The Study On Hydrogen Peroxide Generation And Sodium Dodecyl Benzene Sulfonate Degradation In Natural Water Biofilms System

Diurnal rhythm is one of the basic laws of nature and photochemical process is avery important aspect of the pollutants environmental behavior. In natural waterenvironments, photochemical process can produce reactive oxygen species (ROS)which will have great impact on pollutants environmental behavior. The ROS innatural waters is usually generated by non-living substances dissolved organic matter(DOM) under illumination. In addition, diurnal rhythm periodically altersmicro-environmental parameters (pH and DO) by altering the metabolism of algae,which results in the periodically change of concentrations and forms of heavy metalsin waters, and this has important impact on migration and transformation,bioavailability and ultimate fate of trace metals. However, there are many organicpollutants in natural waters, but studies on the impact on diurnal rhythm of organicpollution in natural waters are very limited. Algal physiology studies indicate that themetabolism (photosynthesis) process can not only generate dissolved oxygen to alterpH, but also can generate ROS.Natural biofilms naturally exist on the surfaces of solid materials such as surfacesediment, sand, rocks and so on in rivers, lakes, wetlands and other natural waterenvironments. Therefore, illumination variation may affect the variation of themetabolism (photosynthesis and respiration) of algae in biofilms and indirectly affectthe generation of ROS, thereby affects pollutants environmental behavior. Sincebiofilms contain almost most of the material composition and pollutants behavior thatmay contain in natural waters environments. The pollutants environmental behavior inwater-biofilm system can better reflect the pollutants in natural water environmentalbehavior than in single artificial algae system. Therefore, it is necessary to carry on the studies on laws and mechanism of biofilms and typical organic pollutants underillumination variation to further understand the impact of illumination variation onmigration and transformation of organic pollutants in water environments, whichcontributes to a better understanding of the actual environmental behavior of organicpollutants under natural diurnal rhythm condition.In this study, the degradation laws and mechanism of sodium dodecyl benzenesulfonate (non-volatile and non-persistent DBS, used as a representative of degradableorganic pollutant) under different illumination conditions were investigated throughsimulation experiments and by the construction of water-biofilm system as a carrier.These include: effects of activity of natural biofilms on DBS and hydrogen peroxide(H2O2) concentration to verify whether the biofilm system can generate H2O2; mainfactors affecting H2O2generation and its impact on DBS degradation in simulationsystem; influences and mechanisms of biofilm components and typical ions on H2O2degradation; the relation between H2O2and other ROS, and its impact on DBSdegradation. On this basis, this paper will analyze and summarize the influence lawsand mechanisms of illumination on natural biofilms and typical pollutants, and furthersummarize the influence of diurnal rhythm laws on organic pollutants environmentalbehavior in water environments.In this study for the research on H2O2generation and DBS degradation, it isfound that under the same biomass condition, the biofilm system which has activitycan generate H2O2, and the concentrations of DBS and TOC are significantly reduced.The amount of H2O2generation was34.0μmol/L and17.2μmol/L, DBS leveldeclined85.2%and12.9%, TOC level declined67.1%and10.9%respectively underillumination and in darkness. It explains that biological activity is the key to H2O2generation and then DBS degradation under illumination and in darkness.Illumination is an important factor on biofilms generating H2O2, and H2O2is one ofthe reasons of DBS degradation. Through degradation of H2O2solution on DBSexperiment, it is verified the degradation effect of H2O2on DBS, and analysis resultsare: there are two main ways for H2O2generated by biofilms to degrade DBS:(1)H2O2can directly degrade DBS;(2) H2O2is likely to generate ROS and then indirectly degrade DBS. Biofilms may also generate other ROS to degrade DBS. Inaddition, illumination can not only promote biofilms to generate H2O2, but also havephotochemical reaction with H2O2and promote DBS degradation. Illumination is animportant factor of H2O2generation and DBS degradation.In the study of existing form and the amount of biofilms, it is found that bothexisting form and amount of biofilms affect H2O2generation and DBS degradationunder illumination and in darkness. Under illumination, existing form of biofilms hasless impact on H2O2generation and DBS degradation than that in darkness. Theamount of H2O2generation and DBS degradation are proportionally increased withthe increase of the amount of biofilms, and the increase amount is higher underillumination than that in darkness.For the study of the influences of dissolved oxygen (2mg/L≤DO≤20mg/L) on H2O2generation and DBS degradation, it is found that under illumination,the amount of H2O2generation and DBS degradation was nonlinear increased with theincreasing of DO concentration. DO is an important factor on H2O2generation andDBS degradation, especially in darkness. DO can not only promote biofilms togenerate H2O2, and affect the concentration of H2O2that have been generated, butalso maybe involved in the degradation process of DBS degradation intermediateproducts.The study of H2O2generation and DBS degradation mechanism in water-biofilmsystem combined with biofilms generating O-2and releasing Fe2+experiments andthe effects on H2O2generation found that: Biofilms can generate superoxide anionradicals (O-2), which has a significant effect on H2O2generation and Fe2+release andis closely linked to H2O2generation and Fe2+release, O-2. Fe2+and illumination willpartly promote H2O2to transform and generate other ROS (such as OH and1O2). Inthe H2O2solution experiments of biofilm components and iron and manganese ionson H2O2degrate DBS, it can be drawn that typical components and iron andmanganese ions (Fe2+、Fe3+and Mn2+) in biofilms will promote H2O2to degrade DBS,especially in the presence of Fe2+. So, DBS degradation in natural biofilms is theresult of various reasons. But this study proved that at least biofilms can generate H2O2and Fe2+, and then on the surface of or near the biofilms can form similarmicro-Fenton system to degrade organic.