By Chris Hendrickson, Monitor
City council passed a motion last week which authorized the mayor to sign an interagency agreement between the city of Monroe and the Washington State Department of Enterprise Services. The agreement authorizes the DES to provide project management services to the city while exploring several energy efficiency improvement opportunities at the wastewater treatment facility.
In order to move forward and study the proposed energy efficiency improvement measures, an investment-grade audit must be completed by an established energy services company in order to better determine project feasibility and projected operating savings. TRANE is the energy services company that has been assigned the task of examining Monroe’s proposed energy efficiency improvements, and will be performing the audit.
The audit will examine the potential upgrades to the wastewater treatment facility’s energy infrastructure, ensuring that they meet a set of criteria specified by the city, including that of achieving a positive cash flow within 10 years of implementation.
Investment-grade audits are routinely utilized on proposed energy infrastructure projects for the purposes of determining the profitability of the project and whether or not a specific return on investment is achievable within a selected period of time. These audits are much more in-depth than general audits, and usually necessitate a comprehensive engineering study to be completed.
Focused on the plant’s secondary treatment processes, the five energy conservation measures to be examined in the audit are:
1. Aeration System Blower and Diffuser Upgrade
The current 75 horsepower centrifugal blowers that supply the necessary oxygen to the aeration basins are working in an inefficient manner. Replacing these with turbo blowers would substantially reduce energy costs. Upgrading the aeration diffusers, which were installed in 2002, could help to further reduce energy costs, along with supporting a potentially more stable pH level. As the wastewater is treated during these biological processes, the pH level often becomes too low, and the facility uses costly magnesium hydroxide to restore the pH to acceptable levels. These proposed upgrades could lead to a decrease in the amount of magnesium hydroxide used for this purpose.
2. Aerobic Digester System
This improvement involves the mechanical mixers and diffusers currently in place in the aeration rooms. The proposal is to replace the diffusers with new technology referred to as Tideflex diffusers. Tideflex diffusers were developed to overcome the constraints of the traditional bubble diffusers.
3. Aeration Basin Odor Control Fans
TRANE will investigate to determine if installing variable frequency drives would lead to an improvement in system efficiency. Variable frequency drives would essentially adjust the speed of the fans’ motors to match output requirements.
4. Sludge Drum Thickener
Installing this technology could improve process efficiency.
5. Odor Control Improvements
TRANE will study the possible utilization of a biological filter to save on energy costs of treating odor sources.
These five energy conservation measures were identified as viable possibilities in meeting the 10-year positive cash flow requirement.
The investment grade audit, which will also provide 30 percent design documents to the city, requires a financial commitment of $117,795 plus tax, which is available in the city’s capital fund for sanitary and sewer improvements. If the study determines that the improvements do not meet the city’s criteria in regards to investment return, there is no financial responsibility to the city.
If the audit reflects that these five measures meet the criteria and the city elects to move forward and support the implementation of the improvements, the $117,795 will end up rolled into the final costs of the project. If the city were to decide not to proceed, the $117,795 would then become payable to the DES.
Once the investment grade audit is completed, the city can move forward with the process of applying for grants to assist with the expense of the project.
City Council was given a tour of the wastewater treatment plant before the council meeting on Sept. 10 in anticipation of this presentation.
“The tour last week was wonderful. I was so moved by just the professionalism and dedication,” said Councilmember Patsy Cudaback. “Clearly our great staff represents the city well.”
The wastewater treatment plant is located at 522 S. Sams St. in Monroe. The average flow of wastewater into the treatment plant is 1.6 million gallons per day.