Anammox reactor exposure to thiocyanate: Long-term performance and microbial community dynamics

[Display omitted] •Effects of thiocyanate (SCN−) on anammox reactors were assessed.•SCN− ≥ 100 mg L−1 exposure led to failure of denitrification by anammox processes.•The SCN−-degrading bacteria competed with the anammox species for NO2–.•SCN− exposure changed the microbial community in the anammox reactors.•Thiobacillus was the dominant genus in the reactor with SCN− addition. Anaerobic ammonium oxidation (anammox) is an autotrophic denitrification process that has broad application potential for treating coking wastewaters. The present study estimated the effects of thiocyanate (SCN−), a common pollutant in coking wastewaters, on anammox processes and microbial communities in anammox reactors for over two years of continuous exposure. The addition of SCN− (from 50 to 200 mg L−1) showed negative effects on the denitrification performance of the anammox reactors. In SCN−-dosed reactors, increased effluent ammonium concentrations indicated the occurrence of SCN−-based biodegradation processes. Microbial analysis revealed that the anammox species almost disappeared in the reactor dosed with SCN− at over 100 mg L−1. Instead, an abundance of chemolithoautotrophic bacteria belonging to the Thiobacillus genus demonstrated a linear increase with SCN− addition. The competition between anammox species and SCN−-degrading microorganisms was expected to dominate the inhibition effects of SCN− addition on the performance of anammox reactors.