Cellulosic Biomass Ethanol Production
    Cellulosic biomass production of ethanol is still being researched but it is expected to be the most energy efficient and cost efficient if it reaches mass production.  This ethanol process can have a net energy content three times higher than corn based ethanol.  Cellulosic biomass production uses the entire plant instead of just the starchy material as in corn based ethanol.  This means that much of the agricultural waste we have now (left over corn stalks) can be used to produce ethanol.  However this process will remove nutrients from the soil instead of returning the nutrients from the plant to the soil.  Besides agricultural waste a wide variety of plants can be used to created ethanol using this process including willow, switchgrass, sugarcane, soybeans and others.  Because the whole plant is used which has a lot of cellulose and other complicated sugars special enzymes have to be used to break down these long sugars into fermentable ones.  It is these enzymes which are currently making the cellulosic ethanol more expensive.  
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