Enhanced removal ability of phenol from aqueous solution using coal-based carbon membrane coupled with electrochemical oxidation process

A treatment system combining the coal-based carbon membrane with electrochemical oxidation process was designed for the enhanced phenol removal ability. The effects of various parameters including electric voltage, phenol concentration, solution pH, rotate speed, electrolyte type and concentration, and electrode distance on the permeate flux and removal efficiency of the treatment system were carried out. The degradation intermediates of phenol were detected by gas chromatography-mass spectrometry (GC-MS). The results showed the phenol removal ability of carbon membrane was significantly improved by coupling with electrochemical oxidation process. High phenol concentration usually increased the load of the treatment system, resulting in low permeate flux and removal efficiency because of limited decomposition ability. When the initial pH increased from 4.0 to 10.0, the enhanced permeate flux and removal efficiency were observed. The permeate flux displayed a decrease trend with the increase of electrode distance, while the removal efficiency showed an opposite trend. The optimum operation parameters of 2.0 V electric voltage, 7.5 r/min pump rotate speed, and 2.50 g/L Na2SO4 were recommended. During the degradation process, the reactive free radicals and H2O2 attacked the benzene ring of phenol to produce catechol, hydroquinone and resorcinol. And then, hydroquinone was degraded to benzoquinone, which was further decomposed to organic acids such as maleic, fumaric, and oxalic acids. Finally, these organic acids were oxidized into CO2 and H2O.