Study On The Application Of Nanofiltration In The Advanced Treatment Of Cotton Printing And Dyeing Wastewater

In China, textile printing and dyeing industry not only consumes a large quantity ofclean water but also discharges a vast amount of wastewater. With the shortage of waterresources and the improvement of discharge standard, to return the treated printing anddyeing wastewater back to the workshop effectively not only relief the shortage of waterbut also benefit the sustainable development. In recent years, there is a mountingconcern about the printing and dyeing wastewater recycling technology. Due to the highchromaticity, complex pollutants, poor biodegradability and high inorganic saltconcentration, how to treat and recycle printing and dyeing wastewater effectively hadalways been a hot research area at home and abroad.In this research, advanced treatment, ultrafiltration-nanofiltration combinedprocess, had been applied to degrade the effluent of dyeing and printing enterprisewhich had reached the discharge standard. The operating pressure, surface flow of themembrane, temperature and the effect of pH on the property of membrane separationhad been analyzed and optimized the operating parameter of the process. The researchstudied the membrane pollution, membrane cleaning drugs and cleaning method of thelong time running devices. The adventure treatment process of cotton printing anddyeing wastewater by dual membrane was invented on this base. Economic analysisshowed that it was reliable.Ultrafiltration membrane can effectively remove the turbidity of the wastewater,the NTU and SDI of the effluent turbidity are lower than0.2and2.5respectively. Thewater quality of Ultrafiltration not only meets the requirement of nanofiltrationmembrane influent but also better than of the recommended water quality. Therefore,ultrafiltration as pretreatment of nanofiltration is feasible. Through the research wefound that the permeate flux are the main factors that influence the membrane fouling.The membrane surface velocity and pressure changes affected the flux of membrane andthen influenced the cleaning period.In the operational process of the nanofiltration, the cake layer resistance andreversible pollution, are not only the main part of the total membrane resistance, butalso the leading cause of membrane flux decline, and validating the nanofiltrationmembrane pollution is composite. The operating pressure, temperature and pH are the main factors that influence the nanofiltration membrane separation performance and themembrane resistance. The higher operating pressure, the higher temperature, the higheror lower pH were, the bigger filter cake layer resistance and the total resistance ofmembrane were, the ratio of filter cake layer resistance was also increased, whichincreases severe membrane fouling.Optimum running parameters of ultrafiltration membrane: recovery rate90%,membrane flux80L/(m~2·h)，0.07MPa~0.10MPa operating pressure; the best cleaningmethod: hydraulic backwashing cycle is30min, and the backwashing time3min. Therun cycle of Ultrafiltration membrane is4months, and then for the chemical cleaning,the cleaning agent is0.03%SDBS(pH=12), the cleaning method is that soaking30min-circulation washing15min-soaking30min-circulation washing15min. Nanofiltrationmembrane running in the operating pressure of feed water flow1.7m~3/h,0.5MPa,recovery rate35%, temperature25~30℃, pH=7~8conditions, the higher removal rateof inorganic salts、 CODCrand chroma in the wastewater. The hydraulic cleaningmembrane for2min until Nanofiltration operated for2h, the run cycle of Nanofiltrationis9months, and then for the chemical cleaning.For the composite pollution ofnanofiltration, using the cleaning method which composite by1.5%citric acid,0.25%SDBS+1.5%NaOH can effectively remove the membrane pollution, and the membraneregeneration performance is relatively good.Advanced treat the standardized discharge effluent of printing and dyeingenterprisesby the project of wastewater reusing, processing capacity is2000m~3/d, thecost estimate of project investment is3.8658million, running cost of project sums to11.283yuan/(m~3·d). Net present value NPV of this system>0, showed that the designscheme of membrane system has better economic benefit.