Humic acid removal from micro-polluted source water in the presence of inorganic salts in a gas-phase surface discharge plasma system

Humic acid (HA), a predominant type of natural organic matter in surface water, had several potential environmental and health risks. A gas phase surface discharge plasma system was employed to eliminate HA from micro-polluted surface water, and the effects of some concomitant inorganic ions on HA removal were evaluated. The experimental results showed that approximately 89.4% of HA could be smoothly eliminated after 40 min of the discharge plasma treatment, and the HA removal process could be fitted well by the first-order kinetic model. The presence of anions such as CO32− and Cl− in the natural water were adverse for the HA removal due to their competition for the active species, whereas the effects of NO3− and SO42− on the HA removal could be neglected; this deduction was also confirmed via the evolution of fluorescence spectra intensity of OH radicals. Although Cu2+ could react with H2O2 via Fenton-like reaction, its presence was still adverse for the HA removal due to the complexing effect of Cu2+ with HA molecules. In addition, the HA removal processes were characterized by UV-Vis spectrum, DOC removal, specific absorbance parameters, and three-dimensional fluorescence spectrum analysis.