In this article we will discuss about:- 1. Animal Waste Potentials 2. Human Meat Consumption 3. Animal Waste Characteristics 4. Waste Treatment and Utilisation 5. Anaerobic Treatment of Animal Waste 6. Animal Feed.
Animal Waste Potentials:
Wastes from farm animals are greatly increasing with the current rise in animal farming. The increased size of these farm operations and their geographical concentration creates large stock-piles of wastes which usually can only be disposed of seasonally. This is because manure has traditionally been used to fertilise agricultural land.
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However, the large quantities of manure effect high handling costs and the increased trucking distances to application sites effect high transportation costs reducing the competitive economics of manure as compared to chemical fertilisers. As with waste oils, animal wastes at one time generated a profit from their sale and not the costs to have it trucked away.
In the past animal waste management techniques have emphasised waste disposal. But the loss of revenues from the sale of manure as a fertiliser results in a net cost to the animal feeder’s operation and hinders the productivity and efficiency sought through large-scale projects.
The higher agricultural efficiencies of today have generated a variety of pollution problems. Over the past few decades, development of animal operations resulted in both water and air pollution due to the accumulation of wastes. These pollutants have affected fish kills, lowered property values and created nuisances to surrounding areas.
Present animal waste handling methods allow odours to be significant problems especially while it is being spread on the soil. Animal wastes contribute to water pollution by increasing organic loads and adding excessive nutrients.
Animal waste characteristics vary from very dilute such as duck wastes which are similar to strong sewage, to semi-solid such as cattle and poultry wastes which may have moisture contents of 75-85%.
Wastes that accumulate at high animal population feeding operations consist primarily of fecal material. They also may include spilled feed, urinary deposits and hair. Fecal wastes’ characteristics vary with animal diet, health, feed preparation procedures, residence time of the wastes before collection on pen floors, and the wastes exposure to weather elements.
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These wastes, as collected, have a content of 70% total solids of which 95% are volatile solids. The organic nitrogen content of slightly over 2% results in a crude protein value of nearly 13%. The amino acids present in this material account for slightly less than 40% of the crude protein value and the remaining portion consists of various non-protein nitrogen compounds. Table 5.30 shows an analysis of a typical animal waste.
Disposal of animal manures is a serious problem affected by the large volume to be handled, the nature of the waste and the vicinity to large populations. Fly and other nuisance problems to nearby inhabitants must be controlled. Under these circumstances a satisfactory method of disposal of animal manure must be utilised. Sources and quantities of animal wastes can vary with such widely diverse activities as human meat consumption and climatological changes.
Human Meat Consumption:
Animal wastes are being generated at an accelerated pace not only because of population increases, but because more meat and broilers are being consumed per capita.
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A fraction of the total waste produced remains on pastures and fields, but the larger portion accumulates in feedlots and buildings and must be handled and disposed in an economical and environmentally safe manner. Each animal species requires different housing and management conditions producing wastes of various quantities and natures. The amount and characteristic of a waste is also dependent on animal size, its diet and metabolic rate.
Animals such as swine with one stomach produce dependent on animal size, its diet and metabolic rate. Animals such as swine with one stomach produce faeces and urine that are similar to human wastes. Both swine and poultry consume food which is easily digested and the amount of excreta produced is relatively small compared to large animals.
Cattle and other ruminants produce a manure of different quality. The bacteria inherent in the stomachs of ruminants enable these animals to feed on cellulosic materials. Plant cellulose is accompanied by compounds such as lignin.
These compounds cannot be digested in the rumen, the portion of the stomach used to digest cellulose and tend to pass right through the digestive tract effecting relatively large amounts of faecal wastes.
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These wastes have a different composition from the wastes from single stomached animals. Urinary wastes from herbivores tend to be more alkaline because their diets are higher in compounds such as potassium, calcium and magnesium.
Animal Waste Characteristics:
Manure from grass fed animals and growing milk stock has lesser soil nutrients than the manure from animals being fattened for slaughter or from work animals fed liberally on concentrates. The biochemical oxygen demand (BOD) of waste from steers with a diet of grain and silage can be higher than steers feeding on grass.
Growing and milk-producing animals retain more nitrogen, phosphorus, calcium and digestible compounds from their feed for weight gain and milk production than is retained by mature stock being fattened. Table 5.31 gives the waste characteristics of some common livestock. Table 5.32 shows the analysis of some typical farm animal wastes.
Waste Treatment and Utilisation:
Animal wastes have great value as soil conditioners because of their plant nutrient and organic substance content. A more complete analysis of animal waste is given in Table 5.33.
There are many problems uniquely common to agricultural wastes. The management of animal manures requires a system of manure removal from its resting place, storage, transportation, treatment and disposal. Present widely accepted disposal techniques merely require application of the manure to farm land.
Collection of the manure is usually by tractor. Water is added to the manure to produce a slurry which can be readily conveyed by centrifugal pumps. The manure slurry is pumped into a tank truck or into a conveying pipeline.
Wastes can be applied, if the slurry viscosity is low enough, via the farm sprinkler system. Application rates from 1/3 – 1″ of manure per farm acre have given good results depending on the soil requirements. Problems inherent in this application technique include large land requirements, capital equipment investment and odour control of the spray.
Sanitary problems are lessened if the manure is immediately applied over farmland upon collection. Fresh manure can be stored only if it is made un-accessible to flies and other pests. Storage piles of solid or semi-solid manure should be covered with fly-tight plastic mesh tarps or layers of soil and dry manure.
The most efficient method of avoiding fly infestation is the spreading of thin layers of the manure from the feeding area on special drying beds and tilling the area frequently. However, a drying bed of about 200 sq. ft. per cow and 1 sq. ft. per chicken is necessary and too costly for farms with large numbers of animals.
Land application of the manure recovers the nutrient content of the wastes, increasing crop production. Presently land application for disposal and nutrient recovery is not widely practised since confinement feeding of animals has altered the practicality of land disposal of such wastes.
Large quantities of waste are concentrated in relatively small areas and must be transported to disposal sites. Furthermore, difficulties occur in the application of the waste to cropland during the growing season and chemical fertilisers usually can be bought and applied more inexpensively than the utilisation of free animal manure.
Laboratory aeration studies of hog wastes demonstrated that the BOD content of hog manure can be reduced by 50% to as much as 90% depending on the system’s detention time which varied from 6 to 12 days. Longer detention times effected higher BOD removal rates. Criteria for the aeration of domestic sewage are not directly applicable to the aeration of hog manure.
The utilisation of an oxidation pond for animal waste disposal is unfeasible. Oxidation ponds depend upon the oxygen given off by algae and the oxygen transferred to the pond by natural causes. The design criteria for these ponds ranges from 30 to 50 lb of BOD per acre per day depending upon location.
The high oxygen demand rates of animal wastes (Table 5.33) would require extremely large surface areas and volumes for adequate disposal. For example, a confinement operation of 1,000 cattle would require an oxidation pond of at least 20 acres; and an operation of 1,000 hogs would necessitate a pond of at least 5 acres.
Aerobic systems using mechanical agitation or diffused aeration systems can be employed to reduce land requirements of aerobic treatment. Studies utilising an underwater air diffusion process for aeration of a 6,500 cu. ft. pond for treating hog wastes were made.
An air diffusion rate of 35 cfm produced an effluent with the following characteristics:
Oxidation ditches can effect BOD removal rates of 90 to 95%, but the ditch capacity per cow and hog must be about 95 cu. ft. and 35 cu. ft. respectively and liquid volumes of 8,000-10,000 gal per foot of rotor length are necessary. These land and equipment requirements of aerobic treatment methods are too great for large-scale animal waste treatment operations.
Anaerobic Treatment of Animal Waste:
The high solids content and high oxygen demand of animal wastes makes them readily available for treatment by anaerobic biological systems. Anaerobic digestion of animal wastes under controlled conditions has been carried out both in the laboratory and in the field.
The anaerobic process has been used for many years in the treatment of municipal sewage sludge. The primary purpose of this process for waste treatment is the maximisation of the destruction of organics in the waste and stabilising the sludge for disposal.
Air compressors are not necessary for anaerobic treatment since it occurs in an atmosphere thus having a very low power requirement. Furthermore, the process produces a methane-rich fuel gas providing plant thermal and electrical energy.
Experiments with anaerobic processing of animal wastes have shown that animal waste slurries with solids contents twice as high as typical municipal sludges can be successfully treated with fermentation times about 30% of municipal systems. Also, animal waste treatment tank volumes are approximately 15% that of the municipal treatment systems producing a waste with excellent stability.
Fig. 5.28 illustrates a flow diagram of an anaerobic process. Initially the wastes are mixed with water to form a slurry which is heated to temperatures conducive to thermophilic bacteria growth. It is then continuously fed into a fermentation tank equipped with agitators to constantly mix the wastes, while a number of processes take place simultaneously.
The first fermentation tank process decomposes carbohydrates into simple sugars through the action of extracellular enzymes. These sugars can then be absorbed through the cell walls and enter the metabolic systems of the micro-organisms. The products of the first stage of fermentation consist primarily of simple acids and alcohols, hydrogen and carbon dioxide. These products are ideal substrates for the methanogenic bacteria which generate methane and carbon dioxide.
A similar degradation and synthesis process is utilised for the fats and proteins. All these processes contribute to the reduction of original solids present in the waste and generate a new mass of single cell protein called the “biomass.” The “biomass” is withdrawn from the fermenter and discharged to a drying bed and then used as an animal feed ingredient.
The gases generated by fermentation contain methane, carbon dioxide and very low level of sulphur (about 0.1 %). The combustion of these gases as fuel yields non-polluting products. The additive reduces the cost of beef production and the fuel gas supplies energy to the farm buildings and other facilities, thereby saving money and eliminating the need to market and distribute the recycle products.
The anaerobic process effects two products – a fuel and an animal feed ingredient. Raw solid wastes are acceptable for treatment and the process is environmentally viable for discharges with no wastewater, solid, or gaseous pollutants.
Another anaerobic process converts animal wastes into single cell protein animal feed. Fig. 5.29 shows the process flow diagram. Initially, manure is collected by mechanical or hydraulic means and filtered to effect fibre recovery. The fibre is washed and pre-digested through treatment with alkali and heat.
The treated fibres are then digested by micro-organisms and converted to SCP in a one or two stage continuous operation. The resulting microbial cells are separated, washed, dried and then recycled to the treatment tank. The major problem of this process is the difficulty in producing a contaminant free animal feed.
A pilot plant in operation processes the wastes from 100 head of cattle. Their waste is digested by thermophilic bacteria to produce a cellular mass of high protein value. This mass is dried and used as a feed supplement for the cattle. From the 350 pounds (dry basis) of manure supplied daily the plant generates 120 pounds of feed supplement.
Lagooning as a means for waste disposal is in widespread use for raw and primary wastewater and for all kinds of industrial wastes. Agricultural wastes can also be disposed of by using the lagooning process but they must be operated anaerobically.
The reason for this is twofold- first, large volumes of water would be necessary to dilute manure solids content to the equivalent solids content of sewage; and second, the land requirements for aerobic or facultative lagoon treatment would be excessively large, also anaerobic animal waste lagoons must be highly loaded anaerobic units.
The main difference between stabilisation ponds used for municipal sewage and industrial wastewaters and the stabilisation ponds used for the disposal of livestock wastes is that the former treat large quantities of waters with relatively low pollutant content, while the latter must treat large quantities of organic solid waste matter. The heavy loaded manure ponds generally are operated under anaerobic conditions, making volume rather than surface dimensions the limiting factor in their design.
Other criteria that must be considered include:
(i) Odour control
(ii) Fly and mosquito control
(iii) Prevention of subsurface water pollution
(iv) The aesthetics of the pond must be acceptable.
Agricultural stabilisation ponds are designed with large depth to surface ratios. The influent wastes are discharged under water at the pond’s centre. Only a portion of the manure is converted to gas as the remaining sludge accumulates at the pond bottom. The water is maintained at designated levels with makeup water.
Experimental work at the University of California utilised 8 small manure lagoons with dimensions of 4 feet in diameter and 7 feet deep. The first year five units processed chicken manure and three units processed dairy manure. The second year swine manure was processed in the units. Manure characteristics processed in these lagoons are given in Table 5.34.
Feeding tests were first made on the surface liquor of the lagoon and on the manure fed. These included total and volatile solids, pH, alkalinity, electrical conductivity and 5-day BOD.
Each week the lagoons were examined on the basis of physical appearance, scum, colour, opacity of the liquor, odour, gasification and microbiological (fly or mosquito) activity. Bottom sludge samples were also tested.
The cattle waste lagoons developed a surface crust of relatively inert lignaceous hay stems and grain hulls. This crust did not harbour fly and mosquito breeding although it did support weed seed growth. These lagoons showed the most promise since the crust covered the units like the floating cover on a municipal digester. This crust is inert and can be easily broken and removed, transported and spread on a field without problems of excessive odours or fly breeding.
The swine manure lagoons periodically developed a thin crust of lignaceous material. About 50% of the time no crust formed on the surface which appeared pale black and clear. In the summer months this liquor supported considerable amounts of drone fly larvae. Variations in loadings did not seem to change lagoon appearance. Well digested animal waste sludges were similar to a well digested municipal sludge.
They were black, well flocculated and dewatered, with a sweet to tarry odour. The less digested sludges from the more highly loaded lagoons had the sour odour of their respective manures and were generally lighter in colour. Sludge appearance appears to be good indicator of lagoon performance.
These experiments can be summarised as follows for animals:
(i) Odour is a very important criteria of the acceptability of a lagoon. Objectional odours were detected upon approaching the experimental area.
(ii) Lagoons have a great appeal to many fanners because they can eliminate or significantly reduce fly problems from manure. Large numbers of flies were attracted to the fresh manures when they were added to the lagoons in the summer. The poultry manure fed to the lagoons often was infested with MUSCA larvae and pupae; these floated to the surface and though some emergence of adults did occur, most maggots drowned and the pupae were waterlogged.
(iii) Organic matter destruction. The reduction of the poultry manure total and volatile solids indicate excellent waste biodegradation and stabilisation.
Stabilisation lagoons for the disposal of agricultural animal wastes have been determined to:
(i) Effect a considerable reduction in the total and organic solids content of manure.
(ii) Effect a nearly complete reduction of the BOD.
(iii) Cause these reductions through utilisation of both biological degradation and infiltration loss.
Animal Feed:
Except for the capita l investment in cattle, the cost of feed is the largest expenditure in cattle production. A 10% reduction in feed expenditures would effect a 50% increase in net return to the farm operator. Therefore, a system of waste management which could utilise the nutritious values of cattle faecal matter would be most desirable.
Animal wastes contain considerable energy and nutritive value. The energy content of chicken faeces ranges from 3.22 to 4.48 calories per gram of dry matter and the nitrogen content from 0.03-0.07 grams per gram of dry matter.
The utilisation of dried chicken manure as a feed supplement for chickens and ruminants can effectively reduce an operator’s costs. It can be fed to dairy cattle upon drying and the milk produced from such cattle on this type of feed was normal.
Beef animals and sheep were able to utilise broiler faeces as a feed supplement. The rate of gain and carcass grade were not significantly different for beef steers fed 25% broiler litter and the taste of the meat was unaffected.
Both sheep and steers consumed a combination of cattle feedlot manure and hay and it was noted that combining such materials offers the cattle feeder an opportunity to improve feed efficiency and at the same time reduce the cost of removing manure from the feeding pens. Another study found that concentrated cattle manure could be successfully fed to pullets and laying hens. Egg production was affected only slightly.
One of the important new sources of food and animal feed protein is single cell protein (SCP). SCP substrates include those derived from oil, wastes and renewable resources as manure.
Some of the advantages of SCP are:
(i) The micro-organisms do not depend on agricultural or climatic conditions, but are cultured in large fermentation vessels,
(ii) They have rapid mass growing rates,
(iii) Genetic experimentation for protein improvement can be readily undertaken,
(iv) Production of SCP is not limited by land surface or sunlight.
Bacterial SCP is generally comparable to fish meal, running around 60-75% crude protein; yeast SCP is more like soy meal, running 45-55% crude protein; and mycelial fungi SCP is usually somewhat lower in protein content.