Water Research 38 (2004) 3167–3178 Anaerobic digestion of olive mill wastewaters in biofilm reactors packed with granular activated carbon and ‘‘Manville’’ silica beads Lorenzo Bertin a , Sara Berselli a , Fabio Fava a, *, Marco Petrangeli-Papini b , Leonardo Marchetti a a DICASM, Faculty of Engineering, University of Bologna, viale Risorgimento 2, I-40136 Bologna, Italy b Department of Chemistry, Faculty of Mathematical, Physical and Natural Sciences, University of Rome ‘‘La Sapienza’’, p.le A. Moro 5, I-00185 Roma, Italy Received 10 April 2003; received in revised form 23 February 2004; accepted 5 May 2004 Abstract Anaerobic digestion is one of the most promising technologies for disposing olive mill wastewaters (OMWs). The process is generally carried out in the conventional contact bioreactors, which however are often unable to efficiently remove OMW phenolic compounds, that therefore occur in the effluents. The possibility of mitigating this problem by employing an anaerobic OMW-digesting microbial consortium passively immobilized in column reactors packed with granular activated carbon (GAC) or ‘‘Manville’’ silica beads (SB) was here investigated. Under batch conditions, both GAC- and SB-packed-bed biofilm reactors exhibited OMW COD and phenolic compound removal efficiencies markedly higher (from 60% to 250%) than those attained in a parallel anaerobic dispersed growth reactor developed with the same inoculum; GAC-reactor exhibited COD and phenolic compound depletion yields higher by 62% and 78%, respectively, than those achieved with the identically configured SB-biofilm reactor. Both biofilm reactors also mediated an extensive OMW remediation under continuous conditions, where GAC-reactor was much more effective than the corresponding SB-one, and showed a tolerance to high and variable organic loads along with a volumetric productivity in terms of COD and phenolic compound removal significantly higher than those averagely displayed by most of the conventional and packed-bed laboratory-scale reactors previously proposed for the OMW digestion. r 2004 Elsevier Ltd. All rights reserved. Keywords: Olive mill wastewater; Anaerobic digestion; Methanogenesis; Granular activated carbon; Biofilm; Packed-bed loop reactor 1. Introduction Olive mill wastewaters (OMWs) are the aqueous effluent from olive oil producing processes. Due to their relevant annual production (about 10 millionm 3 /year) (Fiestas Ros de Ursinos and Borja-Padilla, 1996) and highorganicload(50–150gCOD/l),(RozziandMalpei, 1996) OMWs constitute a problem of environmental concern, in particular in the olive growing Countries of the Mediterranean sea area (Rozzi and Malpei, 1996). Anaerobic digestion is one of the most promising OMW treatment technologies, as it is a process for both decontaminating and valorising (by producing methane) such wastewaters (Fiestas Ros de Ursinos and Borja-Padilla, 1996). Furthermore, this technology produces low amounts of waste sludges and employs bacteria with very low decay rates, that allow the process to carry out seasonal operations without requiring to be fed with OMWs all over the year (Hamdi, 1996). ARTICLE IN PRESS *Corresponding author. Tel.: +39-051-2093212; fax: +39- 051-2093218. E-mail address: fabio.fava@mail.ing.unibo.it (F. Fava). 0043-1354/$-see front matter r 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.watres.2004.05.004