| Combined system overflow pollution(CSO)is an important cause of black and odorous water.The CSO in the old urban area of southern Sichuan has the characteristics of "rapid change of concentration caused by rainfall and rain type,serious limitation of wastewater interception and receiving pipe at source,limited land use for purification facilities due to dynamic acquisition and demolition,and limited project investment".The conventional CSO control strategy may not be scientific and economic at that time.Based on the investigation of the composition of pollution sources and the identification of rain pattern,topography,field and other conditions,the characteristics of the old urban area in the southwest hilly area are analyzed.The water quality reaches class IV of surface water.Through the analysis of the basic theory and key elements of source control and pollution interception of water system,the traditional formula calculation method and hydraulic power are proposed The combination of model software MIKE 11 is conducive to the accurate analysis of the causes of CSO overflow pollution,so as to analyze and optimize the conventional engineering measures in terms of technology and economy,so as to accurately implement the measures.The conclusions are as follows:1)Based on the combination of traditional formula calculation and software simulation,dynamic simulation of confluence Overflow Pollution in the old urban area of Southern Xichuan under various rainfall conditions can accurately predict and reasonably implement countermeasures.Through the comparison of model selection,Mike 11 can better meet the needs of water quality simulation in this study in terms of scalability,effectiveness and data performance,which makes the simulation results more accurate.MIKE 11 is selected as the prediction model of CSO Overflow Pollution in the old urban area of southern Sichuan.2)The HD module of MIKE 11 model is used to establish the hydrodynamic model of the river channel in the study area HD module,ad water quality module and Nam rainfall runoff module were coupled to simulate the discharge and water quality of the river reach in 2018.The measured data of the downstream teacher’s New Village section were used to calibrate the model parameters.The re,R2 and ens of the simulated discharge were 9.8%,0.969 and 0.997,respectively.The simulation error of COD and ammonia nitrogen was 11.29% and 11.29%respectively 16.94% 。 The parameters such as confluence time in soil,maximum water content of water storage layer,roughness of riverbed and confluence time in soil were calibrated.The manning coefficient was 0.003 ~ 0.008 in the constant range of Panlong impact ratio,and the parameters were all within the design specification requirements,which showed that the model could fit the temporal and spatial variation of pollutant concentration.3)Using MIKE11 water quality model to simulate three different rainfall intensities,this paper analyzes the impact of CSO Overflow Pollution on river water quality,evaluates the treatment effect of sewage intercepting pipeline,end regulation and storage,ecological purification pond and combined measures,predicts the effect of pollution control and puts forward the optimization scheme.The results show that:It shows that the sewage intercepting pipeline is the key measure to improve the water quality of the simulated river section.By optimizing the closure time and considering the actual land use,seven kinds of combined measures of CSO storage tank with the scale of 1000m3,800m3,600m3,and two ecological purification ponds of 1200m3,1000m3,were obtained.After applying seven combined measures,the water quality of panlongchong detection section will be improved in different degrees under rainfall events.Under light rain(the rainfall is less than5 mm within 12 hours),the sewage interceptor with interception multiple of 2 can transport pollutants to the downstream,which can ensure the water quality of panlongchong downstream section meets the standard;moderate rain(5 ~ 10 mm rainfall within 12 hours)and heavy rain(15 ~ 30 mm rainfall within 12 hours))Under the event,it is necessary to evaluate and take the combined measures of source,midway and terminal purification on the basis of effective sewage interception.After setting up seven engineering models for river water quality reduction,it is concluded that model three(sewage interceptor + 800 m ~ CSO storage tank + 1200 m ~ecological purification pond)is the better scheme,and the operation cost is comparable(sewage interceptor + 1000 m ~ CSO storage tank + 1200 m ~ ecological purification pond)The results show that the reduction of COD is 27.08mg/l(reduction rate is 56.2%),ammonia nitrogen reduction is 2.77mg/l(reduction rate is 68.3%),COD reduction under heavy rain event is19.9mg/l(reduction rate is 54.3%),ammonia nitrogen reduction is 2.51mg/l(reduction rate is65.3%).Through the analysis of cost and energy consumption,the cost is saved by 10%.4)For example,panlongchong area,a high-density old urban area,downtown commercial district and historical and cultural protection block,has extremely limited ground and underground space,and it is difficult to complete regional rectification according to the total amount control index in a short period of time,or when the overall reconstruction cost is too high and too difficult,the initial rainwater control facilities are used to control part of the pollutants under local and decentralized conditions The other control quantities that are difficult to reach the standard can be considered to achieve the target water quality by combining with the terminal facilities,which is a more technical and economic optimization strategy.In this paper,the research methods and optimization route of confluence Overflow Pollution Control under the specific boundary conditions in the old urban area of southern Sichuan are proposed,in order to provide reference for similar regional water environment treatment projects in South Sichuan. |
PDF Full Text Request