Study On Treatment Of Hypersaline Ammonia Wastewater By Coupling Membrane Absorption And Membrane Distillation

As the integration of membrane technology and traditional separation technologybased on gas-liquid phase equalization, the membrane contactor possesses bothadvantages of them. With the further research and development, membrane contactorhas been gradually applied to the field of chemical engineering, petrochemicalengineering, food industry and bio-pharmaceutical, and achieved good economic andsocial benefits, of which membrane absorption and membrane distillation technologyare the research focus. The discharge of great amount of ammonia wastewater intowaters has caused harm to human habitat as well as ecological environment. As aconsequence, there are more and more demanding nitrogen emission standardsimplemented worldwide. However, traditional ammonia removal technologies havetheir shortcomings in terms of either the effect of the treatment or investment andoperating costs. Therefore, it is meaningful to develop the technology of utilization ofammonia waster by membrane contactor in view of the increasing nitrogen pollutionproblem, freshwater resources shortage and arousal of the public environmentalawareness.In this thesis, membrane absorption (MA) and vacuum membrane distillation(VMD) have been firstly integrated in order to effectively recover ammonia andfreshwater respectively from ammonia-containing hypersaline wastewater dischargedby metallurgical plants. In the membrane absorption stage, cross-flow and parallelflow hollow fiber membrane modules (HFMM）was used for ammonia removal fromsimulation ammonia containing wastewater by membrane absorption, focusing on theammonia removal performance of cross-flow membrane absorption. The effect ofoperational parameters, such as feed pH, feed velocity, absorbent concentration,absorbent velocity and initial ammonia concentration, on the overall mass transfercoefficient, K, was analyzed. On the basis of optimum operational conditions,experimental study on the ammonia removal from saline ammonia-containingwastewater by membrane absorption with both parallel flow and cross-flow HFMMwas conducted and the reason for relatively lower overall mass transfer coefficientvalues was that saline ammonia-containing wastewater has higher salinity and COD.Overall mass transfer coefficient was increased by COD removal via flocculation.Finally, the ammonia concentration was reduced below5mg/L to be used as theinflow of the second stage. In the VMD stage, the qualitative and quantitative effect on permeate flux in VMD process were studied experimentally. The quantitativecontribution percentage of operational parameters on permeate flux was determinedon the basis of above experimental results. Experimental studies on the VMDconcentrating saline ammonia-containing wastewater was invested, and three waysincluding semi-continuous concentrating mode, addition of scale inhibitor andpretreatment of flocculation, was proposed to retard the development of membranefouling while maintain higher membrane flux in concentrating process. Permeate fluxcould be greatly restored through the cleaning technique consisting of alkalinecleaning, acid picking, EDTA washing and drying. Permeate flux loss due to theirreversible membrane fouling was0.7%.