Mobility of biomass ash constituents as influenced by pretreatment and soil – An artificial weathering study

• Published in: Waste management (Elmsford) 2021-02, Vol.121, p.186-197
• Main Authors: Rehl, Erwin, Reimer, Kerry B., Rutherford, P. Michael
• Format: Article
• Language: English
• Subjects: Ash pretreatment; Biomass; Coal Ash - analysis; Gasifier; Serial batch extraction; Soil; Soil amendment; Soil Pollutants - analysis; Trace Elements - analysis; Waste management; Wood ash
• ISSN: 0956-053X; 1879-2456
• DOI: 10.1016/j.wasman.2020.12.014

•Research into treatment of fine-textured soils with biomass bottom ash is lacking.•Ash self-hardening improves handling but changes ash chemistry.•Ash hardening alters mobility of plant nutrients and trace elements of concern.•Adding ash to soil decreases mobility of most but not all trace elements of concern.•Bottom ash addition can provide safe, value-added benefit to fine-textured soil. Biomass ashes are potential soil amendments that reduce soil acidity and provide plant nutrients, but trace elements in ash may be leached from the solid phase, thereby posing environmental concerns. We determined the leachability of selected major elements, trace elements and anions from wood derived bottom ash generated from an updraft gasifier as influenced by ash pretreatments and the presence of soil via serial aqueous batch extraction. We found that self-hardening reduced initial solubility and reactivity of ash (i.e. lowered electrical conductivity), and reduced initial aqueous concentrations of Ba, Ca, Cu, Fe, Hg, Pb, Sr and Zn. But, hardening of ash increased initial aqueous concentrations of B, Cr, P, Se and SO42−. Although mixing ash into soil (5% ash by mass) generally decreased the mobility of most constituents, aqueous concentrations of P and As were increased relative to that of either ash-alone or soil-alone treatments. Overall, extract concentrations of constituents in various treatments were relatively low. Results of this serial batch extraction support the use of clean wood-derived bottom ash as a safe and environmentally suitable soil amendment.