Novel Gas-Bubbled Immobilized Algal Cultures for the Bioremediation of Natural Waters: Exploring Applications in Aquaculture

The biological treatment of nitrogen- and phosphorus-rich waters is increasingly adopting algal cultures over traditional methods. Algae-based treatment offers advantages, including lower energy and chemical use, and generation of reusable biomass. In this study, nitrogen and phosphorus were removed from natural waters using a novel gas-bubbled, immobilized Chlorella vulgaris (C. vulgaris) culture, developed through a patented method (TR2022051245W). This method enables buoyant immobilization, enhancing light exposure, removing the need for post-treatment separation (e.g., filtration), and facilitating harvesting even in high-turbidity waters. Experiments were conducted using a bench-scale batch reactor system. Process optimization was carried out using a 3 × 3 Taguchi design to assess nutrient removal efficiencies under various combinations of light–dark cycle duration, pH levels, and aeration rates. After 45 h of treatment, removal efficiencies reached 78.30% for nitrate nitrogen (NO₃⁻-N), 95.98% for ammonium nitrogen (NH₄⁺-N) and 99.54% for phosphate (PO₄⁻³). Post-treatment analysis showed that the immobilized algal biomass exhibited a 9.1% increase in dry matter, a 200% increase in protein content, and a 191% increase in total nitrogen, with preliminary qualitative observations highlighting its potential as a sustainable feedstock for aquaculture; however, comprehensive quantitative feeding trials are planned for future studies to fully validate this application. While the results promising, the batch-scale setup, limited experimental replications, and 45-h treatment duration may present scalability challenges without innovations in hydraulic retention time, which are discussed in detail in the manuscript. This study introduces a novel buoyant immobilization approach to algae-based bioremediation, offering efficient nutrient removal and valuable resource recovery within a circular economy framework.