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Physical and chemical characterization of waste wood derived biochars

Erin N. Yargicoglu, Bala Yamini Sadasivam, Krishna R. Reddy, Kurt Spokas
Waste management 2015 v.36 pp. 256-268
acceptable risk, adsorption, biochar, biomass, carbon, chemical analysis, electrical conductivity, feedstocks, gases, gasification, groundwater, heavy metals, hydraulic conductivity, hydrogen, nitrogen, nutrients, organic matter, oxygen, pH, particle size distribution, polycyclic aromatic hydrocarbons, porosity, pyrolysis, redox potential, specific gravity, surface area, temperature, waste management, waste wood, water holding capacity, zeta potential, Illinois
Biochar, a solid byproduct generated during waste biomass pyrolysis or gasification in the absence (or near-absence) of oxygen, has recently garnered interest for both agricultural and environmental management purposes owing to its unique physicochemical properties, such as its high surface area and porosity, and ability to adsorb a variety of compounds, including nutrients, organic contaminants, and some gases. Physical and chemical properties of biochars are dictated by the feedstock and production processes (pyrolysis temperature, conversion technology and post-treatment processes, if any), which vary widely across commercially produced biochars. In this study, several commercially available waste wood derived biochars are characterized for physical and chemical properties that can signify their relevant environmental applications. Parameters characterized include: physical properties (particle size distribution; specific gravity; density; porosity; surface area); hydraulic properties (hydraulic conductivity and water holding capacity); and chemical properties (organic matter and organic carbon contents; pH, oxidation-reduction potential and electrical conductivity; zeta potential; C/H/N elemental analysis; PAHs, heavy metals, and leachable PAHs and heavy metals). A wide range of fixed C (0 - 47.8%), volatile matter (28 - 74.1%), and ash contents (1.5 - 65.7%) were observed among tested biochars. A high variability in surface area (0.1 - 155.1 g/m2) and PAH and heavy metal contents among commercially available biochars was also observed (0.7 to 83 mg kg-1), underscoring the importance of pre-screening biochars prior to usage. Production conditions appear to dictate PAH content - with the highest PAHs observed in biochar produced via fast pyrolysis and lowest among the gasification produced biochars. However, all PAHs detected in the solid biochars are below groundwater acceptable levels (for Illinois, USA).