Competitive treatment of tannery wastewater by microalgae consortium cultivated in an outdoor alkaline open- photobioreactor. A simultaneous exploration of bioremediation, lipid accumulation potential and capture of atmospheric CO2

Tannery wastewater presents a significant environmental and technological challenge due to its high pollutant load and complex contaminant removal. This study investigated the use of a native microalgae consortium (NMC) for treating real tannery effluents, focusing on the removal of biological oxygen demand (BOD), chemical oxygen demand (COD), nitrogen ammonia (NH₃-N), and total phosphorus (TP) under environmental conditions. Carbon dioxide (CO₂) capture was also evaluated. The experimental tests used an NMC isolated from wastewater lagoons exposed to high radiation (7094 wm⁻²d ^− 1 ) at 2,300 meters above sea level. This consortium was inoculated in a 24.5 L open photobioreactor with controlled pH. Cultivation tests were conducted using pretreated tannery wastewater and wastewater supplemented with nutrients at 100% and 75% concentrations. Results showed high efficiency in removing NH₃-N (100% in 9 days), TP (100% in 8 days), COD (75.8%), and BOD₅ (86.6%) over 10 days. The NMC fixed atmospheric CO₂ at 281 mgL⁻¹ d⁻¹ during exponential growth, with an annual sequestration potential of 102.5 gL⁻¹. The harvested biomass contained 18.5 wt% lipids after potassium hydrogen phosphate addition, which stimulated lipid accumulation under nitrogen scarcity. Culturing the NMC for 100 days at pH 8, stabilized with sodium bicarbonate, enriched with phosphate, and nitrogen-limited in a high-rate algae pond (HRAP) enhances its environmental tolerance, optimizes system performance, and improves tannery wastewater treatment. This approach mitigates CO₂ emissions while generating valuable bioproducts.