Most of us stop thinking about what goes down the drain once we pull the plug.
But a group of public employees is working to make sure that wastewater is cleaned at a lower cost using less energy.
The Wastewater Treatment Facility serves St. Cloud, Sartell, Sauk Rapids, St. Augusta, St. Joseph and Waite Park. Last year, it treated an average of 9.5 million gallons of wastewater a day. The facility is owned and operated by the city of St. Cloud.
The facility is undergoing a process to look at how to better use energy in the treatment system, which will save money and be better for the environment. Keeping costs down has an effect on residents' wastewater utility rates.
The city spends about $775,000 a year on electricity, motor fuels, natural gas and fuel oil for the Wastewater Treatment Facility. By putting several energy-saving techniques in place, the city could cut those costs by 75 percent in 20 years.
Public Utilities Assistant Director Tracy Hodel said it's important to look at the entire facility, because making changes on one point of the treatment process can affect the entire process.
"All these things tie in together, so we have to make sure we look at the big picture," she said.
Once complete, the master plan will become the guiding document that will help the city make decisions on what process or equipment changes to make.
More cities across the country are looking at making their wastewater facilities more efficient. Last year, the U.S. Environmental Protection Agency put out a guide to help them do that.
Such facilities have pumps, motors and other equipment running 24 hours a day and are some of the largest consumers of energy in a community, according to the EPA. Wastewater and water facilities account for 3-4 percent of total energy use in the country.
The city is contracting with Donohue & Associates for $138,000 to come up with the master plan. The company has worked with other cities to make their facilities energy self-sufficient. Those include Sheboygan and Stevens Point in Wisconsin.
Those cities regularly produce enough energy to operate their facilities for significant time periods throughout the year, according to Donohue & Associates.
One of St. Cloud's big projects is to look at the biosolids program. Biosolids are removed from wastewater and used as fertilizer. There is high demand for the product, but the city has limited storage capacity.
Included in St. Cloud's Capital Improvement Program is a $10 million project to expand the biosolids program.
But doing that has the potential to affect other areas of the treatment process.
The facility is also participating in a pilot program where nutrients taken out during the treatment process will be used to make mineral fertilizer.
The city is also looking to produce more and better use methane gas. The facility produces the gas and uses it during the winter to generate heat. In the summer, it's used to dehumidify incoming air, but most of it is burned off.
Staff would like to make improvements to better capture methane gas and accept high-strength waste from outside businesses to make more methane gas. Then the gas could be used to produce electricity. It also could be used to create compressed natural gas, which is used to fuel vehicles like the new Metro Bus fleet.
The city will also look at what sort of equipment changes can be made to better operate the facility. There are a number of ways those changes can be paid for, including grants and tax credits. There is also the possibility of cost sharing.
One such project is already underway. In September, a 20-watt solar array will be placed at the facility as part of the Minnesota Solar Incentive Program.
The city does not pay anything up front but is obligated to buy power it creates.
A third party will install and operate the array.
Other changes can be made in-house. Blowers are used to supply the oxygen to the biological treatment process to help bacteria remove pollutants.
Staff is looking at ways to better operate the blowers so less energy is used. Right now the blowers work too hard and sometimes put out more oxygen than is needed.
The city can modify the equipment to control the oxygen flow.
Purchasing the equipment to allow the modification can be paid in part with rebates, and the rest will be paid off in less than a year with the energy savings.
It's one part of a larger whole to make the facility more energy efficient and to save dollars, which will help keep wastewater rates down.
"All of it is possible," Hodel said.
Follow Kari Petrie on Twitter @karipetrie.