Precipitation of dissolved sulphide in pulp and paper mill wastewater by electrocoagulation.

The precipitation of dissolved sulphide ions by electrocoagulation was studied at laboratory scale using pulp and paper mill wastewaters. Concentrations of dissolved organic carbon and phosphorus were analysed before and after the electrocoagulation process to examine the suitability of the process for treatment of sulphide odour from pulp and paper mill wastewater. The electrochemical cell used in this study was constructed from monopolar dissolving iron electrodes. The dissolved iron concentration was directly proportional to the applied electric charge (C/L) at the tested current densities. Electrochemically produced ferrous iron (Fe2+) precipitated dissolved sulphide ions efficiently. Electricity consumption of the treatment was 4-8 C/mg S(2-) while iron consumption was 1.1-2.2 mg/mg S(2-) during the initial phase of the sulphide precipitation when the applied electric charge was 10-60 C/L. When 60 C/L was applied, 88% of dissolved sulphides and 40% of phosphorus was precipitated. The reduction in DOC was low during the sulphide precipitation. According to these results, electrocoagulation can precipitate dissolved sulphides effectively and thereby reduce sulphide odours of pulp and paper mill wastewaters.