Mechanisms and influencing factors of biomineralization based heavy metal remediation: A review

Heavy metal contamination of soil and water is one of the most prominent environmental issues worldwide. Through bioaccumulation and biomagnification of the food chain, heavy metals can be enriched hundreds of times and eventually enter the human body, posing a major threat to human health. Biomineralization has the greatest potential to become an efficient and environmentally friendly heavy metal remediation technology and has received much attention in recent decades. This review summarizes the latest progress of biomineralization technology on carbonate precipitation and phosphate precipitation in heavy metal remediation. Both microorganisms (including bacteria and fungi) and enzymes can induce carbonate and phosphate precipitation, converting the free heavy metal ions into insoluble salts. However, the mechanisms of the heavy metal remediation are significantly different. For example, urea hydrolysis, which occurs intracellularly when urease-producing bacteria (UPB) are used, is the most commonly used mechanism for carbonate precipitation based bioremediation. In contrast, phosphate solubilization by either enzymes or organic acids secreted by phosphate solubilizing bacteria (PSB) is extracellular, and both soluble and insoluble phosphorus can be decomposed by PSB. Moreover, some influencing factors such as the different species of microorganism, heavy metals and some environmental conditions that may affect the bioremediation of heavy metals were also summarized in this paper. The challenges of biomineralization based heavy metal remediation are also discussed. Based on the reviews of previous studies, a comprehensive understanding of heavy metal removal through microorganism can be increased, and thus promotes the applications of biomineralization technology in the treatment of large-scale heavy metal contaminated sites.