Phosphate-mediated pseudo-selectivity in calcification control: Substrate-derived alkalinity outweighs kinetic...

The anaerobic granular sludge bed reactors treating calcium-rich wastewater are fundamentally constrained by uncontrolled biomineralization process, particularly through spontaneous CaCO₃ precipitation. While phosphate supplementation demonstrates partial deceleration of precipitation kinetics (50% reduction of reaction rate), its efficacy seems substrate-selective, achieving merely 15.6% calcium interception efficiency in the low-acidified substrate group compared to 60.4% in the high-acidified substrate group. Key findings reveal that phosphate exerts its influence by regulating the formation and crystallization pathway of CaCO₃, while endogenous metabolic alkalinity serves as the primary driving factor for the degree of mineralization. Notably, proton-depleting metabolic processes in the high-acidified substrates override phosphate's kinetic inhibition by generating high concentration of bicarbonate for CaCO₃ formation. These findings establish microbially-mediated alkalinity production as the cardinal determinant in reactor calcification risk, and call for strategies targeting calcium ion deactivation beyond traditional kinetic control.