March 28, 2005 | General


BioCycle March 2005, Vol. 46, No. 3, p. 54
By-products from 2,000 cows in Tillamook County include 150 kilowatts/day going directly to the electric grid, plus digested fiber to Willamette Valley nurseries and compost from manure solids.
Laura Swanson

EVERY EIGHT MINUTES, a truckload of raw manure is pumped into the holding cells at the Port of Tillamook Bay’s Hooley Digester (POTB) in Tillamook, Oregon. Then the truck is filled with liquid nutrient by-products from the digestion process, trucked back to the farms and applied to the fields. “Ten hours a day, seven days a week, averaging 3,000 gallons per truckload, depending on the thickness of the solids coming into the facility,” says the digester’s operations manager, George DeVore. “The generators run 24 hours a day, sending 150 kilowatts of power directly to the grid.” The facility began operations in mid-September 2003.
There are variables everywhere you look in the engineering and digester process. “The thickness of the raw materials is an important issue. Our ideal is a manure that’s 12 percent solids; straight out of the cow, it’s 15 percent. We do regular ‘chip tests’, taking composite samples of the materials coming from the participating farms to make sure our solids aren’t too thick.” Thicker raw materials increase the wear on the truck equipment and the digester pumps. Other foreign raw materials also occasionally get pumped into manure holding tanks. “We’ve had 2×4 lumber, hay and various cow parts float to the top of the tanks. These types of materials cause all sorts of problems with our equipment, so we’re adding chopper pumps and better screening to the digester.”
Modify, modify, modify has been the mantra at the POTB digester. “We’ve had to make modifications to the design throughout the facility to make it work. As we adjust the engineering, we’ve had to get permission from the equipment manufacturers to make modifications because of warranties.” During the past year, one of the digester’s generators (the digester has two total) has required a replacement engine – twice. “The manufacturer of the generator, Martin Machinery, has stood behind their product and replaced the necessary parts. We’re working out the bugs in the engineering.” While DeVore and his crew of six employees continue to keep the equipment functioning, and continue to feed the digester raw manure, the good bugs are generating methane and nutrient-rich by-products.
According to Jack Crider, Port Manager, when looking at the bottom-line financial costs of the digester, “We’ve had some good months this past year, and can see light at the end of the red-ink tunnel. We’ve implemented a tipping fee. With DeVore keeping consistent kilowatts coming from the generators and when Pro-Gro Mixes moves over 1,000 yards per month of the digested fiber, that provides positive contributions to the bottomline.” Transportation costs, the price of diesel fuel in particular, have had a negative impact on operating costs.
“The support and commitment of the Port’s board of directors and Jack to keep the digester running and make these modifications to work out the bugs is really the reason for our continued success,” says DeVore who has been a key component to figuring out innovative solutions to make this all work. “And we’re getting there, but now we’ve got several other construction projects going on, and we’re getting ready to bring a third cell on-line.”
“The digester is operating at half capacity, with two tank cells (of four total) each with 400,000 gallon capacity covered with the gas collecting bladders, and taking in the liquid manure from 2,000 cows. Two more tank cells are awaiting raw materials. The third cell will help keep the two generators running evenly, instead of adding another generator.” When the fourth cell is brought on-line, the facility will need to add another generator, a $140,000 investment, to be able to capture the capacity of methane gases that will be produced by all four cells, and efficiently convert it into electricity.
In addition to overseeing the myriad of engineering, operational and equipment at the digester, DeVore is also an extremely knowledgeable tour guide. The POTB digester has been generating a lot more than just electricity; it has also attracted a great deal of interest from other electric utilities and a variety of community groups and organizations. “We average anywhere from three to four groups touring the facility every week, many from back east and other parts of the country. From just a couple folks to groups of 40 or 50 people, we’re proud of the work and the facility and happy to explain the operation to show off what we’re doing here.”
As the operations of the digester begin to flow more smoothly, the POTB is looking at ways to increase profitability through other “value-added” products. Another by-product of the digester process is the “solids” material or digested fiber. Pro-Gro Mixes of Tualatin, Oregon has contracted to market the material to the wholesale nursery and landscape industries and sells between 1,000 to 3,000 yards of digested fiber, under the FiberLife brand, per month in the Willamette Valley. Digested fiber is a biologically-active, all-natural material which adds beneficial organisms to soil, improving soil structure, and creating optimum growing conditions. “We plan to always have the digested fiber available to citizens of Tillamook County for pickup for $5/yard, which is about a pickup load,” explains DeVore. According to local Master Gardeners, the digester’s fiber is “great stuff.” They are using it with compost and soil for potting up our plants for the group’s biannual plant sale.
“We are exploring the economical feasibility of various options for the fiber,” points out Robert Miller, Utilities Supervisor for Port of Tillamook Bay. “The first new concept is using static pile drying.” This process uses an enclosed vessel with reverse aeration to draw out the moisture of the fiber. The method stabilizes the microbes to reduce the ammonia, the odor and potential for “burning” or plant damage when the material is applied on gardens and landscapes. “In theory, this will create a slow-release fiber product with all the characteristics of high quality peat moss, plus the nutrients of a fertilizer and active microbes,” says Miller.
The experimental static pile drying facility is being constructed on-site, utilizing abandoned concrete structures that served as a drying kiln for an old saw mill. “We are converting one cell, and equipping it with a fully automated system that pressurizes the sealed room by blowing air in the top, sucking air and moisture out the bottom,” adds Miller. “We’ll capture all the liquid moisture leachate. This liquid will also contain active microbes and become a marketable product as well.” The fully automated system incorporates a controller, connected to temperature probes in the piles and air ducts (dissolved diode probes), oxygen content and pressure gauges to maintain a stabilized atmosphere in the sealed room for a time period yet to be determined, but probably at least 60 days to reach optimum moisture and stabilization. The Port is also exploring various configurations for marketing the fiber – pelletizing, bagging and bailing – for landscape applications on golf courses, erosion control and animal bedding products. Future construction projects include a bagging and bailing facility.
For more information about the Port of Tillamook Bay’s Hooley Digester, go to
WHILE the Port of Tillamook Bay’s digester takes in the liquid wastes from 2,000 cows in Tillamook County, adjacent to the digester is Compost Inc.which takes care of the solid wastes from 9,000 cows. “We can’t make enough of the compost for the demand,” says Compost Inc. manager Russ Halvorsen. “And there’s not enough room for all the raw materials available.” The three-acre facility is always operating at capacity with 1,200 yards composting in each row, over 30 semiloads at 500 yards each coming in daily, and 12,000 yards of finished product awaiting screening.
During the past year, Compost Inc. has added a roof over the compost piles, increased its finished material holding area, and added a new leachate pit to collect the liquid from the composting piles. Five of the six farms that process their solid manure waste at Compost Inc. have separators that are intended to reduce the moisture of the materials. “It seems that we are getting wetter material,” says Halvorsen. “We’re at 75 percent moisture and need to get that down to 40 percent. We are experiencing a dry winter season here, too, which isn’t having the positive impact that we’d hope it would to dry out the compost.”
Mixing with mill shavings, turning the piles, and waiting 90 plus days with regular testing of pile temperatures, moisture content and pathogens turns out Compost Inc.’s product. “We continue to produce clean compost with all our tests showing no traces of fecal pathogens, e-coli or herbicides such as clopyralid. In 2008, after a phase-in period, the Oregon Department of Environmental Quality (DEQ) is establishing new rules for compost that will require particular testing and moisture content to ensure a better, more consistent product available to the consumer,” continues Halvorsen, who serves on DEQ’s Compost Rule-making Committee. “We’re already doing these things now.”

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