Aerobic biodegradation of thiocyanate

The biotransformation of thiocyanate (SCN−) and cyanate (OCN−) in a predominantly heterotrophic, activated sludge-derived culture was investigated. Acclimation and enrichment of aerobic, thiocyanate-degrading microorganisms led to complete thiocyanate oxidation to ammonia, bicarbonate, and sulfate. Low levels of cyanate were detected, indicating that its hydrolysis is not the rate-limiting step in the complete aerobic oxidation of thiocyanate. Cyanate removal followed the hydrolytic route to ammonia and bicarbonate under aerobic conditions. Abiotic assays confirmed that the observed thiocyanate removal was biologically mediated while cyanate hydrolysis was enhanced enzymatically. Neither thiocyanate nor cyanate inhibited the aerobic removal and assimilation of organic compounds simulating typical municipal wastewaters. However, partial inhibition of nitrification, especially the conversion of nitrite to nitrate, was observed, and was attributed to thiocyanate and/or free ammonia.