Abstract

POINAPEN, J; EKAMA, GA  and  WENTZEL, MC. Biological sulphate reduction with primary sewage sludge in an upflow anaerobic sludge bed (UASB) reactor - Part 3: Performance at 20°C and 35°C. Water SA [online]. 2009, vol.35, n.5, pp.543-552. ISSN 1816-7950.

The performance of 2 biological sulphate reduction (BSR) upflow anaerobic sludge bed (UASB) reactors fed primary sewage sludge (PSS) and sulphate, one at 20ºC (R2) and one at 35ºC (R1) is described. To maintain the effluent sulphate concentration below 250 mgSO₄^2-/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 SO₄^2- ratio higher at 20ºC than at 35ºC, viz. 20.4 to 21.0 h, 24 d and 1.75 gCOD/gSO₄^2- at 20ºC and 16.4 to 17.0 h, 21 d and 1.75 gCOD/gSO₄^2- at 35ºC respectively. The longer HRT, SRT and higher feed PSS COD/ SO₄^2- ratio is a consequence of a slower PSS hydrolysis/acidogenesis rate at 20ºC 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. The UASB reactor R1 (at 35ºC) was also operated at an increased influent sulphate concentration (1 800 mgSO₄^2-/ℓ) to investigate the inhibition effect by un-dissociated hydrogen sulphide generated from the reduction of this high sulphate concentration. It was found that a high sulphate reduction (~ 92%) was maintained even at the relatively low HRT of 18.5 h. The COD and S mass balances above 95% were achieved over both systems indicating that the performance data obtained from them is reliable for developing and calibrating mathematical models.

Keywords : biological sulphate reduction; hydrolysis; hydraulic retention time; UASB reactor.

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