Decentralized and centralized wastewater management: a challenge for technology developers

The traditional wastewater management concept (urban wastewater collection system plus treatment of the wastewater in a central treatment plant) has b een successfully applied over many decades in densely populated areas of in dustrialized countries. Whether this technology is of ultimate wisdom must be questioned, especially considering the urgent need for improved sanitary infrastructures in developing countries. The problem is that the costs for implementing a centralized system in mega-cities, in particular the invest ment costs for the sewer system, are exorbitant. Decentralized wastewater m anagement systems, with the wastewater treated close to where it is generat ed, are being considered by various researchers and institutions including the World Bank as an alternative to the traditional centralized system. The degree of technological sophistication that should be applied is under dis pute, however. In this paper, we advocate development and application of hi gh-tech on-site treatment plants, designed and fabricated by modern Industr ial methods. When mass produced, the costs for manufacturing such package p lants can presumably be kept at a relatively low level. The plants should b e delivered in a "user ready" state. Local plumbers may connect toilet bowl s and sinks and washing machines, but may not be involved in the manufactur ing of the treatment system. The plant should produce an effluent which is hygienically safe and can subsequently be utilized for toilet flushing, was hing clothes, cleaning floors or watering lawns. In order to keep the plant s operating properly, they should controlled by remote sensing, and maintai ned by specialized service enterprises. The conceptual design of such a com pact plant is discussed in the form of a case study.