Effect of process conditions on the aerobic biodegradation of phenol and paracetamol by open mixed microbial cultures.

In the context of xenobiotics' removal in biological wastewater treatment processes, this study investigated the biodegradation of phenol and paracetamol as sole carbon sources by open mixed cultures. Biodegradation of these chemicals was investigated in batch and SBR (Sequencing Batch Reactor) lab-scale experiments. In batch experiments, phenol was biodegraded by unacclimated microorganisms at concentrations 0.2-0.5 g/l. The acclimation time increased with increasing phenol concentration and no biodegradation was observed with an initial concentration of 1 g/l. However, 1 g/l of phenol was biodegraded after previous exposure of the microorganisms to lower concentrations of phenol or to yeast extract and peptone. Batch degradation of paracetamol (0.5 g/l) only occurred after previous exposure of the microorganisms to yeast extract and peptone. SBR experiments were run with 1.0 g/L feed concentration of phenol or paracetamol in a range of SRT (solids residence time, 1–45 d for phenol and 1–145 d for paracetamol). Both substrates were removed as sole carbon sources and COD removal generally increased as the SRT increased, and was higher than 90% for phenol and 80% for paracetamol. A higher fraction of the removed substrate was assimilated into microorganisms for paracetamol than for phenol with growth yields 0.51 and 0.20 g/g COD, respectively. This study shows how process conditions (acclimation, substrate concentration, medium composition, SRT) affect the removal of phenol and paracetamol and gives guidance on their selection for the optimum biodegradation performance. [ABSTRACT FROM AUTHOR]