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The Milk House

The viability of digesters in the dairy business PDF Print E-mail
Dairy basics - Manure


The EPA’s first comprehensive national system for mandatory reporting of greenhouse gas emissions (GHGs) in the U.S. requires reporting by 25 industrial categories of direct emitting sources – and dairy farms of certain sizes will most likely fall under this regulatory umbrella.

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 CO2 equivalent per year or more, with some exclusions. The smallest operation that could be required to report is a swine operation with 34,100 head, dairy with 3,200 head and beef feedlot with 29,300 head. Higher thresholds depend on the specific manure management practices put in place and local climate.

Based on current Congressional requirements, livestock operations won’t be required to report emissions under the new rule until early fiscal year 2011. Now is the time to put in place necessary reporting mechanisms or introduce systems to stay below the minimum GHG reporting requirements.

One way a dairy operation can keep GHG output below EPA minimums is to install a poop-to-power anaerobic digester system.

Biomass basics
Since the establishment of the EPA AgSTAR program in 1994, the number of operational anaerobic digester systems has grown to 135 systems on dairy, hog and cattle farms across the U.S. In 2008, these systems generated approximately 332,100 MWh of energy. Anaerobic manure digesters are most common on dairy farms. In 2007, the EPA identified only 95 dairy farms that have operational anaerobic digester systems. There are about 59,000 licensed dairy herds in the nation. In comparison, other parts of the world are already deriving a significant benefit.

In 2008, a University of Texas at Austin study found that converting biogas into electricity using standard microturbines could produce approximately 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.

Beyond the power production, farmers are also finding use for the digester solids created from the anaerobic process. Many are using the solids as cattle bedding. An 8,000- to 10,000-cow dairy can save hundreds of thousands of dollars annually on cattle bedding.

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

Some of the risks that have hampered biogas projects in the past 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 availability of contractors capable of designing and installing anaerobic digester systems. These issues are increasingly mitigated by new regulations and technological and efficiency improvements.

One area that often catches dairy owners by surprise is the need for source testing, which can be expensive. Prior to construction, most systems require a certain degree of air quality impact analysis and permitting, environmental assessments and site surveys, as well as geotechnical investigations 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 set emissions regulations for stationary off-highway internal combustion engines. Anaerobic digester systems that include gensets would likely be regulated under this rule. The regulations impose performance obligations on the manufacturers of gensets; however, owners must complete compliance testing to demonstrate that the engine emissions meet federal standards.

Emerging opportunities
Dairy farms may use the biogas produced from anaerobic digesters for on-site energy needs to generate electrical power, fuel boilers and produce hot water on the farm. However, if farm owners wish to sell the excess electricity to local utilities or meter the gas into a natural gas pipeline, they must consider the cost of the 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, Wisconsin, into its natural gas grid in Baldwin, Wisconsin, 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 assisted Vintage Dairy to supply biomethane directly into a nearby Pacific Gas and Electric (PG&E) transmission line. The project processes manure from the dairy through anaerobic digesters to produce methane gas, which is metered into a nearby natural gas transmission pipeline.

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

There are a number of similar biogas projects planned or in the works across the country. With over 65,000 dairy farms in the U.S. that will produce over 1 million pounds of manure every day, the potential to create renewable energy, decrease GHG emissions and meet federal and state regulatory requirements is simply too great to ignore.  PD

Blair Loftis is the director of Renewable Energy for Kleinfelder. He can be reached at This e-mail address is being protected from spambots. You need JavaScript enabled to view it

Andy Marshall

Andy Marshall
Principal
AP Marshall & Associates
This e-mail address is being protected from spambots. You need JavaScript enabled to view it

 

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