Single Cell Protein Production From Ethanol: Model‐Based Bioreactor Operation at Industrial Scale

Alternative fermentation feedstocks such as ethanol can be produced from CO₂ via electrocatalytic processes that coproduce O₂. In this study, industrial-scale fermentation of ethanol with pure O₂ for single cell protein (SCP) production was studied using a modeling approach. This approach considered (i) microbial kinetics, (ii) gas-liquid transfer, and (iii) an exploration of potential operational constraints. The technical feasibility for producing up to 58 kt/y of SCP in a 600 m³ bubble column operating in continuous mode was assessed and attributed mainly to a high O₂ transfer rate of 1.1 mol/(kg h) through the use of pure O₂. However, most of the pure O₂ fed to the fermenter remains unconsumed due to the large gas flows needed to maximize mass transfer. In addition, biomass production may be hampered by high dissolved CO₂ concentrations and by large heat production. The model estimates a microbial biomass concentration of 114 g/kg, with a yield on ethanol of 0.61 g_x/g_ethanol (> 95% <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:mrow> <mml:mrow><mml:msubsup><mml:mi>Y</mml:mi> <mml:mrow><mml:mi>x</mml:mi> <mml:mo>/</mml:mo> <mml:mi>s</mml:mi></mml:mrow> <mml:mi>max</mml:mi></mml:msubsup> </mml:mrow> </mml:mrow> </mml:semantics> </mml:math> ). Although the large predicted O₂ transfer capacity seems technically feasible, it needs further experimental validation. The model structure allows the analysis of alternative substrates in the same way as identifying the best carbon feedstock.