Study On Membrane Distillation Process In The Resource Recovery Of Clean And Turbid Wastewater From Chinese Medicine Manufacturing

The production process of traditional Chinese medicine（TCM）is generating an increasing amount of wastewater as the industry develops rapidly.Traditional treatment methods tend to focus on reducing the concentration of pollutants such as chemical oxygen demand（COD）and biological oxygen demand（BOD）,while neglecting the resourceful reuse of active compounds and water resources in TCM wastewater.Membrane distillation（MD）is a highly efficient membrane separation technology that finds wide application in seawater desalination,wastewater treatment,and juice concentration.Its popularity stems from its ability to achieve high retention rates,low operating pressures,and low sensitivity to concentration.With a focus on the management principle of"different routines for different water qualities",this paper provides a systematic analysis of the potential of vacuum membrane distillation（VMD）technology in the resource recovery of TCM wastewater,taking into account the unique characteristics of this type of wastewater.The main research contents are as follows.The paper firstly investigated the effects of different membrane materials（polytetrafluoroethylene,PTFE and polyvinylidene fluoride,PVDF）and operating conditions on the VMD system using simulated Chinese medicine clean wastewater as the raw liquid,and explored the performance characteristics of VMD for treating Chinese medicine clean wastewater using the indexes of membrane flux,gain output ratio（GOR）and specific thermal energy consumption（STEC）.According to the findings,the membrane flux and GOR in VMD process of Chinese medicine clean wastewater were significantly influenced by the feed temperature and permeate side vacuum,whereas the feed flow rate had a comparatively minor effect.The optimized VMD operating conditions were 65°C feed temperature,80 k Pa permeate side vacuum and 24 L·h^-1 feed flow rate.Under this conditions,after the actual Chinese medicine clean wastewater was treated by VMD,the concentration of main pollutants such as COD in the permeate was reduced by more than 99%,and the water quality fully met the relevant discharge and reuse standards.On this basis,the effectiveness of the ultrafiltration-membrane distillation system for the resource recovery of Chinese medicine turbid wastewater was investigated,using simulated turbid wastewater as the feed liquid.The results show that about 78%of the COD was removed and more than 80%of the active compounds was retained after pretreatment by ultrafiltration.During the concentration of ultrafiltration permeate by VMD,process parameters such as feed temperature have a low effect on the concentration of active compounds,while feed p H significantly affects the recovery of active compounds.In the treatment process of actual Chinese medicine turbid wastewater,the ultrafiltration-membrane distillation system achieves efficient separation of macromolecular organic compounds,small-molecule active compounds and water.After treatment,0.306 g of solid powder containing 4.24 mg chlorogenic acid and 2.22 mg baicalin were obtained per liter of turbid wastewater.Finally,the characteristics and causes of membrane contamination in VMD process of TCM wastewater were studied and a targeted membrane cleaning program was developed.Based on the results,the primary cause of membrane fouling in TCM wastewater was found to be the deposition of macromolecular organic matter on the membrane surface.Membrane fouling can lead to a decrease in membrane flux and membrane wetting,which in turn affects the permeate water quality.Using 2 wt%Na OH solution to clean the contaminated membrane for 25 min can effectively restore the membrane flux and contact angle,but with the increase of cleaning times,the damage of the cleaning agent to the membrane structure will gradually increase,leading to the decrease of cleaning efficiency.