4. Summary
Biochar has the potential to remediate soil and water contaminated with various organic/inorganic contaminants. Studies have demonstrated the biochar capability to serve as a green environmental sorbent. However, one type of biochar may not be appropriate for all contaminants removal. A number of variables are involved in determining the exact role of a biochar for environmental management. Pyrolysis condition and feedstock type are the main factors influencing biochars sorption behavior. The complex nature of soil systems compared to aquatic systems has limited biochar applications to soil.
Investigations have shown that biochar could increase the mobility of some toxic metals (particularly anionic metals) in soils. Therefore, the examination of the biochar efficacy on the mobility/stabilization of contaminants in multi-element contaminated soils should be carried out. It is also important to predict the metal stabilization mechanism of biochar to determine the long-term effectiveness of the remediation technology. In this respect, the recent research has been performed using state-of-the-art analytical techniques such as XAFS spectroscopy. Moreover, long-term field experiments on biochar application to contaminated soils are needed. The distinct physical architecture and molecular composition of biochar will be helpful in determining its long-term functions in soil and water.
Undoubtedly, the biochar use as an environmental sorbent can have strong implications. For example, activated biochar could replace activated carbon, as it has equivalent or even greater sorption efficiency for various contaminants due to its cost-effective production from waste resources such as agricultural wastes. This would make biochar less expensive compared to activated carbon. The estimated break-even price for biochar is US $246 t−1, which is approximately 1/6 of commercially available activated carbon (∼US $1500 t−1) (McCarl et al., 2009 and Ahmad et al., 2012a). Converting waste biomass into biochar will also promise an effective solution for the safe and beneficial disposal of a number of materials. In particular, solid waste material such as animal litter and sewage sludge will be removed of all active pathogens through conversion to biochar. The evolved volatiles and gases can be captured and condensed into bio-oil and syngas during biochar production, which can be further used as a source of renewable energy. Applying biochar to remediate contaminated soil will additionally provide a means of C sequestration, leading climate change mitigation.