Green Insurance

A poplar tree farm allows an Oregon utility to diversify its beneficial use options for Class B biosolids and significantly extends the land application season.
Green Insurance
Poplar trees at Biocycle Farm now receive about 20 percent of the biosolids from the treatment plant serving Eugene and Springfield and surrounding areas.

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In the western Oregon cities of Springfield and Eugene, a successful program provides land-applied biosolids to local farmers, mainly for growing grasses. But 10 years ago, the Metropolitan Wastewater Management Commission (MWMC), which serves the two cities and parts of Lane County, began diversifying.

Facing concerns that farmer customers might be less available someday, the commission took the creative step of planting its own tree farm called the Biocycle Farm. The project offered a new use for biosolids and now takes about 20 percent of the wastewater treatment plant’s output. “One of the values of the tree farm is that it is a fallback for us if for any reason our private land application sites went away,” says David Breitenstein, who as manager of the treatment plant also oversees the biosolids program and the tree farm.

Community collaboration

The MWMC is an intergovernmental agency that represents Lane County as well as Eugene and Springfield, the county’s two main cities. Representatives from the two city councils and the Lane County Board of Commissioners make up the governing body, along with members of the general public appointed by each of the three constituent governments.

The arrangement dates back to the late 1970s, when the cities and the county teamed up to seek federal grants to build a regional wastewater treatment facility. Each city still operates its own local wastewater collection system.

The commission has no employees. Instead, it contracts with Eugene for day-to-day operation of the treatment plant and related services and with Springfield for administrative services.

History of beneficial use

“For the last 30 years or more we’ve had a strong program going with the application of biosolids to farmland,” says Breitenstein, a Eugene city employee. The treatment plant has had little trouble finding an outlet for its product, a class B material, and has maintained strong relationships with area farmers.

At one time the commission had more than 10,000 acres approved through the Oregon Department of Environmental Quality for land application. At any one time, about a half-dozen farmers are partners with the program. “They’re very satisfied and repeat customers,” Breitenstein says. “We never have any difficulty in terms of needing to recruit more. They’re lined up waiting for the product.”

The primary use is for annual rye grass, some of it for animal feed and some as a seed crop. Much of it is exported. In the late 1990s, concerns surfaced that farmland application might fall out of favor with the public or with public officials. A citizen committee was appointed to examine the program’s future prospects. Some worried the MWMC was too dependent on area farmers.

“Biosolids practices do get challenged around the country from time to time,” Breitenstein acknowledges. “We wanted to diversify our program to improve reliability and the assurance that we could continue biosolids recycling in a sound ecological manner. Otherwise, if there was any problem with going to grass fields, and that use went away, our only other option would be to landfill and not use the material in a beneficial manner.”

Change of focus

Based on the panel’s recommendations, the commission established an application site to grow poplar trees. The site includes 394 acres of growing space; with buffer zones, the total size of the site is 595 acres. Project staff visited other communities in the region that were already using biosolids to feed smaller plots of poplars. Breitenstein says those sites more typically used poplar farms for applying treatment plant effluent.

Poplars have a hearty appetite for biosolids, and their growth cycle offered great flexibility for application. “The application rates are greater for the nitrogen uptake compared to the grass,” says Breitenstein. “Also, the application season is much longer.” In 2013, the farm yielded its first harvest: 52 acres of timber used to make pulp and hog fuel (wood chips used for mulch or boiler fuel).  

The biosolids from the treatment process are batch-pumped daily to the biosolids management facility, about 5.5 miles from the plant, where they are held in 25 acres of facultative sludge lagoons. Originally built with clay liners, the four lagoons, each covering 6.25 acres, have been relined with impermeable HDPE liners to bring them up to current design standards.

“Each year in March or April we’ll start harvesting biosolids from the lagoons,” Breitenstein says. After dewatering with a belt filter press to 15 percent solids, the material is laid out in windrows on 25 acres of asphalt-lined air-drying beds. The final air dried product is 50 to 70 percent solids.

“We continue to harvest throughout the summer, and we have our first application ready in July,” Breitenstein says. “We use our own trucks and end-dump trailers that we load and haul to the farm fields.” Most of the farms are within about 5 miles of the lagoons.

After farmers harvest their crop and remove the straw, “We surface-apply the biosolids using tractors and manure spreaders,” Breitenstein says. “After we are done with our application, the farmers work it into the field and then replant.”

Liquid application

The tree farm lies next door to the biosolids management facility. Biosolids for use there bypass the drying beds and are applied as liquid. The material is dredged from the lagoons and placed in holding tanks, then pumped through an underground irrigation system to the farm.

The first of three phases of trees, 156 acres’ worth, was planted in 2004. “We planted hybrid poplars which are more suitable for milling as either saw logs or peelers,” says Breitenstein. For the first two years, the poplars’ growth was a bit stunted for lack of moisture. Irrigation lines have since been installed, and effluent is sent to the site through the same pipeline used to transport biosolids.

The water is the same quality as that discharged to the Willamette River, except that the irrigation water is not dechlorinated. The farm uses about 70 million gallons of effluent per year.

Since that first year, other varieties of poplar have been planted, and they have benefited from the irrigation. “Even though they were planted later, they appear to be of much better quality,” Breitenstein says. “So we hope that with future harvests there can be some alternative wood product options.”

On the 595-acre farm site, 394 acres are planted with 88,000 hybrid poplar trees in seven varieties. The first harvest in 2013 took 9-year-old trees. The farm’s agricultural zoning requires that trees be harvested within 12 years, Breitenstein says.

Application to the poplars is limited only by the winter conditions. “As soon as the ground is dry enough, usually around April or May, we can start applying biosolids clear through to October,” says Breitenstein.

For now, he doesn’t expect the tree farm to change the overall biosolids program: “I foresee that we would continue with a diversified program, with probably about the same proportion of the biosolids going to the farm as we’ve been doing.” If the primary application sites ever fall out of favor, other farmland is available. But knowing the tree farm is in place offers security for the program’s future: “It’s a very good insurance policy.”


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