Study On The Removal Of Dissolved Effluent Organic Matter (dEfOM) In Secondary Tank By Vacuum Ultraviolet/persulfate System

According to statistics,many organic pollutants still remain in the effluent of the sewage plant,among which the dissolved effluent organic matter（d Ef OM）accounts for80%and 85%of the total chemical oxygen demand and total organic carbon of the effluent,respectively.The remaining d Ef OM will not only pollute the receiving water body,but also limit the reuse of the sewage.Therefore,in order to alleviate the problem of water pollution and water shortage,it is very necessary to design a new process for the removal of d Ef OM in the sewage.Vacuum ultraviolet（VUV/UV）advanced oxidation technology is highly efficient and environmentally friendly.It is often used to degrade micro-pollutants in water.The addition of persulfate enables the vacuum ultraviolet/persulfate（VUV/UV/PS）system to simultaneously generate HO·and SO₄·^-,which can enhance the removal ability of pollutants.This paper carried out the research on the removal of d Ef OM by the VUV/UV system and the VUV/UV/PS system.The study uses humic acid（HA）as the representative of d Ef OM,and investigates the removal efficiency of HA by VUV/UV and VUV/UV/PS systems,and explores the effect of reaction parameters and water background components on HA degradation.And the degradation mechanism was further studied.Finally,the effluent from the secondary sedimentation tank of a municipal sewage treatment plant in Chongqing was selected as the research object to investigate the removal effect of VUV/UV and VUV/UV/PS systems on d Ef OM in actual water.The results show that the VUV/UV system can effectively remove HA.When the initial HA concentration is 5 mg/L（DOC=2.15 mg/L）,p H=7,and the reaction time is 60minutes,the removal rates of UV₂₅₄ and DOC reached 95%and 80%,respectively.HO·is the main cause of HA degradation in the VUV/UV system.Compared with the VUV/UV system,the removal effect of the VUV/UV/PS system on HA is significantly improved.When the initial concentration of HA is 10 mg/L（DOC=4.3 mg/L）,PS=0.5m M,and p H=7,the removal rate of UV₂₅₄ and DOC reached 96%and 98.5%in 45minutes,respectively.HO·and SO₄·^-both participate in the degradation of HA,of which HO·plays a leading role.In the VUV/UV system and VUV/UV/PS system,the removal effect of HA increases with the decrease of p H,the decrease of the initial concentration of HA and the increase of the initial dosage of PS.The inhibition of HA by HCO₃^-and NO₃^-increases with the increase of concentration.Cl^-only showed significant inhibition at high concentration（10m M）on the VUV/UV system.The results of ultraviolet-visible spectroscopy,specific absorption parameters and three-dimensional fluorescence spectroscopy indicate that the molecular size of HA gradually decreases during the degradation process,and its aromatic structure is preferentially oxidized.For d Ef OM in actual water,the three-dimensional fluorescence results show that humus-like organic matter（humic acid,fulvic acid）accounts for more than 80%of d Ef OM.The introduction of VUV improves the removal of d Ef OM on the basis of UV and UV/PS,especially the removal of fluorescent organics.In the exploration experiment of COD removal,the VUV/UV/PS system has a good effect on the removal of COD.It can reduce COD from 56 mg/L to about 28.5 mg/L in 60 minutes,and the degradation rate reaches 50%,which is stable below the Grade A standard of the"Urban Wastewater Treatment Plant Pollutant Discharge Standard"（GB18918-2002）,it indicates that the VUV/UV/PS system has potential application value in advanced sewage treatment.