Influence of the hydrostatic pressure on biogas production in anaerobic digesters

This paper aimed to investigate the influence of hydrostatic pressure on methanogens activity and consequently on biogas production in anaerobic digesters. The quality of biogas has been evaluated in terms of methane content in the gas resulting from fermentative processes in anoxic environments. A total of four experimental studies were carried out by using stainless steel pressure vessels, where an organic substrate, consisting of a mixture of cattle manure and unfiltered whey, has been conditioned in mesophylic temperature regime for pressures set at 0 bar, 2 bar, 4 bar and 6 bar, respectively. The activity of methanogens was determined by instrumental chemical analysis, using a gas chromatograph fitted with a flame ionization detector. Biogas generated in fermentative processes has been periodically sampled and analyzed during the period of the highest microbial activity. Furthermore, the number of methanogens before anaerobic digestion and after conditioning under various pressures has been determined by using the most probable number analytical method.