Sulfide removal in wastewater from petrochemical industries by autotrophic denitrification

An alternative flowchart for the biological removal of hydrogen sulfide from oil-refining wastewater is presented; autotrophic denitrification in a multi-stage treatment plant was utilized. A pilot-scale plant was fed with a mixture of the following constituents: (a) original wastewater from an oil refining industry (b), the effluent of the existing nitrification-stage treatment plant and (c) sulfide in the form of Na 2S. Anoxic sulfide to sulfate oxidation, with nitrate as a terminal electron acceptor, proved very successful, as incoming concentrations of 110 mg S 2−/L were totally converted to SO 4 2−. At complete denitrification, the concentration of S 2− in the reactor effluent was less than 0.1 mg/L. Fluctuating S 2− concentration in the feed could be tolerated without any problems, as the accumulated sulfide in the effluent of the denitrification stage is oxidized aerobically in a subsequent activated-sludge treatment stage. This alternative new treatment scheme was further introduced at the refinery's wastewater processing plant. Thus, complete H 2S removal is now accomplished by the combination of the proposed biological method and the existing stripping with CO 2. As a result, stripping, and thus its cost, is reduced by 70%.