Toxicity and degradation of cyanide in batch methanogenesis

Degradation of cyanide and its toxic effects on anaerobic biogranules were investigated in batch serum bottles using synthetic wastewater. Batch anaerobic cultures were exposed to a range of initial cyanide concentrations from 1 to 100 mg l(-1) for a period of 48 hours. Cyanide degradation rate increased with initial cyanide concentration in the batch. Maximum cyanide degradation rate upto 35-40 mg l(-1)d(-1) was recorded. Activity of biogranules was affected due to the presence of cyanide. Methane production rate decreased with increase in initial cyanide concentration in the batch. A methane production rate of 0.11 mi ml(-1)d(-1) was recorded for 10 mgCN l(-1) compared to 0.42 mi ml(-1)d(-1) for control containing no cyanide. Results from Microtox toxicity tests confirmed degradation of cyanide occurring in batch tests. EC50 for exposure time of 5 minutes and 15 minutes increased with respect to batch time indicating reduction in cyanide contents and its toxicity. A generalized procedure to estimate batch rime for reducing cyanide toxicity to a specific level is also included.