Energy accounts for 28 percent of wastewater operations and maintenance budgets — the second largest expense for a treatment facility after labor.

That means cutting energy costs can have a dramatic effect on a municipality with a limited budget. The U.S. EPA estimates that a 10 percent reduction in energy usage could save the nation’s water and wastewater treatment plants some $400 million a year. Wasted energy directly affects plant operation and maintenance costs and contributes to greenhouse gas (GHG) emissions and concerns over global climate change.

In the near future, wastewater treatment plants will be able to qualify themselves under the ENERGY STAR program, jointly sponsored by the U.S. EPA and the U.S. Department of Energy. Already, treatment plants can track energy usage and compare themselves against plants of similar size by using an online Portfolio Manager tool.

The Portfolio Manager is a timely tool that plant managers and operators can use to help monitor and control energy usage and drive down operating costs. A more comprehensive approach to energy savings is to create and implement an energy action plan.

Routes to savings

Saving energy is both more complex and potentially more rewarding than many plant managers imagine. The biggest savings opportunities are in aeration and pumping. This includes aeration for the activated sludge process and aerobic solids digestion, pumping of return and waste activated sludge, and operation of lift and influent pump stations.

In a 2006 EPRI Journal article, “Turning on Energy Efficiency,” B. Barker and L. Sanna identify three basic kinds (or waves) of energy savings:

Energy efficiency. This involves improvement in equipment efficiencies, such as installation of NEMA Premium or EPAct high-efficiency motors and variable-frequency drives, more efficient solids dewatering systems, high-efficiency lighting fixtures, lighting controls, and modern HVAC equipment and controls. These measures typically can achieve five to 10 percent energy savings.

Demand response. This involves adjusting operations to take the best advantage of utility rate structures. It includes measures such as shedding load during higher-priced on-peak periods and shifting load to lower-priced off-peak periods. Specific measures may include control of lighting and HVAC systems with demand-response systems, use of the facility’s most efficient pumps and blowers during on-peak hours, and use of equalization basins to enable shifting of some treatment load to off-peak times. These measures can reduce energy usage by 10 to 20 percent.

Dynamic systems. This holistic approach to energy management — which can achieve energy savings of 20 percent or more — combines energy efficiency measures with demand response using intelligent and automatic monitoring and control systems. Dynamic systems integrate a communication network with smart end-use devices and innovative rate structures, systems and processes to conserve energy.

This approach can include process optimization using multi-variable control systems with predictive and dynamic modeling capability. For example, such a system might automate control of the activated sludge process based on measurement of dissolved oxygen and other variables, enabling staff to optimize blower efficiency while maintaining tight control of effluent quality.

Another potential source of major savings is the use of digester methane for heating, power generation, cogeneration, or peak shaving. Although these approaches are common and long accepted, many treatment plants still flare off excess methane.

Energy action plan

Energy-saving initiatives are most effective when organized around an energy action plan (EAP). The first step in an EAP is to conduct an energy audit using steps similar to those outlined in the accompanying table. Basic audit steps include:

• Kickoff meeting with plant personnel.

• Evaluation of utility bills and rate schedules.

• Review of requirements for federal, state and local grants and incentives for energy conservation measures.

• Collection of data on historic plant operations and energy consumption.

• Field investigation to inventory plant equipment and determine each device’s energy usage and time-of-day operation.

• Development of energy conservation measures and strategies for implementation.

• Monitoring and follow up.

The finished EAP includes an action plan to deploy the conservation measures, and ways to monitor the plant’s performance and keep staff accountable for progress.

Detailed guidelines for energy audits are available in two publications: The Energy/Audit Manual for Water/Wastewater Facilities, published by the Electric Power Research Institute (1994) and Energy Conservation in Wastewater Treatment Facilities, published by the Water Environment Federation (1997).

Being a Star

The ENERGY STAR program can be used as part of an EAP to develop a baseline with other similar wastewater treatment plants. ENERGY STAR, first conceived for consumer goods like household appliances, is designed to help save money and protect the environment through energy-efficient products and practices.

Today, the program helps measure and recognize energy efficiency in specific market segments. The EPA estimates that with the help of ENERGY STAR, Americans prevented 40 million metric tons of greenhouse gas emissions in 2007 alone, equivalent to the annual emissions from 27 million vehicles and a savings of more than $16 billion in utility bills.

Municipal wastewater facilities were added to the program in October 2007 with introduction of the online Portfolio Manager (visit www.energystar.gov). The tool creates a standardized approach to tracking energy usage. It lets plant personnel use a common platform to input plant-specific energy data, establish a baseline for energy efficiency performance, measure their performance over time, and compare their performance to other treatment facilities.

So far, the program is limited to plants that use some form of the activated sludge process. Plants that use trickling filters or nutrient removal are not included because their processes are too different for meaningful comparison. In using the Portfolio Manager, plant personnel enter:

• Facility ZIP code (to normalize for weather)

• 12 months of energy use data for all fuels, by month

• Annual average daily influent flow

• Annual average influent BOD

• Average effluent BOD (12 months)

• Facility design treatment capacity

Users can enter data directly into an online account, or download a spreadsheet, enter data into it, and e-mail it for upload into the tool.

Besides helping facilities monitor energy consumption and measure performance, the Portfolio Manager calculates the impact of the plant on GHG emissions based on energy usage. The tool provides data that facilities can use to quantify improvements and share success stories with their communities. In the future, the program will include ENERGY STAR ratings for outstanding treatment plants, just as it does now for hospitals, schools, universities, and other facilities.

Getting to work

Almost all wastewater treatment plants can reduce their energy consumption — in many cases substantially. A detailed energy audit and energy action plan are the first steps in any energy efficiency program. Monitoring and automation and control systems have especially high potential to help facilities manage energy effectively. Now is the time for treatment plants to decide how they can make the most of their energy to cut operating costs, better manage resources, and reduce pollution.

About the author

Lee E. Ferrell, P.E., is a water wastewater energy and process consultant with the Water Wastewater Competency Center of Schneider Electric, a manufacturer of power and automation control systems with United States headquarters in Palatine, Ill. He can be reached at Lee.Ferrell@us.schneider-electric.com.