Unraveling synergistic effects of Ca2+, Mg2+ and Zn2+ co-removal from high-salinity wastewater induced by Lysinibacillus xylanilyticus DB1-12 via microbially induced carbonate precipitation(MICP).

The simultaneous removal of Ca2+, Mg2+ and Zn2+ from hypersaline wastewater is still challenging due to the complex interactions of multivalent ions. Here, the halophilic bacterium Lysinibacillus xylanilyticus DB1-12 was used to investigate the mechanisms controlling the synergistic immobilization of these divalent cations via microbially induced carbonate precipitation (MICP), which was further enhanced by activated carbon fiber (ACF) immobilization. Zn²⁺ was an active crystallization regulator rather than a passively co-precipitated ion, inducing defective mineral structures and stimulating the formation of Mg-rich calcite, thereby promoting Ca²⁺ precipitation and enhancing Mg²⁺ sequestration within the evolving carbonate mineral phases. Metal stress also promoted the secretion of extracellular polymeric substances(EPS), which provided nucleation sites, enhanced metal complexation and biomineralization. Free-cell systems removed up to 81.5% of Ca2+ and almost 100% of Zn2+. ACF immobilization further improved overall metal removal to above 90% in most systems. More importantly, the Zn2+-mediated evolution of mineral phases finally regulated the synergistic immobilization of multiple divalent cations. These results give new insights into multimetal cations-coupled biomineralization and a promising strategy for bioremediation of complex hypersaline wastewater.