Biodegradation of high phenol containing synthetic wastewater by an aerobic fixed bed reactor M. Bajaj, C. Gallert, J. Winter * Institute of Biology for Engineers and Biotechnology of Wastewater Treatment, University of Karlsruhe, Am Fasanengarten, 76131 Karlsruhe, Germany article info Article history: Received 2 August 2007 Received in revised form 20 February 2008 Accepted 28 February 2008 Available online 28 April 2008 Keywords: Biodegradation Aerobic fixed bed reactor Phenol High loading Synthetic wastewater abstract The continuous aerobic degradation of phenol, mixed with readily degradable synthetic wastewater was studied over a period of 400 days at 25 ± 5 °C temperature in a fixed bed biofilm reactor using ‘Liapor’ clay beads as packing material. The phenol concentration added to the reactor ranged from 0.19 to 5.17 g/l and was achieved by a gradual increase of phenol in wastewater, thus adapting the microbial flora to high contaminant concentrations. A maximal removal rate of 2.92 g phenol/(l d) at a hydraulic retention time (HRT) of 0.95 days and a total organic loading rate (OLR) of 15.3 g COD/(l d) with a phenol concentration of 4.9 g/l was observed. However, this was not a stable rate at such high phenol loading. At the end of reactor operation on day 405, the phenol removal rate was 2.3 g/(l d) at a influent phenol concentration of 4.9 g/l. There were no phenol intermediates present in the reactor, as evident from corresponding COD, phenol removal and the absence of fatty acids. Omission of organic nitrogen compounds or of urea in influent feed was not favourable for optimal phenol removal. The phenol degradation profile that was studied in shake flasks indicated that the presence of a acetate which represent as an intermediate of phenol degradation retarded the phenol degradation. The highest phenol degradation rate observed in batch assays was 3.54 g/(l d). Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction Phenol and its derivatives are widely used in many industrial branches, like petrochemical, chemical, pharmaceutical, pulp, pa- per, tannery and coal refining industries. Thus, phenol is generally present in wastewater coming from these industries (Marrot et al., 2006). Phenol is defined as priority pollutant by US EPA. Removal of phenol along with other pollutants from industrial wastewater streams before their discharge into receiving water bodies is thus obligatory. Phenol is a recalcitrant compound, which exerts toxic- ity to microorganisms during biological treatment, leading to fail- ure of the whole wastewater treatment system, if the microbial flora is not adapted to phenol. Phenol is growth inhibitory to bac- teria at concentrations above 0.05 g/l and is bactericidal at concen- trations of about 2 g/l, if not adapted to phenol (Heipieper et al., 1991). Therefore, microbial acclimatization to phenol is necessary to obtain efficient biodegradation. Phenol can be aerobically de- graded by a wide variety of microorganisms, including pure cul- tures (Erhan et al., 2004; Gonzalez et al., 2001; Cho et al., 2000) as well as mixed bacterial consortia (Esparza et al., 2006; Marrot et al., 2006; Farrell and Quilty, 1999; Mörsen and Rehm, 1990). Shock loads of phenol containing wastewater have been responsi- ble for severe disruptions in conventional industrial biological treatment facilities (Galil et al., 1988). Bioreactors have been used successfully to mineralise various toxic or inhibitory compounds, such as quinoline, dichloroaniline, substituted benzoic acids and phenolic compounds (Erhan et al., 2004). A bioprocess designed for point source treatment should per- mit high flow rates through the reactor (high conversion rate, small reactor volume), guarantee complete mineralization and tolerate concentration fluctuations of the toxic substrate in the feed. It is also important to prevent washout of the cells in continuous reactors. This can be achieved by immobilizing the microorganisms on appro- priate carriers in bioreactors (Giorno and Drioli, 2000; Drioli and Ro- mano, 2001). Immobilization of bacteria in a continuously run bioreactor avoids washout even under conditions of negligible cell growth, while the reaction rates and overall productivity compare favourably with those of suspended cultures. Immobilized cultures are characterized by high biomass concentration of 30–40 g VSS/l, compared to 1.5–2.5 g VSS/l for activated sludge systems (Mulcahy et al., 1980). This is due to the high surface area available for biofilm formation. The high biomass hold up coupled with retention of active biomass on support particles results in cost savings due to shorter hydraulic retention times without the danger of washout in smaller reactors. The volumetric phenol degradation rate by immobilized cells is 5–10 times higher than in an activated sludge system (Don- 0960-8524/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2008.02.057 * Corresponding author. Tel.: +49 721 608 2297; fax: +49 721 608 7704. E-mail addresses: mini.bajaj@iba.uni-karlsruhe.de (M. Bajaj), claudia.gallert@ iba.uka.de (C. Gallert), josef.winter@iba.uni-karlsruhe.de (J. Winter). Bioresource Technology 99 (2008) 8376–8381 Contents lists available at ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech