Performance of various cyanide degrading bacteria on the biodegradation of free cyanide in water.

This study reports on the biodegradation of free cyanide (FCN) by cyanide degrading bacteria (CDB) that were isolated from mining wastewater and thiocyanate containing wastewater. The performance of these isolates was compared to cryopreserved CDBs that were used in previous studies. The performance of the isolates to degrade FCN was studied in batch cultures. It was observed that the CDB from the thiocyanate wastewater showed higher biodegradation rates (2.114 g CN-. L-1.O.D600 nm-1.h-1) compared to the isolates from the mining wastewater. The isolates from the cryopreserved CDBs and from the mining wastewater achieved a biodegradation rate of 1.285 g CN- L-1.O.D600 nm-1.h-1 and 1.209 g CN-.L-1.O.D600 nm-1.h-1, respectively. This study demonstrated that the source of the organisms plays a significant role on FCN biodegradation.

Isolation of high-salinity-tolerant bacterial strains, Enterobacter sp., Serratia sp., Yersinia sp., for nitrification and aerobic denitrification under cyanogenic conditions.

Cyanides (CN(-)) and soluble salts could potentially inhibit biological processes in wastewater treatment plants (WWTPs), such as nitrification and denitrification. Cyanide in wastewater can alter metabolic functions of microbial populations in WWTPs, thus significantly inhibiting nitrifier and denitrifier metabolic processes, rendering the water treatment processes ineffective. In this study, bacterial isolates that are tolerant to high salinity conditions, which are capable of nitrification and aerobic denitrification under cyanogenic conditions, were isolated from a poultry slaughterhouse effluent. Three of the bacterial isolates were found to be able to oxidise NH(4)-N in the presence of 65.91 mg/L of free cyanide (CN(-)) under saline conditions, i.e. 4.5% (w/v) NaCl. The isolates I, H and G, were identified as Enterobacter sp., Yersinia sp. and Serratia sp., respectively. Results showed that 81% (I), 71% (G) and 75% (H) of 400 mg/L NH(4)-N was biodegraded (nitrification) within 72 h, with the rates of biodegradation being suitably described by first order reactions, with rate constants being: 4.19 h(-1) (I), 4.21 h(-1) (H) and 3.79 h(-1) (G), respectively, with correlation coefficients ranging between 0.82 and 0.89. Chemical oxygen demand (COD) removal rates were 38% (I), 42% (H) and 48% (G), over a period of 168 h with COD reduction being highest at near neutral pH.