Synchronous removal of heavy metals and ammonia-nitrogen by magnesium ammonium phosphate (MAP)-enhanced microbial induced calcite precipitation (MICP)

Abstract

Microbially induced calcium carbonate precipitation (MICP) can be used to remediate heavy metal-contaminated soils. However, its remediation efficiency requires improvement, and the generation of ammonia nitrogen limits its practical application. We employed the magnesium ammonium phosphate precipitation method (MAP) to generate bio-struvite, which effectively immobilized ammonia, reduced the leaching toxicity of heavy metals, and promoted the transformation of Pb and Cd into more stable forms, thereby reducing their toxicity and bioavailability. Adsorption simulations have also demonstrated that bio-struvite has a stronger adsorption capacity for heavy metals and forms tighter adsorption bonds. Confocal Laser Scanning Microscope (CLSM) captured the formation process of bio-struvite, which together with the X-ray diffraction (XRD) pattern, corroborated the presence of bio-struvite. The formation of bio-struvite also effectively filled the soil pores. As an environmentally friendly and high-quality slow-release fertilizer, bio-struvite was tested for its N/P slow-release effect through soil column leaching experiments, which confirmed its ability to enhance soil fertility. Therefore, this approach not only provides a perspective for addressing the issue of ammonium nitrogen, but also explores the application of biomineralization in the field of heavy metal pollution. The research outcomes hold promise for future practical engineering applications.