Journal of Hazardous Materials 164 (2009) 720–725 Contents lists available at ScienceDirect Journal of Hazardous Materials journal homepage: www.elsevier.com/locate/jhazmat Biodegradation of phenol by Pseudomonas putida immobilized in polyvinyl alcohol (PVA) gel Muftah H. El-Naas ∗ , Shaheen A. Al-Muhtaseb 1 , Souzan Makhlouf Chemical & Petroleum Engineering Department, U.A.E. University, P.O. Box 17555, Al-Ain, United Arab Emirates article info Article history: Received 20 March 2008 Received in revised form 19 August 2008 Accepted 20 August 2008 Available online 26 August 2008 Keywords: Biodegradation Immobilization Phenol Wastewater Refinery abstract Batch experiments were carried out to evaluate the biodegradation of phenol by Pseudomonas putida immobilized in polyvinyl alcohol (PVA) gel pellets in a bubble column bioreactor at different conditions. The bacteria were activated and gradually acclimatized to high concentrations of phenol of up to 300 mg/l. The experimental results indicated that the biodegradation capabilities of P. putida are highly affected by temperature, pH, initial phenol concentration and the abundance of the biomass. The biodegradation rate is optimized at 30 ◦ C, a pH of 7 and phenol concentration of 75 mg/l. Higher phenol concentrations inhibited the biomass and reduced the biodegradation rate. At high phenol concentration, the PVA particle size was found to have negligible effect on the biodegradation rate. However, for low concentrations, the biodegradation rate increased slightly with decreasing particle size. Other contaminants such heavy metals and sulfates showed no effect on the biodegradation process. Modeling of the biodegradation of phenol indicated that the Haldane inhibitory model gave better fit of the experimental data than the Monod model, which ignores the inhibitory effects of phenol. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Petroleum refineries generate huge amounts of wastewater that usually go through a combination of treatment steps to reduce the concentrations of the different contaminants to acceptable discharge levels. The main contaminants of refinery wastewater include phenols, polycyclic aromatic hydrocarbons (PAHs) as well as heavy metals. Of these toxic pollutants, phenols are considered to be among the most hazardous, and they are certainly the most difficult to remove. Phenol may be fatal by ingestion, inhalation, or skin absorption, since it quickly penetrates the skin and may cause severe irritation to the eyes and the respiratory tract. It is listed among the priority organic pollutants by the US Environmental Pro- tection Agency [1]. It is considered to be potentially carcinogenic to humans and may be lethal to fish at concentrations of 5–25 mg/l [2]. The UAE has one of the most stringent environmental regulations, especially those related to discharge levels. Abu Dhabi National Oil Company (ADNOC) has set a desirable limit of phenol discharge concentration of 0.01mg/l compared to that set by the EPA (USA) of 0.168 mg/l. ∗ Corresponding author. Tel.: +971 3 713 3637; fax: +971 3 762 4262. E-mail address: muftah@uaeu.ac.ae (M.H. El-Naas). 1 Present address: Department of Chemical Engineering, Qatar University, Doha, Qatar. It is essential, therefore, that phenol concentrations in refinery effluents be reduced to environmentally acceptable and harmless levels through utilizing effective and practical treatment methods. Many treatment techniques have been employed in the past few years to reduce the concentrations of phenols, including biodegra- dation, adsorption, ion exchange and the use of bioactive activated carbon. Biological treatment has proved to be the most promising and economical method for the removal of phenol from wastewa- ter. It is believed to lead to complete mineralization of phenol [3] and can handle a wide range of concentrations. The biodegradation of phenols by different types of microbial cultures has attracted the attention of many researchers during the past two decades. Many types of aerobic bacteria, including Pseudomonas putida, are believed to be capable of consuming aromatic compounds as the only source of carbon and energy. P. putida is a rod-shaped, Gram- negative bacterium that has been known for its ability to degrade organic solvents, especially its high removal efficiency of phe- nol [4]. Numerous other types of bacteria and biosorbents were reported to be utilized for the biodegradation or the removal of phenol. These include: Rhodococcus erythropolis [5]; Bacillius sp. [6]; Alcaligenes faecalis [7]; rhizobium Ralstonia taiwanensis [8]; Nocar- dia hydrocarbonoxydans [9]; Candida tropicalis [10] and activated sludge [11]. In recent years, the strain of P. putida has been the most widely used type of bacteria for phenol biodegradation. Under aerobic con- ditions, phenol may be converted by the bacterial biomass to carbon 0304-3894/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jhazmat.2008.08.059