Study On The Removal Of Disinfection By-products And Emerging Organic Micropollutants In Water By Graphene-based Materials

Disinfection by-products(DBPs)are found in drinking water after traditional water treatment process,and emerging organic micropollutants(OMPs)are frequently detected in surface water due to massive discharge of human production and life.New water treatment material and process urgent need to be explored and studied due to pollutants have been caused long-term adverse effects on human health.Four functionalized graphene-based materials were successfully synthesized in present work and applied to water purification.All these graphene-based materials were used to investigate its removal efficiency and mechanism for DBPs and OMPs removal.First,graphene oxide(GO)was used for terminal removal of haloacetic acids(HAAs)in water.30% of HAAs could be rapidly removed by GO within 2 minutes due to interaction of intermolecular hydrogen bonds.The removal efficiency of HAAs decreased with increasing pH from 3 to 11.Temperature is not the main influence factors for haloacetic acids removal,and only affect interaction rate of intermolecular hydrogen bonds.As a type of weak interaction,intermolecular hydrogen bonds are easy to be fractured by water shear force,and continuous adsorption process was used for further removing HAAs.After five adsorption processes,HAAs could be removed by 88%,and total contact time was just 2.25 min.In order to avoid the secondary pollution caused by outflow in water,GO was modified to prepare magnetic graphene oxide(MGO)which was magnetically recyclable.DBPs precursors can be effectively removed by MGO adsorption in surface water.The removal efficiency of DBPs precursors increased from 7-19% to78-98% in four surface water samples after MGO treatment and the process rapidly reached equilibrium within 20 minutes.The DBP precursors removal efficiency decreased with the increasing pH value from 4 to 10.Hydrophobic compounds(humic acid and fulvic acid)are more sensitive to MGO,whereas hydrophilic and nitrogenous compounds(aromatic proteins)are more insensitive.MGO could be regenerated by using 20%(v/v)ethanol and,the DBP precursors removal efficiency can stay stable after five cycles.Magnetic porous graphene(MPG)with high specific surface area was prepared by further optimizing the common graphene-based materials.The well prepared MPG was used for evaluating its adsorption character for triclosan(TCS),one of the mostfrequently used broad-spectrum antimicrobial agent in personal care products.The results indicated that 98% of TCS can be adsorbed by MPG,the adsorption efficiency was much better than that of quartz sand,graphene,GAC,PAC and even MGO.The removal process was found to follow a pseudo-second-order kinetics.Though the ozonation can efficiently remove of TCS,the ozonation intermediates such as2,4-DCP shoud be concerned.The present work investigated the removal efficiency of TCS by the combination of MPG adsorption and ozone oxidation,and the results shows TCS can be totally removed and intermediates can also be minimized by the process of MPG adsorption followed by ozonation(MPG+O3).Comparing to the process of ozonation followed by MPG adsorption(O3+MPG),MPG+O3 can shorten the reaction time and reduce ozone consumption.MPG could be regenerated by using deionized water and,the TCS removal efficiency can stay stable even after five cycles.Moreover,twelve selected organic micropollutants can be effectively removed by MPG contributed to its high specific surface area and rich pore structure.In order to avoid loss of traditional filter medium and difficult to fill up,stable three-dimensional graphene(3DG)was prepared.The well prepared 3DG was fill into a Polymethyl methacrylate column to modify the fixed bed reactor for drinking water purification.With increasing empty bed contact time(EBCT),the removal efficiency of UV254,turbidity,residual chlorine and halogenated volatile DBPs increased.However,the removal efficiency of HAAs decreased with increasing EBCT.The combination use of 3DG and quartz sand can significantly reduce the 3DG consumption and thus reduce the treatment cost.In addition,the combination treatment can effectively increase the removal efficiency of turbidity,residual chlorine and some kinds of DBPs.The combination use of 3DG and quartz sand can either effectively remove all the 12 OMPs,and the removal efficiency was much higher for OMPs with hydrophobic and large molecular weight,that may be contributed to the competitive adsorption effcet on the surface adsorption site of MPG pores.Also,the OMPs removal efficiency increased with the increasing EBCT.In summary,graphene-based materials can be utilized as promising adsorbents for the removal of DBPs and OMPs from water.