Some two billion people in developing countries lack adequate sanitation. In the low-income high-density periurban areas of cities and towns (and the world is periurbanising rapidly), often the most appropriate technical solution to wastewater collection is simplified sewerage - small-diameter sewers laid in-block at fairly flat gradients; for example, a 100 mm diameter sewer laid at a gradient of 1 in 200 can serve around 1000 people at low cost. Four billion people lack waste-water treatment - that is, around two-thirds of the world's population. Most of these four billion live in developing countries where energy-intensive electromechanical wastewater treatment, of the type favoured in industrialised countries, is too expensive and too difficult to operate and maintain. In many situations in developing countries more appropriate technologies will have to be used. These include: waste stabilisation ponds, upflow anaerobic sludge blanket reactors, wastewater storage and treatment reservoirs (or some combination of these). High-quality effluents can be produced which are especially suitable for crop irrigation and fish culture. In the twenty-first century 'from sewage to soya' will have to become more common as the world's population relentlessly increases.
Proceedings of the ICE - Municipal Engineer (2001) 145 (4) 299-303 [doi: 10.1680/muen.2001.145.4.299]