Interaction of pristine and mineral engineered biochar with microbial community in attenuating the heavy metals toxicity: A review

Soil ecology may be economically altered via microbiota and nutrient management in an organic agricultural setting. While biochar may be used to promote microbial activity in the soil, its function in the immobilization and detoxification of heavy metals from soil and wastewater has received considerable attention in recent decades. As compared to the pristine biochar, its enrichment with essential nutrients such as iron (Fe²⁺), manganese (Mn²⁺) and its co-application with other additives has demonstrated encouraging outcomes for microbial colonization and treatment of polluted soil and wastewater. This review discusses the recent findings to evaluate the efficiency of biochar (BC)/mineral enriched biochar (MEB) for nutrient enrichment as well as mechanisms of heavy metal immobilization/sorption. A comparison among different studies revealed the similarity of mechanisms involved in metal immobilization by both types of biochar (BC or MEB), however, the variation was attributed to BC feedstock and type of elemental enrichment. With bacterial combinations to BC/MEB, high pH fluctuations and enzymatic action were appeared to be significantly involved in metal immobilization; similarly, for fungal combinations with BC/MEB, mycelium and metal sorption while with algae association to BC/MEB; ion exchange, chelation and surface adsorption were reported to be significantly involved in metal immobilization. The comprehensive review of literature would be a guide to foster the appropriate selection of biochar engineering technology for nutrient management and to control the metal toxicity in degraded soil and wastewater media.