Reducing Sugar Yield Research Articles

Impact and significance of pretreatment on the fermentable sugar production from low-grade longan fruit wastes for bioethanol production

The feasibility of bioethanol production from low-grade longan fruit waste material was recently studied as a novel substrate for bioethanol production. First, hydrothermal pretreatment followed by enzymatic hydrolysis converted both the cellulosic and hemicellulosic biomass of the low-grade longan fruit wastes into fermentable sugars, which eventually produced ethanol by yeast fermentation. Therefore, an optimal condition of hydrothermal residence time and pretreatment concentration was determined to obtain the high release of sugars. An experimental design was constructed with the Central Composite Design (CCD) response surface method using factors of the hydrothermal residence time and pretreatment concentration in constant temperature and time. The results revealed optimum reducing sugar yield of 240.396 g/L (R2 = 0.9989), sugar productivity of 240.396 g/L.day (R2 = 0.9763), and sugar yield coefficient of 24.04 g/g (R2 = 0.9989). The highest ethanol yield (16.74 g/L) was achieved at 24 h of fermenting time. These results show that low-grade longan fruit wastes are an excellent feedstock for producing ethanol that could be either used as biofuel or as a beverage.

Microwave assisted dilute organic acid pre-treatment of oil palm empty fruit bunch to improve enzyme accessibility

The depletion of fossil fuel is intriguing for researchers to find sustainable energy. Oil palm empty fruit bunch (OPEFB) is abundant biomass in Indonesia which is potential to be converted into bioethanol because of its high cellulose content. Suitable pre-treatment could increase the effectiveness of cellulose conversion into sugars. The aim of this study is to evaluate the effectiveness of Microwave-assisted Oxalic Acid pre-treatment (MOxA) and Enzymatic Hydrolysis (EH) to improve enzyme accessibility through variation of heating temperature, irradiation time, and EH incubation time. The higher the microwave heating temperature, longer irradiation time, and longer EH incubation time, the higher the glucose yield per pulp (GY) and reducing sugar yield (RSY) were observed. After MOxA at 200°C-15 min, as much as 43.22 % GY per initial biomass was obtained by EH for 10 days. SEM images showed more ruptures on the surface area of OPEFB fibre after MOxA that supported in increasing of enzyme digestibility. The XRD spectra demonstrated that the crystallinity index (CI) increased after MOxA because pre-treatment reduced amorphous components in the biomass. In addition, the FTIR spectra showed that peak intensity at 1714 cm−1 corresponded to hemicellulose was gradually reduced after MOxA while peaks corresponded to lignin was more discernible.

Liquid ammonia pretreatment optimization for improved release of fermentable sugars from sugarcane bagasse

Alkali pretreatment of biomass is a widely accepted method for efficient delignification causing significant recovery of pentoses and hexoses to be utilized for second generation ethanol production. Present study is investigated to optimize the conditions of liquid ammonia pretreatment of sugarcane bagasse using statistical design of response surface methodology with respect to liquid ammonia concentration (15–25% v/v), solid loading (5–20% w/v), temperature (70–100 °C) and retention time (16–24 h) for maximum recovery of sugars during enzymatic hydrolysis. Optimized conditions for liquid ammonia pretreatment were found as 15.64% (v/v) ammonia; 10.51% (w/v) solid loading; 84.9 °C temperature; and 23.95 h retention time. The reducing sugar yield of 545.57 ± 7.1 g/kg of raw biomass corresponding to 75.41 ± 1% of maximum theoretical sugars was achieved after 72 h of saccharification using Cellic CTec 2 (20 FPU/g pretreated biomass). Biophysical techniques further validated the efficiency of process via deeper understanding of structural and compositional changes of pretreated as well as saccharified biomass imprinted by optimized pretreatment conditions used in the study.

Pretreatment of rice straw with recycled ionic liquids by phase-separation process for low-cost biorefinery.

An efficient ionic liquids (ILs) recycle technology will increase the economic viability of lignocellulosic biorefinery. The availability of recycling 1-butyl-3-methylimidazolium chloride for rice straw (RS) pretreatment was conducted. The kosmotropic salt K3 PO4 (TKP) solution was used as antisolvent for cellulose precipitation and forming a three-phase system consisting of biomass, ILs-rich, and salt-rich phases. The upper ILs phase and the bottom TKP phase were recycled without additional purification, which significantly simplifies the process for recovering ILs. Subsequently, the RS pretreated with multiple reusing ILs (RPRS) were investigated by components analysis, structure evolution, enzymatic hydrolysis, and fermentation experiments. The results showed that unpurified reusing ILs led to further delignification and improvement of enzyme accessibility of the pretreated RS. The reducing sugar yield of RS pretreated with 8th reusing IL (8th RPRS) could still reach 98.9%, and the ethanol and succinic acid concentrations achieved 91.9 and 29.3g/L by simultaneous saccharification and cofermentation. The present study demonstrated that the ILs recovered by phase-separation process could be used for RS pretreatment, and achieving high titer ethanol fermentation.

Construction of the R17L mutant of MtC1LPMO for improved lignocellulosic biomass conversion by rational point mutation and investigation of the mechanism by molecular dynamics simulations

To enhance the biomass conversion efficiency, the R17L mutant of the lytic polysaccharide monooxygenase (LPMO) MtC1LPMO with improved catalytic efficiency was constructed via rational point mutation based on the HotSpot Wizard 3.0 and dezyme web servers. Compared with the wild-type (WT) MtC1LPMO, R17L exhibited a 1.8-fold increase of specific activity and 1.92-fold increase of catalytic efficiency (kcat/Km). The degree of increase of the reducing sugar yield from microcrystalline cellulose and three plant biomass materials during synergistic hydrolysis using cellulase in combination with R17L was about 2 times higher than with the WT. Molecular dynamics simulations revealed that the R17L mutation reduced the stability of the region R18-I36, which then weakened the direct interactions between region N24-V31 and the substrate cellohexaose. Consequently, the deflection time of the cellohexaose conformation in R17L was prolonged compared to the WT, which enhanced its catalytic efficiency.

Molecular Characterization, Regioselective and Synergistic Action of First Recombinant Type III α-L-arabinofuranosidase of Family 43 Glycoside Hydrolase (PsGH43_12) from Pseudopedobacter saltans.

α-L-Arabinofuranosidase (PsGH43_12) of family 43 glycoside hydrolase and subfamily 12 from Pseudopedobacter saltans was cloned, over-expressed and biochemically characterized. PsGH43_12 displayed molecular mass, ~ 65kDa. It exhibited activity in pH (5-9) and temperature range (35-55°C) with maxima at pH 6.5 and 50°C. PsGH43_12 gave 88.7 U/mg specific activity against rye arabinoxylan and 78.9 U/mg against wheat arabinoxylan. PsGH43_12 displayed Km and Vmax, 3.02mg/ml and 103 µmole/min/mg, respectively, against rye arabinoxylan and 2.17mM and 100.7 µmole/min/mg, respectively, against pNP-α-L-arabinofuranoside. 10mM Mg2+ or Ca2+ ions enhanced PsGH43_12 activity by 54% or 33%, respectively. PsGH43_12 hydrolyzed rye arabinoxylan and released only L-arabinosyl moiety as main product, confirming its specificity towards α-L-arabinofuranoside. The regioselective analysis by NMR showed that PsGH43_12 belongs to type III α-L-arabinofuranoside. The synergistic behavior of PsGH43_12 in saccharification of mild alkali pretreated finger miller stalk (FMS) along with xylanase (CtXyn11A) from Clostridium thermocellum and xylosidase (BoGH43) from Bacteroides ovatus gave twofold higher total reducing sugar (TRS) yield. TLC analysis of pretreated FMS hydrolysed by CtXyn11A and BoGH43 showed xylooligosaccharides and xylose. Addition of PsGH43_12 to above combination gave mostly xylose and arabinose confirming their synergistic behavior and displaying their applicability in hydrolysis of hemicellulosic biomass.

Chemical variation in cell wall of sugar beet pulp caused by aqueous ammonia pretreatment influence enzymatic digestibility of cellulose

Sugar beet pulp (SBP) is considered to be an important feedstock for the fuel ethanol production. The aim of this study is to investigate the relationship between chemical variation in cell wall caused by aqueous ammonia pretreatment and the enzymatic digestibility of cellulose through imaging techniques coupled with enzymatic hydrolysis kinetics analysis. The results revealed that the partly decreased and redistributed lignin could weaken interactions between lignin and cellulose, expose more hydroxyl groups on cell wall, and lead to more absorbed cellulase on cellulose. The maximum amount of adsorbed cellulase (370.37 FPU/g) was obtained from SBP (at 80 °C), which was 37 % more than that of the control. Additionally, the reducing sugar yield, initial hydrolysis rate, and maximum catalytic efficiency were 121 %, 202 %, and 125 % more than that of the control, respectively. Aqueous ammonia provided a good approach for improving enzymatic digestibility of cellulose through weakening the interactions between lignin and cellulose, which might be a suitable pretreatment in fuel ethanol production from SBP.

Optimizing the Synthesis of Lignin Derivatives from <em>Acacia mangium </em>to Improve the Enzymatic Hydrolysis of Kraft Pulp Sorghum Bagasse

The present study is aimed at optimizing the synthesis of Amphipilic lignin derivatives (A-LD) from the isolated lignin of A.mangium black liquor (BL), using the one and two step acid isolation method, and commercial lignin (LS) was used as comparison. The experimental design was conducted using Taguchi method, which consisted of four parameters and two level factors, with reference to the matrix orthogonal array, L8, including temperature, reaction time, amount of polyethylene glycol diglycidylethers (PEGDE) and Kraft lignin (KL). Furthermore, the kraft pulp of sweet sorghum bagasse (SSB) was used as substrate in the enzymatic hydrolysis (NREL method), with addition of A-LD, whose functional group and surface tension were then characterised using ATR-FTIR and surface tension equipment. Conversely, an improvement in the reducing sugar yield (RSY) compared to the control was observed after adding various A-LDs to the substrate during enzymatic hydrolysis. This product was more prospective for L2S than others products under milder circumstances, due to the fact that it possesses the lowest surface tension. Also, Taguchi analysis demonstrated the treatment at 60 °C for 1 h with 3.0 g and 1.0 g of PEDGE and lignin, respectively as the optimum condition, while the amount of lignin present was included as a factor with the propensity to significantly affect A-LD L1S and LS. Therefore, it was established that the A-LDs from A. mangium kraft lignin require milder synthesis conditions, compared to other existing methods and despite the differences in optimum experimental condition for L2S and LS, the functional groups in the IR spectra possessed very identical characteristics.

Statistically designed cellulase mixture for saccharification of pretreated Sorghum durra stalk

The potential of least explored Sorghum durra as a feedstock for enzymatic saccharification in bioethanol production was evaluated as only one report is available. The pretreatment specific, optimization of saccharification of Sorghum durra stalk (Sds) was carried out. The concentrations of crude recombinant endoglucanase (BaGH5-UV2), cellobiohydrolase (CtCBH5A) and β-glucosidase (CtGH1) in cocktail were optimized for saccharification of acid or base pretreated Sds by using mixture design approach. Optimized percentage ratio of BaGH5-UV2, CtCBH5A and CtGH1 with total enzyme loading 2000 U/g of pretreated Sds for acid pretreated Sds was 43.1:10.0:46.9 and for base pretreated Sds was 80:10:10 at 48 h of saccharification. The base pretreated Sds showed 1.8-fold (165.6 mg/g of pretreated Sds) higher total reducing sugar (TRS) yield and 1.2-fold (81.7 mg/g of pretreated Sds) higher glucose yield than acid pretreated Sds. This low sugar yield from acid pretreated Sds was due to the presence of higher acid insoluble lignin content, 11.9 % (w/w) than the base pretreated biomass (2.2 %, w/w). In acid pretreated Sds, ANOVA data showed 3.7-fold higher F value (111.58) for BaGH5-UV2 and CtGH1 interaction than the base pretreated Sds. This indicated that the synergism between BaGH5-UV2 and CtGH1 for acid pretreated Sds was significantly higher. This was due to lower intact hemicellulose content (10.6 %, w/w) in acid pretreated Sds than base pretreated Sds (21.8 %, w/w). The optimized enzyme ratios for saccharification of acid pretreated Sds gave maximum TRS and glucose yield at 72 h, 113 and 85 mg/g of pretreated Sds, respectively, unlike base pretreated Sds at 96 h, 211 and 174 mg/g of pretreated Sds, respectively. These results showed that the ratio of cellulase enzymes in cocktail and their synergism depends on the type of pretreatment used for biomass. Thus, this in-house cocktail design specific to pretreatment can improve the biomass saccharification at large scale.

Novel strategies for glucose production from biomass using heteropoly acid catalyst

Abstract Bioethanol and direct glucose fuel cells pledged clean energy to the world. Cellulose depolymerization for glucose production has been a successful approach in bioethanol production. Heteropoly acids (HPAs) are strong Bronsted solid acid catalysts for biomass hydrolysis. Keggin type HPAs, namely, Silicotungstic acid (HSiW), Phosphotungstic acid (HPW), and Phosphomolybdic acid (HPMo), were used for the hydrolysis of lignocellulosic biomass to glucose. Five different biomass feedstocks, namely, miscanthus, sugarcane leaves, switchgrass, sunflower seeds, and bamboo leaves, were examined for the feasibility of total reducing sugar (TRS) yield through the composition analysis and catalytic biomass hydrolysis. Sunflower seeds contained the maximum holocellulose with 90.6%, and switchgrass contained the least i.e., 77.63%. Among the five biomass tested, switchgrass resulted in the highest TRS (5.77 wt/dry wt. %) with HPMo catalyst at a catalyst to biomass ratio of 30:100 (wt./wt. %), a reaction temperature of 120 °C for 3 h. The reaction parameters for depolymerization were optimized for all three HPAs, and the optimized conditions were 3 h and 120 °C. HPMo showed maximum TRS yield (5.77 wt/dry wt.%) among the three HPAs at 30:100 catalyst to biomass ratio. However, a catalyst to biomass ratio of 20:100 (wt./wt.%) was economical (5.25 wt/dry wt.%) for commercial application.

Steam Explosion and Sequential Steam Explosion – Dilute Acid Pretreatment Optimization of Banana Pseudostem for Polyhydroxybutyrate (PHB) Production

Polyhydroxybutyrate (PHB) is a suitable biodegradable alternative to non-renewable petroleum-based plastics. Readily available agricultural lignocellulosic residues such as banana pseudostem can be utilized as a substrate to reduce the production cost of PHB and improve its feasibility for commercialization. Accordingly, pretreatment of banana pseudostem is needed to efficiently convert the substrate to PHB. In this study, optimization of two pretreatment methods for banana pseudostem – namely, steam explosion and sequential steam explosion – dilute acid pretreatment – were optimized to improve the digestibility of the biomass and consequently increase the production of reducing sugars in the hydrolysate during enzymatic saccharification. Response surface methodology (RSM)-designed experiments showed that among all factors investigated, for both pretreatment methods, the steam explosion temperature had the strongest positive impact on reducing sugar production. Optimum conditions of steam explosion pretreatment were 219.31 °C steam explosion temperature and 10 min of pretreatment time, producing 7.33 g/L (48.87% yield) of reducing sugars in the enzymatic hydrolysate. For sequential pretreatment, optimum conditions were 220 °C steam explosion temperature, 135 °C dilute acid temperature, 44 min of dilute acid reaction time, and 1.57% w/v H2SO4, with a corresponding reducing sugar concentration of 13.02 g/L (86.79% yield). A 90% increase in reducing sugar yield was observed after dilute acid pretreatment of steam-exploded banana pseudostem. Using the hydrolysate from sequentially-pretreated banana pseudostem, PHB (2.64 g/L) was successfully synthesized after 12 h of bacterial fermentation. Hence, sequential pretreatment was proven effective in producing enzymatic hydrolysates from banana pseudostem for PHB production.

Bioethanol production from Codium tomentosum residue

ABSTRACT The present study investigated the feasibility of using residual biomass of marine macroalgae (Codium tomentosum) for bioethanol production. Influence of various parameters was analyzed for optimization of bioethanol production. Pre-treatment was performed with different acids, H2SO4 concentrations, temperatures, and reaction times. Maximum reducing sugar yield achieved was 16.45 ± 0.33 g/l with 4% of H2SO4 at 100°C for 60 min. Cellulase produced from Trichoderma reesei is used for the hydrolysis of biomass. Cellulase activity was estimated at various pH, temperatures, and reaction times. The partially purified cellulase was found to have more activity at 30°C for 48 h of cultivation at pH 5. Enzymatic hydrolysis was analyzed with various biomass concentrations, enzyme concentrations, temperatures, and reaction times. Fermentable sugar yield of 17.05 ± 0.25 g/l was obtained using 5% (w/v) biomass with 4% (w/v) enzyme at 50°C for 48 h. The fermentable sugar was converted to bioethanol by fermentation using Saccharomyces cerevisiae with different parameters such as different pH, temperatures, and reaction times were executed. The maximum bioethanol yield of 4 ± 0.33 g/l was obtained at 30°C for 72 h at pH 5. Further, the bioethanol content was characterized using GC-MS. Thus, the results shows that Codium tomentosum is an excellent biomass resource that can be used as a renewable feedstock for the production of bioethanol.

Enzymatic hydrolysis behavior on malt bagasse for fermentative sugar disposal in thermostatic and ultrasonic bath

AbstractThis study evaluated the effect of enzymatic hydrolysis on malt bagasse for fermentative sugar extraction in thermostatic and ultrasonic bath. The enzymatic reaction was performed using cellulase, α‐amylase, and amyloglucosidase (in separate and combined) on malt bagasse to analyze the hydrolysis effect. For this, a central composite rotational design was applied to evaluate the effect of solid:liquid (malt bagasse w/v) versus enzymatic concentration, considering cellulase, α‐amylase, and amyloglucosidase enzymes in mix solution, on fermentable sugars liberation. Then the kinetic fermentative sugars liberation was evaluated in a hydrolysis reaction using cellulase, α‐amylase, and amyloglucosidase (in separate and combined) after exposure in thermostatic and ultrasonic bath. From enzymatic mix, the maximum total reducing sugar (TRS) yield was 408.8 and 219.9 mg·g−1 in thermostatic and in ultrasound bath, respectively. Kinetic studies showed a TRS variation of 6 to 7 g·L−1 for all enzymes. Amyloglucosidase was more promising in assimilation of malt bagasse, responsible for 43% of sugar releasing. Briefly, a low‐cost procedure using thermostatic bath improved the hydrolysis reaction. The results from the experiments present a new application where malt bagasse can be employed showing the potential of this brewing industry residue in fomenting processes, as bioethanol production.

Enhancing the Enzymatic Saccharification of Grain Stillage by Combining Microwave-Assisted Hydrothermal Irradiation and Fungal Pretreatment.

Grain stillage from the liquor industry was pretreated by using microwave-assisted hydrothermal pretreatment, fungal pretreatments, and their combination to enable efficient enzymatic hydrolysis for sugar production. The microwave-assisted hydrothermal (MH) pretreatment was optimized by using a response surface methodology, and the respective maximum reducing sugar yield and saccharification efficiency of 17.59 g/100 g and 33.85%, respectively, were achieved under the pretreatment conditions of microwave power = 120 W, solid-to-liquid ratio = 1:15 (g·mL–1), and time = 3.5 min. The fungal pretreatment with Phanerochaete chrysosporium digestion (PC) achieved the maximum ligninolytic enzyme activities in 6 days with 10% inoculum size at which the reducing sugar yield and saccharification efficiency reached 19.74 g/100 g and 36.29%, respectively. To further improve the pretreatment efficiency, MH and PC pretreatments were combined, but the sequence of MH and PC mattered on the saccharification efficiency. The MH + PC pretreatment (the MH prior to the PC) was better than PC + MH (the PC prior to the MH) in terms of saccharification efficiency. Overall, the MH + PC pretreatment achieved superior reducing sugar yield and saccharification efficiency (25.51 g/100 g and 66.28%, respectively) over all other studied pretreatment methods. The variations of chemical compositions and structure features of the raw and pretreated grain stillage were characterized by using scanning electron microscopy and Fourier transform infrared spectroscopy. The results reveal that both MH and PC pretreatments mainly functioned on delignification and decreasing cellulose crystallinity, thus enhancing the enzymatic saccharification of the pretreated grain stillage. The combined MH and PC pretreatment could be a promising method to enable cost-efficient grain stillage utilization for downstream applications such as biofuels.

Optimization of pH as a strategy to improve enzymatic saccharification of wheat straw for enhancing bioethanol production

In this work, wheat straw (WS) was used as a lignocellulosic substrate to investigate the influence of pH on enzymatic saccharification. The optimum enzymatic hydrolysis occurred at pH range 5.8–6.0, instead of 4.8–5.0 as has been widely reported in research. Two enzymes cocktails, Celluclast® 1.5 L with Novozymes 188, Cellic® CTec2 and endo-1,4-β-xylanase, were used for the pH investigation over a pH range of 3.0–7.0. The highest concentration of total reduced sugar was found at pH 6.0 for all the different enzymes used in this study. The total reduced sugar produced from the enzymatic saccharification at pH 6.0 was found to be 7.0, 7.4, and 10.8 (g L−1) for Celluclast® 1.5 L with Novozymes 188, endo-1,4-β-xylanase and Cellic® CTec2, respectively. By increasing the pH from 4.8 to 6.0, the total reduced sugar yield increased by 25% for Celluclast® 1.5 L with Novozymes 188 and endo-1 4-β-xylanase and 21% for Cellic® CTec2. The results from this study indicate that WS hydrolysis can be improved significantly by elevating the pH at which the reaction occurs to the range of 5.8 to 6.0.

Process parameter optimization of pretreated pineapple leaves fiber for enhancement of sugar recovery

Pineapple leaves fibers (PALF) is one of the abundant biofibers that have high cellulose content. The complex structure arrangement of PALF that contains a bundle of packed fiber filled with fiber matrix makes it hard to remove lignin and disrupt hemicellulose–lignin complex structure, thus difficult to produce reducing sugar. Dilute sulfuric acid (H2SO4), sodium hydroxide (NaOH), and hot water pretreatment were employed in this study to determine the digestibility of PALF prior to enzyme hydrolysis as a pretreatment method. PALF pretreated with 0.5 % (w/v) NaOH gave the highest yield of reducing sugar (11.65 mg/mL) compared to dilute H2SO4 (8.11 mg/mL) and hot water pretreatment (6.50 mg/mL). The structural changes of PALF after pretreatments were observed through scanning electron microscopy (SEM) and confirmed the structural modification caused by NaOH pretreatment. The optimization of NaOH pretreatment was further carried out by using Box–Behnken design (BBD) to enhance the yield of reducing sugar from PALF and the parameters considered for the optimization include NaOH concentration (0.5 %–2.5 % (w/v)), temperature (80–100 °C), and pretreatment time (30–90 min). The model developed for the response (reducing sugar yield) indicates that the optimum operating condition is 2.43 % (w/v) of NaOH, 87 °C, and 57.15 min of pretreatment time with 17.26 mg/mL of reducing sugar via enzymatic hydrolysis. This result indicates that the pretreatment condition significantly improved the rate of enzymatic hydrolysis and sugar recovery.

Assessment of combination of pretreatment of Sorghum durra stalk and production of chimeric enzyme (β-glucosidase and endo β-1,4 glucanase, CtGH1-L1-CtGH5-F194A) and cellobiohydrolase (CtCBH5A) for saccharification to produce bioethanol

Optimization of pretreatment and saccharification of Sorghum durra stalk (Sds) was carried out. The chimeric enzyme (CtGH1-L1-CtGH5-F194A) having β-glucosidase (CtGH1) and endo β-1,4 glucanase activity (CtGH5-F194A) and cellobiohydrolase (CtCBH5A) from Clostridium thermocellum were used for saccharification. Chimeric enzyme will save production cost of two enzymes, individually. Stage 2 pretreatment by 1% (w/v) NaOH assisted autoclaving + 1.5% (v/v) dilute H2SO4 assisted oven heating gave lower total sugar yield (366.6 mg/g of pretreated Sds) and total glucose yield (195 mg/g of pretreated Sds) in pretreated hydrolysate with highest crystallinity index 55.6% than the other stage 2 pretreatments. Optimized parameters for saccharification of above stage 2 pretreated biomass were 3% (w/v) biomass concentration, enzyme (chimera: cellobiohydrolase) ratio, 2:3 (U/g) of biomass, total enzyme loading (350 U/g of pretreated biomass), 24 h and 30 °C. Best stage 2 pretreated Sds under optimized enzyme saccharification conditions gave maximum total reducing sugar yield 417 mg/g and glucose yield 285 mg/g pretreated biomass in hydrolysate. Best stage 2 pretreated Sds showed significantly higher cellulose, 71.3% and lower lignin, 2.0% and hemicellulose, 12.2% (w/w) content suggesting the effectiveness of method. This hydrolysate upon SHF using Saccharomyces cerevisiae under unoptimized conditions produced ethanol yield, 0.12 g/g of glucose. Abbreviation: Ct-Clostridium thermocellum, Sds-Sorghum durra stalk, TRS-Total reducing sugar, HPLC-High performance liquid chromatography, RI-Refractive index, ADL-acid insoluble lignin, GYE-Glucose yeast extract, MGYP-Malt glucose yeast extract peptone, SHF-separate hydrolysis and fermentation, OD-Optical density, PVDF-Poly vinylidene fluoride, TS-total sugar, FESEM-Field emission scanning electron microscopy, XRD-X-ray diffraction, FTIR-Fourier transform infra-red spectroscopy and CrI-Crystallinity index.

Natural deep eutectic solvents efficient catalytic conversion of cellulose to total reducing sugars (TRS)

Lignocellulosic biomass contains about 45% cellulose. The total reducing sugars (TRS) obtained from lignocellulosic materials is beneficial to the sustainable development. Natural deep eutectic solvents (NADESs) provide an attractive alternative for the “green” conversion of cellulose. In this work, series of amino acids based NADESs with FeCl3.6H2O as ligands catalyst were synthesized and characterized by in situ IR, FT-IR, 1H NMR and TG-DTA. NADESs showed great thermal stability. The efficient hydrolysis performance of cellulose in NADESs was investigated under mild conditions. The influencing factors such as the type of NADESs, reaction temperature, reaction time, and FeCl3.6H2O addition on the TRS yield were studied. The optimized process conditions for hydrolyzing cellulose in L-Proline/ Ethylene glycol/FeCl3.6H2O were molar ratio 1: 2: 1, reaction time 120 min and temperature 120 °C. The yield of total reducing sugar was 66.7%. The conversion mechanism was also investigated.

A combined cellulosic and starchy ethanol and biomethane production with stillage recycle and respective cost analysis

To minimize waste generation in ethanol production from starchy and cellulosic feedstocks, the feasibility of stillage recycle to fermentation process was studied. For sugarcane bagasse (SCB) and palm empty fruit bunch (EFB), optimal hot-compressed water (HCW) pretreatment and enzyme hydrolysis (10% wt) gave the highest total reducing sugar (TRS) yields of 64.2% and 67.3%, respectively. Ethanol fermentation of SCB, EFB and fresh cassava by Saccharomyces cerevisiae TISTR5606 gave the highest yields of 0.31 g g−1, 0.40 g g−1, and 0.31 g g−1 TRS, respectively. For recycling of SCB and EFB stillage, a slight decline of ethanol yield was found while ethanol yield of cassava significantly increased from 60.8% to 89.9%. The ethanol yields from the 2nd recycle of cassava was still 10% higher than no recycle. Addition of 10%–20% v/v black liquor from lignocellulosic HCW pretreatment into anaerobic digestion system noticeably enhanced the chemical oxygen demand removal and methane production. Analysis of variable operating cost showed that stillage recycles for 20% for fresh cassava and 10% for SCB is cost-effective process for ethanol production.

Strategy to enhance the sugar production using recyclable inorganic salt for pre-treatment of oil palm empty fruit bunch (OPEFB)

Inorganic salts were used for the pretreatment of oil palm empty fruit bunches (OPEFB) to enhance the delignification and saccharification yield of OPEFB. The sequential pretreatment of OPEFB using sodium phosphate dodecahydrate (Na3PO4.12H2O) and zinc chloride (ZnCl2) proved to be an effective approach. OPEFB was delignified by 58.8%, producing a maximum total reducing sugar (TRS) yield of 0.97 g/g under optimum pretreatment conditions of 15% Na3PO4.12H2O, 60 min (30 min/stage) pretreatment time, 10% solid to liquid ratio, and pretreatment temperature of 121 °C. In addition, structural and morphological analysis of the pretreated OPEFB using field emission scanning electron microscope (FESEM), Fourier transform infrared (FTIR) spectroscopy, and X- ray diffraction (X-RD) revealed major structural changes, such as the generation of porous structure, which allows for better enzyme accessibility. Moreover, recycle experiments showed encouraging findings, as the spent pretreatment liquid with pH adjustment can be recycled efficiently for at least 5 times without a substantial decrease in its effectiveness.