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Algae Farm

Industrial Symbiosis
in Pasco, WA

Christian Carvajal

Pasco, with a population of about 60,000, is the seat of Franklin County in southeastern Washington. The county enjoys a diverse economy, with a thriving agricultural sector that accounts for over a fifth of its employment. In addition to a municipal water system that treats urban sewage, local food processors release agricultural wastewater that is treated separately at the city’s Process Water Reuse Facility (PWRF) before being reused to irrigate crops. 

The water arrives at the PWRF loaded with nitrogen and requires denitrification so it can be returned safely to the soil. In recent years, Pasco’s aging PWRF has reached the limit of its ability to handle the existing workload, and new processors to the area, Darigold for example, are also interested in using the facility. The proposed Darigold milk-drying plant would be the largest of its kind in North America, creating 200 new plant jobs and over a thousand in related industries.

Michael Henao
“People cannot believe the amount of water that gets sent to our facility. With the new facilities in the city of Pasco, we’re talking about
1.5 billion gallons of industrially processed water.”


Environmental Compliance Coordinator, City of Pasco

The City is moving forward with:
  • Adding Low Rate Anaerobic Digesters to capture methane gas from wastewater to produce natural gas.
  • Nearly 1.5 billion gallons per year of pre-treated water with some nitrogen will irrigate crops, reducing fertilizer needs.
  • Biological, low-energy nitrogen removal system uses algae.
  • Marketable algae-based fertilizer is a resulting product.
  • Creation of 300+ FTE due to year-round capacity for food-processing plus construction.
  • Treating (and capturing value from) waste streams from new Darigold facility.
  • Possible future inclusion of post-consumer food waste in anaerobic digestion.

PICTURED: Tri Cities, Washington
: WA Dept. of Agriculture

Learn more project details

“They decided they wanted to build their new butter and protein-powder plant here,” explained Steve Worley, public works director for the city of Pasco, “partly because we have this industrial wastewater plant. So now was the time to enlarge our facility and update it to more and better technology.” That’s when the Center for Sustainable Infrastructure (CSI) got involved. “They look for opportunities where one industry's waste can be turned into a beneficial resource in another industry,” said Worley. The exchange of byproducts, called industrial symbiosis, reduces strain on the environment while simultaneously improving the bottom line for job creators.

Pasco hopes to use both algae to clean its agricultural wastewater for redistribution, and an “anaerobic digester” that will extract valuable renewable natural gas from methane in the wastewater. The primary goal was to maintain enough nitrogen to feed crops while keeping excess nitrogen out of Pasco’s groundwater. Says Worley, “We were also approached at that same time by a renewable natural gas developer (RNG) who said, ‘Tell me about your system.’ So I told them, and they said, ‘We see an opportunity here. We think we can capture that methane and turn it into RNG, sell it and share the revenues with you.’ CSI experts worked through the value-planning process.” Luckily, an existing natural gas line crosses the “Reimann Industrial Center” property Darigold is planning to occupy.

In the project’s first phase, starting in February 2021, CSI facilitated stakeholder meetings to work around such limitations as funding, water flow rates, and nitrogen acceptance over a finite land area. This informed Pasco’s planning, and they are currently accepting bids to upgrade the existing PWRF. In phase II they will design and build a new storage pond for the winter months, when irrigation goes on hiatus, adding significant year-round processing capacity and another more than 200 jobs. Phase III, says Worley, is “the actual anaerobic digester and Renewable Natural Gas facility.”

Pictured below: Concept for an algae technology developed by Gross-Wen, one of the options that City of Pasco is considering


“People cannot believe the amount of water that gets sent to our facility,” said Henao. “With the new facilities in the city of Pasco, we’re talking about 1.5 billion gallons of industrially processed water.” Keep in mind, that’s aside from household wastewater Pasco must treat in a separate facility.

The county’s agricultural processors are focused on cultivating millions of acres, so persuading them to add algae, natural gas, and a network of industrially symbiotic businesses to their worldview is a tall order. Henao hopes his final report to the Washington State Department of Commerce will “make a strong case to help them understand the benefits of using this technology, so they’ll feel comfortable with it as a mode of treating the water.”

At the close of our conversation, Worley noted, “We’re busy working to get all our utilities, including the reuse facility, ready for the increased flows to the processors and the new flows from Darigold.”

“We have an extremely busy next three years,” Henao agreed, “which is exciting. We expect a really nice growth in the city of Pasco.”

Does it follow, then, that a slow day in Worley’s office is bad news? After a long pause, Henao and Worley both broke into laughter. “Nope!

Please refer to the City of Pasco's webpage on their Process Water Reuse Facility for updates and to learn more.

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