Purpose Renewable energy produced from wind turbines and solar photovoltaics (PV) has rapidly increased its share in global energy markets. At the same time, interest in producing hydrocarbons via power-to-X (PtX) approaches using renewables has grown as the technology has matured. However, there exist knowledge gaps related to environmental impacts of some PtX approaches. Power-to-food (PtF) application is one of those approaches. To evaluate the environmental impacts of different PtF approaches, life cycle assessment was performed. Methods The theoretical environmental potential of a novel concept of PtX technologies was investigated. Because PtX approaches have usually multiple technological solutions, such as the studied PtF application can have, several technological setups were chosen for the study. PtF application is seen as potentially being able to alleviate concerns about the sustainability of the global food sector, for example, as regards the land and water use impacts of food production. This study investigated four different environmental impact categories for microbial protein (MP) production via different technological setups of PtF from a cradle-to-gate perspective. The investigated impact categories include global warming potential, blue-water use, land use, and eutrophication. The research was carried out using a life cycle impact assessment method. Results and discussion The results for PtF processes were compared with the impacts of other MP production technologies and soybean production. The results indicate that significantly lower environmental impact can be achieved with PtF compared with the other protein production processes studied. The best-case PtF technology setups cause considerably lower land occupation, eutrophication, and blue-water consumption impacts compared with soybean production. However, the energy source used and the electricity-to-biomass efficiency of the bioreactor greatly affect the sustainability of the PtF approach. Some energy sources and technological choices result in higher environmental impacts than other MP and soybean production. When designing PtF production facilities, special attention should thus be given to the technology used. Conclusions With some qualifications, PtF can be considered an option for improving global food security at minimal environmental impact. If the MP via the introduced application substitutes the most harmful practices of production other protein sources, the saved resources could be used to, for example, mitigation purposes or to improve food security elsewhere. However, there still exist challenges, such as food safety–related issues, to be solved before PtF application can be used for commercial use.

The production of edible microbial biomass in bioreactors is an attractive alternative to agriculture, which is a major consumer of fresh water, an emitter of greenhouse gases, and a cause of eutrophication. This study examines microbial food production by gas fermentation of two endotoxin-free Gram-positive H2-oxidizing autotrophic bacterial strains, Nocardioides nitrophenolicus KGS-27 and Rhodococcus opacus DSM 43205. The supply of the gaseous substrates H2 and O2 by in situ water electrolysis was investigated as an alternative to providing them from an external source. N. nitrophenolicus KGS-27 produced ≤9.9 ± 2.0 mg of biomass L–1 h–1 and was not affected by in situ water electrolysis, which potentially produces growth-inhibiting reactive oxygen species. With R. opacus DSM 43205, in turn, electrolysis slowed growth considerably and resulted in a volumetric productivity of 2.6 ± 0.8 mg of biomass L–1 h–1, which was a quarter of what was obtained with the gases supplied externally. The macromolecular compositions of biomasses produced by the two cultivation modes using the two bacterial strains were rather similar containing approximately 33–37% protein, 28–56% carbohydrates, and 4–5% fatty acids of the cell dry weight. Relatively high protein concentrations and balanced amino acid profiles, comparable to those of casein and soy protein, were achieved with both strains.

Hydrogen-oxidizing bacteria (HOB) have been shown to be promising micro-organisms for the reduction of carbon dioxide to a wide range of value-added products in bioelectrochemical systems with in situ water electrolysis of the cultivation medium, also known as a hybrid biological-inorganic systems (HBI). However, scaling up of this process requires overcoming the inherent constraints of the low energy efficiency partly associated with the pH-neutral electrolyte with low conductivity. Most of the research in the field is concentrated on the bacterial cultivation, whereas the analysis and evaluation of the electrode material performance have received little attention in the literature so far. Therefore, in the present work, in situ electrolysis of a pH-neutral medium for HOB cultivation was performed with different combinations of electrode materials. Besides conventional electrode types, electrodes with coatings made of earth-abundant cobalt and a nickel-iron alloy, known for their catalytic activity for the kinetically sluggish oxygen evolution reaction (OER), were prepared and tested as potential substitutes for catalysts made of precious metals. The cultivation of HOB with in situ water electrolysis has been successfully tested in a small scale electrobioreactor in order to support the experimental results. A simplified water electrolysis model was developed and applied to evaluate the current-voltage characteristics of an bioelectrochemical system prototype. Application of the developed model allows quantitative evaluation and comparison of reversible, ohmic, and activation overvoltages of different electrode sets. The modeling results were found to agree well with the experimental data. The developed model and the data gathered can be applied to further investigation, simulation, and optimization of HBI systems.

Hydrogen-oxidizing bacteria provide a sustainable solution for microbial protein production. Renewable electricity can be used for in situ water electrolysis in an electrobioreactor. The use of cultivation medium as the electrolyte enhances the hydrogen dissolution to the medium. This paper proposes a stack structure for in situ water electrolysis to improve the productivity of the electrobioreactor. The hydrogen production rate and the energy efficiency of the prototype stack are analyzed.