By CEN Showcase Editor

Tough Choices
To get the job done in the wastewater treatment business, you typically have to choose between using more chemicals or more energy. Managers at the City of Boulder had been at that crossroads many times so when faced with a facility upgrade in 2006, they did what they always have: go the most environmentally-friendly route possible, while using the least amount of energy.

“Wastewater treatment typically represents a city’s single largest investment in the environment,” says Randy Earley, Utilities Project Manager for the City of Boulder’s Public Works Department. “It would be counterproductive to use methods that have adverse impacts on the environment. But energy is an uncontrollable cost so we try to make our processes as efficient as possible to save money in the long run.”

The tricky part is that the rules change every five years when they renew their permit. They’re constantly trying to predict what the new standards will be and forecast accordingly.

Time to Upgrade
A maximum of 20 million gallons of raw sewage can flow through the plant every day. Built in 1968, it was originally designed to treat 5 million gallons. The plant had last been upgraded in 1990 so by early 2006 - with new state and Environmental Protection Agency requirements needing to be met by January of 2008 - it was time for the City of Boulder to consider improvements.

Two things made the priority list:

♦ To increase ammonia removal.  A reduction in the discharge of ammonia would improve the environment for plants and animals in Boulder Creek downstream from the plant. This expansion would include new aeration requirements which meant buying new blowers and motors to provide oxygen, and secondarily some mixing, to the treatment process.

♦ To increase the treatment capacity from 20.5 million gallons a day to 25 million gallons a day to help address future treatment needs.

A consultant conducted an extensive evaluation of motor and blower alternatives and estimated the costs over a 20 year span. The study revealed two things: several options were comparable, but the most efficient blowers would cost $53,000 more than the others up front. The consolation was that over the 20-year timeframe, the city would recoup the amount in lower energy use and lower annual operating costs. In addition, a $20,000 rebate from their electricity provider, Xcel Energy, was also helpful.

“They had already decided to upgrade to higher efficiency equipment to save energy and money,” says Tom Minerick, Xcel Energy account manager. “But of course they liked to hear they’d be eligible for rebate dollars to help keep initial costs down.”

Boulder’s annual energy bill at the plant is $500,000. But knowing the city could save $100,000 in energy costs over 20 years while doing the right thing environmentally was the determining factor. They moved forward with the project and finished it in April of 2008.

Project Summary Totals
→ Net Cost for Blowers: $1,425,999
→ Xcel Energy rebates $20,000 (2% of 20-year energy cost)
→ Total project cost:  $1,405,000
→ Annual energy bills  $500,000 
→ Return on Investment: 1% improved efficiency over 20 year span
→ Outcome   $100,000 in energy savings over 20 years

Clean and Efficient
The wastewater treatment plant staff is happy with the equipment choices they made, the amount of energy they’ll save over time and the fact that they made the best environmental choice possible. Earley says the treatment is safe, thorough and there’s room to add capacity if needed.

For more about the City of Boulder’s Waste Water Treatment plant upgrades, visit www.bouldercolorado.gov. For more on Xcel Energy’s efficiency programs, visit www.xcelenergy.com.