New state requirements for phosphorus removal meant that the wastewater treatment facility in St. Charles, Illinois had to be upgraded to accommodate the change. This meant that the facility needed to convert to a three-stage A2O system, with aerobic, anoxic, and anaerobic zones for biological phosphorus removal. They needed to add a new internal recycle pump station, a primary sludge fermenter, and replace sludge and biogas storage tanks. In the process, they rehabilitated the digesters and biogas system as well. Some of the changes required adding non-linear load variable frequency drives which added harmonics to the system.
The addition of HGP Passive Harmonic Filters on non-linear VFD loads will reduce harmonic distortion to less than 5%. Renovations like this typically include additional stages of pumping that require VFDs, and thus additional harmonics for the entire plant. Applying passive filters to the new VFDs is an easy and inexpensive way to get the facility back to a low level of harmonic content, which is ideal for the equipment in the entire plant.
The article in Treatment Plant Operator magazine, Upgrading to a Bio-P Process Required Open Communication and a Proactive, Patient Approach at Wastewater Facility, by Jim Force, describes in detail how the wastewater facility had to be upgraded, and is the source of the information and picture for this case study.