Inhibition studies for determining the respiration of activated sludge can be used in studies of acute toxic effects of chemical substances and products or waste water towards heterotrophic micro-organisms. The substances must be water-soluble. This method is used when a statement is desired about the effect of the test substance on heterotrophic microorganisms in general. When investigating the effect of the test substance on sludge from activated sludge plants, the method described in DS 298 is used. The test uses a sludge concentration of 100-200 mg of suspended solids per I. Based on the result, a dose-response diagram is constructed. The concentrations for 20%, 50% and 80% inhibition are read from this chart and presented as EC 20, EC 50 and EC 80 respectively.
DS 297:1984 history
1984DS 297:1984 Water quality. Inhibition of heterotrophic microorganisms by determination of oxygen consumption rate