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Anaerobic co-digestion of forage radish and dairy manure in complete mix digesters

Ashley J. Belle, Stephanie Lansing, Walter Mulbry, Ray R. Weil
Bioresource technology 2015 v.178 pp. 230-237
anaerobic digestion, biogas, cover crops, cows, dairy manure, digestion, electricity, farmers, feedstocks, forage, hydrogen sulfide, income, methane, methane production, radishes, sales
Pilot-scale digesters (850L) were used to quantify CH4 and H2S production when using forage radish cover crops as a co-digestion feedstock in dairy manure-based digesters. During two trials, triplicate mixed digesters were operated in batch mode with manure-only or radish+manure (27% and 13% radish by wet weight in Trial 1 and 2, respectively). Co-digestion increased CH4 production by 11% and 39% in Trial 1 and 2, respectively. As H2S production rapidly declined in the radish+manure digesters, CH4 production increased reaching high levels of CH4 (⩾67%) in the biogas. Over time, radish co-digestion lowered the H2S concentration in the biogas (0.20%) beyond that of manure-only digestion (0.34–0.40%), although cumulative H2S production in the radish+manure digesters was higher than manure-only. Extrapolated to a farm-scale (200 cows) continuous mixed digester, co-digesting with radish could generate 3150m3CH4/month, providing a farmer additional revenue up to $3125/month in electricity sales.