Anaerobic production of methane and aminolevulinic acid using mixed cultures of microorganisms

The purpose of this research was to maximize the production of methane (CH4) and aminolevulinic acid (ALA) as a value-added co-product from anaerobic digestion by utilizing different experimental conditions such as substrate composition, substrate pH, and inhibitor concentration. Methane is in increasing demand as it is used as a renewable fuel to produce energy. Aminolevulinic acid has applications as a biodegradable herbicide, insecticide, and in the diagnosis and treatment of cancer.; Optimization of CH4 production was studied by focusing on the substrate pH and by utilizing different substrate combinations. The substrates used were acetic acid, glucose, acetic acid+glucose, and acetic acid+H 2 at initial pH values of 4.5, 5.0, 6.0, and 7.0. Methane production via H2/CO2 by autotrophic methanogens was evaluated by adding 5%--10% H2 in the gas headspace or providing H 2 from glucose degradation. It was expected that additional CH 4 would be produced from H2/CO2 at pH 4.5 as more aqueous CO2 is available at this pH. Results showed that acclimation of cultures reduced the lag phase and increased CH4 production rate at an initial pH of 4.5. The cells were able to reduce the chemical oxygen demand (COD) regardless of the initial pH. However, the addition of H 2 by injecting H2 manually or supplying glucose did not increase CH4 yield at a low pH.; The production of ALA and CH4 was promoted by utilizing different substrates at different inhibitor concentrations. The substrates used were acetic acid, glucose, methanol, and methanol+glucose in the presence of levulinic acid, an inhibitor known to facilitate ALA accumulation. Results showed the concentration of ALA accumulated (338 muM) was higher than those produced (200 muM) by pure culture of Methanobacterium thermoautotrophicum in H2/CO2 medium as reported in previous literature. In addition, approximately 0.016 moles of CH4 was produced per gram of COD reduced.