Water Science & Technology Vol 66 No 3 pp 494–502 © IWA Publishing 2012 doi:10.2166/wst.2012.184

Reliable method for assessing the COD mass balance of a submerged anaerobic membrane bioreactor (SAMBR) treating sulphate-rich municipal wastewater

J. B. Giménez, L. Carretero, M. N. Gatti, N. Martí, L. Borrás, J. Ribes and A. Seco

The anaerobic treatment of sulphate-rich wastewater causes sulphate reducing bacteria (SRB) and methanogenic archaea (MA) to compete for the available substrate. The outcome is lower methane yield coefficient and, therefore, a reduction in the energy recovery potential of the anaerobic treatment. Moreover, in order to assess the overall chemical oxygen demand (COD) balance, it is necessary to determine how much dissolved CH₄ is lost in the effluent. The aim of this study is to develop a detailed and reliable method for assessing the COD mass balance and, thereby, to establish a more precise methane yield coefficient for anaerobic systems treating sulphate-rich wastewaters. A submerged anaerobic membrane bioreactor (SAMBR) treating sulphate-rich municipal wastewater was operated at 33 °C for an experimental period of 90 d, resulting in a high COD removal (approximately 84%) with a methane-enriched biogas of 54 ± 15% v/v. The novelty of the proposed methodology is to take into account the sulphide oxidation during COD determination, the COD removed only by MA and the dissolved CH₄ lost with the effluent. The obtained biomethanation yield (333 L CH₄ kg⁻¹ COD_{REM MA}) is close to the theoretical value, which confirms the reliability of the proposed method.

Keywords: COD mass balance; dissolved methane; Fluorescent In Situ Hybridization (FISH); methane yield; Submerged Anaerobic Membrane Bioreactor (SAMBR); sulphate-rich wastewater

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