Effects of thiocyanate on granule-based anammox process and implications for regulation

The feasibility of using anaerobic ammonium oxidation (anammox) process to treat industrial wastewater containing thiocyanate (SCN^-) was examined in this study. Anammox activity decreased with increasing thiocyanate concentration and pre-exposure time in batch tests. A typical noncompetitive model was used to fit the data for thiocyanate inhibition, and the 50% inhibition concentration (IC₅₀) of thiocyanate on anammox was 620.4mgL^-1 at 200mgL^-1 total nitrogen level. The influent thiocyanate concentration of test reactor (R₁) in phase II gradually increased from 10 to 120mgL^-1, and the average nitrogen removal efficiency (NRE) of R₁ was maintained at 83.0±7.82%. This robustness was attributed to the self-adaptation ability of anammox biomass through long-term acclimatization. The NRE was decreased to 57.1% under 130mgL^-1 thiocyanate within two days. However, the NRE of control reactor (R₀) in absence of thiocyanate was 91.23±4.11% in this phase. Under thiocyanate stress, the specific anammox activity, settling velocity and heme c content of the granules significantly decreased, and the extracellular polymeric substances content slightly increased. The short- and long-term performance inhibition could be reversed in the presence of 10mgL^-1 Fe(III).