Bacterial and Archaeal Communities Influence on Methane Production

Animal manure is a low cost substrate suitable for biofuels production, such as hydrogen and methane, via anaerobic fermentation (Kyazze et al., 2007). Previous studies attributed the higher biogas yield from certain types of manure to the presence of a native microflora (Yeole and Ranande, 1992) and/or a higher or better carbon-nitrogen (C/N) ratio (Fulford, 1988). Probably the main difference between the different types of dung is related to the specific food the animal eat, which changes the overall C content and C/N ratio. We measured the C/N ratio and the native microflora of dung collected during one year. We related it to the biogas yield during anaerobic fermentation both for lactating and non-lactating buffaloes manure. The results showed that the buffalo manure was in both cases plenty of carbohydrates with a C percentage content based on the dry sample weight of 36.2 ± 2.0 % and 31.4 ± 1.5 %, respectively. The C/N ratio was 18.6 ± 1.5 % and 20.6 ± 2.9 %, respectively, and it changed during the different seasons because of the fluctuating N content. Indeed we found an acceptable correlation (R = 0.75) between the average environmental temperature and the C/N ratio of lactating buffalo manure. Neither the C or N content nor the C/N ratio appeared to be strongly correlated to the biogas production. The manure was fermented in batch reactors at 37 °C and pH = 6.0 after different pretreatments of the collected manure. The analysis of the microbial community was carried out using denaturing gradient gel electrophoresis (DGGE) to generate fingerprints of 16S rRNA genes (Carillo et al., 2012). The sequences analysis revealed that the Eubacterial community during fermentation in batch reactors was much more taxon rich and diversified than the Archeal community. The study of Archeal community instead showed the presence of only three main methanogen strains very active in methane production and largely predominant.