| There needs a lot of aggregate with high quality during the construction of hydropower station. Large number of wastewater will be emerged during this man-made process. When this kind of wastewater was discharged into the river without any treatment, it can cause negative impact on water environment of down stream for its high concentration of suspended solid. However, there is no such example of successful operation of this kind of wastewater treatment process. Many existing processes of this kind of wastewater are scrapped for blocked drainage system.According to the study results, our research group decided to dealing with the aggregate processing wastewater with the horizontal flow settling and flocculation settling and made a small pilot test at the Guandi Hydropower Station. The experiment results show that this kind of process used to deal with the aggregate processing wastewater, is effective. In order to confirm the effectiveness of the horizontal flow sedimentation to slove the mud-congestion problems, a further pilot needed to be carried on. The result shows that:①According to the analysis about the sludge resistance and size test in the horizontal flow settling tank, we get that the magnitude changes on the sludge resistance will occur between the front and rear section of mud bucket. So, the mud bucket in which the sludge resistance changed is considered to be the cut-off point between the firstry sludge and the secondary sludge. In the meanwhile, we found that the firstry sludge containing the sand particle size is greater than 100μm and the secondary sludge isn`t, so we can determine the level of sludge by whether the sludge bucket contains large Sand particles in the 100μm diameter. The cut-off point between the firstry sludge and the secondary sludge provide theoretical basis for sludge dewatering and reference for similar projects about sludge treatment.②The test select PAC(5%), PAM(2‰), ferric chloride(5%), industrial caustic soda(1%) as the flocculant. In the light of the orthogonal experiment, the test get the optimal flocculant are PAC(5%) and industrial caustic soda(1%), the dosage was 500mg/L and 25mg/L respectively.③Comparing the removal rate of the horizontal flow settling tank sedimentation tanks, the firstry and the secondary sludge resistance, sludge moisture content, the type and dosage of flocculant, the sludge resistance and moisture content in the flocculation sedimentation tank, the effluent suspended solids concentration and the match between the time of sludge discharge and dewatering in different conditions, the test determine the optimal conditions is that the water flow is 13m3/h, the HRT of the horizontal flow settling tank is 60min, the type and dosage of flocculant is PAC (5%) 500mg/L and industrial caustic soda (1%) 25mg/L, mud discharge cycle of the system is 2.5h. In optimal conditions, The system runs in stable condition, the quality of effluent water is good and reach the first level criteria specefied in Integrated Wastewater Discharge Standard (GB8978—1996) and does not appear compacted sludge, sludge dewatering effect is good. Running results show that the horizontal flow settling and flocculating settling is indeed effective for gravel processing wastewater treatment.④On the basis of the parameters and boundary conditions of small scale simulation, the test carried out the simulation about the medium-sacle pilot and production scale, the results show that the established numerical model in the simulation experiment is reasonable and the simulate effect can reflect the setting condition of gravel particles in the sedimentation tank, the optimum condition can provide working parameters reference for similar projects.
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