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Wastewater Treatment Plant

  • The City’s treatment plant treats 13 million gallons of water daily and serves 114,000 customers in the cities of Gresham, Fairview and Wood Village.
    • Energy Net Zero
    • How the Plant Works
    • Educational Tours
    Energy Net Zero

    In 2015, the treatment plant reached energy net zero.  The plant now produces more energy than it uses, saving the city an estimated $500,000 a year in electricity costs.  

    Fats, oils and grease are trucked to the plant from local food service establishments.  The City collects a tipping fee for receiving and recycling this waste.

    Biogas is fed into two powerful cogen engines that converts biogas into heat and electricity. 

    How the Plant Works
    1. Primary treatment
      Wastewater enters the treatment plant, flows through a screen, which removes large objects that could damage equipment. The remaining solids are minute particles that fall to the bottom of a sedimentation tank.  The particles form a mass of solids called biosolids or sludge.  This sludge is removed and converted to biogas to help create energy to power the treatment plant.

    2. Aeration
      Aeration is an activated sludge process based on pumping air into a tank which promotes microbial growth in wastewater.  The oxygen helps the bacteria break down organic matter and remove contaminants.

    3. Secondary clarification
      The wastewater from the aeration basin is slowed down and any remaining sludge is separated and removed from the wastewater.

    4. Disinfection
      The wastewater is then disinfected with sodium hypochlorite to remove any disease-causing organisms and ensure that water leaving the plant meets the water quality standards set by the Environmental Protection Agency (EPA).

    5. Plant effluent
      Following the treatment, the water is discharged to the Columbia River. 
    Educational Tours

    Schedule a tour of the Wastewater Treatment Plant 

    20015 NE Sandy Blvd.

    • Take a 45-minute guided tour through each step of the treatment process.
    • Learn how the solar array and biogas generation allow the plant to be energy net-zero.
    Tour the Columbia Slough Regional Stormwater Treatment Facilities 
    • Take a 45-minute self-guided tour through this restored parcel of land.
    • School groups can check out a backpack of educational materials full of activities such as a scavenger hunt.

    More information and educational resources


    • Wastewater gallery - Net Zero event
    • Wastewater gallery - Net Zero FOG truck
    • Wastewater gallery - Net Zero FOG building
    • Wastewater gallery - Net Zero FOG system
    • Wastewater gallery - Net Zero Cogenerator
    • Wastewater gallery - Net Zero solar panels

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    • Gresham's Wastewater Treatment Plant is the first in the Pacific Northwest to reach energy net zero status, meaning the plant produces at least as much energy as it uses. We celebrated the achievement with the next generation of great minds on Earth Day 2015.

    • Fats, oils and grease collected by regional restaurants and food service establishments comes in on trucks from three haulers - about 10,000 gallons a day. FOG is fed into digesters and the natural byproduct, biogas, is captured, treated and converted into heat and electricity.

    • Gresham earns up to $250,000 a year from fats, oils and grease collection.

    • The treatment plant got to net zero two ways. It made its operations and equipment more efficient (cutting energy consumption), but mostly it got to net zero by producing renewable energy on site. This is the fats, oils and grease receiving station.

    • The co-generators are powerful gas engines that convert the biogas into heat and electricity - enough to heat the plant and produce 5.2 million kWh of electricity a year. Gresham saves $500,000 a year on electricity.

    • A solar array made up of 1,904 panels operates 365 days a year, producing 475 kWh, or 8% of the renewable power produced at the treatment plant. Clean energy can be used on site or sent back to the grid.

    • Gresham’s plant is one of only a handful in the United States to achieve net zero status. Discover the ingenuity and collaborative spirit that made possible an environmental achievement at the City – engineering the Pacific Northwest’s first energy net zero wastewater treatment plant. Achieving net zero status means that the plant makes about the same amount of electricity as it consumes in a year, saving tax dollars and protecting the environment.