The Study On The Degradation Of Humic Acid In Water By Dielectric Barrier Discharge

Humic substances are the most extensively existing natural organic matter in natural environment, which consist of humic acid（HA）, fulvic acid and humicolin. HA is prevalent in natural water. Previous studies showed that the presence of HA in source water can increase the morbidity of Kaschin-Beck disease and pose the formation of cancerigenic disinfection byproducts. Therefore, it is urgent to develop a new effective method to degrade HA in source water.High voltage discharge plasma technology is one of advanced oxidation processes, which has the characteristics of easy operation and high removal efficiency etc. Dielectric barrier discharge（DBD）, in recent years, has attracted considerable interest because of its characteristics of uniform discharge and protecting electrodes. In terms of these advantages, the present study proposes by means of DBD to remove HA in source water. The mainly study aspects are degradation characteristic and mechanism of HA by DBD, and DBD combination with active carbon（AC） to degrade HA. Main research contents are as follows:1. According to investigating the effects of discharge voltage, air flow rate, initial concentration, original p H and different ions on HA removal efficiency, the degradation characteristic was studied, the results uncovered that removal efficiency of HA by DBD reached 89.4% under 40 min treatment when the discharge voltage and air flow rate were 19.6 k V and 160 L/H, and the initial concentration and p H were 30 mg/L and 6.5; increase of discharge voltage was helpful for HA removal; relatively higher air flow and initial p H inhibited the HA removal after promoting it;higher solution initialconcentration was adverse for HA removal but increased the removal total amount of HA.Cu²⁺,CO₃^2- and Cl^- performed apparently inhibition effects on HA removal, while Fe²⁺ promoted HA removal at the first stage, and then the concentration of HA was almost unchanged with increasing the treatment time. Meanwhile, the effects of SO₄^2- and NO₃^- on HA removal were negligible.2.The degradation mechanism of HAwere analysized via hydroxyl capture agent, fourier transform infrared spectroscopy（FTIR）, specific UV absorbance（SUVA）, excitation-emission matrix（EEM） fluorescence, scanning electron microscope（SEM） etc. The results showed that OH was generated by DBD and contributed a lot for HA removal; after DBE treatment, the C-H bond of HA was opened, and O-containing groups of HA increased; the aromatic structure and colour groups of HA decreased with the increase of the treatment time;surface of HA became more uniform and smoother by reason of Union bridge effect, which is because surface groups of HA reacted with active species produced by DBD. Meanwhile, HA varied gradually from macromolecular organic compound to small one; eventually, part of HA was mineralized as H₂ O and CO₂.3. DBD combination with AC was employed to treat HA in water. Using absorption isotherms, kinetics and the investigation of absoprtion effect of HA onto AC, the absorption characterisitic of HA by AC was studied; according to the analysis of removal effect of HA by DBD combination with AC, and the meatures of determining reactive speices, FTIR and SEM etc, the degradation mechanism of combination system was studied. The findings demonstrated that the absorption behavior of HA by DBD conformed to Langmuir model, and pseudo-first order kinetic model; the HA adsorped amount increased with increasing the AC addition amount.DBD combination with AC could evidently enhance the removal efficiency of HA with respect to using DBD alone; the results of FTIR unveiled that the intensities of C-O bond,-OH bond and C=C double bond decreased after DBD treatment; SEM illustrated porous structure of HA surface reduced, and its morphology became more uniform.