A novel fermentation process was developed in which renewable electricity is indirectly used as an energy source in fermentation, synergistically decreasing both the consumption of sugar as a first generation carbon source and emission of the greenhouse gas CO₂. As an illustration, a glucose-based process is co-fed with formic acid, which can be generated by capturing CO₂ from fermentation offgas followed by electrochemical reduction with renewable electricity. This “closed carbon loop” concept is demonstrated by a case study in which cofeeding formic acid is shown to significantly increase the yield of biomass on glucose of the industrially relevant yeast species Yarrowia lipolytica. First, the optimal feed ratio of formic acid to glucose is established using chemostat cultivations. Subsequently, guided by a dynamic fermentation process model, a fed-batch protocol is developed and demonstrated on laboratory scale. Finally, the developed fed-batch process is tested and proven to be scalable at pilot scale. Extensions of the concept are discussed to apply the concept to anaerobic fermentations, and to recycle the O₂ that is co-generated with the formic acid to aerobic fermentation processes for intensification purposes.

Liquid hot water pretreatment is considered to be a promising method for increaing biomass digestibility due to the moderate operational conditions without chemical additionA necessary step towards the scalability of this pretreatment process is performing pilot plant triaUpscaling was evaluated with a scaling factor of 500, by using 50 mL in the laboratory and 25 L in pilot plant batch reactor. Pretreatment times were varied from 30 to 240 min, and temperatures usewere 180–188^◦ C, while applying similar heating profiles at both scales. The initial mass fraction poplar wood chips ranged from 10% to 16%. Liquid hot water pretreatment at laboratory and pilscale led to analogous results. The acetic acid analysis of the liquid and solid fractions obtained aftpretreatment indicated that complete deacetylation of poplar biomass can be achieved.