Enrichment of acetogenic bacteria and acetoclastic methanogens for enhancing methane production in anaerobic treatment

Because of natural crude oil crisis and global warming issues, biomass-derived fuels (biofuels/bioenergy) are likely to have a future as a replacement for fossil fuel-based energy. Biogas, which is one of the most bioenergy produced by anaerobic digestion of organic polluted wastes, is accomplished by four major microbial groups: hydrolytic bacteria, acidogenic bacteria, acetogenic bacteria and methanogens. The efficiency is depended on the kinds of substrate and the balance of species and quantities of the microbes. Therefore, this study aims to enrich acetogenic bacteria and acetoclastic methanogens, which govern limiting step of biogas production, for use as a starter in further study. To enrich the acetogenic bacteria such as enrich butyric utilizing bacteria (BAUB) and propionic utilizing bacteria (PAUB), and acetoclastic methanogens (ACM), mixed culture obtained from anaerobic pond were fed by butyric acid, propionic acid, and acetic acid, respectively. After that, for 2 months, each enriched microbial group was investigated. The activity of substrate utilization and the number of microbial cell was enumerated. For microbial activity, 10% v/v of each enriched bacteria was incubated in a closed vial containing 75 ml of 20 mM of acetic acid, butyric acid, propionic acid, lactic acid and ethanol, which are intermediates in anaerobic digestion. Gas and liquid samples were taken and analyzed once a day. Results indicated that lactate was less utilized by all enriched microbial group. Enriched BAUB and enriched PAUB, which are acetogenic bacteria, preferred to utilize ethanol 0.1 and 0.334 g COD/g VSS/d, respectively and produced methane as 1.96 ml/d and 0.35 ml/d, respectively, whereas enriched ACM preferred to utilize acetic acid (0.48 g COD/g VSS/d) and produced methane as 1.95 ml/d. Enumerating by most probable number (MPN), microbial cells of enriched BAUB, enriched PAUB and enriched ACM are 9.3 x 10 sup 6, 7.4 x 10 sup 7 and 7.5 x 10 sup 5, respectively. These results showed the microbial activities and the microbial cells of the enriched microorganisms higher than that of mixed culture. Consequently, these enriched microorganisms will be studied further as a triculture to increase methane production and to reduce start-up period of anaerobic reactor.