Pledging to transform Hawaii's largest wastewater treatment plant
February 10, 2026
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Using innovations like an aerobic granular sludge process to protect the environment, support a community, and solve challenges
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In this series, we’ll explore the power of collaboration and co-creation with our clients. These partnerships showcase how we rise to the world’s greatest challenges together.
Most people think of Hawaii as a tropical paradise. The eight main islands offer natural wonders with beaches, Pacific Ocean waves, abundant sea life, and mountains that reach to the sky.
But it’s not easy to maintain paradise. And that’s where a unique pledge comes in.
More on that pledge later.
First, the reason for it. The Sand Island Wastewater Treatment Plant (SIWWTP) is Hawaii’s largest treatment facility. It serves the major population areas of Downtown Honolulu and Waikiki. It’s nearly 50 years old and needs an upgrade.
By 2035, the U.S. Environmental Protection Agency requires the City and County of Honolulu to improve the quality of the water it discharges into the ocean. It needs to go from primary to secondary treatment of wastewater.
But which system is right? After much research, our team—which includes joint venture partner RM Towill—and the City and County of Honolulu settled on the aerobic granular sludge process for the Phase 2 upgrades. This supplements the membrane bioreactor process being constructed as part of Phase 1.
And that leads to the pledge: vowing to do what it takes, not what’s easy.
" }We’re on the right path, and we’re going to get to the end, together.
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Preparing for complexity—as a team
The project is complex. There are energy realities, strict climate action targets, and a limited site footprint—all adding layers of difficulty when implementing the right solution.
And the new facility carries a US$2.5 billion price tag. It’s also a solution that’s not widely used elsewhere in the world, making it truly groundbreaking. When complete, it will be the largest aerobic granular sludge facility in the world.
In addition, the ongoing Phase 2 work includes a strategic Organic Waste Sustainability Plan. It will provide for innovative energy creation through the management of waste streams like food waste and fats, oils, and grease. Other creative solutions at the new facility include thermal hydrolysis and combined heat and power. “We knew the team at Stantec was up to the challenge,” says Roger Babcock, director of the Department of Environmental Services at City and County of Honolulu. “We can’t accomplish a project of this scope and scale on our own, and with Stantec, we’re getting the A team.”
When innovation is the standard, the payoff is large.
“This project brings a level of innovation that’s going to bring the City and County of Honolulu to the forefront as a leader in using this kind of technology,” says Bob Armstrong, vice president and project development leader at Stantec. “It’s a very special project for me and for the people of Hawaii.”
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Dr. Roger Babcock and Bob Armstrong
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An ocean of opportunity
The SIWWTP site is on the edge of Honolulu Harbor, in view of the world-famous Waikiki Beach and Diamond Head—marking Oahu’s primary center of tourism. And, like many coastal cities, rising sea levels are a reality for the community, along with the need to protect the environment.
Project supporters include the Sierra Club and other environmental organisations.
“Protecting our near-shore waters for years to come is imperative to this project,” Armstrong says.
Trust and relationships
Committing to innovation—especially in the face of obstacles—really comes down to trust and relationships.
“Stantec brings a lot of things to the project, but the relationships and the people are what matters,” Babcock says. “And I like the people at Stantec. This project has been successful to date because of those relationships, and it will continue to be successful because of that.”
Phase 2 of the SIWWTP upgrade is well underway with a targeted completion date of 2035 to meet the EPA’s Consent Decree.
As for the pledge? It’s still in full effect.
“We made a commitment to the selected treatment technology through signing a pledge with our partners at the City and County of Honolulu and its consultants, and we’re here to see this through to meet the Consent Decree requirements,” Armstrong says. “We’re on the right path, and we’re going to get to the end, together.”
With every community, we redefine what’s possible. Through collaboration with our clients, together we will unlock outcomes neither could achieve alone.
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