Molecular Weight Classification And Natural Photolysis Characteristics Of Dissolved Organic Matter In Sewage

Dissolved organic matter?DOM?accounts for more than 90%of the total organic matter in the effluent of the sewage plant,and its diverse components and complex properties are an important part of the effluent of the sewage plant.After the effluent from the sewage plant is discharged into the receiving water body,environmental factors such as natural light will have a significant impact on the composition,bioavailability and toxicity of DOM.In this study,the DOM from three typical wastewater treatment plants in Xi'an was used as the research object,and the DOM enrichment method was established and optimized;Using solid phase extraction technology?SPE?and Ultrafiltration centrifugation technology?UFC?,the distribution characteristics,physical and chemical optical characteristics,acute toxicity of photobacterium and SOS/umu genetic toxicity characteristics of DOM with different molecular weights in the effluent of wastewater treatment plants were discussed;Combined with the molecular weight classification of DOM and the masking of reactive photo-induced species?RPS?,the biological toxicity changes of effluent from wastewater treatment plant under natural light were discussed.Based on solid-phase extraction technology,this study established and optimized a method for the enrichment and enrichment of DOM in the effluent of wastewater treatment plants.The optimization content mainly includes the sewage water pretreatment method,the type of solid-phase extraction column activation elution solvent and the type of DOM cosolvent.And the recovery index of total organic carbon?TOC?,unsaturated compounds?UV254?and fluorescent dissolved organic matter?FDOM?were used as evaluation indicators.Experiments show that the established method can achieve a total organic carbon recovery rate of 81.9%,an unsaturated compound recovery rate of 91.7%and a fluorescent substance recovery rate of 66.7%.Studies on the molecular weight distribution of DOM in effluent from wastewater treatment plants show that DOM with a molecular weight of less than 3kDa accounts for80%to 95%of the total DOM,unsaturated compounds with a molecular weight of less than 3kDa account for 85%to 95%of the total unsaturated compounds and fluorescent dissolved organics with a molecular weight of less than 3kDa account for 75%to 95%of the total fluorescent dissolved organics.Among DOM,humic acid fluorescent dissolved organic matter accounts for 63.9%of the total fluorescent dissolved organic matter;Using SPE method and UFC technology to analyze the biological toxicity in the DOM of the wastewater treatment plant.The results showed that the genetic toxicity and acute toxicity of macromolecule DOM?10kDa?0.45?m?accounted for 48.4%and50.2%of total DOM toxicity,respectively.And compared with DOM in other molecular weight ranges,its unit organic carbon has the greatest genetic toxicity and acute toxicity;Further correlation analysis revealed that aromatic organics and fluorescent organics have a greater effect on the genetic toxicity of DOM and total organic carbon content and unsaturated compounds have a greater effect on the acute toxicity of DOM.The genotoxicity and acute toxicity of DOM in the effluent of wastewater treatment plant after solid phase extraction show different trends under simulated natural light conditions:With increasing of light time,the genotoxicity showed a downward trend,and the genotoxicity of DOM with a molecular weight of 1kDa to3kDa decreased the most;In contrast,acute toxicity is on the rise.Further research found that under simulated natural light conditions,masking ¹O₂ would slow down the rate of reduction of genotoxicity of DOM and accelerate the rate of increase of acute toxicity;Masking·OH will accelerate the reduction of the genetic toxicity of DOM and the increase of acute toxicity;Masking ³DOM*has a small effect on the rate of reduction of DOM genotoxicity,but it will accelerate the rate of increase of acute toxicity.