Spectroscopic characteristics and disinfection byproduct formation during UV-assisted photoelectrochemical degradation of humic acid

Abstract

UV-assisted photoelectrochemical processes (UV/E) that produce reactive species are extensively used for degrading pollutants in water, such as natural organic matter (NOM). However, the consequence of the chlorinated disinfection byproducts (DBPs) from smaller compounds broken down is not clear in the UV/E. In this study, excitation-emission matrices (EEM) and parallel factor analysis (PARAFAC) were applied to determine the products formed during decomposition and the influence of UV/E processes on the formation of DBPs. In comparison with UV photochemical and electrochemical processes, the deterioration rate of NOM in the UV/E process rose by 68.45% and 54.47% in 70 min, while it increased up to 48.85% under the electrochemical process in 23 h. Not only does the reaction time affect the degradation, but the electrolyte concentration and current density also disturb it. The EEM peak locations were 275 nm/495 nm (Component 1), 275 nm/410 nm (Component 2), 230 nm/405 nm (Component 3), and <220 nm/290 nm (Component 4), which were considered to humic acids, hum-like compounds, fulvic acid-like compounds, and aromatic proteins, respectively. C1 and C2 were well relevant to dissolved organic carbon (DOC) and UV254 (r = 0.925–0.963, p < 0.01) and the formation of MCAA, DCAA, and TCAA were strongly interrelated with UV254 and DOC (r = −0.711 to −0.584). The generation of DBPs has a good correlation with C2 (r = – 0.673, p < 0.01). DBPs formation and calculated theoretical cytotoxicity were significantly suppressed by the UV/E process with a higher degradation of NOM. A similar amount of DBPs formation was obtained while 52.6% and 82.90% of the DOC was reduced under the electrochemical process and the UV/E process, indicating that a lower DBPs production and higher degradation efficiency in the UV/E process. It was supposed that the UV/E process could be an alternative for natural organic matter oxidation with properly controlled DBP formation.