The Generation Of Reactive Oxygen Species And Degradation Of Typical Organic Pollutant In Natural Biofilm Systems

Natural Water Biofilm is a complex biological community in natural water, which plays an important role in the migration and transformation of organic pollutant in natural water. The Reactive Oxygen Species（ROS） generated by natural water biofilm are important factors to affecting the degradation of organic pollutant. Sodium Dodecyl Benzene Sulfonate（SDBS） is an representative of organic pollutant as its characteristics of non-volatile, non-persisent and easy to determine.In this study, hydrogen peroxide（H₂O₂） was selected as the representative of ROS.We use single variable method to investigate the affecting factors, such as light/dark variation, biofilm quantity, presence of ligands and p H value, on H₂O₂ generated by natural water biofilms. Catalase（CAT）, Isopropanol（IPA）, Superoxide Dismutase（SOD）, Furfuryl Alcohol（FFA） were selected as scavenger or quenching agents of H₂O₂, hydroxyl radical（·OH）, superoxide anion（·O₂^-）, singlet oxygen（¹O₂）, respectively, and the effect of degradation of ROS on DBS was measured by removing a single ROS. Fluorescence probes were used to investigate the removal efficiency of scavenger or quenching agents,and Vanillin anil, 2-（2’- methyl pyridine and amine） phenol and An-Cy were selected as the fluorescence probes of ·OH, ·O₂^-, ¹O₂, respectively.The results showed that in the biofilms simulation system under illumination, H₂O₂ concentration increased significantly over time under illumination and the generation rate was fast at first and then gradually stabilizing. H₂O₂ concentration decreased when the system switched to darkness, and the concentration was above zero when the system was in the darkness. There were H₂O₂ generation and accumulation in the darkness system, but its concentration was significantly lower than that under illumination. The increase and decrease of biofilm quantity could directly lead to the corresponding change of H₂O₂ concentration. The presence of organic ligands could lead to significantly decrease of H₂O₂ concentration in the system. H₂O₂ concentration was higher when the system p H value was5 and 7 than that was 9. These factors affected H₂O₂ concentrations in the biofilm systems by affecting three key processes, which were H₂O₂ generation of natural water biofilms,H₂O₂ decomposition and H₂O₂ removal by biofilms. In the system which had both biofilms and illumination, H₂O₂ generation of natural water biofilms was the most important process.There were H₂O₂, ·OH, ·O₂^- and ¹O₂ in the biofilms simulation system under illumination, and the selected scavenger or quenching agents（CAT, IPA, SOD, FFA） could effectively remove the existing ROS（H₂O₂, ·OH, ·O₂^-, ¹O₂, respectively） in the system.The DBS degradations were different before and after the removal of the four kinds of ROS（H₂O₂, ·OH, ·O₂^-, ¹O₂）, which indicated that these four ROS all had degradation on DBS. In adding SOD system, SOD can dismutase ·O₂^- to H₂O₂ and O2, which could lead to the increasing of H₂O₂ and dissolved oxygen concentration, and then increased the DBS degradation in the system. In adding CAT, IPA and FFA systems, H₂O₂ concentrations decreased because the scavenger or quenching agents could remove the corresponding ROS and break the balance of H₂O₂ and other ROS, which could lead to the decrease of DBS degradation. DBS degradation was the result of different ROS interactions in the natural water biofilm systems. H₂O₂ played a major role in DBS degradation because of its high stable concentration. ·OH, ·O₂^- and ¹O₂ had direct and indirect effects on DBS degradation. The degradation effects of these three ROS were lower than the effect of H₂O₂ because of their short lifetimes and low concentrations.