A systematic comparison of ectoine production from upgraded biogas using Methylomicrobium alcaliphilum and a mixed haloalkaliphilic consortium.

Biogas is the byproduct of anaerobic digestion with the highest valorization potential, however its full exploitation is limited by the lack of tax incentives and the inherent presence of pollutants. The development of technologies for biogas conversion into added-value products is crucial in order to ensure the competitiveness of this bioresource. This study constitutes the first proof of concept of upgraded biogas bioconversion into the high profit margin product ectoine. Ectoine represents the most expensive product synthesized by microorganisms with a retail value of 1000 $ kg-1 and a yearly increasing demand that currently entails a total market opportunity of 15000 M€. First, the production of ectoine from upgraded biogas was assessed in batch bioreactors. The presence of H2S did not exert a negative effect on the growth of the haloalkaliphilic ectoine producers, and ectoine yields up to 49 mg g biomass-1 were obtained. A second experiment conducted in continuous bubble column bioreactors confirmed the feasibility of the process under continuous mode (with ectoine yields of 109 mg g biomass-1). Finally, this study revealed that the removal of toxic compounds (i.e. medium dilution rate of 0.5 day-1) and process operation with a consortium composed of methylotrophic/non-methylotrophic ectoine producers enhanced upgraded biogas bioconversion. This research discloses the basis for the application of this innovative technology and could boost the economic performance of anaerobic digestion.