Separate Hydrolysis And Fermentation Research Articles

Bioprocess development on microalgae-based CO2 fixation and bioethanol production using Scenedesmus obliquus CNW-N

A two-stage cultivation strategy was applied to achieve greater CO2 fixation and carbohydrate productivity with an indigenous microalga Scenedesmus obliquus CNW-N, which was first cultivated using a nutrient-rich medium to promote cell growth, and was then switched to a nutrient-deficient condition to trigger carbohydrate accumulation. The optimal biomass productivity, carbohydrate productivity, and CO2 fixation rate were 681.4, 352.9, and 1192.5 mg L(-1) d(-1), respectively, with a 51.8% carbohydrate content (based on dry weight). This performance is better than the results in most related studies. The microalgal carbohydrate was mainly composed of glucose, which accounts for nearly 80% of total sugars. Dilute acid hydrolysis with 2% H2SO4 can saccharify the wet microalgal biomass effectively, achieving a glucose yield of 96-98%. Using the acidic hydrolysate of the microalga as feedstock, the separate hydrolysis and fermentation (SHF) process gave an ethanol concentration of 8.55 g L(-1), representing a theoretical yield of nearly 99.8%.

Optimization Modeling of Ethanol Production from Shorgum bicolor Grain: Comparison between Separate Hydrolysis Fermentation and Simultaneous Saccharification Fermentation

Two different process configurations, simultaneous saccharification and fermentation (SSF), and separate hydrolysis and fermentation (SHF), were compared for ethanol production from Shorgum bicolor grain. Optimization modeling for glucoamylase and Zymomonas mobilis concentration in both of SSF and SHF were carried out to obtain optimal concentration of ethanol production. The optimum condition was achieved using 0.021 % (v/v) of glucoamylase, and 30.19% (v/v) of Z. mobilis for SHF. In contrast, the optimum condition for SSF was 0.021 % (v/v) of glucoamylase and 17.51% (v/v) of Z. mobilis . The model predicted SHF processing to be superior. The superiority of SHF over SSF was confirmed experimentally, the result showed ethanol yield of SHF was 134.80 g L -1 and ethanol yield of SSF was 115.66 g L -1 after 72 h incubation time. A high similarity was observed between the predicted and experimental results, demonstrating the accuracy of the model.

Unraveling the structure of sugarcane bagasse after soaking in concentrated aqueous ammonia (SCAA) and ethanol production by Scheffersomyces (Pichia) stipitis

BackgroundFuel ethanol production from sustainable and largely abundant agro-residues such as sugarcane bagasse (SB) provides long term, geopolitical and strategic benefits. Pretreatment of SB is an inevitable process for improved saccharification of cell wall carbohydrates. Recently, ammonium hydroxide-based pretreatment technologies have gained significance as an effective and economical pretreatment strategy. We hypothesized that soaking in concentrated aqueous ammonia-mediated thermochemical pretreatment (SCAA) would overcome the native recalcitrance of SB by enhancing cellulase accessibility of the embedded holocellulosic microfibrils.ResultsIn this study, we designed an experiment considering response surface methodology (Taguchi method, L8 orthogonal array) to optimize sugar recovery from ammonia pretreated sugarcane bagasse (SB) by using the method of soaking in concentrated aqueous ammonia (SCAA-SB). Three independent variables: ammonia concentration, temperature and time, were selected at two levels with center point. The ammonia pretreated bagasse (SCAA-SB) was enzymatically hydrolysed by commercial enzymes (Celluclast 1.5 L and Novozym 188) using 15 FPU/g dry biomass and 17.5 Units of β-glucosidase/g dry biomass at 50°C, 150 rpm for 96 h. A maximum of 28.43 g/l reducing sugars corresponding to 0.57 g sugars/g pretreated bagasse was obtained from the SCAA-SB derived using a 20% v/v ammonia solution, at 70°C for 24 h after enzymatic hydrolysis. Among the tested parameters, pretreatment time showed the maximum influence (p value, 0.053282) while ammonia concentration showed the least influence (p value, 0.612552) on sugar recovery. The changes in the ultra-structure and crystallinity of native SCAA-SB and enzymatically hydrolysed SB were observed by scanning electron microscopy (SEM), x-ray diffraction (XRD) and solid-state 13C nuclear magnetic resonance (NMR) spectroscopy. The enzymatic hydrolysates and solid SCAA-SB were subjected to ethanol fermentation under separate hydrolysis and fermentation (SHF) and simultaneous saccharification and fermentation (SSF) by Scheffersomyces (Pichia) stipitis NRRL Y-7124 respectively. Higher ethanol production (10.31 g/l and yield, 0.387 g/g) was obtained through SSF than SHF (3.83 g/l and yield, 0.289 g/g).ConclusionsSCAA treatment showed marked lignin removal from SB thus improving the accessibility of cellulases towards holocellulose substrate as evidenced by efficient sugar release. The ultrastructure of SB after SCAA and enzymatic hydrolysis of holocellulose provided insights of the degradation process at the molecular level.

Ethanol production at high temperature from cassava pulp by a newly isolated <em>Kluyveromyces marxianus</em> strain, TISTR 5925

<em>Kluyveromyces marxianus</em> TISTR 5925, isolated from rotten fruit in Thailand, can ferment at pH 3 at temperatures between 42 and 45 ℃. Bioethanol production from cassava pulp using the simultaneous saccharification and fermentation (SSF) process was evaluated and compared with the separated hydrolysis and fermentation (SHF) process using <em>K. marxianus</em> TISTR 5925. The ethanol concentrations obtained from the SSF process were higher than those from the SHF process. The optimum conditions for ethanol production were investigated by response surface methodology (RSM) based on a five level central composite design involving the following variables: enzyme dilution (times), temperature (℃) and fermentation time (h). Cassava pulp was pretreated by boiling for 10 min, treated with a mixture of enzymes (cellulase, pectinase, α-amylase and glucoamylase), then fermented by <em>K. marxianus</em> TISTR 5925. Data obtained from the RSM were subjected to analysis of variance and fit to a second order polynomial equation. At optimum enzyme dilution (0.1 times), temperature (41 ℃) and fermentation time (27 h), the maximum obtained concentration of ethanol was 5.0% (w/v), which is very close to the predicted ethanol concentration of 5.3% (w/v).

Fuel ethanol production fromEucalyptus globuluswood by autocatalized organosolv pretreatment ethanol–water and SSF

AbstractBACKGROUNDLignocellulosic biomass (LCB) offers the only sustainable alternative to the use of fossil fuels as oil by employing its main components (cellulose, hemicellulose and lignin) as a carbon source for the production of biofuels, energy and value‐added chemicals. The aim of the present study was to investigate ethanol production from organosolv pretreatedEucalyptus globuluswood, carrying out the simultaneous sacharification and fermentation (SSF) process at a substrate loading of 10 and 15% (w/v) and using concentrations of 6 and 12 g L−1of the thermally acclimatizedS. cerevisiaeIR2T9‐a strain. These SSF experiments were also evaluated by increasing the enzyme loading in the reaction medium. Finally, a comparison was made between separate hydrolysis and fermentation (SHF) and SSF processes. With the information obtained and from published information, a general mass balance was developed.RESULTSThe highest ethanol concentration (∼42 g L−1) in the fermentation broth was obtained at a substrate consistency of 15% (w/v), enzyme loading of 20 FPU cellulase 40 UI β‐glucosidase g−1of pretreated material and using bothS. cerevisiaestrain IR2‐9a concentrations (6 and 12 g L−1).CONCLUSIONThe results of enzymatic hydrolysis (EH) show that increasing substrate content from 10 to 15% (w/v) decreases the conversion efficiency of cellulose to glucose. Furthermore, the mass balances of the process indicate that the SSF process is a better alternative than the SHF configuration, because larger amounts of ethanol can be obtained. Copyright © 2012 Society of Chemical Industry

BiotecVisions 2012, August

BiotecVisions 2012, August

Biobutanol production from agricultural waste by an acclimated mixed bacterial microflora

Biobutanol production from cellulosic feedstock is considered promising and economically feasible. A highly efficient butanol-producing bacterial microflora (containing mainly Clostridial species) was obtained from hydrogen-producing sewage sludge. In this work, two types of agricultural waste (i.e. rice straw and sugarcane bagasse) were alkaline pretreated and then hydrolyzed using a cocktail of cellulases originating from Pseudomonas sp. CL3 and Clostridium sp. TCW1. The hydrolysates were used to produce biobutanol by the isolated mixture culture using either separate hydrolysis and fermentation (SHF) or a combination of SHF with simultaneous saccharification and fermentation (SHF–SSF) processes. In the SHF process, the maximum butanol concentration, productivity, yield and ABE (acetone–butanol–ethanol) ratio from bagasse were 2.29g/L, 1.00g/Ld, 0.52mol butanol/mol reducing sugar and 0.12:1:0.06, respectively, and for rice straw were 2.92g/L, 1.41g/Ld, 0.51mol butanol/mol reducing sugar and 0.19:1:0.1, respectively. In the SHF–SSF process, the maximum butanol concentration, productivity, and yield for bagasse were 1.95g/L, 0.61g/Ld and 0.37mol butanol/mol reducing sugar, respectively, and for rice straw were 2.93g/L, 0.86g/Ld and 0.49mol butanol/mol reducing sugar, respectively. This work demonstrated a novel and feasible approach of converting agricultural waste into a valuable biofuel (i.e. butanol).

Efficient Acetone–Butanol–Ethanol Production from Corncob with a New Pretreatment Technology—Wet Disk Milling

Acetone–butanol–ethanol (ABE) production from corncob was achieved using an integrated process combining wet disk milling (WDM) pretreatment with enzymatic hydrolysis and fermentation by Clostridium acetobutylicum SE-1. Sugar yields of 71.3 % for glucose and 39.1 % for xylose from pretreated corncob were observed after enzymatic hydrolysis. The relationship between sugar yields and particle size of the pretreated corncob was investigated, suggesting a smaller particle size benefits enzymatic hydrolysis with the WDM pretreatment approach. Analysis of the correlation between parameters representing particle size and efficiency of enzymatic hydrolysis predicted that frequency 90 % is the best parameter representing particle size for the indication of the readiness of the material for enzymatic hydrolysis. ABE production from corncob was carried out with both separate hydrolysis and fermentation (SHF) and simultaneous saccharification and fermentation (SSF) processes using C. acetobutylicum SE-1. Interestingly, when considering the time for fermentation as the time for ABE production, a comparable rate of sugar consumption and ABE production in the SHF process (0.55 g/l·h sugar consumption and 0.20 g/l·h ABE production) could be observed when glucose (0.50 g/l·h sugar consumption and 0.17 g/l·h ABE production) or a mixture of glucose and xylose (0.68 g/l·h sugar consumption and 0.22 g/l·h ABE production) mimicking the corncob hydrolysate was used as the substrate for fermentation. This result suggested that the WDM is a suitable pretreatment method for ABE production from corncob owing to the mild conditions. A higher ABE production rate could be observed with the SSF process (0.15 g/l·h) comparing with SHF process (0.12 g/l·h) when combining the time for saccharification and fermentation and consider it as the time for ABE production. This is possibly a result of low sustained sugar level during fermentation. These investigations lead to the suggestion that this new WDM pretreatment method has the potentials to be exploited for efficient ABE production from corncob.

Challenges in enzymatic hydrolysis and fermentation of pretreated Arundo donax revealed by a comparison between SHF and SSF

The perennial herbaceous crop Arundo donax is a potential feedstock for second-generation bioethanol production. In the present work, two different process options were investigated for the conversion of two differently steam-pretreated batches of A. donax. The pretreated raw material was converted to ethanol with a xylose-consuming Saccharomyces cerevisiae strain, VTT C-10880, by applying either separate hydrolysis and fermentation (SHF) or simultaneous saccharification and fermentation (SSF). The highest overall ethanol yield and final ethanol concentration were achieved using SHF (0.27gg−1 and 20.6gL−1 compared to 0.24gg−1 and 19.0gL−1 when SSF was used). The performance of both SHF and SSF was improved by complementing the cellulolytic enzymes with hemicellulases. The higher amount of acetic acid in one of the batches was shown to strongly affect xylose consumption in the fermentation. Only half of the xylose was consumed when batch 1 (high acetic acid) was fermented, compared to that 94% of the xylose was consumed in fermentation of batch 2 (lower acetic acid). Furthermore, the high amount of xylooligomers present in the pretreated materials considerably inhibited the enzymatic hydrolysis. Both the formation of xylooligomers and acetic acid thus need to be considered in the pretreatment process in order to achieve efficient conversion of A. donax to ethanol.

Simultaneous saccharification and microbial lipid fermentation of corn stover by oleaginous yeast Trichosporon cutaneum

Simultaneous saccharification and fermentation (SSF) is the most commonly practiced operation in lignocellulose bioconversion to avoid the sugar product inhibition to cellulase enzymes. In this study, for the first time SSF was tested on microbial lipid fermentation using the diluted acid pretreated and biodetoxified corn stover. The results show that SSF was effective than the separate hydrolysis and fermentation (SHF) on lipid accumulation of Trichosporon cutaneum CX1 cells in both the small scale (5L) and the enlarged scale (50L) bioreactors. The solutions for the oxygen transfer and the lipid extraction in SSF practically worked well. The process parameters were optimized and the lipid yield obtained were 3.03g/L in the 5L, and 3.23g/L in the 50L, respectively. The result also shows that the cellulase enzyme could be partially recycled in the SSF. The study provided a practical and efficient way for microbial lipid production from lignocellulose material.

Fermentation of glucose and xylose in cattail processed by different pretreatment technologies

The effects of different pretreatment technologies, including sulfuric acid, hot-water, NaOH, and MgCl2 pretreatments, on the fermentation of xylose and glucose to ethanol by Saccharomyces cerevisiae ATCC 24858 and Escherichia coli KO11 were investigated. In this study, cattail was used as the feedstock. The use of aquatic plant cattails to produce biofuel will add value to land and reduce emissions of greenhouse gases by replacing petroleum products. The pretreated biomass first was enzymatically hydrolyzed for 2 days, followed by a 2-day Simultaneous Saccharification and Fermentation (SSF) using S. cerevisiae. The glucose to ethanol yields were approximately 85 to 91% of the theoretical yield for this S. cerevisiae strain. Glucose and xylose released from cattail cellulose and hemicellulose could be fermented to ethanol using E. coli KO11, resulting in approximately 85% of the theoretical ethanol yield using either a Separate Hydrolysis and Fermentation (SHF) process or a SSF process. In order to improve the sugars to ethanol yields, a detoxification process is necessary to remove the inhibitory compounds produced during the acid pretreatment process. Among the four pretreatment methods, the dilute acid pretreatment was found to be superior, and additional research is required to optimize the economics of the overall biorefinery process.

Cellulosic ethanol production performance with SSF and SHF processes using immobilized Zymomonas mobilis

Bioethanol converted from lignocellulosic feedstock, such as agricultural waste, is considered one of the most promising biofuels being developed. The raw materials usually need to be pretreated and hydrolyzed by cellulolytic enzymes to produce sugars for subsequent ethanol fermentation. Immobilized bacteria or yeasts have been frequently used for batch or continuous ethanol fermentation due to their feasibility for repeated use with high biomass retention during the process. In this study, Zymomonas mobilis cells immobilized in calcium alginate (CA) and polyvinyl alcohol (PVA) were used to produce ethanol from cellulosic feedstock using SSF (simultaneous saccharification and fermentation) and SHF (separate hydrolysis and fermentation) processes. The performance based on different immobilized cells and different processes was compared. The results show that PVA immobilized cells with the SHF process gave the highest ethanol concentration of 6.24g/L, with an ethanol yield of 79.09% and a maximum ethanol productivity of 3.04g/L/h. In contrast, the performance of CA-immobilized cells with SHF was poorer, with the highest ethanol concentration, ethanol yield, and maximum ethanol productivity of 5.52g/L, 69.96% and 2.37g/L/h, respectively. For the SSF process, the maximum ethanol concentration, ethanol yield, and maximum ethanol productivity were 5.53g/L, 70.09%, and of 1.31g/L/h, respectively, for the PVA immobilized Z. mobilis, while they were 5.44g/L, 68.95%, and 1.27g/L/h for CA immobilized cells. The comparison with suspended cells shows that the immobilized cells of Z. mobilis are feasible for ethanol production via SSF and SHF.

Saccharina japonica를 이용한 전처리 및 분리당화발효와 동시당화발효로부터 에탄올 생산

Ethanol fermentations were carried out using simultaneous saccharification and fermentation (SSF) and separated hydrolysis and fermentation (SHF) processes with monosaccharides from seaweed, Saccharina japonica (sea tangle, Dasima) as the biomass. The pretreatment was carried out by thermal acid hydrolysis with H₂SO₄ or HCl. Optimal pretreatment condition was determined at 10% (w/v) seaweed slurry with 37.5 mM H₂SO₄ at 121℃ for 60 min. To increase the yield of saccharfication, isolated marine bacteria Bacillus sp. JS-1 was used and 48 g/L of reducing sugar were produced. Ethanol fermentation was performed using SSF and SHF process with Pachysolen tannophilus KCTC 7937. The ethanol concentration was 6.5 g/L by SSF and 6.0 g/L by SHF.

A Comparison of the Production of Ethanol between Simultaneous Saccharification and Fermentation and Separate Hydrolysis and Fermentation Using Unpretreated Cassava Pulp and Enzyme Cocktail

The processes of separate hydrolysis and fermentation (SHF) and simultaneous saccharification and fermentation (SSF) were employed using Saccharomyces cerevisiae for the production of ethanol from cassava pulp without any pretreatment. A combination of amylase, cellulase, cellobiase, and glucoamylase produced the highest levels of ethanol production in both the SHF and the SSF method. A temperature of 37 °C, a pH of 5.0, and an inoculum size of 6% were the optimum conditions for SSF. For the batch process at a pulp concentration of 20%, ethanol production levels from SHF and SSF were the highest, at 23.51 and 34.67 g L(-1) respectively, but in the fed-batch process, the levels of ethanol production from SHF and SSF rose to 29.39 and 43.25 g L(-1) respectively, which were 25% and 24.7% higher than those of the batch process. Thus SSF using the fed-batch provided a more efficient method for the utilization of cassava pulp.

Ethanol production from steam-pretreated sweet sorghum bagasse with high substrate consistency enzymatic hydrolysis

In this work, separate hydrolysis and fermentation (SHF) and simultaneous saccharification fermentation (SSF) with high substrate consistency (the mass fraction: 12%) were performed with the steam-pretreated sweet sorghum bagasse (SSB). Fermentation ability of four yeast strains and influences of residual solids after hydrolysis on fermentation were investigated in SHF. Meanwhile, influences of inorganic salts on fermentation were assessed to determine their suitable supplementations for ethanol production. Additionally, influences of initial yeast inoculation on SHF and SSF were further investigated. The results showed the adopted yeast strain, Tembec 1, displayed the best fermentation performance on the hydrolysate of pretreated SSB, and the residual solids in hydrolysate had negligible influences on ethanol fermentation. Although the deficiency or overdose of (NH4)2HPO4 or MgSO4·7H2O could reduce ethanol yield in SHF, the suitable supplementation of (NH4)2HPO4 (0.5 g L−1) and MgSO4·7H2O (1.0 g L−1) could increase ethanol yield by 5.2% and 8.3%, respectively. The initial yeast inoculation of 3 g L−1 could satisfy both SSF and SHF, which achieved 63.8% and 57.9% ethanol yield of theoretical one with final ethanol concentration of 23.3 g L−1 and 21.2 g L−1, respectively. In addition, ethanol yield kept almost constant as yeast was inoculated from 3 to 5 g L−1 in SHF, whereas it decreased significantly in SSF.

An evaluation of cellulose saccharification and fermentation with an engineered Saccharomyces cerevisiae capable of cellobiose and xylose utilization

Commercial-scale cellulosic ethanol production has been hindered by high costs associated with cellulose-to-glucose conversion and hexose and pentose co-fermentation. Simultaneous saccharification and fermentation (SSF) with a yeast strain capable of xylose and cellobiose co-utilization has been proposed as a possible avenue to reduce these costs. The recently developed DA24-16 strain of Saccharomyces cerevisiae incorporates a xylose assimilation pathway and a cellodextrin transporter (CDT) that permit rapid growth on xylose and cellobiose. In the current work, a mechanistic kinetic model of cellulase-catalyzed hydrolysis of cellulose was combined with a multi-substrate model of microbial growth to investigate the ability of DA24-16 and improved cellobiose-consuming strains to obviate the need for exogenously added β-glucosidase and to assess the impact of cellobiose utilization on SSF and separate hydrolysis and fermentation (SHF). Results indicate that improved CDT-containing strains capable of growing on cellobiose as rapidly as on glucose produced ethanol nearly as rapidly as non-CDT-containing yeast supplemented with β-glucosidase. In producing 75 g/L ethanol, SSF with any strain did not result in shorter residence times than SHF with a 12 h saccharification step. Strains with improved cellobiose utilization are therefore unlikely to allow higher titers to be reached more quickly in SSF than in SHF.

PURPLE GUINEA GRASS: PRETREATMENT AND ETHANOL FERMENTATION

Treatment with dilute sulfuric acid (H2SO4) or calcium hydroxide (Ca(OH)2) at 121C and 103.4 kPa was used to improve the efficiency of the cellulose digestion of purple guinea grass. Cellulase hydrolysis of the dilute H2SO4-pretreated purple guinea grass under optimized conditions (6% (w/v) in 3% (w/v) H2SO4 for 30 min) yielded a slightly higher level of reducing sugars than that from the Ca(OH)2 pretreatment under optimized conditions (6% (w/v) in 4% (w/v) Ca(OH)2 for 5 min). However, the level of glucose released from the Ca(OH)2-pretreated purple guinea grass was slightly higher than that from the dilute H2SO4 pretreatment. Ethanol fermentation, via the separate hydrolysis and fermentation (SHF) process using Saccharomyces cerevisiae, of the Ca(OH)2-pretreated purple guinea grass and then hydrolyzed with commercial cellulase (9 PFU/g, dry wt.) for 6 h yielded ethanol at 0.44 g/g glucose (0.21 g/g cellulose) within 48 h, while that from the simultaneous saccharification and fermentation process yielded 14.3% less ethanol at 0.18 g/g cellulose within 96 h (including the 6 h saccharification time). The ethanol yield from the SHF process increased 1.14-fold to 0.497 g/g glucose (0.24 g/g cellulose) when the fermentation was performed in a 5 L fermentor.

Alkaline sulfite/anthraquinone pretreatment followed by disk refining ofPinus radiataandPinus caribaeawood chips for biochemical ethanol production

AbstractBACKGROUND:Alkaline sulfite/anthraquinone (ASA) cooking ofPinus radiataandPinus caribaeawood chips followed by disk refining was used as a pretreatment for the production of low lignified and high fibrillated pulps. The pulps produced with different delignification degrees and refined at different energy inputs (250, 750 and 1600 Wh) were saccharified with cellulases and fermented to ethanol withSaccharomyces cerevisiaeusing separated hydrolysis and fermentation (SHF) or semi‐simultaneous saccharification and fermentation (SSSF) processes.RESULTS:Delignification of ASA pulps was between 25% and 50%, with low glucans losses. Pulp yield was from 70 to 78% for pulps ofP. radiataand 60% for the pulp ofP. caribaea. Pulps obtained after refining were evaluated in assays of enzymatic hydrolysis. Glucans‐to‐glucose conversion varied from 20 to 70%, depending on the degree of delignification and fibrillation of the pulps. The best ASA pulp ofP. radiatawas used in SHF and SSSF experiments of ethanol production. Such experiments produced maximum ethanol concentration of 20 g L−1, which represented roughly 90% of glucose conversion and an estimated amount of 260 L ethanol ton−1wood.P. caribaeapulp also presented good performance in the enzymatic hydrolysis and fermentation but, due to the low amount of cellulose present, only 140 L ethanol would be obtained from each ton of wood.CONCLUSION:ASA cooking followed by disk refining was shown to be an efficient pretreatment process, which generated a low lignified and high‐fibrillated substrate that allowed the production of ethanol from the softwoods with high conversion yields. Copyright © 2012 Society of Chemical Industry

A novel integrated biological process for cellulosic ethanol production featuring high ethanol productivity, enzyme recycling and yeast cells reuse

High enzyme loading requirements, slow xylose fermentation and low ethanol productivity are three of the major issues impeding commercial biochemical production of cellulosic ethanol. We report here a novel integrated biological process to overcome these problems. Enzymatic hydrolysis was performed for only 24 h to avoid the slow rate period which begins at about that time. Unhydrolyzed recalcitrant solids with adsorbed enzymes were recycled to the subsequent cycles. By this approach, easily digestible biomass was processed first and recalcitrant biomass was given enough residence time to get hydrolyzed during subsequent processing steps. Fermentation was conducted using a high yeast inoculation level and was also completed in 24 h. The yeast cells were then recycled. With this novel processing approach, the enzyme loading was reduced from 36 to 22.3 and 25.8 mg protein per gram glucan, respectively, for separate hydrolysis and fermentation (SHF) and for simultaneous saccharification and co-fermentation (SSCF) on AFEX™ pretreated corn stover. The process ethanol productivity was enhanced by 2 to 3 fold due to both fast enzymatic hydrolysis and fast fermentation.

Screening of steam explosion conditions for glucose production from non-impregnated wheat straw

Abstract The conversion of wheat straw to fermentable sugar for bioethanol production typically involves a thermal pretreatment step, followed by enzymatic hydrolysis. In this study we have investigated the effect of steam explosion parameters on wheat straw digestibility using a newly designed steam explosion unit and a process without acid impregnation. The wheat straw was steam pretreated using 18 different conditions in the temperature range of 170–220 °C and the resulting material was used directly (i.e. without washing) for enzymatic hydrolysis and fermentation in either a separate hydrolysis and fermentation (SHF)-type or a simultaneous saccharification and fermentation (SSF)-type set-up. Maximum glucose yields upon enzymatic hydrolysis were obtained after pretreatment at 210 °C for 10 min and yields were similar at harsher conditions. Xylose yields increased with temperature and residence time up to 190 °C, but decreased at harsher pretreatment conditions since these led to xylan degradation and concomitant production of furfural. In an SHF-type set-up ethanol formation did not follow enzymatic glucose release and was inversely correlated with furfural levels. An SFF-type set-up displayed a straightforward correlation between the expected amount of released glucose and the ethanol yields. The highest saccharification yields corresponded to about 90% of the cellulose in the substrate. Overall, this study shows that steam explosion without an acid catalyst is a good pretreatment method for saccharification of wheat straw. Optimal steam explosion conditions need to be a compromise between sugar accessibility and sugar degradation.