Selective phosphate calcification and enhanced nutrient removal through sulfide-based autotrophic denitrification

The sulfide-based autotrophic denitrification (SAD) demonstrates effective simultaneous removal of nitrogen and sulfur within the phosphate concentration range of 15-55 mg P/L. The elimination rates of nitrate and sulfide can attain 89.64 ± 3.62 % and 90.52 ± 4.10 % respectively. The phosphate removal efficiency exceeds 33.62 ± 6.41 % in the presence of both calcium and magnesium ions, and attains a maximum of 63.52 ± 6.65 % when the influent phosphate concentration is 45 mg P/L. Spearman correlation analysis study revealed a substantial positive association between the quantity of phosphate removal and the amount of calcium ion removed; however, no significant correlation existed with that of magnesium ion removed. SMT, XRD and SEM analyses confirmed that phosphorus removal products predominantly occurred as inorganic phosphorus (CaHPO₄·2H₂O). Chemical tests results indicated that bio-induced chemical phosphorus removal was the primary mechanism for phosphorus removal in this system. SAD organisms enhance the chemical phosphorus removal process (with an increase rate from 32.27 ± 1.18 % to 60.64 ± 2.66 %), and altered the type of phosphate precipitation. Community study indicated that the dominant functional genera in the sulfur-autotrophic denitrification system were Sulfurovum and Thiobacillus, and variations in phosphate concentration exerted no substantial influence on community diversity and richness. Redundancy analysis indicated that pH was the paramount environmental factor influencing phosphate removal with a contribution rate of 69.80 % (p < 0.05). This study elucidates the mechanism of sulfur-autotrophic denitrification process that facilitates the selective calcification removal of phosphate in aquatic environments containing both calcium and magnesium, thereby offering a mechanistic insight for the technology of concurrent nitrogen and phosphorus removal from wastewater.