Study On The Optimal Removal Mechanism Of Pahs By Artificial Wetland DOM

Based on the Dissolved organic matter(DOM),the dissolved organic matter(DOM)plays a key role in pollutant migration and metabolism,the Polycyclic aromatic hydrocarbons,dissolved organic matter(DOM)are investigated in the in-depth treatment of wastewater in constructed wetland system.Research on the influencing mechanism of PAHs removal.In this paper,the typical wetland plants P.australis and Cladophora were selected to discuss the main dissolution components of DOM and their dissolution rules,and to study the binding pattern and interaction between DOM and PAHs.A lab-scale pilot constructed wetland system was established to explore the feasibility of using different DOM to enhance the removal effect of organic pollutants in the constructed wetland system.The influence of DOM on the adsorption of PAHs in the working wetland matrix and the absorption and migration behavior of PAHs in plants was clarified,and the influence of DOM on the microbial community structure of the system was mastered.Metagenome was used to clarify the changes of PAHs metabolic pathway under the action of DOM.The main experimental contents and results were as follows:(1)Both plant species and state can affect the DOM type and its release process.DOM in reed was mainly composed of humic acid-like components(C3 and C5,52%),proteinoid components(C1 and C2,52%)in fresh setae,and humic acid-like(HA)components(C3 and C5,55%)in dried Setae.There was a strong correlation between TOC/UV254/NH4+-N and DOM components,which reflected that humic acid components were the key factors affecting water quality in the system.DOM release from fresh plants showed a two-stage sequence of first fast and then slow release,while DOM release from suicidal dried green plants presented a linear release(R2 =0.87-0.97),which was related to plant species,tissue structure,biological activity and photodegradation of different substances during the release process.Stern-Volmer equation analysis shows that plant derived DOM interacts with PAHs to form ground-state complexes,and the interaction ability of DOM and PAHs is in order of Benzo[k]fluoranthene(Bk F)> Benzopyrene.(Bap)> Phenanthrene(PHE),and the interaction capacity of DOM components with PAHs was C3 > C5 > C2 > C1 > C4.The hydrophilicity,aromatics,molecular weight and environmental conditions of DOM and PAHs all affect their interaction characteristics.Therefore,scientific management is of great significance to reduce the ecological risk of PAHs during the advanced treatment of tailwater in constructed wetland.(2)DOM can improve the operation effect of constructed wetland system.Compared with the control group,the removal rates of total nitrogen,COD and phosphorus increased by18.7%,20.6% and 15.4%,respectively,and the removal rates of PHE,Bap and Bk F increased by 12-17%,8-15% and 11-13%,respectively.Due to the linear arrangement of benzene ring,the octanol-water distribution coefficient is lower and the tricyclic PAHs has certain volatility.Compared with pentyclic PAHs,the removal rate of tricyclic PAHs is easier to remove,and the removal rate is 3.2-6.7% higher than that of pentyclic PAHs.In addition,the average Σ3PAHs removal rate in the shallot wetland system(SV group)was 9.78%±1.35% higher than that in the plant-free control group(CO group),indicating that the presence of plants can significantly enhance the purification effect of organic pollutants in the constructed wetland.(3)DOM addition decreased the adsorption of PAHs on the substrate surface,Σ3 PAHs content was 5.97 μg/kg in SV-C matrix without DOM addition,which was higher than that of plant DOM(SV-A,5.42 μg/kg)and commercial humic acid(SV-B,SV-B,SV-B).4.96 μg/kg)wetland system.DOM addition increased the uptake of Σ3 PAHs by wetland plants,and the uptake of Σ3 PAHs by plants in SV-A and SV-B constructed wetland systems accounted for11.4% and 15.8%,respectively.DOM promoted the enrichment of Pa Hs-degrading bacteria in the microbial community.Overall,the contribution of microbial degradation to the removal of PAHs in the constructed wetland system accounted for 40%-59%.The key enzymes Geobacter,Rubrivivax,Anaeromyxobacter,Methyllibium,Arthrobacter,Streptomyces,cytochrome P450,cat E and lip V were found in beta 3 through metamenomics analysis The enzymes involved in oxidative phosphorylation and pentose phosphate pathway(fad D,dna E,mdh and sdh A,etc.),which play an important role in PAHs degradation,also increase significantly under the influence of DOM.At the same time,it was found that a high proportion of sulfur-reducing bacteria(such as thiobacillus and erythrobacter)played an important role in promoting microbial sulfur metabolism,which was conducive to the removal of PAHs.