The value of biodegradation screening test results for predicting the elimination of chemicals’ organic carbon in waste water treatment plants

Based on the test results of a large number of chemical substances, the comparability of different biodegradation test methods was assessed in terms of passing or failing threshold values commonly used for the biodegradability characterisation of chemicals. The comparison revealed a high consistency of the ready biodegradability evaluations in OECD 301 tests regardless of the analytical parameter used, i.e., by mineralisation (CO2 evolution or biological oxygen demand/BOD) or by organic carbon removal measurements. Substances meeting the ready biodegradability threshold values in OECD 301 tests exhibited a high (>80%) carbon removal in model waste water treatment plants (OECD 303A). Results from the Modified Zahn–Wellens test (OECD 302B) representing a screening test with high sludge concentration, were also shown to be useful for the prediction of the organic carbon removal under WWTP conditions provided some prerequisites are met. The analysis of the compared data pairs formed a solid basis for the conclusion that positive results of a chemical in biodegradability screening tests can be used for a reliable prediction of their carbon-based removal in waste water treatment plants.