Agricultural use of treated wastewater: the need for a paradigm shift in sanitation and treatment

Shortages in irrigation water in and around urban areas call for alternative sources, particularly in the (sub)tropical zones. Domestic sewage represents such an alternative source and its nutritional value has been known by farmers for a long time. In many situations even raw (diluted) domestic sewage is used for agricultural purposes, especially in those areas that cannot afford extensive sewerage and treatment systems. However, discharge or reuse of non-treated effluents gives rise to serious environmental problems, including threats to human health. Whenever agricultural use of urban effluents is considered, an integrated approach should be pursued, taking into account the agricultural requirements as well as the possible technological solutions for cost-effective sanitation and treatment. Such an integrated set-up questions the existing paradigms in sanitation and treatment and will call for a more decentralized approach, minimizing the requirements for large-scale infra-structural investments, such as sewerage systems. Also, with respect to the available treatment techniques, economic sustainability is often disregarded in making the final choices. Amongst the available compact technologies for wastewater treatment, the anaerobic (pre-)treatment is seen as an appropriate technology, but so far, its potential has hardly been utilized. Most interestingly, anaerobic treatment is ideal for implementation in a decentralized mode. The products of anaerobic treatment consist of nutrient-rich effluents, stabilized digested sludge and energy rich biogas. In particular, the former two can be used beneficially by local farmers, whereas the biogas produced can be used on the site if it is produced in sufficient quantities. The present paper discusses the prospects of anaerobic (pre-)treatment, embedded in centralized and decentralized treatment and re-use concepts. Its cost-effectiveness may lead to a more rapid implementation of productive sewage reclamation, while the environmental problems are concomitantly addressed.