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

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.