Methane emissions from digestate at an agricultural biogas plant.

Baldé, H., VanderZaag, A.C., Burtt, S.D., Wagner-Riddle, C., Crolla, A., Desjardins, R.L., and Macdonald, D.J. (2016). "Methane emissions from digestate at an agricultural biogas plant.", Bioresource Technology, 216, pp. 914-922. doi : 10.1016/j.biortech.2016.06.031  Access to full text

Abstract

Methane (CH{SUB}4{/SUB}) emissions were measured over two years at an earthen storage containing digestate from a mesophilic biodigester in Ontario, Canada. The digester processed dairy manure and co-substrates from the food industry, and destroyed 62% of the influent volatile solids (VS). Annual average emissions were 19 g CH{SUB}4{/SUB} m-3 d-1 and 0.27 g CH{SUB}4{/SUB} kg-1VS d-1. About 76% of annual emissions occurred from June to October. Annual cumulative emissions from digestate corresponded to 12% of the CH{SUB}4{/SUB} produced within the digester. A key contributor to CH{SUB}4{/SUB} emissions was the sludge layer in storage, which contained as much VS as the annual discharge from the digester. These findings suggest that digestate management provides an opportunity to further enhance the benefits of biogas (i.e. reducing CH{SUB}4{/SUB} emissions compared to undigested liquid manure, and producing renewable energy). Potential best practices for future study include complete storage emptying, solid-liquid separation, and storage covering. Keywords: Digestate; Biogas plant; Anaerobic digestion; Methane; Backward Lagrangian Stochastic

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