The Focus on Energy Water and Wastewater Program was developed to support the industry because of the enormous potential to reduce energy use without compromising water quality standards. Through the program, numerous water and wastewater personnel have learned that energy use can be managed, with no adverse effects on water quality. Most locations that have saved energy have found improved control and treatment.
All water and wastewater treatment facilities can save energy. The improvements are often economically attractive – water and wastewater facilities typically see shorter paybacks on energy efficiency projects than their industrial counterparts due to their longer hours of operation. Also, these facilities are necessary public infrastructure and, therefore, have stable financial commitment for long-term viability. In addition, they will not (cannot) close or move to another community or country as can happen in private industry.
Energy Use in Wastewater Treatment and Collection Systems
Wisconsin has approximately 650 public and 360 private wastewater treatment facilities. A summary of the public facilities’ sizes is presented in Table 1 below.
Note that Wisconsin has many small facilities – approximately 85% of facilities treat less than one million gallons per day (MGD). Though they treat only 12% of the total flow, these numerous small facilities use about 24% of the total energy used to treat wastewater in the state, making them excellent candidates for energy efficiency projects.
The remaining facilities, over one MGD, process 88% of the wastewater. Because of their sheer size, even simple energy efficiency projects at these facilities can lead to tremendous savings.
On average, wastewater treatment facilities spend seven percent of their operating budgets on energy, according to the American Water Works Association Research Foundation (AwwaRF).1 Regardless of size, the breakdown of energy end-uses at a wastewater facility remains consistent. All facilities have at least secondary treatment. Figure 1 on the following page shows how energy is consumed at an activated sludge wastewater treatment facility, which represents the majority of Wisconsin wastewater systems.
1 Manager’s Guide for Best Practices for Energy Management, AwwaRF, 2003
The major energy user is the secondary treatment process, partially because this treatment component in this type of facility must operate continuously. Secondary treatment systems are often a good place to start to improve system energy efficiency since even small percentage efficiency improvements will result in significant savings.
Steps to Begin
Step 1) Establish a Baseline Energy Use
Compile your last 12 to 24 monthly utility bills to develop an overall energy profile of your facility and put energy in the context of overall organizational operations by comparing it to more widely tracked measures such as flow (MGD), BOD or labor costs (see example in Table 2). Next, develop your facility’s Energy Profile Summary, showing changes in consumption and Key Performance Indicators (KPI) such as MWh/MG, by year (Table 3). Then graph KPI for each month. This will set your present baseline for your energy use. Tracking this energy consumption over time provides an indication of the effectiveness of your energy efficiency efforts. Projecting usage forward provides a method to set targets and goals for energy use. It can be useful to plot the energy use per month verses MG per month to show how the energy use changes with flow changes. The y-intercept of the line fit to the data indicates the constant energy use of the facility with no flow. The slope of the line fit indicates variable energy use as flow changes. Both the constant energy use and variable energy use can be impacted by efficiency measures.
Step 2) Estimate Energy Use for Major Systems
Determine the energy used by major equipment and energy-using systems. This will point the way to your largest energy uses and the best places to focus your attention (similar to Figure 1 above). Spreadsheets available on the CD under “Energy Use Profile” can also be used to estimate equipment energy use.
Step 3) Identify Best Practice Opportunities
Best practices are techniques or technologies generally recognized as being economical and more energy-efficient than common or typical practices. Review best practices in comparison to your existing equipment and system to identify opportunities for energy efficiency improvement. Recommended best practices for water treatment systems and wastewater treatment systems are provided in this booklet. These practices apply to system retrofits as well as to new system designs. A checklist of best practices is provided in each best practice section for your use to copy and “check off” each “best practice” thatis deemed as considered, determined feasible or implemented. Appendix D includes a list of additional best practices for ancillary end uses, such as lighting and compressed air systems.
Step 4) Quantify Savings and Project Costs of Best Practice Opportunities
Once the best practice opportunities are determined, the next step is to estimate the cost savings associated with each project including energy and maintenance, and the installed cost of the modification. Focus on Energy can provide technical assistance to estimate projected energy savings for projects. Estimating tools for some standard best practices are available on the CD under “Best Practices”.
Step 5) Prioritize Projects
Apply criteria such as ROI, energy savings, associated process improvements or ease of installation to help you prioritize among all the possible energy saving opportunities identified. Select the projects that achieve the energy savings goals within time and budget constraints. The CD contains a spreadsheet to help prioritize projects under “Project Prioritization”.
Step 6) Project Management
Manage each identified energy project as you would any other project within your organization by clearly defining the project parameters, assigning responsibilities for the project implementation and undertaking specific tasks needed to implement the project.
The Focus on Energy Program has been able to identify tremendous energy saving potential and help facilities receive grants for project implementation. Focus on Energy currently has approximately 150 water and wastewater partners representing a variety of facility sizes – from 30,000 gallons per day to 32 million gallons per day.
Energy savings generally range from 20% to 40%. However, some facilities have been more aggressive and have cut nearly 75% from their pre-program participation energy use. General findings from facility surveys completed by Focus on Energy include:
- All facilities have energy saving opportunities regardless of size
- Savings generally ranged from 20% to 40%, even reaching 75%
- Aeration systems provided opportunities for the greatest savings
- Simple modifications to equipment and/or operation can result in significant demand savings
- Proactive operations can achieve additional savings
- Beneficial use of biogas is available
- When facility operators become aware of energy, energy management follows
- Continuing education and training in energy management are necessary and useful
A few of the common energy saving measures have included:
- System Assessment
- Automatic Controls
- Operation Changes
Source: “Water and Wastewater Energy Best Practice Guidebook”, Focus on Energy™, Prepared by: Science Applications International Corporation (SAIC), December 2006. Focus on Energy is a public-private partnership offering energy information and services to energy utility customers throughout Wisconsin. www.werf.org, www.focusonenergy.com.