Removal of sulphide in anaerobically treated tannery wastewater by wet air oxidation

Anaerobic treatment of tannery wastewater in high rate close type reactors leaves sulphide in the range 31–795 mg/l, COD 395–1886 mg/l, BOD 65–450 mg/l and TOC 65–605 mg/l. Thus post anaerobic treatment of wastewater was required to meet discharging standard. High sulphide concentration present in treated wastewater may render aerobic biological treatment unsuitable. Hence, it became essential to include sulphide removal unit operation preceeding aerobic biological unit. Among the techniques available oxidation of sulphide by air using activated carbon as catalyst gained importance for its removal of COD, BOD and TOC inaddition to elimination of sulphide in wastewater. The effect of [S2‐/O2] ratio and hydraulic loading rate on removal of sulphide and organics in counter current reactor containing activated carbon were discussed. The percentage removal of COD, BOD, TOC and Sulphide from anaerobically treated wastewater were respectively 81, 85, 82 and 100. The sulphate content of catalytically oxidised effluent was increased by 24% at [S2‐/O2] ratio of 0.3353 and dissolved solids content was increased by 36%.