Sweet sorghum as a whole-crop feedstock for ethanol production

The potential of sweet sorghum as an alternative crop for ethanol production was investigated in this study. Initially, the enzymatic hydrolysis of sorghum grains was optimized, and the hydrolysate produced under optimal conditions was used for ethanol production with an industrial strain of Saccharomyces cerevisiae, resulting in an ethanol concentration of 87 g L⁻¹. From the sugary fraction (sweet sorghum juice), 72 g L⁻¹ ethanol was produced. The sweet sorghum bagasse was submitted to acid pretreatment for hemicellulose removal and hydrolysis, and a flocculant strain of Scheffersomyces stipitis was used to evaluate the fermentability of the hemicellulosic hydrolysate. This process yielded an ethanol concentration of 30 g L⁻¹ at 23 h of fermentation. After acid pretreatment, the remaining solid underwent an alkaline extraction for lignin removal. This partially delignified material, known as partially delignified lignin (PDC), was enriched with nutrients in a solid/liquid ratio of 1 g/3.33 mL and subjected to simultaneous saccharification and fermentation (SSF) process, resulting in an ethanol concentration of 85 g L⁻¹ at 21 h of fermentation. Thus, from the conversion of starchy, sugary and lignocellulosic fractions approximately 160 L ethanol.ton⁻¹ sweet sorghum was obtained. This amount corresponds to 13,600 L ethanol.ha⁻¹.     

Evaluation the efficacy of extrusion pretreatment via enzymatic digestibility and simultaneous saccharification & fermentation with rapeseed straw

The efficacy of extrusion pretreatment was evaluated by enzymatic hydrolysis and simultaneous saccharification and fermentation (SSF) with straw of rapeseed, Brassica napus, an agricultural residue. An acceptable pretreatment result was obtained at a barrel temperature of 165 °C, acid concentration of 20 g L⁻¹, liquid feeding rate of 13.4 cm³ min⁻¹, solid feeding rate of 1.0 g min⁻¹, screw rotation speed of 6.3 rad s⁻¹, and residence time of 10.2 min, with a yield of xmg, representing the sum of the corresponding hydrolyzed sugars; xylose, mannose and galactose, of 794.3 g kg⁻¹ and a glucose release of 21.0 g kg⁻¹. These were calculated to be 963.0 g kg⁻¹ and 910.3 g kg⁻¹ based on cellulose and hemicellulose recoveries,respectively. The highest enzymatic digestibility of 781.0 g kg⁻¹was higher than that obtained from the batch pretreatment with dilute acid by 1.4-fold. The SSF process afforded an ethanol concentration of 16.0 g L⁻¹, corresponding to an ethanol yield of 790 g kg⁻¹ based on the total available cellulose in the pretreated rapeseed straw.     

Fed batch enzymatic saccharification of newspaper cellulosics improves the sugar content in the hydrolysates and eventually the ethanol fermentation by Saccharomyces cerevisiae

The newspaper is comprised of (w w^?1) holocellulose (70.0%) with substantial amount of lignin (16.0%). Bioconversion of the carbohydrate component of newspaper to sugars by enzymatic saccharification, and its fermentation to ethanol was investigated. Of various enzymatic treatments using cellulase, xylanase and laccase, cellulase enzyme system was found to deink the newspaper most efficiently. The saccharification of deinked paper pulp using enzyme cocktail containing exoglucanase (20 U g^?1), β-glucosidase (60 U g^?1) and xylanase (80 U g^?1) resulted in 59.8% saccharification. Among additives, 1% (v v^?1) Tween 80 and 10 mol m^?3 CoCl₂ improved the enzymatic hydrolysis of newspaper maximally, releasing 14.64 g L^?1 sugars. The fed batch enzymatic saccharification of the newspaper increased the sugar concentration in hydrolysate from 14.64 g L^?1 to 38.21 g L^?1. Moreover, the batch and fed batch enzymatic hydrolysates when fermented with Saccharomyces cerevisiae produced 5.64 g L^?1 and 14.77 g L^?1 ethanol, respectively.     

Efficient ethanol production from inulin by two-stage aerate strategy

A major concern for ethanol production from inulin-containing materials, is the higher unconverted sugar, which increases the cost of ethanol production and wastewater treatment. Some key factors, such as inulinase, biomass or aeration rates, were studied to solve the problems in the process of ethanol fermentation from inulin. It was showed that more inulinase and increasing inoculum size can shorten the fermentation time, but could not reduce residual sugars. Two-stage aerate strategy was developed to utilize the remained sugars: keep the aeration at 5 h⁻¹ at the first 12 h, and drop it to 1.2 h⁻¹. Under this condition, contradiction between fermentation time and high ethanol yield was solved (60 h and 0.43 g g⁻¹), and the final residual sugar concentration decreased to about 10 g L⁻¹ with 98 g L⁻¹ ethanol. The ethanol productivity was up to 1.63 g L⁻¹ h⁻¹, which is the highest productivity of ethanol fermentations from inulin-containing materials.     

Production of ethanol from raw juice and thick juice of sugar beet by continuous ethanol fermentation with flocculating yeast strain KF-7

Sugar beet juice can serve as feedstock for ethanol product due to its high content of fermentable sugars and high energy output/input ratio. Batch ethanol fermentation of raw juice and thick juice proved that addition of mineral nutrients could not improve ethanol concentration, but could accelerate the fermentation rate. Fermentation of thick juice with an initial pH of 9.1 did not affect the fermentation process. The continuous ethanol fermentation of raw juice was performed at 35 °C with a dilution rate of 0.3 h⁻¹, resulting in ethanol concentration, ethanol yield and productivity of 70.7 g L⁻¹, 89.8% and 21.2 g L⁻¹ h⁻¹, respectively. A two-stage reactor was used in the continuous ethanol fermentation of thick juice by feeding fresh yeast cells into the second reactor. This process was stable at a total process dilution rate of 0.11 h⁻¹ with an overall sugar concentration of 190 g L⁻¹ in the influent. The ethanol concentration was kept at approximately 80 g L⁻¹, corresponding to ethanol yield of 82.5% and productivity of 8.8 g L⁻¹ h⁻¹.     

Simultaneous saccharification and co-fermentation of whole wheat in integrated ethanol production

Two of the most important ways of reducing the production cost of lignocellulosic ethanol are to increase the ethanol yield and the concentration in the fermentation broth. This can be facilitated by co-fermentation of glucose and xylose from agricultural residues such as wheat straw, due to the high amount of xylose in the hemicelluloses in these materials.Simultaneous saccharification and co-fermentation (SSCF) of steam-pretreated wheat straw (SPWS) with and without the addition of liquefied wheat meal (LWM) was performed using the pentose-fermenting yeast, TMB3400. The highest overall ethanol yield in batch operation, of around 70%, equivalent to an ethanol concentration of 43.7 g L⁻¹, was achieved using SPWS with 7.5% water-insoluble solids (WIS) and addition of LWM with 1% WIS. Using SPWS with a higher WIS (10%) resulted in a decreased yield, 60%, although the concentration of ethanol increased to 53.0 g L⁻¹. SSCF of 7.5% straw was also performed with a single (after 20 h) or fed-batch addition of 1% WIS LWM (after 20, 24 and 28 h) resulting in an increase in both ethanol yield and concentration compared to the reference, without wheat meal addition, but no significant difference compared to the batch experiments.The addition of wheat meal to SSCF did not improve xylose utilization significantly, probably due to the instant release of glucose from the liquefied meal, which hampers the uptake of xylose. The instant release of glucose was shown to be caused by the high amylase activity of the β-glucosidase enzyme preparation.     

Effect of nutrient supplementation on ethanol production in different strategies of saccharification and fermentation from acid pretreated rice straw

The effect of nutrient supplementation on ethanol production by recently selected thermotolerant yeast (Kluyveromyces marxianus NRRL Y-6860) was investigated in different strategies of saccharification and fermentation employing rice straw pretreated by dilute acid. Among the evaluated strategies, similar ethanol yields (Y_P/S ∼ 0.23 g g⁻¹) were obtained with or without nutrient addition. However, considering the whole process time, the strategy based on simultaneous saccharification and fermentation (SSF), without pre-hydrolysis, was assigned as the most suitable configuration due to the highest ethanol volumetric productivity (1.4 g L⁻¹ h⁻¹), about 2-fold higher in relation to the others. The impact of enzymatic preparation employed in this study was also evaluated on glucose fermentation in semi-synthetic medium. The enzymatic preparation affected both glucose consumption and ethanol production by K. marxianus NRRL Y-6860, but just in the absence of nutrients. Therefore, the enzyme type and loading should be carefully defined, not only by the capital costs involved, but also by the possibility of increasing the fermentation inhibitors.     

Effectiveness of dilute oxalic acid pretreatment of Miscanthus × giganteus biomass for ethanol production

In the present study the effect of temperature, reaction time and dilute oxalic acid (OA) concentration during steam-pretreatment of Miscanthus × gigantueus has been evaluated using the combined severity factor (CS). At the highest CS glucan and lignin content in the water insoluble fraction (WIF) increased, while xylan content decreased. While glucose recovery in the water soluble fraction (WSF) was found at low concentration when mild CS were used (≤5.0 g L⁻¹ at CS ≤ 2.17), xylose and arabinose concentrations were higher at low-mild CS (1.58–2.17) with a concentration peak at CS 2.03 (39.9 and 3.2 g L⁻¹ for xylose and arabinose, respectively). The decrease in pentoses coincided with inhibitory formation in the WSF, namely acetic acid, furfural, HMF and phenolic compounds. Glucan conversion rose from 46.1% at CS 1.54 to 91.2% at CS 2.76. Likewise, maximum ethanol concentration was achieved at CS 2.76, corresponding to 20.2 g L⁻¹ and a volumetric ethanol productivity of 0.28 g L⁻¹ h⁻¹. Negative correlations have been found between xylan vs. glucan conversion and xylan vs. ethanol production, suggesting that decreasing the xylan content in WIF increases both saccharification rate and ethanol concentration (R² 0.91 and R² 0.93, respectively). On the other hand, a positive correlation was found between ethanol production and glucan conversion (R² 0.93). Fermentation of WSF by Scheffersomyces (Pichia) stipitis CBS 6054 at CS 1.54 produced 12.1 g L⁻¹ of ethanol after 96 h incubation with a volumetric ethanol productivity of 0.13 g L⁻¹ h⁻¹.     

ABE fermentation from enzymatic hydrolysate of NaOH-pretreated corncobs

Acetone butanol ethanol (ABE) was produced from enzymatic-hydrolyzed corncobs by Clostridium saccharobutylicum DSM 13864. Pretreatment of corncobs was carried out with 0.5 mol L⁻¹ NaOH followed by enzymatic hydrolysis. The yield of total reducing sugars was 917 g kg⁻¹ pretreated (de-lignified) and washed corncobs. The hydrolysate was used without sediments removal for ABE fermentation. A solvent production of 19.44 g L⁻¹ with 12.27 g L⁻¹ butanol was obtained from 55.22 g L⁻¹ sugars, resulting in an ABE yield of 350 g kg⁻¹ and a production rate of 0.54 g L⁻¹ h⁻¹. A control experiment using 55.3 g L⁻¹ mixed sugars resulted in an ABE production of 16.81 g L⁻¹ with 10.26 g L⁻¹ butanol, corresponding to an ABE yield of 300 g kg⁻¹ and a production rate of 0.47 g L⁻¹ h⁻¹, indicating that the enzymatic hydrolysates may contain stimulating compounds that can improve the ABE fermentation.     

Lignocellulosic ethanol production employing immobilized Saccharomyces cerevisiae in packed bed reactor

Most of ethanol production processes are limited by lower ethanol production rate and recyclability problem of ethanologenic organism. In the present study, immobilized co-fermenting Saccharomyces cerevisiae GSE1618 was employed for ethanol fermentation using rice straw enzymatic hydrolysate in a packed bed reactor (PBR). The immobilization of S. cerevisiae was performed by entrapment in Ca-alginate for optimization of ethanol production by varying alginic acid concentration, bead size, glucose concentration, temperature and hardening time. Remarkably, extra hardened beads (EHB) immobilized with S. cerevisiae could be used up to repeated 40 fermentation batches. In continuous PBR, maximum 81.82 g L⁻¹ ethanol was obtained with 29.95 g L⁻¹ h⁻¹ productivity with initial glucose concentration of 180 g L⁻¹ in feed at dilution rate of 0.37 h⁻¹. However, maximum ethanol concentration of 40.33 g L⁻¹ (99% yield) with 24.61 g L⁻¹ h⁻¹ productivity was attained at 0.61 h⁻¹ dilution rate in fermentation of un-detoxified rice straw enzymatic hydrolysate (REH). At commercial scale, EHB has great potential for continuous ethanol production with high productivity using lignocellulosic hydrolysate in PBR.     

Optimization of ethanol production from sweet sorghum (Sorghum bicolor) juice using response surface methodology

Sweet sorghum juice was fermented into ethanol using Saccharomyces cerevisiae (ATCC 24858). Factorial experimental design, regression analysis and response surface method were used to analyze the effects of the process parameters including juice solid concentration from 6.5 to 26% (by mass), yeast load from 0.5 g L⁻¹ to 2 g L⁻¹ and fermentation temperature from 30 °C to 40 °C on the ethanol yield, final ethanol concentration and fermentation kinetics. The fermentation temperature, which had no significant effect on the ethanol yield and final ethanol concentration, could be set at 35 °C to achieve the maximum fermentation rate. The yeast load, which had no significant effect on the final ethanol concentration and fermentation rate, could be set at 1 g L⁻¹ to achieve the maximum ethanol yield. The juice solid concentration had significant inverse effects on the ethanol yield and final ethanol concentration but a slight effect on the fermentation rate. The raw juice at a solid concentration of 13% (by mass) could be directly used during fermentation. At the fermentation temperature of 35 °C, yeast solid concentration of 1 g L⁻¹ and juice solid concentration of 13%, the predicted ethanol yield was 101.1% and the predicted final ethanol concentration was 49.48 g L⁻¹ after 72 h fermentation. Under this fermentation condition, the modified Gompertz's equation could be used to predict the fermentation kinetics. The predicted maximum ethanol generation rate was 2.37 g L⁻¹ h⁻¹.     

A novel staggered hybrid SSF approach for efficient conversion of cellulose/hemicellulosic fractions of corncob into ethanol

The following study reports bioconversion of corncob into ethanol using hybrid approach for co-utilization of dilute acid hydrolysate (pentose rich stream) and hexose rich stream obtained by enzymatic saccharification employing commercial cellulase Cellic CTec2 as well as in-house cellulase preparations derived from Malbranchea cinnamomea, Scytalidium thermophilium and a recombinant Aspergillus strain. Acid hydrolysis (1% H₂SO₄) of corncob at 1:15 solid liquid ratio led to removal of 80.5% of hemicellulosic fraction. The solid glucan rich fraction (63.5% glucan, 8.3% pentosans and 27.9% lignin) was hydrolysed at 10% substrate loading rate with different enzymes for 72 h at 50 °C resulting in release of 732 and 535 (mg/g substrate) total sugars by Cellic CTec2 and M. cinnamomea derived enzymes, respectively. The fermentation of enzyme hydrolysate with co-culture of Saccharomyces cerevisiae and Pichia stipitis added in sequential manner resulted in 3.42 and 2.50% (v/v) ethanol in hydrolysate obtained from commercial Cellic CTec2 and M. cinnamomea, respectively. Employing a hybrid approach, where dilute acid hydrolysate stream was added to solid residue along with enzyme Cellic CTec2 during staggered simultaneous saccharification and fermentation at substrate loading rate of 15% resulted in 252 g ethanol/kg corncob.     

Conversion of paper sludge to ethanol by separate hydrolysis and fermentation (SHF) using Saccharomyces cerevisiae

The conversion of ethanol from paper sludge using the separate hydrolysis and fermentation (SHF) process with cellulase and Saccharomyces cerevisiae GIM-2 were investigated in this paper. Optimization strategy based on statistical experimental designs was employed to enhance degree of saccharification by enzymatic hydrolysis of paper sludge. Based on the Plackett-Burman design, hydrolysis time, substrate concentration and cellulase dosage were selected as the most significant variable on the degree of saccharification. Subsequently, the optimum combination of the selected factors was investigated by a Box-Behnken approach. A mathematical model was developed to show the effects of each factor and their combinatorial interactions on the degree of saccharification. The optimal conditions were hydrolysis time 82.7 h, substrate concentration 40.8 g L⁻¹ and cellulase dosage 18.1 FPU g⁻¹ substrate, and a degree of saccharification of 82.1% can be achieved. When hydrolysate was further fermented with S. cerevisiae GIM-2, the conversion rate of sugar to ethanol was 34.2% and the ethanol yield was 190 g kg⁻¹ of dry paper sludge, corresponding to an overall conversion yield of 56.3% of the available carbohydrates on the initial substrate. The results derived from this study indicate that the response surface methodology is a useful tool for optimizing the hydrolysis conditions to converse paper sludge to ethanol.     

Use of treated effluent water in ethanol production from cellulose

The bioethanol industry exerts a significant demand on water supplies. Current water consumption rate in corn dry grind ethanol plants is (11–15) dm³ m⁻³ of ethanol produced and (23–38) dm³ m⁻³ for cellulosic ethanol plants. The main goal of this study was to examine the feasibility of use of treated wastewater effluent in place of potable freshwater for cellulosic ethanol production. The effects of using two different types of filtered treated effluent; Bloomington- Normal, IL (Residential type) and Decatur, IL (Industrial/Residential Mix type); on the rate of fermentation and final ethanol yield from a pure cellulosic substrate were evaluated. Characterization analysis of both effluent water samples indicated low concentration of toxic elements. Final ethanol concentrations obtained with Bloomington- Normal and Decatur effluent and with a control treatment using de-ionized water were similar, resulting in 360 g kg⁻¹ (0.36 g g⁻¹), 370 g kg⁻¹ (0.37 g g⁻¹) and 360 g kg⁻¹ (0.36 g g⁻¹), respectively. These findings suggest that with proper characterization studies and under appropriate conditions, the use of treated effluent water in cellulosic ethanol production is feasible.     

Optimization of dilute acid and enzymatic hydrolysis for dark fermentative hydrogen production from the empty fruit bunch of oil palm

Pretreatment of the empty fruit brunch (EFB) from oil palm was investigated for H₂ fermentation. The EFB was hydrolyzed at various temperatures, H₂SO₄ concentrations, and reaction times. Subsequently, the acid-hydrolysate underwent enzymatic saccharification under various temperature, pH, and enzymatic loading conditions. Response surface methodology derived the optimum sugar concentration (SC), hydrogen production rate (HPR), and hydrogen yield (HY) as 28.30 g L⁻¹, 2601.24 mL H₂ L⁻¹d⁻¹, and 275.75 mL H₂ g⁻¹ total sugar (TS), respectively, at 120 °C, 60 min of reaction, and 6 vol% H₂SO₄, with the combined severity factor of 1.75. Enzymatic hydrolysis enhanced the SC, HY, and HPR to 34.52 g L⁻¹, 283.91 mL H₂ g⁻¹ TS, and 3266.86 mL H₂ L⁻¹d⁻¹, respectively, at 45 °C, pH 5.0, and 1.17 mg enzyme mL⁻¹. Dilute acid hydrolysis would be a viable pretreatment for biohydrogen production from EFB. Subsequent enzymatic hydrolysis can be performed if enhanced HPR is required.     

Performances comparison between three technologies for continuous ethanol production from molasses

Molasses are a potential feedstock for ethanol production. The successful application of anaerobic fermentation for ethanol production from molasses is critically dependent to the development and the use of high rate bioreactors. In this study the fermentation of sugar cane molasses by Saccharomyces cerevisiae for the ethanol production in a continuously stirred tank reactor (CSTR), an immobilised cell reactor (ICR) and a membrane reactor (MBR) was investigated. Ethanol production and reactor productivities were compared under different dilution rates (D). When using the CSTR, a decent ethanol productivity (Qp) of 6.8 g L⁻¹ h⁻¹ was obtained at a dilution rate of 0.5 h⁻¹. The Qp was improved by 48% and the residual sugar concentration was reduced by using the ICR. Intensifying the production of ethanol was investigated in the MBR to achieve a maximum ethanol concentration and a Qp of 46.5 g L⁻¹ and 19.2 g L⁻¹ h⁻¹, respectively. The achieved results in the MBR worked with high substrate concentration are promising for the scale up operation.     

Ethanol production by Mucor indicus and Rhizopus oryzae from rice straw by separate hydrolysis and fermentation

Rice straw was successfully converted to ethanol by separate enzymatic hydrolysis and fermentation by Mucor indicus, Rhizopus oryzae, and Saccharomyces cerevisiae. The hydrolysis temperature and pH of commercial cellulase and β-glucosidase enzymes were first investigated and their best performance obtained at 45 °C and pH 5.0. The pretreatment of the straw with dilute-acid hydrolysis resulted in 0.72 g g^?1 sugar yield during 48 h enzymatic hydrolysis, which was higher than steam-pretreated (0.60 g g^?1) and untreated straw (0.46 g g^?1). Furthermore, increasing the concentration of the dilute-acid pretreated straw from 20 to 50 and 100 g L^?1 resulted in 13% and 16% lower sugar yield, respectively. Anaerobic cultivation of the hydrolyzates with M. indicus resulted in 0.36–0.43 g g^?1 ethanol, 0.11–0.17 g g^?1 biomass, and 0.04–0.06 g g^?1 glycerol, which is comparable with the corresponding yields by S. cerevisiae (0.37–0.45 g g^?1 ethanol, 0.04–0.10 g g^?1 biomass and 0.05–0.07 glycerol). These two fungi produced no other major metabolite from the straw and completed the cultivation in less than 25 h. However, R. oryzae produced lactic acid as the major by-product with yield of 0.05–0.09 g g^?1. This fungus had ethanol, biomass and glycerol yields of 0.33–0.41, 0.06–0.12, and 0.03–0.04 g g^?1, respectively.     

Characterization,pretreatment and saccharification of spent seaweed biomass for bioethanol production using baker's yeast

Seaweeds are marine macroalgae found abundantly and viewed as potential source of phycocolloids to produce biofuel. In this study, seaweed spent biomass obtained from alginate production industry and biomass obtained after pigment extraction were found to contain a considerable amount of phycocolloids. These two spent biomasses were investigated for the production of ethanol. In this study, the red seaweed spent biomass of Gracilaria corticata var corticata showed higher content of polysaccharide (190.71 ± 30.67 mg g⁻¹ dry weight) than brown seaweed spent biomass (industrial) (136.28 ± 30.09 mg g⁻¹ dry weight). Hydrolysis of spent biomasses with different concentrations of sulfuric acid (0.1%, 0.5% and 1%) was also investigated. Brown seaweed spent biomass and red seaweed spent biomass exhibited high amount of sugar in 0.5% and 1% sulfuric acid treatment, respectively. Proximate and ultimate composition of seaweed spent biomasses were analysed for energy value. The FT-Raman spectra exhibited similar stretches for both acid hydrolysed spent biomasses with their respective standards. Ethanol produced through a fermentation process using spent hydrolysates with baker's yeast at pH 5.3 was found to be significant. The ethanol yield from brown seaweed spent biomass and red seaweed spent biomass was observed to be 0.011 g g⁻¹ and 0.02 ± 0.003 g g⁻¹ respectively, when compared with YPD (0.42 ± 0.03 g g⁻¹) and d-galactose (0.37 ± 0.04 g g⁻¹) as standard on day 4. The present study revealed the possibility of effective utilization of spent biomass from seaweed industry for ethanol production.     

Energy self-sufficient production of bioethanol from a mixture of hemp straw and triticale seeds: Life-cycle analysis

Industrial hemp shows exceptional potential for cellulosic ethanol production, especially regarding yields per hectare, costs and environmental impact. Additionally, co-products, such as high-value food-grade oil, increase the value of this plant. In this work, hemp straw was steam-exploded for 45 min at 155 °C and hydrolysed with a cellulase/xylanase mixture. Up to 0.79 g g⁻¹ of cellulose was degraded and subsequent simultaneous-saccharification-and-fermentation with added triticale grist resulted in >0.90 g g⁻¹ fermentation of cellulose. Hemp straw is very suitable, as it contains 0.63 g g⁻¹ of cellulose and only 0.142 g g⁻¹ of hemicellulose.A 2000 m³ a⁻¹ ethanol biorefinery requires a land use of 3 km² each for hemp and for triticale. A total of 2630 kg ethanol and 150 kg hemp oil can be gained from 1 ha. Slurry and triticale straw serve as raw material for the biogas fermenter or as animal feed. Biogas supplies thermal and electric energy in combined heat and power. Ethanol will remain at 0.66 € dm⁻³ based on market prices. In addition, data have been calculated for market prices plus and minus 30% market prices (0.51–0.81 € dm⁻³). Carbon dioxide (CO₂) abatement for ethanol achieves 121 g MJ⁻¹ CO_2eq for a combined ethanol/biogas plant. The CO₂ abatement costs vary from 38 € to 262 € t⁻¹ CO_2eq.     

Optimization of alkaline pretreatment on corn stover for enhanced production of 1.3-propanediol and 2,3-butanediol by Klebsiella pneumoniae AJ4

Corn stover is one of the most promising lignocellulosic biomass that can be utilized for producing 1,3-propanediol and 2,3-butanediol. The pretreatment and enzymatic hydrolysis steps are essential for the bioconversion of lignocellulosic biomass to diols. For optimizing the pretreatment step, temperature, time, and NaOH concentration were evaluated based on total sugar recovery. Enzymatic hydrolysis for cellulose and hemicellulose were investigated at different solid-to-liquid ratios. The optimum conditions were found to be alkaline pretreatment with 0.25 mol dm⁻³ NaOH for 1 h at 60 °C followed by enzymatic hydrolysis at 50 °C for 48 h, with a solid slurry concentration of 100 g dm⁻³. Under these conditions, conversion rates of 92.55% and 78.82% were obtained from glucan and xylan, respectively. Diol production from fermentable sugars was 14.8 g dm⁻³, with a conversion yield and productivity of 0.46 g g⁻¹, and 0.98 g dm⁻³ h⁻¹, respectively. Our results are similar for diol production obtained using pure sugars under the same conditions. Therefore, mild alkaline pretreatment of corn stover facilitates delignification, significantly improving the rate of enzymatic saccharification and sugar recovery.