Good news out of Vermont: “Big Bertha,” the anaerobic digester at Vermont Technical College, is fully operational. The digester is utilizing cow manure and food waste to create electricity. It receives a diet of brewery waste, from two of Vermont’s local breweries, along with food waste and cow manure from Vermont farms, glycerol by-product from biodiesel production, leaves, and paper waste. It then sends power to the electric grid.
But that isn’t all. Big Bertha produces residual heat as she digests, used to heat campus buildings. The “waste” from her digestive process is reused as bedding for the college dairy, and provides nutrients for Vermont’s crop acreage. Soon, she will be the first anaerobic digester in the state of Vermont permitted to consume residential food waste, working to increase compliance with Vermont’s Universal Recycling Law, which ultimately bans food waste from landfills.
Big Bertha’s daily capacity is 16,000 gallons of manure and organic waste products, digestion of which produces an output of 8,880 kilowatt hours of electricity per day. This amount is equivalent to that of 200 gallons of heating oil, or enough to power 70 houses on a cold day, according to a press release from Vermont Sustainable Jobs Fund. One of 16 anaerobic digesters operating in the state, Big Bertha is helping Vermont to reach its goal of 90 percent renewable energy use by 2050. The 4.2 million dollar cost of the project was funded via the U.S. Department of Energy, and a bond from the Vermont State Colleges.
One of the challenges in making Big Bertha operational has been the proper formulation of feedstocks to produce biogas in an efficient, effective manner. Some feedstocks have led to issues such as clogged equipment, while others had not yet been tested on a large scale, leaving operators to develop the proper proportions and amounts, learning by doing.
Some issues encountered while formulating feedstock “recipes” have included a variety of bedding waste materials, from sawdust to wood chips, resulting in equipment complications; high levels of sulfur in feedstock, from hoof management in dairy herds, inhibiting digestion; and pH concerns with the glycerol by-product, requiring biodiesel producers to change their formulas.
The digester requires a balanced profile of feedstocks. It is a community digester, and as such is receiving its feedstocks from products available in the surrounding communities. Feasibility studies determined that food waste alone would not have offered enough input, at least not until food waste laws are fully implemented. Manure, however, is adequately available from Vermont’s small farms.
Big Bertha is permitted to increase food waste inputs to 7,700 gallons per day, or 49 percent of its feedstock. However, collecting this amount of pre- or post-consumer food waste could prove challenging in the rural Vermont locale, requiring inputs from a larger region.
Crops for Bioenergy
While Big Bertha and other anaerobic digesters create energy from a wide variety of organic waste products, bioenergy can also be produced directly from dedicated crops. The Biomass Crop Assistance Program (BCAP) was initiated to enhance the available supply of cellulosic bioenergy crops, including grasses or short-rotation woody perennial crops such as shrub willow or poplar.
These dedicated bioenergy crops are not food crops, for people or livestock, and therefore are not diverted from the food stream. Theoretically, these crops would be grown on marginal lands not suitable for food crop production.
According to a paper published by Choices Magazine, finding private landowners willing to grow these crops on their land has been challenging.
According the report, “Inconvenient Truths about Landowner (Un)Willingness to Grow Dedicated Bioenergy Crops,” by Bradford L. Barham, Daniel F. Mooney, and Scott M. Swinton, BCAP has enrolled 900 landowners, and 49,000 acres across the country, far short of the project’s intended goals. The report was based on surveys of landowners and farmers in Michigan and Wisconsin.
While enrolled acreage has fallen short, so has the type of land being utilized. Instead of marginal lands, most bioenergy crop production via the program has been grown on existing cropland. Although marginal land is available, the authors ascertain that the amount of marginal land is not adequate, even if dedicated bioenergy crops were bringing in high returns, and available land was fully utilized.
If farmers and landowners do opt to grow bioenergy feedstocks, cropland already in use is more likely to be converted to bioenergy crops than are marginal lands. The authors found that landowners willing to shift their land to production of dedicated bioenergy crops, even at very high rental rates, remain low.
“The scarcity of marginal land arises because for many landowners, such lands are not ‘in play’ for production. Amenity value is one reason, but transaction cost and inertia play roles as well. Hence marginal lands for bioenergy crops can be economically scarce despite being physically abundant,” the authors conclude.
They also found that the most common bioenergy feedstock crop was corn stover. Corn is a familiar crop, has many uses, and producing it for grain as well as for stover requires no real additional risks or investments. It is also not perennial, so rotating into and out of production quickly is possible.
Crops grown for oil production can include sunflowers, canola, and soybeans. When pressed, the seeds release oil which can be used for livestock feed, human use, or as a fuel. The oil can be used in a diesel engine, with little modification, creating a renewable source of energy and reducing fossil fuel use. Biodiesel production can occur on-farm, as well as in commercial processing facilities.
The National Sunflower Association touts the production of sunflowers for biodiesel. According to their reports, sunflowers can produce 600 pounds of oil per acre.
These crops are often good rotational crops in many cropping systems, so they can be used to enhance the soils as well as produce a renewable fuel source. And, as they are annuals, growing them does not require a long-term commitment.
Depending on Farmers
Farmers can produce bioenergy feedstocks in a variety of ways. Crop residuals, such as corn stover; crop refuse, such as vines or plants; sustainable woodlot harvesting or by-products from forestry operations, such as wood chips or sawdust; non-marketable produce; manure and livestock bedding; dedicated acreage for bioenergy crop production; spoiled livestock feeds; or food waste from those involved in on-farm value-added processing can all become bioenergy feedstocks.
While some of these inputs are simply by-products of typical farming activities, dedicating land for bioenergy crop production — particularly perennial feedstocks — has yet to become widespread. Dedicated perennial bioenergy crops can serve other purposes, such as grassland bird habitat, or be used for livestock bedding, so other markets are often available to limit the risk of growing a crop for the bioenergy sector.
Whether incorporating on-farm anaerobic digesters to digest organic waste and produce energy, growing bioenergy crops for the marketplace, or producing their own biobased fuels for on-farm use, farmers today have the opportunity to play a pivotal role in creating — and using — energy derived from renewable resources, making farming an activity which can actively contribute to reducing the effects of climate change, while feeding people and animals.