City of Gresham: Upgrading a Wastewater Treatment Plant to be Energy Net Zero

An Interview with Senior Wastewater Treatment Plant Engineer, Alan Johnston

Through thoughtful planning and follow-through, the City of Gresham, Oregon was the first city in the Pacific Northwest to operate an Energy Net Zero Waste Water Treatment Plant. This plant generates enough energy on site to meet its demand for electricity to run the plant. In fact, it often generates more energy than it needs. The City of Gresham’s Business Sustainability Coordinator, Gregg Hayward, interviewed Alan Johnston, Senior Engineer and driving force behind the journey to Net Zero, in August 2018.

Left: One of Gresham’s two 400kw co-gen engines running off biogas produced from the wastewater and FOG mixture. Top-right: Engineer, Alan Johnston receiving a Gresham Green Business Award from Gregg Hayward. Bottom-right: The LEED-certified tank meeting room.

By Gregg Hayward, City of Gresham, OR


The inside of a former wastewater treatment tank is an interesting place to meet for an interview. The old concrete walls have been scrubbed and sealed and large windows above cast warm daylight into the space. A projector hangs from beautiful stained beams and a whiteboard has been pressed into a side of the cylindrical wall. Sounds carry easily, but the space is quiet between sentences. This old, out of service tank has become the central meeting space of the Gresham Wastewater Treatment Plant. Surprisingly, the repurposed tank is now a LEED-certified building. It was in that space that I chatted with Alan Johnston, the calm and humble 25-year veteran of the City who helped dream up this innovative movement.

Achieving Net Zero

The City of Gresham’s Mayor, Shane Bemis, signed the US Council of Mayors Climate Action Agreement in 2007. Growing out of that declaration, the City began envisioning new ways to reduce greenhouse gas emissions and increase operational efficiency to save money. Upgrading all street lights to LED, which has saved the City $700,000 per year, and upgrading the Wastewater Treatment Plant to Energy Net Zero are some of the big wins.

“We’ve had a lot of fun figuring out how to put this project together,” the affable Johnston explains. “Back when I started with the City in 1991, we actually had a co-generation engine here at the Wastewater Treatment Plant (WWTP). It was old technology, and only helped power about ¼ of the plant. We wound up turning it off in 2002 when it burned out. When I came on board, I wasn’t really thinking of how to reengineer this whole thing, I was just interested and absorbed in figuring out how to run the facility. But over time, as I came to better understand the system, and learned about new technology, I became interested in trying to find ways to make it more efficient, while still doing its job. We often become absorbed in merely thinking about operating these facilities to take care of our water ecosystems. This continues to be our priority, but these plants consume massive amounts of electricity (the WWTP is one of the largest energy users in the city), and I became increasingly interested in finding ways to change this.”


The Net Zero journey began when the WWTP received a grant from the Oregon Economic Development Commission to study ways to increase the environmental and operational efficiency of the treatment plant. An outcome of that was a study on the benefits of accepting Fats, Oils and Grease (FOG) to remove them from the waste stream and instead use them to generate electricity. The study delved into the potential return on investment (ROI) of the project. The conclusion was that it would be cost effective with an ROI of 7 years with a FOG tip fee (fee paid by haulers of FOG when they deliver FOG to the facility).

“This document was what we passed around to get interest from City management and elected officials. They came on board with it, and it became part of the capital improvement plan for the treatment plant,” says Johnston. Investment began in the 2010 capital improvement cycle where net zero became a real goal. The aim was to make improvements cost-effective and bring the plant into net zero energy use range. A formal Energy Management Team was created, and they established a goal of achieving Energy Net Zero at the WWTP within 5 years (by 2015).  The Energy Management Team met monthly to assign appropriate tasks to staff and ensure the energy net-zero goal was met. In February 2015, on schedule and on budget, the very first energy net zero month occurred. The WWTP generated more electrical energy on site from renewable biogas cogeneration and solar power than the plant consumed. The WWTP is now on its 4th year of operation as a net zero WWTP.


Several consultants were hired to help do studies to prove the feasibility of the plant’s net zero goal, along with design work and construction. Johnston oversaw the project, and currently oversees the management of the WWTP Program. “Once we had the energy net zero path forward figured out in 2010 with support from management and staff, we phased in the capital upgrades to the WWTP with four major capital projects over a five-year span.


Phase 1 (2005):  Installation of the first 400 kw cogeneration engine with a modern biogas scrubbing system.

Phase 2 (2010): Installation of a 420-kW solar system.

Phase 3 (2011): Power conservation project that reduced plant-wide power consumption by 17%.

Phase 4 (2012): Installation of a 10,000-gallon FOG receiving station

Phase 5 (2014): Expansion of the FOG receiving station to 30,000 gallons.

Phase 6 (2015):  Expansion of the cogeneration system from 400 kW to 800 kw (Two, 400 kW cogeneration engines)


Integrating with Your Utility


Passing through the gate at the WWTP today, one is met by a large array of solar panels, a very visible note that sustainability is an important value here. While phasing in this solar array, Johnston worked hand in hand with Portland General Electric, the utility provider for the area. They, along with the