From renewable energy to sustainable protein sources: Advancement, challenges, and future roadmaps

The concerns over food security and protein scarcity, driven by population increase and higher standards of living, have pushed scientists toward finding new protein sources. A considerable proportion of resources and agricultural lands are currently dedicated to proteinaceous feed production to raise livestock and poultry for human consumption. The 1st generation of microbial protein (MP) came into the market as land-independent proteinaceous feed for livestock and aquaculture. However, MP may be a less sustainable alternative to conventional feeds, such as soybean meal and fishmeal, because this technology currently requires natural gas and synthetic chemicals. These challenges have directed researchers toward the production of 2nd generation MP by integrating renewable energies, anaerobic digestion, nutrient recovery, biogas cleaning and upgrading, carbon-capture technologies, and fermentation. The fermentation of methane-oxidizing bacteria (MOB) and hydrogen-oxidizing bacteria (HOB), i.e., two protein rich microorganisms, has shown a great potential, on the one hand, to upcycle effluents from anaerobic digestion into protein rich biomass, and on the other hand, to be coupled to renewable energy systems under the concept of Power-to-X.