Chapter 4
PROCESSING METHODS

“The world is moving so fast these days that the
man who says it can't be done is generally
interrupted by someone doing it.”

Elbert Hubbard

4.1 DEHYDRATION

Dehydration is widely applied for commercial purposes, because dried waste can be used either as feed or as urban fertilizer (Flegal and Zindel, 1971; C.C. Sheppard et al. 1975).

4.1.1 Mechanical drying

Drying reduces the bulk of animal wastes to 20-30% of the original volume (Surbrook et al., 1971)

Nevertheless, it is usually a costly process, involving substantial investment and operational costs. The latter depend greatly upon the initial moisture content, as appears from Table 79.

The drying capacity of a medium-size commercial dryer, for different species of animals, is shown in Table 80.

Animal wastes must be processed immediately to prevent the rapid decomposition of organic matter and to conserve its nutritive properties. Losses of the most valuable substances in poultry litter — crude protein — vary considerably according to the drying method and nature of the processing; ensiling completely preserves the nutritive value (Table 81).

Surbrook et al. (1971) observed the following losses of crude protein in various animal wastes:

Table 79
POULTRY MANURE DRYING COSTS¹

¹ Flock = 40,000 layers; output = 40 tons/week at 75% moisture can be dried to 11 tons at 10% moisture (10 tons moisture-free);
² Evaporation rate: 812 Ib. water per h..
³ At £0.18/gal.
⁴ At $0.50/gal.

Source: Blair, 1974.

Table 80
COMMERCIAL MANURE DRYER CAPACITY
(40 hrs/wk)

Source: North Central Regional Research Publication 222 (1975).

Table 81
EFFECTS OF DRYING AND FERMENTATION METHODS ON CRUDE PROTEIN LEVELS
(PROCESSED POULTRY LITTER)

Source: Dřevjaný and Müller, 1968.

The results clearly suggest that the pH of fresh animal wastes is the main factor contributing to the N losses. Dairy manure, having a low pH (4.5-6.5), is not affected, as compared with highly alkaline poultry and pig manures (pH 7.2-8.6).

The following energy and nitrogen losses as a result of various drying techniques were reported by Shannon and Brown (1969):

On the basis of five trials with two different mechanical driers, Chang et al. (1975) found that the dehydration technique determines the final quality of dried poultry waste, particularly the content of crude protein. Nevertheless, apart from ensiling, the drying process is still less wasteful of nitrogen (crude protein) than other animal waste management systems. The nitrogen losses in an oxidation ditch amount to 53%, aerated storage 55%, aerobic digester 90%, holding pond 35%, anaerobic storage 50%, feedlot surfaces 62%, sprinkler system 23% and land surface disposal 31%.

The acidification of broiler litter with sulphuric acid (up to pH 6) prior to dehydration, tested by Harmon et al. (1974), reduced crude protein losses. The practical applicability of this method is affected by the fact that it raises the already high mineral matter level in litter (sulphuric acid is a mineral acid), by the cost of sulphuric acid and the problems inherent in handling it.

Experiments with the processing of poultry excreta by means of hydrolysis (HPW) and subsequent drying indicated that there was no justifiable difference in performance of cattle from either treatment. The HPW process is an expensive method, requiring equipment and involving high operating costs.

Several drying processes have been patented. For example, Lucas Furance Development Ltd. (US patent 3 831 288) designed an apparatus for drying and sterilizing poultry waste. Manure is first mixed with water to form a slurry which is then thickened to a sludge and then to solids. Dry biomass is then passed through a micro wave radiation dryer and sterilizer. The end product is in the form of pellets or meal.

A similar process was reported by Poultry Digest (Anon., 1971): a British firm has also developed a microwave drier with a capacity 1 tonne per hour. The dried poultry manure is sterile, odourless and suitable as a feed for ruminants.

A similar system was designed by Invento, Per Oskar Persson (Netherlands patent/Swedish patent 5068/72). The process yields an animal feed from fresh or semi-liquid manure which is mixed with dry manure and other ingredients and additives. The product, after drying, is pelleted or used in the form of a meal.

Aniagra Productions AB, a Swedish company, developed (1971) an apparatus for drying poultry manure in two steps; the manure is pre-dried, then pelleted or blocked, and finally dried to the desired moisture content. The process is virtually odourless.

Sobel (1970) reported a process in which poultry waste is formed into large blocks which are air dried and can be stored with a minimum odour. He found that the final weight was 29% of the original weight. The microbial count had decreased considerably.

4.1.2 In-house drying

An economical method of drying poultry manure in two stages was introduced by Pennsylvania State University. The system uses high-velocity air movement and mechanical stirring of the manure in the pit of the poultry house. This reduces the moisture content to about half, and the weight of manure to about 30%. Such manure has a crumb structure and a minimum odour, and contains only about 28–35% moisture as compared to the original 75%; the level of ammonia and other gases in the poultry house is reduced significantly. The second stage comprises heat dehydration using a mechanical dryer, which further reduces the moisture content to about 10%. The final product has typical commercial properties as it can be stored in bulk, has no offensive odour and is easy to handle.

Similar experiments were carried out in the United Kingdom, as reported by the Agricultural Development and Advisory Service of the Ministry of Agriculture, Fisheries and Food (Elson, undated). Droppings fall directly onto timber slats and are held there until the time of cleaning. The framed slats are pivoted on posts under the cages or supported from the catwalks by metal straps or ropes. The reduction of moisture can be varied (from 75% to 12.7%) by using different widths of slats. This system has greatly improved poultry house environment by reducing ammonia levels, odour and the fly population, especially at low ventilation rates. The results obtained from manure samples collected after 2,4 and 6 months, comparing different widths of slats with traditional pit systems, are self-explanatory (see Table 82).

Table 82
EFFECT OF TIME ON MOISTURE CONTENT OF MANURE ON SLATS

Source: Elson (undated).

4.1.3 Solar drying

A solar dryer designed similarly to a greenhouse (using plastic covering) was tested on dairy waste in Indiana (Horsfield, 1975). It was estimated that an 80-cow herd would require a solar dryer of about 1,486 m² (18 m² per cow). The cost of mechanical equipment was estimated at US$4,900 and the annual operating cost at US$833 for the entire herd. The solar dryer would reduce the weight to about 72% of the original input weight. This system appears to be quite simple and practical for most developing countries.

Development status

Mechanical drying is a well-established disposal system. The cost varies with moisture content from about $18 to $45/t. Many economic manure/litter dryers are available on the world market.

Very practical methods of in-house drying are now well established in the United States, the United Kingdom and other countries.

Solar dryers are not yet commercially applied, at least on a large scale, but the system has great potential.

Negative features of any drying process are losses on crude protein and other organic nutrients.

Reliability

The process was proved to be technically reliable.

Health hazards

Safety is fairly good; much depends upon the temperature and time of exposure, but most potentially dangerous microbes are usually eliminated.

4.2 ENSILING

Ensiling of animal wastes is more acceptable than dehydration on ethical grounds. Ensiled cattle manure appears to be nutritionally superior to the dried product (Lucas et al., 1975). The economic advantages of ensiling are obvious, particularly if silos already exist on the farm.

Animal wastes can be ensiled together with crop residues, forages and other roughages, provided that there are sufficient moisture (40–65%) and soluble carbohydrates to ensure the quality of the fermentation process. The ratio of crop residues or other roughages to livestock wastes is adjusted to obtain a minimal moisture content of about 40%; moisture should not exceed 70%. Molasses (1–3%) or other sources of fermentable carbohydrates must be added if sufficient soluble carbohydrates are not present in the ingredients for ensiling. The digestibility of cellulosic constituents can be improved by adding alkali in the form of sodium, potassium or ammonium hydroxide. Where available, liquid or gaseous ammonia or even bleaching agents could be used.

In view of the fact that animal wastes contain high mineral levels, preference should be given to additives which do not increase the mineral content and thus do not add to the accumulation of undigestible material.

Ensiling is a simple process which not only prevents the losses on a total crude protein but also converts part of the NPN into protein-bound protein (true protein) (Table 83).

Table 83
ANIMAL WASTES: EFFECT OF ENSILING ON NITROGEN COMPOSITION

Source: Caswell et al., 1976.

Lower moisture content (22%) apparently reduces the level of uric acid and displaces ammonia nitrogen from the silage.

In another study, Virginia researchers (Caswell et al., 1978) evaluated the effect of moisture on the nutritional value and bacteriological parameters of ensiled broiler litter (see Table 84).

Table 84
EFFECT OF MOISTURE LEVEL ON NUTRITIONAL VALUE AND FERMENTATION
CHARACTERISTICS OF ENSILED LITTER

Source: Caswell et al., 1978.

The results indicate that low moisture (22%) affected the nutritive value of litter in all aspects, while 40% moisture ensured preservation of silage by lowering the pH and yielding a sufficient level of lactic and acetic acid. Both treatments reduced total bacterial count; coliforms were completely eliminated in the silage with 40% moisture. Moisture content in the silage has a significant effect on the ratio of the main nitrogenous fractions as appears from Table 85. The ammonia level rises linearly with moisture content, as does the uric acid content when the moisture content is 30% or more. These changes appear to be due to the protein nitrogen, in view of the decline in proteinbound protein at 50% moisture. The authors attribute the decrease in uric acid to favourable conditions for coryneform bacteria frequently found in the litter.

Smith and Daniels (1977) ensiled old litter from two batches of birds, based on rice hulls or wheat straw, at 40 or 50% moisture, using either water or whey. The authors reported that straw-based litter at 3 weeks had a lower pH, while rice hull-based litter had high pH value. In accordance with the previous results (Müller, 1976) dry matter digestibility (DMD) in vitro was higher for straw-based than for rice hull-based silage. The addition of whey instead of water and a longer fermentation period (6 weeks instead of 3 weeks) produced silage of better quality, but there was no difference between silages containing 40 and 50% moisture.

The potential of whey as a donor of moisture and fermentable carbohydrates was further elucidated by Duque et al. (1978). Broiler litter was ensiled at six different moisture levels (22, 30, 40, 50, 60, and 70% respectively), using water or whey. Whey had a pronounced effect, lowering the pH of all tested silages and increasing the level of lactic and acetic acids. Both whey and water effectively eliminated coliforms at all moisture levels. Faecal coliforms, Salmonella and Shigella were not present in the initial mixtures before ensiling, and Proteus, although found in initial mixtures, was eliminated by the ensiling process. Apparent digestibility tests on sheep fed ensiled broiler litter supplemented either by water or whey did not yield statistically different results.

Comprehensive research with broiler litter ensiled with different levels of maize forage (harvested at two stages of maturity) was conducted by Harmon et al. (1975a,b) in order to compare the fermentation characteristics, bacterial contamination and palatability of these silages. The main results are summarized in Table 86. The nutritional value of individual silages was markedly changed in all critical constituents: crude protein, ash and water-soluble carbohydrates. Incorporation of litter into forage resulted in an expected increase in dry matter, crude protein and ash, while water-soluble carbohydrates decreased. These changes were slightly reflected in the fermentation characteristics of the silage. The maturity stage had the most pronounced effect on the apparent quality of silage. Lack of fermentable carbohydrates in more mature forage significantly reduced lactic and acetic acids and increased the bacterial population, but surprisingly the palatability, as measured by silage intake, was not influenced. While incorporating urea had only a slight effect on feed intake, the incorporation of litter almost doubled the consumption by lambs. In addition, the litter-based silages exhibited the lowest bacterial count and a negligible coliform population compared to silage with urea or unsupplemented control silage.

Table 85
EFFECT OF MOISTURE LEVEL ON DISTRIBUTION OF NITROGEN IN SILAGES

Source: Caswell et al. (1978).

Table 86
ENSILED BROILER LITTER WITH MAIZE FORAGE: NUTRITIONAL AND FEEDING VALUE

Source: Harmon et al., 1975 a,b.

Yokohama and Nummy Jr. (1976) reported on the fermentation characteristics and nutritive value of forage maize silages supplemented on an isonitrogenous level with fresh faeces of cattle (2.16% N), pigs (4.35% N) and poultry (6.16% N). In order to achieve the same crude protein level in each silage it was necessary to use 53% cattle manure, or 23% pig manure or 16% poultry manure. The analytical results are summarized in Table 87.

An attempt guide the ensiling process by inoculation of poultry litter with Lactobacillus acidophilus was carried out by Vezey and Dobbins (undated). The authors claimed that the time of ensiling was reduced by 6–8 weeks, but the effect could be attributable to molasses in the mix rather than to the Lactobacilus culture.

Ensiling cattle manure together with hay and other forages or feeds was successfully developed and applied by Anthony (1969a,b; 1970). His classical silage (wastelage) consists of a mixture of 57 to 60% cattle manure and 40 to 43% hay which, after ensiling, is fed to feeder cattle in a proportion of 40% wastelage to 60% maize grain. The principle of this feeding system is applied in the USA and elsewhere. Fresh manure participates in the ration of wastelage-fed cattle from 8 to 15%, and only 25 to 40% of the manure can be fed back to the same group of cattle.

Table 87
FAECAL WASTES ENSILED WITH FORAGE MAIZE:
COMPOSITION AND FERMENTATION CHARACTERISTICS

Source: Yokohama and Nummy Jr., 1976.

The following cattle manure-based silage modifications were applied by the author (Müller, 1975e):

This silage (55% dry matter) which contained 9% crude protein, 5% true protein and 45% TDN on the DM, was acceptable to cattle, but due to a lack of energy it was suitable only for maintenance or low-intensity production. It was, however, a good forage substitute when fed ad libitum with a liquid molasses supplement or other high-energy forages or feeds.

Lamm et al. (1977) investigated the improvement of cattle manure-based silage by adding 4 different levels of sodium hydroxide (2, 4, 8 and 12%) to a mixture of 60% cattle waste (77% moisture) and 40% ground legume-grass hay (11% moisture).

When more than 2% NaOH was added, the pH value before and after ensiling was too high to ensure proper lactic fermentation, but alkali treatment apparently supported the formation of acetic acid. In general, the ensiling process enhanced the in vitro dry matter digestibility (IVDMD) of the untreated and treated mixtures. The higher levels of alkali (8 and 12%) yielded a marked increase in IVDMD, but only silage with 2% NaOH smelt like good quality silage, while silages with 8 and 12% NaOH had a soapy and ammonia odour due to ammonia displacement by the alkaline reacton.

In the most recent UK studies (Wilkinson, 1978) with NaOH-treated silage comprising either cattle faeces or cattle manure (faeces + urine + bedding) and maize forage (whole-crop maize) the following results were obtained:

1. all silages (or maize ensiled alone) with pH below 4.5 gave predominantly lactic and acetic acids, with butyric acid less than 1%;
2. in silages with pH above 4.5 and ammoniacal nitrogen 10% of the total protein, acetic and butyric acids were the major fermentation products;
3. excreta faeces (or manure) had little effect on in vitro organic matter digestibility (IVOMD), which averaged 58.9% for excreta silages compared to 68.3% for maize ensiled alone;
4. NaOH raised the IVOMD of excreta-based silage;
5. neither coliform nor Salmonella-type organisms were detected in any silage;
6. cattle excreta in silage should not exceed 25% of total dry matter.

Development status

Ensiling of livestock waste is a well-established concept of the processing of animal wastes, applied commercially and at the small-farm level. It is technically reliable provided that the basic principles of silage making (anaerobiosis and moisture above 40%) are observed.

Health hazards

Ensiling is the most reliable process known as regards potential risks and health hazards.

4.3 PROCESSING OF LITTER BY STACKING

Poultry litter, used for one or several batches of birds, is an aerobic, fairly balanced biocoenotic system. In the absence of oxygen the aerobic process is substituted by anaerobiosis, resulting in microbial and chemical changes in the litter. Dana et al. (1978) studied the characteristics of litter, stacked at a depth of 1.4 m in a roofed building open on all sides, over a period of 6 weeks. The investigations are summarized in Table 88. The results suggest that the upper part of the litter (0–457 mm) underwent an intense aerobic process for about 4 weeks, continuing at a lower rate until the end of the experiment; this appears to be supported by the sudden rise in temperature during the first week. The temperature of the lower part of the stack (813 mm) was fairly constant, probably due to lack of oxygen and the prevalence of anaerobiosis. The slight decline in pH, and the lowering of lactic acid from the original level, may have been due to acetic acid-forming bacteria and its subsequent conversion of lactates to butyrates, leading to the temporary disappearance of lactic acid.

Table 88
DEEP-STACKED BROILER LITTER: TEMPERATURE, DM, pH AND LACTIC ACID CHANGES

Source: Dana et al., 1978.

Faecal coliforms, Salmonella and Shigella were not present at any time during the study, indicating that stacking may effectively eliminate these pathogens. This is further supported by the earlier findings of Halbrook et al., 1951 and Botts et al., 1952 (see Section 2.6).

Development status and reliability

Although the technique is applied widely in the field, there have been very few studies to support it scientifically. Moisture content of litter, storage place, C:N ratio, ambient temperature and humidity are among the factors which have not yet been reported.

Health hazards

Sufficient data on health hazards are not available, but litter with a moisture content above 20% and below 35% should, after 6–8 weeks of stacking, be fairly free of potentially dangerous micro-organisms. Higher moisture levels would reduce the time required for stacking, but may on the other hand support thermophilic fermentation and carbonization of litter, with losses of N and organic matter.

4.4 CHEMICAL TREATMENTS

The prime objectives of chemical treatments of animal wastes are to eliminate pathogenic bacteria, preserve nutrients, improve the nutritive value and increase the feed intake of the waste.

Researchers at Virginia Polytechnic Institute and State University (Caswell et al., 1975) compared several processes for pasteurizing wastes: dry heat (150°C for 20 minutes), autoclaving (10 minutes or longer), para-formaldehyde fumigation and treatment with ethylene oxide.

All treatments totally eliminated coliforms present in unprocessed litter. Dry heat treatment was less effective in reducing total bacterial count than autoclaving, which yielded the best results at 121°C and 1.05 kg/cm² steam pressure for 30 minutes. Treatment of litter with 3 different levels of para-formaldehyde (PFA) fortified by dry heat (150°C) gave the following results:

The total bacterial population decreased in a linear relationship with the quantity of PFA, but the response to different depths was inconsistent.

Fumigation with ethylene dioxide (EO) at 22°C for 120 minutes at depth of litter 76 mm gave results comparable to those for PFA at the 4% level.

The effect of processing on the fate of various nitrogenous fractions (total N, protein N, NPN, uric acid and NH₃ N) was as follows:

1. dry-heat treatment of litter resulted in substantial losses in all N fractions, the greatest loss being in ammoniacal N (from 0.88% to 0.36%);
2. autoclaving resulted in the smallest losses in all N fractions and significantly increased the level of protein-bound N derived from NPN;
3. PFA treatment at all levels increased the content of protein N of litters processed at 25 mm depth (from 2.22% to 2.75–2.79%) but was ineffective at 6 mm depth except at the 4% level;
4. EO fumigation reduced total N, protein N and NH₃ N.

A metabolism trial on sheep fed litter processed by dry heat, PFA and EO showed that nitrogen utilization and digestibility were not affected by these processes.

In other Virginia studies Fontenot et al. (1975) tested (in addition to heat, autoclaving, PFA, EO) the effect of beta-propiolacton (BPL) as a sterilizing agent for broiler litter, but found that it was ineffective in completely sterilizing the litter. Only dry heat at 150°C for 3 hours (but not for 1 or 2 hours) produced sterile material, but it also resulted in a large loss of nitrogen (42.5%) and other nutrients.

Runkle and Hatfield (1975) reported that when chemically treated (1.5% formalin) cattle feedlot waste was fed to steers at 50% or higher level, the daily feed intake (calculated on metabolic weight) was significantly greater (6.11 kg) than when untreated waste was fed (4.64 kg).

Canadian scientists (Anon., 1977a) treated layer manure by three processes: a commercial product containing 80% propionic and 20% acetic acid, formaldehyde, and a combination of the two. All chemicals were applied at three levels: 0.25%, 0.5% and 1%. Chemically treated excreta and untreated controls were stored at 22°C and analysed on the 7th, 14th and 28th days of treatment. Untreated manure underwent heavy decomposition, with marked losses in nitrogen and energy and a significant increase of ash, indicating a mineralization process. On the contrary, chemical treatment at the 0.5% level retarded decomposition for 7 days and at the 1% level for 14 days.

A broad research programme aimed to the improvement of the digestibility of structural carbohydrates in cattle manure was carried out by Smith et al. (1969). The study involved treatment with NaOH, Na₂O₂, NaCIO₂, Na₂SO₃, Na₂S₂O₄, KCIO₃, NaOCI, KH₂PO₄, Na₂HPO₄, H₂O₂ and NH₂CH₂CH₂OH. Of all these chemicals, only sodium hydroxide and sodium peroxide significantly reduced the cell-wall, cellulose, hemicellulose and lignin contents. True digestibility of faeces derived from high roughage rations was remarkably increased, as indicated in Table 89. The digestion coefficients of all nutrients were greatly improved by chemical treatment. The most remarkable improvements were in structural carbohydrates, hemicellulose and cell walls.

Table 89
ORCHARDGRASS FAECES IN SHEEP RATIONS: DIGESTION COEFFICIENTS

This study has far-reaching practical implications because NaOH is easily available, and the improvement of digestibility appears to justify the treatment.

Another study, by Lucas et al. (1976), involved low-and high-roughage rations. Cattle manure was collected daily and every collection on even days was treated with 3% NaOH (by weight) and dried. Manure collected on odd days was directly dehydrated without alkaline treatment. The results of feeding the untreated and treated manures to sheep are given in Table 90. Alkali treatment of cattle manure, particularly that derived from cattle fed a high-roughage ration, had a great impact on the digestibility of dry matter and crude fibre.

Table 90
APPARENT DIGESTIBILITY OF RATIONS CONTAINING BASAL AND STEER FAECAL WASTES

Source: Lucas et al., 1976.

The effects of physical fractionation and chemical treatment on the nutritive value of dry pig manure (in vitro and in vivo (sheep)) were studied by Ngian (1977). Separation yielded a fibrous layer which represented about 90% of the total DM of pig manure; the remaining solid fraction (10%) was a fine “slimy” layer rich in crude protein. Mechanical sieving resulted in several fractions of different particle sizes, that showed little difference in chemical composition and digestibility. On the other hand, chemical treatment (NaOH) markedly increased in vitro digestibility.

In separate studies with anaerobic digestion it was observed that NaOH treatment of pig manure also enhanced methane and carbon dioxide production.

Development status

Chemical treatments are fairly new. Costs are the main practical factor to consider. Formaldehyde preparations are now widely used in the field and can be easily applied at the farm level.

Reliability and applicability

Chemical treatments are fairly reliable and simple, but problems arise at the farm level, where some concentrated chemicals (NaOH, H₂SO₄, HCI, etc.) can be dangerous to handle. Only formalin, paraformaldehyde, and propionic and acetic acids can be handled with little or no risk.

Health hazards

Chemical treatments, particularly formaldehyde, appear to be very effective in eliminating pathogens and reducing microbial levels in the waste.

4.5 MECHANICAL TREATMENTS

Various mechanical processes, mainly involving cattle and pig wastes, are aimed at reducing volume and separating liquid and solid fractions.

The effect of grinding and pelleting dry cattle manure was studied by Smith et al. (1971). Grinding had little or no effect on the digestibility of individual constituents. In fact, ground manure showed a substantial decrease in cell-wall and cellulose digestibility and in N retention, possibly due to a by-pass of rumen digestion because of the reduction in particle size.

The particle size distribution of three types of fresh animal wastes is shown in Table 91. The relative proportions in different animal wastes depend upon the nature of feed ingredients, their preparation and processing prior to feeding.

Table 91
FRESH ANIMAL WASTES: PARTICLE SIZES

Source: Chang and Rible (undated).

Mercio and Johnson (1978) attempted to improve the nutritive value of the solid fraction separated from manure by a vibrating screen (8 mesh/cm). The solid fraction was fed to cattle either fresh, ensiled or alkaline treated (7% NaOH). The results are shown in Table 92. The highest voluntary intake of dry matter was recorded with NaOH-treated screened manure solids (SMS) incorporated into rations at the 30% level (on DM).

Table 92
EFFECT OF PROCESSING SCREENED MANURE SOLIDS ON INTAKE AND DIGESTIBILITY

Source: Mercio and Johnson, 1978.

At the University of Nebraska, a conical 500-micron screen separator was used to separate feedlot manure into two fractions, coarse and fine (Wagner, 1977). Their chemical composition is given in Table 93. The fine fraction contained 92% of the total manure protein and 82% of digestible solids, while fibre was evenly distributed. The fine fraction appeared to be nutritionally superior to the coarse fraction. Ration composition, however, had a decisive effect not only on the quantity of individual nutrients in fractions, but also on their IVDMD (Table 94). The nutritional differences between fractions appear to be attributable to the level of cell walls (fibre) and other undigestibles derived from roughage, while high-concentrate feeding of cattle yields a manure with high IVDMD in both fractions, as well as in the whole manure.

Table 93
FEEDLOT MANURE: COMPOSITION OF COARSE AND FINE FRACTIONS

Source: Unpublished data, Dept. of Agricultural Engineering, University of Nebraska, cit. Wagner (1977).

Several commercial processes have been developed (Alfa Laval, Duncalf & Associates, etc.) for separating the liquid and solid fractions of cattle and pig manure. The schematic flow of such a process is shown in Figure 4. Raw slurry is piped into a collecting tank, where a submerged agitator maintains the solids in suspension. The mixed slurry is pumped to a sluice feed tank, with excess slurry automatically returning to the collecting tank. The sluice feed is adjusted to deliver precise flow, according to the consistency of the mixed slurry, which is then separated through a vibrating screen. Solid matter is screened off and the separated liquid is gravity fed through to storage, or diverted for further treatment.

Table 94
EFFECT OF RATION ON CONTENT OF FRACTIONS OF BEEF MANURE

Source: University of Nebraska (cit. Wagner, 1977).

Development status

Equipment is already being manufactured and several mechanical processes are commercially applied at larger farms in developing countries. There is a wide variety in the quality and suitability of the equipment. An economic analysis is not available, as this would inevitably have to be related to the specific conditions of the farm and the mode of disposal or utilization of liquid and solid fractions.

Reliability and applicability

The systems are fairly reliable, but further improvements are needed before they will be suitable for feeding purposes, particularly at the small farm level.

Health hazards

when the solid fraction is fed, any health problem could be overcome by ensiling or chemical treatments. Chemical treatment appears to be preferable for the liquid fraction.

Figure 4 — Separating raw slurry into liquid and solid wastes

4.6 OXIDATION DITCH

The oxidation ditch is a technologically advanced aerobic process applicable to all livestock waste. It comprises a continuous open-channel ditch and an aeration motor that circulates the liquid in the ditch and supplies oxygen. The aerobic action converts organic matter into single-cell protein, enabling the protein level in pig rations to be reduced by 15% (Day, 1977). Feeding oxidation ditch mixed liquor (ODML) in the form of nutrient-rich drinking water or adding it to a regular ration (2:1) was developed by Day and Harmon (1974). The principle of the system and mass balance data calculated for a 384 kg feedlot steer are illustrated in Figure 5.

Two systems for feeding ODML to pigs are shown in Figure 6 (Day and Harmon, 1974). At A, ODML is pumped from the oxidation ditch into a holding tank, from which it is fed by adding it to a regulart ration in a ratio of 2 parts ODML to 1 part dry diet. At B, ODML is pumped from the oxidation ditch directly into the watering trough. No other water is provided.

The amino acid composition of oxidation ditch-treated animal wastes is given in Table 95. The nutritive value of ODML is high in terms of protein (25–50% on DM) and essential amino acids, but the energy content is low because of the high mineral matter level.

Table 95
AEROBICALLY TREATED ANIMAL WASTES: AMINO ACID CONTENT

(a)(b) Grab samples passed through a 200 mesh screen, 1971;
(c) Average of two grab samples passed through a 200 mesh screen, 1971;
(d) Grab sample, 1967.

Source: Day and Harmon, 1974.

The average capital investment required for a large, commercially viable, pig operation would be in the range of $13 per individual in a standing pig population (assuming a properly composed pig herd consisting of boars, sows, piglets, growing and finishing pigs). The annual operating cost would average $2.50 per pig marketed (assuming 1.6 pigs are marketed per year per individual in the standing pig population). The capital includes the cost of land, construction, concrete, fencing, purchase and installation of mechanical equipment, labour and energy (Taiganides, 1976, personal communication).

Figure 5 — Oxidation ditch mass balance of a steer

Figure 6 — System for feeding ODML to pigs

Capital and operating costs for an oxidation ditch for cattle would be as follows:

Based on a 10-year equipment depreciation, operating costs on a non-feed basis are estimated at $0.13 per day (or $47.45 per year) per animal (U.S. Environmental Protection Agency, 1974).

Development status

The system is well established and simple, and when started it is easy to operate. Its disadvantages for developing countries are the high initial investment and high requirements for maintenance, power and water; there is also a danger of harmful gases in case of mechanical failure. Variables such as the type of animal, location and the cost of building materials and land affect the amount of capital needed.

Reliability and applicability

Highly reliable for all livestock operations, the system is quite wasteful from the nutrient recovery viewpoint, because about 80% of organic matter is mineralized or converted into gases.

Health hazards

Health hazards are minimal if the oxidation ditch functions properly.

4.7 ACTIVATED SLUDGE

The product is a sediment of aerobic bacterial digestion from an aerated tank, rich in protein (27–45% crude protein). The input consists of animal wastes, oxygen and chlorine. The products are carbon dioxide, ammonia, renovated water and sludge. The initial investment and power and other operating costs are high.

There are several simple processes. A flexible system is demonstrated in Figure 7.

Sludge can be used as a protein supplement for monogastric animals and ruminants.

Development status

The system is advanced and well established for disposal of municipal sewage. However, despite the fact that the system is already applied on many farms, wider experience with livestock wastes is necessary before the system can be proven to be fully satisfactory.

Health hazards

Ash content (18–35%) and heavy metals (lead, mercury, calcium) are usually limiting factors determining the level of sludge to be incorporated. Activated sludge is a pathogen-free waste.

4.8 COMPOST FOR FEEDING

There are several methods of composting, but basically they can be divided into static or dynamic processes.

In the static process the semi-dry manure, alone or together with other organic material, is spread in layers and turned over once or several times during the composting process. The moisture content should be within the range of 40–50%; otherwise, anaerobic processes take place. A characteristic of the static process is the intense development of the fungi Actinomycetes, Ascomycetes and Basidiomycetes.

In the dynamic process the material is constantly revolved in a digester, and the prevailing microflora is usually represented by bacteria. The significant fungal infestation takes place later in windrows, except that when the organic material remains in the digester for a longer period, fungal development replaces the bacterial population in the final stage of the fermentation process.

The organic matter content of processed compost is a decisive factor in establishing the quantity that can be used in ruminant diets. It is therefore necessary to use fresh compost immediately after processing to avoid its mineralization, which results in lowering its organic matter content.

From the author's experience (Müller, 1975d), it appears that the level of compost in ruminant rations could be in the range of 15–40%. Feeding recommendations cannot however be firm until the exact chemical composition of the composted manure is known.

The composting process, geared to a ripe compost, is wasteful in terms of energy (carbon) and other nutrients: an input of 100 kg of solids results in an output of 40 kg solids, 60 kg solids being lost in the form of CO₂ and other gases. Accordingly, in producing fresh compost for ruminant feeding, the process must be shorter to limit mineralization, but long enough to eliminate pathogens. The mass balance of such a process is more favourable, as losses on carbon are restricted to 15–30%. Aeration of the waste by turning enables the aerobic thermophilic process to be completed within 7–14 days, while mechanical processes with forced aeration can take only 2–4 days.

Source : Feedlot, USEPA, 1974.

Figure 7 — Activated sludge

Mechanical composting processes for converting animal wastes and crop residues into ruminant feed have been proposed by the author (Müller, 1977) to overcome a critical shortage of green or dry forage (or roughages), oil cakes and other traditional ingredients. The treatment involved poultry litter, poultry manure, cattle manure and bagasse, which were the main wastes requiring treatment to improve their palatability and nutritive value and to eliminate the risk of transmittable diseases. A mechanical, revolving digester would convert bagasse (or other crop residues) and wastes of faecal origin within 24–48 hours into biomass containing about 35–40% moisture, which would then be balanced with other ingredients such as molasses, grain or other feeds (10–15%), urea, minerals and vitamins. A small percentage of high-energy concentrates (broken rice, sorghum grain, etc.), is required for energy and to balance the ratio between organic and inorganic matter.

The input of ingredients into the digester would be approximately as follows:

Fermented slurry representing about 60% of the total ration, the composition of the final ration would be as follows:

The complete ration would thus contain, on a DM basis, the following constituents:

Brief description of the proposed plant

The plant would consist of a large apron for receiving materials, storage facilities for poultry waste, bagasse, molasses and other ingredients, a digester and ancillary conveyors, loaders and mixers.

Ingredients would be conveyed in predetermined quantities into the digester for a fermentation period of 24–48 hours. The digested biomass would then be transported on a belt conveyor into a large horizontal mixer, where it would be supplemented with molasses, feed concentrates and other ingredients. From the mixer, the ration would be conveyed into an unloading hopper conveniently situated for rapid discharge of feed within minutes into trailers.

The final biomass, being odourless and pathogen-free, could, after chemical treatment to stop further biodegradation, be preserved for 5–10 days. It would also be economically possible to dry and market it after fortifying it with molasses, feed concentrates and other balancing ingredients.

Development status

Composting is a well established animal waste disposal system, but only for fertilizer use. Little is known about its use to produce feed. A mechanical digestor system is reliable and easy to control, provided the C:N ratio is properly maintained.

Health hazards

Composting is reliable in eliminating pathogens because of their long exposure to high temperatures during thermophilic activity.

4.9 INSECT CULTURES

As reported by Calvert (1977), Lindner was the first to propose the use of coprophagous insects to convert human excrements into protein-rich feed. In 1966, Anderson reported that fly larvae degrade manure effectively and could provide protein for chickens, animals or humans. Significant progress toward the use of insect cultures was made by Calvert et al. (1971), who described a system for the mass production of dried fly pupae containing 63.1% protein, equivalent in quality to soybean protein (see Table 96).

Table 96
DRIED GROUND FLY PUPAE: COMPOSITION

¹ Primarily nitrogen-free extract and crude fibre.

Source: Calvert et al., 1971.

Miller and Shaw (1969) reported that Diptera can develop from eggs to pupae in five to six days at 37°C. The larvae can be harvested by exposing the manure, in thin layers on a screen, to intense light; in an attempt to avoid the light, the larvae crawl through the screen. Harvesting of pupae can be achieved by separating them from the manure by flotation.

It was found that larvae are capable of transforming 80% of the organic matter and reducing the moisture content of waste from 75% to 50%. It was estimated that about 25 to 30 g of larvae can be produced from one kg of fresh poultry manure. This process was later mechanized and a machine was developed to handle manure in tonne lots. The machine was subsequently improved by adding a chute and funnel, by means of which the larvae escaping the light were collected in a deep freezer.

A biodegradation study with bovine manure was carried out by Miller (1969). He reported that a breeder stock of house files can easily be collected from disease-free cattle. Fly eggs in manure can be collected daily and transferred into fresh manure. Hatched larvae live on the manure and rapidly reduce its moisture by 60%. After pupation (2-3 days later) the pupae can be harvested and used as an excellent source of protein feed for poultry. The author stated: “Possibly the most practical method of harvesting may be to permit the flies to emerge as adults under controlled conditions. They could then be killed by heat and utilized as a feedstuff.”

Teotia and Miller (1970) found that a temperature of 25°C and a relative humidity of 38% are the optimum conditions for the maximum reproduction of fly larvae. Manure with a moisture above 80%, temperatures above 37°C and relative humidity above 70% are not suitable for fly larvae. Miller's optimum harvest of pupae (1971), was about 2% of the fresh manure. Similarly, Calvert et al. (1970, 1971, 1972) indicated that the excreta from 100,000 hens could produce 227–453 kg of pupae per day, i.e. about 2.5–3% of the manure, in addition to about 540 kg of odourless soil conditioner.

A unique system for converting layer-cage manure into housefly pupae was patented by Calvert et al. (1973). The abstract of the patent disclosure reads:

“An apparatus for separating negatively phototactic housefly larvae from chicken hen excreta and collecting the larvae to allow them to pupate comprised of two compartments, an upper one having a screened floor and a lower one having a solid floor, a screened tray fitted into the lower compartment and a source of white light. Chicken hen excreta in the upper compartment is seeded with housefly eggs, the eggs are allowed to hatch and the larvae to tunnel and aerate the manure, thus deodorizing and reducing the moisture content of the manure by more than 50%. The larvae migrate out of the manure and pupate in the lower compartment. When dried and ground the pupae can be used as a protein source for growing chicks.”

At later stage, an attempt was made to mechanize the process to facilitate the production of this valuable protein concentrate on a large scale (Calvert, 1977). Although the systems have not met the expectation of inventors, the individual components of the system indicate that a mass rearing of insects is possible, and the screen separation appears to be quite efficient, as 90% larvae were collected by the screen separator.

Equipment for the production of housefly larvae at farm level is illustrated in Figure 8.

In Thailand, Kamchai (1978) demonstrated a similar system on a small scale, feeding the larvae to fish; the residual matter is utilized as a fertilizer for fish ponds.

Development status

The system is still in the development stage, but successful exploitation and application on a small scale is taking place in Asian countries and elsewhere.

4.10 EARTH WORMS AND BEETLES

Biodegradation of animal wastes by earthworms and beetles has been approached by several scientists. Thus, for example, Hancock (1956) raised worms on a mixture of peat moss, laying ration, maize meal, molasses and broiler manure. Broilers raised on the compost reached 1.59 kg (in 1956) in 8 weeks, while broilers on regular commercial feed, required 10 weeks to reach 1.36 kg. The results could also be attributable to the high biological value of worm protein, vitamin B₁₂, unidentified growth factors and other metabolites (antibiotic-like substances) of compost-forming micro-organisms.

Source: Calvert et. al., 1969.

Figure 8 — Device for separating negatively phototactic house-fly larvae from chicken hen excreta

Anderson (1971) observed that some species of African dung beetles have a phenomenal capacity to dispose of manure. He has identified 50 species of flies and 35 species of beetles in cowpats in California pastures, of which only the horn fly and face fly are pests, while the others speed the breakdown of the manure. Only 7 species of flies were found to be adaptable to feedlot manure. Fincher et al. (1970) reported that beetles bury the manure promptly and thus preserve its nitrogen value. Sanchez (1973) found that Afro-Asian dung beetles, being nocturnal, are less subject to elimination by predators and are thus less apt to serve as intermediate hosts for parasites of the predators.

Fosgate and Babb (1972) reported that liming and maintaining optimum moisture content in fresh dairy manure (pH 7.0) would produce one kg of earthworms for each two kg of manure (on DM). Earthworm meal contains 58% crude protein and 2.8% crude fat.

Development status

The system is still in the development stage.