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close this bookBioconversion of Organic Residues for Rural Communities (UNU, 1979)
View the documentFrom the charter of the United Nations University
View the documentForeword
close this folderPerspectives on bioconversion of organic residues for rural communities
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View the documentIntroduction
View the documentSources of available nutrients
View the documentThe most suitable materials for bioconversion
View the documentCharacteristics of residues
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View the documentPhysical and chemical treatments
View the documentMicrobial conversion
View the documentThe animal conversion phase
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close this folderAvailability of organic residues as a rural resource
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View the documentDiscussion summary: Papers by van der Wal and Barreveld
close this folderMicro-organisms as tools for rural processing of organic residues
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View the documentMicrobial utilization of mono- and di-saccharide residues
View the documentMicrobial conversion of starchy residues
View the documentMicrobial conversion of complex mixtures of compounds (Polysaccharides, Proteins, Lipids, etc.)
View the documentMicrobial utilization of cellulose and ligno-cellulose residues
View the documentAlgal culture as a source of biomass
View the documentMicrobial utilization of silviculture biomass
View the documentMicro-organisms and marine and freshwater biomass
View the documentInternational studies on processing organic residues
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close this folderProduction of feed as an objective for bioconversion systems
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View the documentSewage-grown micro-algae
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close this folderEnvironmental goals for microbial bioconversion in rural communities
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View the documentHealth and water economy
View the documentFertilizer and energy economy
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View the documentDiscussion summary: Papers by Porter, Berk and La Rivière
close this folderStrategies for developing small-scale fermentation processes in developing countries
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close this folderProduction of microbial protein foods on edible substrates, food by-products, and ligno-cellulosic wastes
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View the documentPreface
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View the documentContributions to the solution of nutritional problems
View the documentDevelopment of protein-rich vegetarian meat substitutes in the western world
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close this folderThe role of ruminants in the bioconversion of tropical byproducts and wastes into food and fuel
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View the documentNutritional limitations in the use of tropical by-products and waste
View the documentPractical experience with tropical by-products and wastes as feed for ruminants
View the documentAn integrated system for converting tropical feeds and byproducts into milk, beef, and fuel
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close this folderPossible applications of enzyme technology in rural areas
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View the documentBiocatalytic processes
View the documentEnzyme hydrolysis of manioc
View the documentWhole cell systems
View the documentCellulose degradation and utilization
View the documentTransfer of enzyme technology to rural communities
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close this folderIndian experience with treated straw as feed
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View the documentExperience with straw treatment
View the documentField testing and demonstration of straw treatment
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View the documentAnnex 1. The energy efficiency of the two-stage, feed-fuel processing of straw in indian villages
View the documentAnnex 2. Method of calculating the value presented in table 2 for the efficiency of naoh energy usage
View the documentAnnex 3. Recommendations to farmers on the treatment of straw
View the documentAnnex 4. Calculated efficiency of milk production by straw-fed village buffaloes
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close this folderIndian experience with algal ponds
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View the documentCultivation of algae in wastes for feed
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View the documentCultivation of algae for biofertilizer
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close this folderOrganic residues in aquaculture
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View the documentThe range of production in aquaculture
View the documentThe value of organic wastes
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close this folderBiogas generation: developments. Problems, and tasks - an overview
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View the documentWhat is biogas?
View the documentMicrobiology of CH4, or bio-methanogenesis
View the documentThe biogas plant-some technical considerations
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View the documentDevelopments and processes for rural areas
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close this folderMushroom production technology for rural development
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View the documentMaterials and methods for growing mushrooms under natural or field conditions
View the documentGrowing mushrooms under semicontrolled conditions
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close this folderThe combination of algal and anaerobic waste treatment in a bioregenerative farm system
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close this folderA continuous composting system for disposal and utilization of animal wastes at the village level
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View the documentStatus of land utilization and disposal of animal wastes
View the documentA continuous composting system for land utilization of animal wastes at the village level
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close this folderBioconversion of fruit and vegetable wastes
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close this folderIntegrated research on agricultural waste reclamation
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View the documentProduction of yeast from soybean cooking waste at miso factories
View the documentApplication of soy waste as koji substrate for rice miso manufacturing (5, 6)
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close this folderSolid state fermentation of starchy substrates
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close this folderProduction of single-cell protein from cellulose
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close this folderAnalysis of energy cost of integrated systems
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close this folderAnalysis of bioconversion systems at the village level
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View the documentSome results and costs from integrated systems
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close this folderNutritional evaluation of bioconversion products for farm animals
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close this folderBioconversion products: toxicology - problems and potential
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close this folderNutritional evaluation in humans
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View the documentEvaluation of products of bioconversion for human consumption
View the documentProcedures for nutritional evaluation in humans
View the documentThe evaluation of various food products
View the documentConcept of productivity
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View the documentDiscussion summary: Papers by van Weerden, Shacklady, and Bressani
close this folderBiomass from organic residues for animal and human feeding
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close this folderAppropriate biotechnology - summary remarks
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close this folderOther UNU Publications
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Concluding remarks

Fertilization is so widely practiced in aquaculture that it seems almost superfluous to point out the economic advantages that can accrue through judicious use of the inexpensive nutrients present in manure or sewage. These substances, together with other agricultural or organic industrial processing residues, can also provide substitutes for expensive feed ingredients. Obviously, there are regions where few agricultural residues are available, and the aquaculturist must resort to chemical fertilization. But where these residues are available, and where ecological and sociological factors permit the use of such wastes, handling and transportation of the wastes to the ponds are important cost factors that may limit the use of waste residues. The closer the animal pens are to the water, the more economical the fertilization task is and a premium can be placed on planning and modifying new or existing farms to promote optimal operational logistics of joint animal husbandry, market gardening, and aquaculture. We are not aware of any studies concerning the distances between residue sources and ponds, or comparisons of various farm lay-out schematics for this joint agriculture-aquaculture production system, under various edaphic, climatic, and socio-economic conditions.

Manures from pigs and birds are more frequently used than cattle manure, and even in some areas where cattle exist their droppings are often unavailable to aquafarms (e.g., India, Afghanistan) because the dung is dried and used as fuel. In many cases, animal wastes are anaerobically digested in order to allow for multiple benefits, specifically biogas for cooking, and supernatant and sludge for agricultural or aquacultural use. Although the latter two products are largely used for fertilization, their potential use as feed ingredients is high and is currently receiving considerable research attention.

It should be mentioned that plant residues until now have had little use as fertilizers for aquaculture, in contrast to their application in agriculture. This is because of the fundamental physico-chemical differences between water and soil as cultivation media. However, some fish ponds are occasionally or regularly fallowed. Then crops or crop residues are ploughed into the pond as a sort of "green manure." Rice paddies are good examples, where fish can be stocked (ecologically sound pest management permitting), and the rice straw and stubble are ploughed into the paddy soil as soil conditioners.

The use of organic residues in aquaculture is, to a certain extent, dependent on competition for these residues by agricultural production systems. Although detailed studies comparing agricultural and aquacultural use of organic residues from an energy or material-accounting viewpoint are not available, it is quite possible that manure recycling is more efficient in aquacultural animal production (including integrated land animal-cum-fish systems) than in agricultural animal husbandry. Manures produced by fish in a polyculture pond immediately enter a detritus food chain. A portion of this detritus is recycled into higher trophic levels, in this case, table fish. The system, while bearing some resemblance to terrestrial grazing systems (i.e., cattle produce manure, which fertilizes plants, which are eaten by cattle, etc.), is considerably more efficient than that found in intensive agricultural animal production systems. In the latter, manure must be collected and distributed with an attached expenditure of energy and human labour.

Sewage utilization in aquaculture is conditioned by cultural, sanitary, and economic constraints. The simplest use is the establishment of family or village privies over Asian fish ponds, and/or the use of domestic effluents from rural settlements into flowages for cage culture. In these situations, the presence of toxic substances (e.g., trace metals, carcinogens) in the wastes are minimal, and there is less chance for excessive accumulation of harmful substances in the flesh of the fish. Disease and parasite transmission, while still a consideration, is often over-rated. Adequate pond management, as discussed earlier, and careful cooking can overcome most of these potential problems. When the sewage of small or large towns is used for aquaculture (e.g., Calcutta), the presence of materials such as industrial wastes may be potentially dangerous from the standpoint of toxic substances that accumulate in the flesh of the fish. The use of the wastes of such localities for the production of food for man is entirely contingent on segregation of these substances from the normal domestic sewage. The costs of such separation systems will ultimately decide the possibility of their use in food production.

Socio-cultural objections to the use of sewage for fish culture seem to be decreasing in several societies as ecological information becomes disseminated and as fertilizer costs increase. There is, for this reason, urgent need for intensified engineering, economic, and management studies of sewage use under various conditions of light to dense urban development.

The direct use of organic residues as fish feed is highly opportunistic; as intimated in Table 3, it depends on the local availability of anything from various by-products of grain milling to cheap but otherwise unusable animal proteins. Here, as with manure, the location of the feed source in relation to the location of the animals to be fed is a prime economic consideration. Widening the pond berms in China to supply feed for grass carp, as well as locating grouper cage culture near fishing ports, are cases in point. There is urgent need, however, regardless of the nature of the feeds, to have far better characterization of their nutrient values and to incorporate such data in computerized international feed data banks.

The future prospects for the increased use of organic wastes in aquaculture (especially as fertilizers) are clearly influenced by the cost of chemical fertilizers. As the price of fertilizer increases because of increased fossil fuel costs, one can anticipate greatly increased use of organic wastes in aquaculture even without vigorous promotion. Certain key research needs to be undertaken to make such use as beneficial as possible. These investigations should relate to the big-economics of combined agri-aquacultural systems. They should place emphasis on system-wide total and energy accounting with the goal of establishing trade-off values between the use of manure in aquaculture against other agricultural/domestic purposes. The organic value of various wastes, and the cost of handling and treating them under various levels of intensity of operation and development, need to be established. Health problems related to the use of sewage also need attention, especially as they relate to cost trade-offs and permissible risks under various treatment and handling conditions. Questions of the environment need to be addressed vigorously; as the pressure on water supplies increases, fish ponds may be used increasingly to supply water for people. Multiple-use oxidation ponds supplying animal protein and furnishing domestic water will also increase, and problems of eutrophication and contamination of ground and surface waters need to be addressed. The need for interdisciplinary research is obvious if one wishes to aim for optimization in the trade-offs among the several possible goals of fish pond use stated here.

One more caveat seems necessary about aquaculture in general, but more specifically about the seemingly simple, but really complex, subject matter of the use of organic residues in aquatic animal husbandry. This warning is also a challenge embodied in the quotation from Matsuda (26) to follow, which stresses, by implication, the need for multiple-level research, with strong emphasis on pilot installations and culture-oriented extension:

"Aquaculture is not solely a matter of growing a product; it is also a part of rural development, including marketing, distribution of food and income, employment, and living conditions. Thus aquaculture should not be recommended indiscriminately to people who are not ready for it."