| Landfill leachate is a kind of wastewater including high COD, ammonia nitrogen and heavymetal ion. Currently, biological treatment, physical and chemical method, membrane separationare used in handling the wasterwater. Membrane distillation has became a hot research spot andpotential method among separation technology in recent years, especially compared with thetraditional distillation technology. Among the suitable material for the membrane distillation,PTFE is an ideal material with natural hydrophobicity, acid and alkali resistant, and heat resistant.This subject mainly focuses on the preparation of PTFE microporous membranes and applicationin landfill leachate desalination with sweep gas membrane distillation (SGMD).The main research of this dissertation focused on the following aspects:(1) PTFE flat-sheetmembranes were prepared by the “Push-Stretch-Sinter” process. Six kinds of flat-sheetmembranes with different average pore diameter and porosity were produced by controlling thesame compression ratio, sintering temperature, time constant, and changing the draw ratio, drawtemperature and setting temperature. The microstructure and pore size distribution of sampleswere researched.(2) Using the prepared PTFE microporous membranes to design the SGMDexperiments, exploring the influences of microporous membrane structure (including membraneporosity, average pore size) and the experimental operating conditions (including the feed liquidvelocity, sweeping gas velocity, feed liquid temperature) on membrane flux and water quality.(3)The change rule of the feed concentration, feed liquid temperature, and liquid flow rate onmembrane fouling, flux attenuation and water quality were systematacially investigated bylong-operating.(4)30days of continuous operation SGMD device, dealing with the15timesconcentrated landfill leachate to examine the stability of the membrane in the process oflong-term using.(5) when the flux declined25%, exploring the membrane flux recovery andwater quality after the washing order "water cleaning–alkaline cleaning–water cleaning–acidcleaning–water cleaning–drying for24hours " to clean the fouled membrane, and optimize themembrane cleaning agents.The results showed that:(1)the prepared PTFE microporous membranes had the microstructure of "fiber-node", the porosity from30%to51%, the average pore size form0.25μm to0.40μm, and the water static contact angle above125°, which were suitable formembrane distillation with good hydrophobicity.(2) In the experimental range, the water fluxincreased with the increasing of average pore diameter and porosity, feed liquid velocity,sweeping gas velocity and the water quality met the national discharge standard. Simultaneously,conductivity, COD, chromaticity, turbidity of permeate water respectively kept under100μs/cm,100mg/L,20unit,1NTU, and pH values kept from6to9, SS kept at0mg/L.(3) In the samerun-time, increasing of the feed concentration, temperature, flow rate would exacerbate themembrane fouling,and significantly decline the flux, but the quality of water did notdeteriorate.The removal rate of water conductivity, COD, chromaticity, turbidity maintain at99%.(4)30days of continuous running experiments showed that the permeate flux constantlydecay with the attenuation membrane fouling, but the water quality met the national emissionstandards, which indicated that PTFE microporous membranes had the excellent stability.(5)The recovery experiment results showed that filter cake layer on the surface can be obliterated,membrane morphology can restore by cleaning the membrane, and the recovery rate ofmembrane flux can reach98%, the index of permeate water kept at a relatively stable level. |
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