Manure gases; Methane
The effects of pH upon methane production from anaerobic digestion of dairy cattle manure were investigated. One liter digesters were maintained by daily adjustment at the following pH levels: 7.6, 7.0, 6.0, 5.5, and 5.0. After 33 weeks of incubation the working volume of the digesters was increased to 3 liters. Digesters were incubated on a rotary shaker at 37°C. Digesters were loaded at the desired volatile solids concentrations, without an inoculum, and maintained from day one by daily additions and withdrawals to achieve a 3 day retention time. After 50 weeks of operation the manure from a second dairy was utilized as substrate.
Active digestion was achieved at all pH levels except pH 5.0. Biogas production was evident in 4 to 6 days after incubation. Biogas production was highest at pH 7.0 with manure from both dairies (3.047 ± 0.403 liters per liter of digester per day with Dairy II manure and 1.43 ± 0.09 liters per liter per day with Dairy I manure). Methane production was also highest at pH 7.0 (1.43 ± 0.292 liters per liter of digester per day with Dairy II manure and 0.611 ± 0.057 liters per liter per day with Dairy I manure although the highest percentages of methane in the biogas occurred at pH 7.6 (65.9 ± 5.2 from Dairy I manure and 50.4 ± 4.6 from Dairy II manure). Dairy II manure produced significantly more biogas and methane at all pH levels. This increased production could not be attributed solely to differences in volatile solids concentrations of the two substrates.
Total volatile acid concentrations were highest at the highest pH levels and were higher with Dairy II manure as a substrate. Digesters at all pH levels had volatile acid concentrations above 2000 mg/liter normally considered inhibitory for methane bacteria (2314-2890 mg/liter with Dairy I manure and 5.708-7.434 mg/liter with Dairy II manure).
The results reported here indicate that stable methane digestion of dairy cattle manure can be established maintained at 37°C with a 3 day retention time. Digestion at pH levels as low as 5.5 continued for periods up to 24 months without a failure. High levels of volatile acids did not cause digester failure. Characteristics of the manure have significant effects on biogas and methane production.
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Wodzinski, Rudy J.
Master of Science (M.S.)
College of Arts and Sciences
Length of Campus-only Access
Masters Thesis (Open Access)
Stafford, Mary G., "The Effect of pH on Methane Production from Dairy Cattle Manure" (1982). Retrospective Theses and Dissertations. 659.