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Energy efficiency opportunities for wastewater treatment plants
Wastewater treatment facilities are critical to the health of communities and the environment. As a result, operators give more of their attention to effluent quality and meeting standards, sometimes at the expense of energy efficiency.
The wastewater and water treatment sectors account for as much as 3% of electricity use in the U.S. Nationwide wastewater and drinking water treatment plants spend $4 billion a year on energy to pump, treat, deliver, collect, and clean water.
A variety of energy efficient equipment, technologies, and operating practices are available to achieve energy conservation and reduce energy costs.
Energy Usage and Costs
A number of tools exist to assess energy use and reduction in wastewater treatment operations.
- Evaluate tools used for tracking energy use and costs.
- Compare your facility’s energy usage by participating in the Energy Star wastewater treatment plant benchmarking program.
- Determine how electrical loads can be managed more efficiently during off peak hours, for example shutting equipment off.
- Evaluate how improved or additional process controls can contribute to greater efficiency.
Aeration Systems
Plants with aeration systems will find this may be the largest source of energy use in the plant.
- Check your aeration system to determine if it is properly sized so that it isn’t a source of wasted energy and is meeting the oxygen demand.
- Consider replacing a coarse bubble diffuser with a fine bubble diffuser. Increasing oxygen transfer efficiency may result in reduced energy costs.
- Shut aeration basins off when not needed.
- Is dissolved oxygen measured in at least three out of five sections of the aeration basin and used to control blower operation?
- Sequence blowers to maximize efficiency of the air generated.
Anaerobic Digesters
Anaerobic digestion systems can be optimized for the microbial population and can offer benefits in gas production and use.
- Is there an opportunity for you to recover the biogas from the digester and put it to beneficial use?
- Each microorganism has an optimum temperature range in which they are most active. Check anaerobic digesters to see if they are operating at optimum temperature for the microbial population.
Motors
Replacing standard efficiency motors with energy efficient models will likely save money. The U.S. Department of Energy Efficiency and Renewable Energy has developed a free interactive program, Improve Motor System Efficiency with Mastermotors+, to assist you with calculating pay back for one or many motors.
- Conduct a motor inventory to understand numbers, types, and applications.
- Evaluate your motor maintenance program. Establish criteria for replacement and rewinding motors.
- Develop an emergency, premium efficiency motor replacement plan and purchasing protocol. (2010 – NEMA premium)
- Develop a preventative maintenance program.
Variable Frequency Drives
Variable frequency drives (VFDs) on motors can enhance process operations, especially for flow control, and can efficiently cut energy demand for pumps and fans.
- Determine how variable speed drives can save you money and improve your process control by reducing or shifting your electrical load.
- When evaluating VFDs research the difference between electronic and mechanical devices.
- Variable flows that cannot be handled well using on/off pump or fan control are good candidates for variable speed drives. Determine which processes in your facility would be candidates for variable speed drives.
Pumps
Pumping wastewater can account for a large source of energy usage. Your facility may be able to identify areas where pump efficiency could be improved. For additional information visit the U.S. Department of Energy Pumping Tip Sheets
- Determine if pumps are properly sized for their application and loading.
- How can your pump system be modified to run efficiently to meet both peak conditions and flow variations?
- How can pump controls be modified for systems with multiple pumps in parallel?
Lighting
Lighting upgrades are often overlooked, and while not a quick payback, utility rebates are readily available.
- Have you used a light meter to verify light levels?
- How can you improve the efficiency of your indoor and outdoor lighting?
- Do you turn off lighting during process shutdown?
- Are occupancy sensors used?
Additional Resources
Focus on Energy has developed a best management practice sheet for wastewater treatment systems. Best Practices: Wastewater Treatment Facilities.
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