May 17, 2010 | General

Community Digester And Composter Protect Water, Farms And Culture

BioCycle May 2010, Vol. 51, No. 5, p. 36
A former 277-acre farm servicing a nearby state prison is being transformed into a regional organics processing facility that generates power and high-value compost.
Dan Sullivan

A CONSORTIUM of nonprofits including a Native American tribal group, salmon recovery proponents and a farmers’ collaborative have joined forces to form a renewable energy company that includes an anaerobic digester and state-of-the-art composting operation in western Washington state. The company, Qualco Energy, has been turning manure from a local dairy into kilowatts and then composting the manure solids for use as a super clean bedding material and soil amendment for the past 16 months. Once permits are in place, Qualco plans to also begin composting biosolids from the city of Monroe four miles away.
Qualco is housed on the 277-acre former honor farm that once served the state prison in Monroe. The site, worth somewhere between $1.5 million and $2 million, was given over to the innovative biogas project and partnership by the state of Washington, explains Qualco board member John Sayre, a member of the Northwest Chinook Recovery group formed in 1997 to restore and enhance salmon habitat in the Puget Sound region.
“It was surplused and they were going to sell it,” Sayre recalls of the land gift. “We went to the state legislature, and we asked for the site for this project.” The request sailed through both state houses and the governor’s office with everyone’s blessing. One stipulation was that the receiver had to be a government entity. That entity turned out to be the Tulalip Tribes.
“The Tulalip Indian Tribes in turn lease it back to Qualco, an energy nonprofit made up of three nonprofit groups: the Tulalip Tribes, Northwest Chinook Recovery and the Sno/Sky Agricultural Alliance,” Sayre explains. Another condition of the transaction was that the land would be utilized for projects that enhanced recycling, wildlife habitat, renewable energy options for the region and sustainable farming. “Qualco” means “where two rivers come together” in the Tulalip language – fitting for a project joining cutting-edge technologies with very different partners.
With help from Andgar, a local specialty general contractor that currently has half a dozen anaerobic digestion (AD) projects under its belt and others in progress, Qualco installed a modified plug-flow digester built to GHD Inc.’s specifications (Andgar is GHD’s West Coast rep). The digester powers a 450 kW Guascor engine; heat captured from the engine and water jackets helps to maintain internal digester temperatures. The biogas produced is around 54 to 58 percent methane, says Qualco project manager Scott Wadcamp.
Funding for the project included a $500,000 U.S. Department of Agriculture grant and a federal $2.6 million Clean Renewable Energy Bond. “It’s basically a low-interest loan that has to be paid back,” Sayre says. “We’ve got about $3 million invested, plus hundreds of thousands of dollars worth of donated time and effort.”
That “we” included a partnership Sayre says makes perfect sense. “I started working with farmers 12 to14 years ago,” he explains. “I learned that if you want to save fish habitat where it can still be restored, you don’t start by making farmers – who own so much of the land adjacent to critical streams and rivers – your enemy, as some environmentalists did many years ago.” Another critical component of the partnership was getting the Native American tribes and the farmers together. “We had the farmers and tribal council members just sitting and talking,” adds Sayre. “Out of that friendship relationships developed, and one of the tribal members came up with the idea of a digester project. This idea and those relationships have given us a lot of clout and support.”
Joseph Harrison, PhD, a Washington State University (WSU) livestock nutrient-management specialist involved with the Qualco project, notes that “trying to keep farming and the Native American way of life in harmony has sometimes been a struggle.” Whether it’s warranted or not, fingers have been pointed at farming, and the dairy industry in particular, when coastal shellfish beds – important to local tribes for both sustenance and revenue – have been shut down for harvesting due to high bacteria counts. That tolerance level is particularly low because shellfish such as oysters are traditionally eaten raw.
Despite these challenges, Harrison says, the Native American community has generally come to see farming as a preferred alternative to more residential neighborhoods in the river corridor in terms of both cultural appropriateness and environmental stewardship. “It kind of came down to cows are better than condos,” he says. With that choice made, Harrison notes, the question became how to move agriculture in a more sustainable direction, particularly in terms of manure management.
Another key partner in the project is Werkhoven Dairy, connected to the Qualco facility with a mile-long pipeline that transports 65,000 gallons of manure a day to the digester from 1,000 lactating milk cows and as many support stock. “We have a system at the dairy called Biolink that thickens the flush,” explains Steve Peerce of DariTech, whose company provides the Enviro-Drums that compost the separated manure solids once they leave the digester. “That would be too much water to run through the digester. Biolink takes some of the water out of the manure for the digester before it’s piped over.” Two other area dairies are already plumbed to contribute “fuel” to the digester, Harrison explains, and a third and fourth could go online as well. “The ultimate goal is to be a community digester,” he says.

Similar to other manure digesters around the country, the Qualco facility accepts off-farm, high-energy feedstocks for codigestion. Recently issued guidelines from the Washington Department of Ecology, “Operating an Anaerobic Digester Exempted From Solid Waste Handling Permit,” require that 51 percent of feedstock must be dairy manure, 30 percent can come from offsite and the remaining material can be sourced from elsewhere on the farm. “I don’t know how you can make [a digester project] work or pay without additional feedstock,” says Sayre, pointing out that the feedstocks – many of them loaded with sugars – not only function as catalysts but also yield additional tipping fees. “We’re taking a lot of whey, fried foods and seafoods and different types of fish waste, inedible eggs from the chicken industry, and cattle blood and chicken blood and other stuff left over from chicken processing called DAF.”
Qualco also is accepting expired (past the “sell-by” date) beer, wine and soda from grocery stores, he adds. “Tipping fees are turning into potentially as big a source of income as the power sales, and it’s a preferred alternative to [these materials] being dumped in landfills, disposed of illegally or being poured down the drain.” Annual revenues from off-farm tipping fees total about $250,000. According to Sayre and depending on the material and term of each individual arrangement, the fees range anywhere from around $200 to $350 per 6,000-gallon truckload. Qualco also accepts some off-farm solids such as wood pulp.
WSU’s Harrison suggests that in a perfect world all of these off-farm substrates would be held in containers and metered in consistently. The reality is that outside material generally gets added as it’s received. What is consistent, he says, is the amount and rate of manure that gets added and mixed in over the 26-day digestion cycle. “Hot” items such as expired beverages that contain sugars and alcohol and therefore rapidly boost methane production typically get metered in as well in order to take full advantage of their capacity to boost energy production. “It’s much like feeding cow’s rumen,” Harrison explains. “You want to avoid digestion upset, and you want as uniform a mix going into there as possible.” The mix at Qualco is currently about 80 percent manure, which tends to buffer the whole system, Harrison explains.
In terms of power sales, Qualco is paid by the megawatt hour. “The schedule changes annually,” Sayre explains. “We started off with 82 megawatt hours, which means we’re generating about $280,000 worth of electricity,” or enough to power more than 600 homes for a year. “We began selling to Puget Sound Energy; the local Public Utility District (PUD) did not take us seriously at first, but now they are very interested in what we’re doing. We are in a position where we are producing two to three times more biogas than goes to our generator, so we have to expand. We’re flaring the extra gas at this point and looking at expanding to 600 kilowatts. We have the potential for producing as much as 1.3 megawatts of this stuff.”
Qualco gets paid 8.2 cents/kWh; 1.3 cents of that goes to the Snohomish County PUD for “wheeling charges” to use the local power company’s infrastructure to deliver the power to Puget Sound Energy. “When all is said and done and everything is in place and operating, our plan is to show that you can make digesters pay,” Sayre says. “If you can’t make them pay, then why would any dairy farmer or anyone want to get involved?”
In addition to the tipping fees and power sales, Qualco receives revenues from farmers who lease land to grow grain crops and for selling carbon credits to the Bonneville Environmental Foundation. What hasn’t been worked out yet, Sayre says, is what role compost might play in that revenue stream with the addition of biosolids and how and to whom it might be marketed.

When the nearby city of Monroe learned about the Qualco dairy digester project, it saw the potential for working together to solve its biosolids management challenges long term. “We wanted to see what we could do in conjunction with Qualco,” says City of Monroe wastewater treatment plant manager John Lande. “Originally we were looking at digester gas to fire a dryer to treat biosolids.”
Monroe had been composting biosolids for many years, but the recent scarcity of sawdust due to slow housing starts and a sluggish logging industry led to the cost increasing, forcing the city to halt that operation. “By 2008 fuel costs were too high, the logging industry was depressed and sawmills weren’t producing the sawdust,” Lande says. “Ten years ago sawdust provided a cost-effective bulking agent, but it’s getting more expensive.” The rising cost of sawdust also has contributed to local dairy farmers’ increased interest in digested manure solids as bedding material, WSU’s Harrison says.
Lande expects the city to be issued a permit any day now allowing it to transport biosolids for composting with digested dairy solids at Qualco. He says, “My idea was to add biosolids to the composting operation to, one, help the city, but to also be involved in a good program that is not just looking at a short-term fix but can be sustainable long-term. Right now Qualco doesn’t have the capacity to deal with all of our biosolids – maybe half. But as time goes on, maybe they can expand to not only take all of ours but from other facilities as well.”
Currently, all of the biosolids from Monroe are transported to eastern Washington where the Class B material is land applied to agricultural and forest lands in accordance with state and federal regulations. Once composting of the city’s biosolids with the digested manure solids begins just four miles away at Qualco and even with the associated tipping fees (expected to be about $120,000 annually), the city hopes to realize significant savings. “It’s part of why we’re now anxious to get out to Qualco, which will probably look to market [the compost] as a soil amendment, probably for more larger-scale commercial use.” When it was composting, Monroe distributed up to 10,000 cubic yards of compost annually to everyone from commercial landscapers to home gardeners.
Acquiring a permit to process biosolids at Qualco proved the biggest stumbling block of all, Lande says. “One of the biggest challenges that set us back was really our county and the land-use struggles that we had. In the county code, some of the language was archaic and it was difficult to move forward. They were trying to classify our project [with Qualco] as a sludge-utilization site and didn’t differentiate between sludge and biosolids. We weren’t going to be utilizing the material at the site in question; it was more of a treatment process than a utilization process.” Permitting sludge utilization is much more arduous than for composting biosolids, Lande adds. Snohomish County finally ruled that the agricultural component of the Qualco project was paramount and did not ultimately require additional permitting for processing.

Currently, Werkhoven Dairy uses some of the composted digested manure solids as bedding for around 300 dry stock and heifers it keeps at the Qualco site while the home milking herd a mile away continues to be bedded with sand. Besides the anticipated biosolids, the compost recipe will include used sawdust from the Evergreen State Fairgrounds that Qualco already receives. That sawdust first goes under the livestock, then either into the digester or the compost drum. Once the required permit is in place, the dewatered biosolids will be transferred to Qualco where they will be immediately loaded into the mixer with sufficient quantities of the digested manure solids and sawdust to produce high-quality compost. “We’ll probably be using some of it for bedding material, but we hope to be selling most of it as compost,” Andy Werkhoven says.
The Qualco project has two composting drums developed by DT-Environmental, a division of DariTech, Inc. The Enviro-Drums, 40-feet long and 8-feet in diameter each, can each hold up to 60 yards of material at one time. A 700 cubic-foot vertical mixer is placed between the screw press and the drums. “The slurry that comes out of the digester is pumped into a couple of screw-press separators where it falls on the floor,” says Steve Peerce of DariTech. “We load the vertical mixer with whatever the recipe is and it gets conveyed into one of two drums, where I believe the residence time is three to four days. It’s a continuous-feed operation as opposed to a batch.”
Robert Spencer, a composting consultant based in Vernon, Vermont, who works with a variety of vendors matching appropriate technology to appropriate application, calls the idea of combining digested manure solids with biosolids fairly unique. He explains that the Enviro-Drum’s ability to maintain temperatures of at least 55°C for three days (required for pathogen and vector attraction reduction) – and to get there quite rapidly – can be attributed to three main design features. First, small infeed and outfeed openings and a discharge opening at the top of the drum all contribute to greater feedstock capacity and retention and related heat generation. Second, the drums utilize interior versus exterior insulation. And, third, they can be set to turn as rapidly as one revolution per minute. “There is a direct correlation between the speed at which you turn a drum and the amount of horsepower needed and the electrical cost, so there are some trade-offs,” he says. “But they also have variable-speed drives, so you don’t have to turn it at that rate; those who want to conserve energy can figure out the optimum rotation.”
Spencer adds that another key design feature, which the Enviro-Drum shares with some other drum systems on the market, is that the air flowing over the exiting material meets with the fresh material coming in. “You’re introducing very hot air to brand-new feedstock,” he says, suggesting that this may also introduce beneficial inoculants that speed up the composting process and break down pathogens. Internal chambers also make efficient use of that hot air being generated. “You don’t have any one time that air can flow directly between the two openings – it’s staggered,” he explains. “Hot preconditioned air is in contact with the whole mass of material in the drum before it moves out.” The bottom line, he says, is an incredibly brief retention time, “and if you look at the economics, the shorter the retention time the better the numbers are.”
p. 38 Sidebar
WHILE initial goals for the Qualco anaerobic digester and composting project did not include mitigating the migration of potentially harmful bacteria into rivers and streams, it now appears the project may deliver the added benefit, says Joseph Harrison, PhD, a Washington State University (WSU) livestock nutrient-management specialist involved with the project. An initial research grant included biosecurity concerns and minimizing the potential transfer of bacteria and pathogens across herds when manure is applied to grasslands. The study looked at land application – both broadcast and subsurface deposition – of soil when raw manure was applied versus digested solids and measured levels of various pathogenic bacteria in soil-core samples taken over time. Harrison and colleagues found that the bacteria counts in soil when raw manure was applied generally spiked, then died off whereas counts of the same types of bacteria when the digested manure was applied steadily declined until they expired.
A significant implication, Harrison explains, is that if a rain event occurs while bacteria are spiking they are likely to migrate into waterways. Plans are under way to test that theory more fully by intentionally applying raw manure and digested manure solids just prior to a rain event and then measuring bacteria counts in surrounding rivers and slews. “If you kill 90 percent of the bacteria and then land apply it, that should lead to better-quality rivers and streams,” Harrison says.
Composting the digested solids “takes it down another whole level of kill,” he adds. “In some cases, it’s not quite sterile but it’s pretty darn clean.”

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