Industrial Utility Efficiency    

Howden Roots DO Control System Optimizes Bird Island WWTP

A 180 MGD Challenge

 
Tim HilgartTim Hilgart, Sales Manager, Howden Roots

Bird Island Wastewater Treatment Plant (WWTP) in Buffalo, N.Y., had an inefficient aeration control system that, ironically, had been installed in 1998 as an efficiency upgrade. The operating principle was that air flow to all 32 of the plant’s aeration basins, or zones, would be properly controlled by an average of several Dissolved Oxygen (DO) level measurements taken by DO probes in a few of the basins. However, changes in tank loadings and physical dynamics, along with differences in oxygen transfer rates between diffuser grids, prevented a uniform air flow in the aeration zones. The plant also struggled to accurately adjust the air flow from the blowers because the 60-second open/close travel time of the valve actuators was too short.

By 2008, the Buffalo Sewer Authority (BSA) decided it had to cut the energy consumption of the blowers, which used more energy than any other part of the plant. To make that happen, the plant would have to get a new system that independently controlled each aeration basin. Bird Island, the second largest wastewater treatment facility in New York State, with a dry weather design flow of 180 million gallons per day (MGD), had obtained four 5,000 HP Roots single-stage compressors back in 1980, two of which had been rerated to 3,000HP in 1995, and after looking at product options for two years, BSA turned to Howden Roots for another solution to Bird Island’s aeration control problems.

 

“DO-to-Flow” Concept Eases Header Pressure

 Howden Roots worked with BSA to change the aeration control plan for Bird Island and also recommended the replacement of the old valve actuators with RCS actuators that had a 180-second open/close travel time. In the fall of 2011, Howden Roots began operating the largest-ever installation of its Roots IntelliView Controls system at Bird Island’s aeration basins. The system, comprised of RCS actuators and a Roots Aeration Master Control Panel with a remote access VPN portal, has been successfully deployed at more than 300 wastewater treatment plants in the U.S.

Key to its operation is a flow-based configuration where individual DO probes calculate the air flow required for each basin. The accumulated data determines the total flow demand for all basins, and the necessary adjustment in air distribution is communicated to the blower panel. Part of this “DO-to-Flow” concept is the use of “true” Most-Open-Valve logic, where at least one valve always remains in the fully open position. This sets a positive domino effect in motion that eases system header pressure, lessens the load on the blowers, and finally reduces the amount of energy needed to move the required volume of air.

BSA applied to the New York State Energy Research and Development Authority (NYSERDA) for partial funding to defray the estimated $800,000 project cost. BSA documented an expected annual savings of 3.8 million kWh equaling $345,000. This would be accomplished by lowering average DO levels from 3.1 milligrams per liter (mg/L) to 1.5 mg/L. NYSERDA was willing to pay for up to 50 percent of the project, and conducted a measurement and verification review to test those assumptions.

 

Control System Reduces DO Levels and Limit Fluctuations

Roots IntelliView controls significantly improved the stability of the plant’s aeration process, and because the system also handles fluctuations in loading, the plant has been able to operate some of its aeration basins at a DO set point well below the norm – 0.75 mg/L in the first pass of each basin – and keep DO levels within a very narrow range. This has provided additional energy savings. “The system offers a logical approach that makes decisions like a plant operator would when controlling DO levels in the activated sludge basin,” says James Keller, former BSA treatment plant superintendent at Bird Island.

NYSERDA’s completed review showed that annual energy savings would be even greater than expected because of the aeration control system’s success in holding DO levels down and limiting their fluctuations. The findings led NYSERDA to furnish half the total project cost. That generous incentive payment gave BSA a very quick full return on its investment.

Howden Roots Single-Stage OIB Centrifugal Compressor

Howden Roots Single-Stage OIB Centrifugal Compressor

Lessons Applied

Having a reliable DO Control system allows plant operators the flexibility and comfort to make process modifications without having to worry about the control systems ability to handle system upsets (ie. Dump loading, Rain events, etc.). Howden Roots has since applied our DO Control Systems to many advanced Biological Nutrient Removal systems. Having reliable DO Control allows operators to “dial-in” DO targets in control zones for optimum Nitrification and De-Nitrification operations in the system. Designed around current plant capacity and configuration, we can design a control system that will make sense from both a process and an economical basis.

 

About Howden Roots

Howden Roots Intelliview Controls for DO Control Systems have been supplied to numerous facilities worldwide regardless of the equipment manufacturer. Howden Roots Intelliview controls are fast becoming the Industry standard for superior process control coupled with industry leading results in energy efficiency.

 

For more information contact Tim Hilgart, Howden Roots, tel: 414-702-7425, email: Timothy.Hilgart@howden.com, www.howdenroots.com.

To read similar Aeration Blower System Assessment articles visit http://www.blowervacuumbestpractices.com/system-assessments/blower-systems.