Sulfide removal by chemical precipitation from petroleum refinery wastewater was investigated. The wastewater samples were taken from the flocculation pond influent of TUPRAS Kirikkale Middle Anatolia Petroleum Refinery Wastewater Treatment Plant (WWTP) and physicochemical treatments using conventional coagulants which were partial precipitant [FeCl3 center dot 6H(2)O and FeSO4 center dot 7H(2)O] and coagulant-aids [Ca(OH)(2) and CaCO3] were applied to both raw and sulfide added wastewater. Sulfide and chemical oxygen demand (COD) removal efficiencies of Fe3+ ions alone for sulfide added wastewaters having different pH values varied between 62-95 and 45-75%, respectively. In addition, removal efficiencies of sulfide (96-99%) and COD (50-80%) were obtained by using Fe2+ ions together with Ca(OH)2 as precipitant-aid under the same conditions. In experiments performed with raw wastewater which had different pH values, COD removal efficiencies of Fe3+ and Fe2+, ions together with Ca(OH)(2), were 50-80 and 32-50%, respectively. (c) 2007 Elsevier B.V. All rights reserved.