Experimental methods for screening parameters influencing the growth to product yield (Y-(x/CH4)) of a biological methane production (BMP) process performed with Methanothermobacter marburgensis

New generation biofuels are a suitable approach to produce energy carriers in an almost CO2 neutral way. A promising reaction is the conversion of carbon dioxide (CO2) and molecular hydrogen (H-2) to methane (CH4) and water (H2O). In this contribution, this so-called Sabatier reaction was performed biologically by using hydrogenotrophic and autotrophic methanogenic microorganisms from the archaea life domain. For the development of a biological methane production (BMP) process, one key parameter is the ratio of biomass production rate (rx) to methane evolution rate (MER) reflected in the growth to product yield (Y(x/CH4)) because it represents both a physiological and a scalable entity for the bioprocesses development as it quantify the selectivity of reaction with respect to the carbon. Y(x/CH4) needs also to be held constant in order to establish an adaptable media composition for developing a scalable feeding strategy. Identification of parameters and quantification of their impact on Y(x/CH4) is a necessary prerequisite for obtaining a growth kinetic model and developing advanced process control strategies especially for dynamic operation modes. In this work, process conditions and parameters impacting Y(x/CH4) were investigated by using a combination of multivariate and univariate chemostat cultures, as well as dynamic experiments. The proposed combination of methods is a novel modular approach for the development of BMP processes. It allowed determining the effects of multiple process factors on physiology and methane productivity of Methanothermobacter marburgensis. In fact, quantitative analysis of basal medium, sulphide and ammonium dilution rates, as well as the ammonium concentration revealed that all these variables vary rx without affecting MER. Hence Y(x/CH4) can be used to identify limiting or inhibiting conditions during media development tasks as well as for tuning the carbon flux of the bioprocess in an industrial application by reducing Y-(x/CH4) to improve the carbon balance of the reaction.