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OCR for page 124
Chapter 7
Waste Treatment and Utilization
All living systems process materials and energy in such a way as to yield a
desired end-product or use, plus waste substances. The residues of one system
may constitute the raw materials of succeeding systems, although this is not
always the case.
Waste may be defined as any material or energy form that cannot be
economically used, recovered, or recycled at a given time and place. Under
such a definition, wastes could theoretically be disposed of most econom-
ically by their discharge to air, water, or soil. However, where human, animal,
and plant numbers are large, the direct discharge of untreated liquid, gaseous
or solid residues, or wastes frequently leads to severe environmental degrada-
tion and even to disease and death in man and other living creatures.
As public recognition of the consequences of environmental pollution has
increased, so has the enactment of restrictive antipollution laws. Such laws,
together with the increasing cost of raw materials and energy, have led to
renewed studies of waste treatment and disposal. These environmental protec-
tion laws have also led to increased interest in the development of techniques
to recycle and reuse wastes.
Recycling of human, animal, and vegetable wastes has been practiced by
man for centuries. These practices have served their purposes, providing, for
instance, fertilizer or fuel, but they have often been complicated by the
presence of enteric pathogens that have infected the people involved in their
handling. Additional pollution problems have arisen more recently because
modern industry generates a multitude of nonbiodegradable organic material
and heavy metals that find their way into municipal, industrial, and agricul-
tural wastes. Some industrial effluents cause damaging biological effects as
they are recycled through the plant and animal food chain. Fortunately, in
most recycling processes there has been little adverse effect because recycled
toxicants have not entered the food chain.
Some recycled organic materials can be useful as food, feed, crop fertilizer,
fermentable substrates, or soil conditioners for nonagricultural land. In recog-
nition of this diversity, it is important to identify the optimal use of recycled
organic materials as components of food or feed. Those which are to be
124
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WASTE TREATMENT AND UTILIZATION
125
recycled for direct refeeding to animals should be handled separately and
according to procedures that can be readily controlled.
This chapter focuses primarily on the recycling and utilization of wastes
either of biological origin or generated in agricultural processes.
Certain practical but underexploited processes developed for waste and
water treatment provide for nutrient and energy reclamation through bio-
logical (algal-bacterial) systems. Another largely unexploited but valuable pro-
cess is the composting of organic wastes. In contrast to burial or incineration,
comporting enables preservation and reuse of nutrients and minimizes envi-
ronmental pollution. Recycling of animal wastes through refeeding processed
waste to animals, and application of algal-bacterial systems to the treatment
and recycling of animal wastes, are viable processes that also appear to be
underexploited.
Each of these processes is described in detail in the sections below.
Algal-Bacterial Systems
Algae can both utilize light energy and capture and concentrate nutrients
from dilute aqueous solutions. Some algae are capable of growing com-
mensally in an ecosystem with waste-oxidizing bacteria. The results of the
commensal metabolism are the release of oxygen and synthesis of bacterial
degradation products into new, protein-rich plant material. Algae and bacteria
can be used for the treatment and conversion of human and animal wastes
into forms useful for fish and animal feeds. It is even possible that algae and
bacteria grown on selected vegetable wastes can produce cell protein suitable
for human consumption. Algal and bacterial protoplasm are very similar in
chemical composition. Both have similar metabolic pathways, although bac-
teria have more varied metabolisms.
Algal-bacterial processes generally can be divided into two major cate-
gories: 1) those designed to oxidize waste, and 2) those designed for optimal
production of algae and nutrient recycling.
Liquid Waste Treatment
Two waste treatment processes involving algal-bacterial systems are now
available: facultative pending and integrated pending, discussed below.
Facultative Ponding In facultative pending (that is, pending involving
both aerobic and anaerobic treatment), untreated waterborne waste materials
are introduced at a bottom center point of a deep (up to 3 m) pond designed
to hold the waste for 4-12 weeks, depending on the temperature and con-
centration of waste material. Shorter holding periods would be possible in the
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MICROBIAL PROCESSES
FIGURE 7.1 Aerial photograph of facultative pending system in Esparto, California,
U.S.A., consisting of ponds in series: two primary, one secondary, one tertiary, and one
quaternary. (Photograph courtesy of W.J. Oswald)
torrid zones, with longer holding periods required in temperate zones. Under
such conditions, the waste undergoes fermentation. Fermentation product
are either given off as gas (such as CH4 or CO2), or oxidized by aerobic
bacteria that utilize the oxygen produced by algae growing near the surface.
Facultative ponds are usually built in series. Typically, sewage is channeled
through four or five successive ponds (see Figure 7.19. Wastes are pumped
into the bottom of the first pond, where anaerobic digestion begins. Effluent
is removed near the bottom of the first pond and transferred to the bottom
of the second pond, where further decomposition (stabilization) occurs
through aerobic processes. Cleaner water near the surface of the second pond
is in turn transferred to the final two ponds in sequence. The effluent from
the last pond should have a low coliform count and be suitable for crop
irrigation, except for vegetables to be eaten raw.
Facultative pending is applicable to most liquid wastes, including domestic
and municipal sewage. It is also an appropriate treatment for wastes from
vegetable canneries and sugar refineries. In the latter cases, or whenever the
loading to a pond in the tropics exceeds 110 kg of Biochemical Oxygen De-
mand (BOD5) per ha per day, floating surface mechanical aerators may be
necessary. (sODs is the quantity of oxygen required by aerobic microorga-
nisms to oxidize the biologically available organic matter in a waste material
during 5 days at 20°C.) At lower temperatures, the loading limit will be
correspondingly lower.
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WASTE TREATMENT AND UTILIZATION
127
The maximum rate of oxygen production by algae in such systems is about
450 kg per ha per day in the tropics. However, because of cloudy days and
bacterial turbidity, loadings well under llOkg per ha per day are recom-
mended for many wastes. Mixing is critical in determining the maximum load.
Major advantages of facultative pending are low capital costs, low main-
tenance requirement, good effluent quality, and limited potential for adverse
environmental impact. For example, facultative ponds seldom contribute
undesirable nitrate or phosphate to the groundwater.
Disadvantages of facultative pending are: 1) such ponds if overloaded pro-
duce foul odors; 2) they are inefficient in nutrient recovery because nitrogen
is lost to the atmosphere and most phosphates are precipitated out; and
3) when evaporative loss from the pond exceeds the amount of liquid gained
through rainfall, facultative ponds increase in inorganic salt concentration.
When this occurs, the salts in the effluent may render it less desirable for the
irrigation of certain salt-sensitive crops.
Integrated Ponding In the integrated pending process (see Figure 7.2), a
facultative pond is followed by an algal growth pond. Algal ponds are charac-
terized by high decomposition rates due to high oxygen concentrations pro-
duced by the algae. The oxygenated discharge from the algal growth pond is
recycled to the surface of the facultative pond. The algal pond is normally
about one meter deep and is designed to operate on a holding period of 5-10
days for the waste being treated. The algal pond is equipped with channels
and pumps designed to maintain a flow velocity sufficient to bring about the
resuspension of algae that have settled to the bottom, where photosynthesis
and oxygen production cannot occur (see Figure 7.3~.
FIGURE 7.2 Aerial photograph of integrated pending system at St. Helena, California,
U.S.A. The square pond is a primary facultative pond. It is 0.9 ha In area and receives the
waste of 3,500 persons. Next to facultative pond (center right) is a 1.82-ha high-rate
pond. Lower right is a 0.8-ha algae-settling pond. The two ponds at upper left are dispo-
sal ponds. (Photograph courtesy of W. J. Oswald)
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128
MICROBIAL PROCESSES
FIGURE 7.3 High-rate pond at Modesto, California, U.S.A. The pond is 80 ha and
produces an average of 40 t of oxygen per day. Four 100-HP mixing pumps in foreground
move water through a 60-m wide X 1.4-m X 3,600-m circulation channel. (Photograph
courtesy of W.J. Oswald)
Another desirable aspect of an algal growth pond is the tendency of the
pond water to reach a high pH level at about dusk each day as a result of
carbon dioxide utilized by the algae. The high pH (~ 9) causes a reduction in
bacterial level, and effluents from such high-rate ponds often have low
Escherichia cold concentrations.
After retention in the algal growth pond, the wastewaters are introduced
into the bottom of a third, deep, elongated pond, which serves as a settling
pond. Here the algae settle out and a relatively clear algae-free effluent is
produced for disposal or discharge to the environment. Integrated pond sys-
tems, though more costly than facultative ponds, require less land and pro-
duce an effluent superior with respect to both bacterial cell and salt concen-
trations. Integrated ponds principally consume solar energy; yet they produce
an effluent equal in quality to that derived from electrical energy systems in
which oxygen is supplied by mechanical aerators.
The disadvantages of integrated pending systems are their need for solar
energy in excess of 200 g cal/cm2/day and a mild temperature. Occasionally,
predators may disrupt the algal population.
Ponding procedures involving algae provide a number of research oppor-
tunities, including:
· The application of facultative and integrated ponds to developing-
country conditions; and
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WASTE TREATMENT AND UTILIZATION
129
· The possibility of harvesting feed-grade algae from the secondary or
tertiary pond of the series. Where algae harvesting is desirable, it would be
feasible to convert an algal pond from an integrated system into an algal
production system. This conversion could be accomplished by decreasing the
pond depth and recovering the algae by flotation, sedimentation, or straining.
Algal Production
Maximum algal production from domestic sewage and animal wastes is
desirable, providing the wastes contain no toxic substances, because it permits
conservation of fixed nitrogen in a form useful as animal feed. If there is
doubt concerning the quality of the product for feed, it may be usable as a
fertilizer or as a fermentation substrate.
After separation from the pond effluent and subsequent drum or spray
drying (which can be expensive), or on sand beds (relatively simple and
inexpensive), algae constitute a potentially stable product that contains
40-60 percent protein, 10-20 percent carbohydrate, 5-15 percent lipid,
5-10 percent fiber, and 5-10 percent ash. If used daily, moist algae can be
dewatered to about 15 percent solids and incorporated with other ingredients
such as grain at a concentration of up to 5-10 percent in feeds.
Dry algal protein is up to 80 percent digestible by ruminants. If the mate-
rial is free of pathogens and toxic substances, it can be used to replace
soybean meal, meat, or bone meal in animal, poultry, and fish diets.
Although larger microalgal forms are less common in the environment than
unicellular microalgae, they are more desirable for production because they
can be harvested by screening and sedimentation. Among the larger micro-
algal forms, Spirulina is the most promising. Spirulina cells are large enough
to be recovered by simple filtration. In Chad, villagers recover them by using
muslin. Dried Spirulina resists bacterial degradation and is easily stored.
Spirulina protein has a satisfactory balance of essential amino acids, with the
exception of a slight deficiency in those that contain sulfur. A pilot plant has
been set up near Mexico City to collect and process Spirulina; about one t per
day of dry Spirulina is produced and sold as an additive for chicken feed.
Scenedesmus is the most convenient algal genus because it is readily cul-
tured and harvested, particularly when grown under conditions that induce
cloning. Chlorella species, on the other hand, are less desirable because they
are too small to be harvested economically and they are usually eliminated
from waste systems through rotifer predation. Scenedesmus species are not
grazed by rotifers. Infestation by the copepod Cyclops, however, can lead to
their eradication within a few days. Cyclops and other Scenedesmus grazers
may be removed by screening and recirculation of the effluent. Spirulina has
no comparable predators.
Scenedesmus growth for maximum algal production resembles the algal-
ponding process used in waste treatment, except that a lesser pond depth is
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MICROBIAL PROCESSES
involved. The waste is introduced into a shallow, channeled growth pond
(20-30 cm deep) equipped with paddle wheels to provide a mixing action.
Linear flow velocities of 5-15 cm/see are required. Suitable substrates are:
· Liquid wastes such as domestic sewage effluents;
· Effluents from anaerobic ponds used to treat concentrated plant and
animal wastes;
· Digester effluents and residues;
· Effluents from algal and manure fermentation systems used for
methane production; and
· Irrigation return flows, urban runoff, and dilute petroleum wastes after
the addition of nutrients.
Wastewaters should have a suitable sons, plus an algal growth potential
not exceeding 500 mg/1.
An important advantage of algal production systems in conjunction with
animal feed lots is that up to 80 percent of the fixed nitrogen and other
nutrients are recovered. Yields of up to 60 t/ha/year of dry algal feedstuff
may be possible.
Limitations
The algal growth and waste utilization process just described is limited to
climatic regions where ambient solar energy is greater than 200 cal/cm2 /day.
Another restraint is the requirement that the algal growth potential of the
wastewater be sufficiently great to support photosynthetic oxygen produc-
tion equal to or greater than the sons of the wastewater. If the oxygen is
not produced at a sufficient rate, supplementary oxygen is needed, and the
potential yield of algae will be too low to justify the expense of harvesting.
The process, however, is readily adaptable to the treatment of residual ("un-
feedable") wastes from confined feedlots, since most of the potentially
hazardous substances in the wastes can be excluded from such an operation.
In addition to a warm climate and a BODs loading of about 225 kg/ha/
day, requirements include level land on which to construct the ponds, a
market for a high-protein animal feedstuff (in this case, algae), and sufficient
capital to construct the algal growth system.
Algal growth on feedlot wastes poses the risk of possible transmission of
disease-causing organisms or toxic substances, unless care is exercised in waste
management and selection.
Research bleeds
In connection with increasing the use of algal substances, research in the
following areas should be emphasized:
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WASTE TREATMENT AND UTILIZATION
· Improved methods of harvesting algae;
· Technology for processing algae to improve digestibility; and
· Possible disease and toxicity hazards.
Composting
131
Composting is the biological decomposition of organic residues or wastes
under controlled conditions to yield a product useful in agriculture.
Although the art of composting is an old one, it has been underexploited.
For example, in the maize-growing regions of Mexico, composting is not
practiced, despite a great need for organic matter in the soil. In Brazil, Sao
Paulo farmers are very reluctant to use municipal compost supplied to them
free of charge, and use it only because of government insistence.
Composting involves the acceleration of microbial decomposition through
conditions favorable for microbial reproduction and metabolic activity. Con-
trolling factors are temperature, oxygen supply, moisture, and of course the
nature of the substrate.
Temperature There is considerable controversy in temperate climates as
to the relative merits of mesophilic (10°- 45°C) versus thermophilic (50°-
70°C) comporting. In practice, the question is irrelevant, especially in devel-
oping countries, since the temperature of ~ composting mass soon rises to
thermophilic levels. This is because of the excess energy generated by bac-
terial activity combined with the insulating property of the composting mass.
High temperatures serve to kill disease-causing organisms as well as fly eggs,
larvae, and pupae. Temperature rise is a useful indicator of operational
success.
Aeration and moisture content The aerobic approach is followed because
higher temperatures are reached thereby and because anaerobic composting
produces foul odors. Moisture content and aeration are interdependent. The
oxygen used by the microbes comes from air in the spaces between particles
of the composting mass. If the spaces are filled with water, air is excluded and
aerobic activity is reduced or the process becomes anaerobic. The maximum
permissible moisture content varies with the nature of the composted waste.
For example, if the bulk of the compost is straw, the maximum permissible
moisture content is 80-85 percent. If paper is the major constituent (as in the
case of municipal refuse in the United States), 55 percent moisture is the
maximum because the paper tends to compact.
Aeration may be accomplished by fuming (windrow composting), by
mechanical tumbling of the material, or by use of a blower system. Turning,
which can be done either manually or mechanically, involves spreading and
reforming the windrows. Tumbling can be accomplished by placing the wastes
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MICROBIAL PROCESSES
in a rotating drum equipped with vanes or by dropping the material from one
level to another.
Substrate The substrate for composting can tee almost any organic residue
or waste that provides the nutrients required by the microbes. With organic
wastes, the proportion of carbon to nitrogen, the major nutrients, may
require adjustment. These should be present in a ratio no greater than 30: 1.
At higher ratios, the process is slowed and the quality of the finished product
is lowered. At ratios lower than 20: 1, nitrogen loss can occur through vola-
tilization of ammonia. Examples of nitrogen sources that can be used to
adjust the C: N ratio are manures, green plant debris, and animal or fish
scraps. Examples of carbon sources are straw, dry vegetable matter, and
paper. In most wastes (community and agricultural), phosphorus, potassium,
and trace elements are present in sufficient amounts.
Composting is enhanced by uniformity of the particles of substrate. Re-
ducing particle size (grinding) before composting may be advantageous. The
optimum particle-size distribution depends upon the materials to be com-
posted. With paper-rich wastes it is in the order of 5 cm. Green vegetables
wastes can be larger. In fact, garden debris (excepting woody material) need
not be ground.
Any organic waste can serve as a substrate for composting. But care must
be taken when human excrete are composted because of the risk that danger-
ous organisms may not be destroyed.
Organisms The composting process is carried out by a complex mixed
population of naturally occurring bacteria. The addition of inocula in com-
posting is normally unnecessary, since the required numbers and variety of
microorganisms are already present in the wastes, especially in rural areas.
Advantages
A major advantage of composting is its flexibility with respect to volume
of materials handled and degree of mechanization. Composting can range
from the individual farm level to a level that can accommodate waste from a
village or small town. Sophistication can range from an operation involving
manual turning to one in which a complex reactor (digester) is employed.
Another important advantage is that disease-causing organisms are usually
rendered harmless during composting. The inactivation may be brought about
by high temperature, exhaustion of nutrients, and natural antibiosis.
Perhaps the principal advantage of composting is the production of a
product useful in agriculture. Compost can improve the texture of soil, in-
crease its water-holding capacity, and supplement and promote efficient utili-
zation of plant nutrients.
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WASTE TREATMENT AND UTILIZATION
Limitations
133
Under certain circumstances a potentially important constituent, one
which might have a value greater than the compost, might not be reclaimed.
For example, it is more economical to recycle paper than to compost it.
A portion of the nitrogen in the wastes is lost in comporting. This loss can
be reduced by adjusting the carbon: nitrogen ratio of the wastes toalevel
between 20: 1 arid 30: 1.
Wastes such as farmyard manure (unless it contains appreciable amounts of
straw) must be mixed with a bulking material—a rather difficult task.
The cost and energy involved in turning large quantities of waste during
composting may be significant.
A major problem occurs with the composting of untreated human excrete.
Extreme care is essential in carrying out the process itself, and certain restric-
tions must be applied in the use of the product. The product can be safely
used on land that is then allowed to lie fallow for at least a year; even the
more resistant pathogens are killed during this period.
Another constraint pertains to the carbon: nitrogen ratio of the product.
The ratio of carbon: nitrogen must be between 20: 1 and 30: 1. At higher
carbon levels, the microorganisms growing in the compost preferentially use
the nitrogen; this becomes a detriment to plants growing on the land to which
the compost is added.
Research Needs
Project operations should be preceded by small-scale "trial-and-error" runs
to arrive at useful operational parameters. These trials are needed because of
the diversity of waste materials.
Anaerobic Lagoons
Anaerobic lagoons, designed to treat concentrated organic waste, provide a
microbial environment in some ways similar to that found in the rumen or
intestinal tracts of animals, in sewage sludge digesters, and in the muds and
sediments of aquatic areas. Animal wastes are rich in degradable solids and
differ considerably from sewage wastes, which are greatly diluted with water.
An aerial view of an empty anaerobic lagoon is shown in Figure 7.4.
Properly operating anaerobic lagoons are characterized by an array of
microbial associations that ultimately produce methane and carbon dioxide.
Three main groups of organisms are involved. The first group degrades and
solubilizes fats, proteins, and cellulose. A second group converts these degra-
dation products to a mixture of organic acids and carbon dioxide. The third
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134
MICROBIAL PROCESSES
FIGURE 7.4 Aerial photograph of anaerobic pond 1.6 ha X 6.2 m deep created to treat
the wastes of 2,500 feeder cattle. Steve Marks's feedlot, Zamora, California, U.S.A.
(Photograph courtesy of W. J. Oswald)
group utilizes this mix to produce methane. For vigorous fermentation to
occur in lagoons, many months may be necessary for maturation. The matur-
ation process may be shortened by the addition of dewatered digested sewage
sludge from either a vigorously operating city sewage treatment facility or
another functioning lagoon.
The balance among the bacteria may be disturbed by overloading the
lagoons with organic material. Imbalance may also occur because of low
ambient temperatures. With overloading, increased concentrations of short-
chain fatty acids occur, resulting in more substrate than the methanogens can
utilize. In the case of low temperatures, the methanogenic population and its
rate of metabolism are diminished. As acid concentrations increase, a point is
reached where the buffer capacity of the system is overwhelmed and a pre-
cipitous drop in pH results. Under acid conditions methanogenesis ceases and
the acid- and cold-tolerant group of fermentative organisms continues to make
more fatty acids. At high concentrations these acids exert a toxic effect on
methane-producing bacteria.
Recovery of an anaerobic lagoon is a sluggish process. It is aided by dis-
continuing the flow of new waste to the lagoon and bringing the pH to
neutrality. A new start may be initiated by adding lime or sodium bi-
carbonate in amounts calculated from analysis of samples and then waiting
for the slowly proliferating methanogens to reestablish themselves in suf-
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WASTE TREATMENT AND UTILIZATION
135
ficient numbers. The addition of dewatered sludge, with its vigorous popula-
tion of methanogens, will hasten restoration of the microbial balance.
Anaerobic lagoons respond to warm temperatures with increased rates of
catabolism of organic materials and higher populations of microorganisms.
Cold weather diminishes rates of organic degradation and reduces microbial
numbers. Of the three groups of simultaneously operating microorganisms
associated with anaerobic fermentation, the methanogenic bacteria are prob-
ably the most sensitive to charges in temperature, and are thus limiting for
the fermentation process.
Limitations
Anaerobic lagoons operating at optimum rates of activity require tempera-
tures of 29°-35°C and do best in tropical climates. However, anaerobic fer-
mentation with gas production also occurs in lagoons in temperate climates.
Here, lower ambient temperatures are compensated by increasing the pond
size by 50 percent in areas of severe winters. Low seasonal temperatures,
however, may reduce the numbers of methanogenic bacteria, and their lower
rates of metabolism will result in unpleasant odors.
Excavated earthen ponds require relatively nonporous soil to prevent seep-
age of water. Concern about possible contamination of underground water-
ways by wastewater has resulted in requirements for lining the basin with
bentonite clays and polyphosphates to give an almost impervious seal. Manure
ponds in sandy loam soil, however, have been shown to be sealed effectively
in less than 6 months by a layer of largely microbial composition.
Research Needs
· More study is needed to characterize the groups of fermentative,
hydrogen-producing, acetoge~iic, and methanogenic microorganisms in an-
aerobic processes as functions of temperature. If methanogens can be found
with higher rates of metabolic activity at lower temperatures, it might be
possible to increase the rate of organic waste degradation in cool anaerobic
lagoons by adding these bacteria as an augmenting inoculum.
· Additional study will be required for devising an inexpensive method of
collecting methane from lagoons to take advantage of a now-wasted energy
source. Plastic sheeting, relatively unstable in air and sunlight, might serve as a
stable, submerged tent to collect gas from which methane could be separated,
or, since algae are not involved and sunlight unnecessary, opaque coverings
such as ferrocement could be used.
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136
Recycling Animal Waste by Aerobic Fermentation
MICROBIAL PROCESSES
Livestock manures are widely utilized as fertilizer and soil conditioners
because they contain substantial amounts of the major nutrients needed by
agricultural crops. They are also used by some farm families and villages to
produce methane for cooking by fermentation (Chapter 6~. Another possi-
bility for recycling part of the animal waste is to refeed processed material
to the same or other types of animals so that the food value of undigested
plant material and microbes is not lost. This has been tested in a microbial
processing of livestock waste by lactic fermentation, which produces a silage-
like product.
Fresh feedlot cattle-waste solids were separated from the liquid portion.
These solids were then combined with each of a number of various cracked
grains, mainly maize, in a 1: 2 ratio and adjusted to 40 percent moisture
content. The mixtures were tumbled slowly (O.S RPM) in a cement mixer at
25°-30°C for 36 hours. The results were a rapid production of acid and
control of fetid odor in this aerobic, solid-substrate fermentation, with a final
product with an amino acid content 18 percent greater than that of unfer-
mented corn. The organisms in this process came from the waste, not the
grain, and conditions favored proliferation of lactic acid bacteria from less
than 1 percent of initial total microorganisms to dominant numbers within
12 hours. The acid produced reduced the number of coliform bacteria and
other undesirable organisms.
Aerobic culture with substrates of fresh swine waste combined with
cracked corn adjusted to 40 percent moisture also resulted in lactic fermenta-
tion, with early control of fetid odor and production of a silage-like product
in 36 hours. Lactic acid bacteria, indigenous to fresh swine waste, became
dominant within 24 hours and produced lactic and other short-chain acids
from acetic to vale ric. The acidity dropped 2 pH units into the pH 4.2-4.6
range. Although the fermentation product contained 21-39 percent more
methionine than maize, when fed to young pigs it was still found inadequate
for this amino acid as well as for lysine.
This swine waste fermentation product was fed as the major dietary com-
ponent to young pigs, hens, and sheep. Pigs showed gain and gain-to-feed
ratios diminished by one-third in 13-day trials. Laying hens performed com-
parably to controls in a 21-day test, and sheep did not discriminate against
the fermentation product in a 10-day trial.
Fresh cattle waste aerobically cultured with com is dominated by lacto-
bacilli. Initially present in small numbers, two-thirds of the lactic acid bac-
teria are similar to Lactobacillus fermentum. After 6 hours, L. buchneri
dominate and remain high through the 24th hour. In a comparable aerobic
swine waste-corn fermentation, more than 98 percent of the Lactobacillus sp.
initially present were L. fermentum, and this organism remained predominant
for 144 hours, never dropping below 69 percent of the lactobacilli isolated.
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WASTE TREATMENT AND UTILIZATION
137
With either swine or cattle waste, yeasts are a major competing group of
organisms. If the fermentations are sufficiently aerated, yeasts will increase at
the expense of lactic acid bacteria, apparently by inhibiting lactic acid pro-
duction. The observed change in acid levels may possibly result from utiliza-
tion of the organic acids by yeasts. The major species of yeast appears to tee
Candida kneel
Limitations
Aerobic fermentation of cracked cereal grains combined with waste re-
quires tumbling both to mix and to provide oxygen for the microorganisms.
However, power requirements are low because the vessels are rotated slowly.
Moisture content of fermentation material can be flexible, ranging from
35 to 43 percent. Drier material allows less microbial growth and acid produc-
tion; excessively wetted material tends to clump. Lysine is the principal limit-
ing amino acid for growing pigs and layer hens in this fermentation product.
In recycling animal waste for its nutrients, the dung of healthy animals is
required; diminished disease potential is associated with acid production that
kills coliform bacteria. But it is believed that many animal wastes can be refed
to livestock without harmful effects to animals or risks to man.
Research Neecis
· Decreasing the power requirements for mixing would be helpful. Less
power would probably be needed to turn an auger that could mix and aerate
this type of fermentation in a stationary, cylindrical vessel with a conical
bottom; this impeller design has apparently not been tested in this particular
semisolid fermentation.
· The principal limiting amino acid is lysine, and it is desirable to find
microorganisms that excrete lysine. However, such organisms may not survive
as inoculum in a mixed culture of natural flora.
· Culture techniques are needed to yield more fermentation acid to
diminish the disease potential of fermentation products. The effect of aerobic
fermentation of waste cereal grain on parasites and viruses is not known, and
this represents a potential hazard. Aside from the disease potential, the
esthetic and psychological aspects of refeeding processed waste to animals
should be studied to assess acceptance of the process by farmers and con-
sumers.
· The consequences of buildup of nonbiodegradable residues as a result
of continued recycling should be studied.
· The costs of fresh feed vs. costs accrued in collecting and processing
wastes need to be determined for each situation. It may be more economical
to utilize manures to increase crop yields.
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138
Recycling Animal Waste by Anaerobic Fermentation
MICROBIAL PROCESSES
Anaerobic culture of fresh cattle waste with ground coastal Bermuda grass
or Johnson grass in a ratio of 57: 43 produces silage by a lactic acid fermen-
tation. Manure and hay are blended and added to the top of an airtight silo;
the product removed from the bottom can serve as part of a less costly,
adequately nutritious ruminant ration.
The inoculum of lactic bacteria for this fermentation came from feedlot
waste and grass. Lactic acid bacteria were isolated from fresh cattle waste in a
feedlot and were identified as Lactobacillus plantarum, L. cased subspecies
casei, L. cased subspecies alactosus, and L. fermenh~m. Uncut grass has few
lactic acid organisms, but harvesting is an important mechanism for spreading
these microbes, which are usually associated with decayed material in contact
with the soil, providing numbers comparable with those in feedlot waste.
Limitations
In work that has continued since 1962, the potential disease hazards of
refeeding of cattle waste processed by bacterial fermentation appear limited,
as judged by the absence of reports of infection.
Diminished risks of disease are associated with maintenance of apparently
healthy herds; for example, isolation pens are used with new feeder stock.
Reduced risks are also linked with the process of ensiling, which involves
lactic acid bacteria, and produces largely lactic and acetic acids that increase
acidity to near pH 4.0. The effect of these acids on enteric pathogens was
demonstrated by inoculation with each of 27 serotypes of Salmonella into
separate laboratory silos. No Salmonellae survived in the manure-blended
ration, whereas 25 or 27 Salmonella serotypes were recovered in silos that
contained only manure. In another study, eggs of nematodes in manure com-
bined with coastal Bermuda grass hay and ensiled for 4 weeks demonstrated
that parasitic larvae were absent in the finished product.
Research Neecis
Cattle being fed or treated with antibiotics or related substances may
produce waste containing undegraded and diluted drugs. It is known that low
concentrations of antibiotics taken by an animal may favor the development
of microorganisms resistant to the antibiotic in use. It is not known, however,
what effect this fermentation process may have on inactivating antibiotics or
other therapeutic chemicals used with animals, and research is needed to
determine this.
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WASTE TREATMENT AND UTILIZATION
References and Suggested Reading
Algal-Bacterial Systems
139
Gloyna, E. F.; Malina, J. F.; and Davis, B. M., eds. 1976. Water resources symposium.
Vol. 2: Ponds as a wastewater treatment alternative Austin: University of Texas,
Center for Research in Water Resources.
Laskin, A. I., and Lechevalier, H., eds. 1978. CRC handbook of microbiology. 2nd
edition, Vol. II: Fungi, algae, protozoa and viruses. West Palm Beach, Florida: CRC
Press.
Oswald, W. J.; Lee, E. W.; Adan, B.; and Yao, K. H. 1978. New wastewater treatment
method yields a harvest of saleable algae. WHO Chronicle 32:348-350.
Com posti ng
Compost Sczence/Land Utilization. Emmaus, Pennsylvania: Rodale Press, Inc.
Golueke, C. G. 1972. Composting. Emmaus, Pennsylvania: Rodale Press, Inc.
. 1977. Biological reclamation of solid wastes. Emmaus, Pennsylvania: Rodale
Press, Inc.
, and McGauhey, W. J. 1952. Reclamation of municipal refuse by composting.
Sanitation Engineering Research Laboratory Technical Bulletin, No. 9. Berkeley,
California: University of California
Anaerobic Lagoons
Bryant, M. P. 1979. Microbial methane production—theoretical aspects. Journal of Ani-
mal Science 48 (1): 193-201.
Kirsch, E. J., and Sykes, R. M. 1971. Anaerobic digestion in biological waste treatment.
Progress in Industrial Microbiology (London) 9 :155-237.
Miner, J. R., and Smith, R. J., eds. 1975. Livestock waste management with pollution
con trot Midwest Plan Service Series, No. MWPS-l9. Ames, Iowa: Iowa State Uni-
versity.
Zeikus, J. G. 1977. The biology of methanogenic bacteria. Bacteriological Reviews
4 1:5 14-541.
Recycling Animal Wastes by Aerobic Fermentation
Fontenot, J. P., and Webb, K. E., Jr. 1975. Health aspects of recycling animal wastes by
feeding. Journal of Animal Science 40:1267-1277.
Rhodes, R. A., and Orton, W. L. 1975. Solid substrate fermentation of feedlot waste
combined with feedgrain. Transactions ~ f the A m.~7rr~n .~;PtV of ~ ~irt`It1`rn7 F"=
neers (ASAE) 18:728-733.
~ / ~ J ~ JO ~~
Smith, L. W.; Calvert, C. C.; Frobish, L. T.; Dinius, D. A.; and Miller, R. W. 1971. Ani-
mal waste reuse-nutritive value and potential problems from feed additives. ARS-
44-224. Washington, D.C.: U.S. Department of Agriculture.
Weiner, B. A. 1977. Fermentation of swine waste-corn mixtures for animal feed: pilot-
plant studies. European Journal of Applied Microbiology 4:59-65.
Recycling Animal Wastes by Anaerobic Fermentation
Anthony, W. B. 1971. Cattle manure as feed for cattle. In Livestock waste management
and pollution abatement: Proceedings of the International Symposium on Livestock
Waste, April 19-22, 1971, Ohio State University, Columbus, Ohio, pp. 293-296. St.
Joseph, Michigan: American Society of Agricultural Engineers.
OCR for page 140
140
MICROBIAL PROCESSES
McCaskey, T. A., and Anthony, W. B. 1975. Health aspects of feeding animal waste con-
served in silage. In Managing livestock wastes: Proceedings of the Third International
Symposium on Livestock Wastes, April 21-24, 1975, University of Illinois, Urbana-
Champaign, Illinois, pp. 230-233. ASAE Publication 275. St. Joseph, Michigan:
American Society of Agricultural Engineers.
Research Contacts
Algal-Bacterial Systems
J. Benemann, University of California, Richmond Field Station, 1301 South 46th Street,
Richmond, California 94804, U.S.A.
E. F. Gloyna, University of Texas, Austin, Texas 78712, U.S.A.
W. J. Oswald, Division of Sanitary Engineering, University of California, Berkeley, Cali-
fornia 94720, U.S.A.
Composting
Jerome Goldstein, Editor, Compost Science/Land Utilization. Box 351, Emmaus, Penn-
sylvania 18049, U.S.A.
C. G. Golueke, Cal Recovery Systems, Inc., 160 Broadway, Suite 200, Richmond, Cali-
fornia 94804, U.S.A.
Anaerobic Lagoons
M. P. Bryant, Department of Dairy Science and Microbiology, University of Illinois,
Urbana, Illinois61801, U.S.A.
Raymond C. Loehr, College of Agriculture and Life Sciences, Cornell University, Ithaca,
New York 14853, U.S.A.
J. Ronald Miner, Agricultural Engineering Department, Oregon State University, Cor-
vallis, Oregon 97331, U.S.A.
William J. Oswald, Division of Sanitary Engineering, University of California, Berkeley,
California 94720, U.S.A.
B. A. Weiner, Fermentation Laboratory, Northern Regional Research Center, U.S.
Department of Agriculture, Agricultural Research Service, 1 815 N. University,
Peoria, Illinois 61604, U.S.A.
Recycling Animal Wastes by Aerobic Fermentation
J. P. Fontenot, Department of Animal Science, Virginia Polytechnic Institute and State
University, Blacksburg, Virginia 24061, U.S.A.
L. W. Smith, Biological Waste Management Laboratory, Agricultural Environmental
Quality Institute, Science and Education Administration, U.S. Department of Agri-
culture, Beltsville, Maryland 20705, U.S.A.
B. A. Weiner, Fermentation Laboratory, Northern Regional Research Center, U.S.
Department of Agriculture, Agricultural Research Service, 1815 N. University,
Peoria, Illinois 61604, U.S.A.
Recycling Animal Wastes by Anaerobic Fermentation
W. Brady Anthony, Animal and Dairy Sciences Department, Alabama Agricultural
Experiment Station, Auburn University, Auburn, Alabama 36830, U.S.A.
J. P. Fontenot, Department of Animal Science, Virginia Polytechnic Institute and State
University, Blacksburg, Virginia 24061, U.S.A.
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WASTE TREATMENT AND UTILIZATION
141
L. W. Smith, Biological Waste Management Laboratory, Agricultural Environmental
Quality Institute, U.S. Department of Agriculture, Science and Education Admin-
istration, Beltsville, Maryland 20705, U.S.A.
B. A. Weiner, Fermentation Laboratory, Northern Regional Research Center, U.S.
Department of Agriculture, Agricultural Research Service, 1815 N. University,
Peoria, Illinois 61604, U.S.A.
Representative terms from entire chapter:
animal wastes
