Study On The Treatment Of Low Temperature And Low Turbidity Raw Water In Small Cities And Towns Of Northwestern Regions By Using Pellet Flocculation Process

The low temperature and low turbidity water was treated by using a high efficient solid-liquid separator, which invented by Xi'An University of Architecture and Technology. The study includes two parts, part 1 is about the low turbidity water treatment, the system operation, the characteristics of suspended layer and the stability of the system was studied in this part; Part 2 is about the research of the pilot experiments on low temperature and low turbidity water treatment, mainly including the characteristic of tubular reactor and the stability of the system. The main contents and achievements are as follows:(1) The coagulation equipment is constituted with two static mixers and tubular reactor in series. Good effect could obtain when PAC injection point is before two static mixers, PAM injection point before tubular reactor, and backflow sludge injection point is between two static mixers.(2) The water used in the pilot experiment is artificial and simulated the characteristics of TangYu raw water with raw turbidity 4NTU, CODMn 3-4 mg/L, temperature 17-21℃. The treatment effect was satisfactory for the effluent turbidity before filtration reaching 0.8-1.9 NTU, the CODMn removal efficiency 27.42-36.64% and the flow rate 30cm/min-50cm/min When PAC dosage of 3.2 mg/L, PAM dosage of 0.4 mg/L, sludge backflow ratio is 4.8% and sludge concentration about 21.2-23.8 g/L.(3) It could be observed that the Optimal operating conditions were the dosage of PAC 3 mg/L, the initial particle's surface Zeta potential-12.2mV after coagulation, PAM 0.27-0.4 mg/L, sludge backflow ratio 7.46% and sludge concentration about 12.4 g/L under the conditions of the raw water average temperature 3.8℃and the raw turbidity about 6 NTU in the pilot experiment. Based on G and GT,40m and 25mm was respectively the optimal length and diameter of tubular reactor according to effluent effects while the value of G is 156.47s-1. The tubular reactor could obtain a good effect when the value of GT was between 14777.63 to 19164.22. The effluent turbidity could reach 2.07 NTU after continuous operation, and the system had a strong impact resistance on max load capacity with 27m/h. The function of compulsory mixing could contribute to stable operation for the suspended particles uniformly forced, the improvement of the fluidization effect of suspended layer, the avoidance of short flow and local deposits, the persistent balance and replacement of the suspended layer.(4) It is feasible using the efficient solid-liquid separator to treat low temperature and low turbidity water. The results showed that the system has the advantages of high stability, good treatment effects and simple operation, also a low energy consumption by using hydraulic mixing, a lower dosage costs of PAM by using backflow sludge as flocculants, and is suitable for the treatment of low temperature and low turbidity water in small cities and towns of northwest regions.