SANI® process enables sustainable coking wastewater treatment: performance, microbial mechanisms and detoxification

Coking wastewater (CW), characterized by high organic concentration, high toxicity, and poor biodegradability, poses significant challenges for biological treatment. The sulfate reduction-autotrophic denitrification-nitrification (SANI®) process, known for its robustness in treating municipal wastewater with high salinity and low sludge production, has not yet been explored for CW treatment under high-toxicity conditions. This study established a lab-scale continuous-flow SANI system treating real CW at stepwise increasing concentrations (30 %→60 %→100 % of real CW ratio) to investigate toxic pollutants removal performance and sulfur-mediated degradation mechanisms. The SANI process achieved efficient and stable removal of carbon (COD 83.5 %, TOC 93.3 %), nitrogen (NH₄⁺-N 97.5 %, TN 85.1 %), and characteristic toxic pollutants (volatile phenols >99 %, SCN^- >99 %) during 100 % CW treatment, with effluent biotoxicity substantially reduced. 16S rRNA gene sequencing revealed functionally complementary microbial consortia: sulfur-reducing genera (Gudongella, Desulfitobacterium) dominated the anaerobic reactor; mixotrophic denitrifiers (Thauera, Comamonas) enriched in the anoxic reactor; and nitrifiers (Nitrospira) coupled with sulfur-oxidizers (Thiobacillus) prevailed in the aerobic reactor. Metagenomic analysis elucidated complete nitrogen/sulfur metabolic networks and typical toxic pollutant degradation pathways: SCN^- degradation proceeded via the CNO pathway, while phenol degradation followed the meta-cleavage pathway after hydroxylation. This study pioneers SANI process for sulfur-rich real CW treatment, demonstrating it enables simultaneous removal of carbon, nitrogen, and toxic pollutants-offering a breakthrough low-carbon alternative for industrial wastewater.