Mariculture wastewater treatment with Bacterial-Algal Coupling System (BACS): Effect of light intensity on microalgal biomass production and nutrient removal

Mariculture wastewater generated from the mariculture industry has increased public concern due to its impact on the sustainability of aquatic environments and aquaculture practices. Herein, the Bacterial-Algal Coupling System was applied for mariculture wastewater treatment. Microalgae growth in heterotrophy and mixotrophy (2000–8000 lux) were first compared. The best microalgal growth and nutrient removal were obtained at 5000 lux, where biomass productivity of microalgae was 0.465 g L⁻¹ d⁻¹, and 98.1% of chemical oxygen demand, 70.7% of ammonia-nitrogen, and 90.0% of total phosphorus were removed. To further understand the nutrient removal through microalgae cultivation, the enzyme activities involved in the Calvin cycle and the Tricarboxylic Acid cycle at different light intensities were determined. Under mixotrophic cultivation, there was a coordination between photosynthesis and heterotrophic metabolism in agal cells, which resulted in a high algal biomass production and removal efficiency of nutrients. This study provided a novel insight into the bioremediation of mariculture wastewater and microalgae cultivation.