Performance And Mechanism Of Trace Organic Contaminants Removal By Modified Anthracite In Water

Trace Organic Contaminants?TrOCs?are characterized by low content,refractory degradation,high toxicity,and bioaccumulation.In recent years,different concentrations of TrOCs have been detected in different water bodies around the world,which has attracted the attention of researchers and environmental regulators in various countries.Because TrOCs are trace in water,TrOCs cannot be effectively removed from water by conventional drinking water treatment,and the by-products after disinfection may be more harmful than the parent material.Therefore,how to effectively remove TrOCs from drinking water is an urgent problem to be solved.Filtration,as an important process of conventional drinking water treatment,plays a crucial role in the drinking water treatment process and has also been widely used in the deep treatment of sewage.Anthracite filter materials are widely used in filters and canisters due to their good chemical stability,large mechanical strength,and low cost.In this paper,six frequently reported TrOCs,bisphenol A?BPA?,estrone?E1?,17?-ethynylestradiol?EE2?,sulfamethoxazole?SMX?,sulfamethazine?SMZ?and chloramphenicol?CAP?,were used as target materials to study the removal performance of TCOCs by anthracite and modified anthracite,in the hope of that anthracite could adsorb and remove TrOCs in water while retaining particulate matter as filter material.Firstly,an effective method for solid phase extraction-high performance liquid chromatography?HPLC?enrichment and detection of target TrOCs was established.Waters Oasis HLB solid phase extraction cartridge could effectively recover target TrOCs in water samples.The HPLC detection condition was SB-C18 column?5?m,150×4.6mm?.The mobile phase flow rate was 1.0 mL min^-1.The injection volume was10?L.Column temperature was 30oC.UV detection wavelength was 230 nm.When detecting a single target,the mobile phase was 100%methanol.When detecting BPA-EE2 mixture,the mobile phase was acetonitrile and water?1:1,v/v?.The physicochemical properties and structural characteristics of anthracite were analyzed comprehensively by scanning electron microscopy,specific surface area and pore size analysis,X-ray energy spectrum,X-ray diffraction,infrared spectroscopy,surface functional group determination and thermal analysis.The anthracite particles were modified by soaking solution of KOH and H₂SO₄ and by high temperature reduction.Anthracite is a mixed material with uneven surface structure and chemical composition.Anthracite is mainly composed of mesopores and contains a variety of inorganic minerals and surface functional groups.After modified by low concentrations of KOH and H₂SO₄(0.5⁶ mol L^-1),the specific surface area and pore size of anthracite are increased.When the concentration of KOH is higher than 8 mol L^-1,anthracite structure collapses,with specific surface area and pore size reduced.When the concentration of H₂SO₄ is higher than 9 mol L^-1,anthracite has little change in specific surface area and pore size,but concentrated sulfuric acid can form a secondary modification to anthracite,resulting in specific surface area and aperture increased.After modified by KOH,the number of acidic groups decreased and the number of basic groups increased.After H₂SO₄ modification,the number of acidic groups increased,and the number of basic groups decreased significantly,even undetected.After modified by high temperature?400?and 600?in N₂ environment?,anthracite surface is broken,the number of micropores and lactone groups increased,while other functional groups are reduced.KOH modified anthracite has the best removal effect on BPA,E1,EE2 and CAP,while H₂SO₄ modified anthracite has the best removal effect on SMX and SMZ,and the removal ability is greatly improved.The removal effect of high temperature modified anthracite on six TrOCs is worse than that of raw anthracite.The removal rates of TrOCs in different concentrations of KOH and H₂SO₄ modified anthracite were similar,and the changes in specific surface area,functional group and ash content of modified anthracite were similar.The variation trend of TrOCs removal rate of modified anthracite with different concentrations of KOH and H₂SO₄ is similar to the changes in specific surface area,functional group and ash content of modified anthracite.In the static adsorption study,the adsorption of EE2 and BPA by un-anthracite?unmodified anthracite?and 4K-anthracite(4 mol L^-1 KOH modified anthracite)is a single-layer chemical adsorption in heterogeneous system.Under the same conditions,the adsorption capacity of EE2 and BPA by 4K-anthracite is significantly larger than that by un-anthracite,which is about 1.66².38 times.At pH=7,ligand exchange,hydrogen bond and?-?bond exist simultaneously in the adsorption of anthracite on EE2,while the adsorption of BPA by anthracite is mainly?-?bond.At pH=3,the anthracite surface is acidified and positively charged,providing more active sites for the adsorption of EE2 and BPA.At pH=12,the?-?bond is the main mechanism for the adsorption of EE2 and BPA by anthracite.The electrostatic repulsion leads to the reduction of the adsorption of EE2 and BPA by anthracite.In the EE2-BPA bi-component system,BPA has a very obvious competitive adsorption advantage.BPA molecules form?-?bonds with the surface of anthracite,which preferentially occupy the active sites,resulting in a significant decrease in the adsorption of EE2 by anthracite.The site energy distribution of the anthracite surface is not uniform,the site energy heterogeneity values rang from 2.34 to 8.99 kJ mol^-1 and the number of high energy sites is limited.With the increase of temperature?288³08 K?,the site energy of the anthracite surface increases,the average site energy values increase from 4.08¹1.59 kJ mol^-1 to 7.42¹4.56 kJ mol^-1 and the total amount of active sites increases.According to the analysis of site energy distribution curve,the active sites of 4K-anthracite are obviously more than that of un-anthracite,and the increase of high energy sites and low energy sites causes the adsorption amount of EE2/BPA on the surface of 4K-anthracite to be much larger than that of un-anthracite.One end of the EE2 molecule is adsorbed on the anthracite surface,while the BPA molecule is adsorbed in parallel on the anthracite surface,occupying multiple sites.In EE2-BPA bi-component system,smaller BPA molecules are more likely to enter the pores,occupy the active sites,and form higher energy?-?bonds,which hinder the adsorption of EE2 molecules on the anthracite surface.In the dynamic adsorption study,the dynamic trapping EE2 by anthracite filter column is the result of the combined action of physical interception and chemical adsorption.The breakthrough curve is divided into three processes:I.At the initial stage of filtration,the physical interception of the upper layer of the filter column increases rapidly;II.EE2 trapped in the upper layer falls off and is trapped by the lower layer;III.The system is balanced,and EE2 is intercepted by the filter materials of each layer from top to bottom,and the breakthrough curve gradually rises.Bohart–Adams dynamic adsorption model can be well fitted with the data of anthracite filter column after retaining EE2 stability?R²>0.918?.According to the model parameters,the adsorption capacity of EE2 per unit mass anthracite of different layers in 4K-anthracite filter column is 1.2³.5 times that of un-anthracite filter column,and the penetration time of4K-anthracite filter column is 1.3².0 times that of un-anthracite filter column.When anthracite?modified anthracite?is used as the filler of filter column to adsorb and retain dissolved organic matter?such as TrOCs?in water,a relatively slow filtration speed should be adopted,which is beneficial to exert the dual functions of physical interception and chemical adsorption,and is also conducive to ensure the stability of filtration system and effluent quality,and extend the service life of the filler.