Steps towards the upgrading of a municipal WWTP affected by nitrification inhibiting compounds - a case study

The influent to the municipal WWTP of Linz consists of typical domestic sewage and of the discharges of two major industries which results in a severe basic inhibition of nitrification. In the course of a 3-year investigation program, intensive studies were carried out. Pilot investigations showed the nitrification inhibiting properties of this wastewater. On the basis of the operational data, the variation in the inhibition of the maximum specific growth rate was evaluated. In addition, testing procedures which revealed the sources of inhibition - firstly within the catchment area and subsequently inside the industries concerned - were developed. With the results of these tests, risk assessment and a priority schedule became feasible. Based on the information gathered this way and on future steps which will be taken by the industries, major decisions concerning the upgrading of the existing activated sludge plant could be made.