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close this bookBioconversion of Organic Residues for Rural Communities (UNU, 1979)
close this folderAnalysis of bioconversion systems at the village level
View the document(introductory text...)
View the documentIntroduction
View the documentApproach to bioconversion analysis
View the documentSome results and costs from integrated systems
View the documentFuture development possibilities
View the documentConclusions
View the documentSummary
View the documentReferences

Future development possibilities

Organized bioconversion of residues seems to be practiced most in the People's Republic of China (14), but it is in its infancy in other less developed countries. However, the possibilities are immense with both conventional and newer processes. A survey of Microbiology Abstracts, Section A (15), revealed at least 25 papers* on processes applicable to rural residues. Thus, a determined effort to work at the rural level on rural residues would yield the best results.

This section indicates some possibilities for bioconversion in the future. Residues from industries situated near rural centres are also listed, because the waste from a medium-sized industry will probably suffice for a whole community. The possibility of generating employment from use of industrial waste should not be ignored. In the Indian context, large industrial undertakings situated near the outskirts of townships and generating usable waste should be encouraged to recycle and re-use the waste instead of resorting to expensive treatment not leading to agricultural products. This would also prevent pollution of the neighbourhood.

Two requirements have to be met for widespread propagation of bioconversion methods: (a) designs for cheap fermenters, and (b) culture or inoculum banks to supply starter cultures. This is similar to the large-scale effort now being launched to supply blue-green algal cultures (16).

If these facilities are provided, and this does not seem too difficult a task, various kinds of residues can be used (Table 7). The table gives only a representative sample and is not meant to be comprehensive.

Locally available grain, millet, and weed residues are added here to re-emphasize the need to make the best use of existing wastes by supplying starter cultures for better ensilage, or by supplying better designs of biogas digesters or fermenters. The available quantity is so vast that commensurate work seems to be called for in order to solve the urgent problem of food, feed, and energy shortages. In many parts of India, harvested straws rot because the harvest and the monsoon are concurrent. Even good drying systems to prevent deterioration (negative bioconversion?) will go a long way to alleviate the problem. Providing every reasonable-sized community a 6 m x 6 m drying platform of hard plastered mud or cement with embedded pipe flanges in a grid would help the villagers dry and preserve their crop residues more effectively. The pipe flanges are used as anchors to fix tent driers of plastic or thatch.

Items 2 and 8 in the table are examples of the variety of process liquors now being underutilized. Paddy steep liquor is available in millions of litres in most rice-producing countries as a result of the parboiling process, and makes nutrients available for fermentation (17). Similar liquors are biogas effluent (4), silk spin liquor (conservatively estimated at about 50 million I per year in one district to Karnataka State alone), coconut water (0.5 x 10(6) tons per year) (18), turmeric" and areca-processing liquors. All these liquors need to be supplemented by a molasses or glucose source for yeast manufacture; they supply N. P. K, and essential vitamins. Items 3 and 9 point out the need for a close look at CO2 as a resource (19). Both biogas as generated and combustion stackgases are thermally valuable as well as being rich sources of CO2 for algal cultures. These gases, being neutrally buoyant, can be transported in balloons to desired locations. Prosopis and forest residues are extremely valuable resources that are now used only for burning. Thayer (20) has grown cytophaga on such material to make fodder. Items 5 and 11 are very effectively used in China (14), and their use should be propagated in other countries.

Regarding item 6 in the table, in India, wherever illicit liquor is brewed, it is done under conditions of very low sterility. Jaggery and acacia bark with some roots and herbs are added to water and sealed in a pot and buried underground. The brew is ready to distill in 10 to 15 days. If the yeast can be induced to multiply under aerobic conditions, it might be a good source of protein. Item 7 refers to the need to develop valuable starch or sucrose residues as cheap substrates for indigenous fermentation. Cotton dust availability in India is 33,000 tons per year (18), and is in a form suitable for enzymatic degradation to glucose, or for 20-day aerobic compost formation. Fish wastes (item 10) can be ensiled in a remarkably simple process (21). The product is a valuable poultry ration and is stable for up to three years. Silkworm cocoons can be dried immediately (to prevent negative bioconversion) and fed directly or ensiled by the same method used for fish wastes.

TABLE 7. Residues Locally Available in Rural Areas and from Proximate Industries

Rural Residues

  1. Grain, millet residues, aquatic weeds, etc.
  2. Paddy steep liquor, biogas effluent, other processing liquors
  3. CO: from biogas
  4. Prosopis, etc., forest residues
  5. Dung, faecal matter
  6. Illicit liquor process adaptation

Industrial and Urban Residues

  1. Carbohydrate residues: sago (cassava waste, molasses, spent wash, cotton dust)
  2. Paddy steep liquor, silk spin liquor, coconut water, areca, turmeric liquors, etc.
  3. CO: from thermal, cement, and fertilizer plants
  4. Fish wastes, silk worm cocoons
  5. Sewage sludge

This brief review of future possibilities for rural communities would not be complete without a design for a cheap big-solar fermentation device. This design is not now in use, but might serve to stimulate ideas and improvements.

Figure 3 shows a box-type solar cooker (3) adapted for fermentation. This is made of hollow tiles and plastered with cement with a high coefficient of thermal expansion; e.g., lime/wood ash. The cycle undergone is: Expose to the sun to sterilize, cover to ferment, re-expose for broth concentration. To maintain the healthy growth of aerobic organisms, a compressor driven by a biogas engine, or wind power, or bicycle power, is used to aerate the brew. The tiles provide cellular air spaces as insulation during the sterilization cycle. If it is cloudy, wood-fired heat can be used to sterilize the broth. Though this kind of device cannot mass-produce material, it can be used to provide needed protein for village children.

Figure. 3. Box-type Solar Cooker Adapted for Fermentation