Processing wastewater is a hefty task for municipalities, and it requires an equally substantial share of the electric grid. The approximately 17,000 municipal wastewater treatment plants— paired with municipal drinking water treatment systems—make up about 3 percent of total US energy consumption. The combination of numerous motor-driven mechanical systems with high horsepower requirements can, at first blush, make finding tangible energy savings daunting. To help get you started, we’ve listed a breakdown of five of the most effective energy-saving strategies for wastewater treatment plants.
1. Implement an energy monitoring system. Energy monitoring is a simple and cost-effective way to reduce energy consumption. Wastewater treatment plants can install low-cost wireless submeters to help facilities gather additional consumption data. This information can be analyzed with one of the many available energy information software products to provide a thorough picture of energy use and help staff optimize facility performance. The Northwest Energy Efficiency Alliance reported that industrial facilities, including wastewater treatment plants, have the potential to save between 5 and 20 percent of their total energy consumption by installing energy management and information systems and training their operators to interpret the data. As an example, a wastewater plant in Greeley, Colorado, implemented a new energy monitoring system in 2014; it displays the energy-saving results online so the public can to see how efficiently the facility is operating.
2. Commission your facility. Commissioning is a process of ensuring that systems are designed, installed, functionally tested, and capable of being operated and maintained according to the owner’s operational needs. For a wastewater treatment plant, the multitudes of motors and pumps are dynamic and tend to fall out of calibration over time. To maintain their optimal performance, facilities should be recommissioned every three to five years. Existing facilities that have never been commissioned should be retrocommissioned to upgrade their energy systems’ performance to peak levels. To maintain optimal performance over time, ongoing commissioning uses permanently installed monitoring equipment to provide continuous diagnostics to identify system problems before they degrade performance.
3. Upgrade your aeration system. Substantial energy savings can be found by installing alternative aeration system technologies, which may account for more than 50 percent of a facility’s total electrical consumption. Turbo-blowers are a high-efficiency and low-cost upgrade for existing wastewater treatment plant installations. While the most common types of blowers in wastewater treatment plants—such as positive displacement or multistage centrifugal blowers (inlet throttled or variable speed)—can only offer nominal efficiencies of up to 65 percent and 70 percent, respectively, newer turbo-blowers (single-stage and high-speed) can offer efficiencies of up to 82 percent while still providing a competitive level of turndown capability. Since their introduction to the market in 2007, turbo-blowers have become a popular choice among wastewater treatment plants, and they’re offered by several US manufacturers. Greeley’s wastewater treatment facility installed six 300-horsepower turbo-blowers in 2011 that reduced total electrical consumption by about 15 percent. This upgrade translated into cost savings of about $100,000 per year. The simple payback period for the new configuration was about 6.6 years after utility rebates.
4. Install variable-frequency drives (VFDs). As the second-largest energy sink at wastewater treatment plants, pumps are high-potential candidates for energy-saving measures. Energy audits can identify pumps that consistently operate at part load, making VFD retrofits an excellent solution. Be sure to check with your local utility or wastewater treatment consultants; they often offer free or subsidized energy audits to wastewater treatment plants. VFDs allow induction-motor-driven loads such as pumps to operate in a wide speed range from 10 to 300 percent of the nameplate speed. Speed control increases energy efficiency by more precisely matching motor speed with real-time load requirements, and it can produce energy savings of more than 50 percent. VFDs can also contribute to energy savings by improving power factor and process precision, as well as eliminating the need for throttling mechanisms such as control valves and outlet dampers. Many utilities offer incentives for VFD installation projects, resulting in simple payback periods as low as 3.0 years.
5. Switch to LEDs. Upgrading outdoor lighting fixtures to LEDs can be a quick and effective way of reducing unnecessary energy consumption. LED bulbs are especially suited for cooler outdoor temperatures where they can interact easily with lighting controls. Additional advantages provided by LEDs are more-uniform lighting distribution and less light pollution. Cases of LED upgrades in many applications have consistently produced successful energy savings, making the bulbs an excellent option for wastewater treatment settings. The Greeley facility comprehensively upgraded the city’s lighting infrastructure by replacing outdoor metal halides and high-pressure sodium lights with LEDs. The final result was a 70 percent reduction in lighting energy costs and a payback period of 5.7 years.