Value Addition And Nutrient Recovery From Ethanol Coproducts

Abstract

Grain-to-ethanol production has increased steadily in the United States in the past few decades, which resulted in remarkable records in the availability of co-products. Dry-grind is the most common method of ethanol production worldwide, which concentrates the corn and yeast nutrients in the downstream operations. The industrial corn ethanol process consists of a series of chemical, physical and biological operations. Once the fermented corn mash is produced, it is then processed through a series of distillation and rectification, centrifugation and evaporation processes to generate ethanol and the main co-product, Distillers Dried Grain with Solubles (DDGS). Through a series of condensers, the stillage is dried to produce DDGS. Thus, protein, fat, fiber, and phosphorus concentrations are increased several fold in the DDGS compared with corn. The remaining nutrients from the ethanol distillation are the raw material for producing co-products. They are composed of proteins, fats, sugars, and some other lignocellulosic-derived compounds. In the United States, abundant research has been done in improving the quality of the ethanol co-products which yielded the ethanol industry to have animal feed production to be as relevant as the fuel ethanol production. The liquid fraction produced after the centrifugation of the bottoms of the ethanol rectifying and distilling operations is named thin stillage, produced at volumes several times greater than those of ethanol. A portion of thin stillage is normally recycled as backset water, while the remaining goes through a series of evaporations. Evaporating a large amount of water from thin stillage is an energy-consuming process and recycling the thin stillage may lead to the accumulation of nutrients in co-products in distiller’s grains. There are several other industrial processes to utilize thin stillage, such as oil extraction, anaerobic digestion, and secondary fermentation. Recently, promising results have been reported on the production of important commodity chemicals, extracting high-value products, and energy production from thin stillage. Phytate is the primary storage form of phosphorus and inositol in plants. The bioavailability of phosphorus bound to phytate is low for non-ruminants, and thus the phytate-derived phosphate ingested by these species (e.g. poultry and swine) is largely excreted, resulting in both nutritional deficiencies and environmental pollution. On the other hand, phytate is a widely applied valuable chemical as human nutrition, pharmaceutics, cosmetics, chelating chemical, and the raw material to produce myo-inositol. It is primarily produced from rice bran in Asia and imported to the US market. This creates a great opportunity for the US ethanol industry because extracting phytate as a new product from corn ethanol coproducts, knowing that corn germ has up to 5% phytate in its composition, can create additional revenue while increasing the feeding value of coproducts and decrease the phosphorus excretion in the animal manure. This dissertation also provides an overview on the new processes and products via valorization of thin stillage by innovative technologies that are being currently developed. It also provides the technical development background to develop an ion exchange method to extract phytate from thin stillage, as well as potential environmental benefits and further analyses on the impacts of phytate extraction implementation to ethanol plants. The novel application of thin stillage discussed in this dissertation could open new opportunities for the ethanol plants and ethanol researchers by increasing the revenue and simultaneously potentially reducing negative environmental impacts of ethanol production.