The U.S. EPA estimates 30 to 40 percent of a municipality’s energy consumption is for treating water and wastewater. That’s a total of $4 billion annually nationwide. The U.S. Department of Energy (DOE), meanwhile, states that electricity represents about 75 percent of the cost of municipal water processing and distribution.
How does a utility manage energy usage to reduce consumption at the water treatment plant without sacrificing water quality or adding time-consuming steps for staff? The first step is benchmarking — establishing total consumption and comparing it to similar facilities.
Second is an energy audit. This is a study that quantifies the energy consumption of your individual systems, identifies the energy conservation measures (ECMs) you could take to reduce consumption, and estimates the cost to implement the ECMs. The final step is the one least followed through: implementation.
Benchmarking
Benchmarking lets you compare your treatment plant to others and monitor your progress on energy savings year to year. ENERGY STAR Portfolio Manager, a voluntary program created by the EPA, provides guidance and a free online benchmarking tool to help you track energy use and costs. There’s even an ENERGY STAR program specific for drinking water systems that will help you to compare your plant with your peers.
The more detailed your information, the more productive your benchmarking will be. While you can often complete benchmarking for little or no cost, the addition of submetering can increase accuracy.
Energy audit
The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) provides a standardized procedure for energy audits that includes guidelines for different levels of audits. These levels range from a walk-through audit to a detailed survey and analysis audit.
The higher-level, detailed audits provide an in-depth analysis, creating recommendations with a more refined cost/benefit analysis. Recommended ECMs can generally be categorized as retrofits or behavior changes. Retrofits such as high-efficiency lighting and variable-frequency drives can have fast payback. Others require longer-term investments and can be included in your plant’s capital improvement plans.
Behavior changes can include specific actions within the plant, such as implementing an energy management plan or shutting down computers at night. They can also be policy-related: requiring equipment for a life cycle cost rather than first cost when it is being replaced, and negotiating a rate structure with the local utility that includes voluntary peak load shedding.
Implementation
Knowing how much energy your plant uses and how to reduce consumption only gets you so far. To save energy and money, you need to implement the changes. Every excuse has been used: Budget approval is a hassle, hiring contractors is time-consuming, the savings won’t come back to your department, it’s too hard to change people’s behaviors. But efforts to change and investments in more efficient equipment are the only route to savings.
For example, Johnson County (Kan.) Wastewater (JCW) implemented a cogeneration system at its Douglas L. Smith Middle Basin Wastewater Treatment Plant in 2011. “This system converts methane gas produced by the anaerobic digesters to electricity to be used by the treatment plant,” says Susan Pekarek, chief engineer for JCW. “This has resulted in an annual savings of about $250,000 by producing power to be used on site.”
Follow a process
While no two energy efficiency projects are the same, there is a basic process common to many successful projects. To help see your energy audit through to implementation, the DOE offers a guide under its Industrial Technologies Program (ITP): Guiding Principles for Successfully Implementing Industrial Energy Assessment Recommendations. While targeted to industrial manufacturers, the process and advice are essentially the same for water treatment plants.
After implementation, it is important to monitor your results: Energy efficiency is an ongoing process. Plants should track and compare the energy consumption to look for anomalies and additional opportunities to save energy. The best single number to watch is kilowatt-hours (kWh) per million gallons treated.
Reducing energy consumption is the best first step and can be followed by a plan to reduce greenhouse gas emissions. The process is the same: benchmark, audit, implement and monitor. Reductions can be accomplished through additional retrofits, changes in behavior and on-site renewable energy generation.
ABOUT THE AUTHOR
Jennifer Gunby is a project manager with GBA Architects Engineers Energy Group, headquartered in Lenexa, Kan., and with offices in Missouri, Nebraska, Colorado and Illinois. She can be reached at 913-577-8375 or jgunby@gbateam.com.
