High rate aerated biofilters for plant upgrading

Abstract

Biocarbone aerated biofilters were developed more than ten years ago. Almost one hundred plants worldwide provide complete treatment in very short hydraulic retention time. This allows to construct compact plants in sensitive areas such as inner cities, sea or mountain resorts. The filters can be adapted to high effluent qualities expected by the European directive on wastewater treatment. Full oxidation of ammonia can be achieved in less than two hours. A plant for complete removal of nitrogen has been operated for more than a year in Denmark to meet Europe's most stringent effluent requirements by using an anoxic biofilter in series with the Biocarbone. A new aerated biofilter, turning the Biocarbone principle upside down, is presented : a synthetic floating material allows enhanced performance, simplified backwash and a combination of anoxic and aerobic zones in one reactor. Effluent quality of less than 10 mg/l for all components (BOD, SS, TN) was demonstrated in a one-year long on-site test in Denmark and the first facility for 60 000 population equivalents is under startup. Full scale results of the upflow floating filter, Biostyr, are presented for nitrogen and phosphorus removal according to the European directive.