Calcium-mediated interfacial regulation in tourmaline-strain YX13 system for enhanced denitrification: Performance and mechanisms.

Tourmaline (Tm), a natural mineral capable of promoting microbial metabolism, has demonstrated significant potential in water treatment. However, electrostatic repulsion between Tm and bacteria hinders bacterial attachment, thereby limiting its application performance. Calcium ions (Ca2+), commonly present at high concentrations in aquaculture wastewater, were utilized to establish an interfacial regulation strategy in this study. Through Ca2+ bridging and the bio-cementation effect of microbially induced calcium precipitation (MICP), effective immobilization of strain YX13 on Tm was achieved. Compared with the system without Ca2+ addition, the strain exhibited a markedly improved denitrification performance. Under the optimized conditions (C/N = 5, pH = 7, Tm = 2 g L-1, Ca2+ = 180 mg L-1), the removal efficiencies of nitrate (NO3--N), phosphate (PO43--P), and Ca2+ reached 97%, 96%, and 66% within 12 h, respectively. Characterization results indicated that appropriate Ca2+ markedly reduced electrostatic repulsion among particles while increasing the content of extracellular polymeric substances (EPS), thereby enhancing bacterial adhesion and optimizing the interfacial structure. This regulation significantly improved microbial energy metabolism and electron transfer efficiency, while enhancing the redox activity of the system. Microstructural characterization further revealed that the strain was immobilized on the Tm surface through the bio-cementation effect of biomineralization. The findings of this work offer a promising approach for enhancing the efficiency of bacterial nitrogen and phosphorus removal in wastewater treatment systems.