| The application of membrane ultrafiltration to drinking water treatment hasincreased dramatically in the past decades. Most of the membranes applied inwater treatment are made of polymeric materials. However, the oxidants widelyused in dealing with micro-polluted raw water would damage the polymericmembrane. Ceramic membrane is attracting more and more attention because ofits superior oxidation-durability and physical stability. The performances of aseries of ceramic membranes with different pore sizes were investigated with anozone/ceramic-membrane system. The effects of ozonation on the removal ofpollutant and membrane flux were tested, and the mechanism of fouling controlby ozonation was explored. An innovative hybrid ozone/ceramic-BAC processwas proposed to evaluate with micro-polluted water in bench-scale system, andthe results of the bench-scale system were verified through a pilot system of120m3/d.The membrane pore sizes were selected as5nm,10nm,50nm,100nm and200nm specifically. It was found that more than96%of the particulate matter inraw water was removed by the membranes with different pore sizes. The particlecounts in membrane effluent reduced with smaller membrane pore size. Ozonedosage when lower than3mg/L had little effect on the particle counts inmembrane effluent, while the dosage of3~5mg/L slightly increased the particlecounts in effluent. Considering the trans-membrane pressure and membrane flux,the ceramic membranes with pore sizes ranged from50nm to100nm arerecommended in this thesis. The direct ultrafiltration with ceramic membranesremoved about15%~45%CODMnand the removal efficiency of UV254was lessthan10%. Combination of ozonation with ceramic membrane improved theremoval of UV254significantly. However, the removal of CODMndid not increaseunless the ozone dosage was higher than3mg/L. The membrane with smallerpore size and the raw water with higher turbidity would benefit the removal oforganic matters during membrane ultrafiltration. Ozonation is able to alleviate the membrane fouling effectively. Theozonation can take place either in membrane tank or in the porous channel ofmembrane, changing the molecular structures or transforming the organicmolecules into smaller ones. The analysis based on reversible and irreversiblefouling indicated that the organic matter played an important role in membranefouling. The fouling potentials of organic fractions were hydrophilic>hydrophobic> transphilic fractions. Organic matters with molecular weights of400,1100,1500and3180Da contributed most to the irreversible membranefouling.It was demonstrated that the hybrid ozone/ceramic membrane-BAC systemremoved about50%~55%of the total organic carbon (TOC) and UV254, whereozonation enhanced the biodegradability of organic matters, while the BAC unitimplemented the degradation of the organics. The turbidity of the effluent waslower than0.14NTU, the particles larger than2μm were less than60cnt/mL,and the ammonium in effluent was less than0.5mg/L. The analysis of bacterialcommunity structures in BAC indicated that placing ozone/ceramic membraneunit before BAC was able to enhance the major functional bacteria, preventedpathogenic bacteria and algae from growth in the BAC bed. In addition, aerationincreased the concentration of dissolved oxygen in water flow, thus promoted thegrowth of Nitrosomonas and Nitrospira which were the main bacteria for theoxidation of ammonium. It is believed that the hybrid process investigated in thisthesis is of great significance in upgrading of conventional water treatment plantsto purify micro-polluted water and to guarantee the safety of drinking water. |
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