Due to more stringent WWTP-effluent requirements in The Netherlands, caused by adoption of the European legislation, the characteristics of WWTP-effluents need to be improved. For existing wastewater treatment plants extended nutrient removal will be required with final effluent concentrations of Ptot≤0.15 mg/L and Ntot≤2.2 mg/L.

For suspended solids and phosphorus removal flocculation-filtration is used frequently as advanced treatment technique. Simultaneous denitrification would provide a tertiary treatment step for combined nutrient removal under the condition that simultaneous denitrification has no adverse effects on suspended solids and phosphate removal.

Pilot-scale experiments have been carried out at the WWTP in Utrecht and lab-scale investigations at the WWTP in Beverwijk, both in the Netherlands. The removal efficiencies for phosphorus and suspended solids in multimedia filters, operated under optimal denitrifying conditions, had been evaluated by phosphorus analyses and particle counting. It is examined that denitrifying biomass has no negative effect on the removal efficiencies.