Heterotrophic nitrification-aerobic denitrification potential of cyanide and thiocyanate degrading microbial communities under cyanogenic conditions

Abstract

The impact of free cyanide (CN-) and thiocyanate (SCN-) on the CN- (CDO) and SCN- degraders (TDO) to nitrify and denitrify aerobically was evaluated under alkaline conditions. The CDO's were able to nitrify under cyanogenic conditions, achieving NH4+-N removal rates above 1.66 mg NH4+-N.L-1.h(-1), except when CN- and SCN- loading was 15 mg CN-/L and 50 mg SCN-.L-1, respectively, which slightly inhibited nitrification. The TDO's were able to achieve a nitrification rate of 1.59 mg NH4+-N.L-1.h(-1) in the absence of both CN- and SCN-, while the presence of CN- and SCN- was inhibitory, with a nitrification rates of 1.14 mg NH4+-N.L-1.h(-1). The CDO's and TDO's were able to denitrify aerobically, with the CDO's obtaining NO3--N removal rates above 0.67 mg NO3--N.L-1.h(-1), irrespective of the tested CN- and SCN- concentration range. Denitrification by the TDO's was inhibited by CN-, achieving a removal rate of 0.46 mg NO3--N.L-1.h(-1) and 0.22 mg NO3--N.L-1.h(-1) when CN- concentration was 10 and 15 mg CN-.L-1, respectively. However, when the CDO's and TDO's were co-cultured, the nitrification and aerobic denitrification removal rates were 1.78 mg NH4+-N.L-1.h(-1) and 0.63 mg NO3--N.L-1.h(-1) irrespective of CN- and SCN- concentrations.