Bülk, the second largest sewage treatment plant in Schleswig-Holstein, treats the sewage of approximately 310,000 inhabitants and 65,000 inhabitant equivalents (industry and trade) in the state capital of Kiel and 21 neighbouring communities. The sewage treatment plant receives approximately 20 million cubic metres of effluent per year or 50,000 to 60,000 cubic metres per day. Contamination of the facilities with germs is unavoidable depending on the weather and wind conditions, despite intensive hygiene measures, as bacteria are indispensable both for biological purification and sludge treatment.