Hopedale, Massachusetts – Energy Conservation
Energy Conservation
Hopedale, Massachusetts
Prior to upgrades designed by Tata & Howard for the Town of Hopedale, Wastewater Treatment Facility (WWTF) utilized manual control of the aeration system within the aeration basins. The aeration system consisted of four oversized, constant speed blowers and a stainless steel diffuser system. In a system with air blowers run at a constant speed, the blower is either constantly operating at top speed or not at all, resulting in uneven dissolved oxygen (DO) levels. Overnight, when operators are not present to monitor DO and turn the blowers on and off accordingly; the blowers are either on all night raising the DO to well over the necessary level and wasting energy, or the blowers remain off causing the DO to drop and thereby limiting nitrification.
New high-speed blowers were installed and are now controlled by Variable Frequency Drives (VFDs) based on the DO readings from the aeration tanks. A DO probe is located in each basin and transmits the DO level back to the Programmable Logic Controller (PLC) which in turn dictates the VFDs to speed up or speed down to supply the appropriate volume of air to the diffuser system. This setup allows the basin to maintain a relatively constant DO level for optimal nitrification and is far more energy efficient when compared to constant speed systems. Further, by utilizing high-speed blowers, a smaller, more efficient blower can provide the same volume of air as a lower speed blower.