Simulation of the influence of industrial wastewater on a municipal sewage treatment plant-a case study

Industrial wastewater flow caused operational difficulties in the wastewater treatment plant in Debrecen, Hungary. Bioaugmentation was successfully applied to maintain effluent quality in the periods when wastewater of high starch content was accepted, but, at the end of 2008, the nitrification capacity of the plant decreased considerably due to improperly pre-treated pharmaceutical wastewater. Dynamic simulations were carried out in a prototype programme developed by the Environmental Expert System Research Group at the University of Pannonia, Hungary. Several parameters for heterotrophic biomass were adjusted in function of time, and the specific growth rate of autotrophic biomass was altered in function of time and temperature in order to describe the effects of inoculation and toxic influence. Simulations were carried out with both constant and adjusted parameters. Though results on effluent COD of the different modelling versions were similar, the ammonia concentration fitted the measured data only when modified parameters were used. The study revealed that the autotrophic biomass had slowly adapted to the toxic compound. Different control strategies of aeration and decreased excess sludge removal rate were tested to enhance the nitrification in the critical time intervals. The amount of ammonia and inorganic nitrogen decreased in all cases while the oxygen demand increased to a maximum of 10.1%. Reducing excess sludge removal rate gave satisfactory results even without changing aeration. Further improvement could be achieved by introducing aeration into the post-denitrification reactor. The combination of the two modifications can compensate for the effect caused by toxicity.