Biofuel Production Byproducts as Soil Amendments

Abstract

Attempts to reduce reliance on fossil fuel as the sole source of energy has resulted in production of energy from different organic materials. Due to increasing demand worldwide, production of energy from renewable sources has been growing rapidly, and it was estimated in 2002 to contribute to 14% of the world’s energy supply. Several technologies such as biochemical, fermentation, thermo-chemical, gasification and pyrolysis, chemical extraction, and transesterification processes have been employed to convert organic materials to energy. These technologies ­produce not only energy, but also valuable byproducts which include distillers grain, thin stillage, glycerol, ash and biochar. Due to the growing bioenergy production industry, there will be an abundance of byproducts being generated. Recently, some of these byproducts are disposed of by incineration, e.g. glycerol, or landfilling, e.g. ash. This disposal may have adverse effects on the environment. Therefore, a proper method, which can be economically sound and environmentally safe, needs to be sought. As these byproducts are organic and contain carbon and plant nutrients that are potentially valuable to soils and production of crops, consideration of potential uses of the byproducts must include their application to soil. Carbon and other plant essential nutrients in the byproducts can be added to soil and recycled. If fed to animals, such as in the case of distillers grain and thin stillage byproducts, manure is produced containing a higher content of nutrient compared to animals fed regular grain. This type of manure may hurt the environment if not properly managed. The potential for recycling nutrient in soil-plant system through direct or indirect application of bioenergy ­byproducts is not widely ­covered in the literature. This review covers relevant information on the potential use of bioenergy production byproducts as soil amendments and organic fertilizers in agricultural lands, and considers opportunities for future applications.

We found that direct application of distillers grain to soil benefited crop growth, suppressed weeds, and was accessible by soil microorganisms, resulting in organic matter decomposition and therefore contributing to nutrient release and availability for plant uptake. Thin stillage use as a soil amendment has not widely been practiced, and there is a lack of documented information in this regard. It was found to be a viable source of nutrient and provided plant essential nutrient; however, its residual effect on crop production was more evident than its direct application effect. This indicates the slow release of nutrients from thin stillage organic matter persisting into the following growing seasons. Compared to the other byproducts covered in this review, glycerol was the least studied bioenergy production byproduct as a soil amendment. It was found that glycerol application to soil at a high rate of 1,000 kg ha⁻¹ reduced the yield and N uptake and related this to a possible immobilization of available N by soil microorganisms. It was demonstrated in the most reviewed studies that ash application to soil increased crop yield and nutrient uptake, especially P and K. Biochar addition to soil contributed to crop yield increase, and this was attributed to reduction of nutrient losses, resulting in enhancement of nutrient use efficiency. Besides its agronomic benefits, it was reported in some studies that biochar application could have environmental benefits through its ability to reduce nutrient loss by leaching and runoff, absorb pesticides and mitigate greenhouse gas emissions. Inclusion of distillers grain in animal diets was found to have a significant effect on manure nutrients content and forms. This will promote including this type of manure in farm management plan and make it more valuable as organic fertilizer.