Carbonic Anhydrase-Mediated Microbial Conversion of Phosphogypsum Enables Atmospheric CO₂ Sequestration via Non-Ureolytic MICP

Phosphogypsum (PG), a major industrial by-product, poses significant environmental challenges due to its acidity, heavy metal contamination, and large-scale accumulation. In this study, we developed a novel, eco-friendly strategy for PG biotransformation using a consortium of seven indigenous, multi-metal-resistant bacterial strains. These strains, predominantly aerobic chemolithotrophs, were characterized by their ability to produce carbonic anhydrase (CA) and, in most cases, urease, key enzymes involved in microbially induced carbonate precipitation (MICP).

Microcosm-based experiments demonstrated that the bacterial consortium effectively transformed acidic PG (pH ~3.3) into an alkaline system (pH ~8.3) within 14 days, accompanied by significant physicochemical and mineralogical changes. X-ray diffraction and SEM-EDX analyses confirmed the conversion of PG into calcium carbonate (CaCO₃), driven by enhanced carbonate ion formation. Notably, the consortium achieved a substantial increase in carbonate concentration (up to ~3500% in precipitates) and a reduction in sulfate content, indicating efficient PG degradation.

Importantly, this bioprocess enabled atmospheric CO₂ sequestration of ~144.65 mg/kg PG approximately 160-fold higher than abiotic controls, primarily mediated through CA activity without the need for external carbon sources or engineered strains. The process integrates PG detoxification with carbon capture, offering a sustainable, low-cost alternative to conventional sequestration technologies.

This study presents a dual-benefit biotechnological approach for waste valorization and climate mitigation, with potential applications in bio-concrete, soil amendment, and environmental remediation.