Uncovering pathway and mechanism of simultaneous thiocyanate detoxicity and nitrate removal through anammox and denitrification

Thiocyanate (SCN⁻) exists in various industries and is detrimental to the ecosystem, necessitating cost-effective and environmentally benign treatment. In response to alleviate the bacterial toxicity of SCN⁻, this study developed a two-stage coupled system by tandem of anammox in reactor 1 (R1) and SCN⁻-driven autotrophic denitrification in reactor 2 (R2), achieving simultaneous removal of SCN⁻ and nitrogen. The total nitrogen removal efficiency of the coupled system was 92.42 ± 1.98%, with nearly 100% of SCN⁻ elimination. Thiobacillus was responsible for SCN⁻ degradation. The deduced degradation pathway of SCN⁻ was via the cyanate pathway before coupling, followed by the co-action of cyanate pathway and carbonyl sulfide pathway after coupling. Although scaling-up study is needed to validate its applicability in real-world applications, this study contributes to the advancement of sustainable and cost-effective wastewater treatment technologies, being an attractive path for low-carbon nitrogen removal and greenhouse gas emission-free technology.