Harnessing the potential of Chlorella vulgaris in salmon industry wastewater treatment: The role of salinity type in optimizing biorefinery processes

The increasing demand for sustainable wastewater treatment solutions has led to the exploration of microalgae-based systems, which offer dual benefits of pollutant removal and biomass valorization. This study investigates the potential of Chlorella vulgaris cultivated in mixed salmon industry wastewater with varying salinity conditions (synthetic, natural, and industrial sources) for bioremediation and bio-crude oil production. The removal efficiencies for heavy metals reached 64.63 % for Cu in RM treatment, 32.76 % for Zn in RN treatment, and 9.43 % for Pb in YR treatment. Regarding nutrient uptake, YR demonstrated the highest efficiency, removing 75.44 % of N and 16.54 % of PO₄³⁻. These results demonstrate the capability of microalgae to remediate wastewater under different saline conditions. Confocal Laser Scanning Microscopy (CLSM) analysis revealed significant lipid accumulation. The highest relative mean fluorescence intensity was recorded for the YR treatment (2624 ± 806 AU), followed by RM (1468 ± 2160 AU) and RN (1396 ± 1276 AU), confirming the influence of salinity on lipid biosynthesis. The bio-crude oil yield obtained from HTL of microalgal biomass ranged from 3.15 % to 10.26 % for RN and RM, respectively, showing an effect of the salinity conditions and nutrient availability in the culture medium. These results are indicative of its potential, which could be applicable to food or biofuel products developed in support of a circular bioeconomy in the salmon industry. Future research should focus on refining the process conditions to maximize energy recovery and resource efficiency in large-scale applications.