Inhibitory effects of toxic compounds on nitrification process for cokes wastewater treatment

Cokes wastewater is one of the most toxic industrial effluents since it contains high concentrations of toxic compounds such as phenols, cyanides and thiocyanate. Although activated sludge process has been adapted to treat this wastewater, nitrification process has been occasionally upset by serious inhibitory effects of toxic compounds. In this study, therefore, we examined inhibitory effects of ammonia, thiocyanate, free cyanide, ferric cyanide, phenol and p-cresol on nitrification in an activated sludge system, and then correlated their threshold concentrations with the full-scale pre-denitrification process for treating cokes wastewater. Ammonia below 350 mg/L did not cause substrate inhibition for nitrifying bacteria. Thiocyanate above 200 mg/L seemed to inhibit nitrification, but it was due to the increased loading of ammonia produced from its biodegradation. Free cyanide above 0.2 mg/L seriously inhibited nitrification, but ferric cyanide below 100 mg/L did not. Phenol and p-cresol significantly inhibited nitrification above 200 mg/L and 100 mg/L, respectively. Meantime, activated carbon was added to reduce inhibitory effects of phenol and free cyanide.