UNCORRECTED PROOF Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/watres Anaerobic biological treatment of phenol at 9.5–15 1C in an expanded granular sludge bed (EGSB)-based bioreactor Colm Scully, Gavin Collins, Vincent O’Flaherty à Microbial Ecology Laboratory, Department of Microbiologyand Environmental Change Institute, National University of Ireland, Galway (NUI, Galway), University Road, Galway, Ireland article info Article history: Received 2 June 2006 Received in revised form 21 July 2006 Accepted 22 August 2006 Keywords: EGSB Phenol Psychrophilic anaerobic digestion Methanogenic activity ABSTRACT The aims of this study were to demonstrate the (1) feasibility of psychrophilic, or low- temperature, anaerobic digestion (PAD) of phenolic wastewaters at 10–15 1C; (2) economic attractiveness of PAD for the treatment of phenol as measured by daily biogas yields and (3) impact on bioreactor performance of phenol loading rates (PLRs) in excess of those previously documented (1.2 kg phenol m 3 d 1 ). Two expanded granular sludge bed (EGSB)- based bioreactors, R1 and R2, were employed to mineralise a volatile fatty acid-based wastewater. R2 influent wastewater was supplemented with phenol at an initial concentration of 500 mg l 1 (PLR, 1 kg m 3 d 1 ). Reactor performance was measured by chemical oxygen demand (COD) removal efficiency, CH 4 composition of biogas and phenol removal (R2 only). Specific methanogenic activity, biodegradability and toxicity assays were employed to monitor the physiological capacity of reactor biomass samples. The applied PLR was increased to 2 kg m 3 d 1 on day 147 and phenol removal by day 415 was 99% efficient, with p4 mg l 1 present in R2 effluent. The operational temperature of R1 (control) and R2 was reduced by stepwise decrements from 15 1C through to a final operating temperature of 9.5 1C. COD removal efficiencies of c. 90% were recorded in both bioreactors at the conclusion of the trial (day 673), when the phenol concentration in R2 effluent was below 30 mg l 1 . Daily biogas yields were determined during the final (9.5 1C) operating period, when typical daily R2 CH 4 yields of c. 3.3 l CH 4 g 1 COD removed d 1 were recorded. The rate of phenol depletion and methanation by R2 biomass by day 673 were 68 mg phenol g VSS 1 d 1 and 12–20 ml CH 4 g VSS 1 d 1 , respectively. & 2006 Elsevier Ltd. All rights reserved. 1. Introduction Anaerobic treatment of phenol-containing wastewater in upflow anaerobic sludge bed (UASB) and expanded granular sludge bed (EGSB)-based bioreactors has been well documen- ted (e.g. Chang et al., 1995; Fang et al., 1996). However, virtually all laboratory- and full-scale reactor trials were carried out under mesophilic (425 1C) operating conditions. Despite this, most wastewaters in the northern hemisphere (e.g. in EU member states) are released for disposal/treatment at ambient or sub-ambient temperatures (o18 1C; Lettinga et al., 2001), which requires that the wastewater be heated prior to treatment, which can consume up to 30% of the energy produced. The feasibility of psychrophilic, or low-tempera- ture (o20 1C), anaerobic digestion (PAD) has been demon- strated at laboratory-scale for the treatment of various wastewater categories (Rebac et al., 1995; Lettinga et al., 1999; Collins et al., 2003; Enright et al., 2005), including phenolic wastewater (Collins et al., 2005a,b). Studies have shown anaerobic degradation of organic matter as low as 2 1C 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51 53 55 57 59 61 63 65 67 69 71 73 75 ARTICLE IN PRESS WR : 6046 0043-1354/$ - see front matter & 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.watres.2006.08.023 à Corresponding author. Tel.: +353 0 91 493734; fax: +353 0 91 494598. E-mail address: vincent.oflaherty@nuigalway.ie (V. O’Flaherty). WATER RESEARCH ] ( ]]]] ) ]]] – ]]] Please cite this article as: Colm Scully et al., Anaerobic biological treatment of phenol at 9.5–15 1C in an expanded granular sludge bed (EGSB)-based bioreactor, Water Research (2006), doi:10.1016/j.watres.2006.08.023