Growth performance and adaptability of an EPS-producing Chlorella strain in cheese whey with high and low salinity: prospects for the sustainable production of microalgal biomass

Abstract Cheese whey is a high-strength dairy effluent with varying salinity levels, presenting major environmental challenges. An exopolysaccharide (EPS)-producing Chlorella isolate was used to treat dairy effluents from the primary (PCW) and second (SCW) production stage, with low and high salinity respectively. PCW presented a suitable substrate for Chlorella biomass production, which ranged 1,650–1,757 mg cells L −1 . The high salinity of SCW inhibited cell growth and photosynthesis, requiring dilution to achieve growth. The 1:1 mixing of PCW and SCW was employed as an effective strategy to lower SCW’s extreme salinity to the tolerated level of 1.51% w/v NaCl. In mixed whey, Chlorella ’s growth and photosynthetic activity were enhanced compared to SCW, while biomass production exceeded controls. Furthermore, under elevated salinity conditions, Chlorella ’s performance was improved in the presence of casein-based whey solids. Microscopy images showed that Chlorella was attached on the surface of whey solids, forming microcolonies and protecting cells from the saline environment. This attachment is suggested to be facilitated by electrostatic interactions between Chlorella ’s EPS and casein in whey solids. Chlorella -based treatment was effective for the removal of pollutants from saline effluents. A notable decrease in the values of chemical oxygen demand (11,390 mg L −1 ), Kjeldahl nitrogen (626.5 mg L −1 ), total phosphorus (167.0 mg L −1 ) and lactose (15.9 g L −1 ) were found for the treated 1:1 mixed cheese whey samples. These results highlight the potential of naturally evolved microalgae to develop sustainable biological systems for the treatment of saline dairy effluents, while simultaneously producing valuable algal biomass.