Huge energy savings and a significant carbon reduction were achieved in the preliminary water treatment stage, where solids are separated from the sewage inflow. By applying Danfoss VLT AQUA drives to control the levels in the holding tanks, variable speed operation of the 4 x 370kW pumps realised a return on investment within 6 months, and ongoing energy and carbon savings for the future. The additional operation result is a more constant flow through the subsequent processes, improving overall process efficiency.
The project
Pumps are the major electrical load in any wastewater treatment station and the plant is designed to handle not only the day-to-day wasterwater loading but also the peak load imposed by the run-off water in the rainy season. For this reason the pumps installed run most of the time below peak capacity. The initial plant design was for a simple level control scheme with soft-starters controlling the pumps in cascade mode. Danfoss approached the end user, Aguas de Catagena S.A. ESP and explained to them the wide range of benefits to be obtained from constant operation of the pumps in speed control mode. By using VLT AQUA drives to control pump speed proportional to the water level in the tanks, energy usage is reduced dramatically as the level of water in the tanks is reduced and the operation of the whole system is smoothed.