Discovery and profiling of efficient microbial strains for struvite biomineralization in high-salinity wastewater

The microbial mineralization of struvite from high-salinity wastewater offers a promising approach for the simultaneous removal and recovery of phosphorus and nitrogen. Fish processing wastewater (FPW) is characterized by high organic pollutant loads, containing heavy metal copper ions, and variable salinity levels ranging from 2 to 21% NaCl. Such fluctuations in salinity can affect the efficiency of struvite biomineralization. The presence of heavy metal copper ions will also further restrict the function of the struvite-producing strains under high-salt conditions. This study focuses on screening microbial strains capable of producing struvite under high-salt stress and to investigate the impact of salt (NaCl) concentration on the treatment efficiency of synthetic FPW. Microorganisms were screened across a broad salinity range, and key parameters, including yield, pH, phosphate concentration, magnesium ion levels, and other indicators, were evaluated during the mineralization process. Furthermore, the ARTP mutagenesis technique was applied to identify mutant strains with enhanced copper ion tolerance and improved crystal production at 10% NaCl. A total of 54 microbial species were found to produce struvite while achieving elevated phosphorus (P) and magnesium (Mg) removal under 5% NaCl conditions. Among them, Halomonas olivaria MG-4 demonstrated broad salinity tolerance. Strain MG-4 exhibits a high recovery rate of P reaching 67% (p <  0.001) at 5% NaCl, and maintains 48-50% (p < 0.001) at 8-10% NaCl. Strain MG-4 exhibits a high recovery rate of P reaching 67% (p < 0.001) at 5% NaCl, and maintains 48-50% (p < 0.001) at 8-10% NaCl. The mutant strain MG-4(100 s-3) sustained high P and Mg removal and recovery efficiencies even at 8-10% NaCl in artificial wastewater systems. Compared with the wild-type MG-4, the mutant strain MG-4(100 s-3) exhibits enhanced tolerance to copper ions and significantly promotes struvite production at copper ion concentrations of 0.4-1.6 mM. These findings highlight valuable microbial resources for struvite biomineralization in FPW, offering potential for both efficient wastewater treatment and resource recovery.