Interactions between calcium precipitation and the polyphosphate-accumulating bacteria metabolism

Area of Science:

• Environmental Engineering
• Biotechnology
• Water Treatment

Background:

• Biological phosphorus removal is crucial for wastewater treatment.
• Calcium phosphate precipitation can influence nutrient removal processes.
• Understanding calcium's role is key to optimizing wastewater treatment.

Purpose of the Study:

• To investigate the effect of influent calcium concentration on biological phosphorus removal.
• To analyze the calcium phosphate precipitation process in a sequencing batch reactor.
• To determine how calcium influences the metabolism of phosphorus-accumulating organisms.

Main Methods:

• Operated a sequencing batch reactor under varying influent calcium concentrations (10-90 g Ca m⁻³).
• Utilized equilibrium studies and saturation index calculations to analyze precipitation.
• Employed fluorescence in situ hybridization to monitor microbial populations (PAO and GAO).

Main Results:

• Calcium phosphate precipitation, forming amorphous calcium phosphate and hydroxyapatite, was confirmed as the dominant calcium behavior.
• Increased influent calcium led to accumulated precipitated phosphorus.
• A decreased ratio of phosphate release to acetate uptake (P(rel)/Ac(uptake)) was observed at high calcium concentrations.
• Microbial population dynamics did not explain the observed metabolic changes.

Conclusions:

• Influent calcium concentration significantly affects biological phosphorus removal through precipitation.
• Polyphosphate-accumulating organisms (PAOs) can alter their metabolic pathways in response to external calcium levels.
• Phosphate precipitation is a critical factor influencing PAO metabolism in wastewater treatment.