Newsletter and Technical Publications
<International Source Book On Environmentally Sound Technologies
for Wastewater and Stormwater Management>
9.2.2 Opportunities for wastewater-fed aquaculture
Although a review of experience of wastewater-fed aquaculture indicates
static and declining practice overall (Edwards, 2000), there are opportunities
for its incorporation into existing and proposed improved sanitation schemes:
- Developing countries which cannot afford mechanical wastewater
treatment schemes. Stabilization pond systems are more effective than
mechanical systems in terms of pathogen removal although they may be less
effective in terms of producing an effluent with a low suspended solids
content because of the growth of phytoplankton under ambient light.
Incorporation of fish culture into waste stabilization ponds systems will
require extra land than for treatment of waste alone but will produce a
higher quality effluent and therefore better safeguard the environment.
Duckweed-based wastewater treatment systems produce an effluent with a low
suspended solids content because plant cover shades the water column.
Wastewater reuse systems also provide increased employment to hire local
people, and generate revenue from sale of produce, which can be used to
subsidize, in part, the wastewater treatment.
- Arid and semi-arid countries have an increasing need to reuse water as
well as nutrients contained in wastewater. Pilot projects on culture of
fish in treated stabilization pond effluents have been successfully
completed in arid areas in Egypt in the Middle East (Easa et al., 1995;
Shereif et al., 1995) and in the coastal desert of Peru (Cavallini, 1996) in
Latin America (box 4) (Photo 6).
Fish farming has become the main hope of the Egyptian government to
achieve its animal protein production targets for the rapidly increasing
human population. Local authorities have prohibited the use of freshwater
for aquaculture, and even drainage water, in some regions. The aquaculture
authorities have therefore directed their efforts towards obtaining a new
water resource by the reuse of wastewater. It has been predicted that the
reuse of wastewater will increase drastically in Egypt because of continued
population growth, shortage of arable land, and a chronic scarcity of fresh
Photo 6: A pilot project to culture fish in treated wastewater in Peru
|Box 4. Feasibility of fish culture in treated effluents of
wastewater stabilization ponds in Lima, Peru. Source : Cavallini (1996).
A United Nations Development Program / World Bank sponsored project
successfully demonstrated the culture of the fish tilapia in tertiary
treated effluent at the San Juan stabilization ponds in Lima to produce
food and employment as well as to improve the efficiency of water use in a
desert environment. Fish grew well, attaining a marketable size of 250 g
in 4 months, and a pond carrying capacity of over 4 tonnes fish/ha without
use of supplementary feed. Analyses indicated that fish were acceptable
for human consumption with respect to standards for viruses, bacteria and
parasites, as well as heavy metals, pesticides and PCBs. Wastewater-fed
fish were acceptable to Lima city consumers even though they were aware of
the origin of the fish. It was estimated that a commercial farm in the
tropics of 18 ha may produce 127 tonnes of tilapia annually at a rate of 7
tonnes/ha. Sale of fish would cover the entire treatment cost for a 100
l/sec conventional wastewater stabilization pond treatment plant using
primary and secondary treatment located in an arid area with land of no
commercial value. The corresponding figures for a subtropical area are a
32 ha farm producing 106 tonnes fish annually at a rate of 3.3 tonnes/ha.