The ethanol industry is dynamic and has been evolving over the years in order to overcome various challenges associated with both fuel and coproduct processing and use (Rosentrater,

2007) . A modern dry grind ethanol plant is considerably different from the inefficient, input­intensive Gasohol plants of the 1970s. New developments and technological innovations, to name but a few, include more effective enzymes, higher starch conversions, better fermentations, cold cook technologies, improved drying systems, decreased energy consumption throughout the plant, increased water efficiency and recycling, and decreased emissions. Energy and mass balances are becoming more efficient over time. Many of these improvements can be attributed to the design and operation of the equipment used in modern ethanol plants. A large part is also due to computer-based instrumentation and control systems.

Many formal and informal studies have been devoted to adjusting existing processes in order to improve and optimize the quality of the coproducts which are produced. Ethanol companies have recognized the need to produce more consistent, higher quality DDGS which will better serve the needs of livestock producers. The sale of DDGS and the other coproducts has been one key to the industry’s success so far, and will continue to be important to the long-term sustainability of the industry. Although the majority of DDGS is currently consumed by beef and dairy cattle, use in monogastric diets, especially swine and poultry, continues to increase. And use in non-traditional species, such as fish, horses, and pets has been increasing as well.

Additionally, there has been considerable interest in developing improved mechanisms for delivering and feeding DDGS to livestock vis-a-vis pelleting/densification (Figure 10). This is a processing operation that could result in significantly better storage and handling characteristics of the DDGS, and it would drastically lower the cost of rail transportation and logistics (due to increased bulk density and better flowability) (Figure 11). Pelleting could also broaden the use of DDGS domestically (e. g., improved ability to use DDGS for rangeland beef cattle feeding and dairy cattle feeding) as well as globally (e. g., increased bulk density would result in considerable freight savings in bulk vessels and containers).

There are also many new developments underway in terms of evolving coproducts. These will ultimately result in more value streams from the corn kernel (i. e., upstream fractionation) as well as the resulting distillers grains (i. e., downstream fractionation) (Figure 12). Effective fractionation can result in the separation of high-, mid-, and low-value components. Many plants have begun adding capabilities to concentrate nutrient streams such as oil, protein, and fiber into specific fractions, which can then be used for targeted markets and specific uses. These new processes are resulting in new types of distillers grains (Figure 13).

Fig. 13. Examples of traditional, unmodified DDGS and some fractionated products (e. g., high-protein and low-fat DDGS) which are becoming commercially available in the marketplace.

For example, if the lipids are removed from the DDGS (Figure 14), they can readily be converted into biodiesel, although they cannot be used for food grade corn oil, because they are too degraded structurally. Another example is concentrated proteins, which can be used for high-value animal feeds (such as aquaculture or pet foods), or other feed applications which require high protein levels. Additionally, DDGS proteins can be used in human foods (Figure 15). Furthermore, other components, such as amino acids, organic acids, or even nutraceutical compounds (such as phytosterols and tycopherols) can be harvested and used in high-value applications.

Mid-value components, such as fiber, can be used as biofillers for plastic composites (Figure 16), as feedstocks for the production of bioenergy (e. g., heat and electricity at the ethanol plant via thermochemical conversion) (Figure 17), or, after pretreatment to break down the lignocellulosic structures, as substrates for the further production of ethanol or other biofuels.

In terms of potential uses for the low-value components, hopefully mechanisms will be developed to alter their structures and render them useful, so that they will not have to be landfilled. Fertilizers are necessary in order to sustainably maintain the flow of corn grain into the ethanol plant, so land application may be an appropriate venue for the low value components.

As these process modifications are developed, validated, and commercially implemented, improvements in the generated coproducts will be realized and unique materials will be produced. Of course, these new products will require extensive investigation in order to determine how to optimally use them and to quantify their value propositions in the marketplace.

Fig. 15. As a partial substitute for flour, high-value DDGS protein can be used to improve the nutrition of various baked foods such as (A) bread, (B) flat bread, and (C) snack foods, by increasing protein levels and decreasing starch content.

5. Conclusion

The fuel ethanol industry has been rapidly expanding in recent years in response to government mandates, but also due to increased demand for alternative fuels. This has become especially true as the price of gasoline has escalated and fluctuated so drastically, and the consumer has begun to perceive fuel prices as problematic. Corn-based ethanol is not the entire solution to our transportation fuel needs. But it is clearly a key component to the overall goal of energy independence. Corn ethanol will continue to play a leading role in the emerging bioeconomy, as it has proven the effectiveness of industrial-scale biotechnology and bioprocessing for the production of fuel. And it has set the stage for advanced biorefineries and manufacturing techniques that will produce the next several generations of advanced biofuels. As the biofuel industry continues to evolve, coproduct materials (which ultimately may take a variety of forms, from a variety of biomass substrates) will remain a cornerstone to resource and economic sustainability. A promising mechanism to achieve sustainability will entail integrated systems (Figure 18), where material and energy streams cycle and recycle (i. e., upstream outputs become downstream inputs) between various components of a biorefinery, animal feeding operation, energy (i. e., heat, electricity, steam, etc.) production system, feedstock production system, and other systems. By integrating these various components, a diversified portfolio will not only produce fuel, but also fertilizer, feed, food, industrial products, energy, and most importantly, will be self-sustaining.