Use of ferrous sulphate to reduce the redox potential and allow the start-up of UASB reactors treating slowly biodegradable compounds : application to a wastewater containing 4-methylbenzoic acid

Abstract : During the anaerobic treatment of slowly biodegradable wastewaters containing dissolved oxygen, the natural communities of aerobic and anaerobic facultative bacteria present in reactors' sludges may not succeed in lowering the redox potential of their environment to a level compatible with methanogenesis. In order to allow reactor start-up, it is proposed to add a single initial dose of FeSO4 directly to the reactor liquor, together with an inexpensive easily biodegradable compound (i. e. carbohydrates, agroindustrial wastes...). Under the action of sulphate reducing bacteria, FeSO4 is reduced to FeS which in turn lowers redox potential. This method was tested on an Upflow Anaerobic Sludge Bed (UASB) reactor fed at an hydraulic retention time of 5.3 ± 0.3 days with an aerobic synthetic wastewater (dissolved O2, 5 mg.l-1; redox potential referred to the standard hydrogen electrode (Eh ), +119 to +250 mV; pH 7 to 7.4; 6°C) containing p-toluic acid (4-methylbenzoic acid) as sole carbon and energy source. During the first 37 days of reactor operation, sludge Eh was high (+118 to +161 mV; pH 7.2 to 7.4; 30 to 35°C) and no COD (Chemical Oxygen Demand) removal occured. Soon after the addition of FeSO4 (0.15 g FeSO4. 7H2O per g of Volatile Suspended Solids [VSS]) and glucose (0.38 g per g VSS), sludge Eh decreased to -95 mV (pH 7.3; 33°C) while COD removal increased to 51.3%. An economical way to implement this method at full scale is suggested.
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Environmental Technology, Taylor & Francis: STM, Behavioural Science and Public Health Titles, 1995, 16 (12), pp.1185 - 1192. 〈10.1080/09593331608616354〉
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Hervé Macarie, J. Guyot. Use of ferrous sulphate to reduce the redox potential and allow the start-up of UASB reactors treating slowly biodegradable compounds : application to a wastewater containing 4-methylbenzoic acid. Environmental Technology, Taylor & Francis: STM, Behavioural Science and Public Health Titles, 1995, 16 (12), pp.1185 - 1192. 〈10.1080/09593331608616354〉. 〈ird-01728516〉

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