Experimental Studies on the Removal of Chromium from Tannery Wastewater using Chemical Precipitation and Adsorption Techniques

Abstract

Despite trivalent chromium’s manifold functionalities in industrial manufacturing processes, when it is improperly treated and disposed to the environment, due to external environmental factors it could get converted to hexavalent chromium that has toxic effects on humans and our environment. Hence, there is a stringent need to optimize the current industrial practices of chromium handling, management, and disposal. This paper puts forth the inferences from comparative studies conducted using chemical precipitation and biochar adsorption to ascertain if the current chromium removal practice in the chrome tanning leather industry under study is an optimal method or not. Results indicate that the current industrial practice of achieving 86~90 % removal efficiency using 2000 mg/L of MgO at pH6 can be optimized by carrying out chemical precipitation at pH8 for 96~99% removal efficiency; a combination of NaOH and Ca(OH)2 in varying ratios resulted in 80-96 % removal efficiency at pH7 and ~99% at all the ratios at pH8, but the sludge volumes were higher than twice the volumes generated by MgO precipitation; inactivated biochar in similar proportions to that of chemical precipitants did not yield encouraging results and the maximum removal efficiency was 73.2% at 48000 mg/L dosage. Therefore, if not for complete treatment of tannery wastewater with biochar, residual chromium in the supernatant should be treated with biochar as it could be effective in treating lower concentrations of chromium.