Perspectives of Engineered Biochar for Environmental Applications: A Review

Research on using biochar for environmental applications has witnessed unprecedented advances in the past decade. Biochar is universally considered one of the best alternatives to store carbon to fight global warming. Thus, the sequential use of biochar in environmental remediation compatible with carbon sequestration is receiving growing attention. One of the reasons for such huge interest is the possibility to engineer biochar with targeted properties (e.g., surface area and chemistry) relevant to existing environmental issues. These properties can be achieved by selecting appropriate raw materials, processing conditions, carbonization technology, and the possibility of selecting postproduction modification approaches. The objective of this review is to summarize strategies to enhance biochar properties relevant to its use in environmental services (e.g., water purification, air/gas cleaning, construction materials, soil amendments) and the corresponding results on the use of this material for these applications. The main methods for enhancing biochar properties for environmental applications reviewed include activation (physical and chemical), oxidation, metal and metal oxide modification, metal-free heteroatom doping, and biological modification. Both modified and unmodified biochars have been used for soil amendments as adsorbents of pollutants in the aqueous phase (e.g., removal of P and N, heavy metals, and organic pollutants), adsorbents of pollutants in the gas phase (e.g., biogas cleaning), as a catalyst, as an additive for improving anaerobic digestion, and as an admixture to cementitious/construction materials, with promising results in all cases. New opportunities for using biochar are being reported as the science of biochar production, modification, and use advances.