Abstract
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 mgSO42-/., 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 20oCresulting 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/. for R1; 138 and 96 mgCOD/. 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-/.) to investigate the inhibition effect by un-dissociated hydrogen sulphide generated from the reduction of this high sulphate concentration. It was found that a highsulphate 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.
Highlights
The feasibility of a novel system for biological sulphate reduction (BSR) of AMD using primary sewage sludge (PSS) as carbon source in a upflow anaerobic sludge bed (UASB) reactor configuration (R1) was described in Part 1 (Poinapen et al, 2009a)
It was thought that R1 waste sludge would result in a quick and effective start-up of R2 biological processes since R1 was at its maximum efficiency
The effluent sulphate concentration remained stable from periods Day 333-350 and Day 371-392 with a sulphate removal of 83.7% and 79.8% respectively, even though the hydraulic retention time (HRT) was incrementally decreased from 28 h to 24 h, implying that the reactor was at steady state
Summary
The feasibility of a novel system for BSR of AMD using PSS as carbon source in a UASB reactor configuration (R1) was described in Part 1 (Poinapen et al, 2009a). From the successful operation of the UASB reactor R1 at 35oC (fed 1 500 mgSO42-/l for a period of 280 d), the performance of BSR using PSS was evaluated in a second identical UASB reactor (R2) operated in parallel to R1 but at ambient (20oC). ISSN 0378-4738 (Print) = Water SA Vol 35 No 5 October 2009. ISSN 1816-7950 (On-line) = Water SA Vol 35 No 5 October 2009. (see timeline Fig. 2 in Poinapen et al, 2009a). Reactor status/activities performed HRT (h) BRT (h).
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