| In this study, DAF process operating parameters and operating characteristics were studied, as for the algal turbidity problems, after the South-to-North Water Diversion project in Shandong Province. Different types of raw water were mixed together, and the sedimentation tank could not run in effectively, when low temperature and low turbidity period and high algae period. The adhesion mechanism between microbubbles and particles in order to strengthen the contact flocculation, and the new efficient Mixed-flow DAF technology was developed. The removal of turbidity and algae were studied and the purification mechanism of the new Mixed-flow DAF technology was discussed simply.The contents of study include four aspects:(1) The static test of Dissolved Air Flotation; (2) Proposed the new Mixed-flow DAF process and research the operating characteristics; (3) water clarifying mechanism of the mixed-flow DAF and the micro-kinetics of the process.In the static test, the factors of DAF process were researched, such as the types and dosage of coagulant, the way of flocculation, flocculation time, dissolved air pressure and reflux ratio and other factors, when the South to North water was purified by the DAF process. The operating conditions were optimized, and the optimum operating parameters of the process were determined. The results demenstrated that the pollutant removal of flotation was best when the dosage of PAFC which was chosen as the best flocculant was 5mg/L(Al3+ in total), the first coagulation intensity(G1) was 63s-1(operating 4min), the secomd coagulation intensity(G2) was 22s-1(operating 4min), the dissolved air flotation recycle ratio was 12%, and the standing time was 5min.The traditional flat and countercurrent DAF operating characteristics were contrast in the study, and the difference of the removal between the two DAF process was analysised. The way of reflow in DAF was improved and the new Mixed-flow DAF process was developed. In the new DAF process, the contact flocculation of microbubbles was carried on twice by the grade reflux of the dissolved air and water, so that the copolymerization between the bubbles and the flocs was strengthened. The new DAF equipment was applied for invention patents(Patent No. CN103964529A). Studies have shown that the new Mixed-flow DAF effluent could achieve the better results, when the total recycle ratio was simple by improving the way of reflow. And when the raw water quality had changed, the distribution ratio of dissolved air and water should change respectively.In the Mixed-flow flotation process for pollutant removal effectiveness research, the Mixed-flow flotation test device (0.5m3/h) was operated continuity, with detecting the turbidity, CODMn, UV254, DOC, SUVA, ammonia, suspended particulate matter and disinfection byproducts precursors and other water quality indicators.The results showed that the average removal efficiency of turbidity, algae, CODMn, UV254, DOC, SUVA and ammonia has achieved 95.2%、94.3%、43.2%、48.5%、38.2%、20.5% and 77.3%, respectively. And for more than 2um particle removal efficiency was up to 93.6%, while a molecular weight greater than 3000Da for organics removal rate was 85%. During the test, the DBPFP was controlled well, while the removal rate of CHCl3, CHCl2Br, CHClBr2, CHBr3 were 22.9%,16.0%,21.9% and 18.2%, respectively. On removal, the new DAF process could achieved 5.0% in turbidity,4.0% in CODMn,5.0% in UV254,2.0% in DOC better than traditional flat flotation process. In terms of the particulate matter, the new Mixed-flow DAF has less particulate matter relative to the flat traditional flotation process.Through the dynamic observation of different stages of Mixed-flow DAF process, the adhesion mechanisms were consisted of microbubbles-floc particles collision and adhesion, microbubbles-floc particles copolymerization and microbubbles-floc particles-bubble flocs meshing and adsorption-bridging mechanisms. By simplifying the assumptions of flotation model, and decomposing the bubble-particle collision section, dynamic model equations were obtained. By solving the equations, the law of the flocs which were adhered by i bubbles changed with time complied with right skew distribution. |
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