Anaerobic Digesters: A Community Approach
Anaerobic Digesters: A Community Approach
by Steve Werblow
Three thousand cows in Tillamook, Ore., power 150 homes with their manure, collected and processed through the Port of Tillamook Bay’s community digester. Leftover liquid is returned to participating farms for land application.
Manure management is an issue that doesn’t stop at the edge of the lagoon or the ditch at the fencerow—in many areas, it’s a community issue, and some of those communities are finding collective solutions. Community digesters offer some areas with high concentrations of livestock an efficient way to turn manure into natural gas, and then into profit—or at least energy.
On the plus side, building a few relatively large facilities to digest manure into methane gas can be more efficient than building a lot of farm-scale ones. But not surprisingly, there are many challenges along the way, from the logistics of hauling manure to central sites to the hurdles of securing funding for community-scale projects.
Up and running
IEUA’s two manure-driven biogas plants utilize classic anaerobic digester technology to use microbial activity to convert manure into natural gas. Three hundred tons of manure are trucked in every day and warmed to 105 to 110 degrees Fahrenheit. Those are ideal conditions for the bacteria that convert solids in the manure into methane and carbon dioxide. As the bacteria work their way through the manure over the course of days or weeks, the gas is captured, cleansed to enhance its energy value and fed to methane-powered engines that generate electricity. Heat from the process feeds the manure-warming system and other industrial processes, including Inland Empire’s reverse-osmosis desalination plant, which produces 14 million gallons of drinking water daily for local residents.
While the generators spin out 1 megawatt (MW) of electricity per day—enough to supply about half of what IEUA consumes—the environment wins in other ways, too. Odors and pathogens are controlled, volatile organic compounds (VOCs) and particulate matter are reduced by 99 percent and more than five tons of salts and nitrates are kept out of the Santa Ana River watershed. Meanwhile, solids separated from the processed manure—135 tons per day—are sold as organic fertilizer.
It’s a shining example of the capabilities of a community system, but it’s hardly a get-rich-quick scheme. “As a public utility, we’re just trying to cover our costs,” says Rich Atwater, IEUA’s CEO and general manager. “The renewable energy value generates a couple of million dollars a year in income, so at least it’s a break-even proposition. It covers operations and maintenance and our return on capital investment in the project.”
Still, Atwater’s team is working on optimizing its digester technology as it expands its capacity to take in 700 wet tons of manure per day and generate 2.5 MW of power. That could extend the benefit to local food processors as well as dairy producers. “In Europe, they’re seeing that blending manure with food waste enhances methane gas production,” he notes. “We’re working on a menu to optimize that.”
A thousand miles to the north, the Port of Tillamook Bay on the Oregon coast has built three 140-by-30-by-14-foot digester cells on existing concrete pads. Together, those cells generate power from the manure of 3,000 of the valley’s 30,000 dairy cows. At $1 million each, the cells are a bargain compared to a $16 million county-wide plant that had been proposed, and they generate 300 kW of electricity, enough to power 150 homes.
Gas and heat are circulated back to feed the digester’s heating system and generators, as well as pumps and other equipment. “Everything we put in here had better run on methane,” says George DeVore, who heads up the operations team and research and development efforts for the digester. Separated solids are composted into a high-quality soil amendment, and processed liquid is returned to the farms for land application in the same trucks that will turn around and bring back fresh manure for the digesters.
Feasibility studies in the MidwestThe success of Western community digesters has John Reindl, recycling manager for Dane County, Wis., excited. His county recently launched a study on manure management options that follows up on a 2003 feasibility study on the community digester idea. With 125,000 cows, thousands of hogs and Wisconsin’s second-largest city, Dane County enjoys a promising combination of nearby manure and a big sewage treatment infrastructure. Including a community digester among several other technologies may turn out to be a good fit, says Reindl.
In fact, the 2003 study penciled out in favor of a community digester over several farm-scale ones. In the analysis, a $190,000 system on a 200-head dairy lost $2,900 per year after factoring in the value of electricity, compost sales and carbon/renewable energy credits. A community system that could serve 4,000 cows from 18 farms would cost $4.4 million to build and $798,000 to operate, but showed an annual net profit of nearly $200,000. That didn’t count the benefits of removing tons of phosphorus from farms that were already loaded with the nutrient.
But the writers of the report were clear - the value of electricity isn’t enough to keep a digester viable. Selling composted solids and selling or utilizing waste heat are also vital to a healthy bottom line.
In Oregon, DeVore agrees strongly. “You’d damned well better have a good plan for marketing your solids,” he warns. “You will not realize how fast those separated solids build up if there’s no market for them. There’s no money in electricity, in reality, so we’re drying our separated solids and planning on bagging them.” The Port of Tillamook Bay is working with a retail fertilizer company to build the market for its rich solids.
Trucking: the tipping pointCovering transportation is also vital. “We were supporting the whole project, but the growers could see how bad we were losing our butt, so they volunteered to pay 80 percent of the hauling costs,” says DeVore, who points out that Tillamook farmers at first resisted any hauling or tipping fees.
Adds Atwater, “We try to adjust the tipping fee and work with the producers so it’s cost-competitive to hauling out to the field. At least it’s a break-even proposition.” He notes that the high cost of transportation creates a delicate balance, so the 10-mile haul for Chino dairymen makes IEUA’s digester far more feasible than one located in an area that requires even just an extra five miles of transportation from the farm.
Some community digester plans have included pipelines instead of truck delivery, notes Gail Lisse, agricultural engineer with the Wisconsin Department of Natural Resources in Madison, Wis., which highlights other challenges.
“Piping, in theory, is a great idea as far as reducing truck traffic and therefore your cost,” she says. “You can also pipe and pump a greater distance—the dollars and cents for doing that make more sense than trucking it. But the farmer says, ‘I can’t afford to bury four miles of pipe to get rid of my manure.’ And right now, the benefits are not going to be for the farmers in the area, but for other entities.”
The biggest challenge: funding
“You can’t continue to give small amounts of money to each farmer and expect to get a sustainable manure management plan - it just doesn’t work that way,” DeMichele says. Plus, he adds, livestock producers have enough to do every day without adding “wastewater treatment plant operator” to their job description.
“Given half a chance, a municipal consultant could help solve some of these problems,” says DeMichele. “But up until a year or two ago, a farmer could only use USDA money to get technical advice from USDA. That eliminated all the consultants who had already solved problems in the municipal arena.”
DeMichele sees some hope in the current draft of the Conservation Resource Recovery section of the 2007 Farm Bill. And the Water Environment Federation is trying hard to make community projects and local utilities eligible for EQIP and other manure management cost-share funds. The Federation is also trying to encourage consultants with experience in municipal waste management to qualify for USDA Technical Service Provider (TSP) status. “Learning experience from municipal professionals should be transferred to ag professionals,” he notes.
Back in Wisconsin, John Reindl is looking for as much insight as he can gather. He’s amassed an extensive online bibliography and resource on digesters around the world. And he’s an eager participant in industry conferences like the Exploring the Profit Potential of Cow Manure meeting held in Madison for the past two years.
“We’re all trying to learn about this,” Reindl says, “and we all need to help each other.” FOR MORE INFORMATION
Tillamook’s diagram: A Community Digester At Work US