Study On Degradation Of Trichloromethane And Humic Acid In Water By Liquid-phase Radio Frequency Discharge Plasma

Trichloromethane is a common halogenated organic pollutant,widely used in industrial processes and life,and it can also be produced during the disinfection with chlorine.Long-term exposure to high levels of trichloromethane poses serious harm to human health.Humic acid,the precursor of chlorine disinfection by-products,exists widely in natural water.It can increase the morbidity of Kashin-Beck disease,leads to water turbidity and other environmental problems.In recent years,liquid-phase radio frequency plasma has gained increasing attentions due to the characters of low breakdown voltage,being able to form at atmospheric pressure,and high energy utiizing efficiency.In this paper,a new liquid phase radio frequency system was designed,and the degradation of trichloromethane and humic acid by this reactor were investigated.The main conclusions are as follows:(1)The main free radicals produced in the liquid-phase radiofrequency plasma are·OH and ·H.When the conductivity is in the range of 0.10～0.80mS/cm,the spectral intensity of ·OH increases with the increase of conductivity.When the conductivity is in the range of 0.80～6.00mS/cm,the spectal intensity of ·OH decrease with the increase of conductivity.(2)Increasing the solution pH,and adding free radical scavenger and NO3-to the solution can improve the removal of CHCl3.As HCO3-can play as a buffer and consuming ·OH(indirectly increased the amount of ·H),with no formation harmful product is the ideal material to enhance the removal of CHCl3.The main intermediates formed during the discharge treatment include HCOOH,H2C2O4 and CH2Cl2.·H and egq-are the key substances that trigger dechlorination of CHCl3 and play an important role in the production and transformation of organic acids and dichloromethyl radicals.·OH mainly contributes to the degradation of organic acids.The final products are CO2,H2O and HCl.The enrichment and pyrolysis of CHCl3 by partial high temperature during the discharge process also contribute to increase of the removal.Liquid-phase radio frequency plasma technology can also be effective for the removal of CH2Cl2,and the degradation mechanism is similar to that of CHCl3.(3)Addition of Fe2+ to the solution to react with the H2O2 formed during the plasma treatment lead to the increasing removal of HA.The optimum pH range is 3.50～5.50.When the initial concentration of HA is 30mg/L,the optimum concentration of Fe2+ is 20mg/L,where the removal of HA can reach to 90.23%.High concentration of HA can also be removed,when the initial concentration of Fe2+ is 20mg/L and the initial concentration of HA is 60mg/L,the removal can reach to 95.33%.After the discharge treatment,the aroma of HA is weakened,the macromolecules are decomposed into small molecules,the intensity of C=C,C-O and hydroxyl decrease,and the intensity of-CH-increase.