Biochar-Assisted Bioengineered Strategies for Metal Removal: Mechanisms, Key Considerations, and Perspectives for the Treatment of Solid and Liquid Matrixes

Biochar has drawn the scientific community’s attention during the last few years due to its low production value and unique physicochemical properties, which are helpful for numerous applications. The development of biotechnological processes for the remediation of heavy metal environmental pollution is one central research avenue in which biochar application has shown promising results, due to its positive effect on the bacteria that catalyze these activities. Biochar stimulates bacterial activity through adsorption, adhesion, electron transport, and ion exchange. However, before biochar implementation, a complete understanding of its potential effects is necessary, considering that those interactions between biochar and bacteria may help improve the performance of biological processes designed for the remediation of environmental pollution by metals, which has been historically characterized by limitations related to the recalcitrance and toxicity of these pollutants. In this review, the key biochar–microorganism interactions and properties of unmodified biochar with the potential to improve metal bioremediation in both solid (mine tailings, polluted soils) and liquid matrixes (metal-laden wastewaters) are summarized. Knowledge gaps regarding the mechanisms involved in remediation strategies, the effect of long-term biochar use and the development of improved biochar technologies and their combination with existent remediation technologies is summarized. Additionally, an up-to-date summary of the development of biochar-assisted bioengineered strategies for metal passivation or removal from solid and liquid matrixes is presented, along with key perspectives for the application of biochar-based biotechnologies at full scale during the treatment of mining effluents in the real scale.