INFLUENCE OF PREDATORS ON NITRIFICATION IN AEROBIC BIOFILM PROCESSES

The influence of predators on nitrification in aerobic biofilm process es was investigated in a laboratory study carried out using two aerobi c continuous flow suspended-carrier biofilm reactors operating in para llel on the same synthetic wastewater. After nitrification was establi shed in the reactors and stable operating conditions at 3 h hydraulic retention time were achieved, nystatin and cycloheximide, substances i nhibitory to eucaryotic organisms, were added to one of the reactors t o selectively inhibit the predators. The other reactor was operated as a reference, without inhibitors being added. Adding the inhibitors to the test reactor led to a rapid decrease in the quantity of biofilm-c onsuming predators, most of them rotifers and nematodes, and a simulta neous increase in nitrification, which finally stabilized at a level t wice as high as in the reference reactor. The addition of inhibitors w as then switched between the reactors, resulting in a rapid increase i n nitrification in what had been the reference reactor, and a slow dec rease in nitrification in the reactor in which the adding of inhibitor s had been stopped. Again, approximately twice as high a nitrification rate was achieved with addition of inhibitors than without. The resul ts clearly show that biofilm predators can have a strong negative effe ct on nitrification in aerobic biofilm processes.