Abstract
AbstractAs a waste‐derived soil amendment with a long history, biochar has received extensive attention for its capability to improve soil fertility/health; remove or immobilize contaminants in soil, water and air; and mitigate climate change. With the aim of producing engineered biochars with excellent performances, new trends in biochar pyrolytic production and modification strategies have emerged. This review critically summarizes novel pyrolysis methods (e.g., microwave‐assisted pyrolysis, co‐pyrolysis and wet pyrolysis) and modification approaches (e.g., mineral modification, photocatalytic modification, electrochemical modification) with a focus on (a) the mechanisms involved in environmental remediation processes including soil immobilization, contaminant adsorption and catalytic oxidation; (b) effects of feedstock and pyrolysis conditions on physicochemical properties; (c) sustainability considerations in novel modification and pyrolysis strategies; and (d) the feasibility of extrapolating the results from wastewater treatment to soil remediation. It is argued that in order to achieve the maximum net environmental benefits, ‘greener’ modification methods are warranted, and the risks associated with pyrolysis of contaminated feedstock in soil amendment and contaminant sorption can be minimized through various novel approaches (e.g., co‐pyrolysis). Furthermore, novel pyrolysis methods can be combined with emerging modification strategies to synthesize more ‘effective’ biochars. Considering the similar aims of modification (e.g., increase surface area, introduce oxygen‐containing functional groups, increase aromaticity), the applicability of several novel approaches could in future can be expanded from contaminant adsorption/degradation in aqueous media to soil remediation/fertility improvement.
Highlights
Biochar has been used in environmental applications for millennia
It is hypothesized that biochars produced through steam-assisted pyrolysis could effectively immobilize organic aromatic contaminants such as polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs), since a decrease of oxygen-containing functional groups may result in enhanced π-π interactions, as has been described above
Various biochar modification methods aimed at improving the pore structure, increasing certain functional groups, promoting the generation of activated oxygen species and reducing risks associated with contaminants have been proposed and tested
Summary
Biochar has been used in environmental applications for millennia. Pre-Columbian Amazonians produced biochar by covering burning biomass with soil, forming a black soil (terra preta de índio) that can be used to increase soil fertility (Ahmad et al, 2014; Glaser et al, 2002; Palansooriya et al, 2020). In order to synthesize engineered biochars with excellent performances, more studies have recently been conducted to investigate the effects of various modification strategies on biochar properties (Figure 1) (Sajjadi et al, 2019; Wu et al, 2019; Yang et al, 2019a). Many novel attempts have only explored the contaminant sorption or degradation performances of engineered biochars in aqueous media to date. The aims of this review are to 1) summarize recent advances in biochar pyrolytic production and modification, with a focus on the relationship between biochar properties and remediation mechanisms; 2) unveil new trends in biochar utilization in environmental applications with a focus on sustainability considerations, and 3) investigate the feasibility of expanding the applications of some novel strategies into soil remediation/fertility improvement. The combination of novel strategies and the extension of biochar applicability to various fields are suggested, and several research directions are proposed
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