For many years, maintaining efficient aeration control was a challenge for the 24 MGD Muncie, Indiana, Water Pollution Control Facility (WPCF). A manually operated system combined with severe mixing-limited conditions resulted in over-aeration and wasted energy. The plant recently alleviated this problem with the CASPERON process and VEMA controller, allowing it to satisfy the needs of the bacteria while expending less energy.
According to John Barlow, Muncie WPCF Superintendent, operators initially attempted to maintain DOs in the aeration system at 2-4 mg/l, with varying degrees of success.
Barlow finally made the decision to maintain DO levels in the aeration system at 5-7 mg/l at all times.
“I decided to run the blowers higher because maintaining the needs of the bacteria is our primary goal,” he says. “We were getting inconsistent ammonia levels in our final effluent due to the roller coaster action from trying to maintain 2-4 mg/l DO levels. Plus, running our operators around all day turning blowers up and down and adjusting header valves was an inefficient use of manpower.”
To bring efficiencies to the system, the plant automated its aeration system. This included the addition of membrane diffusers and the OSCAR system with VEMA controller.
The plant’s diffusers were replaced with Sanitaire Silver Series II membrane disc diffusers. To support real-time monitoring and control, YSI instruments were installed in the basins, including FDO dissolved oxygen probes and VARiON ion selective electrode sensors, which measure ammonium, nitrate, and potassium.
The Sanitaire OSCAR system includes the biological process control panel that houses a PLC and HMI. The control system uses the DO measurements to automatically adjust the blower speed and air valve position.
Once the upgrade was completed, the aeration system immediately delivered significant energy savings, but high DO levels resulting from severely mixing-limited conditions indicated there was room for improvement.
As a result Xylem implemented the Sanitaire VEMA controller. The controller ensures the basin is continually aerated, but allows the air supply rate to be reduced significantly the majority of the time. During its normal operation mode, air supply is based on DO readings to match bacterial demand. For short-sequenced durations, however, the system operates at a higher rate to re-suspend any solids that may have settled during the time it was running at the lower rate.
“We initially struggled to have our DO levels close to where we wanted them to be but still get enough mixing in the tanks so that they didn’t become settling tanks, however our controller’s new program took care of that,” Barlow says. “We now save more than $5,000 per month with the new aeration system.” The plant has reduced its power consumptions by >20%.
Aside from power efficiency, Barlow says there’s more efficient use of staff by having more precise aeration control. “From an operations standpoint, if our operators want to change DOs, they no longer have to manually turn blowers and then adjust 12 different header valves because it’s all automated,” he says.
Editor's Note: Scranton Gillette Communications and the SGC Water Group are not liable for the accuracy, efficacy and validity of the claims made in this piece. The views expressed in this content do not reflect the position of the editorial teams of Water & Wastes Digest, Water Quality Products and Storm Water Solutions.