Exploring the Influence of Sulfide on Nitrogen-Removal Performance in Anammox Processes: An Investigation of Short-Term and Long-Term Effects

Sulfide-based pathways for generating nitrite to sustain anaerobic ammonium oxidation (anammox) have garnered increasing attention. However, the presence of sulfide can also impact the anammox process, necessitating a comprehensive understanding of both its short-term and long-term effects on anammox. This study aimed to investigate the influence of sulfide on anammox, including its effects on the microbial community and process kinetics. During long-term operation, the maximum sulfide dosage tested was 30 mg S/L over 50 days of operation, exhibiting good nitrogen removal efficiency of 83.9%+/- 4.8%. Conversely, under short-term exposure to sulfide, nitrogen removal efficiency was notably affected, decreasing to 68.98% at a considerably lower sulfide concentration of only 16 mg S/L. Within the context of long-term sulfide exposure, the maximum contribution of anammox to nitrogen removal reached 86.72% at a sulfide dosage of 25 mg S/L. However, when the influent sulfide concentration was increased to 50 mg/L, the contribution of anammox to nitrogen removal sharply declined to 41.3%. Microbial community analysis revealed as the sulfide concentration increased from 8 to 16 mg S/L, the abundance of anammox bacteria decreased from 2.46x105 to 1.67x105 copies/mL, whereas the abundance of Nitrobacter spp. increased from 2.73x102 to 8.13x102 copies/mL. However, during long-term operation, there was a more pronounced decrease in the microbial abundance of anammox, reducing from 5.3x105 to 3.77x102 copies/mL. Taking this decrease together with the improved efficiency of anammox observed during long-term operation, these findings suggest that sulfide's influence on anammox primarily impacts its metabolic activity rather than its microbial abundance.