| The textile printing and dyeing industry is a pillar industry in China,but it uses a lot of water and produces a large amount of wastewater,which causes serious environmental pollution.It is also a typical heavily polluting industry.Mercerization is an extremely important process in the printing and dyeing production process.In the mercerizing process,a large amount of concentrated lye needs to be added to improve product quality.The wastewater discharged from the mercerizing process not only has high COD and SS,but also contains a large amount of alkali.It is of great significance for the recovery and utilization of alkali in mercerizing wastewater.A large number of studies have shown that the evaporation and concentration of mercerizing wastewater can obtain high concentration lye,which has good economic benefits.However,the impurities in the mercerizing wastewater will reduce the evaporation efficiency and reduce the life of the evaporator.Therefore,the mercerizing wastewater needs to be purified to remove impurities and improve the purity of the lye to facilitate evaporation and concentration.This topic is derived from the sub-topic of the National Water Project.The wastewater is from the mercerizing section of the printing and dyeing industrial park in Wujin District,Changzhou City.The mercerizing wastewater is first purified and then evaporated and concentrated to obtain a high-purity and high-concentration lye.Laboratory data analysis is used to guide field engineering implementation.This paper systematically optimizes the parameters of the coagulation process,and compares various types of alkali-resistant membranes available in the market.The characteristics of membrane fouling are analyzed.Cleaning agents?phosphoric acid,nitric acid,SDS,and SDBS?,and the technical and economic analysis of the combined process is performed,and the operating costs of coagulation-membrane separation and evaporation concentration are calculated.?1?Coagulation sedimentation is used as a pretreatment method for mercerizing wastewater.The dosage of PAC is 150 mg/L.The stirring method as follow:fast stirring?300 r/min?,4 min;slow stirring?50 r/min?,5 min.The SS and turbidity removal rate of the effluent is about 82%,and the alkali recovery rate is greater than 96%.?2?PES tubular ultrafiltration membranes with different molecular weights?10000/30000/60000 Da?,6000 Da molecular weight PES hollow fiber membranes and special nanofiltration membranes are selected to adjust the pressure and temperature.Among the tubular ultrafiltration membranes,10000 Da molecular weight ultrafiltration membranes perform well.The average water production in the first two hours is 34.8 L·m-2h-1,the removal rate of COD is 52.6%,and the removal rate of chromaticity is 60%.The average water production for the first two hours of the hollow fiber membrane is 42.6 L·m-2h-1,the COD retention rate is 82%,and the color removal rate is 90%.The average water production of the nanofiltration membrane is 34.2 L·m-2h-1,the retention rate of COD is 88%,and the removal rate of chromaticity is 92%.In addition,various types of membranes perform well under different circulating fluid flow rates and feed fluid concentrations.?3?Characterization of membrane pollution shows that when the ultrafiltration membrane is operated for 2 hours,the membrane surface pollution increases sharply due to the effect of concentration polarization.The membrane pollution mainly includes organic pollutants,including ethers,alcohols and aromatics,and a small amount of Inorganic salts.?4?The mass concentration of 0.2%phosphoric acid,nitric acid and 0.1%SDBS are used to clean the membrane,and the membrane flux recovery rate is above 99%.?5?The purified lye has good economic benefits through evaporation and concentration.Excluding electricity,medicine,labor costs and other operating costs,a profit of 291.6-318.3 yuan can be obtained for each ton of concentrated lye produced. |
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