Sulphate reduction and zinc precipitation from wastewater by sulphate-reducing bacteria in an anaerobic moving-liquid/static-bed bioreactor

Abstract

Sulphate and zinc removal from a synthetic wastewater by sulphate-reducing bacteria was evaluated using an anaerobic moving-liquid/fixed-bed bioreactor packed with ceramic media. The system was initially augmented by adding sewage sludge as a source of the bacteria. Calcium sulphate dihydrate as a source of sulphate and sodium lactate as a source of carbon were added to the reactor. The system was operated under batch and anoxic conditions with inlet zinc concentrations from 30 to 110mg/L at different retention times (4-24h). After adaptation of the system and reaching a steady-state, for a zinc inlet load of 100mg/L, a maximum removal of 98.7 was attained with a retention time of 24h. With an optimum inlet sulphate concentration (1,500mg/L) and with a retention time of 24h, a maximum sulphate removal efficiency of about 89.2 was achieved. However, these values were declined by decreasing the retention time. The system showed low capacity to COD removal, e.g. at a COD/ loading ratio of 2.26, the effluent COD was eliminated by 35. The amount of hydrogen sulphide (H2S) produced among the processes, the concentrations of sulphide (S2-) and sulphite () in the effluent were also measured.