How A Manure Digester Works


How Does a Manure Digester Work? 

Farm Power News and Events  

Why Dairy Farms?


Watch KVOS 12's segment explaining how our digester works.

Dairy farmers are very aware of the value of their manure. They recycle the nutrients from cow manure by spreading it back on the fields. The manure fertilizes the crops so they will grow and create more food for the cows and thus more milk for humans. We call this process a closed loop, where the nutrients are used and reused in a continuous circle. Ecologically speaking, it is a good system. Dairy farming is much more sustainable than other forms of farming because the presence of animals and their manure constantly replenishes the soil. Still, the manure nutrient loop has some drawbacks. As you can see in the diagram below, storing manure creates odors and methane, a greenhouse gas.

Dairy Farm Nutrient Cycle Without Digester

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We at Farm Power believe that manure digesters can advance Skagit County dairy farming into the 21st century. A digester holds manure in an air-tight tank and heats it to about 100 degrees--just like a cow's stomach. Bacteria in the manure thrive in these conditions and they consume solids in the manure while releasing methane gas. We capture the methane gas at the top of the digester, and burn in a generator just like natural gas in an engine. The excess heat from the generator warms the digester.

Anaerobic Digester Diagram
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Farm Power insert's a digester into a dairy farmer's existing nutrient loop, so that all the raw manure is processed and then sent to the farmer for use on his fields. Instead of releasing methane into the atmosphere, however, we have captured all the methane biogas. When we burn that methane, we create lots of electricity that we sell to the utility company. We also create Green Tags, since the electricity we are selling comes from renewable sources. The Federal Government pays Farm Power tax credits for producing this renewable energy. Farm Power also can sell carbon offsets, since our digester causes a large net reduction in greenhouse gases. Finally, the digestion process creates a large amount of clean, pure fiber product that has many horticultural uses or can be used on the farms as cow bedding. The odor and the chance of runoff from the manure have been reduced or nearly eliminated. As you can see by comparing the two nutrient loops, a manure digester eliminates many problems with manure handling and generates a great deal of positives instead.

Dairy Farm Nutrient Cycle With Digester

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