Experimenttal Study On Reflux Enhanced Coagulation Of Production Wastewater From Water Supply Plants

With the rapid development of economy and the continuous improvement of living standards,people have put forward higher requirements for water quality,while the contradiction between supply and demand of urban water resources is increasing.In recent years,the reuse of wastewater from water supply plants has become one of the effective ways to alleviate the shortage of water resources.Production wastewater mainly includes sludge water from sedimentation tanks and backwashing wastewater from filter tanks,accounting for about 3%to 10%of the water supply of the water supply plant.Reusing it can not only strengthen coagulation and improve the quality of effluent,but also reduce environmental pollution and save costs,responding to the national sustainable development strategy.This study collected raw water quality data from the water supply plant,and tested and analyzed the sludge discharge water from the sedimentation tank and the backwash water from the filter.A separate reflux test was conducted in the laboratory for production wastewater,using four reflux methods:direct reflux of sludge discharge water,supernatant reflux of sludge discharge water,direct reflux of backwash water,and supernatant reflux of backwash water.The impact of sedimentation water on the effluent quality was tested under different reflux methods and reflux ratios,And explore the mechanism of enhanced coagulation by reflux of production wastewater.Then,the optimal reflux method and optimal reflux ratio of production wastewater were determined based on the individual reflux of production wastewater.Response surface analysis experiments were designed to optimize the combined reflux parameters and determine the optimal reflux parameters for different reflux combinations,determining the primary and secondary factors that affect the reflux of production wastewater.Finally,after understanding the impact of production wastewater reflux on the quality of settled water,we went to the water supply plant for production wastewater reflux production tests to explore the safety of production wastewater reflux in actual operation.At the same time,we analyzed the impact of production wastewater reflux on the dosage and sludge discharge cycle,and conducted an economic analysis of production wastewater reflux,providing technical support for the actual production transformation of the water plant.Research shows that production wastewater reflux can enhance the concentration of particles in mixed water,promote the destabilization of particles in water,and improve the collision efficiency of colloidal particles,thereby enhancing coagulation.After sedimentation,the residual turbidity of the water tends to increase first and then decrease,and is lower than 1NTU at the lowest point of residual turbidity.In terms of turbidity removal efficiency,the enhanced coagulation effect of direct reflux of sludge discharge water is better than that of supernatant reflux of sludge discharge water,and the optimal reflux ratio of direct reflux of sludge discharge water is 4%;The enhanced coagulation effect of backwash water direct reflux is better than that of backwash water supernatant reflux,and the optimal reflux ratio of backwash water direct reflux is 6%.Although the effect of production wastewater reflux on ammonia nitrogen removal is poor,which will slightly increase the ammonia nitrogen value of the settled effluent,reflux will not increase the chlorine addition amount for subsequent operation of the water supply plant.After refluxing and sedimentation of production wastewater,the COD_Mnvalue and UV₂₅₄of the water show a trend of first decreasing and then increasing,and the refluxing of production wastewater is conducive to the removal of organic matters.From the perspective of COD_Mnremoval efficiency,the removal efficiency of direct reflux of sludge discharge water is superior to that of supernatant reflux of sludge discharge water.The optimal reflux ratio of direct reflux of sludge discharge water is 2%,and the removal efficiency of direct reflux of backwash water is superior to that of supernatant reflux of backwash water.The optimal reflux ratio of direct reflux of backwash water is 4%.In terms of the removal efficiency of UV₂₅₄,the removal efficiency of supernatant reflux from sludge discharge water is better than that of direct reflux from sludge discharge water.The optimal reflux ratio of supernatant reflux from sludge discharge water is 4%,and the removal efficiency of supernatant reflux from backwash water is better than that of direct reflux from backwash water.The optimal reflux ratio of supernatant reflux from backwash water is 4%.Al and Fe are not found to be enriched after refluxing production wastewater,while Mn tends to be enriched after refluxing.However,as long as the reflux ratio is controlled,the content of Mn in the settled water is within the range of drinking water safety standards.On the basis of separate refluxing of production wastewater,a combined refluxing of production wastewater was conducted by directly refluxing sludge water（reflux ratio2%）+directly refluxing backwash water（reflux ratio 3%）,refluxing sludge water supernatant（reflux ratio 2%）+refluxing backwash water supernatant（reflux ratio 2%）The study on three conditions of direct reflux of sludge discharge water（reflux ratio 1%）+direct reflux of backwash water（reflux ratio 2%）found that the combined reflux had significant removal rates for turbidity and UV₂₅₄.Combined reflux increases the utilization rate of production wastewater,making full use of both the sludge water from the sedimentation tank and the backwash wastewater from the filter.Combined reflux can also enhance coagulation and contribute to the removal of turbidity and organic matter.The reflux ratio has the most significant impact on the removal rate of pollutants in raw water,followed by the reflux point,and the smallest impact is on the dosage of coagulant.According to the production test results of the water supply plant,the best reflux point for production wastewater is the front section of the flocculation tank.Reflux can enhance the coagulation effect,save the dosage,extend the sludge discharge cycle,and maintain the stable quality of the effluent from long-term continuous reflux,without causing excessive organic pollutants and microorganisms.As long as the reflux ratio is controlled properly,it will not cause the accumulation of heavy metals.The factory water meets the standards for domestic drinking water.Through economic analysis,it is found that the reuse of production wastewater can not only save water resources,but also increase considerable income for the water plant.The test results provide reliable technical support for the renovation of the water plant.