|Bioconversion of Organic Residues for Rural Communities (UNU, 1979)|
|Environmental goals for microbial bioconversion in rural communities|
The discussion was concerned primarily with the microbiological treatment of sewage and the use of the resulting bioconversion products. Some doubt was expressed as to the applicability to rural communities of the methods employed to handle human and animal wastes in cities. There was also some dissent as to whether it was preferable to use the solid waste as a nutrient medium for the growth of algae that could be incorporated into animal feeds, to compost it for fertilizer, or to digest it anaerobically for biogas production.
It was noted that algae grown on these residues contain a variable, but high, percentage of elements generally regarded as undesirable, e.g., lead, mercury, etc. However, in the experiments described by Berk, the level of these elements in the tissues of animals whose diets had contained 15 - 20 per cent of algae as a percentage of the dry matter was no higher than in those of control animals on algae-free diets. It appeared that the elements were present in a form not available to the animal. While this is reassuring in one sense, it creates a problem in another, in that these substances were concentrated in the droppings from animals to which the algae had been fed. Consequently, any further use of the manure from algae fed animals would have to be effected with this in mind.
It was suggested that the methods of utilizing feedlot residues, partly as liquid manure, partly for producing biogas, or even by re-feeding to ruminant animals, might be applied successfully, mutatis mutandis, in developing countries. This led to the concept of fully integrated systems for residue utilization in rural communities. In this connection, the use of algal ponds for fish farming seems attractive because it avoids the need to harvest and dry the algae. The relatively high digestibility of the algal preparations used in the experiments described by Berk was attributed to the rupture of the cell walls during drum drying. However, such a method of drying is not applicable in most rural situations. Less costly alternatives are now being developed for use in village communities.
Reservations were expressed about the feasibility, or even desirability, of transferring technology from industrialized countries to the less technically developed ones. It was emphasized that training is extremely important for the people putting new methods into operation, and audio and visual aids now being developed will be of great help in this regard.