Biochars as media for air pollution control systems: Contaminant removal, applications and future research directions

Abstract

biochars are low-cost and renewable biomaterials with several applications, including soil amendment, mitigation of greenhouse gas emissions, and removal of both in organic and organic contaminants in aqueous systems. An increasing body of recent evidence indicates that biochars can also remove gaseous chemical contaminants, such as those occurring in industrial flue gases. However, unlike other applications such as in agroecosystems, soil amendments,and aquaticsystems, comprehensive reviews on biochar applications inthe field of air pollution control arestilllacking.The current paper examine dexisting evidence to understand the nature of contaminants, particularly the gaseousones, potential applications, constraints, and future research need spertaining to biochar applications in air pollution control.The preparation of biochar sand their functionalized derivatives, and the properties influencing their capacity to remove gaseous contaminants are summarized. The removal capacity and mechanisms of various organic and inorganic gaseous contaminants by biochars are discussed. Evidence shows that biochars effectively remove metal vapours, particularly elemental mercury (Hg0), acidic gases(H2S, SO2, CO 2), ozone, nitrogen oxides (NOx), and organic contaminants including aromatic compounds, volatile organic compounds, and odorous substances. The mechanismsfortheremovalofgaseouscontaminants,including; adsorption,precipitation,and size exclusion were presented.Potential industrial application domain sincluderemediation of gaseous emissions from incinerators, waste-to-energy systems, kilns, biomass and coal-fired boilers/cookers, cremation, smelters, waste water treatment, and agricultural production systems including livestock husbandry. These industrial applications, coupled with the renewable, low-cost and sustainable nature of biochars, point to opportunities to further develop and scale up the biochar technology in the air pollution control industry. However, the biochar-based air filter technology still faces several challenges, largely stemming from constraints and several knowledge gaps, which were highlighted. Hence, further research is required to address these constraints and knowledge gaps before the benefits of the biochar-based air filters are realized.