demonstration of biogas production using low moisture content

Results and Discussion
diffusion through the threads used to seal the cap onto the container. Samples analyzed immediately after
removal from the water had the highest methane contents.
Total biogas volumes for Experiment 3 were variable within the same moisture content (Figures 10a-10e and
Table 3). In an experiment comparing biogas production between dry and fresh dairy manure, Chen et al.
(1988) found that varying levels of methane were produced because of microbial variations. This is supported
by Hashimoto et al. (1981) who stated that the degree of contamination by inorganics also affect ultimate
methane yields (B 0 ). The biogas production volumes for Experiments 1 and 2 are significantly lower than
previously published values for beef cattle manure (Safley et al., 1992). Safley states that B 0 should be
approximately 0.33 m 3 /kg VS. As expected, production volumes increased as moisture content increased, with
minimal production below 40% moisture content for both Experiment 1 and Experiment 2. As shown in Table 1,
there were no statistically significant differences in mean biogas production rates among the first five moisture
contents, but mean biogas production rates were significantly higher for the two highest moisture contents for
Experiment 1.
Field Demonstration Project
The first cell began biogas production on August 1, 1999, and ceased quickly on October 23, 1999. During the
12 week period, the first cell produced a total of about 1,500 m 3 (53,000 ft 3 ) of biogas with a maximum
methane concentration of 52%. This was considerably less than was produced in the laboratory experiment 3,
thus we believe that all of the volatile solids have not been expended, and biogas production should occur
again during the summer 2000 as soon as the temperature is warm enough.
Biogas production volumes and methane concentrations are shown in Table 4 and plotted in Figure 11. A
photograph of the biogas cell when it was full of biogas is shown in Figure 12.
Shown in Figure 13 is the temperature of the manure within cell no. 1 since it was loaded in January, 1999.
Initially the manure temperature was about 25° C (77° F), but temperatures dropped rapidly during the first
month as the manure became anaerobic. Temperatures began rising during the summer months, a result of
warmer ambient temperatures, and peaked around the first of August at 22.4° C (72° F). The manure
temperature dropped below 15° C (59° F) in the middle of October and has remained below 15° C until the
present (May, 2000). The pH of the manure in cell 1 was tested immediately after cessation of biogas
production. The pH of the three samples was 7.26, 6.98, and 7.00.
The total volatile solids in cell 1 was 1.55 x 10 7 g. The total volume of biogas produced in cell 1 was 1.51x 10 6 L
for the 12 weeks of production, which equates to a biogas production rate of 0.10 L/g VS.
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