| During the daily operation of the sewage pipeline network,sediment will gradually form at the bottom of the pipeline.When washed by rainfall,the sediment will be suspended and transported again,overflowing into the river with sewage,ultimately forming a black and odorous water body,seriously affecting the natural water ecological environment.However,as the most widely used measure for regulating overflow pollutants,the regulating capacity of storage tanks is difficult to further improve due to limitations such as land occupation.In this study,by adding baffles to change the flow field of traditional storage tanks,a pilot test system was established to simulate pipeline overflow and the control process of overflow pollutants by storage tanks under different rainfall intensities in a newly constructed sewage pipeline storage tank linkage regulation system.The overflow pollution law of sediment erosion in the combined sewage pipeline network and the strengthening of storage characteristics and mechanisms were explored,providing new ideas for the overflow regulation of sewage pipelines,The main conclusions are as follows:(1)Explored the overflow patterns of pollutants such as carbon,nitrogen,and phosphorus during pipeline overflow for different rainfall intensities.The results show that under high rainfall intensity(1.6 mm/h),the maximum concentrations of COD,SS,TN,and TP can reach 757.15 mg/L,990 mg/L,60 mg/L,and 5.32 mg/L,respectively;Under moderate rainfall intensity(0.9 mm/h),the concentrations of COD,SS,TN,and TP can reach 537.23 mg/L,733.67 mg/L,59.61 mg/L,and 4.69 mg/L;Under low rainfall intensity(0.68 mm/h),the concentrations of COD,SS,TN,and TP can reach449.17 mg/L,516 mg/L,84.41 mg/L,and 6.81 mg/L.From this,it can be seen that as the intensity of rainfall increases,the overall concentration of overflow pollutants increases,with a particularly significant increase in COD and SS concentrations.The overflow time of the highest concentration is also significantly earlier,shortening from10 minutes under low rainfall intensity to 4 minutes under medium to high rainfall intensity.Relatively speaking,TN and TP are less affected by rainfall intensity.(2)Three new types of storage tanks are formed by adding perforated baffles with different number of aperture gradient distribution at 1/3 and 2/3 along the storage tank.The concentration variation law of overflow pollutants in the storage tank is analyzed,and the storage potential under different rainfall intensities is determined.The research results show that all three new types of storage tanks exhibit excellent characteristics of enhanced storage,with certain improvements in the removal rates of COD,SS,TN,and TP,with an average increase of 7.50%,13.18%,11.28%,and 6.98%.Among them,the storage tank with baffles installed at 1/3 has the best enhanced storage effect.Under low rainfall intensity,the removal rates of COD,SS,TN,and TP are 62.05%,60.47%,50.06%,and 11.53%,respectively;Under moderate rainfall intensity,the removal rates of COD,SS,TN,and TP were 74.23%,63.35%,12.62%,and 10.55%,respectively.Under high rainfall intensity,due to the overall high concentration of pollutants,the original storage tank itself has a good removal effect.Therefore,after strengthening,only SS has a higher removal rate of 73.63%,but the storage time of all pollutants is significantly shortened.(3)A flow regime model of the regulation and storage tank was constructed using simulation methods,and the impact of flow regime changes on pollutant concentration was analyzed.The control mechanism for strengthening regulation and storage was explored.The results show that after the addition of baffles,the reflux area in the settling zone significantly decreases,the overall streamline becomes smoother,and the flow velocity distribution is more uniform.When the inlet water impacts the baffle,some of it consumes energy when directly passing through the baffle hole,while the other part directly impacts the surface of the baffle,forcing it to change its direction of movement and reducing the kinetic energy of the inlet water,thereby enhancing the natural sedimentation of particles.By comparison,it was found that the flow field in the storage tank with a baffle installed at 1/3 is the most stable,with the largest effective settlement area.After the collision energy consumption process and perforation energy consumption process,more small and medium-sized particles that are not easy to settle can gradually sink,and the adsorbed dissolved pollutants are also removed.In summary,it can be seen that the storage characteristics,storage time,and flow field streamline of the storage tank with a baffle installed at 1/3 of the site are more beneficial for strengthening the regulation ability.This study can provide new theoretical basis and technical support for the control of overflow pollutants. |
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