Six municipal wastewater treatment plants in New York State were examined to determine whether using process audit and electrical submetering techniques would be an effective way to identify energy conservation opportunities.
By Linda Ferguson, P.Eng., CH2M Gore & Storrie Limited
Municipalities are responsible for running their wastewater treatment facilities efficiently for the benefit of their residents, businesses, and industries. The challenge is to identify available energy conservation opportunities (ECOs) within the plants and take the necessary steps to seize those opportunities. CG&S has developed an innovative program to meet this challenge.
CG&S examined six municipal wastewater treatment plants in New York State to determine whether using process audit and electrical submetering techniques would be an effective way to identify energy conservation opportunities. It is a simple approach measure what you have, what you are using, and the performance achieved, and then make decisions on improving performance efficiency based on the results.
A combination of techniques
The three-year study was sponsored by the New York State Energy Research and Development Authority (NYSERDA), the Empire State Electric Research Corporation, and the Electric Power Research Institute. A combination of techniques some developed by CG&S specialists in plant analysis technologies was used to obtain real-time process and electrical consumption data. The ultimate goal was to find ways to optimize treatment efficiency and reduce operating costs. Recommendations ranged from minor operational changes and housekeeping activities to major capital upgrades. The results indicate that the audit approach is an appropriate tool for identifying ECOs at existing facilities.
Recommendations
Several maintenance and housekeeping items were identified at the six plants. Common problems included pumps with inoperable or worn backflow prevention valves, inappropriate valve or gate settings, and worn pumps. Operating procedure changes were recommended at some plants, including changes to pump control strategies and solids-handling procedures.
Excess capacity in one or more unit processes was found to contribute to increased energy consumption at some sites. Excess blower capacity resulted from upgrades from coarse- to fine-bubble aeration, excess aeration basin volume, and excess solids stabilization capacity. Recommendations included removing basins from service and downsizing equipment.
Lessons learned
The plants included within this study were operating well within their effluent discharge requirements and providing good to excellent treatment levels. The project combined process audit, energy audit, and electrical submetering techniques to identify low-capital-cost ways to improve plant performance and energy efficiency.
This approach has several advantages:
The audit approach, a systematic and rigorous methodology for obtaining accurate performance information, is an appropriate tool for identifying ECOs at existing wastewater treatment facilities. Online process data, equipment performance characteristics, and electrical submetering information are required to predict the benefits of implementing energy conservation measures on plant performance.