IMPLEMENTING THE CONCEPT
ANAEROBIC DIGESTION ADVANCES
New projects are recovering methane and producing compost from varied feedstocks that range from yard trimmings to livestock manures.

Jerome Goldstein

Organics recycling projects using anaerobic digestion systems are getting underway in different regions of the United States, indicating that the first decade of the new millennium will see rapid growth in this conversion technology. Municipal, commercial and agricultural feedstocks are being loaded into digesters to produce methane gas and high-quality fertilizer.

The latest site is located at the White Street Landfill in Greensboro, North Carolina, where an anaerobic fermentation composting facility is scheduled to begin loading this month. It’s designed to process approximately 30,000 tons per year of yard trimmings. Several local food processing companies that are now paying to have their high-nitrogen waste streams buried in landfills are expected to utilize the new facility.

Duke Engineering & Services (DE&S), based in Charlotte, teamed up with the city of Greensboro to develop the project. DE&S invested two-thirds of the required capital, with the city financing the remaining one-third. DE&S will operate the facility, with profits to be shared proportionately. Duke has peen working with city officials on a gas recovery operation at the White Street Landfill, adjacent to the site where municipal yard trimmings have been composted since 1992 under a contract with O.M. Scott & Sons. When Scott indicated it was phasing out its compost site management operations, Greensboro sought a new private operator. The satisfactory working relationship in the landfill gas recovery project led to the city choosing Duke to process its yard trimmings.

“Right now, we’re expecting to get a demonstration permit from the North Carolina Department of Natural Resources to operate the facility,” says Wayne Turner, the city’s Waste Reduction Superintendent and Recycling Coordinator. “Since the state banned landfilling of yard trimmings in 1992, regulations have been around open windrow composting. Our demonstration permit will show that anaerobic digestion (AD) is viable for green waste.” According to Turner, the city is interested in targeting other organic feedstocks in its waste stream to provide long-term solutions and value-added products. “Waste reduction is actually secondary. Our goal,” he explains, “is to generate a premium compost product using AD technology.”

RENEWABLE ENERGY AT DUKE

Three years ago, as part of the industry deregulation, Duke Energy Company formed a “Renewable Energy Corps Team” to explore technologies in the emerging renewable energy market. “Our first AD project was at Smith Farms in Princeton, North Carolina dealing with caged poultry,” says Harold Backman, Strategic Initiatives Manager for Duke Engineering & Services. Greensboro is the utility’s second AD venture.

As explained by Duke spokesperson Tommy Smith, Duke Engineering and the Corporation for Future Resources of Tallahassee, Florida provided the proprietary technology for the anaerobic fermentation process. “Bacteria that thrive in an oxygen-free environment at approximately 95°F,” notes Smith, “will convert the biomass material into water, nitrogen-rich compost and biogas in a totally enclosed process.” Biomass decomposition is confined to three digester tanks, each approximately 670,000 gallons in capacity. Plans call for sale of biogas to a nearby industrial customer as boiler fuel, with compost marketed to the public and water recirculated in the system.

At the end of the year, there were about 10,000 tons of leaves and trimmings on-site ready to be put through the tub grinder and screens. That quantity — mostly loose leaves from the city’s fall collection program — will be supplemented over the next 12 months by deliveries of 15,000 tons of bagged trimmings plus 5,000 tons of woody residuals(including pallets) from private haulers. “This is an important demonstration project for us and the emerging AD industry,” sums up Backman. “We see ourselves in the development mode during this first year. Meanwhile, we expect to be launching additional projects elsewhere in the nation.” The Greensboro project will be using an innovative arrangement of doubledecker tanks, which feature a 250,000 gallon slurry preparation tank atop a 350,000 gallon process water tank.

“Our approach is that compost from our AD system is more valuable than energy,” says 72-year-old Richard Glick, founder of the Corporation for Future Resources (CFR) and a former chemistry professor at Florida State University. Glick designed his fermentation technology mainly to process fast-growing plants such as Leucaena — a giant, perennial woody legume with a high nitrogen content and annual yields up to 25 dry tons per acre. “We grow it on land that can’t be used for much else, like reclaimed phosphatic clay soil,” adds Glick who provides the following information about his system:

“The proprietary anaerobic fermentation process is closed cycle so that nothing is discharged into the environment. The methane produced can be used under the most efficient energy-to-work conditions, i.e., on both an electrical and thermal basis, without particulate impact on the atmosphere. Returning substantial quantities of biomass produced carbonaceous compounds to the soil, that would have otherwise been released to the atmosphere under classical biomass burn conditions, further accomplishes carbon sequestration objectives related to reducing atmospheric carbon dioxide.”

HOGS, COVERED LAGOONS AND GREENHOUSE TOMATOES

Working with researchers at North Carolina State University, hog farmer Julian Barham built a biogas digester to control odors from his 4,000 sow, farrow-to-wean operations. His covered lagoon system allows biogas from the manure to be collected and transferred to an engine generator. The system is connected with Carolina Power and Light, but it mostly generates electricity for the farm. Total cost for the cover, lagoon and generator is estimated at $300,000.

Currently, the farm’s lagoon water is used to irrigate fields of Bermudagrass, but Barham is about to implement a new approach on his Zebulon, North Carolina farm. It’s growing tomatoes inside a greenhouse with heat coming from the digester and irrigation from the wastewater.

“We’re building the greenhouse right now and hope to have the 30,000 square foot structure covered with plastic and ready for planting tomatoes by February,” Barham told BioCycle in mid-December. NCSU faculty have done experimental work using wastewater and early results look promising. They expect that hot water from the digester will provide enough warmth until outside temperatures drop below 38°F.

PARTNERSHIP APPROACH MOVES DIGESTER PROJECTS

For approximately 20 years, Richard Mattocks of Environomics in Riverdale, New York and Mark Moser of Resource Conservation Management (RCM) in Berkeley, California have played key roles in AD progress. Last week Mattocks sent us the following summaries of farm projects using RCM digesters. “I thought you might appreciate a symmetrical approach,” Mattocks wrote. “Mark Moser is the design engineer for the RCM digester. I’m fortunate to be able to work with him.”

AA Dairy, Candor, New York

The reasons for construction of the mesophilic plug flow digester with plastic liner top were to control odors and reduce water quality risk at a 1,000 cow confinement operation generating 8,000 to 10,000 gpd of manure. Total system cost was $240,000 with annual O&M at $15,000. Gas production is calculated at 40,000 CF/day (4,000 tons/year CO2 equivalent); electrical energy is 500,000 kWh/yr; and thermal energy generated is 2,500 MMBtu/yr. Completed in 1998, the digester was installed as part of the Dairy’s plan to reduce its environmental impact on the community. It was the recipient of the New York State Governor’s Environmental Award for 1999.

Crestland Coop, Thayer, Iowa

Odor control was the primary reason for construction of an intermittent mix, mesophilic digester at a 5,600 sow farrow-to-wean operation generating 22,000 gpd of manure. Total system cost was $550,000 with annual O&M cost estimated at $9,000. Gas production is 30,000 CF/day (3,000 tons/yr CO2 equivalent); electrical energy is 600,000 kWh/yr; and thermal energy generated is 3,300 MMBtu/yr.

Haubenschild Dairy, Princeton, Minnesota

Three reasons for construction are odor control, reduced water quality risk, and energy utilization at a 1,000 cow confinement operation generating 8,000 to 10,000 gpd of manure. System cost came to $250,000 (with $40,000 of the engineering cost supplied by the federal AgSTAR program)and annual O&M estimated at $7,500. Gas production is 40,000 CF/day (4,000 tons/yr CO2 equivalent); electrical energy is 500,000 kWh/yr; and thermal energy produced is 2,500 MMBtu/yr. Recovered hot water is used for floor heating in the parlor area, with plans to heat alleyways in the new barn now under construction.

Colorado Park, Lamar, Colorado

Primary reason for construction intermittent mix, mesophilic digester at this 5,600 sow farrow-to-wean farm with up to 18,000 gpd of manure was odor control. System cost was $250,000 ($40,000 of engineering cost provided by AgSTAR) and annual O&M at $6,000. Gas production is 30,000 CF/day (3,000 tons/yr CO2 equivalent); electrical energy is 400,000 kWh/yr; and thermal energy produced is 2,200 MMBtu/yr.