The search for energy savings and more sustainable operations never ends at the LOTT Clean Water Alliance.

The wastewater management utility formed by the cities of Lacey, Olympia and Tumwater and Thurston County, Washington, has already done a great deal. Accomplishments include:

-Constructing a LEED Platinum certified administration building that has a green roof and uses reclaimed water for toilet flushing

-Operating a combined heat and power system with a Jenbacher (GE) engine at the Budd Inlet Treatment Plant for more than a decade, supplying heat to the digesters, the administration building and a children’s museum, while also supplying electricity to the administration building.

-Producing Class A reclaimed water at two treatment plants for irrigation, cleaning, process water and aquifer recharge

-Producing Class B biosolids used in agriculture

-Replacing an old blower with a more efficient turbine blower for aeration and installing new diffusers in the aeration basins

-Converting to LED lighting and installing motion-detector switches. 

Constant search

In short, the utility has checked many boxes for energy efficiency and sustainability, along the way reaping substantial savings. Mark Petrie, environmental compliance supervisor, estimates that replacing a 500 hp centrifugal blower with a Neuros high-speed turbine blower with a variable-speed drive has saved $48,000 a year. The combined heat and power system saves about $99,000 a year. An energy committee makes sure efforts like these continue.

“LOTT has always been on the forefront to ensure that we use our resources appropriately,” Petrie says. “We keep on looking, walking through the plant seeking new ways to improve energy efficiency.”

The Budd Inlet plant (28 mgd design, 11 mgd average summer, 15 mgd winter), discharges UV-disinfected water to Puget Sound; about 10% of the flow goes through sand filtration or a membrane bioreactor and then chlorination to create the Class A reclaimed water.

Ammonia-based control

One new way of saving power is to use probes that measure ammonia, instead of dissolved oxygen, to control aeration. “Most places use DO as the control to set appropriate levels of aeration in different zones of the process,” says Petrie.

“We started using nutrient probes, measuring ammonia and the reduction of ammonia. We saw about 25% power savings in our blowers. We’ll be adding more probes — pH probes, DO probes, ammonia-nitrate probes — throughout the process so we can measure and be prudent about reducing our total inorganic nitrogen and at the same time save energy.”

The ammonia probes have been more reliable than DO probes. Petrie credits Terri Prather, assistant operations and facilities director, and Paul Jue, process control supervisor, for figuring out how to best use the probes.

“They help the operators understand the biological nutrient removal process,” says Petrie. “They added more probes into the process so that operators can see live data coming in and adjust a blower or air control as necessary, or add methanol when needed. The more probes we install, the more data we provide to the operators and the process control supervisor to help them forecast and model the flows for future process control.”

Adjustments required

The nutrient probes require some operator attention. “They can be very finicky,” Petrie says. “They require some TLC to keep them calibrated and adjusted appropriately, but with our tight permit requirements, they help us meet or outperform the parameters of our permit. There are definitely some costs to keep them operating correctly, but in the long run, it helps keep us in compliance.”

Operators, not the probes connected to the SCADA system, are still in charge of managing the treatment process: “We rely on the probes to give us good information and to instruct the blower to ramp up or ramp back, but at times the operators have to put their hats on. They still have to intervene and adjust as necessary.”

Although LOTT has partnered with power companies and consultants for many of its projects, the agency also relies on team members for energy-saving ideas for the treatment plants and administration building; they’re encouraged to submit ideas to the energy committee. In one case, workers suggested replacing some old windows with double-paned windows. 

Upgrade in progress

The Budd Inlet plant is in the middle of an upgrade that will include a variety of energy savers. Two more APG-Neuros turbine blowers have been ordered, and Sanitaire Silver Series II fine-bubble diffusers (Sanitaire, a Xylem brand) and a compressed-gas solids mixing system (EnviroMix) will be installed.

LOTT stresses reducing peak electrical loads, and that makes variable-frequency drives especially important. “When we have to fire up multiple pieces of heavy equipment, sometimes we’ll reach a peak demand that can cost up to $22,000 a month,” Petrie says. “Our operations team tries to coordinate and sequence powering up when they can. The Neuros blowers being on VFDs make great buffers. They ramp up slowly, so it’s a lot more cost-effective.”

The utility is also looking to boost its power generation capacity by adding solar panels. There is some rooftop real estate that might be used for that purpose: “We make use of all our resources as best we can and try not to waste them.”