Effect of cyanide on phenolics and aromatic hydrocarbons biodegradation under anaerobic and anoxic conditions

• Coke oven wastewater contains phenolics, aromatic hydrocarbons along with cyanide.
• Earlier studies focused on biodegradation of mixed organic compounds in aerobic conditions.
• Study focused on degradation of complex organic pollutants with cyanide in anoxic/anaerobic conditions.
• Anoxic condition was more effective for pollutants removal than anaerobic condition.
• A mathematical model is proposed to model the degradation of mixed pollutant system.

The objective of this study was to investigate the biodegradation of a mixture of pollutants commonly found in coke oven wastewater such as phenol, cresol, xylenol, quinoline, indole and cyanide under anaerobic and anoxic conditions. It was found that xylenol was highly recalcitrant under anaerobic and anoxic conditions. In presence of free cyanide (>2.5 mg/L), the organic compounds (100 mg/L) were degraded before the biodegradation of free cyanide under both the conditions. However, the biodegradation of pollutants prolonged under anaerobic conditions compared to anoxic conditions. All the organics, especially xylenol and indole, inhibited the degradation of cyanide. Experimental results highlighted the detrimental effects of the combined toxic influence of cyanide and organics on the anaerobic and anoxic microbes treating coking wastewater. The proposed mathematical model was able to simulate the biodegradation of organic compounds along with cyanide satisfactorily.