Chemical treatment for treating cyanides-containing effluent from biological cokes wastewater treatment process

A pre-denitrification process has been used to treat cokes wastewater containing toxic compounds such as phenols, cyanides and thiocyanate in Korea, and has showed very good removal efficiencies in carbon and nitrogen removals. However, a considerable amount of cyanides in the form of ferricyanide remained in the effluent of biological treatment process. Though ferrous iron is known to be more efficient in removing ferricyanide than ferric iron, ferric chloride solution has been used as a chemical precipitant due to its low cost for a long time. In this study, ferrous sulfate and ferric chloride solutions were used to remove cyanides remained in the effluent of the pre-denitrification process. The optimum dosage of each iron solution was evaluated in batch experiments with or without PAC solution. In addition, the amount of produced chemical sludge and the settling performance of it were also examined numerically. In conclusion, economic assessment indicated that ferrous iron is more economically profitable than ferric iron in spite of its high cost.