Methane and hydrogen sulfide production during co-digestion of forage radish and dairy manure

• Published in: Biomass & bioenergy Vol. 80; pp. 44 - 51
• Main Authors: Belle, Ashley J., Lansing, Stephanie, Mulbry, Walter, Weil, Ray R.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.09.2015
• Subjects: Anaerobic digestion; autumn; Biochemical methane potential (BMP); Biogas; carbon nitrogen ratio; Cover crop; cover crops; dairy manure; farmers; food availability; forage; harvest date; hydrogen sulfide; methane; methane production; radishes; Raphanus sativus L; solids; synergism; winter; Biogas; Biochemical methane potential (BMP); Raphanus sativus L; Anaerobic digestion; Cover crop
• ISSN: 0961-9534; 1873-2909
• DOI: 10.1016/j.biombioe.2015.04.029

Forage radish, a winter cover crop, was investigated as a co-substrate to increase biogas production from dairy manure-based anaerobic digestion. Batch digesters (300 cm3) were operated under mesophilic conditions during two experiments (BMP1; BMP2). In BMP1, the effect of co-digesting radish and manure on CH4 and H2S production was determined by increasing the mass fraction of fresh above-ground radish in the manure-based co-digestion mixture from 0 to 100%. Results showed that forage radish had 1.5-fold higher CH4 potential than dairy manure on a volatile solids basis. While no synergistic effect on CH4 production resulted from co-digestion, increasing the radish fraction in the co-digestion mixture significantly increased CH4 production. Initial H2S production increased as the radish fraction increased, but the sulfur-containing compounds were rapidly utilized, resulting in all treatments having similar H2S concentrations (0.10–0.14%) and higher CH4 content (48–70%) in the biogas over time. The 100% radish digester had the highest specific CH4 yield (372 ± 12 L kg−1 VS). The co-digestion mixture containing 40% radish had a lower specific CH4 yield (345 ± 2 L kg−1 VS) but also showed significantly less H2S production at start-up and high quality biogas (58% CH4). Results from BMP2 showed that the radish harvest date (October versus December) did not significantly influence radish C:N mass ratios or CH4 production during co-digestion with dairy manure. These results suggest that dairy farmers could utilize forage radish, a readily available substrate that does not compete with food supply, to increase CH4 production of manure digesters in the fall/winter. •Effect of co-digesting forage radish and dairy manure on CH4 and H2S determined.•Forage radish had 1.5 times more CH4 production than dairy manure.•Radish fraction in mixture had a positive linear relationship with CH4 production.•Harvest date of the radish crop did not influence CH4 production.