Sanitary sewer overflow | EPFL Graph Search

Sanitary sewer overflow (SSO) is a condition in which untreated sewage is discharged from a sanitary sewer into the environment prior to reaching sewage treatment facilities. When caused by rainfall it is also known as wet weather overflow. Causes of sanitary sewer overflows include: Blockage of sewer lines, infiltration/Inflow of excessive stormwater into sewer lines during heavy rainfall, malfunction of pumping station lifts or electrical power failure, broken sewer lines. Prevention of such overflow events involves regular maintenance and timely upgrades of infrastructure. SSOs can cause gastrointestinal illnesses (waterborne diseases), beach closures and restrictions on fish and shellfish consumption. Magnitude of the problem Developed countries such as the United States, Canada, most Western European nations (e.g. Italy and France), Australia, Singapore, South Korea and Japan are struggling with public health problems of SSO prevention. The magnitude of the problem is

Identifying contaminated sediment problems associated with urban stormwater discharges in lakes

Tom Hugo Antoine Benejam

Urban stormwater discharges during wet weather has always been a sensitive issue to deal with. By inducing combined sewer overflows, substantial impacts on receiving water are commonly feared. Aware of this problematic situation, the VSA already created the STORM guideline to cope with this issue in small rivers. However, such a guideline is still lacking for large rivers and lakes. This project is a first step towards this direction and tries to prospect the necessity of such instructions for lakes. For this purpose, the present master thesis studies the impact of urban stormwater discharged via the Flon river into the Vidy Bay of Lake Geneva, next to the city of Lausanne. A Sediment Quality Triad, meaning a combination of three assessment methods (chemistry, ecotoxicology and in situ benthic communities), was implemented to assess the impact of stormwater discharges on the sediments in this part of the lake. On a large sampling grid composed of 15 sites, heavy metals were measured and ostracod bioassays were performed with the sediment samples collected at these sites. Subsequently, on the five sites located in the central transect of this sampling grid, further experiments were led to understand the incidence of stormwater discharges on sediment quality while moving away from the Flon river’s effluent. In addition to heavy metals, PAHs and PCBs were measured at these sites. A battery of three extra ecotoxicological bioassays was also carried out. These tests were implemented with the following organisms: chironomids, macrophytes and nematodes. Finally, two kind of in situ communities were studied in these five sites: microbial communities in order to perform a pollution-induced community tolerance (PICT) and oligochaete communities in order to implement the oligochaete index of lake bioindication (IOBL). The implementation of these experiments showed that the contamination induced by urban stormwater discharges is limited to the proximity of the combined sewer overflow. A set of pollutants mainly composed of copper, zinc, PCBs and PAHs was identified within this contaminated area. Although no toxicity was observed on the sites affected by this contamination, in situ community studies revealed substantial shifts towards resistant species in both oligochaete and microbial community structures. Another contamination area, observed in remote sites and mainly composed of cobalt, chromium, iron, manganese and nickel, remains not well understood. The laboratory toxicity tests detected some toxicity in benthic invertebrates but the benthic communities studied in situ showed no apparent alteration. Modeling tools are required to get a better understanding of the source of this contamination.

2017

Constructed wetland for the treatment of surface waters from combined sewer overflow (CSO) of La Chaux-de-Fonds

Blaise Adrien Devaud

The Doubs river is an ecosystem-rich river which is threatened by several anthropic activities. The three dams placed in the river as well as the discharge of pollutants contribute to the degradation of its natural habitats. The city of La Chaux-de-Fonds is directly concerned by this issue. The combined sewer overflow (CSO) waters generated by the city discharge in la Ronde, an affluent of the Doubs. These waters represent a potential threat to the Doubs water quality, this is why the authorities of La Chaux-de-Fonds need to take measures to limit the impacts of these waters in the natural environment. These measures have to be taken without causing excessive costs. Several solutions have been considered according to the objectives set during the development of the « plan d’évacuation des eaux (PGEE) » of the city. The implementation of a constructed wetland was the selected solution. This system is widely used in a number of European countries and especially in France, but is not yet much developed in Switzerland. Topographic and design constraints have lead the choice of a vertical flow constructed wetland. Its technical feasibility has been deeply studied. The design of the constructed wetland has been examined using the simulation tool Orage (which is currently in phase test in the IRSTEA research institute in Lyon). A second tool, the Rebeka software, allowed to determine the impact of the CSO water on the water quality of the Doubs. The STORM approach helped to integrate these impacts in the design of the system from the beginning of the the project. The costs of the project are detailed in investment costs for the building of the wetland and operation costs which represent essentially functioning and maintenance costs. The treatment system consists of three planted filters which operate in parallel. Simulation results demonstrate that the objectives of the project are fulfilled. The installation has a removal efficiency of 29% on ammonium, 44% on COD and 95% on TSS. The initial investment is 3.6 million Swiss francs. This system offers a solution to resolve pollution issues originating from the CSO waters of the city of La Chaux-de-Fonds with a reasonable initial investment.

2016

Flow measurements in sewer systems based on image analysis: automatic flow velocity algorithm

David Andrew Barry, David Jeanbourquin, Salim Kayal, Laurent Son Nguyen, Luca Rossi, Daniel Sage

Discharges of combined sewer overflows (CSOs) and stormwater are recognized as an important source of environmental contamination. However, the harsh sewer environment and particular hydraulic conditions during rain events reduce the reliability of traditional flow measurement probes. An in situ system for sewer water flow monitoring based on video images was evaluated. Algorithm to determine water velocities was developed based on image-processing techniques. The image-based water velocity algorithm identifies surface features and measures their positions with respect to real world coordinates. A web-based user interface and a three-tier system architecture enable remote configuration of the cameras and the image-processing algorithms in order to calculate automatically flow velocity on-line. Results of investigations conducted in a CSO were presented. The system was found to measure reliably water velocities, thereby providing the means to understand particular hydraulic behaviors.