The Edmonds Wastewater Treatment Plant has taken big steps toward sustainability.

Those steps were outlined several years ago in a document called the Pathway to Sustainability, prepared with the Washington Department of Enterprise Services and Ameresco, an energy services company.

As Edmonds prepares to take its next big step down the path — conversion from incinerating solids to a gasification process — the outline is proving its value. In 2020 Edmonds, a short drive from Seattle, was honored as a Utility of the Future Today in the category of energy efficiency by the Water Environment Federation.

“Basically, we followed a planned sequential order of process equipment upgrades designed to move us closer to having the ability to replace the incinerator with a gasification process” says Pamela Randolph, wastewater treatment plant manager. “Had we not upgraded our solids equipment first, we would not have been in a position to install a gasification system at all, because our older equipment did not have the ability to dewater solids dry enough for a future gasification project.” 

Major upgrades

The Edmonds treatment plant sits in the downtown area; the city (population 43,000) has grown up around it. The location of the activated sludge plant (11.8 mgd design, 4 mgd average in summer, 6.5 mgd in winter) makes limiting truck traffic a priority. The plant does not accept waste from septic haulers. Solids are dewatered and incinerated, and the ash is landfilled; the effluent discharges to Puget Sound. The plant serves about 75,000 people.

Edmonds has completed three big energy-saving projects that were the basis for its Utility of the Future Today award:

-Replacing several blowers with smaller, high-efficiency Aerzen blowers

-Replacing and repairing the entire aeration system piping

-Replacing the diffusers with Sanitaire Gold diffusers (Xylem)

-Replacing the biosolids dewatering equipment with a more energy efficient system that includes two Ishigaki screw presses and Austin Mac conveyors.

Those projects have saved about $200,000 a year, cutting the plant’s electric bills by about 45%. The next big project, solids gasification, is to be completed in late 2021. Along the way there have been numerous smaller projects, including upgrades to the nonpotable water system, valve replacements, lighting changes, and the rebuilding of a fountain. “We are trying to create a culture of energy efficiency,” Randolph says. 

Plenty of support

The wastewater utility has received support from the city government. In 2017, the City Council passed a resolution committing the city to achieve or exceed the goals established in the Paris Climate Accord at the local level.

Randolph says it is important for everyone from top to bottom to keep energy savings in mind all the time: “If we stay diligent, it has a better opportunity for success. You can’t let it be second. It’s hard to keep everybody involved in moving it forward.”

Edmonds plant team members stay engaged with peers from other utilities though a Wastewater Energy Cohort that meets regularly. “It’s a group of people who come together, and share stories and best practices to try to lower the cost of the industry,” Randolph says.

Limited space

Although Edmonds has generally stayed on its path, one step was contemplated but not taken. Conversion to UV disinfection was deemed unsuitable. “It wasn’t viable for a couple of reasons,” Randolph says. “One, it was energy intensive. We were going to try to offset that with less truck traffic and better process control and other things.

“But the real issue was the way the plant was constructed. Our chlorine contact channel was buried underground. To do UV, we would have to retrofit, and it would have been outrageously expensive. We would have had to daylight the chlorine contact channel. We’re in downtown Edmonds; that wasn’t going to happen.”

The relatively small plant site drives some decision-making around energy efficiency and process changes. For example, when the solids-handling process was changed, only two screw presses were installed, because at current flows two are sufficient. Space was left for a third, which the plant would need if the average flows increased significantly.

Similarly, the plant has three aeration basins, but the aeration upgrades were done on only two of them. That’s because the plant can handle its normal flows with just two basins, and the operators believe the third may be needed to add more nutrient removal processes in the future.

“We have no space to expand,” Randolph says. “So, when we retrofit a process, we right-size it for current operations and planned growth and leave options for the future.” The plant team has been replacing aging equipment and upgrading processes, always with energy efficiency in mind.

Incentives for savings

One partner is the Snohomish County Public Utility District, the local electricity provider, which offers financial incentives for energy-saving projects, such as putting variable-frequency drives on the clarifier drives.

“If you put a VFD on a clarifier drive, you can slow it down so it’s not working so hard, which means you are saving energy,” Randolph says. “SnoPUD offered a $2,000 incentive. The project cost $7,000, but we get a lower energy bill and we also get better process control.”

Whatever changes come along, the Edmonds team stays on the path it laid out years ago.

“The major processes in the treatment plant have been upgraded,” Randolph says. “The aeration basins, the blowers and solids processing have been upgraded. If we had started with the incinerator first, we couldn’t have done those other things. We had to start with a sequential approach. That’s why we have this Pathway to Sustainability.”