Environmental pollution management using biochar-mineral complexes Dr. Ondřej Mašek, School of Geosciences, University of Edinburgh,
[email protected] Dr. Margaret Graham, School of Geosciences, University of Edinburgh A project summary Biochar and biochar-mineral complexes (BMCs) are promising materials that can be used simultaneously in environmental pollution management and carbon sequestration. This project will identify and optimise sustainable production and applications of BMCs. Project background Almost any form of organic material, such as crop residues, forestry byproducts, anaerobic digestate, animal manure, and sewage sludge, can be converted to biochar by pyrolysis under a wide range of processing conditions. The key process parameters include the peak temperature, holding time at peak temperature, heating rate, etc. Biochar typically consists of both carbon and mineral fractions. Although, the carbon fraction has been generally considered to determine the biochar’s properties and applications, an increasing body of research has demonstrated that mineral components inherent in biochar also influence the properties and thus biochar applications. The variability in feedstock and pyrolysis conditions has a significant effect on the content and form of minerals in biochar (Zhao et al., 2013). In general, the mineral content of sludge biochar is normally above 30%, and can reach up to 90%. For manure biochar, the mineral content ranges from 20% to 80%. Biochars derived from plant residues contain far fewer minerals than sludge and manure biochars, with content mostly below 20%. These mineral compounds exist either as discrete mineral phases or are associated with the surface functional groups of biochars. The mineral content of biochar generally increases with increasing pyrolysis temperature. Mineral elements, such as K, Na, Si, Mg, and Ca, can be involved in the carbonization processes of biomass, thus influencing the pyrolysis reactions and products. Minerals can also influence the surface electrochemistry and ion-exchange properties of biochar (Buss et al., 2015). An increasing number of studies have shown that both carbon and mineral fractions of Fig. 1. Mineral-components related mechanisms of biochar biochar can contribute to for removal of heavy metal (a) and organic contaminant (b). immobilization of heavy metals and (Xu et al., 2017) organic pollutants (Xu et al., 2017). For biochars with a low mineral content, the sorption of heavy metals occurs mainly through the formation of surface complexes between heavy metals and organic O-containing functional groups on biochar. However, for biochars rich in minerals interactions between heavy metals
and mineral components may be the dominant factor in sorption. Minerals could be responsible for up to 90% of metal removal by biochars. Recently, minerals have been also found to enhance the carbon retention and stability of the solid product (biochar) of biomass pyrolysis for carbon sequestration. It has been reported that minerals could catalyze several thermal reactions and greatly alter the product distribution and composition during pyrolysis. Overall, inherent minerals should be fully considered while determining the most appropriate application for any given biochar. A thorough understanding of the role of biochar-bound minerals in different applications will also allow the design or selection of the most suitable biochar for specific applications based on the consideration of feedstock composition, production parameters, and post-treatment. Key research questions 1) What are the mechanisms behind mineral-induced biochar carbon stabilisation? 2) How can the role of minerals in biochar be optimised to maximise carbon stabilisation and environmental pollution removal potential in terms of mineral selection and incorporation into biochar? 3) What are the suitable and sustainable sources of mineral-rich organic materials and mineral additives for biochar production? Methodology and timeline Year 1. Research training. Familiarization with pyrolysis processes and technologies. Literature review and sample collection of minerals, high-mineral content organic residues (e.g., sludges, digestates), and biomass. Quantitative and qualitative assessment of mineral content and speciation in gathered samples. Year 2. Production and characterisation of biochar and biochar-mineral composites (BMCs) from selected feedstock. Training on advanced analytical techniques. Identification and analysis of interactions between minerals and organic carbon structures. Testing of efficacy of BMCs in environmental pollution management applications (laboratory studies). Year 3. Optimisation of BMCs and their environmental applications. Experimental testing of BMCs and their effects on soil properties and plants to identify potential benefits and risks. Re-activation, subsequent use of spent BMCs. Training A comprehensive training programme will be provided comprising both specialist scientific training and generic transferable and professional skills. Advanced training in laboratory analytical techniques, data management and analysis will be provided. In addition, there will be opportunities to attend international environmental and biochar summer schools and workshops (e.g., organised by the IIES network, of which both Dr. Masek and Dr. Sohi are members and GreenCarbon H2020 project). Requirements Students should have at least an upper 2.1 degree in a related engineering or science subject. All training will be provided, but lab-based skills and experience with analytical techniques would be an advantage. The ideal student will have interest in multidisciplinary environmental and engineering research and be opened to collaboration with researchers from different disciplines. Further reading Buss, W. et al. (2015) ‘Inherent organic compounds in biochar–Their content, composition and potential toxic effects’, Journal of Environmental Management, 156, pp. 150–157. doi: 10.1016/j.jenvman.2015.03.035. Xu, X. et al. (2017) ‘Indispensable role of biochar-inherent mineral constituents in its environmental applications: A review’, Bioresource Technology, 241, pp. 887–899. doi: 10.1016/j.biortech.2017.06.023. Zhao, L. et al. (2013) ‘Heterogeneity of biochar properties as a function of feedstock sources and production temperatures’, Journal of Hazardous Materials. Elsevier B.V. doi: 10.1016/j.jhazmat.2013.04.015.
