The nitrification inhibition test with activated sludge determines the potential impact of test substances or wastewater samples on nitrifying bacteria, which oxidise ammonium to nitrate. Due to their long generation time, these bacteria are particularly sensitive, a fact that can lead to disturbances in the nitrification process of wastewater treatment plants.
A serial dilution of the test substance is prepared within the relevant concentration range. In parallel, a negative control without the test substance and a reference substance (nitrification inhibitor N-allylthiourea) are tested. To each test vessel, a defined amount of activated sludge, the nutrient medium and the test item are given. After an incubation time of 4 hours, the concentrations of ammonium, nitrite and nitrate are determined. By comparing the oxidised N-compounds in the test flasks with those in the blank sample it is possible to calculate the percentage inhibition for each test concentration.
Concentration of oxidised N-compounds (nitrate and nitrite)