Biological sulphate reduction with primary sewage sludge in an upflow anaerobic sludge bed (UASB) reactor – Part 3: Performance at 20°C and 35°C

Abstract

The performance of 2 biological sulphate reduction (BSR) upflow anaerobic sludge bed (UASB) reactors fed primary sewage sludge (PSS) and sulphate, one at 20 oC (R2) and one at 35oC (R1) is described. To maintain the effluent sulphate concentration below 250 mgSO 42-/ℓ, the hydraulic retention time (HRT) and bed solids retention time (SRT or sludge age) both needed to be longer and the feed primary sewage sludge (PSS) COD to SO 42-ratio higher at 20 oC than at 35oC, viz. 20.4 to 21.0 h, 24 dand 1.75 gCOD/gSO42-at 20oC and 16.4 to 17.0 h, 21 dand 1.75 gCOD/gSO42-at 35oC respectively. The longer HRT, SRT and higher feed PSS COD/ SO42-ratio is a consequence of a slower PSS hydrolysis/acidogenesis rate at 20 oC resulting in a lower biodegradable particulate organics conversion to volatile fatty acids (VFA). Solid liquid separation in both systems was good yielding average particulate and soluble organic COD concentrations of (150 and 100 mgCOD/ℓ for R1; 138 and 96 mgCOD/ℓ for R2). The sulphate reduction was >90% in both systems.

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