The Growing Viability of Biomass

Release of the first comprehensive national system for mandatory reporting of greenhouse gas emissions (GHGs) in the United States is likely to change the lives of many farmers and ranchers across the country. With these new regulations, the Environmental Protection Agency (EPA) requires reporting by 25 industrial categories of direct emitting sources – which includes some farm facilities. The rule (40 CFR Part 98) requires reporting of methane and nitrous oxide emissions from facilities with manure management systems that emit GHGs of 25,000 metric tons or more CO2 equivalent per year, with some exclusions.

The mandatory reporting rule goes into effect this year; however, EPA cannot implement the manure management subpart in fiscal year 2010 due to a congressional restriction prohibiting spending any money for this purpose. Livestock operations will be required to report emissions under the rule likely beginning in fiscal 2011, which begins October 1. (Left: The anaerobic digester system on Bettencourt’s Dry Creek Dairy in Idaho. Courtesy Cargill)

The smallest operation that could be required to report is a swine operation with 34,100 head, a dairy herd with 3,200 head and a beef feedlot with 29,300 head (see graphic below). Higher thresholds depend on specific manure management practices and local climate.

One way a cattle operation can ensure it falls below the minimum GHG reporting requirements is to install an anaerobic digester, which will greatly diminish the methane the operation emits.

Biomass Basics

The EPA AgSTAR Program has successfully encouraged the development and adoption of anaerobic digestion technology. Since its inception in 1994, the number of operational digester systems has grown to 135 systems on dairy, hog and cattle farms across the United States. In 2008, roughly 332,100 MWh of energy was generated by anaerobic systems. Although projects of up to 5 MW are under construction, biomass energy accounts for only about 0.5 percent of the nation’s current power needs. There is much room to grow.

For example, anaerobic manure digesters are most common on dairy farms. In 2007, the EPA identified 95 dairy farms that have operational anaerobic digester systems out of about 59,000 licensed dairy herds in the nation.

EPA rules that take effect this year require emissions reporting for livestock operations with an animal count of at least:

In comparison, other parts of the world are already deriving significant benefit. A large number of on-farm digesters are in operation across Europe and other parts of the world. According to the Ontario Large Herd Operators Group, Germany has more than 3,700 anaerobic systems in operation, producing about 800 MW – enough to power 400,000 homes.

In 2008, a University of Texas at Austin study found that converting biogas into electricity using standard microturbines could produce around 88 billion kWh, or 2.4 percent of annual electricity consumption in the U.S. The process would also reduce U.S. GHG emissions by about 3.9 percent of the annual GHG emissions from electricity generation.


Biogas recovery systems incorporate an air-tight anaerobic digester – typically plug-flow or mixed reactor – with a biogas capture and combustion system. Organic material, such as animal manure, is fed into the anaerobic digester where the solids are separated and water is removed. A bacterium in the tanks breaks down the solids, releasing methane gas (biogas), carbon dioxide and other gases. The biogas is used to fuel a generator, where it is converted to electricity for use on the farm or sold to a utility.

Anaerobic digester technologies provide enhanced environmental and financial performance when compared to traditional waste management systems such as manure storage pits and lagoons. Anaerobic digestion is particularly effective in converting waste to methane gas, which can be collected for energy recovery. The systems reduce GHG emissions and provide other air and water pollution control advantages.

An AgSTAR report, Market Opportunities for Biogas Recovery Systems, and economic trade studies indicate that a farm owner should have more than 500 head of dairy cows or more than 2,000 swine to make anaerobic digestion financially viable. Average per-cow gas generation equals about 2.5 kWh per day.

Beyond power production, farmers are finding use for the digester solids created from the anaerobic process. Many use the solids as cattle bedding; in one example, an 8,000-cow dairy farm with an installed anaerobic digester system saved $1 million a year on cattle bedding.

Viability and Challenges

Some of the risks that have hampered earlier biogas projects have included capital costs, gas quality, operational challenges, finding a utility willing to buy the electricity at a price that makes the project viable and locating contractors able to design and install the systems. These issues are increasingly mitigated by new regulations and technological and efficiency improvements.

Raw biogas from dairy manure is typically 54 to 70 percent methane. The rest is carbon dioxide with trace amounts of hydrogen sulfide and other compounds. To improve the gas quality and remove harmful constituents that could have a corrosive effect on pipeline infrastructure, the raw biogas must be cleaned to increase its methane content and meet gas quality specifications. This is done by removing the H2S and CO2 from the biogas by absorption, adsorption or membrane permeation. Sulfur compounds react well with iron and zinc oxides to form insoluble sulfide compounds. Packed column water scrubbers can be used to remove hydrogen sulfide and carbon dioxide simultaneously. However, these applications require a large available water source. Adsorbent processes include molecular sieves or activated carbon.

Another area that often catches owners by surprise is the need for source testing, which can be expensive. Prior to construction, most systems require a degree of air quality impact analysis and permitting, environmental assessments and site surveys, as well as geotechnical study to ensure structural stability for the necessary equipment and structures.

Regulatory compliance in the form of air permitting is also a challenge. The EPA recently regulated emissions from stationary off-highway internal combustion engines. Anaerobic digester systems that include gensets likely would be regulated under this rule. The regulations impose performance obligations on genset manufacturers; however, owners must also complete compliance testing to demonstrate the engine emissions meet the federal standards. (Left: The generator set used in an anaerobic digester system on a dairy farm. Courtesy Kleinfelder)

Emerging Opportunities

Dairy farms may use biogas produced from anaerobic digesters to generate on-site electrical power, fuel boilers and produce hot water. However, if farm owners wish to sell the excess electricity to utilities or meter the gas into a pipeline, they must consider the cost of interconnection and transmission infrastructure, such as a pipeline between the biogas plant and the network injection point.

Despite the risks, the biomass energy business is poised for growth with support from federal and state funds, as well as development of more affordable, off-the-shelf commercial technologies; and some innovative pioneers.

For instance, Northern Natural Gas is injecting dairy-manure-based biogas generated at Emerald Dairy in Emerald, Wis., into its natural gas grid with the help of Agri-Waste Energy. The dairy produces energy from the manure of 4,000 cows, which is transported by tube trailer. BioEnergy Solutions helped the dairy process manure from the dairy through anaerobic digesters to produce methane gas, which is metered into a nearby Pacific Gas & Electric natural gas transmission pipeline.

And Cargill built a 2.25 MW digester/genset system for a 10,000-head dairy operation owned by Bettencourt Dairies LLC, near Twin Falls, Idaho. The project started producing power in August 2008 and Cargill is currently developing two additional dairy digester projects in Idaho.

Similar biogas projects are planned or are in development across the country. With more than 65,000 dairy farms in the U.S. producing over 1 million pounds of manure every day, the potential to create renewable energy, cut GHG emissions and meet federal and state regulatory requirements is simply too great to ignore.

Andy Marshall, PE is a principal for AP Marshall & Associates assisting clients with the development and planning of renewable energy projects. He can be reached at

Blair Loftis is the director of renewable energy for Kleinfelder. He can be reached at

Previous articleAnalyst: SMA dominated PV inverters in 2009, but others gaining
Next articleWindurance Gets ISO 9001 Certification

No posts to display