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

Area of Science:

• Environmental Science
• Microbiology
• Chemical Engineering

Background:

• Wastewater treatment requires efficient removal of nitrogen, sulfur, and phosphorus.
• Sulfide-based autotrophic denitrification (SAD) is a promising method for nitrogen and sulfur removal.
• Understanding phosphate removal mechanisms within SAD systems is crucial for optimizing wastewater treatment.

Purpose of the Study:

• To investigate the efficiency and mechanism of phosphate removal during sulfide-based autotrophic denitrification.
• To determine the influence of calcium and magnesium ions on phosphate removal.
• To identify key environmental factors affecting phosphate removal in SAD systems.

Main Methods:

• Sulfide-based autotrophic denitrification (SAD) experiments were conducted.
• Phosphate, nitrate, and sulfide removal efficiencies were measured.
• Spearman correlation analysis was used to assess ion removal relationships.
• SMT, XRD, SEM, and chemical tests were employed to identify phosphorus removal products and mechanisms.
• Microbial community analysis and redundancy analysis were performed.

Main Results:

• SAD achieved high removal rates for nitrate (89.64%) and sulfide (90.52%).
• Phosphate removal efficiency exceeded 33.62% in the presence of Ca²⁺ and Mg²⁺, reaching 63.52% at 45 mg P/L.
• Bio-induced chemical phosphorus removal, forming CaHPO₄·2H₂O, was the primary mechanism, enhanced by SAD organisms.
• pH was identified as the most significant factor influencing phosphate removal (69.80%).

Conclusions:

• SAD is effective for simultaneous nitrogen, sulfur, and phosphate removal.
• The process promotes selective calcification removal of phosphate, primarily as inorganic calcium phosphate.
• pH is a critical parameter for optimizing phosphate removal in SAD systems.
• This study provides mechanistic insights for concurrent nitrogen and phosphorus removal technologies.