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
- Grain, millet residues, aquatic weeds, etc.
- Paddy steep
liquor, biogas effluent, other processing liquors
- CO: from biogas
- Prosopis, etc., forest residues
- Dung, faecal matter
- Illicit liquor process adaptation
Industrial and Urban Residues
- Carbohydrate residues: sago (cassava waste, molasses, spent wash,
- Paddy steep liquor, silk spin liquor, coconut water,
areca, turmeric liquors, etc.
- CO: from thermal, cement, and fertilizer
- Fish wastes, silk worm cocoons
- 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