Variable Speed Wastewater Pumping

Wastewater pumps have traditionally been operated in an on-off mode for small as well as large wastewater pump stations. Because the inflow of wastewater is varying over time and is often only a fraction of a pump’s required capacity engineers have looked for ways to operate wastewater pumps at a reduced capacity in order to optimize performance while reducing operating costs. Before solid state variable frequency drives became commonplace speed control solutions such as two-speed motors and variable voltage windings were used to achieve variable flow pumping. During the last 10–15 years the industry has seen a significant increase in the adaptation and acceptance of variable frequency drives (VFD’s) in wastewater transport systems. A general desire is to optimize the wastewater flow through the pump stations. Variable speed systems can provide a more flexible and powerful solution compared to using constant-speed pumps. Pumping with variable speed pumps can result in better process control, energy savings, smoother operation and reduced maintenance costs for the pump station, when applied correctly.