Culex Mosquitoes at Stormwater Control Measures and Combined Sewer Overflow Outfalls after Heavy Rainfall

Mosquito borne diseases are increasingly problematic as climate change continues to alter patterns of precipitation, flooding, and temperatures that may favor mosquito habitats. Stormwater control measures (SCMs), ecologically sustainable methods of stormwater management, may have varying impacts on Culex mosquitoes, such as in areas with combined sewer overflows (CSOs). We studied spatial and temporal associations of SCMs and Culex mosquito counts surrounding the SCMs, stratifying our examination amongst those that do/do not use pooling and/or vegetation, as well as surrounding CSO outfalls after heavy rainfall (≥95th percentile) during summer 2018. Results indicate Culex mosquito counts after heavy rainfall were not significantly different at SCMs that use vegetation and/or ponding from at those that do not. We also found a 35.5% reduction in the increase of Culex mosquitoes the day of, and 77.0% reduction 7–8 days after, heavy rainfall at CSO outfalls treated with medium SCM density compared to those without SCMs. Our results suggest that SCMs may be associated with a reduction in the increase of Culex mosquitoes at the CSO outfalls after heavy rainfall. More research is needed to study how the impacts of SCMs on mosquito populations may affect human health.

Microplastics in Combined Sewer Overflows: An Experimental Study

One of the main sources of microplastics inside surface waters is represented by combined sewer overflows (CSOs), involving severe risks for the environment. The entry of microplastics into water bodies also depends on the characteristics of sewer diversion structures used as flow control devices. In this work, an experimental investigation was carried out to evaluate the outflow of microplastic particles, consisting of different types of nylon fibers, from a side weir located on a channel with a rectangular section. A specific methodology was developed for the fiber sampling and outflow assessment after the tests were performed. For the tested configurations, an increase in fibers discharged up to 196.15% was measured as the water flow rate increased by 62.75%, combined with an increase in the side weir length up to 40% and a decrease in the crest height up to 20%. The size and weight of the different fibers showed a low impact due to their low inertia, and their motion was governed by the water flow. An empirical equation to evaluate the fiber outflow as a function of water flow rate and side weir geometric characteristics was also proposed and calibrated for the experimentally tested ranges of the dimensionless lateral water outflow Q* = 0.51–0.83 and of the dimensionless geometric parameter S* = 0.114–0.200. These first experimental results make it possible to carry out a preliminary assessment of the impact of CSOs in terms of microplastics spilled into water bodies.

Optimal Design of Combined Sewer Overflows Interception Facilities Based on the NSGA-III Algorithm

The interception facility is an important and frequently used measure for combined sewer overflow (CSO) control in city-scale drainage systems. The location and capacity of these facilities affects the pollution control efficiency and construction cost. Optimal design of these facilities is always an active research area in environmental engineering, and among candidate optimization methods, the simulation-optimization method is the most attractive method. However, time-consuming simulations of complex drainage system models (e.g., SWMM) make the simulation-optimization approach impractical. This paper proposes a new simulation-optimization method with new features of multithreading individual evaluation and fast data exchange by recoding SWMM with object-oriented programming. These new features extremely accelerate the optimization process. The non-dominated sorting genetic algorithm-III (NSGA-III) is selected as the optimization framework for better performance in dealing with multi-objective optimization. The proposed method is used in the optimal design of a terminal CSO interception facility in Wuhan, China. Compared with empirically designed schemes, the optimized schemes can achieve better pollution control efficiency with less construction cost. Additionally, the time consumption of the optimization process is compressed from days to hours, making the proposed method practical.

A Detention Reservoir Reduced Combined Sewer Overflows and Bathing Water Contamination Due to Intense Rainfall

Combined sewer overflows (CSOs) close to water bodies are a cause of grave environmental concern. In the past few decades, major storm events have become increasingly common in some regions, and the meteorological scenarios predict a further increase in their frequency. Consequently, CSO control and treatment according to best practices, the adoption of innovative treatment solutions and careful sewer system management are urgently needed. A growing number of publications has been addressing the quality, quantity and types of available water management and treatment options. In this study, we describe the construction of an innovative detention reservoir along the Arzilla River (Fano, Italy) whose function is to store diluted CSO wastewater exceeding the capacity of a combined drain system. River water sampling and testing for microbial contamination downstream of the tank after a heavy rain event found a considerable reduction of fecal coliform concentrations, which would have compounded the impact of stormwater on the bathing site. These preliminary results suggest that the detention tank exerted beneficial environmental effects on bathing water by lowering the microbial load.

Hydrodynamic assessment of object on the sewer network in the city of Trnava

As in most Slovak cities, there is a combined sewer network in the city of Trnava. Therefore, combined sewer overflow (CSO) must be provided on these networks in order to mix rainwater and sewage water. The purpose of these CSO’s is to reduce the amount of rainwater supplied to the treatment plant and to discharge part of the rainwater to the recipient. However, these waters contain various contaminants, including coarse solids, fine suspended solids, and solutes. Due to this, reduced water quality was recorded in the Trnávka recipient. This reduced quality is also due to the increased number of reliefs as prescribed by Government Regulation n.269/2010. The aim of the work is the analysis and selection of unsuitable relief chambers that do not meet the given limits. Hydrodynamic simulations are performed on these chambers, which demonstrate the need to reduce the amount of rainwater or reconstruction of CSO’s.

Combined sewer overflow chamber analysis based on CFD modelling.

The paper deals with CFD simulation of a real combined sewer overflow chamber using Ansys fluent software. Simulations are created for various structural modifications. Within the results, the hydraulic parameters of the individual are evaluated with a proposal for optimal operation of the given relief chamber.

Alternatives how to mitigate urban flooding and CSO in urbanized areas used in European cities and towns

Urban flooding and combined sewer overflow in city, or town areas represents potential risk in environmental, economic, or social aspects. The goal of this study is to process and evaluate efficiency of individual solutions to reduce occurrence of flooding in urban areas caused by intense rainfall events. The known conventional solutions are stormwater chambers, or storage drains. The new trend in reduction of stormwater drainage into combined sewer system are parts of blue-green infrastructure. Blue-green infrastructure represents environmental urban infrastructure which consists of sensitively selected urban vegetation combined with ingenious hydrological elements of urban city drainage. The study also deals with experimental usage of decentralized real time control, based on a gossip-based algorithm of moveable gates in sewage network. Experiment was proposed for drainage system of the city of Cosenza in Italy. Evaluation will assess application value of individual proposed solutions for the reduction of combined sewer overflow for Slovak republic and its urban cities, or towns.

The Capital’s Waterways Could Be Swimmable by 2030

Scientists, community groups, and the Clean Water Act are behind Washington, D.C.’s massive project to reduce combined sewer overflows by 96%.

Hydraulic and Structural Analysis of Complex Cross-Section Reinforced Concrete Pipes to Improve Sewage Flow in a Combined Sewer System

A complex cross-section reinforced concrete pipe that combines a sub-pipe for the flow of sewage in dry weather and a main pipe for the flow of rainwater was developed to reduce sedimentation of the combined sewer system in dry weather. The sub-pipe was designed, considering the flow velocity, constructability, and maintenance. By fitting the sewage data in the dry weather to the normal distribution, the ratio of the cross-sectional area of sewage flow to that of the pipe was determined to be approximately 0.418, which could cover 99.85% of the sewage volume of the target site. Based on this ratio, the diameter of the sub-pipe corresponding to the combined sewer system with a pipe diameter between 450 and 1300 mm was determined. The hydraulic performance analysis results showed that the flow velocity increased by 11 to 12% compared to the circular pipe based on the full sub-pipe and by more than 15% depending on the water level. The shear stress increased by more than 16.5%, and higher tractive force was observed. Structural safety was determined as the crack load and failure load far exceeded the minimum criteria, thereby verifying the feasibility and field applicability of the complex cross-section reinforced concrete pipe.