CHROMIUM (III) REMOVAL FROM TANNERY WASTEWATER BY CHEMICAL PRECIPITATION.

The removal of trivalent chromium [Cr(III)] from tannery wastewater is necessary for health regulation compliance. In this work, two precipitating agents, namely, sodium hydroxide (NaOH) and calcium hydroxide [Ca(OH)2] were used to remove Cr(III) from Amatong Tannery wastewater by chemical precipitation. Wastewater characterization along with the most affecting parameters such as the effect of pH on Cr(III)) removal and sludge volume, average sludge volume and the settling time were investigated. The results show that optimum pH for Cr(III) removal by NaOH and Ca(OH)2 were found as 8.5 and 8.5-9.0, respectively, with supernatant Cr(III) concentration as 1.23 and 4.1 mg/L, respectively; the removal efficiency of NaOH was 99.94% and 99.8% for Ca(OH)2. At optimum pH, NaOH exhibited much sludge volume, whereas Ca(OH)2 displayed higher supernatant volume. NaOH: Ca(OH)2 volume ratio for sludge volume at optimum pH and average sludge volume were 1:1.24 and 1:1.8, respectively. [ABSTRACT FROM AUTHOR]