Then up on a hill, there appears a dome-capped silo...

Over the years, the oft-maligned dairy cow in this country has been blamed for a number of local, national and international ills including the great Chicago fire, childhood obesity and global climate change. It's encouraging to see that some savvy systems thinkers have developed systems that provide Bessie and Elsie with opportunities to impact climate change in positive way by transforming their waste into renewable energy. (GW)

Dairy farm feeds grid with manure and food waste

by Martin LaMonica
Green Tech
April 4, 2011

RUTLAND, Mass.--The road up to Jordan Dairy Farm here offers a typical New England view of rolling hills, wood-frame houses, and shade trees. Then up on a hill, there appears a dome-capped silo, a structure that's bringing renewable energy to agriculture.

The silo-like building is an anaerobic digester, one of five that will be installed at small dairy farms here in western Massachusetts. If they perform as hoped, they will allow these farmers to reduce their wastes and make some money in the process. They will also recycle food residue that would normally be thrown away.

The digester, which is expected to go online in the coming weeks, will convert cow manure from this family-owned dairy farm and food wastes into biogas. That biogas will be pumped into an adjacent generator to make electricity that will be fed to the grid, giving owner Randy Jordan additional revenue beyond milk. Any residual material will be converted into animal bedding and fertilizer for his fields.

Anearobic digesters have been on farms for years and even the people behind this project admit that most have fallen into disuse. But the project's organizers have changed how things have traditionally been done, creating a model for these dairy farms to earn some money and reduce their environmental footprint.

"Getting a methane digester has been a dream for more than 10 years," Jordan said standing in a barn that houses his 300 head of dairy cows. "We could have done it with just manure but then we would have had to hire another man just to run it and the numbers didn't work out."

In this case, both manure and liquid food waste from food processing plants will be shipped in, giving the operation more waste volume and more biogas. Farms are part investors along with New England Organics, a division of Casella Waste Systems, which will operate the facility. Since the operation will be making renewable energy, it benefits from a 30 percent federal tax credit.

The most significant difference from the majority of farm digesters is that these farms will be making electricity. The 300-kilowatt generator will run on the biogas, a combination of 60 percent methane and 40 percent carbon dioxide, and will operate around the clock, producing an estimated $20,000 a month in additional revenue and enough to power about 2,000 homes, according to New England Organics.

Progressive policies also made the project possible, said Jay Kilbourn, director of business development at New England Organics, who was one of the leaders of the tour organized by MassRecycle here last week. In 2008, Massachusetts passed a law that allowed distributed generation systems to get full retail price for electricity fed to the grid, rather than the much lower wholesale price.

But because the project is unusual--there are two similar anaerobic digesters operating in Ohio--it still took about five years to go from concept to this point because the rules around permitting don't address this technology. "We had to deal with everything from the definition of biogas not being in the building codes to working with local fire officials, up to dealing with state officials at multiple agencies," Kilbourn said.

Using anaerobic digesters to turn organic material into biogas, which can be burned for heat or electricity, is far more common in Europe. But there has been growing interest in recycling organic material in the U.S. through municipal composting programs. Massachusetts is pushing for collection of organics, including food wastes, to boost the household recycling beyond paper, plastics, and yard waste.

The Jordan Farm generates about 10,000 gallons of manure every day. From the barn, manure falls through slots in the barn floor and is collected in a chamber below. Before, Jordan pumped the slurry and stored it until he could pump it onto his fields in the warmer months.



With the new system, the slurry will be pumped into a storage tank and mixed about half and half with liquid food wastes. The liquid food waste will come from food, juice, or milk processors, who typically have to pay for disposal of their waste, either as waste water or by incinerating the waste. In this case, the food processors will pay the farm to take the waste, which will be transported in trucks.

Eventually, New England Organics intends to get feed stocks, in the form of a slurry, from restaurants or grocery stories, said Kilbourn. Wastes need to be separated at the source so they aren't comingled. In the second phase of the project, the company envisions an organic material recycling center in the metro Boston area.

To make the biogas, anaerobic digesters rely on naturally occurring microbes that digest organic material and give off methane and carbon dioxide gas. The digester operates with no oxygen at about 100 degrees Fahrenheit. A combined heat and power unit will use the heat from the generator to keep the temperature high and to dry residual material. The starter microbes will come from other digesters.

Inside the silo-like structure is a column into which the waste is pumped and where the gas is produced. At the top of the column is a flexible membrane that expands during digestion. Designed as a continuous process, gas is siphoned off and sent to the generator. To maintain the correct milkshake-like consistency, the slurry is aerated at the barn and mixed with big propellers once inside the digester.

Any residual material after gas has been produced will be dewatered, creating a fiberous material that can be used for animal bedding. The remaining liquid will be pumped to a storage tank where it will be used to fertilize fields. Since nothing is thrown away, both the energy content and nutrients will be recycled, noted Kilbourne.

The farms anticipate getting slightly different food feedstock, so getting the biology right can be tricky process, said Shannon Carroll, who will manage this and the four other anaerobic digesters. The digesters will be heavily instrumented with sensors and connected to the Internet so she can monitor the status of the plants from a PC and remotely control gauges or other settings.

New England Organics said the project will cost about $2.5 million, although Kilbourn declined to say what the exact return on the investment is. He said the farms will get a steady financial return in the form of revenue from electricity. But there are significant environmental benefits to removing manure from lagoons, since methane is a potent greenhouse gas and all the organic material is recycled, Kilbourn noted.

Jordan said this model could work just about anywhere with a sufficient volume of waste. New England Organics will operate the facility, which means he can continue to focus on farming, but he expects to learn how the digester works along with plant manager Carroll so he's ready when things go wrong.

Meanwhile, Jordan is already thinking about putting up a wind turbine on his farm. "Milk and power are both livelihoods for us," he said. "I want to do it all and I'll just keep cows as a hobby."

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