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Biochar increases biogas production in a batch digester charged with cattle manure

TitleBiochar increases biogas production in a batch digester charged with cattle manure
Publication TypeJournal Article
Year of Publication2012
AuthorsInthapanya, Sangkhom, Preston TR, and Leng R. A.
JournalLivestock Research for Rural Development

Two in vitro incubation experiments were conducted to test the hypothesis that  biochar  would serve as support media for biofilm development in a  biodigester and would as a result  increase the yield of biogas whether added separately or enclosed in a nylon bag  The treatments in experiment 1 were: control (no biochar), biochar added at 1% of the substrate DM in the biodigester, biochar added at 3% of the substrate DM in the biodigester. The substrate was fresh manure from cattle fed dried cassava root, fresh cassava foliage and urea. Proportions of water and manure were arranged so that the manure provided 5% of the solids in the biodigester. Gas production was measured daily over the fermentation period of 30 days; methane in the gas was measured after 21 and 28 days. In experiment 2, a 2*2 factorial arrangement with 4 replications was used to compare level of biochar: 1% of solids in the digester or none; and presence or absence of a cloth bag in the biodigester. The fermentation was followed over 21 days with daily measurement of gas production and content of methane in the gas at the end of the fermentation.

In experiment 1, incorporation of 1% (DM basis) of biochar in the biodigester increased gas production by 31% after 30 days of continuous fermentation; there were no benefits from increasing the biochar to 3% of the substrate DM. The methane content of the gas increased with the duration of the fermentation (24% higher at 28 compared with 21 days) but was not affected by the presence of biochar in the incubation medium.  In experiment 2, adding 1% of biochar (DM basis) to the substrate increased gas production by 35%, reduced methane content of the gas by 8%, increased the DM solubilized (by 2%) and increased methane production per unit substrate solubilized by 25%. Presence of the cloth bag increased gas production when it also contained biochar but decreased it when added to the biodigester without biochar. There was a similar interaction for methane produced per unit substrate solubilized.