BIOGAS FROM WATER BUFFALO MANURE. INVESTIGATION OF THE H2-PRODUCTION POTENTIALITY

The growing global environmental concerns related to the use of fossil-derived fuels together with the political instability in major oil exporting countries have drastically prompted the interests for alternative environmental-friendly energy sources. Biogas from waste products is one of them. This work experimentally investigates the production of mixture of bio-methane and bio-hydrogen from water buffalo manure anaerobic dark fermentation. Bio-methane production through anaerobic fermentation of animal manure is already broadly applied. In this process, hydrogen is usually not available because it is rapidly converted into methane by methanogenic microorganisms. Indeed, manure usually contains both H2-producer and H2-consumer bacteria, and the latter prevails on the former. Anyway, the selection of opportune pre-treatment processes, inhibiting the methanogenic activity, and adequate fermentation parameters can greatly enhance the H2 production. In this work, the dark anaerobic fermentation of water buffalo manure, used both as inoculum and substrate, is performed in 250 ml batch reactors. The effect of different parameters on biogas composition is investigated. In particular, in order to maximize the H2 production we considered different initial fermentation pH values (5 and 6), temperatures (37°C and 55°C) and manure thermal pre-treatments (90°C for 3 hours). The biogas composition is measured with a micro gas chromatograph (Agilent 3000) equipped with two capillary columns: a MolSieve 5A and a Poraplot U. The phylogenetic analysis of 16S-rRNA gene sequences resulting from denaturing gradient gel electrophoresis (DGGE) is used to individuate the bacterial community of water buffalo manures as enhanced by the fermentation process. Results show that the favourable conditions to increase the production of CH4 are initial pH = 6 and temperature of 37°C, while hydrogen requires a more acid environment, pH = 5, and a higher temperature of 55°C. The choice of these parameters are already suggested in literature for the anaerobic fermentation of other kinds of dungs and hold also for the water buffalo manure here considered. In addition, it is observed that the use of heat-shocked manure can double the productivity of bio-hydrogen. This enhancement is principally due to the thermal inhibition of methanogenic bacteria and the selection of the acidogenic one (like Clostridium cellulosi), as suggested by the comparison of the DGGE profiles of fresh and thermally pre-treated manure.