The Energy Blog – by Andy Silber

This should never happen

On April 12th a lagoon holding cow manure failed, causing a spill of millions of gallons of waste into the Snohomish River. In the annals of industrial accidents this is pretty low on the horrific scale. But the tragedy is that the lagoon that failed should not have been there in the first place. Our attention is grabbed by failure and size, not by the slow, steady release of pollution that these lagoons routinely emit. As the manure breaks down methane, a powerful greenhouse gas, slowly rises, along with other noxious gases. In addition E Coli and other pathogens collect and are spread in fields when the manure is used as fertilizer.

This might be acceptable if it was a difficult problem to solve. But the opposite is true. Anaerobic digesters for dairy cow waste is a fully-realized commercial technology. In the digester the manure is eaten by bacteria in an oxygen-free environment and methane is created.  The gas is captured and can be used to power a generator, while the waste heat can be used to warm a barn or greenhouse or other farm uses. The manure in the digester is heated to a higher temperature than it would be in a lagoon, which kills off most of the pathogens like E coli. The benefits are many:

  • Improved air quality
  • Reduced greenhouse-gas emissions
  • Renewable electricity
  • Co-generation of heat for the dairy
  • Removed or greatly reduced risk of spills
  • High-quality bedding for the dairy cows
  • High quality fertilizer for the fields growing the feed for the dairy cows

A small percentage of dairy farms do have digesters, but most don’t. If they are so great, why doesn’t every dairy farm have one? This is a classic example of a market failure:

  • The farmer doesn’t pay for the reduced air quality, so he has no economic incentive to improve it.
  • The farmer doesn’t pay for the greenhouse-gas emissions, so he has no economic incentive to reduce them.
  • These projects are capital intensive and fall outside the expertise of the farmer, so the farmer doesn’t bother.

Though these projects do generate electricity and useful heat, the value of those products alone don’t generate enough revenue to make these projects happen. By selling renewable energy credits (RECs) and carbon offsets some projects do happen, but most dairy farms still use open lagoons to hold their waste. Since dairy farming is already a financially risky proposition, legislatures are loath to require digesters and the farmers are unwilling to invest in these projects themselves.

Even broad policy measures like Washington State’s I-937 and other renewable energy portfolio standards aren’t very effective in encouraging digesters. Utilities aren’t very interested in these projects because they are small (typically less than 1 MWatt or equivalent to less than one utility scale wind turbine) and more expensive than electricity generated at a large wind farm.  Also, these renewable standards still don’t capture all the value these projects have. Grants like those from the Department of Agriculture and the Recovery Act (Federal Stimulus) do help these projects happen, but not very quickly. A requirement for the largest dairy farms and Concentrated Animal Feeding Operations to install digesters would go a long way to bringing this technology into the mainstream, but I don’t expect to see that happen any time soon.

3 replies
  1. Bill
    Bill says:

    It used to be that the primary use of cow manure was to place fertility back into the fields. Lets remember that the most simple low-tech use of cow manure is fertilizer and not anerobic digestion to energy.

    Michael Pollan has made the excellent point that our over specialized and over industrialized farming system has taken what used to be somewhat of an agricultural ecosystem where the waste from one part of the farm from the animals was the nutrients needed to build the soils of the vegetable gardening. Unfortunately the farm bills we have have favored larger and larger farms and specialization and efficiency, putting small farms that produce at a more sustainable pace out of business. These small farms, because of the ecological cycling mentioned above were more environmentally sustainable.

    I kind of view anerobic digestion as a “least worst” senario. Yes toxic manure ponds present a big threat in their concentrated wastes, in the GHG emissions from methane, and from potential lost energy, but this is only if you accept Concentrated Animal Feeding Operations as acceptable at all, which I don’t from a sustainability perspective.

    Don’t by meat from souces that support such horrendous farming practices.

  2. Andy Silber
    Andy Silber says:

    Actually anaerobic digesters improve the quality of the nutrients that are returned to the field by composting the waste at a higher temperature and cooking out the pathogens. Even with the current typical practice of the lagoons the nutrients are sprayed onto the fields after composting for a time.

    Anaerobic digesters work at small dairy farms or CAFOs. I just feel they should be required at CAFOs and strongly encouraged at smaller, family farms. In either case they reduce the footprint of drinking milk and eating cheese.

  3. Bill Reiswig
    Bill Reiswig says:

    Why not just use the manure from small family farms to fertilize the fields? Why spend money and resources building a anaerobic digester when a simpler and less energy intensive good use already exists. I would not encourage them in this context.


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