Microalgal cultivation on ricotta cheese whey: Modulating nutrient supply during cultivation to improve culture...

Dairy industry generates significant effluent streams, comprising wastewaters and nutrient-rich by-products such as cheese whey, which pose environmental challenges for disposal, but also offer valorisation opportunities. Microalgae cultivation on whey represents a sustainable biotechnological approach that couples biomass production with effluent treatment. This study aimed at optimizing microalgal cultivation using ricotta cheese whey as substrate. Eighteen microalgal strains, mainly belonging to Scenedesmus and Chlorella, were initially screened for their ability to grow on whey. Selected strains were further tested in 300-mL photobioreactors under different management options: Low Whey Load (LWL), High Whey Load (HWL), Salinity and Micronutrient (S&M), and Moderate Whey Load (MWL) trials. Results showed that most of the tested strains grew better when cultivated on diluted whey than on standard synthetic media, with increases from 56 to 590 % during the first days, and with high removal efficiencies. Several issues were identified during the trials, including nutrient shortage, salinity increase, micronutrients deficiency and potential inhibitory effects of whey compounds, which have hindered long term cultivation of microalgae on whey. In MWL trial, optimization of whey concentration (12 % v/v), replenishment strategy (30 % of the culture volume every 3-days), and micronutrient supplementation overcame these issues extending the cultivation period and improving biomass yield (203.6 billion cells L^-1 whey^-1 with the best strain). Overall, this work underscores the importance of carefully optimize microalgal cultivation management to maximise exploitation of dairy by-products and minimize growth-limiting effects of whey accumulation, thus offering a promising starting point for large-scale applications of whey in microalgae cultivation.