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• At least one error?
  "Manure is also nobody's friend. It can cause algal blooms--an increase in algae in aquatic systems--and other problems."
  
  Algal blooms is caused by excess phosphorus. The methane in natual gas is CH4. Do you see any P in that formula? The phosphorus remains and will probably be land-applied just the way the manure originally would have been, meaning it's subject to the same runoff that manure is. So this digester really doesn't solve the algae problem and probably makes it worse because now the P is more concentrated than the manure P.
  
  Did the author actually think the P just disappears?
  
  Shipping manure which is mostly water to the digester from farms, then shipping solids back to the farms is extremely expensive in terms of equipment, labor and energy. An interesting question for the author to have asked is what the net energy is from the process? And what government subsidies are involved?
  
  Having the digesters on-farm perhaps makes more sense.

  March 28, 2007

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