Observations on the Kinetics of Nitrification under Inhibiting Conditions Caused by Industrial Wastewater Compounds

Within the next few years nitrogen removal will be obligatory for both municipal and industrial wastewater treatment plants in Austria. During the operation of pilot plants, severe inhibition of the nitrification process has been observed in several cases. Further investigations have been carried out at two biochemical factories at temperatures in the range of 22 to 32 ±C, in one case at two pilot plants, in the other case at a full-scale plant in order to estimate kinetic parameters of nitrifying biomass under the particular inhibiting conditions of these wastewaters. In both cases competitive inhibition occurred during the start-up period for about two months. The ammonia nitrogen half-saturation coefficient for autotrophic biomass was in the range of 10 mg/l. In one case also maximum autotrophic specific growth rate varied in a wide range. It could be proved that the compounds of this wastewater have an inhibiting but no toxic effect on Nitrosomonas. The effluent ammonia concentration can be kept within the limits in case of competitive as well as non-competitive inhibition up to about 60% by increased minimum SRT. In case of severe non-competitive inhibition it is not possible to achieve feasible biological nitrification. In any case the inhibiting compounds should be located and removed from the wastewater.