Hydrogen-dependent control of the continuous anaerobic digestion process

Abstract

Membrane inlet mass spectrometry was used to directly measure the concentrations of CH4 and H2 in a mesophilic (37°C) completely mixed, laboratory scale, anaerobic digester, continuously fed at a retention time of 7 days with a glucose (50 mM) mineral salts medium. When the digester was overloaded by an increase in the influent substrate concentration, equivalent to 15.5 kg (COD) m-3 (digester) day-1 the concentrations of H2 and short chain fatty acids increased with a concomitant decline in the pH: following an initial stimulation methanogenesis was inhibited. Regulation of the H2 signal from the mass spectrometer in a closed feedback loop by controlled addition of carbon source under a potential overload condition, enabled the H2 concentration to the controlled around 1μM and a high steady state rate of methanogenesis of 42 μM min-1 to be maintained; this is equivalent to 1.4 volumes of CH4 per culture volume per day. The hydrogen-dependent control system was also used to prevent inhibition of methanogenesis when the digester was subject to volumetric overloading potentially equivalent to a retention time of 1 day.