Study On Removing Pahs Characteristics In Secondary Effluent By Nanofiltration

Polycyclic aromatic hydrocarbons(PAHs),as a type of persistent organic pollutants widely present in nature,have the characteristics of refractory,carcinogenic,teratogenic,mutagenic,etc.They have a wide range of pollution and many sources,and have always been the focus of environmental monitoring Target,and in recent years it has gradually become one of the potential sources of pollution in water safety.At present,the conventional wastewater biological treatment process has limited ability to remove PAHs,resulting in a large amount of PAHs in the effluent,and further research is urgently needed.In this paper,naphthalene and phenanthrene are selected as representatives of polycyclic aromatic hydrocarbons,and three nanofiltration membranes of NF270,NF90 and DK are used for treatment.By studying the retention characteristics of nanofiltration on PAHs under different types of nanofiltration membranes,operating pressures,and p H values,the optimal operating conditions were determined.On this basis,humus,protein,and glucose were added separately to study the coexistence of organic matter and polycyclic aromatic hydrocarbon The effect of the removal effect was finally studied on the characteristics of membrane pollution during the removal of polycyclic aromatic hydrocarbons by nanofiltration membranes.In order to provide scientific basis for nanofiltration membrane to remove PAHs in water environment.Research indicates:(1)NF270,NF90 and DK nanofiltration membranes were subjected to nanofiltration membrane treatment experiments under the operating pressures of 0.3,0.5,0.7,0.9 and 1.1 MPa.The results showed that:(1)The membrane fluxes of the three nanofiltration membranes increase with the increase of operating pressure,and under the same pressure conditions,the membrane flux size is accordingly: NF270> DK>NF90.The rejection rate of PAHs is inversely proportional to theoperating pressure.The lower the pressure,the higher the rejection rate.However,the lower membrane flux is smaller when the pressure is 0.3MPa.Therefore,the optimal operating pressure was determined to be 0.5MPa.(2)At a pressure of 0.5 MPa,the removal efficiency of NF270 for PAHs is low,among which the removal rate of phenanthrene is 88.99%,and the rejection rate of naphthalene is only about 73.10%,and the rejection effect of NF90 and DK nanofiltration membranes on PAHs is better.The removal rate of naphthalene reached more than 88% and the removal rate of phenanthrene reached 97%.However,due to the low permeation flux of NF90,DK membrane was determined as the best membrane module for PAHs removal in this study.(2)DK nanofiltration membrane treatment experiments were carried out under the conditions of p H 5.0,6.0,7.0,8.0,and 9.0.The results show that the membrane flux of DK membrane increases with the increase of p H.Among them,the removal efficiency of naphthalene With the increase of p H,the phenanthrene reached a very high removal efficiency at the experimental p H value.Among them,the retention rate under acidic or alkaline conditions reached more than 98%,and the retention rate under neutral conditions was relatively low,at 97.90%.(3)The effect of coexisting organic matter(humic acid,protein,glucose)on the removal of PAHs by nanofiltration.The results show that the membrane flux of nanofiltration membranes is reduced and the removal efficiency of PAHs is increased.The coexistence of organic matter can promote the removal efficiency of nanofiltration membranes for PAHs.Among them,the promotion of naphthalene is as follows:glucose>humic acid>protein,and the promotion of phenanthrene is as follows: humic acid>protein>glucose.At the same time,the nanofiltration membrane has a good removal effect on humic acid and protein,generally reaching 100%,and a poor removal effect on glucose.(4)The results of membrane fouling studies show that the flux ofnanofiltration membranes gradually decreases with the running time of the experiment,especially at the initial stage of the experiment.The degree of pollution impact is as follows: protein> humic acid> glucose>no organic matter.The ATR-FTIR results also indicate that the protein has a greater degree of contamination of the nanofiltration membrane.