Managing anaerobic digestate is a key environmental challenge due to nutrient overload and the risk of eutrophication. Cultivating microalgae offers a sustainable route to valorize this waste, coupling nutrients recovery with the generation of valuable biomass. The aim of this study was to evaluate the feasibility of using anaerobic digestate as a nutrient source for the industrially relevant microalga Chlorella vulgaris and to investigate, as a possible valorization route, the properties of the biomass produced as a biostimulant for land plants. Chlorella vulgaris cells were successfully grown using diluted farm-derived digestate, without any pretreatment or additional supplementation. Optimal growth and nutrient removal were obtained with 4–8% ( v /v) digestate dilutions, yielding up to 1.2 g L −1 dry biomass. Although cultures were exposed to high irradiance, photosynthetic measurements revealed features typical of low-light acclimated algal cells, likely caused by limited light penetration in the digestate medium. Pilot-scale cultivation in a 300 L photobioreactor confirmed process feasibility at 4% digestate, resulting in more than 96% total nitrogen removal and almost complete phosphorus depletion within ten days. Metabarcoding analyses showed a shift in the microbial community toward Pseudomonas and Aeromonas , suggesting the formation of potentially beneficial consortia. The resulting biomass displayed potential biostimulant activity on tomato ( Solanum lycopersicum ) seeds, increasing germination by 29% and root elongation by 143% at low application rates (0.01–0.1 g L −1 ). Altogether, these findings demonstrate that cultivating Chlorella vulgaris on digestate represents a cost-effective and circular approach for nutrient recycling, waste valorization, and sustainable bioproduct development. • Chlorella vulgaris grew on digestate liquid fraction as the sole nutrient source • Pilot scale at 300 L reached >96% N removal and near-complete P depletion • Low light-like acclimation response was observed in cells grown in digestate • Metagenomic analysis revealed microbial community dynamics due to algae cultivation • Algal biomass showed strong biostimulant effects on tomato seed and plants
Miotti et al. (Fri,) studied this question.