Defluoridation by positive single-pulse current electrocoagulation from photovoltaic wastewater: Energy consumption assessment and mechanism analysis

The presence of fluoride ions (F^-) in photovoltaic (PV) wastewater significantly affects the integrity of the ecological environment. In contrast to direct current electrocoagulation (DC-EC), positive single-pulse electrocoagulation (PSPC-EC) shows a significant reduction in both the formation of passivation films on electrodes and the consumption of electrical energy. Under the experimental conditions of an Al-Al-Al-Al electrode combination, an electrode spacing of 1.0 cm, a NaCl concentration of 0.05 mol L^-1, an initial pH of 5.6, an initial F^- concentration of 5 mg L^-1, a current density of 5 A m^-2, a pulse frequency of 500 Hz, and a 40 % duty cycle, the achieved equilibrium F^- removal efficiencies were 84.0 % for DC-EC and 88.0 % for PSPC-EC, respectively, accompanied by power consumption of 0.0198 kWh·mg^-1 and 0.0073 kWh·mg^-1. The flocs produced in the PSPC-EC process were characterized using scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy and it is revealed that the F^- removal mechanisms in the PSPC-EC process include co-precipitation, hydrogen bond complexation, and ion exchange. When the actual PV wastewater was finally subjected to treatment under the optimal PSPC-EC conditions, the F^- concentration in the wastewater was reduced from 4.6 mg L^-1 to 1.4 mg L^-1. This paper provides both a theoretical framework and a technological basis for the application of PSPC-EC in the advanced treatment of PV wastewater.