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Poop and Poplars: a match made in heaven?

By Cat Gowan, WSU Extension | October 2017

I was lucky to have a seat at the table at Oregon’s Association of Clean Water Agencies (ACWA) conference at the end of July in Bend, Oregon. Attending the conference was an excellent opportunity for AHB Extension to get to know more about a unique grower of poplars for ecosystem services: wastewater treatment operations.

Poplar trees grow behind a wastewater treatment pond.
Poplar trees at the wastewater treatment plant in Gervais, WA

ACWA was started in 1987 as a way to improve collaboration amongst wastewater agencies and increase consistency in the wastewater permitting process in Oregon. ACWA is now a state-wide network of 126 wastewater and stormwater utilities, along with related engineering, environmental, and energy consulting firms. The yearly ACWA conference is an exciting affair, filled with presentations from national water quality leaders and innovative public utilities sharing their successes and perspectives on the future. Here are just a few examples:

  • The City of Prineville, Oregon constructed a wetland to filter the discharged treated wastewater while restoring the Crooked River. Click here to see a time lapse video of the project.
  • The City of Portland, Oregon has plans to install and supply a biogas pumping station at the Colombia Boulevard Wastewater Treatment Plant
  • A representative from the WateReuse Association outlined the potential benefits of recycled water and direct potable reuse of wastewater.
  • But what does all this have to do with poplars?

    It’s possible that growing poplars could be the answer to some of these public utilities’ needs. Many wastewater treatment plants need better options for making use of biosolids (treated organic matter from sewage) and effluent (treated wastewater) produced by the wastewater treatment process. Some plants store the biosolids in lagoons and discharge the effluent to rivers. However, wastewater treatment plants with access to land can turn biosolids and effluent into valuable resources instead, by using them for fertilizing and irrigation.

    On the left, an aerial view of dark green poplar trees growing in large, rectangular patches amid green fields with hills in the background. On the right, an image of a white cart spraying biosolids on the green, leafy poplar trees.
    Aerial view of poplars at the biocycle farm run by the Metropolitan Wastewater Management Commission in Oregon (left); biosolids application to poplars at the biocycle farm (right)

    In order to gauge interest in growing poplars, I hosted a roundtable discussion called “Poplar Tree Possibilities: Clean Water, Healthy Soil, and Renewable Products” with Todd Miller (who manages a poplar biocycle farm for the Metropolitan Wastewater Management Commission in Eugene-Springfield). The roundtable discussion provided a venue where representatives from various wastewater treatment operations, engineering firms, and environmental organizations could learn more about using poplars for ecosystem systems. Importantly, it was also a venue where we could get an idea of what wastewater treatment operators would need to know in order to grow poplars as well as the concerns, obstacles, and values they see in growing them.

    Many of the questions raised during the discussion were well-trodden land for AHB. What are the markets? What kind of fields do you need? However, we had not thought to ask how poplar chips could be combined with biosolids to create compost, whether a public utility could sell their own poplar cuttings to others, whether the poplars would take so much water that the rivers traditionally replenished with effluent would run dry, or if the poplars couldn’t be grown too close to the airport runway for fears of attracting wildlife.

    Some of the participants saw potential for poplars to create an aesthetically-pleasing landscape feature in their rural community, while another city was inspired to see AHB’s Jefferson site. Another participant saw an opportunity to work together on future research.

    AHB Extension hopes to continue making connections with wastewater treatment professionals in the PNW, learning more about particular operations, and identifying situations where poplars might be a good option. A major theme from the speakers at the ACWA conference was that public utilities need to be able to try creative strategies—perhaps that could mean growing poplars.