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close this bookBioconversion of Organic Residues for Rural Communities (UNU, 1979)
close this folderPerspectives on bioconversion of organic residues for rural communities
View the document(introduction...)
View the documentIntroduction
View the documentSources of available nutrients
View the documentThe most suitable materials for bioconversion
View the documentCharacteristics of residues
View the documentBioconversion systems
View the documentPhysical and chemical treatments
View the documentMicrobial conversion
View the documentThe animal conversion phase
View the documentSummary
View the documentReferences

Bioconversion systems

Figure 3 shows the pathways for the bioconversion of residues into food. In the upper box, cellulose-rich, starchy and sugary residues, and animal manure are represented. The lower box shows the goal of bioconversion systems: food for man. In most cases this will be in the form of meat, milk, or eggs.

It is frequently said that there seems to be a certain competition for food between animals and man. One easily overlooks that this is the exception rather than the rule. Most animals are kept for the purpose of producing food for man. They are mainly converters (biological ones) of products inedible by man. As such, they do not compete significantly for human food supplies.

We have many options for making food from wastes. The ones by-passing the animals are represented by the dotted lines in Figure 3. Direct use as food is non-existent, otherwise the product would not be a waste. Chemical and physical treatments of waste seldom create food. Microbial conversion, either direct or after treatment, permits mushrooms to grow and favours the production of fermented oilseed cakes. Unfortunately, this method is not yet used for the conversion of millions of tons of residues to any significant degree.

The solid lines on the right side of the figure represent bioconversion systems making use of animals. Grass, straw, and quite an amount of poor-quality roughage follow the direct route to food. Animal feeds may also be wastes that are treated via chemical or physical means and/or by microbial conversion, which the animal also converts to food. The potential and efficiency of bioconversion should be exploited to a much greater degree. In general, the right side of Figure 3 shows the most realistic potential for bioconversion of the bulk of residues into food.

Figure. 3. Bioconversion of Residues into Food