What it took to rehabilitate wastewater infrastructure for the Puget Sound

"Through those evaluations, we identified we can minimize centrate handling storage volumes in anticipation of high flows and use that additional storage for primary clarification during the high flows," said Matt Kennelly, LOTT Clean Water Alliance executive director. "This operational change for centrate is managed through our existing high flows protocols.  Looking at the economic, social, and environmental benefits, it became obvious we could gain the added benefit of wet weather treatment with minimal additional effort and cost."

LOTT treats an average of 13 MGD, and it can manage storm peaks approaching 70 MGD, due to replacement of influent valves, influent channel mondifications, electrical updates and the addition of flow monitoring instrumentation. Even with that average and peak capacity, the facility faced growing strain on its systems as climate change intensified wet weather events. 

At the same time, decades-old infrastructure, including corroded steel, outdated electrical systems and failing odor scrubbers, posted operational and safety risks. Rather than demolish and rebuild, LOTT opted for a creative rehabilitation that would deliver both structural renewal and function innovation.

The result is a multi-use facility that expandes centrate storage during dry weather to protect the biological process from ammonia shocks and shifts to primary treatment during storm events to manage peak flows.

"The Budd Inlet Treatment Plant permit has very low effluent limits from April through October," Kennelly said. "To help ensure those limits are achieved, we need to be able to manage the high strength centrate from our centrifuges. This equates to about 20% of the overall nitrogen load at the BITP."

The project preserved eisting concrete structures, installed seismic and electrical upgrades and integrated a new odor control system, which dramatically improved working conditions and reduced community impacts.

"We met interior air quality by ensuring we have adequate air exchange within the building," Kennelly said. "This discharges the foul air outside the building. Knowing that we do not want to send foul air outside of the LOTT site, LOTT directed the design consutant to conduct air quality modeling to determine the level of air treatment so foul air does not reach beyond the LOTT site and impact the public." 

A key innovation lies in the centrate management system which now allows precise control over ammonia-rich return streams that account for up to 25% of the nitrogen load. The centrate management facility, Kennelly said, allows the plant to keep the inert solids out of its secondary process and instead sends those solids back to the digesters.

"It allows us to meter in the centrate that's high in ammonia back into the secondary process when loading is reduced," he added. "This minimizes the toxicity to our microbiology, reduces energy costs, reduces supplemental carbon costs and overall lowers the nutrients in our plant effluent."

In tandem with the centrate change came new roof-mounted solar panels to power onsite EV charging, which cut emissions in line with LOTT's Greenhouse Gas Emissions Policy.

"It takes a lot of energy, typically through carbon usage, to create concrete and the centrate building had hundreds of cubic yards of concrete that we did not demolish or recreate," Kennelly noted. "For the building fans, we included the ability to reduce air flow when odors are not at peak levels, so we can turn down the air handlers to reduce power demand, foul air discharge, and consumption of treatment medium."

By combining adaptive reuse, sustainable design, and operational foresight, LOTT delivered a cost-effective alternative to new construction. The project demonstrates how existing infrastructure can be reimagined to meet modern performance standards, safegaurd water quality in Budd Inlet and build resilience against the pressures of climate change.