Study On Vacuum Membrane Distillation And Air Gap Membrane Distillation For Treating Copper-containing Solution

The wastewater of copper plating industry and other industries usually contains high concentration of copper,these copper-containing wastewater should be purified to reclaim water and valuable raw materials.In this paper,it emphatically investigated the performance of vacuum membrane distillation（VMD）and air gap membrane distillation（AGMD）for treating copper-containing wastewater by employing porous hydrophobic polypropylene hollow fiber membrane module.The impacts of operating parameters and module parameters on VMD performance including permeate flux（J）,total water production（P_v）,specific heat energy consumpution（SHEC）,and specific heat energy consumpution（SEEC）were investigated.It could be found that J increased with increasing vacuum pressure（P）,feed temperature（T）,feed flow velocity（v）and declined with increasing feed concentation（c_f）.As membrane length（L）increased,J decreased but P_v and SHEC（SEEC）increased simultaneously,and the maxium J was 21.82 kg/m²·h.As packing density（D）increased,J and SHEC decreased but P_v and SEEC increased.The maxium P_v and minimum SHEC were 0.816 L/h and 674.5 k Wh/m³ respectively.The Pearson correlation analysis showed that P had most significant impact on J.A vacuum membrane concentration experiment was carried out under optimal conditions,permeate flux decreased and conductivity of produced water increased during the experiment.After the experiment,it was found that the inner surface of used membrane was particaly contaminated by crystallization.The tensile strength of used membrane increased,but the molecular structure of used membrane did not change significantly.In the AGMD process,a series of experiments were conducted to investigate the effects of various parameters including hot feed temperature（T₃）,coolant temperature（T₁）,feed flow rate（F）,feed concentration（c_f）,membrane length（L）,and the rate of hollow fiber membranes and heat exchange hollow fibers（N_m/N_d）on J,P_v and gained output ratio（GOR）.As L increased,J declined,P_v and GOR increased.With the increment of N_m/N_d,J decreased,but P_v and GOR firstly increased and then declined as cooltant temperature increased.When the operating parameters kept the same,AGMD process was superior to VMD process for high total water production obtaining and energy saving.This study showed that VMD and AGMD had great potential to treat heavy metal wastewater,and provide useful insights for scale-up experiment to purifty heavy metal wastewater by membrane distillation process.