For the removal of toxic and recalcitrant organic substances from wastewater, bioaugmentation with bacteria harbouring specific degradation pathways in activated sludge could constitute a relevant process. In this study, we examined the behaviour of a 3-chlorobenzoate (3CBA) degrading Pseudomonas putida BN210 carrying the self-transferable clc-element containing the clc-genes for 3CBA metabolism in a conventional activated sludge system (CAS) and a membrane separation bioreactor (MBR). It was shown that bioaugmentation in the MBR resulted in an increased resistance towards shock loading of 3CBA in terms of improved COD removal. Respirometry showed that the MBR sludge was less destabilized by 3CBA shock loadings than the CAS sludge. Molecular techniques including PCR-DGGE to follow strain BN210 and PCR using specific primer sets to follow the clc-element showed that strain BN210 was rapidly lost in both reactors or seems only to survive in low cell numbers. Other 3CBA degrading populations were observed in both CAS and MBR reactors.

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