“ New challenges for small wastewater treatment plants ”

INTRODUCTION Safe wastewater treatment methods have always been a challenge to the society. During the last 50 years, pollution abatement measures have been given high priority, particularly discharges from the growing urban areas. Early objectives were to reduce the emissions of organic matter and pathogens, while other objectives related to the emission of heavy metals and nutrients (phosphorous and nitrogen) have been more focused during recent years. This pattern of pollution control objectives has of course led to the development of yieldand costefficient urban treatment technologies, using various process concepts.