Research On The Wig Wastewater Treatment By Membrane Distillation

Membrane distillation is a new membrane separation technology driven by the temperature difference between the two sides of a hydrophobic microporous membrane.It is often used in seawater desalination,wastewater treatment and juice concentration etc.In the study,direct contact membrane distillation,vacuum membrane distillation,and air-gap membrane distillation were used to treat acidic wig wastewater.The effects of different operating paraments on membrane performance were discussed,and the optimal operating conditions were selected to treat the wig wastewater.The membrane fouling and the membrane cleaning methods were also investigated.It was concluded as follows:a)After the treatments of acidic wig wastewater by three membrane distillation,the retention rate was more than 99%,the pH of produced water was about 6.82,and the COD and TDS were not detected,which fully meets the external drainage quality requirements and shows good separation results.In these three membrane distillation processes,the permeate flux increased significantly with the increase infeed temperature,feed flow and permeate side vacuum.The retention rate decreased with the increase in SDS concentration.In the range of pH of the feed liquid(1.5~5.6),the permeate flux of the DCMD and VMD processes will firstly be increased and then gradually decreased with the decrease in pH,and the permeate flux of the AGMD process was not affected by pH.The DCDM and AGMD processes had relatively stable membrane properties,and neither the permeate flux nor the retention rate changed significantly.However,the permeate flux of the VMD process decreased during 36-hour running.b)DCMD still showed a good treatment effect when running time extended from36 hours to180 hours.The permeate flux was kept at 61.0~65 kg/m~2·h and the retention rate was maintained at 99.25%when the simulated wastewater was treated for 100 hours.The permeate flux was 66.0kg/m~2·h when the real wastewater was treated for 100 hours,the retention rate remained above97.74%during the whole process.With the increase of the operating time to 180 hours,the permeate flux and retention rate of the types of wastewater decreased slightly.c)The vacuum degree of the permeate side for the VMD process has a more significant effect on the permeate flux.The permeate flux first gently increased and then sharply increased with the increase in vacuum degree,and the permeate flux increased from 0.90 kg/m~2·h to 89.39 kg/m~2·h when the vacuum increased from 10.0 kPa to 85.0 kPa.During the 36-hour running,the average permeate flux was 32.66 kg/m~2·h,and the retention rate remained above 99.83%.the produced water quality fully meets emission standards.However,there was a drop in permeate flux for VMD.d)The influence of the operating conditions of the AGMD process on the membrane performance was also investigated,and compared with the DCMD and VMD processes,it was found that the permeation flux of the AGMD process was small but the stable.During the 36-hour running,the permeate flux remained at approximately 6.61 kg/m~2·h,and the rejection rate remained above 99.80%.e)In the experiment,three kinds of cleaning methods were used to clean the contaminated membrane,and the recovery rate of membrane performance of different cleaning methods was examined.The results showed that when the contaminated membrane could be cleaned by physical or chemical methods,the membrane performance could be recovered to different level,but the permeate flux decreased rapidly after running for a while.