Chemical Characterization of Ash from Gasification of Alfalfa Stems: Implications for Ash Management

Electricity generation from biomass is an attractive option from an environmental perspective. Pilot studies have indicated that alfalfa (Medicago sativa L.) stems are suitable feedstock for energy generation via gasification. Detailed information on chemical characteristics of the ash generated from gasification of alfalfa stem is required to develop environmentally and economically sound ash management strategies. Alfalfa fly and bottom ashes were characterized with respect to chemical properties that are important in developing ash management practices with emphasis on beneficial utilization as a soil amendment. Mean concentrations of total C, K, Ca, and Cl were 424, 120, 85, and 26 g kg−1, respectively, in fly ash. In bottom ash, the mean concentrations of C, K, and Ca, were 63, 61, and 193 g kg−1. Concentrations of total Pb, As, Cd, Co, and Se were below detection limits in both ash types. Naphthalene ranged from 6.2 to 74 mg kg−1, but concentrations of many other polyaromatic hydrocarbons were low or below mg kg−1 detection limits. Available K and P in fly ash were 90 to 120 and 8 to 10 g kg−1, respectively. Mean CaCO3 equivalent value of fly ash was 400 g kg−1, its electrical conductivity (EC) and pH were 127 dS m−1 and 11.5, respectively. These results suggest that when managed properly, gasified alfalfa ash could potentially be utilized as a beneficial soil amendment with few potential environmental concerns.