Maximizing nutrient recycling from digestate for production of protein-rich microalgae for animal feed application

• Published in: Chemosphere (Oxford) 2022-03, Vol.290, p.133180-133180, Article 133180
• Main Authors: Seelam, Jai Sankar, Fernandes de Souza, Marcella, Chaerle, Peter, Willems, Bernard, Michels, Evi, Vyverman, Wim, Meers, Erik
• Format: Article
• Language: English
• Subjects: Animal Feed; Animals; Biomass; Chlorella vulgaris; Digestate; Microalgae; Microplate experiments; Nutrients; Paper-filtration; Photobioreactor; Refuse Disposal; Waste Water
• ISSN: 0045-6535; 1879-1298
• DOI: 10.1016/j.chemosphere.2021.133180

The integration of phototrophic microalgal production and anaerobic digestion can recycle excess nutrients across European surplus hotspots to produce protein-rich biomass for nutritional applications. However, the challenging physico-chemical properties of raw digestate constrain microalgal growth and limit digestate valorization potential. This study focused on the pre-treatment of food waste-based digestate using paper-filtration to improve its properties for cultivating Desmodesmus sp. and Chlorella vulgaris. The microalgal growth performance in paper-filtered digestate (PFD, 10 μm-pore size) was then compared to growth in membrane-filtered digestate (MFD, 0.2 μm-pore size). A microplate-based screening coupled with Cytation device assessment of PFD and MFD samples after dilution and with/without phosphorus supplementation showed that PFD was the best substrate. Moreover, phosphorus supplementation resulted in improved growth at higher digestate concentrations (5–10% v/v PFD), indicating the importance of using a balanced growth medium to increase the volumetric usage of digestate. Results were validated in a 3-L bioreactor at 10% PFD with phosphorus supplementation, reaching a biomass concentration of 2.4 g L−1 with a protein and carbohydrate content of 67% and 13% w/w respectively. This trial indicates that paper-filtration is a promising pre-treatment technique to maximize digestate recycling and deliver a sustainable animal feed-grade protein alternative. [Display omitted] •Paper-filtration of digestate to maximize nutrient recycling was demonstrated.•Microplate-based screening was performed to compare two digestate pre-treatments.•Paper-filtered digestate was better substrate than membrane-filtered digestate.•Phosphorus supplementation improved biomass concentration from 1.4 g L−1 to 2.4 g L−1.•Protein content of microalgae biomass grown on 10% paper-filtered digestate was 67%.