Introduction

Rapid population growth, industrial development and intensified agricultural production have generated increasing amounts of wastewater, which are causing contamination of receiving water bodies in many places around the world at an alarming rate. The current concept of water supply is to distribute large amounts of water to the communities for indiscriminate use with the subsequent need to collect and to transport the produced wastewater out of the urban areas to be treated in centralised wastewater treatment plants. A new concept has to be developed to control the growing water pollution problems around the world ( Graaf et al. , 1997 ; Larsen and Gujer, 1997 ; Gijzen and Ikramullah, 1999 ). This will be possible only with a combination of different approaches: firstly, via the development and implementation of strategies to reduce or to prevent wastewater generation. Secondly, via the development of technologies that, effectively remove pollutants, facilitate reuse and, at the same time, are technically and economically accessible by most countries. These changes are not expected in a short term as an enormous amount of money will have to be spent in order to modify the existing infrastructure in water supply and sewerage systems. In the meantime strategies for water saving and pollution prevention should be implemented, and sustainable treatment technologies for wastewater treatment should be developed.