Performance of an anaerobic bioreactor with biomass recycling, continuously removing COD and sulphate from industrial wastes.

Abstract A 30-l anaerobic bioreactor with biomass recycling was used to provide a continuous reduction in sulphate and a continuous COD removal from wastewater, which consisted of the effluent from an industrial pig fattening farm, enriched with technical FeSO 4  · 7H 2 O, a waste product from ferrous metallurgy. The concentrations of sulphate and COD in the wastewater amounted to 2.73 g l −1 and 3.15 g l −1 , respectively. The HRT (hydraulic retention time) of 10–1.7 d produced an extent of sulphate and COD reduction which totalled 98% and 88%, respectively. When the HRT was further shortened, the efficiency of reduction in sulphate and COD decreased. The maximum removal rate constants for both the pollutants, calculated by means of a modified Stover–Kincannon model, were 80.9 g COD l −1  d −1 and 41.8 g SO 4 2 -  l −1  d −1 , the values of the saturation constants being 91.582 g COD l −1  d −1 and 42.398 g SO 4 2 -  l −1  d −1 .