Low-temperature anaerobic biological treatment of solvent- containing pharmaceutical wastewater Anne-Marie Enright, Sharon McHugh 1 , Gavin Collins, Vincent O’Flaherty à Microbial Ecology Laboratory, Department of Microbiology, Environmental Change Institute (ECI), National University of Ireland, Galway (NUI, Galway), University Road, Galway, Ireland Received 26 April 2005; received in revised form 8 July 2005; accepted 16 August 2005 Available online 19 October 2005 Abstract Low-temperature or psychrophilic (o20 1C) anaerobic digestion (PAD) has recently been demonstrated as a cost- effective option for the treatment of a range of wastewater categories. The aim of this work was 2-fold: (1) to screen three anaerobic sludges, obtained from full-scale reactors, with respect to suitability for PAD of pharmaceutical-like, solvent-contaminated wastewater; (2) to assess the feasibility of PAD of this wastewater category. Toxicity thresholds of key trophic groups within three candidate biomass samples were assessed against solvents prevalent in pharmaceutical wastewaters (propanol, methanol and acetone). Specific methanogenic activity (SMA) assays indicated that the metabolic optimum of each candidate biomass was within the mesophilic range. One biomass sample exhibited higher SMA assays than the other candidate samples and was also the sample least methanogenically inhibited by the addition of solvents to batch cultures. This sludge was selected as the biomass of choice for laboratory-scale trials. Two identical expanded granular sludge bed (EGSB)-based anaerobic reactors were used for the treatment of solvent- contaminated wastewater at 15 1C, and at applied organic loading rates (OLRs) of 5–20 kg chemical oxygen demand (COD) m À3 d À1 . COD removal efficiencies of 60–70% were achieved during the 450 day trial. In addition, SMA assays carried out at the conclusion of the trial indicated the development of a putatively psychrophilic hydrogenotrophic methanogenic community. r 2005 Elsevier Ltd. All rights reserved. Keywords: Anaerobic digestion; EGSB; Methanogenic toxicity; Solvents; Specific methanogenic activity; Wastewater 1. Introduction Anaerobic digestion (AD) is a proven and established wastewater treatment option, which is applied to a variety of wastewater streams from the food and beverage, agricultural and fine chemicals sectors (McHugh et al., 2003). The application of this naturally occurring methanogenic process offers several advan- tages over aerobic wastewater treatment options, such as lower operating costs, less land requirements and, primarily, the production of biogas (450% methane), a renewable energy source, which can be used for generation of heat and electricity for industrial or domestic use. The increased application of AD to a broader range of wastewaters, including more recalcitrant streams such as ARTICLE IN PRESS 0043-1354/$ - see front matter r 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.watres.2005.08.037 à Corresponding author. Tel.: +353 91 493734; fax: +353 91 525700. E-mail address: vincent.oflaherty@nuigalway.ie (V. O’Flaherty). 1 Present address: Environmental Microbiology Research Unit, Department of Microbiology, National University of Ireland, Galway, University Road, Galway, Ireland.