulose (77). Determinations were made of the specific
oxygen demand (QQ2) of exponentially grown fungus; the maximum specific
growth rate (y max) and the saturation constant (kg). The maximum specific
growth rate = 0.294/hr. and the saturation constant = 0.083 mg/ml. There
was a substantial time lag (approximately 30 hours) during which the fungus
adapted from growth on glucose to cellulose. Average batch productivity as-
suming 48 hours down time was 13.80 X 10-3 filter paper units (FPU/ml. X
hr, (c.f. calculated from Mandels and Weber, 5.39 X 10-3 FPU/ml. X hr.).
Wilke has produced a complete economic analysis of the capital and operating
costs of a commercial process to hydrolyze domestic wastes to glucose with
TJu.ckod&una v&tide. (78).
Acid Hydrolysis
The bench scale production of sugar by acid hydrolysis of MSW was Investi-
gated by the Thayer School of Engineering. The process was carried out
continuously to produce about 52$ - 54/6 yield of glucose. The reaction took
place isothermally at 230° C using 1% weight of sulfuric acid and with a
reaction time of 20 seconds. The yield was found to be a function of time
of reaction, temperature, concentration of the acid and solid-to-liquid
ratio in the slurry. As the hydrolysis conditions also favor the decompo-
sition of glucose, higher yields cannot be expected (79).
Anaerobic Processes
Digestion of cellulosic wastes in the absence of air produces the gases
methane and carbon dioxide, and leaves a biodegraded sludge. The emphasis
of research and development activities relating to anaerobic digestion of
manures has been on maximization of methane production. However, many in-
vestigators have mentioned the possible utilization of the sludge as either
a fertilizer or a feed. The sludge retains its nitrogen and is superior to
undigested manures in that it is odorless and biologically stable. Also,
the sludge is probably pathogen free (80).
The marketing of the sludge as a feed (or fertilizer) would significantly
improve the economics of the process. Jewell zt aJi at Cornell University
have determined the number of animals required to make methane generation
from cow manure economically feasible for a New York dairy farm (80). They
found that if the sludge could be commercially exploited for its nitrogen
49
-------
content, that the number of animals required to support methane generation
was surprisingly small (see Table 15). Their estimates were based on selling
the sludge as a fertilizer, but presumably utilization of the sludge as a
feed would show similar results.
Hamilton Standard Division, United Aircraft, for the Northern Regional Research
Center, USDA, has completed the first phase of a study of anaerobic digestion
of cattle wastes. This study included both economic feasibility and preliminary
trials of the feed quality of the sludge (8l). The 20 litre fermenters were
maintained in continuous stable operation at thermophilic temperatures, with
loading rates as high as 16.0 g volatile solids/litre/day.
Analysis of the effluents indicated that the crude protein content had risen
to 25% or double the protein of the fed material. At the same time, there
was a mass reduction of 50JE. A four-fold increase in the amino acid concentra-
tion (to 20£) indicated that non-protein nitrogen was converted to protein.
The effluents were non-toxic to baby chicks. An inhibition in feed efficiency
was attributed to high levels of ammonia in the sludge. As ruminants can
assimilate large amounts of ammonia, this inhibition is not expected to
occur when feeding to cattle.
TABLE 15
NUMBER OP ANIMALS REQUIRED TO ECONOMICALLY SUPPORT METHANE GENERATION
TREATMENT OP ANIMAL WASTES (80)
Number of Animals
Animal Energy Only Energy & Nitrogen Value
Beef 570 155
Dairy 380 80
Poultry 57,000 5,200
Swine 2,800 585
50
-------
The second phase of the project Involves the building of a more sophisticated
digester in Nebraska. Extensive feeding trials with cattle hopefully will
clarify the feasibility of utilizing the sludge of digested manures as a rumi-
nant feed. The new digesters will be batch fed; one tenth of the volume of
the fermenter will be withdrawn each day after the reaction has reached the
steady state (82). The solid/liquid residue will be centrifuged and dried.
In extensive feeding trials, the feed-cake will replace all but the com and
wheat portion of the animals1 present feed (83).
SHWRD is funding a study at the University of Wisconsin which will assess
anaerobic digestion and other bioconversion processes applicable on the farm
In terms of technical and economic feasibility as well as energy consumption
(84). The study will examine possible uses of the effluent of digestion:
(a) as a refeed;
(b) as a substrate for algal growth;
(c) in aquaculture;
(d) as a fertilizer.
Jfethodlcal systems analysis applied to the bioconversion processes will do
much to clarify the options available for waste utilization on the farm.
Commercial methane production from Montford Peedlot waste is slated to be in
the range of 120 million cubic feet of gas/month. Seventy million cubic
feet of gas will be sold to Colorado Interstate Gas and fed directly into
Interstate pipelines (85). The sludge will be evaluated as a feed and a
fertilizer.
Because anaerobic digestion of manures produces both energy (as methane) and
a potential feed (the sludge), it looks potentially a very attractive waste
management technique. Ongoing research into the nutritive potential of the
effluents should give a clearer indication of the feasibility of this process.
Anaerobic fermentation of the soluble portion of manures (as opposed to the
insoluble cellulose) is also under study. A number of companies are Investi-
gating fermentation of manures in a silo or covered ditch. Digestion of the
solubles by streptococci and lactobacilll leaves the fibers untouched so that
the wastes require further treatment to degrade the cellulose. The Ceres
Ecology Corporation of Chino, California, will ferment the manure from over
100,000 dairy cattle to produce a refeed, and to minimize salt pollution of
ground water. It is reported that a 10 - 20% savings in feed costs can be
attained by replacing 8 - 10/8 of the protein in the regular feed with the
ensiled manure (24).
51
-------
Direct Feeding of Wastes and Related Methods to Improve the Digestibility
of Cellulosic Wastes
Manures
A measure of the crude protein potential of animal wastes can be found in
Table 16 which gives estimates of the amount of nitrogen in livestock excreta.
This nitrogen comes from undigested feed, by-products of digestion, mlcrobial
cells and sloughed tissue (86).
The simplest way to recover the nitrogen is to refeed excreta to either the
same or a different species. Scavenging of manures occurs in nature, and
cattle are known to lick their own excreta with no apparent ill-effects.
On the farm, there are a number of problems associated with refeeding man-
ures, especially the possibilities of accumulation of feed additives, pest-
icides, toxins and/or pathogens in animal tissues.
Fontanet aJL aJL (87) reported a copper toxicity in ewes fed poultry litter and
Oriel ut aJL (88) reported a high rate of abortion in heifers fed poultry
litter. Nevertheless, poultry litter has been successfully fed to gestatlng/
lactating ewes, fattening steers, beef heifers and calves, and dairy cows
(89) as well as laying hens and broilers (50). Feeding trials with ruminants
indicate that the litter is slightly less digestible than soybean meal (50).
Prior to feeding, the wastes must be dewatered (thermal or air-drying) and
sterilized. Heat treatment at 150° C for three hours effectively destroys
pathogens in poultry litter (89). Though heat processing reduces crude pro-
tein content of the litter, acidification with sulfuric acid to pH 6 lowers
nitrogen loss.
Refeeding dehydrated poultry manure to laying hens is an incomplete waste
management system. The hens can tolerate up to 25% of manure in their diets
before egg production is affected. Therefore, about 75% of the manure must
still be disposed of (90).
In the past, the U.S. Department of Agriculture has discouraged feeding of
poultry litter to other species of livestock for health reasons. More re-
cently, the Department has encouraged and sponsored research into refeeding
of all types of manures.
Cattle manure can be dehydrated and fed to ruminants (86). Alternatively,
the solid and liquid components of cattle wastes can be physically separated
and the washed fiber fed to cattle (91). A series of feeding trials has in-
dicated that the fibrous component of manure could successfully replace a
portion of the basal diet with no ill-effects. No advantage was demonstrated
by heat treating and washing the manure prior to feeding. As washing re-
sulted in production of polluting waste^water, this treatment was kept to
a minimum (91)•
Both poultry and cattle excreta may be ensiled to produce acceptable feeds.
52
-------
TABLE 16
N 5ROM U.S. LIVESTOCK IN 1972 —
BASED UPON LIVESTOCK PRODUCTS MARKETED,
THEIR PROTEIN CONTENT, AND FEED-TO-PRODUCT
PROTEIN CONVERSION EFFICIENCY (86)
Product
Product
Amount * Protein
Conversion
efficiency t
Excreta
protein
factor f
Excreta N §
Milk
Chicken
Broiler
Turkey
jl
*^SEffi
Sheep and
Hogs
Cattle
Calves
Total
lamb
Ibs x 103 %
120,278,000 3.5
1,118,723 21
11,477,931 21
2,424,145 21
8,725,500 10
1,081,254 16
20,258,557 15
37,185,295 15
767,496 15
30
25
25
20
20
10
20
15
15
kg x 10:
2.3
3
4
4
9
4
5.6
5.6
704,173
51,259
525,898
148,093
253,833
113,237
884,010
2,271,683
46.887
4,999,073
Production and slaughter estimates from U.S. Department of Agriculture,
Agricultural Statistics, 1973, Tables 536, 582, 595, 602, 485, 467, and
453.
-1)
t Source: Philips, R.W., 1967
f Excreta protein factor = kg of excreta protein «( 1
kg of product protein conversion efficiency
§ Excreta (kg) = Ib of product x % product protein x excreta protein factor
x 2.2 kg/lb. x 0.16 kg N/kg protein
# Eight eggs assumed to weigh 1 Ib.
53
-------
The University of Auburn has Investigated a number of ensiled mixtures con-
taining cattle manure and hay and/or corn. An ensiled mixture of cattle
manure (5750 and ground hay (43JO was fed to breeding ewes and beef-breeding
cattle. During the former study, lasting 389 days, "wastelage" fed ewes
were noticeably more alert than the control fed hay. The 'breeding cows re-
produced and lactated similarly on either a "wastelage" or corn silage diet.
Animals on corn silage gained more weight than the test group. No harmful
effects were noted in either feeding trial. Chemical studies have indicated
parasitic nematodes were destroyed in the ensiling process.
An ensiled mixture of corn (48$), bermuda grass hay (12%) and manure
was fed to yearling cattle for 152 days prior to slaughter. The cattle were
of the same live weight as a control group fed a conventional feed. Peed
costs for the test were 8% less than the control. The meat was of the same
high quality and reportedly tasted delicious. Anthony of Auburn University
stresses that the manure was collected from "healthy cattle fed approved
feed mixtures" (91) .
Ccmposting cattle manures to feed to ruminants has received little attention
to date. Experience with refeeding swine manures to swine is also limited,
though nutrient recovery frcm swine oxidation ditches has been investigated
(92).
Crop Wastes
As previously mentioned, rice straw is a poor quality feed for ruminants be-
cause of its low digestibility and protein content, poor palatability and
bulk. Both the lignin and silica content of the straw limit its acceptabil-
ity.
One method of Improving the digestibility of rice straw is to heat the straw
with an aiimn. Mild sodium hydroxide treatment has proved most effective.
Holding rice straw at 100° C for 15 minutes increased digestibility from
30% to 73% (57). It is also possible to acid or enzyme hydrolyse the straw
to sugars which are then used as a substrate for yeast growth. Ehsilage of
rice straw with various additives to supply nitrogen also improves the
quality of the feed.
Caustic soda treatment Improves the in vitro rumen digestibility of ryegrass
straw. Han, Lee and Anderson have demonstrated that if the hemi-cellulose
is first removed from the straw that the caustic soda treatment is ineffec-
tive (93). Dioxane treatment was found to improve the microbial digestibil-
ity of the hemi-cellulose free fibers (acid detergent fibers).
Wood and Wood Based Residues
Wood and wood based residues have been evaluated as a source of energy for
livestock and as a roughage extender for ruminants. Because of the low di-
gestibility of woods by ruminants (see Table 17) untreated wood wastes are
-------
TABLE 1?
IN l/ITRO DRY-MATTER DIGESTIBILITY
OP VARIOUS WOODS AND THEIR BARKS (94) t
Substrate
Digestibility*
Wood Bark
Substrate
Digestibility*
Wood Bark
Hardwoods
Red alder 2
Trembling aspen 33
Trembling aspen
(groundwood fiber) 37
Bigtooth aspen 31
Black ash 17
American basswood 5
Yellow birch 6
White birch 8
Eastern cottonwood 4
American elm 8
Sweetgum 2
Shagbark hickory 5
Soft maple 20
Soft maple buds 36
50
45
25
16
27
Hardwoods
Soft maple small
Twigs 37
Sugar maple 7
Red oak 3
White oak 4
Softwoods
Douglas-fir 5
Western hemlock 0
Western larch 3
Lodgepole pine 0
Ponderosa pine 4
Slash pine 0
Redwood 3
Sitka spruce 1
White spruce 0
14
* For comparison: Digestibility of cotton llnters 90/6; of alfalfa, 6l%.
t Reprinted from Baker, A.J. et al. In: Cellulose Technology Research, ACS
Symposium Series, Vol. 10, p.78, 1975.
55
-------
not useful as an energy source. Wood and paper mill sludges could be used
as a roughage extender, as a partial replacement for hay in the ruminant diet
(94).
Many methods of improving the digestibility of both woods and pulp and paper
mill sludges have been investigated. These methods include:
electron Irradiation;
vibratory ball-milling;
gaseous and liquid ammonia;
gaseous sulfur dioxide;
dilute sodium hydroxide;
white rot fungi.
Baker &£ at (94) have measured the effects of the above pre-treatments on a
number of woods and wood based wastes. In vitro rumen and cellulase diges-
tion assays were followed by digestibility and palatabllity studies on goats.
Sulfur dioxide treatment improved digestibility without removing the lignin.
Hardwood sawdust was maintained for two hours in an atmosphere of sulfur
dioxide at 3 Ib/sq. ins. and a temperature of 120° C. Softwood sawdust re-
acted for three hours. After removal of the gas, the woods were neutralized
with caustic soda and then air-dried. The results of the treatment are sum-
marized in Table 18. The treated woods were well accepted by ruminants in
extensive feeding trials.
Delignification of pulp and papermill residues and wood pulp improved their
in vitro digestibility. The degree of improvement depended on the extent of
removal of the lignin. IVRD of the residues was from 45 - 6Q% In vivo
digestibilities were of the same order of magnitude. Hardwoods showed a
greater improvement in digestibility on removal of lignin than did the con-
iferous species. Some residues were unacceptable as a feed because of a
high ash content and heavy metal contamination, but as indicated below, the
parenchyma cell fines were well accepted by the test animals.
Up to 50 - 755? of parenchyma cell fines were successfully included in the
feed of ewes for one year. During gestation and lactation, additional grain
was fed to the pregnant animals. Ewes fed a diet containing aspen bark also
maintained satisfactory growth. Beef cows fed a ration of hay, parenchyma
fines, grain and mineral supplement for seven months maintained growth.
Both ewes and cows in the test group consumed more rations than the controls
fed hay.
Municipal Solid Waste
Van Soest and Msrtens (95) have investigated the composition and digestibil-
ity of low quality cellulosic wastes including MSW and various types of
paper. They point out that as lignin remains unattacked by anaerobic organ-*
isms, that it will accumulate in anaerobic systems and ultimately have to be
removed. Hence, anaerobic fermentation of municipal solid waste, while
56
-------
TABLE 18
COMPOSITICN AND OSLLULASE DIGESTION
OP VARIOUS WOODS BEFORE AND ASTER S02 TREATMENT (94) *
Lignin Carbohydrate Digestibility
Species
Quaking Aspen
Yellow birch
Sweetgum
Red oak
Douglas-fir
Ponderosa pine
Alfalfa
Before
20
23
20
26
30
31
17
After
9!
7
9
5
8
24
19
—
Before
70
66
66
62
65
59
51
After
71
67
64
60
63
58
—
Before
9
4
2
1
0
0
25
After
63
65
67
60
46
50
—
Reprinted from Baker, Andrew J. et al. Wood and Wood-based Residues in
Animal fleeds. In: Cellulose Technology Research, ACS Symposium Series,
Vol. 10, p.90, 1975.
57
-------
increasing the protein content of the wastes (see Table 19) also slightly in-
creases the lignin concentration, and so reduces digestibility.
Feeding edible garbage to swine has been tried, but cannot be considered a
waste management technique with any future potential. Residential wastes
contain inedible and harmful materials, and are not a favored hog feed (50).
The digestibilities of paper products are usually acceptable, as they have
already been treated and at least partially delignified (see Table 20).
Van Soest and Mertens point out that as the composition of papers from dif-
ferent sources varies widely, so does their digestibility. If papers are
fed to livestock, various additives including heavy metals, chlorinated
organics, inks, clays, plastics, etc. may accumulate in animal tissues and
eventually enter the human system. It is therefore suggested that future
research should concentrate on the development of non-toxic easily removable
additives.
Other Methods of Converting Animal Wastes to Nutrients
Colorado State University has Investigated the stabilization of poultry
wastes by the larvae of the common house fly, Muieo. domeAtica. (96). Tubs
of poultry manure were inoculated with fly eggs at rates of 2 to 5 g eggs/
4000 g of manure. The tubs were subjected to different temperatures and
humidities to determine the best conditions for hatchability of the eggs
and stabilization of the wastes. Pupae were harvested from the manure by
flotation, and then force air dried at 65°C overnight. At 27°C, it was
found that the optimum yield of dry pupae was obtained with an inoculum of
3 g fly eggs/4000 g of fresh poultry excreta at a humidity of 415?. Too high
a concentration of eggs resulted in lower yields of pupae.
Within a week, the moisture content of the feces dropped from 78.5 to 55?.
The manure was stabilized with a slight ammonia odor still remaining. The
treated manure had a granular consistency and was much easier to dry than
the untreated excreta.
The protein quality of the fly pupae was similar to meat and bone or fish
meal, and superior to soybean meal. In a series of feeding trials, hens
and broilers were fed rations containing up to 30? of either the pupae,
the stabilized manure or a mixture of both pupae and manure. Chicks fed
pupae as all or part of-their protein ration showed no statistically
significant difference in weight from controls fed soybean meal. New
Hampshire and Indian River chicks fed both pupae and stabilized manure at
levels of 5 to 10? also maintained their weight and feed conversion compara-
tive to the control.
The study concluded that fly pupae have potential as a protein supplement
for chick starter and broiler rations.
As a waste management technique, growth of larvae under caged layers reduces
58
-------
TABLE 19
EFFECT OP FERMENTATION ON COMPOSITION AND ZW I/ITR0
DIGESTIBILITY OP MUNICIPAL WASTES (95) *
Composition %
Description
Raw waste
Treated waste
protein
9
26
cellulose
38
43
hemicell
16
10
lignin
5.0
6.3
Digestibility %
dry matter cell wall
73
65
64
44
* Unpublished data of Robertson and Van Soest.
TABLE 20
CCMPOSITICN AND DIGESTIBILITY OP PAPERS (95) *
Paper type
Office bond
Brown paper
Cardboard
Glossy
magazines
Newsprints
Coarse
magazines
Organic mat-
ter true Hemi-
Ash % dig. % Cellulose
6
1
4
23
0.5
7
96
91
72
62
33
33
10
9
10
6
14
14
Lignin
% %
4
7
- 12
11
24
21
Cellulose
%
77
81
70
50
56
53
Lignin-to-
cellulose
ratio
0.05
0.10
0.17
0.23
0.42
0.41
* UhpubiisBed data of Robertson and Van Soest.
59
-------
the weight by 50/& as well as stabilizing the wastes and reducing odors. Before
land disposals the conpost-like wastes would have to be heat-treated to kill
any fly larvae present (50). If the manure is to be used as a specialty
soil conditioner or a feed, it would have to be dewatered to 10% moisture.
The costs of treatment, labor and land-disposal are not attractive (50).
The USDA at Beltsville, Maryland, has considered growth of fly larvae on
manure held in a rotating drum, as well as other automated techniques to
reduce labor costs. Clear-cut cost estimates for such a process are not
yet available. It is felt, however, that the complexity of the system
would eliminate its use by the small farmer (50).
Algal Systems and Aquaculture
Growth of Algae
Controlled growth of algae In oxidation ponds developed as a waste management
technique to provide oxygen to stabilize organic wastes. The value of the
algae as a protein supplement was recognized, though not at first exploited.
Improvement in growth, harvesting and processing techniques made it appear
that large scale production of algae could provide a low cost protein of
food or feed quality.
In 1969, Oswald and Golueke (18) prophesized that if world research into con-
trolled algal cultures continued to progress at past rates of logarithmic
growth, that by the mid 1980's, it would be possible to satisfy .the entire
protein requirements of the United States.
Today, it appears that the costs of production of algae and the land require-
ments for growth, together with other factors summarized In Table 8, make
gigfti growth for protein much less promising, at least in the immediate
future. The maintenance of a specific algal culture In an outdoor pond has
proved difficult. Growth of algae is limited by available sunlight to a
geographic region between latitudes 35° N. and S.
While a number of companies are actively funding research and development
projects into bacterial, fungal and yeast production, only the Ihstitut
Francais du Petrole (IFF) with Sosa Texcoco, S*.A. are investigating algal
cultivation. SpibuJUncL algae have been grown in culture basins In Southern
Prance, in Algeria and near Mexico City (97). The surface area of the
basins was from 5 to 700 sq. metres. The culture medium contained mineral
salts as nutrients and was maintained at pH values from 8.5 - 11, with ad-
dition of sodium carbonate and bicarbonate. Continuous circulation of the
culture was produced by alternately injecting combustion gas into one of
two connected compartments in the basin.
Semi-natural basins were constructed in Lake Texcoco to exploit the algae
which normally grow in the Lake. On harvesting, it was necessary to pre-
concentrate the SpUuuJLLna. by filtering over an Inclined plane prior to
60
-------
horizontal strip filtering and drying, either on heated rollers or by spray-
drying. ' In 1972, a serai-industrial plant began operation with a capacity of
1 ton of dry algae/day.
Long range comprehensive feeding trials and toxicity assays with rats, chick-
ens and pigs, have so far been very encouraging. In Mexico, the algae have
been successfully Incorporated into beverages, cereals, soups and other human
foods. Though clinical tests of SpiUmUjna, as a human food are not complete,
the Mexican government has cleared the algae for human consumption (97) .
All varieties of waste can be stabilized by algal growth in the presence of
bacteria. The bacteria oxidize the carbon wastes to nutrients which are as-
similated by the algae in photosynthesis . Oxygen produced by the algae is
used by the bacteria to oxidize more wastes (18) .
In the United States, Oswald and Golueke in California have investigated
growth of unicellular chlorophytes (Chton&JULa. and Scen£de6mu6) on sewage,
animal wastes and MSW. The California group is interested in combined
energy/food production systems. They have operated a pilot plant to digest
manure from a poultry house, in order to stabilize the solids and produce
methane. The supernatant liquid was used as a nutrient, the clear liquid
was recycled to the poultry house as wash water. The methane generated could
be used to dry the algae. Gas production from the 400 gallon digester averaged
12 cu. ft. of gas per Ib. of volatile solids added (98).
The California group has also studied the possibilities of algal growth on
wastes for digestion to methane. Again the supernatant could be recycled
as a nutrient for further algal growth, and the methane could be used to dry
harvested algae (98), (99).
The projected cost of algae produced in such an integrated energy/food system
would depend on the method of harvesting. As of 1973 , the cost of harvesting
by centrifugation followed by spray drying was estimated at 6 cents per pound
(98). Alum flocculation, centrifugation to dewater and heat drying would
produce a slightly cheaper product. The most economical method of harvesting
would- be alum precipitation followed by drying on a sand bed and recovery on
a shaker screen, a process which would tend to denature the protein.
Dr. Way good of the University of Manitoba has investigated the mass culture
of EugluuL QMLCAJU&. E. QMAJULJik was chosen for a number of reasons including:
- It contains no cellulose cell wall and should therefore
be readily digestible;
- It is motile, eliminating the need for expensive stirring;
- It can utilize the organic wastes and/or carbon dioxide
from the air during photosynthesis, i.e., it is both
photo^x-otrophic and heterotrophic (73).
61
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Ihe algae was grown on sewage, secondary effluents, abattoir waste and various
livestock manures. Ihe manures were diluted depending on the source, while
the other wastes were used as generated.
The cultures were grown in trays (8 litres, 7.5 cm. depth) or ponds (275 to
550 1., 15 to 30 cm. deep) with no oxygen or carbon dioxide enrichment. At
a pH of 4.0 bacterial and protozoal contamination was restricted though fungal
growth was enhanced. As the fungi were metabolized by E. g/zac/cttA, this was
not a problem.
After four to five days, growth of algae ceased, even though nutrients remained
in the culture. Addition of whey to the media improved growth of the algae
and utilization of nitrogen and phosphorus nutrients.
For sewage or swine manure, optimal growth of E. gtuicAJUt, gave a dry product
containing 60 to 705E protein, 15 to 20% fat, and 15 to 20% carbohydrates.
The yield of algae was between 10 to 40 g dry wt./sq. metre/day. In Manitoba,
this corresponds to a productivity of 5 to 20 tons/acre per 100 frost free
growing season.
Aquaculture
Mass production of marine algae in outdoor cultures has been studied at
Woods Hole, Massachusetts, and Port Pierce, Florida. Duplicate pools of
2,000 litre capacity were used to grow diatoms on a substrate of sea water
(50/S) and secondary waste effluent (50%}. The water was continuously pumped
through the constantly agitated culture, and approximately steady state con-
ditions were established for each flow rate (100). At Woods Hole, the
phytoplankton dominant in the culture depended on the season; Pfiaeodactt/£um
&iic.oJimutum predominated in the late spring, with other successions of
diatoms predominating the rest of the year. In Florida, N^utzdUa
was the prevailing species.
Table 21 shows the effect of dilution rate on the mean algal yield In the
two locations. Note that the yields clearly show the effect of latitude
on algal growth.
Inorganic nitrogen and phosphorus were added as nutrients. The nitrogen
uptake for all species in the culture was up to 99.9% (101).
The phytoplanktcn were fed to oysters and clams in raceways maintained at
15° to 20° C. It was estimated that 92 tons of oyster meat/acre could be
produced during the summer months at Woods Hole (101). Separate studies
with seaweeds have shown that though the seaweeds grow faster than the
phytoplankton, they are less efficient at nitrogen removal (90$).
There is a pilot estuarine aquaculture system at The Tallmans Island Pollu-
tion Control Plant in Queens, New York. The study is sponsored by the
62
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TABLE 21
EFFECTS OF DILUTION RATE CN MEAN ALGAL YIELD
IN TWO LOCATIONS (100)
Dilution rate
0.25
0.50
0.75
1.00
1.50
Msan algal yield 0
Woods Hole
(lat. 41° 52'N)
7-6 (2)*
12.4 (8)
13.3 (2)
12.4 (1)
g dry weight m-^
Ft. Pierce
(lat. 27°
18.0 (6)
15.3 (1)
23.6 (1)
0 t (1)
d-1)
28 »N)
* Values in parentheses represent number of replicate experiments. Each
experiment consisted of determining the steady-state algal yield at the
stated dilution rate. The mean algal yields where applicable were deter-
mined by averaging the data from the replicates. Variations from the means
were less than ± 20/6.
t Steady-state algal growth could not be maintained and the culture washed
out.
63
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City University of New York and the New York City Department of Water Re-
sources. Ihe project is similar to the Woods Hole study but greater con-
centrations of secondary sewage effluent are being used in order to reduce
space. Fresh water phytoplankton are also under study (101).
For a 50:50 ratio of secondary sewage effluent to harbor water, phosphorus
removal was about 90/8. Nitrogen removal was also regularly more than 90S?
before phosphate detergent use was restricted in the area. The nitrogen:
phosphorus ratio should be between 10:1 and 15:1 for most effective uptake
of nutrients. The phytoplankton culture is diluted with harbor water be-
fore removal by filter-feeding mussels and clams.
In feeding trials with chicks, the shellfish proved nutritionally superior
to commercial feed (101). Toxicology studies are underway to determine the
pesticide and heavy metal concentrates in both the shellfish and the chick-
ens.
A number of marine and fresh water phytoplankton have been screened for
their ability to utilize the nitrogen and phosphorus In the wastewater.
In addition, a number of shellfish species Including; M#tt&64 edu&ta,
Modta£o6 demci.fi04, Mt/a atenatui, Lamp&jJiU 4p. and Cot&ccula moju£en6
-------
considerations, the economic dimensions of SCP production will be compared
to waste conversion into glucose, into a variety of fuels, and to direct
fuel use of waste (co-firing with coal or oil).
In the following discussion of waste conversion costs, it should be remem-
bered that, for the most part, cost estimates used are derived from labo-
ratory studies or computer simulations on technologies that are, at best,
in a formative stage. Some authors claim to compute costs for "optimum"
plant size, or to present some estimate of a "minimum cost"- It is better,
in the absence of greater commercial experience with waste conversion, to
look on these cost estimates as reasonable first approximations, base line
figures to be used for rough ordering among the various techniques, (for
further comments on making and using cost estimates, see Appendix 2).
To measure the cost of using waste in different ways, it is necessary to
remember the distinction between private and social costs and returns. This
distinction is important in judging profitability of a private venture that
buys waste from a public disposal authority. For example, if the waste dis-
posal authority sells waste to a private user at $1.00/ton, and the private
user replaces another fuel (at $2.00/ton) with waste, the fuel input compon-
ent of his cost will be $1.00. This is wholly private cost, and his addi-
tional private return will depend on conditions in the market for his product
(in the short run, he should enjoy a profit thanks to cheaper fuel). At
the same time, if it costs the disposal authority $5.00/ton to discard the
waste, social costs of disposal have been reduced by a subsidy of $1.00/ton,
for every ton sold to the private user. The social returns of reduced dis-
posal costs may accrue directly to the taxpayer, or indirectly in realloca-
tion of resources from waste disposal to private production with the possi-
bility of greater total product and/or lower product prices. If, of course,
waste disposal and waste conversion are both public activities, social costs
are "internalized" and "credits" in the form of reduced costs of waste dis-
posal and gains from final products sale (resource recovery) should be
weighed by the public authority in decisions on a choice of waste recycling
technology.
It is important at this point to clarify a misapprehension. Many environ-
mentalists feel that the stress placed upon the private profit motive in
resource recovery from waste materials is improper. This is basically be-
cause they believe that such an emphasis encourages the generation of more
wastes (where wastes = money) instead of resource conservation at source.
The Environmental Protection Agency agrees with the principles of conser-
vation and is of course mandated by law to uphold these principles. At
the same time, the Agency recognizes that polluting wastes are generated
which must be treated at a central disposal facility. Being realistic, no
local authority is going to opt for a resource recovery scheme, however
environmentally sound, if the economic costs of the technology are pro-
hibitive.
65
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Process Cost Comparisons - Protein Production
Waste materials may substitute for other sources of food Including:
- conventional animal and vegetable food sources;
- substrates that might be used to produce food,
such as hydrocarbons and alcohol;
- oilseed proteins
- other unconventional sources such as leaf
proteins.
When discussing the choice of a substrate for SCP production, cellulose is
often described as a low or negative cost material. As is made clear in
Table 22, many forms of cellulosic waste have a value. The cost of cellu-
lose depends on its quality, note the comparatively high value of paper
pulp. Dunlap predicts that as the resource recovery industry develops and
expands, no waste cellulose will have a zero value (104). He expects that
the higher cost cellulosic "wastes" will be used for the higher cost pro-
ducts. Table 23 gives the value of products produced from cellulose,
updated by a 10% inflation factor.
For the private producer, it is critical to compare costs of food stuffs
produced from wastes with the costs of competing sources of protein and
carbohydrates. Costs for production of feed grade SCP vary by substrate
as shown in Table 24. If these figures are reasonable, then feed grade
SCP grown on any substrate Including cellulose, is not competitive with
soybean meal, fish meal or any of the other high-protein feeds listed at
approximate U.S. market prices. Dunlap has calculated that feed-grade SCP
must sell at about $220/ton (1975 figure updated 10% for Inflation), while
Humphrey has used the value of $275/ton (1976 updated figure) (105).
However, yeast grown on hydrocarbons sells on European markets for two to
three times this value (106). In a nutritional evaluation of "Pruteen",
ICI used the figure d£ 245/tonne for British markets, i.e. approximately
$400Aon at current rates of exchange. In the same evaluation, it was con-
cluded that even with soybean meal at<£ 100/tonne, a 50/50 "Pruteen"/soy
mixture was more economic than the 100$ soy control, because of increased
egg production in test hens (47).
The ICI study makes the valid point that not all proteins are created equal!
Table 24 makes no distinction between the quality of the proteins listed.
Peanut meal may cost the least per pound of crude protein, but the PER value
is low compared to processed SCP products, see Figure 4. As far back as
1971, Callihan and Dunlap stated that it would be most desirable to compare
the cost of protein sources In terms of their nutritional quality. The need
for such a study is even more obvious today. As Table 25 Indicates, as
"Torutein" is upgraded in protein quality, its cost rises from 42^/lb. to
66
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TABLE 22
COST OF CELLULOSE WASTES*
Source
Hay
alfalfa
grass
clover grass
Sugar cane bagasse
Waste paper
News
Mixed
Paper pulp
bleached
sulflte
unbleached
sulflte
Ground wood
Wheat 'straw
Rice straw
Corn stalks & cobs
Rice hulls
Municipal refuse
Value
$/ton
52-78
26-52
39-65
11-14
10-30
5-18
315-363
266-306
240
-
-
-
-
—
Cellulose
Content
13-34
20-35
11-2?
50-55
75-80
70-85
95-98
95-98
95-98
80-85
45-50
•45-50
35-50
35-50
50-55
$/ton
Cellulose
154-604
74-261
145-594
20-38
12-41
6-26
322-382
271-322
285-302
-
-
—
-
—
* Figures adapted from Dunlap (104) and Dunlap (106) by updating
to 1976 $'s to allow for inflation.
67
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TABLE 23
VALUE OF PRODUCTS PRODUCED FTOM CELLULOSE (KM)*
o\
CD
Product or Use
Direct burning
as fuel
Methane
Ethanol
Single cell protein
Glucose
Units
lO^tu
U%bu
Ib
Ib
Ib
Value
(Vunit)
0,33-0.88
0.88-2.2
10
16.5-27.5
10.8-28.6
Units produced
from 1.0 Ib dry
cellulose
0.010
0.004
0,56
0.45
0.80
Value of product
from 1.0 ob dry
cellulose
0.33-0.88
0,33-0.88
5.6
7.5 -12,3
8.6 -23
» Note: These figures are not related to cost of production. They are derived from current
market prices multiplied by an efficiency factor for each process. The figures
have been adjusted from the original source to reflect an inflation factor of 10JC
per annum.
-------
TABLE 24
COSTS OP NUnunONAL PROTEIN
Crude Cost of Crude
Cost Protein Protein
Source
Gelatin
Casein
Flaxseed
Hominy feed
Bran, wheat
Flshmeal
Alfalfa pellets
Linseed meal
Feather meal
Meat-bonemeal
Com gluten feed
Brewers grains
Cottonseed meal
Soybean meal
Peanut meal
165-275
77-110
16.7
4.1
4.2
12.9
3.9
7.4
9.9
8.7
4.2
3.9
6.3
6.7
5.6
100
100
24
10
17
60
18
35
55
50
25
24
42
46
46
165-275
77-110
69.6
41.0
24.7
21.5
21.7
21.2
18.0
17.4
16.8
16.2
15.0
14.6
12.2
Note that all of the acove figures were derived from Dunlap (106)
They have been updated 10$ for Inflation, and do not represent current
market values of the products which fluctuate a great deal.
SCP from;
n-parafflns* 28.1 (37.5) t 61 14.1 (61.5) t
gas-oil* 25.2 (36.3) t 68 37.1 (53.4) t
methanol* 27.5 (34.5) t 83 33.1 (41.6) t
natural gas* 21.2 (29.2) t 75 28.3 (38.9) t
Cellulose f 16.5-27.5 50 33.0-55-0
bagasse § 17-3 50 34.6
MSW (yeast vla#
acid hydrolysis) 22.8-40.2 45 50.6-89.3
* Adapted from Brownsteln & Constantlnldes (22) - inflation factor 0.19.
t iQjg return after 5056 taxes added by Maclaren (12)
f Adapted from Dunlap (104) - based on value of product x efficiency of
process, does not in&Lcate production costs.
§ Adapted from CalBhan & Dunlap (55), Bechtel figure said to be lower
than this.
# Adapted from IRTC (50).
69
-------
As a high grade food protein with unique functional properties, this
cost competes very favorable with casein and the low quality protein, gelatin.
The value of any product is the highest price the market can command. There-
fore, the extent of acceptance of "Torutein" and similar products derived
from petrochemicals must be some indicator of future prospects for high grade
functional proteins grown on waste cellulose.
If SCP grown on cellulose is to compete with conventional feeds, then there
must be an improvement in utilization of the cellulose and increased yields
of products with a higher protein content. Note that while Table 24 uses a
figure of 50/K crude protein for SCP grown on cellulose, as is made clear in
Table 13, the protein content is often much less than this.
TABLE 25
CURRENT TRUCKLOAD PRICES F.O.B. FOR "TORUTEIN"
HltfCHINSQN PLANT (1976) (23)
$/cwt
Product Prices
"Torutein"
"Torutein-LP"
42.00
50.00
"Torutein-94" 67.00
* Note; Torutein is food-grade yeast grown on ethanol. The prices
reflect the additional processing required to upgrade the
yeast to a replacement for non fat dry milk (Torutein-LF)
or further treatment to Torutein-94, a replacement for eggs,
70
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Mention has been made of the potential value of refeeding the sludge of an-
aerobic digestion, especially to ruminants. Many scientists feel that exploi-
tation of the nutritive value of the sludge will be more profitable than
selling the methane (80), (8l), (107). Weisberg and Krishnan (107) have
stated that for a 200 ton/day plant processing manures of 50,000 head of
feedlot cattle, the price of high quality, high pressure methane can drop
from $2.87 per 1,000 cubic feet (mcf) of gas to $2.43/mcf. This figure would
still realize a 10% after-tax return on investment. Weisberg and Krishnan
reported a 13% protein content of sludge, while other scientists have in-
dicated a 2^% protein content. It would be premature to make any predic-
tions of cost for a product still undergoing evaluation.
As research into anaerobic digestion has concentrated on the optimization of
gas production, little attempt has been made to evaluate the protein content
or quality of the sludge. Certainly the possibility of manipulating reaction
conditions to optimize protein production has been neglected. Ongoing stud-
ies of the digestibility and acceptability of the sludge to livestock have
been mentioned previously. The results and recommendations of these inves-
tigations are awaited with interest.
Process Cost Comparisons - Edible Carbohydrates
The food value of organic wastes is not confined to protein production.
Cellulose may be enzymatically or acid hydrolyzed to glucose. The glucose
syrup may be crystallized and sold as an edible carbohydrate, fermented to
ethanol, or used as a substrate for microblal growth. A maximum production
cost of $50 to $60/ton glucose is considered essential in order to produce
either ethanol competitive with the ethylene process, or SCP competitive
with soybean meal (108), (109).
As is clear from Table 26, the cost estimates for acid hydrolysis of cel-
lulose are much lower than the current estimates for enzyme hydrolysis.
Fermentation of glucose from acid hydrolysis of MSW is probably competitive
at 9.2 - !6.3
-------
TABLE 26
COSTS OP NOTRITIONAL CARBOHYDRATES*
Source
Cost
-------
Summary - Food/Peed Production from Celluloslc Wastes
A comprehensive, up-to-date economic analysis of SCP production from cel-
lulosic wastes does not exist in the public sector. Data quoted are de-
rived from either estimations based on small scale studies or are extra-
polated from limited pilot plant experience. Similarly, even recent
analyses of the economic feasibility of enzyme hydrolysis are based upon
data from 1970 (Rosenbluth and Wilke) (78). The economic potential of
refeeding the sludge from anaerobic digestion is unclear though promising.
Based on the limited data available, it does not appear that feed-grade SCP
produced from waste cellulose is competitive with conventional high-protein
feeds at present or for the near future. That being said, it must be re-
membered that the cost/lb of protein must always be qualified with reference
to the protein quality.
The near future prospects for food-grade SCP are much more promising. An
additional factor to remember when discussing marketing SCP as a human food
must be the psychological acceptability of the substrate to the general
public. Crop residues are probably more acceptable than animal excreta as
substrates.
Acid hydrolysis to glucose followed by yeast fermentation to ethanol is
probably economically feasible at present.
One factor not previously identified as "economically sensitive" is the cost
of transporting wastes to a centralized processing plant. Nyiri and Tannen
have shown by a computer simulation that transportation costs are unaccept-
ably high beyond a 10 mile radius. This constraint must apply to a greater
or lesser extent to all processing utilizing wastes, whether for food or
energy production.
While the economic picture is not clear, it must be considered hopeful at
least for the long range exploitation of cellulosic wastes as sources of
protein or edible carbohydrates.
Process Cost Comparisons - Energy Resource Recovery
It is not possible to compare costs/unit output between food and fuel
recovery from wastes, since measures of output are not comparable. Rather
than rank methods by cost per unit output, one can compare costs of process-
ing a ton of waste; in effect the "value added" to waste in obtaining a
marketable product. Processing costs vary widely as can be seen in Table
27. Ifrifortunately, the figures given are for varying sizes of plant, so
direct comparisons are not valid.
Prom these figures it would appear that energy recovery from manures tends
to be more expensive than from MSW, in spite of the fact that the MSW costs
include an elaborate front end system to reclaim inorganic materials.
Credits for the nitrogen value of the sludge from manure digestion will make
73
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TABLE 2?
COST OF VARIOUS WASTE PROCESSING TECHNOLOGIES
($/ton dry waste input)
Process
Scale
$Aon Input
Anaerobic Digestion
MSW to methane #
MSW to methane t
Feedlot waste to methane f
fleedlot waste to methane §
Pyrolysis
MSW (oil and char) #
MSW (no. 6 oil) #
Feedlot waste (29$ MC) H
Peedlot waste (50% MC) H
Combustion
Coflriiig (coal+MSW) #
MSW to steam #
1000 ton/day (TPD) 12.7(a)
15. Kb)
1000 18. 7
(8.1)
200 12.4(a)
25.0(b)
28.3(c)
22.3
9120
1000
1358
I6l.6-l6l6
115 -2960
980
1600
8.7
7.0
39.8-18.9
8.1
11.4
SCP Production
MSW~# ~ r ••
Manured
Carob *
Acid Hydrolysis
MSW to glucose #
MSW to ethanol #
Enzyme Hydrolysis
MSW to glucose t
400
400
1763 tons/yr
190
190
20
47.4
13.2
42.5 (a)
52.7 (b)
11. 2-22. 3
15.2-26.8
223
A brief explanation of this table appears on the following page. Except
where indicated this cost/ton does not include credits for products formed
or reclaimed nor penalties for sludges requiring additional treatment and/or
disposal. All values given here have been updated for inflation to 1976 $'s.
74
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Key to Table 27
It is recognized that because of differences in scale of production and because
of different methods of estimating capital and manufacturing costs that these
figures are NOT directly comparable. They are quoted because these were the
figures most readily available, or In some cases the only figures available.
* Pfeffer (in)
(a) Figure with incineration of organic residues
(b) No incineration
Neither figure contains credits for inorganic recovery or sale of
methane.
Ash and inorganic disposal are included in the costs.
t Kispert nJL oJL (112)
First figure does not include any penalties or credits for inorganic
recovery.
Figure in brackets Includes penalties and credits (except sale of gas).
Weisberg & Krlshnan (10?)
(a) low purity, low pressure methane
(b) high purity, low pressure methane
(c) high purity, high pressure methane
All cattle manure.
§ Hamilton Standard (8l)
Cattle manure
# International Research and Technology (50)
MSW (oil and char) figure updated from calculations in Ware (113).
Coflrlng - includes credit for replacement of coal (1/4 of charge).
SCP - does not include marketing and distribution, nor credit for
the product.
MSW to glucose based on Meller(ll4) and Converse (79).
MSW to ethanol based on Meller (114) and Converse (79).
190? The report does not make clear the scale of these two reactions.
1 Inman (115)
* Tate and lyle (51)
The first figure is for labor at $1000/man year (developing country).
The second figure is for labor at $10,000/faan year.
t Roseribluth and Wilke (78)
(Further details relating to these estimates can be found in Appendix III.)
75
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this process more attractive. Pyrolysis of manures is relatively expensive
because of the high moisture content (MC) of the excreta. Pyrolysis and
co-firing of MSW are in the same range. Pyrolysis may be favored because
the fuel produced is transportable.
SCP production from MSW is nearly four times as expensive in terms of cost/
ton input as SCP production from manures. Municipal solid waste requires
more initial preparation than manures. If the manure is processed close to a
feedlot and the SCP is returned for fodder, then SCP production from man-
ures would not incur heavy transportation costs. Both these figures for
SCP production are derived from an initial analysis prepared by Meller for
the Ehvironmental Protection Agency (H4). The initial analysis referred
to yeast production. It has been pointed out that bacterial production from
MSW will cost slightly more per ton, because of higher yields of protein
(50). It should not be assumed that these figures are close to the present
economic, reality.
The figure for SCP production from carob beans relates to a "village-tech-
nology" process. The capacity of the plant is very low and of course the
cost/ton would drop significantly for a larger scale operation. It must be
remembered, however, that the figures for production in the united States
would be much higher due to higher wage scales.
The cost of acid hydrolysis to produce either glucose or ethanol compares
favorably with the fuel production technologies. Note that the cost of
ethanol production from MSW is probably now competitive with the ethylene
process. It has been suggested that ethanol could be used as a fuel ex-
tender or even partially replace many petrochemicals as a source of anti-
biotics, vitamins and other inportant chemicals. In this event, acid
hydrolysis of MSW looks very promising economically.
Although the food production processes cost more per ton input than do the
fuel recovery technologies, it must be remembered that both SCP and glucose
are potentially more valuable products than fuels derived from wastes (see
Table 23).
Summary
For the Immediate future at least in the United States, it is unlikely that
SCP production from cellulosic wastes could be considered a commercially
viable process. Similarly, it appears that enzyme hydrolysis cannot com-
pete economically with acid hydrolysis/fermentation to alcohol, which may
now be commercially feasible.
However, several facts must be emphasized:
(a) Data are limited, out-of-date and Incomplete relative
to the economics of the above processes. There is a
definite need for pilot scale projects to gather fresh
data for computer simulations, so to identify the areas
76
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of economic sensitivity for both SCP production
and enzyme hydrolysis.
(b) Any economic evaluation of SCP from wastes must
recognize the Importance of considering the nu-
tritive value of the protein produced before
condemning the process as uneconomic for a par-
ticular cellulose source.
(c) It is possible to predict that for certain wastes,
either anaerobic digestion for methane and refeed,
or SCP production to produce a soybean replacement
would be favored processes. This is especially
true for feedlot wastes, which could be processed
In situ to eliminate transportation costs and de-
fray feedlot expenses (for energy and/or food).
Energy Comparisons Between Alternative Pood Production Systems
U.S. farming Is heavily dependent upon usage of fossil fuels to achieve high
productivity. Prom 1950 - 1970 the general consumption of energy in this
country doubled. During the same period, certain sectors of the agricultur-
al Industry experienced a threefold increase in demand (116). The reliance
of the farming Industry upon fossil fuels Is Illustrated by the following
figures: while agriculture consumes about 2.5$ of annual production of
electricity, it uses about 10% of petroleum products (117). Table 28
gives some Indication of the disappearance of energy on the farm and In the
food processing industries. Note that after consumption of fuel to manu-
facture and operate farm machinery, that the energy required to produce
fertilizers is the third largest component of on farm energy usage. Trans-
portation and energy consumption within the food processing Industry ac-
counted for 1.5H% and 1.9% respectively of total U.S. energy expenditure
In 1970.
The Increased consumption of energy on the farm has been accompanied by a
decrease In labor. In 1970, about 2.9 million kilocalories of fuel energy •
were used to raise one acre of corn (116). In 19^5, 23 hours of labor per
crop acre were required for corn production. By 1970, this figure had
dropped to 9 hours per crop acre, a decrease of 60% (116). During the same
period, the number of tractors increased from 2.4 million to nearly M.5
million, with an accompanying Increase in horsepower. For the entire U.S.
corn production, there was an Increase In energy expenditure for machinery
from 15 gallons/acre In 19*15 to 22/gallons/acre In 1970 (116).
The use of fertilizers for com production has also exploded since 19^5.
Nitrogen use alone increased by a factor of 16, phosphorus usage by a
factor of 5, and potassium quantities applied per acre increased 14 fold
(116). According to Pimental vt at, corn production accounted for 17%
of all insecticides manufactured for agricultural usage (116).
77
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TABIE 28
CN FARM AND POOD PROCESSING INDUSTRY ENERGY USAGE
IN THE UNITED STATES FOOD SYSTEM, 1970 (118)
Item
Approximate Ehergy
Usage as % of Total
U.S. Energy Consumption,
1970*
Sub Total
On Farm
Fuel (direct use)
Electricity
Fertilizer
Agricultural steel
Farm machinery
Irrigation
Processing Industry
Food processing industry
Food processing machinery
Paper packaging
Glass containers
Steel cans and aluminum
Transport (fuel)
Trucks and trailers (manufacture)
Sub Total
1.45
0.4
0.6
0.013
0.6
0.22
3728JK
1.9
0.04
0.24
0.30
0.76
1.54
0.47
*Note: Total U.S. energy consumption for 1970 taken as 1.6 x 1016
kilocalories (114).
78
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Transportation and electrical requirements Increased 3.5 times, irrigation
and the resultant water costs rose 1.8 times and the energy for seeds for
planting nearly doubled.
The introduction of strains of hybrid com after the Second World War resulted
in an increase In yield of corn per acre from 34 bushels in 19^5 to 8l bushels
In 1970. In 1972, the corn yield per acre rose to an all-time high of 97.1
bushels (5). If this increase in productivity is examined in relation to
increase in energy consumption, there has been a decrease in the ratio of
energy production of the crop per energy expenditure from 1950 to 1970. This
decrease In efficiency is around 11% if the input of solar energy is included
and an incredible 2^% if only the fossil fuel usage is considered. It should
be noted that Pimental e/t at chose com production to make this analysis be-
cause not only was more data available for com than any other crop, but corn
production is an "average" crop in terms of energy consumption.
The Energy Analysis
In this analysis of various methods of protein production, the system was
defined as the process itself and did not include marketing of products.
The comparative unit employed was the term British thermal units per gram
of protein (Btu/g protein). Protein was defined as the crude protein content
(Kjeldahl nitrogen X 6.5) of the product.
In most cases the analysis was based on incomplete information with data
extrapolated from bench-scale operations. The ultimate scale of fermenta-
tion is industrial. While complete energy analyses for commercial single
cell protein production undoubtedly exist, the information is proprietary
to the individual companies and was not made available for this report.
For single cell protein production, it must be remembered that it is possible
to use different cellulosic substrates of varying composition. Also the end
product concentration of SCP was not always clearly indicated in the reports
studied.
Protein yields depend on mass transfer, oxygen transport to and across the
cell surface, environmental conditions within the reactor and the genetic
makeup of the growing microorganisms. Protein yields were usually estimated
for SCP analyses.
Most of the conventional farming figures presented were extrapolated and
indexed for 1976 figures.
Due to the varying units used in the different energy analyses, all of the
comparisons were made on the Btu/g protein basis. This permits a ready con-
version to fuel consumption if needed. The actual energy cost to process
water, electrical power, steam and gas as well as the raw materials input
for ammonia, phosphoric acid etc. was included for each of the processes
in the energy inventory.
79
-------
It was assumed that certain economies of scale would hold from one process
to another if certain factors were eliminated. For example, for production
of more than 500 tons SCP/year, refrigeration is required to remove heat of
fermentation. This factor is not included in the analysis.
If specific data were not reported, as a rough approximation, the raw ma-
terials energy input, packaging and general overheads were taken as about
equal to the electrical energy input. The estimates are rough, but as di-
mensional figures would impart a variation of no more than ± 15%.
Processes which are extremely energy dependent per gram of protein show up
as a larger Btu/g protein figure. This is especially obvious for deep-sea
fishing where the fleets sail longer distances in order to obtain their
catch compared to coastal fishing.
It should be noted that these figures are dependent upon first principle
derivations, data supplied through references, and the best possible ex-
trapolations from these. The reported percentage protein content of each
of the listed crops was used in the analysis, as well as the conventional
figures for fuel input and fertilizer production and other inputs to the
system.
It should be noted that solar energy was not considered a fuel for this
analysis. If solar energy becomes a technically useful source of fuel on
a large scale, this may involve use of land. If the land could be used for
food production then the trade-off between solar fuel, power output and
food production must be studied. If the solar device does not take up use-
ful land (e.g. rooftops, etc.) then it competes with nothing and has no
meaning in terms of energy costs. Purthermore,- including solar energy with
fuels and human and animal working energy Inputs to food production would
overshadow these inputs dimensionally. The energy analysis would be
nothing more than a study of photosynthetic conversion from solar energy
to food energy and would not Illustrate the energy intensiveness of the al-
ternative methods of producing food. For this analysis, the primary energy
resources were the fossil fuels; nuclear fuels were not Included.
The comparative energy usage table includes com production, fishing, cat-
tle raising and manufacture of SCP on different substrates. The substrates
included are methanol, carob pods, petroleum stock, whey and cellulose. An
In-depth analysis of two of these processes (the Wilke system of enzymatic
hydrolysis and the Abcor system for SCP production from whey), is included
in Appendix IV.
The energy recovered as SCP averages 5500 kilo calories per kilogram (119).
This is the energy of the protein which will be utilized by man or animal
and is not included in the protein equation of the energy analysis. In
addition, the plant energy and the energy used by manual labor Is not in-
cluded as energy input.
80
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The removal of large amounts of heat during metabolism in the mlcrobial
processes Is assumed to be accomplished by the process water and the heat
exchangers. Occasionally, data not available for calculation were derived
on the basis of the process water alone.
It is recognized that mLcrobial fermentation is an exothermic process. None
of the systems examined appeared to include a heat recycle though energy
conservation might usefully be applied to the SCP processes discussed.
Discussion
It cannot be over-emphasized that the energy analysis presented in this
report is a rough approximation. Bench scale operations have not yet
reached the stage of a complete energy analysis and much of the industrial
scale data is confidential information. It is recommended that a complete
energy analysis of fermentation of cellulose to single cell protein be
considered a priority item for research and development funds. The energy
analysis of byconversion schemes now underway at the University of Wisconsin
should do much to clarify the energy intensiveness of a number of processes
applicable on the farm.
That being said, it is interesting to see that the processes designated
"Single Cell Protein" fall within a range. The low energy figure for whey
as a substrate reflects the fact that the whey is a source of whey protein
concentrate through ultrafiltration as well as yeast single cell protein
grown on the lactose permeate. The energy figure for SCP production on
carob beans is less than the value for growth of petro-proteins, and for
production of glucose from cellulosic wastes. This is expected as the
Tate and lyle process is being developed as a "village-level" or "inter-
mediate" technology, less energy intensive and more reliant on labor.
The figure for enzymatic hydrolysis Is artificial, note the unit - Btu
input/g potential protein. The main product of enzyme hydrolysis is of
course glucose with only small amounts of fungal protein recovered. The
glucose amount has been converted to the quantity of protein potentially
available using glucose as the growth medium. At the same time, the
energy required to make this conversion is not included in the analysis.
Hence, the figure given is unreal but is included for comparative purposes
only.
Amoco Poods now marketing the food grade yeast "Toruteln", has indicated
that the energy consumption of their process is about one-half the energy
required to produce an equivalent weight of beef protein processed to the
wholesale level of marketing. They did not indicate whether the beef was
range-fed, grass-fed or raised on a feedlot. If it is assumed that the
comparison was made considering the energy input/protein production for
grass-fed beef, then the figures presented in Table 29 look to be in the
correct range — note the value for the petroleum based process.
Appendix IV contains an approximate analysis of the anaerobic digestion
process. As digestion of agricultural residues produces both a fuel and
81
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TABLE 29
A ROUGH APPROXIMATION OP ENERGY CONSUMPTION
FOR A NUMBER OF POOD PRODUCTION SYSTEMS
INCLUDING MICROBIAL PROTEIN
Item
Energy input per
protein produced
(Btu in/g protein)
Reference
Commercial Fishing
Coastal Pishing
Distant Fishing
Prawn Fishing
Pish Protein Concentrate
Conmsrclal Beef
Range Fed Beef
Grass Fed Beef
Feed Lot Beef
Single Cell Protein
SCP from Methanol CICI)*
SCP from Petroleum (Italy)*
SCP from Whey
SCP from Carob Pods
SCP from Cellulose
SCP from Bagasse •'•
Corn Production (all
124
1240-1500
2500-5000
900-1000
60
360
1500-2000
Steinhart & Steinhart (118)
+ Leach (120)
it
it
ti
it
it
Corn (1970)
Com (1945)
Com (1945)
Com (1950)
Com (1954)
Com (1959)
Corn (1964)
Com (1970)
Com (1970)
Soybeans (1970)
161
185
48
87
98 Btu/ poten-
tial
protein
59
75
47
55
65
61
57
62
44
14
Leach (120)
n
Pace & Goldstein (121)
Tate & Lyle (51)
Rosenbluth & Willce (78)
Leach (120)
n
Plmental (116)
it
Heichel (117)
Peed grade processes, additional processing and hence energy expenditure
required to produce food grade products.
Insufficient data available.to make calculation (55), (74).
82
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a food (either directly as protein in the sludge or indirectly exploiting
its fertilizer potential) it is an attractive process. As reported prev-
iously, in 1970, the energy required to produce fertilizers for farm use in
the United States was 0.65? of the total energy consumption, i.e. 94 X lO^K
cals (118). The potential of the sludge as a fertilizer should be examined
in depth with an emphasis on the survival of pathogens, the heavy metal
content and pesticide build up in the sludge. Several universities are ex-
amining the safety factors Involved in land-spreading of the undigested
solids. The feed potential of the sludge is also under investigation (vide.
In summary, while the figures presented in this analysis are by no means de-
finitive, they do look encouraging and do not eliminate SCP production from
cellulosic wastes from consideration as an effective method for stabilizing
wastes with a financial subsidy (i.e. selling SCP) at a comparatively low
energy expenditure.
TABLE 30
PRODUCTION PER TON INPUT FOR
ANAEROBIC DIGESTION TO METHANE
Waste
Capacity
TPD
net Btu out
ton Input
Reference
Beedlot waste
Peedlot waste
MSW
MSW
200
9120
1000
1000
8.05 x 106
6.37 x 106
3.25 x 106
3.15 x 106
Weisberg & Krlshnan (107)
Christopher (122)
Kispert at aJL (112)
Pfeffer (111)
83
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Ehvironmenbal Impact
There is no doubt that many current methods of disposal of cellulosic
wastes have a negative effect on the environment. Incineration produces
polluting emissions and may not destroy pathogens which survive in incom-
pletely burned residues (caused by overcharging, compaction or spontaneous
water production during burning). The costs of complying with Federal
standards for stack emissions have placed an Impossible economic burden on
small-scale Incineration operations. The burning of crop residues in situ
is now limited by enforcement of environmental legislations.
Land disposal of wastes is dependent upon suitable and available land which
is Increasing in cost as it decreases in supply. Leachate problems have oc-
cured even with sanitary land fills. Fecal conforms, fecal streptococci,
salmonellae and enteroviruses have been found in leachates from land fills.
Animal wastes eroded from feedlots have been identified as the cause of
fish kills and eutrophlcation.
Single cell protein growth on cellulosic wastes may produce waste effluents
at several stages in the process:
(a) washings from pretreatment to improve digestibility
of the cellulose;
(b) supernatant liquor after harvesting and drying of
the protein;
(c) effluents from washing the product;
(d) solids remaining after fermentation.
The washings described in (a) may or may not present a disposal problem
depending on the nature of the pretreatment. For example, if the cel-
lulosic substrate undergoes alkaline heat treatment, the alkali must be
either neutralized or removed prior to fermentation. If the latter, wash
waters generated at this stage will contain relatively high concentrations
of solubilized lignin, heml-celluloses and hydrolyzed sugar monomers as
well as caustic soda (123).
It might be possible to subject the washings to a chemical recovery process
to regenerate the alkali and separate the lignin for burning, but this would
require a large plant. Another alternative might be to burn the organics in
an oxidation furnace to recover the energy.
If only crude SCP for a feed is required, the alkali could be neutralized
with hydrochloric acid and the sodium chloride permitted to pass through
the fermentation to come out In the centrifuge wash. For a high quality
product, the lignin must be removed prior to degradation.
The polluting potential of the treatment liquor depends on the composition
-------
of the wastes. For example, Black Clawson fibers produce a much cleaner
stream than do agricultural wastes (123).
It is also possible to choose a pretreatment which is less likely to pro-
duce a waste with a high chemical oxygen demand (COD). For exanple, physical
or gas-phase treatments might be chosen instead of alkaline and other liquid
chemical treatments.
With alkaline pretreatment of the wastes, the effluents generated at stages
(b) and (c) above, contain almost no suspended solids and therefore have a
low BOD. These liquors are, however, relatively high in inorganic nutrients,
and so some fraction would be recycled to the fermenter for better utiliza-
tion. Remaining effluents would require some treatment in a waste stabili-
zation pond.
The amount and composition of any sludge remaining depends on the substrate,
the method of pretreatment, harvesting techniques and further processing of
the product. The residue may be small if undigested fiber is included with
SCP as part of the feed mixture (50). It has been reported that for MSW,
overall waste reduction is small, though of course the wastes are stabilized.
Enzyme hydrolysis does not produce volumes of polluting effluents or solids
as the process design includes recycle phases. After filtering, the enzyme
broth goes to the hydrolysis reactor. The filter cake consists mainly of
protein with some undigested cellulose. It may be sold as a feed cake.
Effluents from the saccharification vessel are filtered to produce glucose
syrup. The unhydrolyzed cellulosic waste is recycled to the hydrolysis
vessel after drying and regrindlng to improve susceptibility of the cellu-
lose to enzyme action. Solid wastes from the reactor are mainly llgnin
which could be used as a fuel (61). The percentage of solids remaining af-
ter hydrolysis presumably depends on the composition of the waste. Temper-
ature control during the process results in hot water which must be cooled
prior to disposal to prevent thermal pollution.
Though the main product of anaerobic digestion of agricultural wastes is
energy (methane), the sludge remaining has potential as a feed or ferti-
lizer. If 'the sludge does prove a useful feed or fertilizer, this is
obviously an extremely environmentally acceptable process in that it re-
covers both energy and nutrients while reducing the BOD of the wastes.
If the potential of marketing the sludge is not realized, there is still
a 50% decrease in mass for manures (81). Liquid effluents from the pro-
cess will require further treatment to stabilize them.
All of the above systems result In biodegradation of materials with a high
BOD, so that they are comparatively odor free, and do not attract insects
and vermin. All result in a greater or lesser degree of solid waste re-
duction. Less land is therefore required for ultimate disposal of the
solids remaining after reaction. Also, biodegraded wastes are less likely
to cause settling problems in land fills, so that the land may be used for
building purposes soon after the closing of the fill.
85
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All the three processes mentioned above result in conservation of resources
by reclaiming either nutrients and/or energy. The enzyme hydrolysis process
is more flexible in this respect, in that the glucose produced could be fer-
mented to ethanol, and hence to other chemicals normally derived from fossil
fuels; or else used as a substrate for SCP growth. Alternatively, glucose
could be directly used as an energy source in human food and animal feed.
Anaerobic digestion could also produce both food and fuel. Aerobic fermen-
tation to SCP produces either a food or a feed, and consumes energy. How-
ever, it is not as energy intensive as modern farming to produce animal
protein vide.
NCN-CELLULOSIC CARBOHYDRATES
Spent Sulf ite Liquor
Spent sulfite liquor is a waste product of the pulping process in paper
making. The composition of waste sulfite liquors varies, depending on the
species of wood used and the nature of the pulping process (10). Hardwoods
tend to yield a liquor with up to 7058 pentose sugars (mainly xylose) , while
soft woods may contain up to 75% hexose (principally mannose). Table 31
illustrates the composition of spruce wood liquors.
In 19^8, the first U.S. plant to grow yeast on spent sulfite liquor started
production. Today, the firms of Boise Cascade and St. Regis Paper have pro-
duction facilities of capacity 6,000 tons/year and 5,000 tons/year respec-
tively.
Though yeasts contain around 45 - 505? protein, the original market in the
United States was as a source of B-complex vitamins and other minerals.
Growth of yeasts on sulfite liquor is a satisfactory means of pollution
control. Yeast production removes 90 - 96/K of reducing sugars and acetic
acid present in waste liquors, reducing the BCD^ more than 605? (10). The
exact reduction in polluting capabilities of the liquor depends on their
composition.
The liquors usually require treatment to remove excess sulfur dioxide prior
to use as a medium for microbial growth. Stream stripping is the favored
method in the United States. The amount and distribution of oxygen in the
fermenter is crucial for growth of yeasts. Nitrogen, phosphorus, potassium
and other nutrients must be added to the culture. As the reaction is
exothermic, heat removal is required. Candida utcttd is a favored species,
as it can utilize both pentose and hexose sugars (124).
can only ferment hexoses.
The "Pekilo1' process under development by the Finnish Pulp and Paper Re-
search Institute involves submerged cultivation of microfungi (notably
Paec^£om(/ce6 va'u.o.fcO on sulfite waste liquor and molasses. The chemical
composition of "Pekilo" protein is shown In Table 32. Note that the protein
content is slightly higher than Torula yeast grown on sulfite liquor
(45 - 50*).
86
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TABLE 31
COMPOSITION OP A SPENT SPRUCE SULFTTE LIQUOR (125)
Component %
Llgnosulfonic acids 43
HemLllgiin ccnpounds 12
Incompletely hydrolyzed
hemlcellulose conpounds
and uronic acids 7
Monosaccharides —
D-glueose 2.6 —
D-xylose 4.6 —
D-marmose 11.0 —
D-galactose 2.6 —
L-arabinose 0.9 22
Acetic acid 6
Aldonic acids and substances
not investigated 10
87
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TABLE 32
CHEMICAL COMPOSITION OP PEKILO PROTEIN (69)
Item % of Total
Dry matter 95
Crude protein 55-60
Nucleic acids 10-11
Crude fat 1
Ash 5
TABLE 33
BOD7 OP A SPENT SULPITE LIQUOR BEFORE AND AFTER
CONTINUOUS PEKILO FERMENTATION IN A 450 LURE FERMENTOR (69)
BOD? Before Alter
fermentation fermentation
BOD7, g 02A SSL I 46 6
BOD?, kg 02 of pulp 370 48
* Note: The BOD7 readings show higher oxygen demand reductions than would
conventional BOD5 values. They are quoted because BODc values
were not found in the literature.
-------
The hexoses, pentoses, aldonlc acids and acetic acid In the liquors are
readily deccnoposed by the fungi (69). The lignosulfonlc acids and hemi-
lignln sulfonlc acids are not utilized In the "Pekllo" process. One ad-
vantage of the process is the ease with which the fungi may be harvested
by filtration and mechanically dewatered.
Costs of production of "Pekllo" protein are estimated at $110 per ton
(for a 10,000 ton per year plant). The market price should therefore be
very competitive In the European market for feed-grade SCP (c.f. ICI fig-
ures for "Pruteen"). For the same size plant, energy consumption of the
process is estimated at 1,250 kilowatt hours/ton (126).
The composition of the product is found In Table 32. The protein will be
marketed as a feed for calves, pigs and poultry. Feeding trials have con-
firmed the value of the protein as a feed for pigs and poultry. Mixed with
whey it is suitable for calves. It is reportedly &7% digestible (126).
Fungi and yeast grown on sulfite waste liquors have been found to contain
small percentages of lignosulfonlc acids adhering to the cell wall (127).
In a study conducted in Norway, large concentrations of lignosulfonic acids
(to 13%} fed to pigs resulted in diarrhea, poor weight gain and low feed
conversion (127). It was felt that the very low level of lignosulfonic
acids in the SCP products studies ("PekLlo" protein 0.1; C. wtiLi& 0.15;
S. cetev-cA-oie 0.6) would probably not prevent consumption of SCP even as
the sole protein source.
Food Industry Wastes
As Indicated in Table 2, food Industry wastes are highly polluting and cause
immense environmental damage when discharged untreated. The industry is well
aware of the problem and has investigated a number of treatment and disposal
methods (see Table 34).
Though each food processing facility has its own particular problems, cer-
tain procedures are found helpful throughout the industry. For example,
for all wastes, separation of the solid or liquid components of the waste
stream facilitates handling. The solid waste may be burned, landfllled,
anaerobically digested or composted.
The Municipal Environmental Research Laboratory, U.S. Environmental Protec-
tion Agency, has investigated the growth of fungal protein on starchy sub-
strates. The processing of potatoes results in the generation of from 2.6
to 5.3 million tons of high BOD wastes annually. Rogers and Coleman (128)
have reported that growth of A&puigUlM nJu^eJi (NRRL 5474) on homogenized
and pre-sterllized starchy wastes results in the complete utilization of
the substrate within 20 to 48 hours. In addition to potato wastes, their
process Is applicable to whey, citrus and other fruit wastes.
Homogenlzatlon and sterilization of the wastes prior to fermentation was
found most effective in reducing the time requirements. Hcmogenization
89
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increases the surface available for microbial attack, and heat steriliza-
tion swells the fibers. The concentration of the wastes which can be
successfully utilized is described in a recent patent as from 6 to 10/8
by weight AOO mis. of culture medium (128). The fungus grows aerobically
at temperatures from 25° C to 50° C at pH values from 2.0 to 5.0. After
20 to 48 hours, the culture is sterilized and the fungus removed by filtra-
tion. The protein content of the mycelia is from 35 to 40/8 (by .amino acid.
assay) and compares very favorably with the FAO reference protein.
Church
-------
TABLE 3*»
COMPARISON OP VARIOUS TREATMENT
AND DISPOSAL METHODS FOR POOD
INDUSTRY WASTES (2)
Method
BOD
reduc-
tion %
Relative Special requirements
costs and limitations
Primary
Screening 10 to 20
Grit removal 10 to 20
Oil & grease 10 to 40
Sedimentation 10 to 50
Secondary
Chemical 35 to 60
treatment
Lagooning 80 to 95
Low
Low
Low
Low
Moderate
Low
Irrigation
ridge
and
furrow
spray
80
90+
Low
Low
Trickling
filter
Activated
sludge
90+
90+
Moderate
High
Provisions must be made for cleaning
to prevent binding of screens.
Must have continuous scrapes & remov-
al system to prevent accumulation
decomposable organic materials.
Mechanical sklmraing desirable, flota-
tion may be required.
Detention times must be short enough
to avoid anaerobic composition of
settled solids.
Useful in seasonal operations. Large
volume of sludge produced requires
extensive drying bed area.
Low cost land and distance from
residential areas important.
Major portion of a year required
for total treatment.
Limited to rural areas because of
odor nuisances. Only a limited
number of crops can.be grown on
land so irrigated, may create
ground pollution problems. Land
must be located within economic
pumping distance. Only cover
crops can be grown on spray
irrigated land.
Suitable for year-round operations.
Difficult to operate with seasonal
and variable waste flows.
Effective for high BOD wastes; diffi-
cult to use in seasonal operations.
91
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TABLE 35
GENERAL EFFICIENCY OF FUNGI IMFERFECTI PROCESS (129)
Component
BODtj removal (%)
COD removal (50
TOG removal (50
Jfycelium produced per unit BODc
removed
Sulfuric acid use (lb/1000 gallons)
Retention time (hours)
Corn Canning
Wastes
96
88
93
0.5
4.0
22
Pre-Carming
Wastes
95
81
87
0.6
6.5
18
Silage
Wastes
80
83
85
0.3
8.1
18
TABLE 36
EFFICIENCY OF REDUCING SUGAR UTILIZATION BY MoteheJUbcL hovten&i& (131)
Yield
Grams of Mycelium
per 100 g
Reducing Sugar
Substrate
Whey
Pumpkin
Supplied
23.5
27.5
Consumed
43.6
48.1
Protein
Content
of
Ifycellum
%
34.5
35.2
Protein
Efficiency
grams per 100 g
Reducing Sugar
Supplied Consumed
8.12
9.69
14.6
16.9
Extractor
Waste
Com
Canning
Waste
22.3
33.5
32.7
7.29
11.3
92
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an average for the pilot plant ditch. More complete BOD and COD removal was
accomplished in the laboratory (BODc reduction above 99%, COD reduction about
96%) (129). The reasons given for this discrepancy were; the finer fungal
mass produced in the pilot plant, lower temperatures of operation and the
variable composition of the wastes stabilized in the pilot study.
A 1973 economic analysis of the process based on an annual BODc of 1.08 x
106 Ib indicated that with sale of the protein, the wastes could be treated
with profit. A net surplus of overl
-------
vo
-tr
TABLE 37
REDUCING SUGAR UTILIZATION AND YIELDS OP ORGANISMS GROWN ON
BREWERY WASTE (134)
GPL
Red. sugar
Organism usage % (1)
S. e«iufe.tat
S. uvasuw
C. u£iUt>
C. AteatolytLca
?. oAfieatu
M.
-------
trub press Uquor(TPL), fermented sludge was In the range of 20 - **5% 03*0.
In a related study, Shannon and Stevenson found that addition of ammonium
sulfate and fermented sludge to GPL and TPL improved BOD reduction ("133) .
•Die highest BOD reduction for growth of C. gigantea. on augmented GPL was
The same yeast reduced the BOD of enriched TPL by 655?.
Hang e£ aZ at Cornell University have Investigated growth of
•age*. on spent grain liquor (135). They have reported a 97% conversion of
sugar to fungal mass and yields of approximately 575? (based on sugar usage) .
BOD reduction approached 96% (decreasing from 22,500 rag/litre to 900 mg/
litre).
Acid Food Wastes
One stabilization of acid food wastes has also been studied at Cornell.
Wastes such as sauerkraut brine, pickled beets, and olive brine have a
very high biochemical oxygen demand, a large concentration of sodium chlor-
ide and low pH values. Table 38 gives the typical composition of acid brine
obtained from a sauerkraut factory. Hang e£ al have investigated both growth
of fungi and yeasts on sauerkraut brine. They have reported that the fungi
Geo-t^tc/ium cjowtidum, completely neutralized the brine and reduced the BODc
by 88$ (72). The mycelium was easily harvested by filtering at a yield of
around 13 g/1 of brine (or a 62% yield based on BOD removal). The fungi
contained approximately 39% protein and could be sold as a feed supplement.
Aeration requirements for yeast production on sauerkraut waste were found
to limit the growth of the organisms and impede removal of BOD and lactic
acid (71).
TABLE 38
TOPICAL COMPOSITION OP SAUERKRAUT BRINE (72)*
Component mg/1
BOD 24,000
Lactic acid 19,900
Kjeldahl nitrogen 1,100
Total phosphorus 192
Sodium chloride 26,500
* pH value of 3.4
95
-------
C. titctci neutralized the brine and reduced BOD by 9Q%. Pilot plant studies
in comnercial factories have so far indicated that C. utcfcta is a promising
organism for biograding sauerkraut brine (136).
Growth of fungi on beet brine has also been investigated at Cornell (137).
AApeAg£fc£u6 cttgeA reduced ODD by 93.456 In 72 hours. Nitrogen reduction was
75% and phosphorus removal 725?. The pigments in the beet juice were almost
entirely degraded (up to 96/0. The yield of A. iugeA was approximately 52
gms/100 gms of COD removed.
Many food processing wastes of differing compositions have been investigated
as possible substrates for microbial growth. Carbohydrate wastes and acid
brines have high polluting potential and must be stabilized prior to disposal.
The biodegradation of these wastes by yeasts or fungi-is technically feasible.
The limited economic analyses performed are encouraging. If the micro-
organisms grown do find a market as an animal feed, this type of management
technique will possibly operate with profit. It is emphasized that toxicologi-
cal and nutritional studies must establish the safety, digestibility and
palatability of the SCP product for each category of waste.
WHEY
Though whey was a popular beverage in seventeenth and eighteenth century
Europe, it presents a serious disposal problem in twentieth century America.
In 1975, in this country alone, approximately 30 billion poinds of whey were
produced as a by-product of the cheese-making industry (138). Only half
this quantity is currently used as a food or feed (139); the remainder pre-
sents an ever more costly treatment problem, as cheese-making factories
struggle to comply with Federal water pollution standards.
Liquid whey has a 6005 ojf from 32,000 parts/million (ppm) (140) to 60,000
ppm. Thirty billion pounds of whey are equivalent to a sewage demand of
21 million people (138). The cost of building waste treatment plants to
handle this quantity is estimated at $1 billion with annual operating and
maintenance costs of approximately $39 million (138).
Composition
Liquid whey from a cheese plant is 93 - 9^% water (139). Sweet and acid
wheys produced from Cheddar and cottage cheeses respectively, differ slightly
in total solids composition (see Table 39) • The main solid ingredient of
whey is lactose (approximately 66 - W by weight). High quality protein
represents some 12 - 1358 total solids, together with smaller quantities of
ash, fat and lactic acid. Cottage cheese whey has a higher lactic acid
content than Cheddar whey. The cost of concentrating and drying the highly
perishable liquid has in the past limited utilization of the solids. For
some uses of whey (e.g. baby food), it is also necessary to remove the ash
content of the whey which may constitute 1156 of solids. Technical improvements
stimulated by enforcement of pollution control legislation, make utilization
of the whey preferrable to disposal.
96
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Thirty billion pounds of whey could provide 1.3 billion pounds of lactose and
0.25 billion pounds of protein (138). Whey protein has an excellent amino
acid pattern, and with a protein efficiency ratio of 3.0 to 3.2 (c.f. casein
at 2.5) is second only to the protein of egg white in quality (l4l). The
energy value of whey solids is slightly higher than most feed grains and is
equivalent to the energy value of shelled com (141). Lactose is more than
just an energy source. It increases protein digestibility and nitrogen
retention when fed to nonruminants , aids mineral balance in the blood stream
and is the source of galactose, a sugar needed for repair of delicate brain
and nerve tissue (138). It must be noted at this point that some individuals
with a low lactose enzyme activity experience Intense gastro-intestinal dis-
comfort on consumption of lactose.
Utilization of Whole Whey
Because of the expense of transportation, in relation to its solids content,
and problems of spoilage, liquid whey has been used as a feed for swine and
cattle only on farms close to the site of production. For swine, growth
rates were acceptable for consumption of whey up to 20% dry matter Intake
(141). Both sweet and acid wheys have been successfully fed to cattle. The
few problems encountered include excessive urination at high intakes, and
some scouring and off-feed if high levels of whey consumption were introduced
too suddenly. Teeth erosion was noted when whey was stored for some time
and mixed with molasses prior to feeding
Many possible whey utilization systems have been proposed (see Figure 8). It
is possible to concentrate and dry whey liquid to produce a powder for food/
feed consumption. Kraft spray dries sweet whey from its cheese-making
facilities to produce a food-grade powder primarily utilized In-house as a
substitute for nonfat milk solids (1^2) although the lower protein content
of dry whey limits this substitution for some uses. Whey powder reportedly
has special properties which are not demonstrated by nonfat dry milk (NEW) .
Whey powder is a flavor enhancer and according to Kraft, adds shortness
and tenderness to bakery products .
Condensed whey has been fed to cattle and pigs with satisfactory results.
Addition of molasses improves the palatability to cattle. Addition of
urea and/or silage to whey Increases the nutritive value but reduces the
palatability (141) . Anaerobic fermentation of whey to lactic acid followed
by addition of anhydrous ammonia produces a feed with digestibility approxi-
mately equal to soybean meal. The ammonium lactate together with un-
separated bacterial cells can be fed to cattle to provide up to 85$ of
required nitrogen (1*0 .
Addition of dry whole whey to alfalfa silage, urea-treated corn silage and
other grass or legume silages improved the fermentation characteristics of
the silage. Feeding trials with whey-treated silages have generally resulted
97
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TABLE 39
DRY SOLIDS IN CHEESE WHEY (138)
Component Cottage Cheddar
Protein
Lactose
Ash
Eat
Lactic Acid
13.0
66.5
10.2
0.1
8.6
12.9
73.5
8.0
0.9
2.3
in higher digestibility than the control. Though nutritional trials with
lactating animals have been limited, cows fed urea-treated corn silage
with a 1% addition of dry whey ad libitum showed a 6.5% increase in milk
production over the control (urea-treated com silage)
Whey liquid can be concentrated, sterilized and flavored (particularly with
citrus fruits) to produce nutritious beverages. Many recipes for flat
and carbonated, alcoholic and non-alcoholic beverages have been tested.
Perhaps the most conmercially successful product to date is a fermented
beverage prepared from deproteinized whey and sold in Western Europe under
the trade name of Rivella. Twenty to thirty million litres of RLvella are
sold annually (144).
Utilization of Whey Components
In addition to recovering and utilizing the whey solids intact, it is
possible to separate the protein and lactose components and to remove the
mineral salts. In the United States, mineral salts which adversely affect
palatability, functionality, etc., are removed by electrodialysis. Elec-
trolytes pass through ion-selective, semi-permeable membranes under the
influence of an electric potential (138). Removal of salts on ion-exchange
columns presents a greater problem of sanitation, uses large volumes of
water, and thus produces copious quantities of waste water.
98
-------
feed , J
1
acidulant wney
VO soft drink
vo
alcoholic
drink
food _
r
IUHRV ppwnra
____.
SYRUPS
i SCP
1
pharmaceutical
etc.
concentrate.
dry
concentrate ,
crystallize
concentrate,
pasteurize, etc.
ferment, etc.
hydrolysis of
acid whey
aerobic
fermentation
B
WHEY
fractionate (' pRjj
1 FRA£
LAC
KRAC
1 food (nutritive value)
i
L. — food additive
as nutritive value)
3>j£N as "UencMW vaj.«5|
, food
i
aerobic | | t__^
fermentation I ^"^
oonc^ntrat^.
sterilize.etc BEVERAGE nutrition-
diqestion LACTATE + lt=cj
crystallize UCK "^^ reed
dry ..,,— .. -.....-
L_. ._ feed
I
1 ioala
Figure 8. Possible Whey Utilization and Salvage Systems
-------
Several methods are in conmercial production for either crystallization of
the lactose or precipitation of the protein. Lactose may be crystallized
from cooling concentrated whey with or without chemical solubilization of
the protein, though chemical solubilization produces a higher yield (138).
Protein may be precipitated from the whey by addition of various chemicals
(including ferric chloride, aluminum chloride, carboxymethyl cellulose,
etc.) or by heat coagulation. Most chemical additives produce denatured
protein with poor functional properties, though addition of long chain
polyphosphates followed by centrifugation results in undenatured protein.
Most recently, techniques to concentrate and/or separate the solid
components have been developed. In reverse osmosis, water, ionizable salts
and lactic acid are removed from the whey by applying a pressure in excess
of the osmotic pressure, to force small molecules through a semi-permeable
cellulose acetate membrane about 1/3 micron thick (145). A backing of
porous material supports the membrane yet allows water to pass through.
Several designs are available including: the spiral wound module, the
membrane stack and the most popular tubular model. The tubular model
consists of a hollow support, tube lined with a continuous membrane through
which the" whey is circulated. The water passes through the tubes and collects
outside. The extent of water, salts and lactic acid removal depends on the
pressure used. Too great a pressure will destroy the membrane or shorten
its life considerably (145).
Ultrafiltration uses hydraulic pressure with a special membrane to separate
the smaller sized molecules including lactose, from the larger protein
molecules and fat globules. Because of the nature of the membrane, lower
pressures are required for Ultrafiltration than for reverse osmosis. Pro-
tein concentrations ranging up to 60% of solids may be obtained. Ultra-
filtration produces a pure, undenatured protein concentrate with a composi-
tion equivalent to skim milk, and a watery fraction containing lactose (138).
The cost of the membrane accounts for around 30% of the total cost of the
process and the membrane has a life time of about one year (146). The de-
velopment of membranes with a longer lifetime would reduce the cost of
Ultrafiltration. Also needed are membranes which can be easily sterilized
by heat and/or chemicals without damage to them.
Whey protein concentrate produced by Ultrafiltration costs around $l/lb. for
a 50% protein product (dry weight). The cost of nonfat dry milk is around
73
-------
Agriculture. The essential amino acids are all present In concentrations
exceeding the PAO reference. Addition of W WPC to nonfat dry milk raised
the protein efficiency ratio of the milk from 2.51 to 2.83 (1^7). The
digestibility of the protein, as measured in feeding trials with rats, was
superior to casein. Whey protein concentrate demonstrated very acceptable
functional properties; it retained water well, and formed stable whips by
manipulation of heat and pH, but was denatured (about 20?) at normal pas-
teurization temperatures (148).
Human taste panels more easily detected the flavor of acid WPC than sweet
WPC In a blend with skim milk. Even when whey was detected, the majority
of tasters rated a MO/6 sweet WPC concentration and a 20% acid WPC concen-
tration at least "satisfactory" in flavor
While there are many possible markets for the high quality WPC, uses for
the immense volumes of permeate are perhaps more limited. The volume of
the lactose fraction is 90/6 of that of the original whey and has only a
slightly reduced BOD (150). The U.S. Department of Agriculture, Beltsville,
Maryland, has investigated the preparation of solid feed blocks from the
permeate. The deproteinized whey was evaporated to a total solids concen-
tration of about 30% and the pH was adjusted to 6.2 - 6.4 with anhydrous
ammonia. When the total solids concentration reached 65 - 70/6, the
concentrate was pumped into forms and air-dried for 1 to 2 days. A 45 -
50 Ib. dry cake could be prepared from an initial volume of 90 gallons of
permeate.
The cake was evaluated as a lick block for cattle. The ammonia increased
the protein equivalent of the block and Improved palatability, especially
of the acid whey permeate blocks (150). Other materials which could be
added to the block include urea, soybean meal, molasses, potato peelings,
etc. The initial phase of controlled feeding studies at the Ruminant
Nutrition Laboratory, U.S. Department of Agriculture at Beltsville, is
substantially complete. Holsteln calves fed pelleted alfalfa and com
ad libitum voluntarily consumed from 15 to 25% total dry feed from the
blocks. Weight gains equivalent to the control were maintained. Nutri-
tional trials are continuing and will eventually Include feeding the
lick block to lactating animals. A number of companies are moving to
commercialize this process.
It is easier to spray dry the permeate of acid whey produced through ultra-
filtration than it is to dry the whole whey. The deproteinized whey powder
can be used in foods, feed mixtures and in bacterial media (151).
Another possible use of the permeate is as a substrate for growth of
Sa.cc/iaAorm/ce6 £taig-c&tA. A recent evaluation Indicated that the economics
of combined ultrafiltration to produce WPC and fermentation of the permeate
to produce yeast are very attractive. It is reported that for plants of
varying capacities (1/4 million to 1 million Ibs. of lactose permeate/day)
the sale of WPC would cover costs, while the marketing of the yeast would
represent profit (121).
101
-------
Yeast can, of course, be grown on the lactose In whole whey without prior
fractionation. Khudsen Wheast* (Sa.c£fuvu)myc.e£ ty&$Wi&) was grown on fresh
cottage cheese whey and contained 54 - 56/C protein. The firm has now been
taken over by the Stauffer Chemical Company which has just built a new
combined ultrafiltration/gel-filtration plant in California (146).
Growth of the fungus, A5peAgx£fcua n/qj&t., on the lactose of acid whey has
been studied at Cornell University. Beta-galactosidase manufactured by the
fungus hydrolyzed the lactose to mono-saccharides. The syrupy product was
concentrated to 70/E total solids and either heat-treated to precipitate the
protein, or deprotelnized and demineralized to produce a non-salty neutral
syrup. Both types of syrup were satisfactorily added to a variety of foods
(152).
Summary
It is clear that whey is changing its status from an unwanted polluting by-
product of the cheese-making industry to a valuable and versatile food/feed
additive with a high nutritional value and unique properties. The technology
exists either to concentrate and dry whole whey, or to fractionate it into
two potentially valuable components.
While whey consumption will probably never have the social and medical status
achieved in the seventeenth and eighteenth centuries, the future for whey
salvage looks very promising.
* Trade name
102
-------
LIST OF REFERENCES
1. Anderson, L.L. Energy Potential from Organic Wastes: A Review of
Quantities and Sources. 8549, U.S. Bureau of Mines Information
Circular, 1972.
2. Litchfield, J.H. Pood Industry Wastes: Technological Aspects of
Disposal and Utilization. Chemical Engineering Symposium Series,
67(108), 1971.
3. U.N. Pood and Agriculture Organization. Provisional Indicative World
Plan for Agricultural Development. PAO, Rome, 1970.
4. Scrimshaw, N.S. Single-Cell Protein for Human Consumption - An Over-
view. In: Single-Cell Protein II, S. Tarmenbaum and D. Wang, eds.
M.I.T. Press, 1975.
5. U.S.D.A. Agricultural Statistics, 1975. G.P.O., 1976.
6. Thaysen, A.D. Pood and Fodder Yeast. In: Yeasts, W. Roman, ed.,
Academic Press, 1957. pp. 155-246.
7. Gray, W.D. Develop. Ihd. Microbiology, 3(63), 1962.
8. Meadows, D.H., D.L. Meadows, J. Randers, and W.W. Behrens. The Limits
to Growth. New American Library, New York, 1972.
9. Gormcner, B., M. Gentler, R. KLepper, and W. Lockertz. The Effect
of Recent Energy Price Increases on Field Crop Production Costs.
N.S.F./P.B. - 238 659, December 1, 1974.
10. Wiley, A.J. Pood and Feed Yeast.- In: Industrial Fermentations,
L.A. Underkoker and R.J. Hickey, eds. Chemical Publishing Company,
New York, 1954. pp. 307-343.
11. Pringsheim, H., and S. Idchtenstein. Cellulosochem. 1(29), 1920.
12. Ffeclaren, D.D. Single Cell Protein - A Food for the Future? A paper
to be presented at the First North American Chemical Congress, Mexico
City, December, 1975-
13. Litchfield, J.H. Food Technology, 21:55, 1964.
14. Humphrey, A.E. Current Developments in Fermentation. Chemical
Engineering, December, 98-112, 1974.
103
-------
15. Hatch, R.T. Fermsntor Design. In: Single-Cell Protein II, S.R.
Tannenbaum and D.I.C. Wang, eds. M.I.T. Press, 1975.
16. Slater, L.E. SCP: The Methanol Way. Pood Engineering, July:
68-71, 1974.
17. Marr, A.G. Growth of MLcroorganisms-General. In: Single-Cell
Protein, R. Mateles and S.R. Tannenbaum, eds. M.I.T. Press,
Cambridge, Massachusetts, 1968. pp. 169-180.
18. Oswald, W.J. and C.G. Golueke. Large Scale Production of Algae. In:
Single-Cell Protein, R.I. Mateles and S.R.* Tannenbaum, eds. M.I.T.
Press, Cambridge, Massachusetts, 1968. pp. 271-305.
19. Humphrey, A.E. Biological Synthesis of Pood Components, 1975.
20. Health Issue Halts Petro-Protein Plans. Chemical and Engineering
News, March 5, :9-10, 1973.
21. Cooney, C.L., D.W. Levine and B. Snedecor. Production of Single-
Cell Protein from Methanol. Pood Technology, February, : 33-42,
1975.
22. Brownstein, A.M. and A. Constantides . Comparative Economics of
Petrochemical-Based SCP Processes. Prepared for: 169th American
Chemical Society National Meeting,- Division of Industrial and
Engineering Chemistry, Philadelphia, Pa., April 9, 1975.
23. Shay, J.C. Personal Communication, June 1, 1976.
24. Bellamy, W.D. Fermented Agricultural Wastes as a Source of Single-
Cell Protein for Animal Feed. Manuscript to be submitted to World
Animal Review,
25. Humphrey, A.E. Outlook and Technical Feasibility of SCP. In:
Single-Cell Protein H, S. Tannenbaum and D.I.C. Wang, eds., M.I.T.
Press, Massachusetts, 1975- pp. 1-23-
26. Bellamy, W.D. Single-Cell Proteins from Cellulosic Wastes. Biotechnology
and Bioengineering, 16:867-880, 1974.
27. Litchfield, J.M. The Pacts About Food from Unconventional Sources.
Chemical Processing, September, 1974.
28. Sinskey, A.J. and S.R. Tannenbaum. Removal of Nucleic Acids in SCP.
In: Single-Cell Protein n, S.R. Tannenbaum and D.I.C. Wang, eds.,
M.I.T. Press, Cambridge, Massachusetts, 1975. PP- 158-177.
29. Protein Advisory Group of the United Nations (PAG). PAG Guideline No.
12, on the Production of Single-Cell Protein for Human Consumption, 1970.
104
-------
30. Waslien, C.I., D.H. Galloway and S. Margen. Uric Acid Production of
Men Fed Graded Amounts of Egg Protein and Yeast Nucleic Acid. American
J. of Clinical Nutrition, 21:892, 1968.
31. Edozien, J.C., U.U. Udo, V.R. Young and N.S. Scrimshaw. Effects of
High Levels of Yeast Feeding on Uric Acid Metabolism of Young Men.
Nature, 228:180, 1970.
32. Sucher, R.W., E.A. Bobbins, E.H. Schuldt, R.D. Seeley and J.A. Newel.
A Process for the Production of Three New Pood Ingredients from Bakers '
Yeast. Paper No. 166, presented at the 33rd Annual IPT Meeting,
Miami, Florida, June 10-13, 1973.
33. Wang, L.C. Ultrasonic Extraction of Proteins from Autoclaved Soybean
Flakes. Journal of Food Science, 40:459, 1975.
34. Childs, E.A. and J.F. Forte. Enzymatic and Ultrasonic Techniques for
Solubilization of Protein from Heat-Treated Cottonseed Products .
Journal of Food Science, 41:652-655, 1972.
35. Castro, A.C., A.H. Sinskey, and S.R. Tannenbaum. Reduction of Nucleic
Acid Content in Candida. Yeast Cells by Bovine Pancreatic Ribonuclease A
Treatment. Applied Microbiology, 22, 1971.
36. Meffert, M.E. and W. Pabst. Nutr. Dieta, 5:235, 1963-
37. Hedenskoy, G. and Mogren, H. Some Methods for Processing of Single-
Cell Protein. Biotechnology and Bioengineering, 15:129-142, 1973.
38. Labuza, T.P., K.A. Jones, A.J. Sinskey, R. Gomes, S. Wilson and B.
Miller. Effect of Drying Conditions on Cell Viability and Functional
Properties of Single-Cell Protein. Journal of Food Science, 37:
103-107, 1972.
39. Davidson, S., R. Passmore, J.F. Brock and A.S. Truswell. Human Nutrition
and Dietetics, Edinburgh: Churchill, Livingstone, 1975.
40. Johnson, A.H. and M.S. Peterson. Encyclopedia of Food Technology.
Avi Publishing Co., Westport, Connecticut, 1974.
41. Protein Advisory Group of the United Nations (PAG) . PAG Guideline
No. 7, Human Testing of Supplementary Food Mixtures. PAG Guideline
No. 8, Protein Rich Mixtures for Use in Weaning Foods. 1972.
42. Galloway, D.H. and C.I. Waslien. Bioregeneration of Food. Environ-
mental Biology and Medicine, 1:229, 1971.
43. Laskin, A.I. Ethanol as a Substrate for SCP Production. Paper
presented at: First North American Chemical Congress, Mexico City,
December, 1975-
44. lammartino, N.R. Fabricated Protein Foods. Chemical Engineering,
August 5, 1974.
105
-------
45. Shacklady, C.A. Value of SOP for Animals. In: Single-Cell Protein
H, S.R. Tannenbaum and D.I.C. Wang, eds. M.I.T. Press, Cambridge,
Massachusetts, 1975. pp. 489-505.
46. Sherwood, Martin. Single-Cell Protein Comes of Age. New Scientist,
November 26, 1974. pp. 634-639.
47. ICI Agricultural Division. Pruteen - A New Protein Source. Billingham,
England, 1975.
48. Wilson, M. World Prepares for Single-Cell Protein: Special Report.
Pood Engineering, July, 1974. pp. 67-72.
49. Hammonds, T.M. Marketing Single-Cell Protein in Sophisticated
Markets. In: Single-Cell Protein II, S. Tannenbaum and D.I.C. Wang,
eds., M.I.T. Press, Massachusetts, 1975.
50. International Research and Technology Corporation. Problems and
Opportunities in the Management of Combustible Solid Wastes. EPA
68-03-0060, October, 1972.
51. Tate and Lyle, Ltd. Production of Single-Cell Protein from Agricul-
tural and Pood Processing Wastes. Reading, England, May, 1975.
52. Imrie, P. Single-Cell Protein from Agricultural Wastes. New
Scientist, May 22, 1975. p. 458.
53. Rogers, C.J., E. Coleman, D.P. Splno and T.C. Purcell. Production
of Fungal Protein from Cellulose and Waste Cellulosics. Environ-
mental Science and Technology, 6(8):715-718, August, 1972.
54. Dunlap, C. Production of Single-Cell Protein from Insoluble
Agricultural Wastes by Mesophiles. In: Single-Cell Protein U,
S. Tannenbaum and D.I.C. Wang, eds. M.I.T. Press, Massachusetts, 1975.
55. CalUhan, C.D. and C.E. Dunlap. Single-Cell Protein from Waste
Cellulosics. EPA Report PB-223 872, October 1973.
56. Mandels, M., L. Hontz and J. Nystrom. Enzymatic Hydrolysis of
Waste Cellulose. Biotechnology and Bioenglneerlng, 16:1471-1493,
1974.
57. Han, Y.W. and A.W. Anderson. The Problem of Rice Straw Waste-
A Possible Peed through Fermentation. Economic Botany, 28(3):338-344,
July/Sept. 1974.
58. Crawford, D.L. Use of a Thermophilic Actlnomycete for the Production
of MLcrobial Protein from Cellulosic Wastes. Paper presented at:
American Chemical Society's Symposium on Single-Cell Protein,
Philadelphia, Pennsylvania, April 9, 1975.
59. Crawford, D.L. Personal Communication, June 1976.
106
-------
67.
60. Bellamy, W.D. Conversion of Insoluble Agricultural Wastes to SCP
by Thermophilic MLcrobrganisms . In: Single-Cell Protein H, S.
Tannenbaum and D.I.C. Wang, eds. M.I.T. Press, Massachusetts,
1975. pp. 263-271.
61. Spano, L.A., J. Medelros and M. Mandels. Enzymatic Hydrolysis of
Cellulosic Wastes to Glucose. U.S. Amy, Natick Laboratories,
January 7, 1975.
62. Updegraff, D.M. Utilization of Cellulose from Waste Paper by
tyHjo&iz.cJLm veAJujLoeviia.. Biotechnology and Bioengineering, 13:77-97,
1971.
63. Crawford, D.L. and R.L. Crawford. Microbial Degradation of . Ligno-
cellulose: the Lignin Component. Applied and Environmental
Microbiology, 31(5): 714-717, May 1976.
64. Han, Y.W. Microbial Fermentation of Rice Straw: Nutritive Composi-
tion and In Vitro Digestibility of the Fermentation Products .
Applied Microbiology, 29(4): 510-514, April 1975.
65. Han, Y.W. and A.W. Anderson. Sendsolid Fermentation of Ryegrass
Straw. Applied Microbiology, 30(6) : 930-934, December 1975.
66. Humphrey, A.E., A. Moreira, W. Armiger and D. Zabriskie. Production
of Single Cell Protein from Cellulosic Wastes, 1976.
Griffin, H.L., J.H. Sloneker and G.E. Ihglett. Cellulase Production
by TtLickodeJima VAJVL&L on Feed Lot Waste. Applied Microbiology,
27(6):106l-1066, June 1974.
68. Szabo, M., P.V. Scarpino and C. Rogers. Effect of Auxins and
Herbicides on Enhancement of Protein Synthesizing Fungi. J. Agr.
Food Chemistry, 23(2), 1970.
69. "Forss, K. Utilization of the Spent Sulfite Liquor Components
in the Pekilo Protein Process and the Influence of the Process on
the Environmental Problems of the Sulfite Mill. Paper presented at:
Symposium on Wood Chemistry, Pure and Applied. American Chemical
Society National Meeting, Los Angeles, March 31-April 5» 1974.
70. Harkin, J.M., D.L. Crawford and E.McCoy. Bacterial Protein from
Pulps and Paper Mill Sludge. Tappi, 57(3): 131-134, March 1974.
71. Hang, Y.D. , D.F. Splittstoesser, D.L. Downing, R.L. Landshoot
and S.E. Allen. Influence of Aereation Rate on Yeast Production
In Sauerkraut Brine. J. Milk Food Technology, 38 (2) -.111-112,
February 1975.
72. Hang, Y.D., D.F. Splittstoesser and R.L. Landschoot. Propagation
of Geo#tcc/tum candidum in Acid Brine. Applied Microbiology, 27(4):"
807-808, April 1974.
107
-------
73. Waygood, E.R. Mass Culture of Eug£ewa gtta.(u&ii> on Animal Waste.
What's New In Plant Physiology, 8:2, February 1976.
74. Callihan and Dunlap. Construction of a Chemical-Microbiological
Pilot Plant for Production of SCP from Cellulosic Wastes. SW-24c/
5502-0027, Washington, D.C., GPO, 1971.
75. Ek., M. and K. Eriksson. Conversion of Cellulosic Waste into Protein.
Swedish Forest Products Laboratory, 1975-1976.
76. Eriksson, K. Personal Comnunication, May 3, 1976.
77. Mitra, G. and C.R. Wilke. Continuous Cellulase Production. Bio-
technology and BioengLneering, 17:1-13, 1975.
78. Rosenbluth, R.F. and C.R. Wilke. Comprehensive Studies of Solid
Waste Management: Enzymatic Hydrolysis of Cellulose. Bureau of
Solid Waste Management, USPHS Grant: EC 00260-05, December, 1970.
79. Converse, A.O. and H.E. Grethlein, et al. Acid Hydrolysis of
Cellulose in Refuse to Sugar and its Fermentation to Alcohol.
Thayer School of Engineers, EPA No. PB-221 239- June 1973.
80. Jewell, W.J., G.R. Morris, D.R. Price, W.W. Gunkel, D.W. Williams
and R.C. Loehr. Methane Generation from Agricultural Wastes: Review
of Concept and Future Applications. Paper presented at: Hie 1974
Northeast Regional Meeting, American Society of Agricultural Engineers,
West Virginia University, Morgantown, West Virginia, August 18-21,
1974.
8l. Hamilton Standard Division, UAC for USDA. Production of Power Fuel
by Anaerobic Digestion of Feedlot Wastes. Northern Regional Marketing
and Nutrition Research Division, Peoria, Illinois,
82. Davenport, M.R. Hamilton Standard Division, United Aircraft. Personal
Communication, July, 1976.
83. Cams, Dr. Harry. Workshop on Related Products at the Conference,
Capturing the Sun through Bioconversion, Washington, D. C., March 10-
12, 1976.
84. Abeles, T.P. Energy and Economic Analysis of Anaerobic Digesters
for Farms.
85. Methane from Manure. Chemical Week, 115(1) :13, July, 1974.
86. Yeck, R.G., L.W. Smith and C.C. Calvert. Recovery of Nutrients from
Animal Wastes - An Overview of Existing Options and Potentials for
Use in Feed. Paper presented at: International Symposium on Livestock
Wastes, University of Illinois, April 21-24, 1975-
108
-------
8?. Fontenot, J.P., K.E. Webb Jr., B.W. Harmon, R.E. Tucker and W.E.C.
Moore. Am. Soc. Agriculture Engineers Publication, Proc: 271:301,
1971.
88. Oriel, I.e., D.C. Rrudel and E.W. Weickersham. Cornell Vet. 59:226
1969.
89. Fontenot, J.P. and K.E. Webb Jr. Poultry Wastes and Peedstuffs for
Ruminants. Paper presented at: The Symposium on the Nutritional
Potential for Recycling Waste. 57th Annual Meeting of the Federation
of American Societies for Experimental Biology, Federation Proceedings
33:8, Atlantic City, New Jersey, August 1973-
90. Couch, J.R. Evaluation of Poultry Manure as a Feed Ingredient.
91. Anthony, W.B. Nutritional Value of Cattle Waste for Cattle.
Federation Proceedings 33(8): 1939-19*0-, August 1973.
92. Harmon, E.G., D.L. Day, D.H. Baker and S.H. Jensen. Nutritive Value
of Aerobically or Anaerobically Processed Swine Waste. J. Anim.
Science, 37(2):510-513, 1973.
93. Han, Y.W., J.S. Lee and A.W. Anderson. Chemical Composition and
Digestibility of Rye-grass Straw. J. Agricultural and Food Chemistry,
23:928, Sept/Oct 1975.
94. Baker, A.J., M.A. Millet and L.D. Satter. Wood and Wood-based
Residues in Animal Feeds. In: Cellulose Technology Research, ACS
Symposium Series, No. 10, 1975-
95. Van Sbest, P.J. and D.R. Mertens. Composition and Nutritive Charac-
teristics of Low Quality Cellulosic Wastes. Federation Proceedings,
23(8) -.1942-1944, August, 1973-
96. Miller, B. Biological Conversion of Animal Wastes to Nutrients.
EPA Report No. 670/2-73-09, June 1973.
97. Clement, G. Producing Sp&tuLina. with Carbon Dioxide. In: Single-
Gen Protein H. S.R. Tannenbaum and D.I.C. Wang, eds. M.I.T. Press,
Cambridge, Massachusetts, 1975. PP. 476-483.
98. Golueke, C.G. Bioconverslon Energy Studies at the University of
California, Berkeley. In: Proceedings of the Bioconversion Energy
Conference, held at Massachusetts University, Amherst, June 25-26,
1973- pp. 58-78.
99- RANN Report CI3 5970. An Inquiry into Biological Energy Conversion.
1972.
109
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100. Goldman, J.C., J.M. Ryther, and L.D. Williams. Mass Production of
Marine Algae in Outdoor Cultures. Nature, 254:594-595, April 17,
1975.
101. Walrath, D. and A.S. Natter. A New Broom in Wastewater Cleanup,
1976.
102. Murray, C. Weed Holds Promise for Pollution Cleanup. Chemical
and Engineering News, March 22, 1976. pp. 23-24.
103. Ragnal 1, L.O., R.L. Shirley, and J.P. Hentges. Processing,
Chemical Composition and Nutritive Value of Aquatic Weeds. Publi-
cation No. 25, Florida Water Resources Research Center, OWRR Project
No. A-017-Fla, November 16, 1973-
104. Dunlap, C.E. A Note on the Value of Cellulose. Biotechnology and
Bioengineering Symposium No. 5> 1975. PP- 73-75.
105. Humphrey, A.E. Economics and Utilization of Enzymatically Hydrolyzed
Cellulose. In: Proceedings of Symposium on Enzymatic Hydrolysis
of Cellulose, March 1975-
106. Dunlap, C.E. Economics of Producing Nutrients from Cellulose, Pood
Technology, December 1975- PP- 62-67.
107. Weisberg, E. and R. Krishnan. Engineering Design and Economic
Feasibility of a Feedlot Waste Bioconversion Scheme. Paper presented
at: Conference on Energy Recovery from Solid Wastes, College Park,
Maryland, March 1975.
108. Nylri, L.I. Economic Evaluation of Cellulose Based SCP or ETOH
Production. Presented at: 68th Annual Meeting of the American
Institute of Chemical Engineers, Los Angeles, California,
November, 1975.
109. Humphrey, A.E. Economical Factors in the Assessment of Various
Celluloslc Substances as Chemical and Energy Resources. Biotech.
and Bioeng. Symposium No. 5, 1975- PP- 49-65.
110. Nyiri, L.K. and L.P. Tannen. Studies on Systems Engineering for
Production of SCP vs. ETOH from Carbohydrates. Presented at: First
Chemical Congress of the North American Continent, Mexico City, Mexico,
December 5, 1975.
111. Pfeffer, J. Reclamation of Energy from Organic Refuse: Anaerobic
Digestion Processes. Paper presented at: Third National Conference
on Waste Management Technology and Resource Recovery, San Francisco,
California, November 14-15, 1974.
112. Kispert, R.G., L.C. Anderson and D.H. Walter. Fuel Gas Production
from Solid Waste. Dynatech R/D/ Company Report No. 1207, July 31,1974.
no
-------
113. Ware, S.A. Fuel and Energy Production by Bioconversion of Waste
Materials — State-of-the-Art. Ebon Research Systems Report No. 1207,
July 31, 1976.
114. Meller, P.J. Conversion of Organic Solid Wastes into Yeast - An
Economic Evaluation. Ehvii-onmental Protection Agency, Rockville,
Maryland, 1969.
115. Inman, R. An Evaluation of the Use of Agricultural Residues as
Energy Feedstock.
116. Pimentel, D., L.E. Hurd, A.C. Bellotti, M.J. Foster, I.N. Oka,
O.D. Sholes and R.J. Whitman. Food Production and the Energy
Crisis. Science, November 1973. PP.
117. Heichel, G.H. Comparative Efficiency of Energy Use in Crop Production.
Bulletin 739, Connecticut Agricultural Experiment Station, New
Haven, 1973.
118. Steinhart, J.S. and C.E. Steinhart. Energy Use in the U.S. Food
System. Science, 184:307-316, 1974.
119. Prochazka, G.J., W.J. Payne and W.R. Mayberry. Calorific Contents of
Microorganisms. Biotechnology and Bioengineering, 15:1007-1110,
1973.
120. Leach, G. Energy and Food Production, International Institute for
Environment and Development, London, 1975.
121. Pace, G.W. Economic Analysis of Ultrafiltration-Fermentation Plants
Producing Whey Protein and SCP from Cheese Whey. In: Single-Cell
Protein II, S.R. Tannenbaum and D.I.C. Wang, eds., M.I.T. Press,
Cambridge, Massachusetts, 1975. pp. 330-343.
122. Christopher, G. Anaerobic Fermentation of Wastes. Proceedings of the
Bloeonversion Energy Conference held at Massachusetts
University, Amherst. June 25-26, 1973. PP. 109-113.
123. Dunlap, C. Personal Communication, July 1976.
124. Bunker, M.J. Sources of Single-Cell Protein: Perspective and Prospect.
In: Single-Cell Protein, R.I. Mateles and S.R. Tannenbaum, eds. M.I.T.
Press, Cambridge, Massachusetts, 1968.
125. Forss, K. The Consumption of Carbohydrates in the Pekilo-Protein
Process. Paper presented at: Second International Congress on
Industrial Waste Water and Wastes, Stockholm, February 4-7, 1975.
126. Rdmantschuk, H. The Pekilo Process: Protein from Spent Sulfite
Liquor. In: Single-Cell Protein H. Tannenbaum, S.R. and D.I.C.
Wang, eds., M.I.T. Press, Cambridge, Massachusetts.
in
-------
127. Naess, B. Biological Effects of Sulflte Waste Liquor Components for
Swine. In: Single-Cell Protein II. Tannenbaum, S.R. and D.I.C.
Wang, eds., M.I.T. Press, Cambridge, Massachusetts.
128. Rogers, Charles J. and W. Bnile Coleman. Process for the Production
of High Quality Fungal Protein from Starch and Starchy Wastes. U.S.
Patent No. 3, 829, 363- August 15, 1974.
129. Church, B.D., H.A. Nash and W. Brosz. Use of fungi AmpeAiuLti In
Treating Pood Processing Wastes. Developments In Industrial Micro-
biology, 13:30-46, 1972.
130. Church, B.D., E.E. Erikson, and C.M. Wldmer. Fungal Digestion of
Pood Processing Wastes. Pood Technology, February, 1973. PP. 36-42.
131. Litchfleld, J.H., and R.C. Overbeck. Submerged Culture Growth of
MoicJieJUa Species In Food Processing Waste Substrates. Proceedings of
First International Congress of Food Science and Technology. Vol. 2.
Gordon and Breech, New York, 1965. pp. 511-520.
132. Litchfield, J.H. Converting Food Industry Wastes to Utllizable Pro-
ducts. Proceedings of Conference on Waste Management and Pollution Con-
trol, Blacksburg, Virginia, Feb. 8-10, 1971. PP. 62-64.
133* Shannon, L.J. and K.G. Stevenson. Growth of Catv&tia. gAgawfoa. and
Candida. Ateatolytuia. In Brewery Wastes for Microblal Protein Production
and BOD Reduction. J. Food Science, 40:826-829, 1975-
134. Shannon, L.J. and K.E. Stevenson. Growth of Fungi and BOD Reduction in
Selected Brewery Wastes. J. Food Science, 40:826-829, 1975-
135. Hang, Y.D., D.F. Splittstoesser and E.E. Woodams. Utilization of
Spent Grain Liquor by fapeAg-ittuA nigesi. Applied Microbiology,
30(5): 879-880, November 1975.
136. Hang, Y.D. Treating Kraut Waste and Possible By-Product Recovery.
New York State Agricultural Experiment Station, Special Report No.
11, December 1974. pp. 13-14.
137. Hang, Y.D. Fungal Treatment of Beet Waste. Second International
Congress on Industrial Waste Water and Wastes. Stockholm, February
4-7, 1975. PP. 1-6.
138. McDonough, F.E. Whey Solids Utilization and Salvage Systems. Dairy
Foods Nutrition Laboratory, Nutrition Institute, ARS, Beltsville,
Maryland,
139. Schingoethe, D.J. Feeding Whey to Cattle. Dairy Science Update
76 SU-76-5, Dairy Science Department, South Dakota State U., 1976.
140. Kbsikowskl, F.V. Greater Utilization of Whey Powder for Human
Consumption and Nutrition. J. Dairy Science 50(8): 1343-1345, 1967.
112
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141. Schlngpethe, D.J. Our Industry Today: Whey Utilization Animal
Feeding - A Summary and Evaluation. J. Dairy Science 59: 536-570,
March 1976.
142. Kraft Poods Industrial Division. Whey Products from Kraft. No.
5A-7715, Chicago, Illinois.
143- Schlngoethe, D.J., and G.L. Beardsly. Feeding Value of Corn Silage
Containing Added Urea and Dried Whey. J. Dairy Science, 58:196-201,
February 1975.
144. Hblslnger, V.M., L.P. Posati and E.D. DeVilblss. Whey Beverages:
A Review. J. Dairy Science, 57(8):849-859, 1974.
145. McDonough, F.E. Whey Concentration by Reverse Osmosis. Food
Engineering, March I960.
146. McDonough, F.E. Personal Communication, June 1976.
147. McDonough, F.E., W.A. Mattingly and J.M. Vestal. Protein Concentrate
from Cheese Whey by Ultrafiltration. Journal of Dairy Science, 54(10):
1406-1409, October 1971.
148. McDonough, F.E., J.A. Alford and M. Womack. Whey Protein Concentrate
as a Milk Extender. J. Dairy Science, 59:34-40, January 1976.
149. McDonough, F.E., R.E. Hargrove, W.A. Mattingly, L.P. Posati and J.A.
Alford. Composition and Properties of Whey Protein Concentrates from
Ultrafiltration. J. Dairy Science, 57:1435-1443, December 1974.
150. Hargrove, R.E. and E.P. Lynch. Solid Animal Feeds from Whey and Whey
Products. Dairy Food and Nutrition Laboratory, ARS/USDA.
151. Hargrove, R.E., McDonough, F.E., La Croix, D.E. and J.A. Alford.
Production and Properties of Dejjrotelnized Whey Pewters. J. Dairy
Science, 59:25-33, January 1976.
152. Wlerzbicki, L.E., and F.V. Kosikowski. Food Syrups from Acid Whey
Treated with Beta-galactosldase of tepesigUluA ruge/t. J. Dairy
Science, 56(9):1182-1184, November 1972.
153. Singh, R.B. The Bio-Gas Plant: Generating Methane from Organic
Wastes. Compost Science, 13:1. 1972. pp. 20-25.
113
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APPENDICES
APPENDIX I, A Note an Cost Updating
Costs and prices presented In text tables were adjusted to March, 1976 figures
using specific cost series, when available. Ihe Bureau of Labor Statistics
Indexes (Monthly Labor Review, 99:5« May, 1976) with their inplied yearly cost
changes were applied. Specific adjustments used the following series:
Product (series base = 1967) Average yearly price increase
Soy bean oil .07
Crude fuel .21
Pood stuffs .10
Iron and steel .12
Hay .09
Plant fibers .10
Sugar and confectionary products .11
Coal .30
Electric power .11
Refined petroleum products .19
In the absence of specific indexes, costs were adjusted by an annual .10
Inflation factor. Capital, as well as product costs, were adjusted in
this manner.
She reader should remember that many products covered in text analysis are
subject to severe seasonal and cyclical price fluctuations. !Ehis is partic-
ularly the case with agricultural products of all kinds.
APPENDIX H, A Discussion of Cost Estimates
Methods of generating cost estimates, based almost entirely on computer sim-
ulation and/or a patching together of opinion and fact about equipment and
-------
performance, differed widely among studies reviewed. As was mentioned in the
text, it Is Impossible to be confident about "optimum" plant size and cost
configuration without production and marketing data. But some areas of esti-
mation that were treated quite casually by most researchers deserve special
mention:
— Labor cost: techniques of estimation varied here from selecting
plausible hourly wage averages to taking labor cost as a per-cent
of total Investment. It is Impossible to check these estimates
with reasonable figures from existing processing plants.
— Capital: in some cases, researchers in this field confused start-
up costs with long-run capital costs. Average total costs will
fall over time, once start-up costs have been paid and experience
with the technology gained. Long-run costs reflect the level of
equipment and other capital needed to support an operating plant.
— Ownership: some researchers make the distinction between private
ownership (which Implies tax payments as part of costs) and public
ownership (which does not), though most ignore the difference.
In general, studies reviewed seemed to have equipment specifications and costs
fairly well In hand. Other costs, however, tended to reflect Informed Judg-
ment or unsupported guesses.
Unit costs used in text tables for this report were computed from data provided
or recorded in published studies, if usable figures were available. For most
of the studies used, computations were required:
— costs/input: in food and fuel studies, costs/input were obtained
by computing average dally costs and dividing by rated dally capac-
ity. In some cases where the tonnage of product out was given, it
was necessary to calculate the tons input from the mass balance
sheet.
APPENDIX III, Treatment of Capital in Various Studies
1. Brownstein and Constantinides Petro-Chemlcal-Based SCP Processes, (1975)
Total capital costs (301.37 tons/day capacity)
SCP growth on:
paraffins $ 90.5 million
gas oil 106.7 million
methanol 66.0 million
methane 72.2 million
Break-down
Not broken down by type, module
115
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2. Inman An Evaluation of the Use of Agricultural Residues as Energy
Feedstock, (1975)
Total capital costs
Pyrolysis
29% moisture content manure, low Btu gas $6.9 million
161.1 tons/day capacity
High Btu gas, methanation of 29% MC gas 2.0 million
additional — same capacity
50/6 moisture content manure, low Btu gas 7.4 million
229.6 tons/day
35% moisture content crop residue, 300 Btu 6.9 million
gas 133.6 tons/day capacity
Break-down
Not broken down by type, module
Amortization: 10$/year
3. IR&T Problems and Opportunities in Management of Combustible Solid
Wastes, (1972)
Total capital costs
Waste co-fired with coal
900 tons/day capacity $5.2 million
I960 tons/day capacity 8.8 million
Break—down
Units 900t 1960t
Front-end $811,000 $1,288,000
Processing 3,427,000 6,432,000
Firing 973,000 1,060,000
Start-up costs not included
\
4. Dynatech Fuel and Gas Production from Solid Waste, (1974)
Total capital costs (1000 tons/day capacity)
Anaerobic digestion $22.2 million
Break-down
Units capital
Front-end $ in, 500
Processing and upgrading 11,995,746
Buildings 1,000,000
Contingency, design and
working capital 9,084,914
116
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Land not Included
Amortization: 20 years, straight line
5. Pfeffer Reclamation of Energy frcm Organic Refuse; Anaerobic
Digestion Processes7 (197*0
Total capital costs (1000 tons/day capacity)
$14.3 million
Break-down
Units capital
Front-end . $2,917,000
Processing and incineration 9,340,000
Upgrading 2,032,000
No start-up costs, no specific building and land costs
Amortization: 10 years base, sensitivity test on various
figures from 10 to 25 years
6. Rosenbluth and Wilke Enzymatic Hydrolysis of Cellulose, (1970)
Total capital costs (10 tons/day capacity)
$2.2 million
Break-down
Units capital
Plant $1,375,810
Start-up contingency 860,000
Amortization: 10 year, straight line
7. Tate and Lyle Production of Single Cell Protein from Agricultural
and Food Processing Wastes, (May, 1975)
Total capital costs
.33 tons/day capacity $ 56,000
1.5 tons/day capacity 156,000
Breaks-down
Units .33t 1.5t
Front-end $ 7,000 $ 12,000
Processing 44,000 139,000
Buildings 5,000 14,000
No start-up costs
No land costs
117
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Amortization: 5 years, straight line
8. Weisberg and Krlshnan Engineering Design and Economic Feasibility
of a Feedlot Waste Bio-Conversion System, (1975)
Total capital costs (200 tons/day capacity)
low pressure, low purity methane $1.7 million (Iplp)
low pressure, high purity methane 2.8 million (Iphp)
high pressure, high purity methane 2.9 million (hphp)
Break-down
Units Iplp Iphp hphp
Front-end $ 168,000 $ 168,000 $ 168,000
Processing 1,148,000 1,148,000 1,148,000
Upgrading 130,000 1,030,000 1,130,000
"Engineering
contingency" 289,000 470,000 489,000
Amortization: 15 years, straight line
APPENDIX IV, Energy Calculations
A. Recalculation of Data
1. Enerffi Consumption Corn Production based on Plmental &t &£ (116)
In 1945, for com production in the U.S.,
K cal return = 3-70
f K cal input
Corn contains 9% protein and 1 Ib. of corn returns 1800 K cals,
therefore, to convert to gms of protein,
Protein In corn = 1 Ib corn x 454 g corn x 0.09 protein
1800 K cala Ib corn Ib
Ib com
= 0.0227 gm protein in corn/K cal return
To convert to Btu's, multiply by 1 Btu,
0.252 K cal
Energy consumption = K cal input x 1 Btu
g protein in com 0.252 K cal
or,
118
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Ehergy consumption
K cal return x 0.0227 g protein x 0.252 K cal
K cal input K cal return Btu
* 1 Btu
•3.70 x 0.0227 x 0.252 g protein
«47.2 Btu Input/g protein
Note the following ratios were used for K cal return,.
K cal input
1945 1950 1954 1959 1964 1970
3.7 3715" 2J57 2TB8i 3^5" 2^2
2. Corn production, USA 1970, based on Leach C12Q)
Energy in ~ 62.1 x 10^ Joules
protein Kg protein
1 Btu is approximately equivalent to 1055.79 joules
therefore, energy in = 62.1 x 106 joules x 1 Btu
protein Kg protein 1.05579x103 joules
= 58.8 Btu x 103
Kg protein
= 58.8 Btu input/g protein
3. Soybean Production. USA 1970. based on Helchel (117)
For soybeans, protein = 0.28 K protein
energy input M cal input
For corn, protein = 0.09 Kg protein
energy Input M cal irput
for corn, therefore, energy in = 44.09 Btu/g protein (converting M cals
protein to Btu*s and Kg's
tog)
If we assume the same calorific value for 1 3b of soybeans as 1 Ib of corn,
i.e. 1800 K cals per pound of crop, using the protein ratio 0.09/0.28, it
is possible to estimate the energy input/g protein for soybeans
For soybeans, Ehergy in - 0.09 x 44.09 Btu - 14.17 Btu Input/g protein
protein 0.28 g protein
119
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B. More detailed Analyses
1. SCP from Whey based on Pace and Goldstein (121)
(a) raw materials:
k cals to K cal/day
ffeterial Ibs. amount/day manufacture total
CH8)
ammonia 2544 5000 12.72 x 106
phophorlc add 1152 540 0.62 x 106
potassium chloride 1224 530 0.65 x 1Q6
sulfuric acid 456 nil -0-
u.f. cleaning solution 200 1000 0.20 x 106
Raw material energy input = 14.19 K cal/day
= 14.19 K cal/day x Btu
0.252
= 56.31 Btu input/day
0>) Utilities
Electricity
electrical power = 1400 Kwhr x 3000 K cal x Btu
day IMir 0.252 K cal
= 16.6? x 106 Btu input
day
i . '.
Steam '
steam input = 216 x 103 OJbs x 361 K eal x Btu
m 0.252 K cals
= 309.0 x 106 Btu input
day
Water
Note that the heat input is calculated without consideration of the
heat generated in the fermentor which must be removed by the process
water. Bie raw data considered did not make any mention of a heat
recycle.though it should be noted that an increased awareness of
energy conservation would lower the energy needs of the system.
120
-------
AT = (168,000 gal( (8.34 Ibs) (0.32 Btu) (94° - 40° P)
day gal
= 24.2 x 106 Btu Input
day
Totals
Item Btu Input/day x 10
Raw material 56.3
Electricity 16.67
Steam 309.0
Water 24.2
Bldg, supplies, 16.67 (same as electricity, rule
packaging, etc. of thumb)
Total = 422.84 x 106 Btu Input
day
Note: Not counting labor energy or material preparation
Prom 24,800 Ibs SCP daily in bulk production if we assume the yeast is
50? protein, then total single cell protein (approximation) - 12,400 Ibs/
day.
Combined ultrafiltration and fermentation produces whey protein concen-
trate yeast protein.
For every 100 Ib SCP produced there is also an additional 28.6 Ib of
whey protein concentrate.
Hence 24,800 Ibs SCP win also be associated with 24,800 x 28.6 Ibs of WPC
100
7092.8 Ibs/day
Total protein (WPC + SPG) =19,492.8 Ibs/day
= 19,492.8 Ibs/day x 454 g
= 8.8 x 106 g/day
Total Btu Input = 422.84 x 10^ Btu input = 48.05 Btu input/ day
8.8 x I06g/day day
121
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2.
SCP from Carob based on Imrle and Vlltos (511
Fewer consumption of plant = 3,000 K cal/Kg dry SCP
= 3.000 K cal x Btu
Kg SCP 252 cal
= 11.9'Btu Input/g protein
Inputs
Paraffins
(calorific value)
Electricity
Fuel
Steam
Chemicals
Water
General Supplies
Bldg. Equipment
Packaging
General Overhead
Labor
Total
Protein from
Petroleum
(Btu input/g protein)
58.537
10.9
34.0
51.095
10.44
16.32
0.43
2.58
0.143
0
184.63
Tate & Lyle
(Btu input/g protein
0
11.9
0(no cooling or
refrigeration)
51.1
5.00 (economy of scale)
16.32
0.43
2.58
0
0
0
87.33 (based on best
estimates)
3.
Enzymatic Hydrolysis of Cellulose to Glucose based on Rosenbluth and
Wilifle (78)
Use charts show that the process begins with 20,000 Ibs/day of cellulose
and ends with 700 3bs of protein and 18,300 Ibs/day of glucose
122
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Utilities
(a) Electrical Power * 380 Kw = 9120 Kwhr
C24 hour day)
Electrical input = 9120 Kwhr x 3000 K cal x Btu
Kwhr 0.252 K cal
= 108.6 x 106 Btu/day
(b) Steam = 5,542 Ibs/hr
= 5,542 Ibs x 24 hr x 361 K cal x Btu
hr day Hi 0.252 K cal
= 190.5 x 106 Btu Input
day
(c) Gas = 193 scf
hr
» 193 scf x 24 hr x 0.0448* Ibs x 6100 K cal x Btu
hr day scf Ib 0.252 K-cal
Gas input = 5.02 x 10^ Btu/day
*at STP
(d) Process Water
Note: The heat input to the preheat section of the process was
inventoried. Since the microbial reaction is exothermic it is
assumed that this reaction heat is used to heat up the reaction
vessel and contents to proper temperature while the remaining
heat is dissipated without contribution to the system. It should
be noted that an increased awareness of energy conservation and
heat recycle to the system should lower the energy needs of the
system.
Q * M C A T
energy input = (42,000 gal) (8.34jb_! (0.32 Btu) (392° - 84°P)
day gal IFF
- 34.5 x 106 Btu input
day
Raw materials, plant supplies, buildings, etc. estimated at around
100 x Ifl6 Btu
day
123
-------
Total energy input = 438.6x10^ Btu
day
Products are 700 Ibs protein and 18,300 Ibs glucose.
According to Humphrey (25):
Ys = g cell = 0.51
g substrate
Thus the protein potential of the glucose is approximately equal to 9,150 obs.
Total protein potential/day = 9850 Ibs.
9850 Ibs protein = 9850 Ibs protein x 454 g protein
day day 1 Ib protein
= 4.4? x 106 g protein/day
energy input - 98.12 Btu input
protein production g potential protein*
*Note: These calculations do not include energy needed to convert glucose
to protein. The conversion to potential protein was made simply to facili-
tate comparison.
4. Anaerobic Digestion based on Singi (153)
In general for various wastes, the amount of volatile solids available for
digestion varies from 33% to 57% (154).
For example:
Assuming that of 3.5 Ibs of solids of chicken manure that 1 Ib is converted
to biogas leaving 2.5 mass.
gas production/day = 5 ftVlb.v.s. (w. 59% methane)
Assuming a volume reduction of 33% and a 30/K heat recycle to digesters
900 Btu x 60 x 5 ft3 = 540 Btu x 5 ft3
ft3 100 Ib v.s. 5 ft3
Sludge remaining = 2.5 Ibs (containing 5.3 to 9% N)
Assume 7% N by weight
124
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(a) fertilizer
This constitutes almost 40/8 of the non-solar input into agriculture.
energy to produce N/lb = 8400 K cal
(for commercial fertilizer) Ib. N.
• 3.33 x 101* Btu
IB"
Fertilizer value
2.5 Ibs x 0.07 nitrogen = 0.175 Ibs nitrogen
energy savings for
fertilizer substitute * 0.175 Ibs x 3-33 x 101* Btu
Ib
» 5827.5 Btu
Ib v.s.
Total energy savings = 8527.5 Btu less 3056 to heat reactors
= 7,717.5 Btu/lb v.s.
« 2205 Btu
Ib manure
(b] Missed opportunity protein
Assume 2556 protein in remaining solids (81)
Protein = 0.25 x 2.5 Ibs protein
3.5 Ib. manure
- 0.625 Ibs protein
3.5 Ib. manure
• 283 g/3.5 manure
The system will either produce gas plus fertilizer of total
energy production/savings of 2205 Btu/pound manure or gas at a
rate of 568 Btu/pound manure and 80.8 gm of protein/pound manure.
Anaerobic digestion is a bonus system in that not only does it
produce energy but food (either directly as increased protein
or Indirectly as a fertilizer).
Note: Gas production from vegetable matter would be about 5
times the amount given for chicken manure.
125
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GLOSSARY
acid detergent fibre: The residue remaining after a cellulosic waste has been
treated with acid detergent to remove hemi-celluloses.
actinomycete: A member of an order of filamentous and rod-shaped bacteria.
aerobic (organism): An organism which requires air or free oxygen in order to
survive.
algae: Generally aquatic non vascular plants with chlorophyll.
amino acid: One of a group of organic acids containing an amino group (-
amino acids are the building blocks for protein molecules.
anaerobic (organism): An organism which does not require air or free oxygen
in order to survive.
bacteria: Microscopic plant in the same class as the fungi with a round, rod-
like, spiral or filamentous body.
bagasse: The pulp remaining after the Juice has been extracted from sugar cane.
biochemical oxygen demand: A measure of the amount of oxygen used by micro-
organisms to break down organic wastes.
bioconversion: The biological conversion of waste materials to useful products,
biodegradable: Material which is capable of being biologically broken down to
simpler compounds.
cellulase: One of a group of enzymes manufactured by micro-organisms to turn
cellulose into soluble sugars readily consumed by the microbes.
cellulose: A polymer of glucose with chains of from 2,000-4,000 units.
chemical oxygen demand: A measure of the amount of oxygen required to com-
pletely oxidize wastes.
chlorophytes: A class of green algae.
digestibility: A measure of how well the food/feed is utilized by the diges-
tive system; the ratio of absorbed nitrogen to total nitrogen intake.
digestion: Fermentation, especially anaerobic fermentation.
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electrodlalysls: A method for removing unwanted particles from solution by
passing through an electrically charged membrane.
ensiling: The anaerobic fermentation of crops to preserve and enrich the
fodder.
enzyme: One of a group of proteins produced by living organisms which hasten
metabolic reactions and are not destroyed In the process; a "living"
catalyst.
enzyme hydrolysis: A process in which a cellulose containing material is
broken down to glucose by the action of enzymes.
essential aminc acid: One of eight amino acids which cannot be manufactured
by the human body and which are essential for nitrogen balance.
fermentation: An enzymatic reaction generally accompanied by the evolution
of gas and with growth of micro-organisms.
fungi: A group of saprophytic spore-bearing plants lacking chlorophyll.
glucose: A simple sugar.
hammer milling: Crushing or pulverizing material in a hammer mill.
hemi-cellulose: A polysaccharide (type of sugar) found in plant cell walls.
ion exchange: A technique for separating materials by the reversible exchange
of ions of the same charge.
leachate: A liquid draining out of land-fills and containing decomposed
waste, bacteria, chemicals, etc.
lignin: A three dimensional aromatic polymer found in wood — closely as-
sociated with cellulose as lignocellulose.
limiting amino acid: The amlno acid the furthest below the FAO standard which
lowers the quality of the protein source.
mesophilic (organism): An organism which grows most successfully at temper-
atures between 20° - 40° .C.
methionlne: A sulfur containing essential amino acid, often deficient in
yeast SCP.
monosaccharide: A simple sugar.
mycelium: A mass of fungal filaments which compose the vegetative body of
a fungus.
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net protein utilization: A measure of how well a protein source is utilized
by the body; defined as
retained N x 100, the perfect score is 100
intake of N
petroprotein: Single cell protein grown on a petroleum-based substrate.
phytoplankton: Floating microalgae.
protein efficiency ratio: A measure of how well a protein is utilized by the
body expressed as grams gain in body weight per 100 grams of protein con-
sumed (adjusted to an assumed value of 2.5 for casein).
pyrolysis: dermal decomposition in the absence of air.
reverse osmosis: A method of concentrating a solution by applying hydraulic
pressure to force water through a membrane.
single cell protein: The non-viable dried cells of micro-organisms grown on
a variety of carbon sources.
substrate: The material which the SCP utilizes for growth.
ultraflltration: A technique permitting solids separation from a solution
using pressure to force water and small molecules through a membrane.
vascular (plant): A plant with tissues capable of conducting water and nutri-
ents from the roots to the leaves (xylem) and food from the leaves to the
roots (phloem).
whey: The watery part of milk separated from the curds (semi-solid) in cheese
making.
yeast: A species of fungi.
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/8-77-007
2.
3. RECIPIENT'S ACCESSION>NO.
4. TITLE AND SUBTITLE
SINGLE CELL PROTEIN AND OTHER POOD RECOVERY
TECHNOLOGIES FROM WASTE
5. REPORT DATE
May 1977 (Issuing Date)
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
Sylvia A. Ware
8. PERFORMING ORGANIZATION REPORT NO,
9. PERFORMING ORGANIZATION NAME AND ADDRESS
10. PROGRAM ELEMENT NO.
Ebon Research Systems
10108 Qulnby Street
Silver Spring, Maryland
1DC618
20901
11. CONTRACT/GRANT NO.
d-7-0088
12. SPONSORING AGENCY NAME AND ADDRESS
Municipal Environmental Research Laboratory—Gin.,OH
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
13. TYPE OF REPORT AND PERIOD COVERED
Final- March-Septem. 1976
14. SPONSORING AGENCY CODE
EPA/600/14
15. SUPPLEMENTARY NOTES
16. ABSTRACT
Current research into methods of solid waste management is focusing
on formation of marketable products to defray the costs of treatment
prior to land disposal. Some wastes are already being commercially
exploited for their energy value. It is also possible to produce
a food or feed through a number of technologies including single
cell protein production, enzyme hydrolysis, anaerobic digestion,
and various methods to improve the digestibility and acceptability
of cellulose wastes.
This report examines the technological, economic and environmental
feasibility of the above processes. Single cell protein production
from wastes is compared to SCP production on other substrates(alcohols,
alkanes, etc.) and to conventional methods of farming.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Proteins, Cellulose,
Regenerated cellulose,
Waste, Waste disposal,
Cost comparison, Economic
factors, Waste treatment,
Nutritive value, Fermentation,
Substrates, Biomass. Anaerobic
processes
Single cell protein production,
Cellulosic wastes, Enzyme hydroly-
sis, Anaerobic digestion, Food
recovery, Recycling, Sociological
acceptable, Solid waste managementa
Bioconversion, Municipal solid
waste, Solid waste disposal, Resour
recovery, Cellulose degradation
6A
ce
18. DISTRIBUTION STATEMENT
Release to Public
19. SECURITY CLASS (This Report)
Unclassified
21. NO. OF PAGES
20. SECURITY CLASS (Thispage)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
129
£.U.S.60VERNM£HTPRIHTm6 OFFICE: 1977-757-056/61*09 Region No. 5-11
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