Fuel ethanol and high protein feed from corn and corn-whey mixtures in a farm-scale plant

Distiller's wet grain (DWG) and 95% ethanol were produced from corn in a farm-scale process involving batch cooking-fermentation and continuous distillation-centrifugation. The energy balance was 2.26 and the cost was $1.86/gal (1981 cost). To improve the energy balance and reduce costs, various modifications were made in the plant. The first change, back-end (after liquefaction) serial recycling of stillage supernatant at 20 and 40% strengths, produced beers with 0.2 and 0.4% (v/v) more ethanol, respectively, than without recycling. This increased the energy balance by 0.22-0.43 units and reduced costs by $0.07-$0.10/gal. The DWGs from back-end recycling had increased fat. The second change, increasing the starch content from 17-19% to 27.5%, increased the ethanol in the beer from 10.5-14.9% at a cost saving of $0.41/gal. The energy balance increased by 1.08 units. No significant change was seen in DWG composition. The third change, using continuous cascade rather than batch fermentation, permitted batch-levels of ethanol (10%) in the beer but only at low dilution rates. Both the cost and energy balance were decreased slightly. The DWG composition remained constant. The last change, replacing part of the corn and all of the tap water in the mash with whole whey and using Kluyveromyces fragilis instead of Saccharomyces cerevisiae during fermentation, resulted in an energy balance increase of 0.16 units and a $0.27/gal cost reduction. Here, 10% ethanolic beers were produced and the DWGs showed increased protein and fat. Recommendations for farm-scale plants are provided.     

Grain sorghum stillage recycling: Effect on ethanol yield and stillage quality

Stillage obtained from ethanol production of grain sorghum was separated into two fractions: thin stillage and wet solids. A portion of the thin stillage was recycled as cooking water in subsequent fermentation runs using both bench- and full-scale ethanol production plants. When thin stillage replaced 50-75% of the cooking water, large increases occurred in solids content, COD, and EC of the resulting thin stillage. It was found that while the volume of thin stillage requiring treatment or disposal was reduced, there was little reduction in the total pollutant load. Stillage rcycling had little effect on the quality of the stillage wet solids fraction. At the high levels of stillage recycle used, ethanol yield was reduced after three to five runs of consecutive recycling.     

Anaerobic digestion of thin stillage for energy recovery and water reuse in corn-ethanol plants

Recycling of anaerobically-digested thin stillage within a corn-ethanol plant may result in the accumulation of nutrients of environmental concern in animal feed coproducts and inhibitory organic materials in the fermentation tank. Our focus is on anaerobic digestion of treated (centrifugation and lime addition) thin stillage. Suitability of digestate from anaerobic treatment for reuse as process water was also investigated. Experiments conducted at various inoculum-to-substrate ratios (ISRs) revealed that alkalinity is a critical parameter limiting digestibility of thin stillage. An ISR level of 2 appeared optimal based on high biogas production level (763 mL biogas/g volatile solids added) and organic matter removal (80.6% COD removal). The digester supernatant at this ISR level was found to contain both organic and inorganic constituents at levels that would cause no inhibition to ethanol fermentation. Anaerobic digestion of treated-thin stillage can be expected to improve the water and energy efficiencies of dry grind corn-ethanol plants.     

Enzymatic hydrolysis and fermentation of corn for fuel alcohol

The integration of enzyme saccharification with fermentation reduces the total time required to produce acceptable levels of ethanol. The use of a more concentrated mash (84.8 L total mash/bu corn) results in a 26.6% increase in ethanol productivity and a 21.4% increase in beer ethanol concentration compared to standard corn mash (96.6 L total mash/bu corn). Thus, the energy requirement and cost of distillation can be reduced. The addition of waste cola syrup at 30 g invert sugar/L total mash gave a 19% increase in ethanol concentration in the final beer and required only a small increase in the period of fermentation. Surplus laundry starch can replace 30-50% of the weight of corn normally used in fermentation without influencing ethanol production or the time required for fermentation. Both of these waste materials reduce the unit cost of ethanol and demonstrate the value of such substances in ethanol systems.     

Impact of recycling stillage on conversion of dilute sulfuric acid pretreated corn stover to ethanol

Both the current corn starch to ethanol industry and the emerging lignocellulosic biofuels industry view recycling of spent fermentation broth or stillage as a method to reduce fresh water use. The objective of this study was to understand the impact of recycling stillage on conversion of corn stover to ethanol. Sugars in a dilute‐acid pretreated corn stover hydrolysate were fermented to ethanol by the glucose–xylose fermenting bacteria Zymomonas mobilis 8b. Three serial fermentations were performed at two different initial sugar concentrations using either 10% or 25% of the stillage as makeup water for the next fermentation in the series. Serial fermentations were performed to achieve near steady state concentration of inhibitors and other compounds in the corn stover hydrolysate. Little impact on ethanol yields was seen at sugar concentrations equivalent to pretreated corn stover slurry at 15% (w/w) with 10% recycle of the stillage. However, ethanol yields became progressively poorer as the sugar concentration increased and fraction of the stillage recycled increased. At an equivalent corn stover slurry concentration of 20% with 25% recycled stillage the ethanol yield was only 5%. For this microorganism with dilute‐acid pretreated corn stover, recycling a large fraction of the stillage had a significant negative impact on fermentation performance. Although this finding is of concern for biochemical‐based lignocellulose conversion processes, other microorganism/pretreatment technology combinations will likely perform differently. Biotechnol. Bioeng. 2010;105: 992–996. © 2009 Wiley Periodicals, Inc.     

Cofermentation of sweet sorghum juice and grain for production of fuel ethanol and distillers' wet grain

In an attempt to reduce the costs associated with fuel ethanol production from grain, the authors used sweet sorghum juice as a partial or complete replacement for tap-water in mash preparation and fermentation. This juice, which was an unutilized by-product of sweet sorghum silage preservation by the Ag-Bag method, contained 6·5–7·6% (wt/wt) reducing sugar and produced up to 3·51% (v/v) ethanol beers after fermentation. Varying amounts of this juice were mixed with water and corn or wheat, either before or after liquefaction (front-end or back-end loading, respectively). When over 60% juice replacement was used in front-end loading trials, salt buildup, due to required pH adjustments during cooking, inhibited yeast metabolism and thereby reduced yields. This inhibition was not observed during back-end loading trials since acid and base usage during cooking were reduced. However, in all trials we noted yeast inhibition by some factor(s) present in juice from sweet sorghum variety NK 8368. This inhibition was not observed with variety NK 405. If sweet sorghum juice is used to replace 40% of the water and either 12·5% of the corn or 12% of the wheat in mash preparation, production costs can be reduced by $0.032/liter ($0.12/US gallon) for corn and $0.040/liter ($0.15/US gallon) for wheat.     

Effect of corn preparation methods on dry-grind ethanol production by granular starch hydrolysis and partitioning of spent beer solids

Two corn preparation methods, rollermill flaking and hammermill grinding, were compared for efficient processing of corn into ethanol by granular starch hydrolysis and simultaneous fermentation by yeast Saccharomyces cerevisiae. Corn was either ground in a hammermill with different size screens or crushed in a smooth-surfaced rollermill at different roller gap settings. The partitioning of beer solids and size distribution of solids in the thin stillage were compared. The mean particle diameter d₅₀ for preparations varied with set-ups and ranged between 210 and 340 μm for ground corn, and 1180-1267 μm for flaked corn. The ethanol concentrations in beer were similar (18-19% v/v) for ground and flaked preparations, however, ethanol productivity increased with reduced particle size. Roller versus hammermilling of corn reduced solids in thin stillage by 28%, and doubled the volume percent of fines (d₅₀ ∼ 7 μm)in thin stillage and decreased coarse (d₅₀ ∼ 122 μm) by half compared to hammermilling.     

A continuous, farm-scale, solid-phase fermentation process for fuel ethanol and protein feed production from fodder beets

Fuel ethanol (95%) was produced from fodder beets in two farm-scale processes. In the first process, involving conventional submerged fermentation of the fodder beets in a mash, ethanol and a feed (PF) rich in protein, fat, and fiber were produced. Ethanol yields of 70 L/metric ton (7 gal/ton) were obtained; however, resulting beers had low ethanol concentrations [3-5% (v/v)]. The high viscosity of medium and low sugar, beet mashes caused mixing problems which prevented any further increase of beet sugar in the mash. The severely limited the maximum attainable ethanol concentration during fermentation, thereby making the beer costly to distill into fuel ethanol and the process energy inefficient. In order to achieve distillably worthwhile ethanol concentrations of 8-10% (v/v), we developed and tested a solid-phase fermentation process (continuous). In preliminary trials, this system produced fermented pulp with over 8% (v/v) ethanol corresponding to an ethanol yield of 87 L/metric ton (21 gal/ton). Production costs with this novel process are $0.47/L ($1.77/gal) and the energy balance is 2.11. These preliminary cost estimates indicate that fodder beets are potentially competitive with corn as an ethanol feedstock. Additional research, however, is warranted to more precisely refine individual costs, energy balances and the actual value of the PF.     

Starch hydrolysis and its effect on product yield and microbial contamination in yeast ethanol fermentation

The influence of temperature and incubation time on starch gelatinization in wheat, rye and corn grain were studied. Rye starch was the most susceptlble to enzyme hydrolysls. Heat treatment of ground grain during starch gelatinlzation significantly reduced microblal contamination. In the batch fermentation of wheat, a high sugar utillization ranged from 92 to 94%. The highest alcohol yield was 65% from rye starch. The results obtained show that the high pressure cooking used for mash preparation can be replaced successfully by low temperature treatment.The authors are with the Institute of Food Technology of Plant Origin, The University of Agriculture, 60-624 Poznan, ul. Wojska Polskiego 31, Poland.     

Fate of Fumonisin B(1) in Naturally Contaminated Corn during Ethanol Fermentation

Two lots of corn naturally contaminated with fumonisin B(1) (15 and 36 ppm) and a control lot (no fumonisin B(1) detected) were used as substrates for ethanol production in replicate 8.5-liter yeast fermentations. Ethanol yields were 8.8% for both the control and low-fumonisin corn, while the high-fumonisin corn contained less starch and produced 7.2% ethanol. Little degradation of fumonisin occurred during fermentation, and most was recovered in the distillers' grains, thin stillage, and distillers' solubles fractions. No toxin was detected in the distilled alcohol or centrifuge solids. Ethanol fermentation of fumonisin-contaminated corn coupled with effective detoxification of distillers' grains and aqueous stillage is suggested as a practical process strategy for salvaging contaminated corn.     

Fate of Fumonisin B1 in Naturally Contaminated Corn during Ethanol Fermentation

Two lots of corn naturally contaminated with fumonisin B₁ (15 and 36 ppm) and a control lot (no fumonisin B₁ detected) were used as substrates for ethanol production in replicate 8.5-liter yeast fermentations. Ethanol yields were 8.8% for both the control and low-fumonisin corn, while the high-fumonisin corn contained less starch and produced 7.2% ethanol. Little degradation of fumonisin occurred during fermentation, and most was recovered in the distillers' grains, thin stillage, and distillers' solubles fractions. No toxin was detected in the distilled alcohol or centrifuge solids. Ethanol fermentation of fumonisin-contaminated corn coupled with effective detoxification of distillers' grains and aqueous stillage is suggested as a practical process strategy for salvaging contaminated corn.     

HTST-extrusion cooking in ethanol production from starchy materials

Starch syrup for ethanol fermentation is conventionally produced by acid or enzymatic hydrolysis. Recently, however, promising results have been obtained using HTST-extrusion cooking in starch liquefaction. The starchy material was pregelatinized and preliquefied in a Creusot-Loire BC45 twin-screw HTST-extrusion cooker before simultaneous saccharification by amyloglucosidase and fermentation by Saccharomyces cerevisiae or Zymomonas mobilis. With pretreatment of milled whole grain or starch by HTST-extrusion cooking a significantly shorter fermentation time could be achieved. Maximum ethanol yield was obtained in 45 h using conventional yeast and amyloglucosidase (1,4-α-d-glucan glucohydrolase, EC 3.2.1.3) dosage, even without addition of Termamyl α-amylase (1,4-α-d-glucan glucanohydrolase, EC 3.2.1.1) during thermomechanical liquefaction. Immobilized yeast could also be used to produce ethanol both by a batch or continuous process. In this case, for a continuous process the DE-value of the syrup should be sufficiently high. A model for ethanol production as a function of dry matter, fermentation time, and yeast and Termamyl quantities has been developed.     

Ethanol fermentation of HTST extruded rye grain by bacteria and yeasts

High temperature extrusion cooking of rye was used as a pretreatment for ethanol fermentation, and yeasts and bacteria were compared for their fermentation rates. Extrusion cooking caused, on average, a 7.5% increase in ethanol yield in comparison to autoclaved samples. The best results were achieved for grain with a moisture of 21-23% which was extruded at temperatures of 160-180 °C. Extrusion decreased the relative viscosity of rye grain water extracts, so it was possible to mash it without α-amylase. The efficiency of fermentation of extruded rye without Termamyl was equal to that of autoclaved and traditionally mashed rye (using α-amylase). The rate of fermentation of extruded rye grain by Zymomonas was higher during the first stage, but the final ethanol yield was similar for the bacterium and the yeast. Though both microorganisms gave good quality distillates, the concentration of compounds other than ethanol achieved from extruded rye mashes, which were fermented by Z. mobilis, was five times lower than for yeasts.     

Real‐time monitoring of high‐gravity corn mash fermentation using in situ raman spectroscopy

In situ Raman spectroscopy was employed for real‐time monitoring of simultaneous saccharification and fermentation (SSF) of corn mash by an industrial strain of Saccharomyces cerevisiae. An accurate univariate calibration model for ethanol was developed based on the very strong 883 cm^?1 C–C stretching band. Multivariate partial least squares (PLS) calibration models for total starch, dextrins, maltotriose, maltose, glucose, and ethanol were developed using data from eight batch fermentations and validated using predictions for a separate batch. The starch, ethanol, and dextrins models showed significant prediction improvement when the calibration data were divided into separate high‐ and low‐concentration sets. Collinearity between the ethanol and starch models was avoided by excluding regions containing strong ethanol peaks from the starch model and, conversely, excluding regions containing strong saccharide peaks from the ethanol model. The two‐set calibration models for starch (R² = 0.998, percent error = 2.5%) and ethanol (R² = 0.999, percent error = 2.1%) provide more accurate predictions than any previously published spectroscopic models. Glucose, maltose, and maltotriose are modeled to accuracy comparable to previous work on less complex fermentation processes. Our results demonstrate that Raman spectroscopy is capable of real time in situ monitoring of a complex industrial biomass fermentation. To our knowledge, this is the first PLS‐based chemometric modeling of corn mash fermentation under typical industrial conditions, and the first Raman‐based monitoring of a fermentation process with glucose, oligosaccharides and polysaccharides present. Biotechnol. Bioeng. 2013; 110: 1654–1662. © 2013 Wiley Periodicals, Inc.     

Prospective and development of butanol as an advanced biofuel

Butanol has been acknowledged as an advanced biofuel, but its production through acetone–butanol–ethanol (ABE) fermentation by clostridia is still not economically competitive, due to low butanol yield and titer. In this article, update progress in butanol production is reviewed. Low price and sustainable feedstocks such as lignocellulosic residues and dedicated energy crops are needed for butanol production at large scale to save feedstock cost, but processes are more complicated, compared to those established for ABE fermentation from sugar- and starch-based feedstocks. While rational designs targeting individual genes, enzymes or pathways are effective for improving butanol yield, global and systems strategies are more reasonable for engineering strains with stress tolerance controlled by multigenes. Compared to solvent-producing clostridia, engineering heterologous species such as Escherichia coli and Saccharomyces cerevisiae with butanol pathway might be a solution for eliminating the formation of major byproducts acetone and ethanol so that butanol yield can be improved significantly. Although batch fermentation has been practiced for butanol production in industry, continuous operation is more productive for large scale production of butanol as a biofuel, but a single chemostat bioreactor cannot achieve this goal for the biphasic ABE fermentation, and tanks-in-series systems should be optimized for alternative feedstocks and new strains. Moreover, energy saving is limited for the distillation system, even total solvents in the fermentation broth are increased significantly, since solvents are distilled to ~ 40% by the beer stripper, and more than 95% water is removed with the stillage without phase change, even with conventional distillation systems, needless to say that advanced chemical engineering technologies can distil solvents up to ~ 90% with the beer stripper, and the multistage pressure columns can well balance energy consumption for solvent fraction. Indeed, an increase in butanol titer with ABE fermentation can significantly save energy consumption for medium sterilization and stillage treatment, since concentrated medium can be used, and consequently total mass flow with production systems can be reduced. As for various in situ butanol removal technologies, their energy efficiency, capital investment and contamination risk to the fermentation process need to be evaluated carefully.     

Protease digestion from wheat stillage within a dry grind ethanol facility

As the current starch based ethanol market increases at its rapid pace, finding new markets for the primary coproduct, distiller's grains, has gained considerable interest. One possibility is to isolate the protein-rich fraction for use as precursors to biochemicals and bioplastics, further decreasing fossil fuel consumption. This research focuses on enzymatic extraction of protein peptides from wheat heavy stillage using commercially available proteases. The energy saved due to this process ranged from ～ 1.5 to 3.0 GJ/ton wheat stillage compared to fossil fuel-based chemicals. Using Protex 6L (Genencor), ～ 57% of the protein in the stillage was soluble 24 h after protease addition at 0.1% w/w loading. Of these proteins, ～ 32% were already soluble, indicating the importance of using wet heavy stillage as the feedstock rather than dried distiller's grains. Peptide size was less than 6 kDa. Further improvements in protein removal may be obtained through a fed batch addition of protease and improved protease cocktails.     

High ethanol yields using Aspergillus oryzae koji and corn media

Summary High ethanol and stillage solids have been achieved using whole corn mashes. Ethanol yields of 14% (v/v) (89.5% of theory) and stillage levels of approximately 23% (w/v) were obtained in 74–90 hours using mild acid pretreatment with Aspergillus oryzae wheat bran koji saccharification. High ethanol yields were also obtained with bacterial amylase, instead of the acid treatment, when the sterilization step was omitted. The implications of ethanol fermentation process modifications are explored.     

Production of mannitol and lactic acid by fermentation with Lactobacillus intermedius NRRL B-3693

Lactobacillus intermedius B-3693 was selected as a good producer of mannitol from fructose after screening 72 bacterial strains. The bacterium produced mannitol, lactic acid, and acetic acid from fructose in pH-controlled batch fermentation. Typical yields of mannitol, lactic acid, and acetic acid from 250 g/L fructose were 0.70, 0.16, and 0.12 g, respectively per g of fructose. The fermentation time was greatly dependent on fructose concentration but the product yields were not dependent on fructose level. Fed-batch fermentation decreased the time of maximum mannitol production from fructose (300 g/L) from 136 to 92 h. One-third of fructose could be replaced with glucose, maltose, galactose, mannose, raffinose, or starch with glucoamylase (simultaneous saccharification and fermentation), and two-thirds of fructose could be replaced with sucrose. L. intermedius B-3693 did not co-utilize lactose, cellobiose, glycerol, or xylose with fructose. It produced lactic acid and ethanol but no acetic acid from glucose. The bacterium produced 21.3 +/- 0.6 g lactic acid, 10.5 +/- 0.3 g acetic acid, and 4.7 +/- 0.0 g ethanol per L of fermentation broth from dilute acid (15% solids, 0.5% H(2)SO(4), 121 degrees C, 1 h) pretreated enzyme (cellulase, beta-glucosidase) saccharified corn fiber hydrolyzate.     

Grain sorghum is a viable feedstock for ethanol production

Sorghum is a major cereal crop in the USA. However, sorghum has been underutilized as a renewable feedstock for bioenergy. The goal of this research was to improve the bioconversion efficiency for biofuels and biobased products from processed sorghum. The main focus was to understand the relationship among “genetics–structure–function–conversion” and the key factors impacting ethanol production, as well as to develop an energy life cycle analysis model (ELCAM) to quantify and prioritize the saving potential from factors identified in this research. Genetic lines with extremely high and low ethanol fermentation efficiency and some specific attributes that may be manipulated to improve the bioconversion rate of sorghum were identified. In general, ethanol yield increased as starch content increased. However, no linear relationship between starch content and fermentation efficiency was found. Key factors affecting the ethanol fermentation efficiency of sorghum include protein digestibility, level of extractable proteins, protein and starch interaction, mash viscosity, amount of phenolic compounds, ratio of amylose to amylopectin, and formation of amylose-lipid complexes in the mash. A platform ELCAM with a base case showed a positive net energy value (NEV) = 25,500 Btu/gal EtOH. ELCAM cases were used to identify factors that most impact sorghum use. For example, a yield increase of 40 bu/ac resulted in NEV increasing from 7 million to 12 million Btu/ac. An 8% increase in starch provided an incremental 1.2 million Btu/ac. JIMB-2008: BioEnergy-Special issue.     

Thin stillage fractionation using ultrafiltration: resistance in series model

The corn based dry grind process is the most widely used method in the US for fuel ethanol production. Fermentation of corn to ethanol produces whole stillage after ethanol is removed by distillation. It is centrifuged to separate thin stillage from wet grains. Thin stillage contains 5–10% solids. To concentrate solids of thin stillage, it requires evaporation of large amounts of water and maintenance of evaporators. Evaporator maintenance requires excess evaporator capacity at the facility, increasing capital expenses, requiring plant slowdowns or shut downs and results in revenue losses. Membrane filtration is one method that could lead to improved value of thin stillage and may offer an alternative to evaporation. Fractionation of thin stillage using ultrafiltration was conducted to evaluate membranes as an alternative to evaporators in the ethanol industry. Two regenerated cellulose membranes with molecular weight cut offs of 10 and 100 kDa were evaluated. Total solids (suspended and soluble) contents recovered through membrane separation process were similar to those from commercial evaporators. Permeate flux decline of thin stillage using a resistance in series model was determined. Each of the four components of total resistance was evaluated experimentally. Effects of operating variables such as transmembrane pressure and temperature on permeate flux rate and resistances were determined and optimum conditions for maximum flux rates were evaluated. Model equations were developed to evaluate the resistance components that are responsible for fouling and to predict total flux decline with respect to time. Modeling results were in agreement with experimental results (R ² > 0.98).