Photoelectrocatalytic reactor improvement towards oil-in-water emulsion degradation

Oil-in-water (O/W) emulsion is critical wastewater that is challenging to eliminate and requires a long treatment process, and it is necessary to develop highly effective removal methods before releasing it into natural water sources. This research has selected the photoelectrocatalytic (PEC) technique to solve this problem by developing a PEC reactor for high efficiency in O/W degradation and understanding the essential factors related to the PEC reactor's efficiency improvement. The PEC reactor has been designed on a large scale with suitable positioning of an electrode that is, designing a light source near the anode electrode to enhance light irradiation efficiency and including a circulating pump to provide continuous flow to the solution through the electrode surface. We studied the main factors of supporting the electrolyte, electrode characteristics, and catalytic process. We investigated the O/W-degradation efficiency using a UV/Vis spectrophotometer, chemical oxygen demand (COD) measurement, and GC-MS analysis. We optimized the PEC reactor using the developed BiVO₄ photoanodes and placed them parallel with the zinc plates. Then, we controlled the applied potential at 1.0 V in 0.1 M Na₂SO₄ supporting an electrolyte under visible light irradiation. The developed PEC reactor can be degraded in the O/W emulsion up to 76% and decreased the COD value up to 78% for 7h. This PEC cell can be completely decomposed of many functional groups, such as carbonyl, ester, nitrile, amine, phosphate, chloro group, and nitro group, that were contained in the O/W substance. The highlight of this research is the designed light source and circulating pump inside of the PEC reactor to enhance the light irradiation, refresh the anode electrode, and understand the critical factor for the improvement of O/W-degradation efficiency. This PEC reactor presents a high-efficiency O/W degradation with practical use and a fast process suitable for further application in high turbidity of wastewater treatment from the oil industry.