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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

The most suitable materials for bioconversion

To identify the most suitable areas in which bioconversion of residues may be important and therefore worthwhile, the residues are divided into three categories, each susceptible to a common method of bioconversion. Cellulose-rich substrates form a total of more than 1,800 million tons annually of renewable resources (Table 1). They are to a great extent found in Asia, and it is therefore not surprising that they consist primarily of rice straw. The present use is often none; in some areas it is used for fuel. Straw could form an extensive base for reeding ruminants. There is no doubt that bioconversion would greatly improve the use of these materials, particularly in rural areas. To what extent in vitro SCP (single-cell protein) production can play a major role here depends greatly on local circumstances and on the results of research efforts in this field.

TABLE 1. Straw Production, 1974 (in millions of tons)

Crop World Africa South America Asia
Paddy rice 323 8 10 294
Wheat 360 8 10 90
Maize 586 54 58 100
Other straws 441 41 18 123
Total straws 1,710 111 96 607
Sugar-cane 116 9 28 46
Total 1,826 120 124 653

The second major residue category consists of starchy and sugary wastes (Table 2). Because their carbohydrates are more easily accessible, they require a somewhat less difficult form of SCP bioconversion. As shown in Table 2, cassava and sugar beets provide the greatest amount of residue. High productivity in relatively poor soil has made cassava a popular staple food, especially in countries most in need of food.

TABLE 2. Starchy, Sugary Residues (in millions of tons)

Crop World Africa Latin America Asia
Cassava 106 42 33 30
Sugar beets 482 4 5 39
Bananas 8 1 4 2
Citrus fruits 12 1 3 3
Coffee 5 2 3 -
Total 613 50 48 74

A third category of residue is manure, a by-product of all animal production systems. It is calculated that approximately 1,900 million tons of manure are produced per year.