The Storm Water Management Model (SWMM) was established to simulate rainfall-runoff dynamically, and the internal runoff component of the SWMM was used to simulate rainfall operation in each watershed, including rainf...
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The Storm Water Management Model (SWMM) was established to simulate rainfall-runoff dynamically, and the internal runoff component of the SWMM was used to simulate rainfall operation in each watershed, including rainfall-runoff and scour pollution load. Then, using the routing component in the SWMM, the properties of runoff into the tank system are calculated through pipelines and other facilities to obtain the optimal tank volume. The coupling optimization model was established, and the algebraic function of the storage capacity, total runoff, and total cost was established by using the multiple linear regression method, which was transformed into the optimization model aiming at the minimum total runoff and total cost. The NSGA-II is improved by using a reverse learning mechanism. By solving the optimization model, the non-dominant solution of the proxy model is obtained. The non-dominant solution was substituted into the SWMM, and the rationality of the optimization results was analyzed. The experimental results show that the reservoir volume determined by this method can effectively accept the pollutants brought by the initial rain, so as to reduce the hydraulic pollution caused by the confluence overflow and the overflow pollution of the urban integrated pipe network.
The issue of combined sewer overflow (CSO) triggered by rainfall has become a significant obstacle to the improvement of water environment quality. This study conducted a long-term monitoring of three types of rainwat...
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The issue of combined sewer overflow (CSO) triggered by rainfall has become a significant obstacle to the improvement of water environment quality. This study conducted a long-term monitoring of three types of rainwater outlets, i.e., combined sewer overflows (Test-CSO), separated sewer outlets (Test-SSO), and partially separated sewer outlets (Test-PSSO), to reveal the characteristics of overflow pollution and trace its sources by monitoring the pollutants from different underlying surfaces across various urban functional areas. The results showed that the major pollutants in overflow events exhibited the following order: COD >= TSS > TN > TAN > TP. Rainwater elevated COD and TSS in the Test-CSO, while reducing nitrogen and phosphorus concentrations by dilution. The Test-PSSO experienced varying degrees of overflow pollution, primarily due to the sewer sediment. A negative relationship between the rainfall and peak time of overflow pollution was observed. The traceability analysis indicated the overall pollution intensity exhibited the following order: residential areas > industrial parks > commercial areas. In addition to commercial areas, the pollution intensity across underlying surfaces generally exhibited the following order: roofs > roads > grasslands. The roof runoff was an important source of pollutants for overflow pollution, and TSS and COD were the major contributors. Notably, grasslands had a buffering effect on pollutants and pH.
In recent years, combined sewer overflow (CSO) has been identified as a significant contributor to the deterioration of the urban water environment. It is thought that remolding it to a separate sewer system is a thor...
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In recent years, combined sewer overflow (CSO) has been identified as a significant contributor to the deterioration of the urban water environment. It is thought that remolding it to a separate sewer system is a thorough and effective method of controlling the CSO in the appropriate area. However, according to current research, the separate stormwater sewer systems will also have overflow pollution due to functional defects, damaged or inappropriately connected with sewage, which has serious consequences for the separate system's operational efficiencies and the urban water environment. The event mean concentration, first flush effect, source apportionment, and correlation analysis of variables in overflow pollution generated in three residential catchments in Nanning, China, were investigated in this study. The results showed that the event mean concentration values in drainage outlets inappropriately connected with sewage were 2-4 times higher than those in stormwater outlets, especially for NH3-N, TN, and TP. Meanwhile, more than 80% of overflow events at outlets inappropriately connected with sewage had a weak first flush or even a weak dilution effect, with peak pollutant concentrations occurring 40-60 min after the overflow began. Besides, the discharge pollution load was primarily derived from the inside of the sewer. When the rainfall was heavy, the contribution rate of sewer sediment erosion exceeded 60%, which was much higher than the contribution rate of rainfall runoff and sewage. The variability in event mean COD and TSS concentrations was primarily attributed to the antecedent dry period and rainfall intensity. The COD concentration increased from 140.7 to 277.1 mg/L with the increase of antecedent dry period from 3 to 10 days. This study could help guide the implementation of targeted measures to treat overflow pollution in urban residential catchments, as well as the development of strategies to mitigate the effects on receiving water bodies.
To probe the overflow pollution of separate storm drains with inappropriate sewage entries, in terms of the relationship between sewage entries and the corresponding dry-weather and wet-weather overflow, the monitorin...
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To probe the overflow pollution of separate storm drains with inappropriate sewage entries, in terms of the relationship between sewage entries and the corresponding dry-weather and wet-weather overflow, the monitoring activities were conducted in a storm drainage system in the Shanghai downtown area (374 ha). In this study site, samples from inappropriately entered dry-weather sewage and the overflow due to storm pumps operation on dry-weather and wet-weather days were collected and then monitored for six water quality constituents. It was found that overflow concentrations of dry-weather period could be higher than those of wet-weather period;under wetweather period, the overflow concentrations of stormdrains were close to or even higher than that of combined sewers. Relatively strong first flush mostly occurred under heavy rain that satisfied critical rainfall amount, maximum rainfall intensity, and maximum pumping discharge, while almost no first flush effect or only weak first flush effect was found for the other rainfall events. Such phenomenon was attributed to lower in-line pipe storage as compared to that of the combined sewers, and serious sediment accumulation within the storm pipes due to sewage entry. For this kind of system, treating a continuous overflow rate is a better strategy than treating the maximum amount of early part of the overflow. Correcting the key inappropriate sewage entries into storm drains should also be focused.
The commonly employed design of detention tanks cannot effectively control overflow pollution because of non-stormwater entry and sewer sediments in the urban drainage system. Herein, a multi-source overflow model con...
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The commonly employed design of detention tanks cannot effectively control overflow pollution because of non-stormwater entry and sewer sediments in the urban drainage system. Herein, a multi-source overflow model considering both overflow water quality and quantity has been developed for simulating real overflow events. Subcatchment and drainage information is extracted through geographic information system (ArcGIS) and a multi-source overflow model is developed in Stormwater Management Model (SWMM) by coupling runoff mode, non-stormwater mode, and sediment mode. This model is successfully calibrated and validated with the reasonable root-mean-square error (RMSE) of 8.2 and 5.8% for water quality and quantity, respectively. The simulated results suggest that the misconnected non-stormwater entry can affect overflow contaminant concentrations over the period of overflow due to its continuous pollution, while sewer sediments mainly exert effects on the peak pollution period of overflow. Based on model prediction, an approach called overflow peak pollution interception (OPPI) is proposed for model application and design optimization. The OPPI designed detention tank is suitable for high non-stormwater entries and long antecedent dry days (large amount of sediment). A case study is conducted in a high-density urban area of Shanghai, and compared with two commonly employed design methods in Germany and China, which have the similar design principle of volume, relying on amount of precipitation multiplying area of region, the combination of overflow model and OPPI approach enables to offer more accurate and effective design of detention tanks for pollution control in urban areas.
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