Recovery behavior of sulfur-based autotrophic denitrification in an MBR under temperature, pH, and aeration...

This study systematically compared disturbance-recovery behavior of a suspended-growth sulfur-based autotrophic denitrification (SAD) process using powdered elemental sulfur in an SAD-MBR under temperature, pH (alkalinity limitation), and dissolved oxygen (DO) disturbances within a single 90-day controlled trial. Such direct cross-stressor comparison has rarely been reported for suspended-growth powdered-sulfur SAD systems. During cooling from 20 to 15 °C, nitrate removal efficiency remained stable at 93-95 %, whereas further cooling to 10 °C decreased nitrate removal efficiency to 83 % within 12 h; after reheating to 20 °C, nitrate removal efficiency recovered to 95 % within about 2.5 h. Under adequate alkalinity, the reactor maintained near-neutral pH (6.91-7.10) with high nitrate removal efficiency (90-96 %). When alkalinity supply was stopped, pH dropped to 5.8 within 8 h, resulting in a sharp decline in nitrate removal efficiency (62.4 % and 29.3 % after about 4 days) and nitrite accumulation up to 14 mg/L. Although pH returned to 7.1 within 1 day after alkalinity restoration, recovery of nitrate removal efficiency to >90 % required about 10 days. During aeration at 3.0 L/min, DO remained low (about 0.3 mg/L) and nitrate removal efficiency stayed >95 %, whereas sulfur-deficient conditions increased DO to 3.62 mg/L and reduced nitrate removal efficiency to near 0 %. After sulfur readdition, DO decreased to 0.31 mg/L within 1 day and nitrate removal efficiency recovered to >95 % with continued sulfur availability. Microbial community analysis showed the predominance of Sulfurimonas (29.9 %) and Thiobacillus (19.5 %).