Anaerobic biodegradation of phenol in wastewater treatment: achievements and limits

Anaerobic biodegradation of toxic compounds found in industrial wastewater is an attractive solution allowing the recovery ofenergy and resources but it is still challenging due to the low kinetics making the anaerobic process not competitive against theaerobic one. In this review, we summarise the present state of knowledge on the anaerobic biodegradation process for phenol, atypical target compound employed in toxicity studies on industrial wastewater treatment. The objective of this article is to providean overview on the microbiological and technological aspects of anaerobic phenol degradation and on the research needs to fillthe gaps still hindering the diffusion of the anaerobic process. The first part is focused on the microbiology and extensivelypresents and characterises phenol-degrading bacteria and biodegradation pathways. In the second part, dedicated to processfeasibility, anaerobic and aerobic biodegradation kinetics are analysed and compared, and strategies to enhance process performance,i.e. advanced technologies, bioaugmentation, and biostimulation, are critically analysed and discussed. The final sectionprovides a summary of the research needs. Literature data analysis shows the feasibility of anaerobic phenol biodegradation atlaboratory and pilot scale, but there is still a consistent gap between achieved aerobic and anaerobic performance. This is whycurrent research demand is mainly related to the development and optimisation of powerful technologies and effective operationstrategies able to enhance the competitiveness of the anaerobic process. Research efforts are strongly justified because theanaerobic process is a step forward to a more sustainable approach in wastewater treatment.