Performance of treatment schemes comprising chromium-hydrogen peroxide-based advanced oxidation process for textile...

The present study investigated the performance of a chromium-based advanced oxidation process using chromium (as Cr³⁺ or Cr⁶⁺) and H₂O₂ for the treatment of synthetic and simulated textile wastewaters. With the Cr³⁺/H₂O₂ system, the maximum total organic carbon (TOC) and color removals from the synthetic dye wastewater (Remazol Brilliant Violet 5R dye concentration = 100 mg/L) were 75% and 99%, respectively, within 30 min duration ([Cr³⁺]:[H₂O₂] = 1:30, stoichiometric H₂O₂ dose = 2.01 ml/L and pH = 7). Whereas the same catalyst and oxidant combination resulted in chemical oxygen demand (COD) and color removals of ~ 46%, and 84%, respectively, after 3 h of reaction at the optimized reaction conditions (i.e., [Cr³⁺]:[H₂O₂] = 1:50, stoichiometric H₂O₂ dose = 11.6 ml/L and pH = 7) from the simulated textile wastewater (initial pH = 10.2, and COD = 1820 mg/L). Further, the addition of stoichiometric H₂O₂ dose to the pretreated wastewater and pH adjustment increased the overall COD removal to 77%. Both oxidation and precipitation reactions were found responsible for organics removal from the wastewater. The other alternative involving activated carbon adsorption as second step, was not found as effective as the above scheme. The data on COD removal from simulated textile wastewater could be fit adequately in the retarded first-order kinetic model. Based on the COD and color removal results and preliminary cost analysis, this can be suggested that the Cr³⁺/H₂O₂ oxidation process followed by pH adjustment and further H₂O₂ treatment was the best option for the removal of COD and color from the simulated combined textile wastewater.