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

摘要

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 (H₂) 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 (r_x) 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 r_x 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.