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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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126 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 20C.) 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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130 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- 45C) versus thermophilic (50- 70C) 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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132 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 materiala 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 29-35C 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 25-30C 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 productiontheoretical 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.

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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.