Novel method for determination of gas consumption in Cupriavidus necator: assessing feasability of CO2 fixation from biomass-derived syngas

Abstract

Synthesis gas (syngas) is an industrially important feed stock for electricity, hydrogen and liquid fuel production. Biomass-derived syngas has high CO2 levels and alternative methods of CO2 removal are needed to implicate biomass gasification systems. This research identified and tested a possible method of biological CO2 fixation from syngas. The chemolithoautotrophic organism Cupriavidus necator produces PHB and offers a valuable product as a result of CO2 fixation. The energy efficiency of biological CO2 fixation using chemolithoautotrophic growth supported by hydrogen, oxygen and carbon dioxide was theoretically analyzed and then tested in C. necator using a novel experiment. The experimental design included cultivating C. necator in a mineral solution inside of plastic gas sampling bags under constant temperature and pressure. The gas composition of the bag was monitored over time using a GC/TCD system. To determine the consumption of the individual gasses H2, O2 and CO2 the total moles of the gas mixture in the bag was monitored using the inert gas methane (CH4). The efficiency of chemolithoautotrophic growth was determined from gas consumption. It was found that there was a large discrepancy between the maximum theoretical energy efficiency and the actual efficiency. It was found that the gas consumption requirements of C. necator are 1:1.8:5.8 (mol CO2 : mol O2 : mol H2). This hydrogen requirement is almost three times more than the theoretically possible, and results in less than 30% of hydrogen consumed for growth being stored as reduced CO2, or bacterial biomass.