Iron and manganese removal from textile effluents in anaerobic attached-growth bioreactor filled with coirfibres

A laboratory scale study on Fe and Mn removal in upflow anaerobic bioreactor of a working volume of 20 L with coir fibre as the filter medium was investigated for a period of 312 days. The maximum Fe and Mn levels considered were 10 and 5 mg/L respectively, which are the typical average values of textile effluents subsequent to the primary and secondary treatments. Ten sub-experimental runs were conducted with varying HRTs (5 days to 1 day), ratios of COD:SO42- (20 to 3.5), Fe levels (0.005 to 10 mg/L) and Mn levels (0 to 5 mg/L). COD:SO2 of 3.5 was identified as the optimum point at which sulphate reducing bacteria (SRBs) out competed methane producing bacteria (MPBs) and further reduction of this ratio caused total and/or significant inhibition of MPBs, thus building sulphate reducing conditions. The effluent contained Fe and Mn below the permissible levels (1.6 and 1.1 mg/L for Fe and Mn, respectively) stipulated by US National Pollution Discharge Elimination System (NPDES) for inland surface waters at HRTs higher than 3 days. Results of the mass balance showed more Fe accumulation (60%) in sediments whereas 27% in the filter media. An opposite observation was noticed for Mn.