Advances in Bioslurry Remediation of Potentially Toxic Elements (PTEs) in Polluted Soils

Soil contamination by potentially toxic elements (PTEs) remains a major global challenge due to their persistence, toxicity, and bioaccumulation capacity. Despite being widely used for the ex situ remediation of soils polluted by organic contaminants, bioslurry reactors (BSRs) have been scarcely employed for the bioremediation of PTE-polluted soils. BSRs are indeed capable of treating a wide range of contaminated soils, which are often unsuitable for remediation by conventional biological treatments. BSRs allow control of mixing, aeration, and nutrient conditions, thus enhancing mass transfer, pollutant desorption, and microbe-pollutant interactions. In addition, diverse microbial metabolic mechanisms can be exploited to mobilize or transform PTEs through bioleaching, redox reactions, complexation, and acid generation. Numerous studies have demonstrated substantial removal efficiencies for PTEs, such as Cd, Co, Cu, Ni, Zn, and As. Despite their advantages, large-scale implementation of BSRs faces challenges related to operational costs, reactor design, energy demand, and the need for precise control of physicochemical parameters. Advances in microorganism immobilization, genetic engineering, and online parameter monitoring may represent levers for a wider application of this technology. This review represents the first systematical attempt to address the issue of BSR application to PTE-polluted soil remediation. The principles of BSR functioning are discussed together with the mechanisms of microbial bioleaching, highlighting the potentialities of BSR technology and addressing gaps and opportunities to fully exploit BSRs as a sustainable and economically viable tool for remediating PTE-polluted soils.