Abstract
A novel internally illuminated airlift photobioreactor was developed to enhance light distribution, hydrodynamics, and energy efficiency in microalgal wastewater treatment. The reactor integrates a central white LED source surrounded by a 9,10-diphenylanthracene fluorescent medium, acting as a wavelength-shifting and light-diffusing layer for improved photon delivery. A major innovation is the direct cultivation of a native mixed microalgal consortium in real fish farm effluent, eliminating the need for sterilization and synthetic media. System performance was evaluated under three light–dark regimes (24:0, 19:5, and 12:12 hours). The 19:5 photoperiod exhibited the highest biomass productivity (2.61 g L⁻¹ over 14 days) and the greatest photon to biomass conversion efficiency (0.66), significantly surpassing continuous (0.59) and shorter (0.18) cycles. Under the 19:5 photoperiod, final residual nutrient concentrations reached 1.4, 1.5, and 1.9 mg L⁻¹ for ammonium, nitrate, and phosphate, respectively, corresponding to energy efficiencies of 0.161, 0.139, and 0.096 g kWh⁻¹. Mechanistic interpretations, derived from physiological principles, indicate that the controlled dark phase improved energy conversion by mitigating photoinhibition and supporting cellular recovery. Overall, these results demonstrate that coupling internal illumination with optimized light–dark cycling and native algal consortia significantly enhances both nutrient removal and energy sustainability in wastewater-based photobioreactors.