Study On Membrane Absorption For Stripping Ammonia By Using PTFE Hollow Fiber Membrane

Ammonia is a common kind of water pollutant, which is of serious harm to human healthand the ecological environment. The diversity and complexity of ammonia wastewater fromdifferent industries bring great trouble to ammonia removal. Traditional methods for ammoniaremoval such as physical and chemical methods, biological denitrification, which haveshortcomings, such as high energy consumption, big covering area and low efficiency.Membrane absorption is a new separation technology combining chemical absorption methodand membrane separation technology, which is energy saving, covering a small area, etc.The choice of membrane materials has great influences on the removal effect of membraneabsorption, most of the membrane materials are polypropylene (PP), polyvinylidene fluoride(PVDF). However PTFE has been the most promising membrane materials due to its superiorhydrophobicity, chemical resistance and thermal stability. In recent years, our research group hasfabricated PTFE hollow fiber membranes through “paste-extrusion-stretching-sintering” method.In this paper, PTFE hollow fiber membranes were prepared through “paste-extrusion-sintering” method, six kinds of PTFE hollow fiber membranes with different structures weremade by changing extrusion head sizes and stretching ratios, the effects of extrusion head sizesand stretching ratios on the structure of PTFE hollow fiber membranes were investigated.Self-made membrane modules were prepared to carry out ammonia removal experiments viamembrane absorption. The effects of membrane structure (wall thickness, pore size) andmembrane module design (packing density, membrane length, placement mode, running mode)on the ammonia mass transfer performance were investigated. Results show that the masstransfer coefficient and the removal rate increase with the decrease of wall thickness and theincrease of the pore diameter. It exists a best packing density to make the ammonia mass transfercoefficient largest, which also can achieve high ammonia removal. The ammonia mass transfercoefficient decreases and the ammonia removal increases when the membrane length increases. The placement modes almost have no effect on the ammonia mass transfer process. It’s better forthe feed solution running through shell side than lumen side.The effects of pH value, velocity, temperature of feed solution and temperature,concentration, velocity of absorbent on the ammonia mass transfer performance were studied indetail based on the membrane absorption process. Results show that factors of feed solution havebigger influence on the ammonia mass transfer performance than absorbent especially the feedsolution pH, the ammonia mass transfer performance can be improved by increasing pH value,velocity and temperature of feed solution. The temperature and velocity of absorbent have anegligible effect on the ammonia mass transfer performance, thus you can set them according toactual demands. The ammonia concentration can decrease below4mg/L and achieve removalrate of over99%, pH value of feed solution after treatment is between7.05~7.20, meeting thefirst grade of discharge standard.A pilot-scaled ammonia stripping system was designed to conduct field experiments usingnickel plating wastewater from a chemical factory in Suzhou. The effects of pH value, velocityof feed solution and concentration, velocity of absorbent on the ammonia mass transferperformance were investigated. The results are almost in consistent with the laboratoryexperiments.