298 Organic waste recycling: technology and management
fish ponds, organic wastes to be applied to fish ponds have to be properly
treated to ensure destruction of these pathogens, or feeding of organic wastes to
fish ponds should be discontinued temporarily. Fish to be used as animal feed
will normally have to be processed further e.g. through drying, silaging and/or
pelletization which will result in die-off of most pathogens.
Another major problem relating to the consumption of fish raised on wastes
is the public acceptability of the fish. As far as taste and texture is concerned,
personel observations by various workers indicate that fish grown in well-
treated domestic wastes are equal to or even superior in taste or odor to non-
wastewater cultivated fish (Allen and Hepher 1976). Fish grown in manure-fed
ponds have a different taste and texture since they are much leaner, with only
6% fat, which is excellent compared to fish raised on high protein feed pellets
with 15% fat, and fish rose on grain with 20% fat (Wohlfarth and Schroeder
1979).
Probably the most critical prerequisite before we can obtain public
acceptance of waste-grown fish is the public health concerns. All legitimate
public health concerns must be adequately assessed and resolved and adequate
public health safeguards provided. Perhaps a way to overcome this public health
problem is to treat the waste prior to use in fish culture to meet the WHO
standard for aquacultural reuse (Table 2.28). Lime treatment of sludge can
inactivate a large number of bacteria and viruses, but not helminthic ova. Waste
stabilization ponds in series or sedimentation basins with a detention time of at
least ten days can settle out most of the helminthic ova, but care has to be taken
with the second and third types of helminthic problems, described earlier. An
increased destruction of pathogens would also take place if the waste were
treated by a biogas or composting system before adding to the fish pond since
both processes, especially the latter, lead to an increased temperature which kills
pathogens. An additional step could involve depuration, the maintenance of the
fish in clean water for a week or two, which may eliminate any disease
organisms that survived the earlier treatments. The final step would be to have
good hygiene in all stages of fish handling and processing, and to ensure that the
fish intestines are removed and the meat thoroughly washed and cooked before
consumption. Another strategy could involve feeding the waste-grown fish to
other animals that can be consumed by humans, so that the fish raised on waste
are not consumed directly by humans. Both strategies would reduce the
possibility of disease transfer.
Public need will probably determine the degree of public acceptance of
waste-grown fish in a particular area. Table 6.1 shows that the practice of fish
production in waste-fed ponds, although at a small extent, has been undertaken
in both developed and developing countries. The social, economic and political
considerations that influence human behaviour are very complicated. However,