Role of colloidal biochar in metals sequestration and transport

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Biochar a product of the natural pyrolysis of plants by fire, and via anthropogenic pyrolysis of numerous types of biomass for use in agricultural soil amendment, carbon sequestration, and water treatment technologies.  While biochar is well-studied in terms of its physical and chemical properties, a considerable fraction of it is comprised of nanoparticulate pyrogenic carbon (NPC).  Few studies have investigated the nature of NPC, and of those, only a handful have developed an understanding of the surface chemistry and reactivity of NPC towards metals and nutrients found in water and soils.  To address this gap, this research program proposes to extract NPCs from biochars produced from numerous types of biomass - including wood, grasses, sewage sludge, and municipal waste - and thoroughly characterize their composition, surface chemistry, and reactivity towards aqueous species.  Using wet chemical and spectroscopic approaches, surface complexation models will be developed to predict metals and nutrients binding to NPC across a wide range of environmental conditions.  Understanding the aging of biochar and degradation of NPCs in the environment is also a critical consideration in predicting their surface reactivity.  Using the same set of biochars discussed above, wet-dry accelerated aging will be applied to the bulk biochars to simulate up to 100 years of aging, and NPCs extracted from a time series of these aged biochars used to constrain differences in NPC surface chemistry over time - critical to understanding changes in metals and nutrients binding, and NPC transport through aquifers.  A considerable fraction (as much as 32%) of the annual wildfire-produced biochar is ultimately transported to the oceans, much of this via rivers and streams.  For this reason, we will also conduct photooxidation experiments to simulate the effect of sunlight on increased functionality and reactivity of NPC.  By combining these lines of inquiry with existing constraints on global pyrogenic carbon production, we aim to constrain the role of NPC in metals and nutrients transport in hydrologic catchments and to the global oceans, both in the present and in the geologic past.  Forest fires emerged in the Devonian and peaked in the Cretaceous and early to middle Permian, when atmospheric oxygen levels may have reached as high as 35%.  At these conditions, NPC may have had a considerable role - even as compared to clays and planktonic microorganisms - in the transport of aqueous species to estuaries.  If NPC is a source or sink of nutrients and bioessential metals, it may have had a direct and profound impact on primary productivity in estuaries by limiting or promoting the growth of microorganisms.  This, in turn, would have a direct effect on the degree of flocculation of cells with other particulate matter such as clays, iron oxyhydroxides, and black carbon, the formation of sediments, and ultimately the geochemistry of the marine rock record we observe today.