A lamellar flow multiplate biofilm reactor has been developed in this work and tested with a synthetic waste water effluent. A mixed culture biofilm readily develops within a few days and attaches itself to the synthetic textile used as a support medium. Conversion levels are promising. The bioreaction has been modelled with first order kinetics for COD levels < 125 mg/L and with zero order kinetics for higher COD values. The aerobic conversion predominates at lower COD levels while at higher COD levels, the aerobic conversion is confined solely to the external surface of the biofilm and the remainder of the digestion is done anaerobicly.