Simultaneous Saccharification And Co-fermentation Process Research Articles

Enhancing efficiency in ethanol production from high solid corn stover: Insights into enzymatic hydrolysis parameters and cellulase recovery

BackgroundThe simultaneous saccharification and co-fermentation (SSCF) at high solid loading is an effective approach to improve the economic feasibility of bioethanol. MethodsIn this study, the high-solid SSCF of superfine grinding corn stover was treated with cheap and readily available deionized water (DW) instead of sodium citrate buffer solution (SCBS). Additionally, the evaluation of temperature, enzyme loading, solid loading, and cellulose recovery were carried out to determine their impact on ethanol production. Significant FindingsThe results of the analysis indicated that replacing SCBS with DW had negligible effects on the SSCF of ethanol and byproducts (acetic acid and glycerol). The ethanol yield increased by 18 % at 35 °C compared to the yield at 30 °C. As enzyme loading increased, more cellulose active sites in corn stover were bound by cellulase, which increased the ethanol yield by improving the efficiency of enzymatic hydrolysis. The SSCF process didn't incorporate any buffer, resulting in an even higher ethanol titer (55.42 g/L). Furthermore, the cellulase productivity increased by 71 % after recovery, compared to the non-recovery. The results indicated that the optimized SSCF process is a potential technique for producing bioethanol on a commercial level because it improves the production efficiency while keeping costs low.

Exploration of separate hydrolysis and fermentation and simultaneous saccharification and co-fermentation for acetone, butanol, and ethanol production from combined diluted acid with laccase pretreated Puerariae Slag in Clostridium beijerinckii ART44

In this study, an efficient pretreatment technology was developed for the bioconversion of puerariae slag (PS) into biobutanol. To accelerate the enzymatic saccharification of PS, the method of dilute acid combined with laccase pretreatment (DALP) was performed. With this effort, the highest concentration of reducing sugar was 48.96 ± 1.69 g/L after enzymatic hydrolysis of the whole slurry pretreatment under the optimal condition. Subsequently, the highest butanol productivity (0.15 g/L/h) was obtained by the simultaneous saccharification and co-fermentation (SSCF), which was 114.29% higher than that of the separate hydrolysis and fermentation (SHF). Furthermore, the microstructural changes of PS after different pretreatment were initially investigated by FT-IR, and we found that the DALP method resulted in more severe damage during the pretreatment process, which could improve the efficiency of enzymatic saccharification. This study suggests that the DALP is an attainable and efficient pretreatment method for production of butanol in the SSCF process.

Comparative Studies on Bioethanol Production from Some Sugar Based Agricultural Wastes

The suitability of some sugar-based agricultural wastes (pineapple peels, banana peels, and plantain peels) were examined for bioethanol production. They were subjected to different physico-chemical pretreatments in order to identify the most effective process and optimize the yield of bioethanol. They were further hydrolyzed by cellulase enzymes from Trichoderma ressei micro-organism isolated from the soil. The various hydrolysates obtained were subsequently fermented to bioethanol using co-cultures of Pichia stipitis and Saccharomyces cerevisiae fermentative yeasts. Separate hydrolysis and co-fermentation (SHCF) and simultaneous saccharification and co-fermentation (SSCF) methods were adopted and their bioethanol yields compared. The fermentation results revealed that the maximum bioethanol yields for pineapple peels, banana peels, and plantain peels were 4.94, 3.85, and 4.57 (% w/v wet biomass) respectively at 72 hours fermentation period. SSCF strategy was observed to be more effective as it gave better bioethanol yields in all the considered substrates and was less time consuming. Mixed cultures of Trichoderma ressi, Pichia stipitis and Saccharomyces cerevisiae through SSCF process resulted to a better fermentation yield when compared with previous studies by other workers.

Ethanol Production from Oil Palm Trunk: A Combined Strategy Using an Effective Pretreatment and Simultaneous Saccharification and Cofermentation.

Background Oil palm trunk (OPT) with highly cellulose content is a valuable bioresource for bioethanol production. To produce ethanol from biomass, pretreatment is an essential step in the conversion of lignocellulosic biomass to fermentable sugars such as glucose and xylose. Several pretreatment methods have been developed to overcome biomass recalcitrance. In this study, the effects of different pretreatment methods such as alkali pretreatment, microwave-alkali, and alkaline peroxide combined with autoclave on the lignocellulosic biomass structure were investigated. Moreover, ethanol production from the treated biomass was performed by simultaneous saccharification and cofermentation (SSCF) under different temperatures, fermentation times, and cell ratios of Saccharomyces cerevisiae NCYC 479 and pentose-utilizing yeast, Pichia stipitis NCYC 1541. Results Pretreatment resulted in a significant lignin removal up to 83.26% and cellulose released up to 80.74% in treated OPT by alkaline peroxide combined with autoclave method. Enzymatic hydrolysis of treated OPT resulted in an increase in fermentable sugar up to 93.22%. Optimization of SSCF by response surface method showed that the coculture could work together to produce maximum ethanol (1.89%) and fermentation efficiency (66.14%) under the optimized condition. Conclusion Pretreatment by alkaline peroxide combined with autoclave method and SSCF process could be expected as a promising system for ethanol production from oil palm trunk and various lignocellulosic biomass.

The advanced performance of microbial consortium for simultaneous utilization of glucose and xylose to produce lactic acid directly from dilute sulfuric acid pretreated corn stover

BackgroundLignocellulosic feedstocks have attracted much attention as a potential carbon source for lactic acid (LA) production because of their ready availability, sustainability, and renewability. However, there are at least two major technical challenges to producing LA from lignocellulose. Inhibitors derived from lignocellulose pretreatment have a negative impact on the growth of cells producing LA. Furthermore, pentose sugars produced from the pretreatment are difficultly utilized by most LA producers, which is known as the carbon catabolite repression (CCR) effect. This complex feedstock can be utilized by a robust microbial consortium with high bioconversion efficiency.ResultsIn this study, a thermophilic consortium DUT50 producing LA was enriched and employed to improve corn stover (CS) utilization. Enterococcus was the dominant family in the consortium DUT50, accounting for 93.66% of the total abundance, with Lactobacillus, Bacillus, Lactococcus, and Trichococcus accounted for the remaining 2.68%. This consortium could be resistant to inhibitors concentration up to 9.74 g/L (2.88 g/L acetic acid, 2.46 g/L furfural, 2.20 g/L 5-HMF, and 2.20 g/L vanillin derived from pretreatment of CS), and simultaneously metabolizes hexose and pentose without CCR effect. Based on the promising consortium features, an efficient process of simultaneous saccharification and co-fermentation (SSCF) was developed to produce LA from acid pretreated corn stover, in which solid–liquid separation and detoxification were avoided. The key influencing factors were investigated and optimized, including dry biomass and cellulase loading, corn steep liquor powder concentration, and the pre-hydrolysis time. The highest LA titer of 71.04 g/L with a yield of 0.49 g/g-CS was achieved at a dry biomass loading of 20% (w/v), which is the highest LA production from non-detoxified acid pretreated corn stover via the SSCF process without wastewater generation reported to date. The simultaneous metabolism of hexose and pentose revealed collaboration between Enterococcus in the consortium, whereas xylose may be efficiently metabolized by Lactobacillus and Bacillus with low abundance via the pentose phosphate pathway.ConclusionsThe experimental results demonstrated the potential advantage of symbiosis in microbial consortia used for LA production from lignocellulosic biomass.

Life cycle assessment of bioethanol production fromPennisetumsp. using fed‐batch simultaneous saccharification and cofermentation at high solid loadings

Considerable progress has been achieved for the production of bioethanol from lignocellulosic biomass. However, increasing the substrate concentration has been shown to decrease ethanol productivity. Therefore, Saccharomyces cerevisiae (S. cerevisiae) and Pichia sp. were used for ethanol production from glucose and xylose sugars in the present investigation. Furthermore, coculture fermentations were conducted for 13 g/L of sugar (10 g of glucose and 3 g/L of xylose). It was further used for ethanol production from ultrasonication-assisted NaOH (UA-NaOH) pretreated and enzymatically saccharified biomass in batch and fed-batch fermentation conditions. Furthermore, fed-batch fermentation was used for separate hydrolysis and cofermentation (SHCF) and simultaneous saccharification and cofermentation (SSCF) in shake flask conditions. The highest ethanol production of 12.2 and 7.9 g/L was observed for fed-batch SSCF deenanath grass (DG) and hybrid Napier grass (HNG) (Palkonal MBW as the enzyme) biomass (80 g/L), respectively, in shake flask conditions. However, increasing the biomass concentration to 270 g/L produced an ethanol concentration of 77.6 and 51.3 g/L for DG and HNG, respectively, in fed-batch SSCF conditions in a bioreactor. Furthermore, nuclear magnetic resonance studies of the residual biomass of DG revealed lower carbohydrate content, demonstrating the efficiency of the fermentation strategy. Life cycle analysis of DG and HNG revealed DG had a higher yield as well as lower environmental impact than HNG. Thus, the fed-batch SSCF process can be considered a promising technique for biorefinery-based bioethanol production from Pennisetum sp. in the future. Novelty Statement For making lignocellulosic fuel ethanol economically competitive as compared to fossil fuels, it is important to achieve higher titers of ethanol from increased substrate concentration. But an increase in the substrate concentration decreases the ethanol productivity. In this study, the fed-batch simultaneous saccharification and fermentation produced higher titers of about 77.6 g/L ethanol even at higher substrate loadings. Besides, The LCA results demonstrated lower environmental toxicity, indicating the efficiency of the pretreatment and simultaneous saccharification and cofermentation process.

Simultaneous saccharification and co-fermentation with a thermotolerant Saccharomyces cerevisiae to produce ethanol from sugarcane bagasse under high temperature conditions

Lignocellulosic ethanol production at high temperature offers advantages such as the decrease of contamination risk and cooling cost. Recombinant xylose-fermenting Saccharomyces cerevisiae has been considered a promising strain for ethanol production from lignocellulose for its high inhibitor tolerance and superior capability to ferment glucose and xylose into ethanol. To improve the ethanolic fermentation by xylose at high temperature, the strain YY5A was subjected to the ethyl methanesulfonate (EMS) mutagenesis. A mutant strain T5 was selected from the EMS-treated cultures to produce ethanol. However, the xylose uptake by T5 was severely inhibited by the high ethanol concentration during the co-fermentation in defined YPDX medium at 40 °C. In this study, the simultaneous saccharification and co-fermentation (SSCF) and the separate hydrolysis and co-fermentation (SHCF) processes of sugarcane bagasse were assessed to solve this problem. The xylose utilization by T5 was remarkably improved using the SSCF process compared to the SHCF process. For the SHCF and SSCF processes, 48% and 99% of the xylose in the hydrolysate was consumed at 40 °C, respectively. The ethanol yield was enhanced by the SSCF process. The ethanol production can reach to 36.0 g/L using this process under high-temperature conditions.

Preliminary study on integrated production of ethanol and lignin from bagasse pulp waste

Bagasse pulp waste (BPW) is a material generated from the depithing of sugarcane bagasse stems prior to pulping. It was subjected to a modified oxygen delignification or ammonia catalytic steam explosion (AE) pretreatment for delignification and retaining carbohydrates of raw materials, followed by simultaneous saccharification and co-fermentation (SSCF) to ethanol. Based on this process, an environmentally sustainable two-stage process for lignin purification was employed to obtain nontoxic “green lignin”. The results indicated that both pretreatment methods, particularly AE, had outstanding performance in the SSCF process. The highest ethanol yield (based on dry matter of BPW), 67.5% for the AE pretreatment, was obtained from the SSCF procedure at 8% (w/v) solids loading. Furthermore, the obtained lignin products from this process possessed better structural integrity.

Process analysis and optimization of simultaneous saccharification and co-fermentation of ethylenediamine-pretreated corn stover for ethanol production

BackgroundImproving ethanol concentration and reducing enzyme dosage are main challenges in bioethanol refinery from lignocellulosic biomass. Ethylenediamine (EDA) pretreatment is a novel method to improve enzymatic digestibility of lignocellulose. In this study, simultaneous saccharification and co-fermentation (SSCF) process using EDA-pretreated corn stover was analyzed and optimized to verify the constraint factors on ethanol production.ResultsHighest ethanol concentration was achieved with the following optimized SSCF conditions at 6% glucan loading: 12-h pre-hydrolysis, 34 °C, pH 5.4, and inoculum size of 5 g dry cell/L. As glucan loading increased from 6 to 9%, ethanol concentration increased from 33.8 to 48.0 g/L, while ethanol yield reduced by 7%. Mass balance of SSCF showed that the reduction of ethanol yield with the increasing solid loading was mainly due to the decrease of glucan enzymatic conversion and xylose metabolism of the strain. Tween 20 and BSA increased ethanol concentration through enhancing enzymatic efficiency. The solid-recycled SSCF process reduced enzyme dosage by 40% (from 20 to 12 mg protein/g glucan) to achieve the similar ethanol concentration (~ 40 g/L) comparing to conventional SSCF.ConclusionsHere, we established an efficient SSCF procedure using EDA-pretreated biomass. Glucose enzymatic yield and yeast viability were regarded as the key factors affecting ethanol production at high solid loading. The extensive analysis of SSCF would be constructive to overcome the bottlenecks and improve ethanol production in cellulosic ethanol refinery.

Optimal Design of Cost-Effective Simultaneous Saccharification and Co-fermentation Through Integrated Process Optimization

This study presents an integrative design of experiment (intDoE) methodology for process optimization using a combination of experimental design, process flowsheet simulation, and economic model. This multilayered framework was implemented to simulate and optimize a simultaneous saccharification and co-fermentation (SSF) process of sugarcane bagasse to ethanol for improving process economic efficiency. Using intDoE based on product titer and economic profit criteria, the SSF process was designed for operation at optimal xylanase/cellulases enzymes, optimal Scheffersomyces stipitis/Saccharomyces cerevisiae yeast cells, and optimal oxygen supply to maximize ethanol titer and to minimize ethanol selling price. The optimal SSF process achieved an ethanol titer of 81.5 g/L, equivalent to the minimal ethanol selling price of 1.4 USD/gal. The results proved the efficiency of intDoE approach that permitted the design and optimizing of fully integrated processes which was not considered by the traditional design of experiment methods. Hence, this novel intDoE optimization tool is useful for bioprocess design in which the integrated process simulation can be performed to select the optimal operating conditions for maximized production efficiency and process economy.

Model-based optimization and scale-up of multi-feed simultaneous saccharification and co-fermentation of steam pre-treated lignocellulose enables high gravity ethanol production.

BackgroundHigh content of water-insoluble solids (WIS) is required for simultaneous saccharification and co-fermentation (SSCF) operations to reach the high ethanol concentrations that meet the techno-economic requirements of industrial-scale production. The fundamental challenges of such processes are related to the high viscosity and inhibitor contents of the medium. Poor mass transfer and inhibition of the yeast lead to decreased ethanol yield, titre and productivity. In the present work, high-solid SSCF of pre-treated wheat straw was carried out by multi-feed SSCF which is a fed-batch process with additions of substrate, enzymes and cells, integrated with yeast propagation and adaptation on the pre-treatment liquor. The combined feeding strategies were systematically compared and optimized using experiments and simulations.ResultsFor high-solid SSCF process of SO2-catalyzed steam pre-treated wheat straw, the boosted solubilisation of WIS achieved by having all enzyme loaded at the beginning of the process is crucial for increased rates of both enzymatic hydrolysis and SSCF. A kinetic model was adapted to simulate the release of sugars during separate hydrolysis as well as during SSCF. Feeding of solid substrate to reach the instantaneous WIS content of 13 % (w/w) was carried out when 60 % of the cellulose was hydrolysed, according to simulation results. With this approach, accumulated WIS additions reached more than 20 % (w/w) without encountering mixing problems in a standard bioreactor. Feeding fresh cells to the SSCF reactor maintained the fermentation activity, which otherwise ceased when the ethanol concentration reached 40–45 g L−1. In lab scale, the optimized multi-feed SSCF produced 57 g L−1 ethanol in 72 h. The process was reproducible and resulted in 52 g L−1 ethanol in 10 m3 scale at the SP Biorefinery Demo Plant.ConclusionsSSCF of WIS content up to 22 % (w/w) is reproducible and scalable with the multi-feed SSCF configuration and model-aided process design. For simultaneous saccharification and fermentation, the overall efficiency relies on balanced rates of substrate feeding and conversion. Multi-feed SSCF provides the possibilities to balance interdependent rates by systematic optimization of the feeding strategies. The optimization routine presented in this work can easily be adapted for optimization of other lignocellulose-based fermentation systems.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-016-0500-7) contains supplementary material, which is available to authorized users.

D-lactic acid production from renewable lignocellulosic biomass via genetically modified Lactobacillus plantarum.

d-lactic acid is of great interest because of increasing demand for biobased poly-lactic acid (PLA). Blending poly-l-lactic acid with poly-d-lactic acid greatly improves PLA's mechanical and physical properties. Corn stover and sorghum stalks treated with 1% sodium hydroxide were investigated as possible substrates for d-lactic acid production by both sequential saccharification and fermentation and simultaneous saccharification and cofermentation (SSCF). A commercial cellulase (Cellic CTec2) was used for hydrolysis of lignocellulosic biomass and an l-lactate-deficient mutant strain Lactobacillus plantarum NCIMB 8826 ldhL1 and its derivative harboring a xylose assimilation plasmid (ΔldhL1-pCU-PxylAB) were used for fermentation. The SSCF process demonstrated the advantage of avoiding feedback inhibition of released sugars from lignocellulosic biomass, thus significantly improving d-lactic acid yield and productivity. d-lactic acid (27.3 g L(-1) ) and productivity (0.75 g L(-1) h(-1) ) was obtained from corn stover and d-lactic acid (22.0 g L(-1) ) and productivity (0.65 g L(-1) h(-1) ) was obtained from sorghum stalks using ΔldhL1-pCU-PxylAB via the SSCF process. The recombinant strain produced a higher concentration of d-lactic acid than the mutant strain by using the xylose present in lignocellulosic biomass. Our findings demonstrate the potential of using renewable lignocellulosic biomass as an alternative to conventional feedstocks with metabolically engineered lactic acid bacteria to produce d-lactic acid. © 2016 American Institute of Chemical Engineers Biotechnol. Prog., 32:271-278, 2016.

METABOLIC ADAPTATION STRATEGY USING Zymomonas mobilis CP4 CELLS FOR THE PRODUCTION OF SECOND GENERATION ETHANOL

During the past few decades, considerable effort has been made to utilize agricultural and forest residues as biomass feedstock for the production of bioethanol as an alternative fuel. The bacterium Zymomonas mobilis was shown to be extremely attractive for the production of second-generation ethanol from glucose of the cellulose fraction due to its ability to uptake high amounts of this sugar, resulting in high ethanol productivity values. However, the wild-type strains are unable to metabolize xylose that arises from the hemicellulose fraction. Molecular biology techniques were incorporated to render the strain used in this study capable of fermenting xylose into ethanol and thus increase the efficiency of second-generation ethanol production. Thus, the aim of this study was to evaluate the performance of a recombinant strain of Z. mobilis in simultaneous saccharification and co-fermentation (SSCF) processes, in which the fermentation of both sugars (glucose and xylose) occurs in one step. Regarding the genetic transformation,the 1,565 kb Z. mobilis plasmid pZMO1 was chemically synthesized and cloned into a synthetic vector that contains the E. coli and Z. mobilis replication checkmark origin,the XI, XK, TAL, and TKL genes and tetracycline resistance. Metabolic adaptation was performed by transferring the recombinant strain to media containing increased xylose concentrations. Then, an experimental response surface methodology was used to evaluatethe addition of glucose and xylose with different concentrations, as well as the incorporation of hemicellulosic hydrolyzate in different proportions. The recombinant Z. mobilis CP4 strain reached 25 g/L ethanol, confirming that approximately 50% of this pentose was consumed in the SSCF process when using 30% solids, 20.5% hemicellulose hydrolysate, 10 mg/L tetracycline, an enzyme load of 25 FPU/g cellulignin, and 10% of the initial inoculum.Â

Simultaneous saccharification and co-fermentation of aqueous ammonia pretreated corn stover with an engineered Saccharomyces cerevisiae SyBE005

Co-fermentation of glucose and xylose from lignocelluloses is an efficient approach to increasing ethanol production. Simultaneous saccharification and co-fermentation (SSCF) of corn stover pretreated with aqueous ammonia was performed using engineered yeast with xylose utilization pathway. Thus far, the effect of the several key factors on SSCF was investigated, including temperature, inoculation size, pre-hydrolysis and pH. Ethanol concentration was achieved to 36.5g/L during SSCF process with 6% glucan loading. The addition of Tween 20 reduced enzyme loading, i.e., from 15 to 7.5FPU/gglucan with the same final ethanol concentration. The ethanol concentration was achieved to 70.1g/L at 12% glucan loading. Yeast feeding, combined with substrate and enzyme feeding, was proved to be an efficient approach for SSCF with high solid loading.

Production of l - and d -lactic acid from waste Curcuma longa biomass through simultaneous saccharification and cofermentation

Simultaneous saccharification and cofermentation (SSCF) of Curcuma longa waste biomass obtained after turmeric extraction to L- and D-lactic acid by Lactobacillus coryniformis and Lactobacillus paracasei, respectively, was investigated. This is a rich, starchy, agro-industrial waste with potential for use in industrial applications. After optimizing the fermentation of the biomass by adjusting nitrogen sources, enzyme compositions, nitrogen concentrations, and raw material concentrations, the SSCF process was conducted in a 7-l jar fermentor at 140 g dried material/L. The maximum lactic acid concentration, average productivity, reducing sugar conversion and lactic acid yield were 97.13 g/L, 2.7 g/L/h, 95.99% and 69.38 g/100 g dried material for L-lactic acid production, respectively and 91.61 g/L, 2.08 g/L/h, 90.53% and 65.43 g/100 g dried material for D-lactic acid production, respectively. The simple and efficient process described in this study could be utilized by C. longa residue-based lactic acid industries without requiring the alteration of plant equipment.

Optimized simultaneous saccharification and co-fermentation of rice straw for ethanol production by Saccharomyces cerevisiae and Scheffersomyces stipitis co-culture using design of experiments

Herein an ethanol production process from rice straw was optimized. Simultaneous saccharification and co-fermentation (SSCF) using Saccharomyces cerevisiae and Scheffersomyces stipitis co-culture was carried out to enhance ethanol production. The optimal saccharification solid loading was 5%. Key fermentation parameters for co-culture including cell ratio, agitation rate and temperature was rationally optimized using design of experiment (DoE). Optimized co-culture conditions for maximum ethanol production efficiency were at S. cerevisiae:S. stipitis cell ratio of 0.31, agitation rate of 116 rpm and temperature of 33.1°C. The optimized SSCF process reached ethanol titer of 15.2g/L and ethanol yield of 99% of theoretical yield, consistent with the DoE model prediction. Moreover, SSCF process under high biomass concentration resulted in high ethanol concentration of 28.6g/L. This work suggests the efficiency and scalability of the developed SSCF process which could provide an important basis for the economic feasibility of ethanol production from lignocelluloses.

Simultaneous saccharification and co-fermentation for bioethanol production using corncobs at lab, PDU and demo scales

BackgroundWhile simultaneous saccharification and co-fermentation (SSCF) is considered to be a promising process for bioconversion of lignocellulosic materials to ethanol, there are still relatively little demo-plant data and operating experiences reported in the literature. In the current work, we designed a SSCF process and scaled up from lab to demo scale reaching 4% (w/v) ethanol using xylose rich corncobs.ResultsSeven different recombinant xylose utilizing Saccharomyces cerevisiae strains were evaluated for their fermentation performance in hydrolysates of steam pretreated corncobs. Two strains, RHD-15 and KE6-12 with highest ethanol yield and lowest xylitol yield, respectively were further screened in SSCF using the whole slurry from pretreatment. Similar ethanol yields were reached with both strains, however, KE6-12 was chosen as the preferred strain since it produced 26% lower xylitol from consumed xylose compared to RHD-15. Model SSCF experiments with glucose or hydrolysate feed in combination with prefermentation resulted in 79% of xylose consumption and more than 75% of the theoretical ethanol yield on available glucose and xylose in lab and PDU scales. The results suggest that for an efficient xylose conversion to ethanol controlled release of glucose from enzymatic hydrolysis and low levels of glucose concentration must be maintained throughout the SSCF. Fed-batch SSCF in PDU with addition of enzymes at three different time points facilitated controlled release of glucose and hence co-consumption of glucose and xylose was observed yielding 76% of the theoretical ethanol yield on available glucose and xylose at 7.9% water insoluble solids (WIS). With a fed-batch SSCF in combination with prefermentation and a feed of substrate and enzymes 47 and 40 g l-1 of ethanol corresponding to 68% and 58% of the theoretical ethanol yield on available glucose and xylose were produced at 10.5% WIS in PDU and demo scale, respectively. The strain KE6-12 was able to completely consume xylose within 76 h during the fermentation of hydrolysate in a 10 m3 demo scale bioreactor.ConclusionsThe potential of SSCF is improved in combination with prefermentation and a feed of substrate and enzymes. It was possible to successfully reproduce the fed-batch SSCF at demo scale producing 4% (w/v) ethanol which is the minimum economical requirement for efficient lignocellulosic bioethanol production process.

Continuous SSCF of AFEX™ pretreated corn stover for enhanced ethanol productivity using commercial enzymes and Saccharomyces cerevisiae 424A (LNH‐ST)

High productivity processes are critical for commercial production of cellulosic ethanol. One high productivity process-continuous hydrolysis and fermentation-has been applied in corn ethanol industry. However, little research related to this process has been conducted on cellulosic ethanol production. Here, we report and compare the kinetics of both batch SHF (separate hydrolysis and co-fermentation) and SSCF (simultaneous saccharification and co-fermentation) of AFEX™ (Ammonia Fiber Expansion) pretreated corn stover (AFEX™-CS). Subsequently, we designed a SSCF process to evaluate continuous hydrolysis and fermentation performance on AFEX™-CS in a series of continuous stirred tank reactors (CSTRs). Based on similar sugar to ethanol conversions (around 80% glucose-to-ethanol conversion and 47% xylose-to-ethanol conversion), the overall process ethanol productivity for continuous SSCF was 2.3- and 1.8-fold higher than batch SHF and SSCF, respectively. Slow xylose fermentation and high concentrations of xylose oligomers were the major factors limiting further enhancement of productivity.

Evaluation of environmental impacts of cellulosic ethanol using life cycle assessment with technological advances over time

Abstract Life Cycle Assessment (LCA) has been used in quantifying the environmental impacts of materials, processes, products, or systems across their entire lifespan from creation to disposal. To evaluate the environmental impact of advancing technology, Life Cycle Assessment with Technological Advances over Time (LCA-TAT) incorporates technology improvements within the traditional LCA framework. In this paper, the LCA-TAT is applied to quantify the environmental impacts of ethanol production using cellulosic biomass as a feedstock through the simultaneous saccharification and co-fermentation (SSCF) process as it improves over time. The data for the SSCF process are taken from the Aspen Plus® simulation developed by the National Renewable Energy Lab (NREL). The Environmental Fate and Risk Assessment Tool (EFRAT) is used to calculate the fugitive emissions and SimaPro 7.1 software is used to quantify the environmental impacts of processes. The impact indicators of the processes are calculated using the Eco-indicator 95 method; impact categories analyzed include ozone layer depletion, heavy metals, carcinogens, summer smog, winter smog, pesticides, greenhouse effect, acidification, and eutrophication. Based on the LCA-TAT results, it is found that removal of the continuous ion exchange step within the pretreatment area increases the environmental impact of the process. The main contributor to the increase in the environmental impact of the process is the heavy metal indicator. In addition, a sensitivity analysis is performed to identify major inputs and outputs that affect environmental impacts of the overall process. Based on this analysis it is observed that an increase in waste production and acid use have the greatest effect on the environmental impacts of the SSCF process. Comparing economic analysis with projected technological advances performed by NREL, the improvement in environmental impact was not matched by a concomitant improvement in economic performance. In order to implement technologies which are environmentally sustainable, it is critical to perform LCA for future technological advances.

Two-step SSCF to convert AFEX-treated switchgrass to ethanol using commercial enzymes and Saccharomyces cerevisiae 424A(LNH-ST)

It is well known that simultaneous saccharification and co-fermentation (SSCF) reduces cellulosic ethanol production cost compared to separate hydrolysis and fermentation (SHF). However, the traditional SSCF process of converting Ammonia Fiber Expansion (AFEX) pretreated switchgrass to ethanol using both commercial enzymes and Saccharomyces cerevisiae 424A(LNH-ST) gave reduced ethanol yield due to lower xylose consumption. To overcome this problem we have developed a two-step SSCF process, in which xylan was hydrolyzed and fermented first followed by the hydrolysis and fermentation of glucan. Important parameters, such as temperature, cellulases loading during xylan hydrolysis and fermentation, initial OD 600 for inoculation of S. cerevisiae 424A(LNH-ST), and pH, were studied for best performance. Compared with traditional SSCF, the two-step SSCF showed higher xylose consumption and higher ethanol yield. The sugar conversion was also enhanced from 70% by enzymatic hydrolysis to 82% by two-step SSCF. One important finding is that the residue from enzymatic hydrolysis plays a significant role in reducing xylose consumption and ethanol metabolic yield during SSCF.