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, an initial pH of 5.6, an initial F concentration of 5 mg L, a current density of 5 A m, 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 and 0.0073 kWh·mg. 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 to 1.4 mg L. This paper provides both a theoretical framework and a technological basis for the application of PSPC-EC in the advanced treatment of PV wastewater.