The Study On Dynamic Test Of DENSADEG Using Raw Water From Xining City With Low Temperature And Low Turbidity

The DENSADEG is a new kind of water treatment process combined of inclined-plate sediment tank, outside sludge recirculating system, and sludge condense tank. Through mechanical stirring and highly concentrated sludge recirculation, the sludge capture layer is formed. The flocculation is strengthened in the small-volume flocculation area. In the sediment area, inclined-plate tank is used to improve the separation effect, which guaranteeing the after-sedimentation-water quality. Through a great deal of modeled experiments, the low-temperature and low-turbidity raw water of Xining city has been studied systematically, using the DENSADEG. The main purpose of the study is to provide operating parameters and technical guiding for the stable operation of the seventh water company in Xining City. The main contents and achievements are as follows:The static coagulation experiments were initially carried out to select Zibo PAC, Gongyi PAC as the coagulants, with a dosage 2-8 mg/L;the initially selected flocculants were Zibo PAM¹, Zibo PAM², Gongyi PAM^-1, Gongyi PAM^-2, with a dosage of 0.2-0.8 mg/L each. The turbidity of the outflow water was below 1 NTU.The dynamic tests have chosen Zibo PAC and Gongyi PAC as the optimum, with a dosage 6-8 mg/L, 7-9 mg/L, respectively. The optimum flocculants were chosen to be Zibo PAM¹, Zibo PAM², Gongyi PAM^-1 and Gongyi PAM^-2, with a dosage of 0.6, 0.45, 0.5, 0.45 mg/L, respectively. And the turbidity of the outflow water was below 1.5 NTU.The cost of water treatment using PAC was 0.013-0.016 Yuan/t each. The PAM treatment costs were 0.007, 0.006, 0.008 and 0.010 Yuan/t, respectively.With the optimum agent dosage, and a optimum stirring strength G value equals 600 s^-1 or so in the mixing tank, the outflow turbidity was 1.1 NTU. When G was120-160s"', the outflow turbidity was below 1.3 NTU. And a moderate G 140 s"1 resulted in outflow turbidity 1.1 NTU.With the optimum agent dosage, and the sludge recirculation 288-380g solids/h (the solids concentration of the recirculated sludge 7.6g/L, the related recirculation ratio 1.47-1.9%), the outflow turbidity was 1.5 NTU. And when solids recirculation was 330g/h (sludge recirculation ratio 1.66%), the outflow turbidity was lowest (0.8 NTU), and the optimum operation reached.Through the experiments above, the initially designed agents dosing system and the clarifier in Xining's seventh water company were checked of their operation condition and equipments type, with our conclusions and recommendations.