Energy Efficiency Analysis of the Final Lift Station of an Activated Sludge Wastewater Treatment Plant in Brazil Based on the Hydraulic Design and Pumps Operation – Case Study

Abstract

As the demand for wastewater treatment increases, treatment plant energy efficiency becomes an essential topic of study, since modern treatment processes requires a significant amount of energy. Whereas optimal energy consumption is desired, laws and guidelines have been established to encourage plant operation improvements. This work shows the importance of energy efficiency in wastewater treatment plants and its main energy consumption processes. The literature shows that aeration and sewage pumping are the two most energy demanding systems, therefore, this work focuses exclusively on the pumping system. A methodology to analyze a wet well lifting system operation is presented and applied to a case study of a large, activated sludge wastewater treatment plant. Three conditions that can compromise the performance of the pumping system were studied: the suction system inlet screen, siltation of the suction duct, and pump wear. Only the suction system inlet screen proved to be significantly prejudicial to pump performance. For this condition, it is shown that, when obstructions occur, the water level in the wet well increases, as does the energy consumption of the pumping system. In the case study, variable speed pumps proved to be more susceptible to power variations due to obstructions in the inlet screen, while constant speed pumps are less susceptible. Although the energy consumption variation in the case study may look small, when considering the total volume of treated wastewater over a month’s period, the difference in power consumption is significant. The methodology presented here can be adapted to emulate the final lifting systems of similar wastewater treatment plants.