Use of rumen fluid to inoculate dairy excrement for bio-fuel production by anaerobic digestion
Ross, Carrie Lynn
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The major limitations with anaerobic digestion of dairy waste are related to its initial rate of microbial activity and concentrations of volatile organic compounds as substrates for methanogenesis. One area of interest is the development of a mixed microbial inoculum to more quickly establish fermentative methanogenic activities to aid in the efficiency and effectiveness of the anaerobic digestion process. This project investigated the use of fresh rumen fluid from cattle as a source of mixed microbial inoculum using the model bio-methane potential system to enhance methane production of anaerobic digestion in batch culture. Experiments were conducted with varying levels of fresh rumen fluid as inoculum (1 to 30% of the bioreactor volume) as compared to treatments with pasteurized rumen fluid that relied on the dairy fecal excrement as the source of inoculum. Model systems for testing inoculation for anaerobic digestion were evaluated. Incubations were conducted with different dilutions and extracts of dairy excrement as substrates including those with fresh material, as well as dried and liquid fractions of processed excrement. Processing dairy excrement was found to manipulate the concentration of low molecular weight volatile organic compounds as substrate. Vessels used as model anaerobic digesters were evaluated including 160 mL septum bottles, 2 L Erlenmeyer flask, and 300 mL Mason jars. Incubations were conducted from 2 d to 16 d over the course of several experiments. Overall results from the several experiments concluded that viable rumen fluid inoculum, as low as 10% of the total incubation volume, can substantially enhance (12-89%) the production of methane as compared to microbial populations inherently present within the fecal excrement alone. It was also concluded that dairy excrements processed to contain higher levels of volatile organic compounds in a liquid fraction enhanced the methane production of anaerobic digestion as compared to dried excrement and that the septum bottle system provided the most useful model system for evaluating viable rumen fluid as inoculum for anaerobic digestion of dairy excrement.