FERRIC CHLORIDE (FeCl3) AS REGULATORY AGENT FOR THE REDUCTION OF HYDROGEN SULFIDE (H2S) IN MUNICIPAL WASTEWATER

In the present study, the use of trivalent iron (Fe), added as ferric chloride (FeCl3), in untreated wastewater was investigated for the reduction of hydrogen sulphide (H2S) concentration. The area under study was the Municipal Enterprise for Water and Sewage of Chania (DEYACH) (Crete, Greece). FeCl3, at concentrations varied from 0.5 to 5,930 mg FeCl3 per liter wastewater, was added into wastewater, which it was previously passed through the coarse and fine screens. Experimental data that simulated the procedure of grit/oil removal for 15 minutes and the primary sedimentation for 3.5 hours indicated that the reduction of the dissolved H2S was achieved up to nearly 100 % when the concentration of the added FeCl3 increased from 0 to 296.5 mg per L of wastewater. Thereby, the pH of the Fe-treated wastewater at the concentration of 296.5 mg FeCl3 / L reached values which varied between 4.7 and 6.5. Atomic absorption spectroscopy was used to determine the partition of the iron between the primary treated wastewater (supernatant) and the primary waste sludge (sludge). Our results show that after the FeCl3 treatment, the majority of iron (85 %) remained in the supernatant, whereas only 15 % of it was found in the sludge.