Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/watres Methane formation in sewer systems Albert Guisasola 1 , David de Haas 2 , Jurg Keller 3 , Zhiguo Yuan à Advanced Water Management Centre, The University of Queensland, St. Lucia, 4067 Queensland, Australia article info Article history: Received 14 August 2007 Received in revised form 8 October 2007 Accepted 9 October 2007 Available online 15 October 2007 Keywords: Methane production Methanogens Sewer systems Sulphate reducing bacteria Sulphide abstract Methane formation and emission in sewer systems has not received as much attention as hydrogen sulphide formation. Through field measurements from two rising mains, with an average sewage temperature of 28.4 and 26.6 1C, respectively, at the time of sampling, this study shows that a significant amount of methane can be produced in sewer systems, and that this production is positively correlated with the hydraulic retention time of waste- water in these systems. The experimental results from a laboratory-scale sewer system fed with real sewage with a temperature of approximately 21 1C confirmed these field observations and further revealed that methanogenesis and sulphate reduction occur simultaneously in sewers, with methane production contributing considerably more to the loss of soluble COD in sewers than sulphate reduction. The production of methane in sewers at levels revealed by this study is a serious environmental concern as it potentially results in greenhouse emissions that is comparable to that caused by the energy consumption for the treatment of the same wastewater. Further, methane production in sewers influences sulphide production and its management due to the competition between methanogens and sulphate-reducing bacteria for potentially the same electron donors. The potential interactions between sulphate-reducing and methanogenic bacteria in sewer networks are discussed. & 2007 Elsevier Ltd. All rights reserved. 1. Introduction The production and emission of hydrogen sulphide in sewer systems is a well-known problem (Pomeroy, 1959; US EPA, 1974; Boon, 1995; Hvitved-Jacobsen, 2002). The build-up of hydrogen sulphide in the sewer atmosphere causes major detrimental effects, such as sewer wall corrosion, serious health hazards and odour nuisance. A lot of research has been conducted in recent decades in an attempt to better understand and model hydrogen sulphide formation in sewer networks (inter alia Boon, 1995; Tanaka and Hvitved-Jacobsen, 2001; Hvitved-Jacobsen, 2002; Yongsiri et al., 2004). However, hydrogen sulphide is not the only potentially dangerous compound present in these systems. Due to the anaerobic nature of the sewer systems, methanogenesis is also likely to occur. However, few studies on methane formation in sewer systems have been reported in the literature. Understanding methane production in sewer systems is important for several reasons:  Uncontrolled methane release is potentially unsafe since it forms an explosive mixture in air at low concentrations ARTICLE IN PRESS 0043-1354/$ - see front matter & 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.watres.2007.10.014 à Corresponding author. Tel.: +61 7 3365 4374; fax: +61 7 3365 4726. E-mail addresses: albert.guisasola@uab.cat (A. Guisasola), ddhaas@awmc.uq.edu.au (D. de Haas), j.keller@awmc.uq.edu.au (J. Keller), zhiguo@awmc.uq.edu.au (Z. Yuan). 1 Current address: Department of Chemical Engineering, ETSE, Universitat Auto ` noma de Barcelona, 08193 Bellaterra (Barcelona), Spain. Tel.: +34 9 3581 2695; fax: +34 9 3581 2013. 2 Tel.: +61 7 3366 7205; fax: +61 7 3365 4726. 3 Tel.: +61 7 3365 4727; fax: +61 7 3365 4726. WATER RESEARCH 42 (2008) 1421– 1430