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

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 110 mg/L at different retention times (4–24 h). After adaptation of the system and reaching a steady-state, for a zinc inlet load of 100 mg/L, a maximum removal of 98.7% was attained with a retention time of 24 h. With an optimum inlet sulphate concentration (1,500 mg/L) and with a retention time of 24 h, 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/SO42- 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 (SO32-) in the effluent were also measured.