Study on the Effect of Synergistic Action of Fe(II) and Sodium Acetate on the Performance of the Coupled Sulfur-Based Autotrophic Denitrification and Anammox System

Under the synergistic action of Fe(II) and sodium acetate, the SDDA reactor was effectively started up within 25 days. When the Fe(II) concentration was 0.1 mmol/L, with a C/N ratio of 1.1 and an S/N ratio of 1.5, the denitrification performance was optimal, achieving a total nitrogen removal efficiency (TNRE) of 93.57%, with a kinetic parameter kTN of 0.1722 h-1, and significant sludge granulation (PN/PS = 2.54). High concentrations of Fe(II) inhibited microbial activity and reduced denitrification efficiency. The experiment showed that under optimal carbon source conditions provided by sodium acetate, the TNRE reached 95.95%, with a kTN of 0.2045 h-1, and a PN/PS ratio of 2.07. The synergistic effect of Fe(II) and sodium acetate effectively balanced the activities of heterotrophic, sulfur-based autotrophic, and anammox bacteria in the system, enhancing the nitrogen removal efficiency. Under conditions of a C/N ratio of 1.1 and an S/N ratio of 1.5, TNRE reached 97.77%, with a sulfate generation efficiency (SGE) of 85.75%, effluent pH ranging between 7.56 and 7.83, and COD below 13.65 mg/L. At this point, the denitrification contributions of Anammox, SAD, and HD were 65.63%, 16.12%, and 14.67%, respectively. The dominant functional bacterial genera included Candidatus Brocadia, Thiobacillus, and Thermomonas, accounting for 5.87%, 28.34%, and 7.62%, respectively.