COLLECTION OF WASTEWATER

As cities grew in size in the USA, installing wastewater collection systems became a necessity for preventing waterborne disease. Achieving this, in turn, facilitated accelerated growth of those cities. By the year 2001, about 210 million people in the USA were served by centralized wastewater collection systems.

Depending on the geography of the area, collection systems use gravity to pass flow through sewers or use lift stations and force mains to transmit wastewater over elevations and great distances to a centralized treatment plant. When a plant is fed by gravity sewers, it also may be equipped with station pumps to lift the wastewater and start the gravity flow process through the plant.Lift stations collect the wastewater from a township or subdivision by gravity and then pump that wastewater through a force main to a centralized wastewater plant. These stations can be designed as either a wet well or a wet and dry well design where the dry well contains the pumps and related equipment.

The valves in a lift station are located in the wastewater basin, dry well or a separate valve vault. The three types of valves typically found in lift stations include check valves, shutoff valves and air valves. The purpose of the check valve is to prevent reverse flow when the pump is turned off. Shutoff valves are used for isolation when repair or maintenance is needed. Air valves expel air from the pump column and the force main to provide flow efficiency and minimize surges. Selecting valves for wastewater applications is similar to that of selecting pumps in that consideration must be given to the solids content of the flow media.

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