| The surface water resources in China not only has the problem of the shortage of timeand space, but also widely polluted of organic matter and ammonia nitrogen.Nevertheless, the capacity of conventional drinking water purification process to removethese substances is very limited. This study with the core technology of ultrafiltration+nanofiltration process, combined with pre oxidation, and on-line coagulation pretreatmentprocess to remove the organic matter, ammonia nitrogen, nitrate nitrogen and totalnitrogen in the surface water, simultaneously optimize the operational parameters.Firstly, the factors included types of coagulants, coagulant dosing quantity andcoagulation time influence on the removal of organic pollutants of coagulation-ultrafiltration+nanofiltration process. The results showed that: coagulant dosage is themost significant factor to the removal of CODMn, while the type of coagulants obviouslyinfluences the removal of UV254. Considering all the factors, the best coagulationconditions of this study was15mg/L AlCl3with coagulation60s. Meanwhile, theinfluence of dosage of oxidant potassium permanganate to remove organic pollutants andultrafiltration membrane fouling of preoxidation-coagulation-ultrafiltration processwas studied through single factor experiment. The results showed that the increment oforganic removal rate reaches the maximum, and the decrement of ultrafiltrationmembrane flux achieves the minimum when the dosage of potassium permanganate was1mg/L.Secondly, all kinds of pollutant treatment effect between coagulation-ultrafiltration+nanofiltration process and the optimized preoxidation-coagulation-ultrafiltration+nanofiltration process in different temperature were compared. The results showed thatthe ultrafiltration+nanofiltration process mainly remove organic matter with removalrate is over80%, and removal rate of nitrogen, nitrate nitrogen and total nitrogen is lowerthan40%, and mainly completed with pretreatment-ultrafiltration unit. Preoxidationincrease the removal rate of organic matter with pretreatment-ultrafiltration, and DOCremoval rate in raw water increased30%. The initial concentration, temperature and thequantity of other pollutants in water will affect the removal efficiency of the process. Theinitial concentration significantly influences the removal of organic matter, while thetemperature significantly affects the removal of ammonia nitrogen and nitrate. In addition, the removal rate of ammonia nitrogen with pretreatment-ultrafiltration increased from16%~24%to25%~31%, and the removal rate of nitrate nitrogen increased from13%to20%when the temperature decreased from26℃to8℃.Finally, the influence of water temperature, pollutant species and concentrations ofultrafiltration, nanofiltration membrane fouling was investigated. The results showed thathumic acid in water is the important material that leads to ultrafiltration membranefouling. Ultrafiltration membrane flux reduced0.04when the concentration of humicacid increased from2mg/L to9mg/L. Temperature and ion concentration will affect thenanofiltration membrane fouling. Membrane flux decreased0.08when the concentrationof ammonia nitrogen increased1mg/L. Nitrate is not only increased the decline ofmembrane flux, but also speeds up the decline. Nanofiltration membrane seriouslypolluted was easier affected by other factors in summer than winter. Compared withdirect coagulation, preoxidation can effectively reduce membrane pollution, themembrane flux rate of ultrafiltration increased0.04after running90min whenultrafiltration treat the water which after preoxidation treatment, the downtrend ofspecific flux after the pre-oxidation significantly decreased during the0~60min.Preoxidation can also reduce the nanofiltration membrane fouling. It was necessary tonotice that preoxidation makes an increase of the membrane flux rate of0.07than directcoagulation with the treatment of high nitrate in summer.The study found that coagulation-ultrafiltration+nanofiltration process andpreoxidation-coagulation–ultrafiltration+nanofiltration process have a goodperformance on organic matter removal in surface water, meanwhile the removalefficiencies of ammonia, nitrate, total nitrogen performance is not very well. Twoprocesses run stable, especially preoxidation-coagulation-ultrafiltration+nanofiltrationprocess, the membrane flux has remained at the initial flux of80%and membrane fluxachieve a good recovery though flush and back flush, therefore chemical cleaning wasnot used during the experiment. |
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