Fertilizer Potential of Biofuel Byproducts

Abstract

Ethanol and biodiesel production have become important industries worldwide. For example, ethanol production in the United States has increased exponentially from 6.0 billion liters in 2000 to 49 billion liters in 2010, an increase of 800% (RFA, 2011). Similarly, biodiesel production increased in the U.S. from 424 million liters in 2005 to 1,191 million liters in 2010 (NBB, 2011). These booming industries have not only changed how we view our automotive fuel, they have also forced us to consider uses for their valuable byproducts. The majority of ethanol produced in the U.S. is through the dry grind process. Dried distillers grains (DDGS) is the predominate byproduct of dry-grind ethanol production. It has been estimated that for every liter of ethanol produced, 3.5 kg of DDGS are left over (Rausch and Belyea, 2006). Based on the production estimates listed above, this would have equated to 34.9 million metric tonnes of dried distillers grain produced in the U.S. in 2010. Soybean oil and canola oil are the most commonly used vegetable oils for biodiesel production in the U.S. The oil is extracted from soybeans and canola seed through a process of cold-pressing, leaving behind valuable seed meal byproducts. An estimated 80% of soybean seed 60% of canola seed is left from the extraction process as seed meal, creating a significant quantity of this important byproduct (NBB, 2008; Herkes, 2010). The most common use of DDGS, soybean meal, and canola meal is for animal consumption as animal feed. DDGS, soybean meal, and canola meal contain an estimated 26, 47, and 35% crude protein, respectively, therefore these byproducts are considered highly valuable animal feed sources (Table 1). However, issues including over-saturation of DDGS in animal feed markets, animal feed quality issues, and the extremely high costs associated with oilseed meals has forced some biofuel producers to consider other markets for these byproducts. A potential market for DDGS and oilseed meals that biofuel producers may consider is the fertilizer/agriculture market. DDGS and oilseed meals are rich in plant macronutrients (nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and sulfur (S)) and plant micronutrients (zinc (Zn), iron (Fe), manganese (Mn), and boron (B)). In addition, these materials have a relatively low carbon-N ratios (ranging from 5:1 to 15:1), therefore these materials are highly decomposable and are able to release organic forms of N to plant available forms of N shortly after field application. This property is of particular interest to organic agriculture markets, where nutrient sources and fertilizers containing enough readily mineralizeable N to impact yield are scarce. The purpose of this chapter is to discuss byproducts of ethanol and biodiesel production as effective nutrient sources for plants. Specifically, we will cover 1) how these byproducts are