Decentralized wastewater system

Decentralized wastewater systems (also referred to as decentralized wastewater treatment systems) convey, treat and dispose or reuse wastewater from small and low-density communities, buildings and dwellings in remote areas, individual public or private properties. Wastewater flow is generated when appropriate water supply is available within the buildings or close to them. Decentralized wastewater systems treat, reuse or dispose the effluent in relatively close vicinity to its source of generation. They have the purpose to protect public health and the natural environment by reducing substantially health and environmental hazards. They are also referred as "decentralized wastewater treatment systems" because the main technical challenge is the adequate choice of a treatment and/or disposal facility. A commonly used acronym for decentralized wastewater treatment system, is DEWATS. Centralized wastewater systems are the most widely applied in well-developed urban environments and the oldest approach to the solution of the problems associated with wastewater. They collect wastewater in large and bulk pipeline networks, also referred as sewerage, which transport it at long distances to one or several treatment plants. Storm water can be collected in either combined sewers or in a separate storm water drains. The latter consists of two separate pipeline systems, one for the wastewater and one for the storm water. The treated effluent is disposed in different ways, most often discharged into natural water bodies. The treated effluent may also be used for beneficial purposes and in this case it is referred as reclaimed water. The main difference between decentralized and centralized systems is in the conveyance structure. In decentralized systems the treatment and disposal or reuse of the effluent is close to the source of generation. This results in a small conveyance network, in some cases limited only to one pipeline. The size of the network allows for applications of different conveyance methods, in addition to the well-known gravity sewers, such as pressurized sewers and vacuum sewers.

Optimisation du système d’assainissement des eaux urbaines Réseau-STEP-Milieu récepteur par une approche de gestion intégrée

Jean-Baptiste Razurel

Water management is a recurring problem that has occupied mankind for years. Nowadays, the multiple stakeholders involved in this management have the willingness to cooperate to make it more integrated and take into consideration all social, economic and environmental components across an ideal functional unit which is the hydrological watershed. The urban wastewater system plays a central role because of its triple dimension Sewer, Wastewater treatment plant, Receiving water and well often determines the quality of the water on which depend many other sectors. Insurance that the system is in a good health allows having a functional and efficient water resources management. This work explores the possibilities of optimization of the urban wastewater system by the establishment of an integrated management which takes into account the three subsystems. For this, an understanding of the process of optimization and the knowledge about the conventionally used algorithms is deepened. Furthermore the importance of modeling and real time control for the improvement of knowledge and decision making is emphasized by a review of the available tools involved in concrete examples. An approach of integrated management of the urban wastewater system is proposed, focusing on two aspects : the identification of the critical points of the system by analyzing performance indicators and the implementation of the optimization process. This approach is applied to a case study and allows highlighting the presence of important overflows at a pumping station due to the infiltration of parasitic clean water. At this problematic station the optimization process is applied with the help of CVX tool on matlab. This optimization reduces spills using existing infrastructure while following sizing, economic and environmental constraints established by the system. This study shows that improvement of the urban wastewater system performance by following an integrated management approach exists and can be considered in Switzerland.

2016

Optimisation du système d’assainissement des eaux urbaines Réseau-STEP-Milieu récepteur par une approche de gestion intégrée

Jean-Baptiste Razurel

2016