[Examination of sewage for nitrification inhibitors with the help of a simple and accessible bioassay]

The biotest presented permits the investigation of sewage as for the presence of nitrification-inhibiting substances. A waste-water sample has to be aerated together with activated sludge for 5 h. The concentration of ammonia and nitrate will be analysed at the beginning and the end of the test. The intensity of nitrification can be detected comparing the increase of nitrate in the sewage sample with a control. In order to verify the reliance of the test the effect of different parameters on the test system like pH, BOD of the sludge, content of ammonia, nitrite and nitrate and different sewage-relevant compounds were investigated. The biotest was successfully applied in order to find out the inhibition of nitrification in a communal purification plant. An emission of nitrification inhibiting substances was determined by screening of the supplies of the purification plant.