BIOLOGICAL PHOSPHORUS UPTAKE IN SUBMERGED BIOFILTERS WITH NITROGEN REMOVAL

This paper introduces biological phosphorus removal (Bio-P) from wastewater on a submerged biofilter. Pilot scale research was carried out over a period of two years using a floating upflow aerated filter, originally designed for nitrification and denitrification of sewage. The factors which influence Bio-P on fixed film processes and the possible biofilter configurations which eliminate C, N and P are discussed. The procedures are applicable to all types of treatment plants using biofilters, both new and already in existence, making no distinction between the different processes available today, co-current and counter-current filters. Biological phosphorus removal can be associated to the different treatment levels required : organic matter removal; secondary nitrification secondary nitrification and denitrification. For the third option - complete nutrient removal, treatment is completed with a hydraulic retention time in the filter bed of under four hours. Because of the simultaneous filtration with effluent SS below 10 mg/l, low phosphorus residuals can be achieved by Bio-P alone. The modifications required for setting up this operating procedure on any treatment plant are presented.