Cost-efficiency and performance of individual and small-scale treatment plants

The problem of diffuse pollution by individual housing can be tackled by in stallation of individual wastewater treatment systems. At the moment there are initiatives towards standardisation and certification of these systems to ensure efficient installations. Treatment results of recently installed individual plants prove to be very good towards BOD, COD and SS removal. Fa ctors such as frequency of maintenance, control and mechanical breakdown ma y however affect these promising results. Investment and operation costs pe r PE are discussed and compared with a more centralised approach, emphasisi ng the highly variable nature of these costs for individual wastewater trea tment. Additional long-term experience is needed to evaluate the potential weak points and achieve improved cost-benefit analysis.