Fate and transformation of thiocyanate and cyanate under methanogenic conditions

The fate of thiocyanate (SCN-) and cyanate (OCN-) under methanogenic conditions was investigated at 35 degrees C. Thiocyanate and cyanate were added to mixed methanogenic cultures along with an organic mixture. Thiocyanate was stable under these conditions, and had no adverse effect on methanogenesis at a concentration as high as 2.5 mM. In contrast, cyanate at a concentration as low as 0.3 mM initially inhibited methanogenesis but, after the complete removal of cyanate, methanogenesis gradually recovered. The inhibitory effect of cyanate on methanogenesis became more profound with repeated additions of cyanate. The transformation of cyanate followed the hydrolytic route to ammonia and bicarbonate under anaerobic conditions and its hydrolysis rate was enhanced by microbial activity. Cyanide was not detected as a cyanate transformation product under the methanogenic conditions bf this study.