Stable nitrite accumulation in partial sulfide autotrophic denitrification (PSAD) systems under extremely low S/N ratios - Kunming Fu; Aotong Huo; Jia Kang; Tengyue Zhang; Teng Guan; Xueqin Li; Ruibao Zhang; Yuanan Cao; Shixing Zhang; Jinyi Liang; Yihao Bian; Fuguo Qiu (Journal of Water Process Engineering, 2026)