Simultaneous removal of hydrogen sulfide, phosphate and emerging organic contaminants, and improvement of sludge dewaterability by oxidant dosing in sulfide-iron-laden sludge

• The benefits of dosing oxidants in sulfide-iron-laden sludge were demonstrated. • H 2 O 2 , ClO 2 , and NaClO 2 were cost-effective to control H 2 S release from the liquid sludge. • Radicals from Fe II -oxidant interactions destructed organic pollutants, EPSs and improved sludge dewaterability. • Fe III , product of the Fe II -oxidant interactions, precipitated/adsorbed phosphate in the liquid sludge. • The principles can be applied to treat various pollutants in iron-sulfide-laden sludge systems. Liquid sludge often contains odorous and toxic hydrogen sulfide and high levels of Fe II compounds (e.g., iron sulfides), due to the extensive use of iron salts for hydrogen sulfide control in sewers and for enhanced primary treatment and phosphate removal in wastewater treatment plants. We proposed and verified that dosing appropriate chemical oxidants in the sulfide-iron-laden sludge can be a simple and cost-effective strategy to remove hydrogen sulfide, phosphate, and emerging organic contaminants, and to improve sludge dewaterability simultaneously. Among the seven oxidants investigated, H 2 O 2 , ClO 2 and NaClO 2 were the more cost-effective oxidants than others to control hydrogen sulfide release from the liquid sludge. Dosing these three oxidants also improved sludge dewaterability and removed dissolved phosphate from the liquid sludge, with H 2 O 2 performing the best. Hydrogen sulfide was removed via both direct oxidation by the dosed oxidants and indirect oxidation by the Fe III that was in-situ formed from oxidation of the Fe II compounds in the sludge. The in-situ formed Fe III also precipitated/adsorbed the soluble phosphate into the solid form (FePO 4 ). Fenton-like reactions occurred between H 2 O 2 and the Fe II compounds in the sludge, and hydroxyl radicals (HO•) were generated. HO• oxidized hydrogen sulfide, destructed refractory organic emerging contaminants and sludge extracellular polymeric compounds (EPSs), and improved the sludge dewaterability. The formation of HO• can be enhanced by hydrogen sulfide and the sludge EPSs present in the sludge through providing more available Fe II for the Fenton-like reactions. This study demonstrates the importance of selecting and dosing suitable oxidants to the sulfide-iron-laden sludge with due consideration for the multiple benefits in engineering practices. The same principles may be also used in formulating a dual oxidant-iron strategy to treat sulfide-iron-laden sewage, sludge, and sediments for simultaneous abatement of various pollutants.