Low-cost cocultivation of Vischeria stellata and Tribonema sp. biomass using molasses vinasse: A novel wastewater reuse model for functional aquatic feed production

Microalgae can effectively sequester CO₂, cultivating dense algal populations and producing high-value biomass in acidic environments poses significant challenges. This study explored the growth of unicellular Vischeria stellata GXU-A13 and filamentous Tribonema sp. GXU-A10 in acid molasses vinasse (MV). Results revealed that GXU-A13 exhibited strong acid tolerance, with maximum biomass reaching 2.71 g/L in MV wastewater (pH 5) and a COD removal rate of 49.4 % after 12 days. Notably, a mixed culture of the easily harvested GXU-A10 and acid-resistant GXU-A13 demonstrated enhanced wastewater treatment, with COD removal rates of 64.3 % and NH₄-N removal rates of 54.9 %. Additionally, the GXU-10 and GXU-A13 co-culture also achieved efficient biomass recovery, and examined the effects of this biomass as feed on the growth and immune function of Oreochromis niloticus. Feeding O. niloticus with 2.5 % or 5 % GXU-A13 (V2 and V5 group) resulted in significant improvements in specific growth rate (SGR). Additionally, GXU-A13 significantly enhanced glutathione peroxidase (GSH-PX) activity and decreased malondialdehyde (MDA) levels, which contributed to a marked increase in intestinal microbial diversity. Furthermore, diets containing 2.5 % GXU-A13 (V2 group) and 2.5 % GXU-A10 (H2 group) exhibited stronger antioxidant capacity and immune response. The dual metabolic benefits of mixed algae (VH group) that contained 2.5 % GXU-A13 and 2.5 % GXU-A10 significantly improved intestinal and liver health, while enhancing O. niloticus tolerance to high-ammonia nitrogen wastewater (NH₄⁺ concentration of 114 ± 3.2 mg/L). This study effectively integrates the unique characteristics of the two microalgae, enabling MV purification and recycling, advancing the development of a microalgae-based circular economy, and enhancing the quality and sustainability of aquatic feed.