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Mining waste represents a global issue due to its potential of generating acidic or alkaline leachate with high concentrations of metals and metalloids (metal(loid)s). Microbial-induced calcium carbonate precipitation (MICP) is an engineering tool used for remediation. MICP, induced via biological activity, aims to precipitate calcium carbonate (CaCO3) or co-precipitate other metal carbonates (MCO3). MICP is a bio-geochemical remediation method that aims to immobilize or remove metal(loid)s via enzyme, redox, or photosynthetic metabolic pathways. Contaminants are removed directly through immobilization as mineral precipitates (CaCO3 or MCO3), or indirectly (via sorption, complexes, or inclusion into the crystal structure). Further, CaCO3 precipitates deposited on the surface or within the pore spaces of a solid matrix create a clogging effect to reduce contaminant leachate. Experimental research on MICP has shown its promise as a bioremediation technique for mining waste. Additional research is required to evaluate the long-term feasibility and potential by-products of MICP-treated/stabilized waste. [ABSTRACT FROM AUTHOR]

Surfactants and nanoparticles have been effectively used for environmental remediation for many years. Over the years, various methods have been developed to synthesize nanoparticles using different surfactants to obtain a s higher treatment efficiency for organic contaminated soil. Compared to conventional remediation methods, the in-situ remediation technique provides advantages, such as being more eco-friendly and cost-effective. This review provides an overview of the remediation of organic contaminated soil using surfactant-stabilized Fe-based nanoparticles, mostly surfactant-stabilized nanoscale zero-valent iron (nZVI). In addition, the use of other stabilizers and the mechanisms of stabilization are discussed. The combination of surfactants and Fe-based nanoparticles can be effectively used to remediate organic contaminants from soil, such as trichloroethylene (up to 99%), polychlorinated biphenyls (up to 80%), perchloroethylene (up to 93%). The treatment efficiency organic contaminants in soil by surfactant-stabilized nanoparticles is higher than only surfactant (less than 90%) or nanoparticles (less than 80%) due to the synergistic effects between surfactants and nanoparticles. This technique is generally more effective to use as a strong reductant, such as reductive dehalogenation or reductive immobilization of metals, while less cost-effective as an adsorbent. In addition, the remediation rate depends on various factors, such as pH, temperature, natural organic matter, ionic strength, type and concentration of stabilizers, site characteristics, contaminant features, nanoparticle and surfactant properties. However, short lifetimes or potential toxicity of nanoparticles are some limitations of this technique. [ABSTRACT FROM AUTHOR]

Oil (or petroleum), consisting of a mixture of hydrocarbons, can leak from oil exploration, production, and use. Due to their complex mixture and interaction with the subsurface soil and water, they are hard to treat and can become a significant environmental concern. Rhamnolipid and sophorolipid biosurfactants, biologically produced surfactants, can be used to remove petroleum hydrocarbons. Nanoparticles have gained attention as promising materials for soil remediation. In this study, suspensions of Fe-Cu nanoparticles and biosurfactants were employed for the remediation of oil-contaminated soil. The results showed that these suspensions displayed a high oil removal rate from contaminated soil, which followed the first-order reaction. For batch experiments, the oil remediation efficiency was up to 84%. Optimum conditions to achieve the highest oil remediation performance included a rhamnolipid biosurfactant: nanoparticle ratio of 10:1 (wt%: wt%), pH 7, room temperature, and shaking speed of 60 rpm for 60 min. The remediation rate was improved by higher temperature and lower ionic strength. In the presence and absence of nanoparticles, rhamnolipid biosurfactant demonstrated a higher remediation efficiency than sophorolipid biosurfactant and ultraplex surfactant. The presence of other surfactants decreased the treatment productivity by 9-14% compared to using only rhamnolipid biosurfactant. Nanoparticles were reused with a remediation efficiency of 59% after three cycles by rhamnolipid biosurfactant. These results suggested that biosurfactants/Fe-Cu nanoparticle suspension showed promise for the remediation of oil-contaminated soil. [ABSTRACT FROM AUTHOR]