Title : Reinforcement of alginate beads of microalgal-bacterial immobilized consortia with cellulose nanofibers for aquaculture wastewater treatment
Abstract:
The increasing demand for sustainable wastewater management has driven the development of innovative solutions integrating biological and nanotechnological approaches. This study focuses on enhancing the mechanical and functional properties of alginate beads for microalgal-bacterial immobilization by incorporating cellulose nanofibers (CNFs) for efficient aquaculture wastewater treatment. CNFs were synthesized using TEMPO oxidation and enzymatic hydrolysis, then integrated into alginate beads at varying concentrations (2%, 5%, 10%, and 15%). The beads were evaluated for structural stability, mechanical strength, and nutrient purification efficiency under static and dynamic conditions. Experimental results demonstrated that CNF-reinforced alginate beads exhibited improved resistance to degradation and enhanced structural integrity, as evidenced by stable weight and diameter in phosphate solutions. Dynamic analysis in photobioreactors revealed that TEMPO-oxidized CNFs provided superior mechanical reinforcement compared to enzymatically derived CNFs. Mechanical testing further confirmed that 5% CNF incorporation optimized compressive strength, while higher concentrations caused structural weakening due to excessive agglomeration. The purification capacity of CNF-modified beads was assessed for nitrate, phosphate, and ammonium removal from recirculated aquaculture system (RAS) water. Beads containing CNFs achieved significant reductions in nutrient concentrations, with 91% phosphate removal, 100% ammonium elimination, and accelerated nitrate depletion within five days. The presence of microalgae in CNF-alginate beads contributed to enhanced purification through synergistic metabolic interactions with bacterial consortia, promoting nutrient uptake and conversion into biomass. Confocal microscopy confirmed the homogeneous distribution of CNFs and microalgae within the alginate matrix, ensuring uniform performance. This research highlights the potential of CNF-reinforced alginate beads as a scalable and eco-friendly solution for aquaculture wastewater treatment, addressing nutrient recycling and environmental sustainability challenges. Additionally, complementary studies have demonstrated that the microalgae immobilized in these biomedia can also function as agricultural fertilizers due to their nutrient profiles rich in nitrogen and phosphorus, which are essential for plant development. This potential is currently under investigation to broaden its applicability.
Keywords: Cellulose Nanofibers, Alginate Beads, Aquaculture Wastewater, Microalgae, Bioremediation, Nutrient Removal.
