| Organic micropollutants(OMPs,including pesticides,endocrine disrupting compounds,pharmaceutical and personal care products,etc.)are ubiquitous in the aquatic environment wastewater.Low concentrations of these organic contaminants(ng/L to mg/L)have been shown to cause significant effect on vertebrate and ecosystem health.However,most of OMPs could not be completely removed by conventional wastewater treatment processes.Activated carbon adsorption method is the most common used technologies for OMPs removing.However,activated carbon adsorbent also has lots of shortcomings,such as bad mechanical strength,difficult to regeneration and reuse,limiting their practical application.Moreover,the initial concentration effect is particularly important in water treatment by activated carbon,where the concentration of natural organic matters(NOMs,mg/L level)is about 3-6 orders of magnitude larger than the concentration of most OMPs.NOMs blocked the pores of the carbon,significantly decreasing its adsorption capacity.Besides activated carbon,resin sorbent is also widely used owing to their high selectivity(pollution resistant ability),large adsorption capacity and easy regeneration property.The diameter of the traditional resin is about 0.3 to 1.2 mm,leading to slow adsorption speed,high investment,complex operation,which can't be effectively used in large amount micropolluted water purification process.The magnetic resins have been used in a completely-mixed process for wastewater treatment.This process could significantly increase the water treatment amounts and decrease the costs in contrast to fixed-bed,extending the application of resins in micropolluted water purification.Magnetic resins are mostly in diameter about 150 ?m,2-5 times smaller than the non-magnetic resins.The small particle size caused excellent dynamic performance,large adsorption capacity and the magnetite in resins make the adsorbent could be quickly separated from water.Then,the resin could be reused via simple,rapid regeneration,which greatly increases the water treatment capacity,reduces the cost.MIEX(?),a magnetic anion exchange resin produced by Orica in Australian,is a representative magnetic sorbent.It can effectively remove hydrophilic natural organic matter(NOM)by ion exchange interactions,playing an important role in drinking water purification.However,MIEX(?)shows the poor performance on OMPs which are mostly non-ionic.This purpose of our work was to develop an efficient technology for OMPs removing.The main research contents and conclusions are as follows:(1)Three kinds of magnetic hypercrosslinked resins were developed via different process.The factors such as nanoparticles modified agent,polymerization monomer and porogen etc were optimized,to successfully obtain the magnetic hypercrosslinked resins.Microporous resin M150,mesoporous resin Q100 and microsphere resin Q150 were synthesized,they all had high specific surface area of more than 1000 m2/g,well magnetic separation performance.(2)Adsorption mechanism of OMPs as tetracycline,nitrophenol and atrazine using synthesized resins were evaluated.It was found that the adsorption of atrazine and nitrophenol was mainly by physical effects,whereas the adsorption of tetracycline was more complicated,with combined action of physical adsorption and chemical adsorption such as van der Waals force,hydrophobic effect,?-? and cationic-? bond.The influence of pH value showed that the molecules of OMPs had important influence to adsorption,and alkaline environment(pH =12)was suitable desorption condition for nitrophenol and tetracycline,and ethyl acetate was more effective for atrazine desorption.(3)The pore structure of the resin directly influences the adsorption effect and pollution resistant performance.Magnetic microporous resin M150 had excellent adsorption properties for nitrophenol,but for the relatively large molecular tetracycline,M150 showed much less adsorption capacity than the mesoporous resin Q100.The results show that,when the molecular size of target compounds increased,the resin with smaller average pore size would be pore-blocked and caused a large amount of internal sites invalid.In contrast,the mesopore resin Q100 with much larger average pore size,could increase the utilization of the resin internal hole and improve its adsorption capacity.Meanwhile,the mesoporous resin materials could provide more mass transfer channel,enhance the internal diffusion of target substance in the resin,and further increase the resin adsorption efficiency.For the pollution resistant performance,although microporous resin could via the size exclusion effect to reduce influence of the NOMs,but its microporous structure would be easily blocked by NOM and caused adsorption performance fall sharply.Different from pore-blocked effect of microporous resin,the mesoporous resin were mainy influenced by directly competing for adsorption sites of NOMs.Tannin acid(TA)was chosed as model compound of NOM,to evaluated the influence of pore structures and NOMs for tetracycline adsorption using mesoporous resin Q100.It was found that the existence of TA significantly decreased the adsorption capacity of tetracycline using Q100-1,2 and 4,because the adsorption of tannic acid cause pore blockage,resulted in tetracycline adsorption quantity of three kinds of resin all decreased more than 80%.But for Q100-3 with more lager pore size,the adsorption ability of tetracycline reduce in 10%because of its unobstructed internal channel,which was useful for adsorption and desorption.(4)The particle size also significant influenced the adsorption capacity of magnetic resins.Especially for adsorption resins,which had the much slower dynamics process than ion exchange resins.When particle size of the resin reduced,the contact of adsorbent and adsorbate was enhanced,thus,OMPs could quickly diffused into the pores and the adsorption rate was greatly increased.Compared with the magnetic resin Q1 with large particle size(400-600 ?m),adsorption dynamics of Q150 with much smaller particle size(10 to 30 ?m)had a lot of advantages.From pseudo-first-order equation,k2 value of Q150 was about 30 times large to Q1.Meanwhile,the smaller particle size improved the outer surface of the resin,reduced the pore-blockage and decreased the loss of the effective adsorption sites.The results in our work showed that the adsorption capacity of Q100 was 10.2%decreased after 20th batch adsorption and desorption,while Q1 was 24.8%decreased.(5)The time of adsorption is also important factors,which affects resin adsorption-desorption process.When shorten the contact time of the resin and OMPs,the pollution-resistant ability of resin can be significantly improved though the adsorption capacity reduced.Weber-Morris model showed that adsorption dynamics included two process:external mass transfer and internal diffusion.The pore-blockage was most probably caused by the internal diffusion.Therefore,to control the external mass transfer process and maximize the adsorption amount,and avoid the internal transfer,could improve the pollution-resistant performance of resin.(6)A novel adsorption purification technology using magnetic hypercrosslinked microsphere resin Q150 for atrazine was developed.The commercial powder activated carbon 1240AC was chosen for comparison.Humic acid and NOM from the Yangtze river were used as a background,to simulate atrazine removal by Q150 and 1240 AC.The results showed that removal ability of Q150 was a little better than 1240AC.The adsorption of atrazine using two kinds of adsorbent were negatively influenced when NOM existed.NOM was easily adsorped into the pore of the resin,caused pore-blockage.Moreover,Q150 resin had better reusable ability and regeneration performance compared to 1240 AC. |
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