Recent advancements in biochar applications for effective removal of various toxicants from wastewater: a Review

Biochar, a carbon-rich material, is usually prepared by thermochemical processes from a diversified biomass or organic waste. It is a plentiful and environmentally sustainable product commonly used as an adsorbent to eradicate various organic contaminants, including heavy metals and nutrients, from wastewater. When compared with conventional biochar, the engineered or modified biochar usually possesses improved properties, including developed surface area with high adsorption capacity or more surface functional groups (SFG) chemically. This makes it a potential material for a variety of wastewater treatment applications. The present paper summarizes research work of various investigators and researchers pertaining to biochar and modifications of its properties in terms of its synthesis, usage, and regeneration as compared with conventional biochar. It is also inferred that precursor material composition, preparation parameters, and modification methods have a major impact on biochar properties. The chemical alkali treatment produces the most surface-functionalized biochar. Also, the chemical changes that outperform steam activation enhance the biochar surface functioning. It is reported that biochar composites, when treated with alkali or that have been impregnated with nanomaterials, enhance the adsorption of different types of wastewater and thereby prove to be very beneficial and cost-effective. Similarly, biochar surfaces with acidic treatment have a higher concentration of oxygenated functional groups. The present review work further depicts the modified biochar process as the most economical and ecologically friendly method for removing toxic pollutants from different types of wastewater. It is further concluded that for heavy metals and anionic pollutants, the sorption equilibrium is best designated by the Langmuir isotherm model. Also, for emerging contaminants, the Freundlich isotherm model is more appropriate, while the pseudo-second-order model best captures the sorption kinetics for all pollutants.