Influence of short- and long-term exposure on the biodegradation capacity of activated sludge microbial communities in ready biodegradability tests

Ready biodegradability tests (RBTs) are extensively used to screen the potential of chemicals to be biodegraded. The use of RBT protocols often result in large variations of test results and lead to wrong interpretations. The present study aims to obtain a fundamental understanding of this variability. For this we subjected the compounds 4-chloroaniline (4CA), carbamazepine (CBZ), metformin (MET), and N-methylpiperazine (NMP) to a varie-ty of different test conditions. Inocula from five local wastewater treatment plants (WWTPs) were used in an attempt to enhance the Organisation for Economic Co-operation and Devel-opment (OECD) 310 biodegradability tests. The biodegradation capacity in RBTs, commu-nity composition and adaptation of the communities were compared after one week of pre-exposure in batch and four months exposure in chemostat. The results confirm that none of the test compounds is readily biodegradable in the standard OECD 310 RBT. However, when pre-exposure under either batch or chemostat conditions was included, 4CA was de-graded in some cases and less variability among different inocula was observed for the trans-formation of MET. Microbial communities from the five locations were found to be signifi-cantly different from one another. In addition, pre-treatment performed before the RBT sig-nificantly changed the composition of each community. Results of this experiment show that pre-exposure is one of the solutions to increase the absolute number of degrader and reduce the outcome variability of RBTs.