Building Farm And Food Scrap Digesters

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Courtesy of BioCycle Magazine

In the past several weeks, we received invitations to two ribbon cuttings for newly installed farm-based digesters — one at a dairy farm in western Massachusetts and another at a swine operation in North Carolina. We also received a press release from the University of California, Davis, about its new food scraps digester on campus. And then there were a few new projects that we had been tracking, but needed to reach out to for details.

A visible driver for project development, especially in New England, are state policies to ban disposal of organic waste streams. Connecticut’s law has been in effect, requiring generators producing >2 tons/week of commercial organics and located within 20 miles of a composting or anaerobic digestion facility to divert those organics. The Massachusetts disposal ban on commercial organics (for those generating >1 ton/week) goes into effect in October 2014. And Vermont’s Universal Recycling Law kicks in July 1 for commercial, institutional and industrial operations generating >2 tons/week of food scraps and located within 20 miles of an organics processing facility (to date, only composting sites are available).

Less of a driver, but still significant, are the renewable energy incentives. All of the farm digesters are selling power to the grid under fairly favorable arrangements. And the three projects profiled in this article all received federal Section 1603 funds (an incentive that is no longer available) to cover a portion of the fixed capital costs.

Part I of this article focuses on agricultural digesters. Part II, to appear in the July issue, focuses on merchant or institutional digesters processing primarily food waste streams (including two in development in Connecticut).
Barstow’s Longview Farm

The anaerobic digester installed at Barstow’s Longview Farm in Hadley, Massachusetts began operating at the end of December 2013, meeting the Section 1603 requirement to be operational in 2013. The digester facility was developed by BGreen Energy, a special purpose company comprised of the facility investors and owners. “It is the same project development model we used under the name AGreen Energy, the entity created for the digester at Jordan Dairy Farm in Rutland, Massachusetts, which began operating in the spring of 2011,” explains William Jorgenson of AGreen and BGreen Energy. “But the shareholders are different. In both cases, the farms have significant ownership in the digesters.” Also in both cases, Casella Organics, a regional resource management and recycling company, is a partner and supplies the source separated food waste as well as operates the digesters.

A 600,000 gallons capacity RCM digester was installed at Longview Farm, along with three receiving tanks for food waste. (Jordan Dairy’s digester was supplied by quasar energy group.) “We take so many different feedstocks and know the energy level of each because we monitor all incoming loads once the baseline testing is done for each source,” explains Jorgenson. “We store these materials based on the energy level, e.g., glycerin goes into the ‘high energy’ tank and whey goes into the ‘low energy’ tank. Then we mix and dose these substrates in to maximize the gas, and thus the power output, of the system.” He adds that the recipe at both the Jordan and Longview dairy digesters is about one-third manure and two-thirds food waste. At Jordan Farm, with 375 cows, that equals about 20 to 25 tons/day of manure and 45 tons/days of food waste. On Longview Farm, with 250 dairy cows, manure is about 20 tons/day and food waste is about 30 tons/day.

“What we are learning, based on our experience at Jordan Dairy, is how much better we can do with energy production given the amount of material received,” notes Jorgenson. “The industry needs to realize that every renewable energy feedstock becomes a determinant of business profitability and that the availability of that feedstock will be more competitive overtime. And we need to plan for the long term — we need to produce as much power out of every ton of feedstock we get as the day will come when we will be paying for feedstock and have to be maximizing energy generation.” Longview Farm started out with a 350 kW engine, with the intention of going to a 500 kW engine within a year. (Jordan Dairy started out with a 350 kW and now operates a 500 kW unit.) Both installations use Guascor engines supplied by Martin Machinery.

The Commonwealth of Massa-chusetts has a net metering law, requiring utilities to pay retail price for all distributed power (such as from anaerobic digesters) put onto the grid. In addition, the distributed power generator retains ownership of the Renewable Energy Credits (RECs), and has the right to sell those as offsets to other entities. “This is huge,” says Jorgenson. “We get paid retail rates for electricity and sell our own RECs.”

In the case of the AGreen and BGreen projects, one buyer of the power is Agri-Mark/Cabot Creamery Cooperative, one of the food processing companies sending feedstock to Longview Farms. Casella Organics initially was hauling whey buttermilk from the creamery to Jordan Dairy, which is 75 miles one way. The new BGreen digester, however, is 15 miles from the Creamery, improving the transportation economics of recycling the material — and Longview Farms is a member of the Agri-Mark dairy cooperative. “The energy credits for power we are buying represent 10 to 12 percent of the total electric bill for the creamery,” explains Jed Davis, Director of Sustainability for Cabot Creamery Cooperative. “From the perspective of Longview being a member dairy, in addition to providing us with milk, they are providing — via a ‘net metering credit allocation agreement’ — some of the load to run our facility. And we are closing the supply chain loop, so to speak, by sending our source separated organics to the dairy’s anaerobic digester.”

Casella arranges the service contracts with food processors and other generators, looking for longer term arrangements, ideally five years. At this time, food waste is only received via tanker trucks at both Jordan and Longview farms. “One lesson we learned early on is balancing our requirements for food waste inputs with those of food processors, who have their own production cycles and seasonal fluctuations,” notes Jen McDonnell, Director of Sales and Marketing for Casella Organics. “We were fortunate in that, given our customer mix, we ‘oversold’ our actual capacity at Jordan Farm, which gave us momentum in aggregating feedstocks to start up Longview Farm. We are managing the materials so each digester is able to absorb the excesses at different times.” Soon the digesters will get material from a Whole Foods Market in the Boston area that is doing the first commercial test of the Grind2Energy™ food waste slurry process (see “Grinding Food Waste For Bioenergy,” September 2013). This is the first retailer to be sending organics to the digesters.

The digester at Longview Farm is permitted under Massachusetts’ new General Permit, which allows it to process up to 100 tons/day of organic materials, including the manure. “There is significantly less expense and time involved in permitting a facility under this new rule,” says Jorgenson. “In exchange, we are required to comply with testing protocols, annual reporting and certify that these protocols are being followed. The Jordan Dairy digester was permitted under a Determination of Need, the previous permit for this type of operation prior to the state’s rule revisions in 2012. Jordan just switched to a General Permit this month.”

Liquid digestate is being stored on the farm to fertilize corn and hay. A plan is being tested to transport the digestate to an off-site storage tank at a nearby farm that has adequate acreage of sweet corn to utilize the nutrients as well. Jordan Dairy Farm grows about 450 acres of corn silage and 450 acres of hay (grass/legume mixes). It utilizes manure/digestate on approximately 350 acres of corn and 200 acres of the hay. A March 2014 progress report from the USDA Natural Resources Conservation Service in Amherst, Massachusetts states that “since applying the manure/digestate fertilizer on their hay lands, the Jordans have noticed that now most of their fields are yielding four cuts of hay rather than three cuts.” Manure/digestate is applied after the second, third and fourth cuts. “With the added fertility and moisture from the manure/digestate, hay yields have increased approximately 25 percent from an average of 4 tons/acre to 5 tons/acre,” notes the report, adding that the Jordans have saved about $40,000 in nitrogen fertilizer expenses by using the manure/digestate.

Read the full article in BioCycle Magazine

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