Generally in a wastewater treatment plant, the effluent to be treated is conveyed by gravity through an underground pipeor channel. To avoid to make the water treatment processes in tanks completely underground, with a consequent increase in the costs of civil works and with the difficult management of them, it is necessary to provide a lifting sump at the head of the plant, possibly after the step of screening for safeguard the itself group. .
The lifting system is constituted by a series of pumps, generally submerged, which are controlled by level controls of the water level in the same tank. If the water level in the tank is low, only one pump is in operation; as the water level rises, it comes into operation also the other pumps of the lifting unit. In this way it is possible to handle variations in the effluent inlet, ensuring the lifting even with the maximum capacity, and reduce the energy consumption in case of minimum flow.
The factors that characterize a pumping group are:
- Flow Q (m3/h), based on the maximum capacity;
- Prevalence H, which considers both the geodetic prevalence, both distributed and localized losses of the pumping system;
- Yield η of pump;
- Power P of the pump;
- Kind of impeller, which must ensure free passage because the lifted liquids contain solids.
This technology is an integral part of the treatment process of a Biological plant.