Review on arsenic removal using biochar-based materials

Arsenic (As) is a ubiquitous carcinogen element, occurring due to geogenic and anthropogenic actions and posing major global public health concerns. This review work significantly summarized the current state of knowledge for arsenic-contaminated water treatment. Firstly, this paper insight a brief understanding of arsenic speciation, toxicity, and accumulation in the food chain, and secondly, explains the adsorption techniques for As remediation from the contaminated water. Arsenic adsorption, using biochar-based sorbents, is summarized as an efficient and economically feasible approach. Biochars, renewable carbonaceous and sustainable materials, synthesized through pre/post-pyrolysis treatment of biomass under limited oxygen supply conditions, resulting in high surface area, dual-porosity, surface charge, and enhanced functional groups. Thirdly, this review discusses various factors, such as acidic pH, initial concentration, biochar dose, co-existing ions, and temperature, including regeneration and reusability of biochar-based sorbents. Arsenic adsorption increases at 2-6 pH and decreases until pH 10. In aqueous solution, pH-influenced As species, as H2AsO4- and HAsO42- dominate in the range of 3-6 pH, and AsO43- are primarily present in alkaline solution. Thus, electrostatic interactions and surface complexation are dominating mechanisms occurring at arsenic-biochar interfaces in aqueous solutions. Lastly, mechanistic understanding for arsenic adsorption onto biochar materials has been discussed, considering equilibrium adsorption isotherms, kinetics, and thermodynamics analysis. In conclusion, this review also highlighted major challenges and future scope relevant for implications of biochar sorbents in continuous flow systems to scale up for commercial and industrial purposes.