DIN 38412-3:2010-10

This standard specifies a biological method for the determination of toxicity by the dehydrogenase activity using 2,3,5-Triphenyltetrazoliumchlorid (TTC) of domestic and industrial waste waters and waste water constituents from sewage and comparison with activated sludge from a activated sludge treatment. The incubation time is one hour for 20 °C in the dark. Colourless, water soluble TTC, used as an indicator, is reduced to red, water unsoluble Triphenylformazane (TPF) using the dehydrogenase in activated sludge. TPF the is extracted using ethanol and photometrically determined at 485 nm. On the amount of TPF produced compared to control samples, the inhibition or activation by the tested substrate can be determined. An inhibition above 20 % is significant.