Microbial diversity in two-stage anaerobic digestion system using two different substrate : organic waste and biodiesel wastewater

Abstract

This study aimed to analyze microbial diversity of biogas production in two-stage anaerobic digestion system using two different substrates: organic waste and biodiesel wastewater. The microbial diversity was analyzed by using polymerase chain reaction-denaturant gradient gel electrophoresis (PCR-DGGE) and 16S rDNA clone library. For bacterial communities, DGGE profiles of biodiesel wastewater-feeding reactor indicated that the band from acid tank was different from the band from methane tank. It is known that conditions can affect the species of microbial community. In comparison between using organic waste and biodiesel wastewater as substrate, the DGGE profiles obtained were different. It is known that type of substrate can affect the species of microbial community. While the profile of archaeal community showed a little bit different in each tank and each substrate. Major bacterial groups represented in the clone library of acid tank using organic waste as substrate were Pseudomonas acephalitica (94%) and uncultured Firmicutes bacterium (6%). In methane tank using organic waste as substrate, major bacterial groups represented Weissella cibaria (28%), Clostridium jejuense (18%), uncultured bacterium (15%), Sedimentibacter sp. (15%), Clostridium sp. (11%), uncultured Firmicutes bacterium (8%) and Tissierella praeacuta (5%). In the clone library of acid tank using biodiesel wastewater as substrate were assigned to Klebsiella sp. (69%) and Sphingomonas sp. (31%) while the clone library of methane tank were assigned to uncultured Chloroflexi bacterium (76%), uncultured bacterium (22%) and Pseudomonas putida (2%). In addition, this study assessed the genes involved in biogas production: hydrogenase genes and methyl-coenzyme M reductase genes. These genes could be detected in acid tank and methane tank of two reactors. Finally, the real-time PCR was carried out to quantify the mcrA genes from reactor using biodiesel wastewater as substrate. For the result, the amount of mcrA gene in methane tank tended to increase. On the contrary, the amount of mcrA gene was decrease in the last week. For production of biogas in methane tank tended to increase in every week and dropped in the last week. The quantification of mcrA genes in the system revealed a similar pattern as accumulated biogas production. For acid tank, the amount of mcrA genes in week 0 and week 1 was similar. For week 2, the amount of mcrA genes in sludge was decrease because pH in the system was decreased which can inhibit the activity of metanogens. On the contrary, the amount of mcrA gene in week 3 to last week tended to increase because pH was higher. Based on the data obtained, it was useful for the startup and control of biogas digesters to increased ability of biogas production.