Performance of fenton oxidation towards sulfide removal for spent caustic remediation

In wastewater, sulfides are the primary culprit among malodorous compounds that are most complained about by the general public. A study is made to explore the oxidation process for remediating sulfide from refinery spent caustic solution by means of Fenton´s Reagent i.e. ferrous ion, Fe²⁺ and hydrogen peroxide, H₂O₂ under acidic condition. The pH adjustment step also contributed towards the objective as 65-70% of sulfide removed in the form of hydrogen sulfide gas, H₂S. Elevation in the operating temperature indicates no advantage in terms of sulfide removal percentage thus the process is best done in ambient conditions i.e. 30°C. The optimum Fe²⁺ and H₂O₂/COD obtained from this experimental work is 75mg/L and 1.1, respectively. Almost all of sulfide is believed to convert to sulfate within 30-minutes of reaction time. Complete sulfide removal also caused the COD to be reduced by 43% and formation of sulfate in the form of sulphuric acid may be the reason of pH reduction of final effluent from 3.5 to 2.8.