Salinity-driven shifts in microalgal–bacterial granules: Unlocking nutrient removal, microbial synergy, and biomass potential

Abstract

This study revealed the effect of moderate salinity on microalgal-bacterial granules (MBG)-based wastewater treatment. Four photobioreactors were simultaneously operated under low-cost conditions (no aeration, pH adjustment, and artificial light) at salinities of 0 ‰, 5 ‰, 10 ‰, and 15 ‰. Results showed that MBG systems sustained effective performance at salinities up to 15 ‰, with NH₄⁺ and total phosphorus (TP) removal efficiencies of 64–71 % and 40–98 %, respectively, compared to 58 % and 29 % under non-saline conditions. Biodiversity in MBG systems declined and stabilized at 5–10 ‰, but rose markedly at 15 ‰. Nitrobacter, Sphingopyxis and Rhodocyclales genera increased with salinity, while Bacteria_unclassified, Cyanophyceae_unclassified, and Sphingomonas declined. Protein content increased at salinities below 10 ‰, carbohydrate accumulation was promoted above 10 ‰, while lipid content remained relatively stable across 5–15 ‰ salinity. Overall, this study highlighted MBG's potential in saline wastewater treatment and provided insight into MBG's biomass component and microbial community at the salinity range up to 15 ‰.