Resumo:
Oil exploration is one of the main sources of global energy, but it also generates large volumes of produced water (PW), an effluent with a high concentration of pollutants, which impacts the environment and creates a significant environmental liability for the fossil fuel industry. Therefore, the treatment of PW becomes a priority to mitigate these impacts, and among the treatment approaches, biological treatment with microalgae presents itself as an efficient and sustainable alternative. In this context, the present study evaluated the bioremediation of PW using the microalga Chlorolobion braunii, a green freshwater alga known for its tolerance to toxic environments. The cultivation was carried out in 250 L bioreactors using a mixture containing 50% PW and 50% BG-11 medium (AP50%), while the control cultivation was conducted using only BG-11 medium. The results demonstrated high efficiency in removing components from the produced water, such as nitrate (99.54%), phosphate (77.78%), iron (94%), and manganese (75%), in addition to a reduction in the alkalinity of the medium (61%). The total biomass yield was 40 g in the AP50% cultivation, using 100 L of PW. The biomass composition revealed 11.40% protein, 13.07% carbohydrates, and 8.50% lipids, with the remaining 67.03% composed of biochar. The presence of lipids, mainly saturated and monounsaturated fatty acids, with emphasis on palmitic acid (C16:0) and elaidic acid (C18:1ω9t), is relevant for biodiesel production, as they meet international quality standards for biodiesel. Additionally, the cultivation of Chlorolobion braunii in AP50% resulted in the production of exopolysaccharides (EPS), with approximately 30 g of EPS generated, which exhibited pseudoplastic characteristics, a property of interest for various industrial sectors. The pyrolysis of the biomass generated from the microalga cultivation resulted in 35.12% bio-oil and 57.69% non-condensable gases, with the bio-oil containing hydrocarbons, nitrogenous compounds, and oxygenated compounds, which can be used in different sectors. The integration of bioremediation with the production of bioproducts, such as biodiesel, exopolysaccharides, and bio-oil, presents an efficient microalgal biorefinery model, where produced water is not only treated but also used as a source for generating high-value-added bioproducts.
