TRADITIONAL communities developed ingenious ways of making use of wastewater. And, experts involved in the modern science of ecological engineering can learn a great deal from them.

There is a growing realisation that the term "wastewater" is a sign of human inability to recognise a valuable resource. Traditional societies throughout the world developed systems to make optimum use of wastewater, rather than allow it to run down the drain. Unfortunately, many of these practices have since fallen into disuse. Now, however, there is a renewal of interest in the old systems and efforts are being made to develop them further.

An international conference on ecological engineering for wastewater treatment, held in March 1991 in Stensund, Sweden, attempted to bring together ecologists, engineers, politicians and administrators so they could share their experiences and perspectives. Emerging firm the conference was a book entitled Ecological Engineering For Water Treatment, which documented some traditional wastewater management practices and highlighted the need for further experimentation.

The book noted China has a tradition of using wastewater whereby farmers store their cooking and washing wastes in small tanks that are then drained into ponds in which fish are reared. This ingenious system of wastewater treatment converted the energy and nutrient content of wastewater into edible fish tissue.

In the 1950s, the Chinese government embarked on schemes to raise fish in ponds and lakes in the suburbs of large cities. Water bodies like Donghu lake in Wuhan, Xuanwuhu lake in Nanjing, Xihu lake in Hagzong and Tianchi Lake in Gunming, which have always functioned as wastewater receptacles, served as large, fish culture centres.

In India, the wetlands of eastern Calcutta represents one of the world's largest systems of utilising urban sewage to promote pisciculture. The entire 3,000-ha wetland is made up of a series of ponds into which wastewater drains through a network of drainage canals. Effluents from the fisheries are used to to irrigate adjoining paddy fields.

The Mudially Fishermen's Cooperative Society (MFCS), situated on the southwestern fringe of Calcutta city, is a remarkable example of a waterlogged area of about 50 ha becoming transformed into an income-generating ecosystem. About 100 MFCS member produce about 5.6 tonnes of fish per ha annually and in the process, about 23,000 cu m of municipal and industrial waste that is generated daily, gets treated. And, this entire ecosystem was built without any external financial help.

Inspired by the Chinese tradition of domestic sewage-fed aquaculture, Hungary launched a similar experiment using the sewage generated by the city of Fonyod. An experimental farm, consisting of six large and six small ponds, was built in 1971-72 near the city's old sewage fishpond. The sewage flowed daily into the experimental farm through a pipe system supplied with rotary sprinklers. The entire project was considered a viable model of a domestic sewage fishpond.

There is also much interest countries such as Norway in developing sewage systems that are not energy and resource intensive. Because domestic sewage contains substantial amounts of plant nutrients and organic matter, discharging it into watercourses or the sea is essentially a great waste. Groups such as the Norwegian Centre for Soil and Environmental Research have evolved systems that make it possible to separate the different kinds of sewage water and recyle its nutrients almost completely. It is estimated that if the total amount of nitrogen and phosphorus in domestic sewage in Norway is reclaimed and reused in agriculture, the country can reduce its consumption of artificial fertilisers by 15 per cent.

These are only some isolated examples that highlight the potential of ecological engineering, which brings together the skills of the engineer and the vision of the ecologist.