Sustainable algal proteins produced on potato and other controlled agri-food streams: A’propos project : environmental impact assessment of microalgae production as feedstuff (WP4)

To investigate potential benefits of using protein from microalgae production as an alternative to conventional soybean-based protein, the microalgae cultivation from two different production systems is investigated. Goal of the present study was to conduct a comparative life cycle assessment (LCA) of protein production from microalgae biomass in a closed tubular photobioreactor (PBR), and an open thin-layer PBR as well as soybean protein. A focus was to extrapolate the data from the lab-scale systems to industrial-scale production scenarios. Primary data regarding the protein production in the closed and open system stems from experiments carried out by project partners. For the background data, the ecoinvent 3.10 database was used and the modelling and impact assessment was carried out in SimaPro. Next to the different PBR systems, a focus point of the study was further to compare two different nutrient media. In the closed tubular PBR, the microalgae biomass was cultivated using potato wastewater as the nutrient medium, which is rich in ammonium sulphate and requires a pre-treatment of cartridge membrane filtration and UV treatment. In contrast, the microalgae in the open thin-layer PBR were cultivated using a standard mineral medium, where the nutrient input is based on microalgae production quantities. The outcome of the impact assessment showed a trade-off between the two cultivation systems, regarding different environmental impacts. The closed system has a considerably higher electricity consumption than the open system, due to the use of LEDs, which are absent in the open system, as well as a higher electricity consumption by the pumps. GHG emissions of protein produced from microalgae biomass in the closed system were therefore found to be higher than those of the protein from the open system. In contrast, for certain impact categories such as ecotoxicity, the open system which is operated with a mineral medium and exposed to losses showed distinctly higher impacts than the closed system, as it has a higher demand for chemically produced ammonium sulphate. Regarding the comparison between the two different nutrient medium, the potato wastewater is therefore the recommendable option, as it naturally contains ammonium and reduces the amount of chemically produced ammonium needed. An extrapolation from lab-scale to industrial-scale production of the microalgae-based protein, showed a potential reduction of the environmental impacts by up to 73% in the closed system, from 125 kg to 40 kg of CO2-eq per kg of protein, and up to 40% in the open system, from 52 kg to 32 kg of CO2-eq per kg of protein. Results further showed that the environmental impacts of the best-case scenarios of the microalgae-based protein from both systems may reduce environmental impacts compared to protein from soybean meal, depending on the environmental impacts considered. However, it strongly depends on where the soybeans are cultivated. Soybean protein produced in the United States and Switzerland showed considerably lower environmental impacts for all categories analysed. Compared to protein from soybeans cultivated in Brazil, the protein from microalgae biomass can come into a competitive range, in particular if the production of algal protein would lead to a reduction of land use change and pesticide application for soybean cultivation. To further improve the environmental performance of protein produced from microalgae biomass, all processes need to be fully operated by renewable energy, while energy efficiency and nutrient uptake need to be increased.