Critical Reviews in Environmental Science and Technology, 42:1631–1690, 2012 Copyright © Taylor & Francis Group, LLC ISSN: 1064-3389 print / 1547-6537 online DOI: 10.1080/10643389.2011.569872 Aerobic Biodegradation of Phenols: A Comprehensive Review TAGHREED AL-KHALID and MUFTAH H. EL-NAAS Department of Chemical and Petroleum Engineering, UAE University, Al-Ain, United Arab Emirates Phenol and its derivatives are hazardous pollutants that are highly toxic even at low concentrations. The management of wastewater containing high concentrations of phenols represents major eco- nomical and environmental challenges to most industries. Biotech- nology has been very effective in dealing with major environmental challenges through utilizing different types of bacteria and bio- catalysts to develop innovative processes for the biodegradation, biotreatment, and biosorption of various contaminants and wide range of hazardous materials. Biological treatment has proved to be the most promising and most economical approach for the removal of many organic water pollutants such as phenol. Numerous studies have been published in the literature dealing with the biodegrada- tion of phenols utilizing different types of biomasses and different types of reactors. The authors offer a comprehensive review of the present research on the biodegradation of phenols and presents trends for future research and development, with emphasis on an integrated approach that may be adopted to get synergistically en- hanced removal rates and to treat the contaminated effluents in an ecologically favorable process. KEY WORDS: biodegradation, bioreactors, immobilization, kinet- ics, phenol, wastewater 1. INTRODUCTION Chemical and petroleum industries generate a wide variety of highly toxic organic pollutants, which have led to cumulative hazardous effects on the Address correspondence to Muftah H. El-Naas, Department of Chemical and Petroleum Engineering, UAE University, PO Box 17555, Al-Ain, United Arab Emirates. E-mail: muftah@ uaeu.ac.ae 1631