Evaluation of CH₄ and H₂ Yield with Different Mixtures of Digested and Fresh Buffalo Manure

Abstract

In this work hydrogen and methane production from buffalo manure has been scrutinized, by means of the anaerobic dark fermentation process and different process conditions. Animal manure characteristics are largely variable during different periods of the year because of the unavoidable changes in animal food supply and digestion apparatus of buffalo. A very significant variability was observed for water buffaloes manure, collected from the same supplier. This implies also a large variability in biogas production by anaerobic fermentation of such substrates. To overcome this variability, we mixed fresh with digested manure. This procedure is consolidated as regard methane production. We also investigated a similar strategy to optimize and stabilize H2 yield. We were able to find optimal process conditions for hydrogen and methane production with this type of substrate. The experiments have been run in batch mode. The products of fermentation, H2, CO2 and CH4, have been measured with a micro-gas chromatograph. Moreover the potential production of H2 has been maximized by thermally pre-treating the substrate and using a process temperature of the fermenter equal to 55 °C and an initial pH value of 5.5, while very high levels of potential production of CH4 have been obtained at 37 °C and with an initial pH of 7.0. The effect of different strategies has also been analyzed to highlight the different microbial community present in the substrate using the denaturing gradient gel electrophoresis (DGGE). This investigation has been carried out with the aim at isolating and selecting of natural bacterial species to use as inoculum to improve and stabilize the fermentation process of buffalo manure. More results concerning the microbial communities present in the substrate and responsible for biogas production are presented in a companion paper. Here we only list the main types of bacteria identified in the manure.