| As for the algal turbidity and odor problems, 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, after the South-to-North Water Diversion project in Shandong Province. Four aspects were studied in this study.(1) Switching conditions static experiment between DAF and precipitation process. In the static test, the factors of DAF/precipitation process were researched, such as the types and dosage of coagulant, the way of flocculation, flocculation time, reflux ratio. The results demenstrated that the pollutant removal of DAF process 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, the secomd coagulation intensity (G2) was 27s-1, the dissolved air flotation recycle ratio was 12%, and the standing time was 8min. Corresponding, the pollutant removal of precipitation process was best when the dosage of PAFC was 6mg/L (Al3+ in total), G1was 50s-1, G2 was 22s-1, and the standing time was 15min.Switching conditions study of the DAF process and sedimentation process indicated that the sedimentation process was better than the flotation process for the removal when the turbidity was greater than 80 NTU. The flotation process was better than the sedimentation process for the removal when the turbidity was less than 80 NTU in turn, for treating the raw water of different turbidity and organic matter.(2) Test between DAF and precipitation process for low turbidity and high algal water. Both processes were rearched for pollutant removal effectiveness, such as the turbidity, CODMn, UV254, TOC, suspended particulate matter, GSM and MIB. The results showed that DAF process had better removal efficiency for the conventional indicators. Compared with the sedimentation process, the removal efficiency of DAF process higher 5%,5.2%,7.8%, 2.0%,7.8%,11.4% and 11.5% respectively.(3) Study on precipitation-flotation combined process treating high algae and low turbidity water. The combination process of sedimentation-flotation were rearched for treating low turbidity and high algae water. Studies had shown that the combination process had better removal efficiency under the condition of less energy consumption,less dosage and bigger water treatment load.Compared with the DAF and sedimentation process unit, the tubidity removal efficiency had increased 2% and 5% respectively, the particles removal efficiency had increased 4% and 7% respectively.The content of organic matter in water is reduced.The average removal rate for algae can reach 96%. The odor substances can be effectively remove at the same time.(4) CFD numerical simulation on flotation/sedimentation tank. Numerical simulation was carried out on the inclined tube sedimentation tank.The result showed that inlet and outlet of settling tank have influence on the flow condition of settling basin. Using punched tracery wall distributing water can reduce reflux phenomenon. Downflow weir could reduce the sedimentation tank water pump, control backflow phenomenon in the same processing load. Particles’settlementation follows the stokes law in sedimentation tank.The particles larger than 80 microns could be removed completely. When the particle size, only a small number of particles of 20 microns sedimentation. The precipitation efficiency was very low.The flow regime in the flotation pool was gradually getting better with fewer water flow, the floating backflow phenomenon reduced or disappeared, comprehensive consider treatment effect and water treatment capacity, air flotation pool water flow taking 0.5 m3/h. The numerical simulation about the gas-water ratio in flotation pool showed that, the gas-water ratio increased with the increase of dissolved air pressure.But as the dissolved air pressure increasing, the enhancement effect was gradually warming.Micro bubbles quantity could meet the requirements of DAF when gas ratio increased to a certain degree. |
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