Biochemical Engineering Journal 56 (2011) 46–50 Contents lists available at ScienceDirect Biochemical Engineering Journal j o ur nal homep a ge: www.elsevier.com/locate/bej Immobilization of Pseudomonas putida in PVA gel particles for the biodegradation of phenol at high concentrations Sulaiman Al-Zuhair ∗ , Muftah El-Naas Chemical and Petroleum Engineering Department, UAE University, 17555 Al-Ain, United Arab Emirates a r t i c l e i n f o Article history: Received 3 October 2010 Received in revised form 9 May 2011 Accepted 11 May 2011 Available online 17 May 2011 Keywords: Phenol degradation Spouted bed bioreactor Bubble column Immobilized bacteria Substrate inhibition a b s t r a c t Pseudomonas putida, immobilized in polyvinyl alcohol (PVA) particles, has been successfully utilized for the bioremoval of phenol from simulated wastewater, using two immobilization techniques and two types of bioreactors. The biodegradation efficiency of P. putida immobilized within the PVA gel before the cross-linking stage of the polymer (T1) was compared to that of the same bacteria immobilized by soaking blank PVA particles in bacterial suspension (T2), a procedure that avoids subjecting the bacteria to sub-freezing temperature during the cross-linking stage. The effects of nutrient deprivation and expo- sure to high phenol concentrations on the activity of P. putida were also evaluated. The experimental results indicated that the immobilized bacteria remained active for a period of 72 h, even without the addition of nutrients. Subsequently the activity gradually decreased, but the bacteria easily regained their original activity with the addition of nutrients. Sudden exposure to high phenol concentrations resulted in immediate decline in the biodegradation activity, but the bacteria adapted to the new concentrations and regained their activity within 24 h. The biodegradation experiments were carried out in two types of bioreactors namely, bubble column and spouted bed bioreactor (SBBR). Both reactor configurations and both immobilization techniques proved to be effective in the biodegradation of phenol. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Phenol, which is a major constituent in the wastewater of most chemical and petroleum industries, is known to be carcinogenic and toxic even at relatively low concentrations of 5–25 g m -3 [1]. Biodegradation is an environmentally friendly and cost effective treatment alternative to the conventional techniques that do not degrade phenol, but rather remove it from the wastewater and pass it to another phase [2]. A considerable amount of research has been carried out in recent years on the biodegradation of phenols by Pseudomonas putida because of its high removal efficiency and low cost [3–5]. Under aerobic conditions, the bacterial biomass converts phenol to carbon dioxide and other intermediates such as benzoate, catechol, cis–cis-muconate, -ketoadipate, succinate and acetate [6]. Analysis of the products suggests that these intermediates are present in negligible amounts, which indicates the degradation proceeds to completion [7]. Immobilization of bacterial biomass is an effective technique, usually employed to protect the bacteria from high phenol concentrations, which cause substrate inhibi- tion, and to allow reutilization. P. putida has been studied by many researchers in free and immobilized forms in different types of bioreactors. The authors of this work used P. putida immobilized in ∗ Corresponding author. Tel.: +971 37133636; fax: +971 37624262. E-mail address: s.alzuhair@uaeu.ac.ae (S. Al-Zuhair). polyvinyl alcohol (PVA) gel particles for the bioremoval of phenol in a spouted bed bioreactor (SBBR) in both batch [7] and continuous [8] operations. PVA was a preferable immobilization matrix due to its porous structure that allows the substrate and oxygen to dif- fuse into the internal pores, where biodegradation takes place. The main drawback of the typical biomass-entrapment immobilization technique is subjecting the bacteria to sub-freezing temperature during the cross-linking stage. Although this did not affect the activ- ity of P. putida, as previous results have shown [7,8], other types of bacteria could be destroyed during this step. It has been reported in the literature that some unicellular microorganisms, including bacteria, are destroyed by rapid chilling. For example, it was found that 99.98% of Bacterium typhosurn (Salmonella typhi) were killed after freezing at -17.8 ◦ C [9]. Therefore, it is important to assess the effectiveness of another immobilization technique that avoids subjecting the bacteria to subfreezing conditions. The effectiveness of the new immobilization technique has been evaluated using dif- ferent bioreactor configurations. The results of this work provide useful information for effectively using immobilized bacteria and optimizing bioreactor design. 2. Materials and methods 2.1. Chemicals Analytical grade phenol was purchased from BDH Chemicals, UK. Synthetic phenol solutions were prepared for the desired 1369-703X/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.bej.2011.05.005