Study On Dyeing Wastewater And Its Characteristic Pollutant In Membrane Distillation Process

As one of major pollution discharge industries,energy saving and emission reduction technology in textile printing and dyeing industry are always research hotspots in environmental area.The characteristic pollutants of dyeing wastewater,such as aniline derivatives,also raise concern in recent years.In this study,direct contact membrane distillation(DCMD)system as treatment technology combining with the feature of membrane distillation and dyeing wastewater and study on the characteristic of characteristic pollutants in membrane distillation process by using simulative wastewater and actual dyeing wastewater.The porosity,micromorphology,hydrophobicity and thermostability of polytetrafluoroethylene(PTFE)and polyvinylidene fluoride(PVDF)influence on membrane distillation process were analyzed and the influence of operating parameters,as feed temperature,feed flow rate,feed concentration,on the permeate flux and on rejection have been investigated.Additionally,the rejection efficiency about different dye intermediates and the performance about two kinds of membrane were discussed.Three type of dyeing wastewater contain: dye vat wastewater,effluent of textile mill and dyeing wastewater,as the feed were treated and study on the performance of rejection of organic matter,colourity and dissolved solids.The rejection of chemical oxygen demand(COD)and colourity have been calculated.The type of residual organic matter was analyzed by using three-dimensional fluorescence(3D-EEM)and Gas chromatography-mass spectrometry(GC-MS).As for membrane fouling,contact angle(CA)test is used for contrast the variation of hydrophobicity.Environmental Scanning Electron Microscope-Energy Dispersive Spectrometer(SEM-EDS)and Fourier Transform Infrared Spectrometer(FTIR)were employed.For the DCMD experiment of treating characteristic pollutant,using five representative Intermidates containing: phenol,aniline,sulfanilic acid,3,4-Dihydroxybenzoic acid and p-Chloroaniline,coming from dye biodegradation process.Obtained results indicate that with the increasing of feed temperature,the rejections of different dye intermediates have great differences,especially for low-boiling substance.So,the feed temperature can influence the rejection to some extent.Obviously,the higher rejection could been acquired when the organic substance that boiling point over 400 °C,remained above 95 % uncorrelated with feed temperature and increasing the feed temperature and flow rate can contribute to obtain higher flux.Besides,the rejection of organic substances possess high-boiling dispense from the influence of feed flow rate and concentration.It is noteworthy that the performance of PTFE membrane is superior to PVDF membrane in the premise of same pore diameter.As for DCMD experiment of treating dyeing wastewater,higher rejection has been acquired on CODcr and colourity,remained above 88 % and 94 % respectively.The change of flux and conductivity of the permeate indicates fouling and wetting of PTFE membrane.The result of 3D-EEM shows that polysaccharide and protein from microorganism product penetrates membrane pore,but humic acid-like organics rejected by membrane.Some organic substances with low boiling point and molecular weight were found and most organic substances were resisted by GC-MS test.The phenomenon of membrane fouling demonstrate that dye,organic matter and inorganic particle are easily adhere to membrane surface,leading to decline of CA value and destruction of the hydrophobicity.In summary,DCMD system in treating dyeing wastewater and characteristic pollutants can acquire outstanding result for high-boiling organic matter,colourity,dissolved solids at moderate temperature range apart from low-boiling substance and membrane fouling.Exploiting more super-hydrophobic and anti-pollution material apply in membrane distillation process will be the hotspot.Nevertheless,membrane distillation technology is a promising way in dyeing wastewater treatment.