Remediation of cyanide in biologically treated coke plant wastewater by chemical treatment method

Biological treatment with a stable activated sludge process, followed by chemical treatment is one of the potential and accepted cyanide remediation processes for coke plant wastewater treatment. Biologically treated coke plant wastewater contains free cyanide above permissible limit. Presently, chemical treatment with NaOCl is being used to attenuate free cyanide below permissible limit in biologically treated water. This process increases the TDS and colour content in discharge water. Ca(OCl)(2) can be used as an alternative to NaOCl for cyanide remediation in biologically treated coke plant wastewater without increasing TDS. In the present work, cyanide removal efficiency of NaOCl and Ca(OCl)(2) for real coke plant wastewater after biological treatment has been studied. Optimisation of chemical dosage, treatment time and pH study has been done for Ca(OCl)(2) and NaOCl treatment. It was found that up to 90% of free cyanide removal could be achieved through Ca(OCl)(2) treatment without increasing the TDS value. In addition, more than 50% colour of the wastewater was removed. pH elevation step required in NaOCl treatment can be eliminated in Ca(OCl)(2) treatment, thereby reducing caustic consumption. The study indicated that the use of Ca(OCl)(2) is economically more viable than that of NaOCl in cyanide treatment.