November 22, 2006 | General

Anaerobic Digester Installations From Coast To Coast

BioCycle November 2006, Vol. 47, No. 11, p. 32
New projects in California, Vermont and Michigan will process agricultural and municipal organics using a range of digester technologies.

IF INCOMING emails count toward providing a sign of the times, there is no doubt that selection of anaerobic digestion technologies to process agricultural, municipal and industrial organic waste streams is on the rise. Within the span of just a few days, we received press releases or article submissions on a half-dozen new projects or ones that have gone into operation.
This article highlights several facilities. More detailed articles on these operations will follow in upcoming issues of BioCycle. It is interesting to note that in each case, the partners pulled together to make the projects happen include public and private sector entities, as well as an academic institution. These collaborations provide insight into critical components necessary to move from the drawing board to operational reality and economic feasibility.
In late October, the University of California at Davis (UC Davis) announced that its large-scale demonstration anaerobic digester was starting to accept waste materials. The Biogas Energy Project uses a new technology developed in the past eight years by Ruihong Zhang, a UC Davis professor of Biological and Agricultural Engineering. The technology, called an anaerobic phased solids digester (APS), has been licensed from the university and adapted for commercial use by Onsite Power Systems Inc. (See “Biogasification Of Organic Solid Wastes,” January 2002 for a detailed description of the technology.) The APS digester uses a nonmechanical, hydraulic mixing system, and is designed to process organics with a solids content of around 30 percent. The system also processes liquid residuals. Acceptable feedstocks include food processing residuals, municipal and commercial organics (including yard trimmings) and agricultural wastes including manure and animal renderings.
Zhang proved in the laboratory on a small scale that in anaerobic, or oxygen-free, conditions, naturally occurring bacteria can quickly convert food and green wastes into hydrogen and methane gases. Now the challenge is to make the gases in consistently high quality and large volumes over the long term. “My UC Davis students and I have determined the efficient bacterial species and their favorite environmental conditions for turning various wastes into gases,” says Zhang. “We know what happens with bacteria in 10 to 5,000 gallons of water and waste. Now we expect to see those bacteria perform as well, if not better, when they are in 50,000 to 300,000 gallons.”
One of the first committed waste streams for the Biogas Energy Project are eight tons/week of leftovers (and later as much as eight tons daily) from restaurants in the San Francisco Bay area. Norcal Waste Systems, Inc. collects 300 tons/day of food residuals from 2,000 restaurants in San Francisco and 150 restaurants in Oakland. The bulk of that material goes to Norcal’s Jepsen Prairie Composting facility in Vacaville, California. For the UC Davis project, Norcal is delivering pulped food and green waste. “New technology like UC Davis’ offers California opportunities to harvest energy out of approximately 50 percent of the waste material that the state currently sends to landfills and to significantly reduce landfill disposal,” says Chris Choate, the firm’s vice president of sustainability.
Onsite Power Systems has invested almost $2 million in helping Zhang refine the technology and prepare it for transfer to the commercial market. The other major funding source for the research has been the California Energy Commission’s Public Interest Energy Research (PIER) program, which has awarded the university grants of nearly $1 million. Other supporters include: California Integrated Waste Management Board, with research grants of $125,000; Graybar, which donated computer controls for plant operations, valued at $50,000; Propane Education & Research Council (PERC), which contributed to the purchase of two propane-fueled boilers, a low-emission, California Air Resources Board-certified propane engine, and a generator for the project, valued at $32,000; and Norcal Waste Systems Inc., which is supplying the restaurant leftovers and yard clippings (“green wastes”), valued at $50,000.
Central Vermont Public Service (CVPS) in Rutland, Vermont developed an innovative renewable energy program that connects power from farm-based anaerobic digesters to customers in search of green energy. The utility’s Cow Power™ program provides customers a choice to receive all, half or a quarter of their electrical energy through anaerobic digestion of manure and other agricultural residuals, and pay a premium of 4 cents per kilowatt hour. The premium goes to participating farm-producers to purchase renewable energy credits (RECs) when enough farm energy isn’t available, or to the CVPS Renewable Development Fund. The fund provides grants to farm owners to develop generation capacity. Farm-producers are paid 95 percent of the market price for the energy sold to CVPS in addition to the 4-cent premium.
Blue Spruce Farm in Bridport, Vermont was the first CVPS Cow Power producer, starting in January 2005. Manure and other farm waste are held in a sealed concrete tank at 101°F, creating methane while killing pathogens and weed seeds. The biogas fuels an engine/generator; the electricity is fed onto the CVPS electric distribution system. Blue Spruce Farm recently added a second generator to increase its production. Several other farms are in the process of developing generators and are expected online late this year and in 2007.
Four farms recently received grant offers totaling more than $660,000 from the CVPS Renewable Development Fund to help get them started. They include: Green Mountain Dairy Farm in Sheldon, Montagne Farms in St. Albans, Newmont Farms LLC in Fairlee,, and Deer Flats Farm in West Pawlet.
CVPS also has signed a contract to purchase renewable energy credits and environmental attributes associated with the farm generation system of Berkshire Cow Power LLC in Richford, Vermont. It is just completing construction of a methane digester on its 2,000-cow Pleasant Valley Farms. The farm is not in CVPS’s territory, but the company is seeking permission from the Vermont Public Service Board to consummate the agreement. If approved, the deal will provide RECs and associated environmental benefits from approximately 3.5 million kilowatt-hours of generation.
Green Mountain College in Poultney, Vermont has become the first CVPS Cow Power campus. It is also the largest customer enrolled in the farm-to-consumer renewable energy program. “We focus on sustainability at every level, from how we teach to how we use energy,” says Bill Throop, Green Mountain College (GMC) Provost. “Enrolling in CVPS Cow Power will fundamentally change our environmental footprint and provide an excellent educational opportunity for our 750 students.”
One of the nation’s top liberal arts colleges, GMC has committed to 50 percent Cow Power for its main campus in Poultney, and enrolled the Killington campus, president’s house, campus farm, an inn and the alumni house at 100 percent. GMC is expected to purchase 1.2 million kilowatt-hours of renewable energy through CVPS Cow Power annually.
“GMC’s enrollment in Cow Power demonstrates a tremendous financial and philosophical commitment to improving air and water quality, farm economics and renewable energy in the Green Mountain State,” explains CVPS President Bob Young. “GMC is setting a high standard for itself and others who care about the environment.” Customers like GMC provide farms an opportunity to improve their manure management and their bottom lines.
The college’s commitment to sustainability has been evolving. Initiatives have included a campus-wide energy overhaul to low-flow toilets and shower heads, compact fluorescent light bulbs, remote-controlled thermostats, and wind and photovoltaic demonstration projects. “Cow Power is a great fit with our mission,” Throop adds. “It serves the region and the environment, two ideas we emphasize with students. As global warming looms ever larger, we need to go beyond teaching, and set examples for students and society at large. Nearly every department on campus allocated money in their budgets to help offset the cost increase of the program.”
Tim den Dulk’s dairy farm in Ravenna, Michigan will be home to a new anaerobic digester that will process manure from the 700-plus cow operation. Construction of the dairy farm biomass conversion plant was announced in mid-October by the Michigan Public Service Commission, Grand Valley State University (GVSU), and farmer Tim den Dulk. It will utilize the EnTec biogas gmbh system from Austria. “This is the first EnTec system to be built in the United States,” says Sarah Lineberry, Biomass Project Manager at the Michigan Alternative and Renewable Energy Center (MAREC) at GVSU in Muskegon. “It has a continuous stir tank reactor, which is critical to yielding a high biogas production rate, and a hydrogen sulfide scrubber that uses a proprietary bacterial technology.” The scrubber will be installed between the digester and the gas holding tank.
The project is being conducted with MAREC and is funded with a $1 million grant from the Michigan Public Service Commission. The den Dulk farm will contribute $1.2 million for the site preparation required to host the biodigester. A Capstone microturbine and gas preparer that was purchased by MAREC with a Department of Energy grant for another project will be placed on the dairy farm. The den Dulk Dairy also will be purchasing a reciprocating engine to utilize the remaining biogas. All the electricity generated will be used by the den Dulk dairy farm operation.
The digester being installed is 48 feet in diameter and 47 feet tall. The manure will be kept in the digester tank for an average of 21 days at around 98.6°F. Biogas is expected to have 60 percent methane content. Site prep is scheduled for December, with tank installation starting next February. “We are looking for full completion of the digester tank by June, after which we expect it will take six to eight weeks to get the acidification in the right range for bacteria proliferation,” says Lineberry. “We hope to be at 100 percent organic load by August 2007.”
MAREC was established as a SmartZone created by the Michigan Economic Development Corporation in 2001 as part of an effort to promote and attract high technology business development in the state. It functions as a R&D facility, an educational facility, and a business incubator for companies working on developing commercial applications for alternative and renewable energies. – N.G.

Sign up