Dilute sulfuric acid pretreatment of cardoon for ethanol production

High Solid and Low Cellulase Enzymatic Hydrolysis of Cardoon Stems Pretreated by Acidified Γ-Valerolactone/Water Solution

Lignocellulosic biomass is a nonedible matrix that can be efficiently exploited as feedstock in an integrated biorefinery after a proper pretreatment. An organosolv pretreatment using an acidified γ-valerolactone (GVL)/water solution was proposed to improve the cellulose enrichment and enzymatic saccharification of cardoon (Cynara cardunculus L.) stems. At the optimal pretreatment condition (140 °C, 0.6 GVL/water, and 2.24% H2SO4), xylan was efficiently removed from the cardoon, and up to 50% of its content was recovered in the aqueous fraction, while 86% of the cellulose was retained in the solid fraction. The resulting cardoon pulp showed a cellulose content of 91.5% and an enzymatic digestibility of 100%. An overall glucose production of 37.17 g/100 g raw material (90% theoretical maximum) was obtained using high solid loading (20% w/w) and a high enzyme dosage (60 FPU/g cellulose). At a low enzyme dosage, glucose concentrations of 169 g/L and 210 g/L were achieved using 10 FPU/g cellulose and 20 FPU/g cellulose, respectively. Therefore, an organosolv pretreatment can be an effective process for producing cellulose-enriched pulp with enhanced enzymatic digestibility from cardoon stems, providing a promising option for green lignocellulosic biorefineries that aim to produce high concentrations of glucose with low cellulase addition.

Cardoon Hydrolysate Detoxification by Activated Carbon or Membranes System for Bioethanol Production

Advanced biofuels incorporation into the transportation sector, particularly cellulosic bioethanol, is crucial for attaining carbon neutrality by 2050, contributing to climate changes mitigation and wastes minimization. The world needs biofuel to be commercially available to tackle the socioeconomic challenges coming from the continued use of fossil fuels. Cynara cardunculus (cardoon) is a cheap lignocellulosic raw biomass that easily grows in Mediterraneous soils and is a potential renewable resource for a biorefinery. This work aimed to study the bioethanol production from cardoon hemicellulosic hydrolysates, which originated from dilute sulfuric acid hydrolysis pretreatment. A detoxification step to remove released microbial fermentative inhibitors was evaluated by using both activated carbon adsorption and a nanofiltration membrane system. The Scheffersomyces stipitis CBS5773 yeast and the modified Escherichia coli MS04 fermentation performances at different experimental conditions were compared. The promising results with E. coli, using detoxified cardoon by membrane nanofiltration, led to a bioethanol volumetric productivity of 0.30 g·L−1·h−1, with a conversion efficiency of 94.5%. Regarding the S. stipitis, in similar fermentation conditions, volumetric productivity of 0.091 g·L−1·h−1 with a conversion efficiency of 64.9% was obtained. Concluding, the production of bioethanol through detoxification of hemicellulosic cardoon hydrolysate presents a suitable alternative for the production of second-generation bioethanol, especially using the modified E. coli.

Acid-Assisted Organosolv Pre-Treatment and Enzymatic Hydrolysis of Cynara cardunculus L. for Glucose Production

Lignocellulosic biomass is a non-edible feedstock that can be used in integrated biorefinery for the production of biochemicals and biofuel. Among lignocellulosic biomass, Cynara cardunculus L. (cardoon) is a promising crop thanks to its low water and fertilizer demand. Organosolv is a chemical treatment that uses numerous organic or aqueous solvent mixtures, and a small amount of acid catalyst, in order to solubilize the lignin and hemicellulose fractions, making the cellulose accessible to hydrolytic enzymes. Lignocellulosic residues of cardoon underwent a two-step treatment process to obtain fermentable glucose. In the first step, the milled biomass was subjected to microwave-assisted extraction using an acidified γ-valerolactone (GVL)/water mixture, yielding a solid cellulose pulp. In the second step, the pre-treated material was hydrolyzed by cellulolytic enzymes to glucose. The first step was optimized by means of a two-level full factorial design. The investigated factors were process temperature, acid catalyst concentration, and GVL/water ratio. A glucose production equal to 30.17 g per 100 g of raw material (89% of the maximum theoretical yield) was achieved after conducting the first step at 150 °C using an acidified water solution (1.96% H2SO4w/w).

Production of Carbohydrates from Cardoon Pre-Treated by Acid-Catalyzed Steam Explosion and Enzymatic Hydrolysis

Cardoon (Cynara cardunculus) is a promising crop from which to obtain oilseeds and lignocellulosic biomass. Acid-catalyzed steam explosion is a thermochemical process that can efficiently pre-treat lignocellulosic biomass. The drawback is the production of a high number of carbohydrate degradation products in the liquid fraction that could inhibit microbial growth. In this work, the lignocellulosic biomass of cardoon, gathered from a dedicated field, were used as the raw material for the production of fermentable monosaccharides by employing acid-catalyzed steam explosion. The raw material was pre-soaked with a dilute 1% (w/w) sulfuric acid solution and then subjected to steam explosion under three different severity conditions. The recovered slurry was separated into solid and liquid fractions, which were individually characterized to determine total carbohydrate and inhibitor concentrations. The slurry and the washed solid fraction underwent enzymatic hydrolysis to release glucose and pentose monosaccharides. By conducting the pre-treatment at 175 °C for 35 min and hydrolyzing the obtained slurry, a yield of 33.17 g of monosaccharides/100 g of cardoon was achieved. At the same conditions, 4.39 g of inhibitors/100 g of cardoon were produced.

Enhanced lipid and starch productivity of microalga (Chlorococcum sp. TISTR 8583) with nitrogen limitation following effective pretreatments for biofuel production

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To enhance the lipid and starch productivity of Chlorococcum sp. TISTR 8583 for biofuel productions.

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To identify suitable pretreatment strategy for release of fermentable sugars and lipids extraction from algal biomass.

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To convert the released fermentable sugars and lipids into bioethanol and biodiesel respectively.

The study was conducted to evaluate the conditions to enhance the accumulation of lipids and starch in Chlorococcum sp. TISTR 8583 for the production of biofuel. The Chlorococcum sp. TISTR 8583 was cultivated on BG-11 medium under optimized light intensity. The nitrogen limitation (NL) enhanced the accumulation of both starch and lipids and resulted in 34.02% total sugars as compared to 22.57% on nitrogen supplemented (NS) media only. Similarly, the nitrogen supplemented (NS) media produced 17.05% lipids as compared to 29.59% lipids by NL media. The biomass was investigated for biodiesel and bioethanol production by adopting different pretreatment strategies, such as enzyme, acid and alkaline pretreatments. The alkaline pretreatment was found to be efficient strategy (23.67 wt% sugars/g algal biomass: 1.2% (w/v) at 140 ⁰C for 30 min) while the acid pretreatment (1%: v/v; 140 °C) was least effective pretreatment strategy with the yield of 14.83 wt% sugars/g algal biomass.

Pre-treatment of corn stover, Cynara cardunculus L. stems and wheat straw by ethanol-water and diluted sulfuric acid: Comparison under different energy input conditions

Ethanol-water (EW) and diluted sulfuric acid (DSA) pre-treatment have been studied for lignocellulosic biomass (corn stover, Cynara cardunculus L. stems and wheat straw). Both pre-treatments have been compared taken into account: solids recovery, glucans recovery, xylans removed, delignification and glucose yield. In all cases, the amount of energy involved has been taken as a criterion for sustainability. In general terms, EW is more efficient to remove lignin and DSA more appropriate to hydrolysate xylans. The combined effect of delignification and xylans removal is responsible for the improvement in the enzymatic cellulose hydrolysis. Under conditions of moderate-low energy inputs, EW pre-treatment yields better results than DSA with glucose yields in the range of 50-60% for EW pre-treated corn stover and cardoon stems; while wheat straw pulps reach up to 80%. So, multiple raw materials biorefinery needs a previous study to fit the type and conditions of the pre-treatment to each feedstock.

Ethanol production from dilute-acid steam exploded lignocellulosic feedstocks using an isolated multistress-tolerant Pichia kudriavzevii strain

Renewable and low‐cost lignocellulosic wastes have attractive applications in bioethanol production. The yeast Saccharomyces cerevisiae is the most widely used ethanol‐producing microbe; however, its fermentation temperature (30–35°C) is not optimum (40–50°C) for enzymatic hydrolysis in the simultaneous saccharification and fermentation (SSF) process. In this study, we successfully performed an SSF process at 42°C from a high solid loading of 20% (w/v) acid‐impregnated steam explosion (AISE)‐treated rice straw with low inhibitor concentrations (furfural 0.19 g l⁻¹ and acetic acid 0.95 g l⁻¹) using an isolate Pichia kudriavzevii SI, where the ethanol titre obtained (33.4 g_p l⁻¹) was nearly 39% greater than that produced by conventional S. cerevisiae BCRC20270 at 30°C (24.1 g_p l⁻¹). In addition, P. kudriavzevii SI exhibited a high conversion efficiency of > 91% from enzyme‐saccharified hydrolysates of AISE‐treated plywood chips and sugarcane bagasse, although high concentrations of furaldehydes, such as furfural 1.07–1.21 g l⁻¹, 5‐hydroxymethyl furfural 0.20−0.72 g l⁻¹ and acetic acid 4.80–7.65 g l⁻¹, were present. This is the first report of ethanol fermentation by P. kudriavzevii using various acid‐treated lignocellulosic feedstocks without detoxification or added nutrients. The multistress‐tolerant strain SI has greater potential than the conventional S. cerevisiae for use in the cellulosic ethanol industry.

High-pressure carbon dioxide/water pre-treatment of sugarcane bagasse and elephant grass: Assessment of the effect of biomass composition on process efficiency

The performance of two lignocellulosic biomasses was studied in high-pressure carbon dioxide/water pre-treatment. Sugarcane bagasse and elephant grass were used to produce C₅-sugars from hemicellulose and, simultaneously, to promote cellulose digestibility for enzymatic saccharification. Different pre-treatment conditions, with combined severity factor ranging from -1.17 to -0.04, were evaluated and maximal total xylan to xylose yields of 59.2wt.% (34.4wt.% xylooligomers) and 46.4wt.% (34.9wt.% xylooligomers) were attained for sugarcane bagasse and elephant grass, respectively. Furthermore, pre-treated biomasses were highly digestible, with glucan to glucose yields of 77.2mol% and 72.4mol% for sugarcane bagasse and elephant grass, respectively. High-pressure carbon dioxide/water pre-treatment provides high total C₅-sugars and glucose recovery from both lignocellulosic biomasses; however it is highly influenced by composition and intrinsic features of each biomass. The obtained results confirm this approach as an effective and greener alternative to conventional pre-treatment processes.

Effects of fertilizer application and dry/wet processing of Miscanthus x giganteus on bioethanol production

The effects of wet and dry processing of miscanthus on bioethanol production using simultaneous saccharification and fermentation (SSF) process were investigated, with wet samples showing higher ethanol yields than dry samples. Miscanthus grown with no fertilizer, with fertilizer and with swine manure were sampled for analysis. Wet-fractionation was used to separate miscanthus into solid and liquid fractions. Dilute sulfuric acid pretreatment was employed and the SSF process was performed with saccharomyces cerevisiae and a cocktail of enzymes at 35°C. After pretreatment, cellulose compositions of biomass of the wet samples increased from 61.0-67.0% to 77.0-87.0%, which were higher than the compositions of dry samples. The highest theoretical ethanol yield of 88.0% was realized for wet processed pretreated miscanthus, grown with swine manure. Changes to the morphology and chemical composition of the biomass samples after pretreatment, such as crystallinity reduction, were observed using SEM and FTIR. These changes improved ethanol production.

Bioethanol production from extracted olive pomace: dilute acid hydrolysis

Residues from olive oil industry such as Extracted Olive Pomace (EOP) are potential substrates for bioethanol production. In this work, enzymatic hydrolysis of EOP pretreated by dilute acid hydrolysis (DAH) was assessed, and the enzymatic hydrolysis and bioconversion were carried out both by separate hydrolysis and fermentation (SHF) and pre-saccharification followed by simultaneous saccharification and fermentation (PSSF). DAH led to a significant removal hemicellulose, but the subsequent enzymatic treatments showed that the resulting residue was still partially recalcitrant to cellulase hydrolysis. Size reduction and further treatment of EOP-DAH with an alkaline solution were also tested. Alkaline post-treatment allowed a decrease in lignin content, but had little effect on enzymatic saccharification comparing to size reduction. Hence fermentation study was performed with ground EOP-DAH. The PSSF process showed a relatively higher bioethanol fermentation yield (0.46 gg-1) when compared to the SHF process.

Enzymatic saccharification and bioethanol production from Cynara cardunculus pretreated by steam explosion

The correct choice of the specific lignocellulosic biomass pretreatment allows obtaining high biomass conversions for biorefinery implementations and cellulosic bioethanol production from renewable resources. Cynara cardunculus (cardoon) pretreated by steam explosion (SE) was involved in second-generation bioethanol production using separate hydrolysis and fermentation (SHF) or simultaneous saccharification and fermentation (SSF) processes. Steam explosion pretreatment led to partial solubilisation of hemicelluloses and increased the accessibility of residual polysaccharides towards enzymatic hydrolysis revealing 64% of sugars yield against 11% from untreated plant material. Alkaline extraction after SE pretreatment of cardoon (CSEOH) promoted partial removal of degraded lignin, tannins, extractives and hemicelluloses thus allowing to double glucose concentration upon saccharification step. Bioethanol fermentation in SSF mode was faster than SHF process providing the best results: ethanol concentration 18.7 g L(-1), fermentation efficiency of 66.6% and a yield of 26.6g ethanol/100 g CSEOH or 10.1 g ethanol/100 g untreated cardoon.

Augmented digestion of lignocellulose by steam explosion, acid and alkaline pretreatment methods: a review

Lignocellulosic materials can be explored as one of the sustainable substrates for bioethanol production through microbial intervention as they are abundant, cheap and renewable. But at the same time, their recalcitrant structure makes the conversion process more cumbersome owing to their chemical composition which adversely affects the efficiency of bioethanol production. Therefore, the technical approaches to overcome recalcitrance of biomass feedstock has been developed to remove the barriers with the help of pretreatment methods which make cellulose more accessible to the hydrolytic enzymes, secreted by the microorganisms, for its conversion to glucose. Pretreatment of lignocellulosic biomass in cost effective manner is a major challenge to bioethanol technology research and development. Hence, in this review, we have discussed various aspects of three commonly used pretreatment methods, viz., steam explosion, acid and alkaline, applied on various lignocellulosic biomasses to augment their digestibility alongwith the challenges associated with their processing.

Use of Empty Fruit Bunches from the oil palm for bioethanol production: a thorough comparison between dilute acid and dilute alkali pretreatment

In the present work, two pretreatment techniques using either dilute acid (H2SO4) or dilute alkali (NaOH) have been compared for producing bioethanol from Empty Fruit Bunches (EFBs) from oil palm tree, a relevant feedstock for tropical countries. Treatments' performances under different conditions have been assessed and statistically optimized with respect to the response upon standardized enzymatic saccharification. The dilute acid treatment performed at optimal conditions (161.5°C, 9.44 min and 1.51% acid loading) gave 85.5% glucose yield, comparable to those of other commonly investigated feedstocks. Besides, the possibility of using fibers instead of finely ground biomass may be of economic interest. Oppositely, treatment with dilute alkali has shown lower performances under the conditions explored, most likely given the relatively significant lignin content, suggesting that the use of stronger alkali regime (with the associated drawbacks) is unavoidable to improve the performance of this treatment.

Pretreatment based on two-step steam explosion combined with an intermediate separation of fiber cells--optimization of fermentation of corn straw hydrolysates

Pretreatment is necessary for lignocellulose to achieve a highly efficient enzymatic hydrolysis and fermentation. However, coincident with pretreatment, compounds inhibiting microorganism growth are formed. Some tissues or cells, such as thin-walled cells that easily hydrolyze, will be excessively degraded because of the structural heterogeneity of lignocellulose, and some inhibitors will be generated under the same pretreatment conditions. Results showed, compared with one-step steam explosion (1.2 MPa/8 min), two-step steam explosion with an intermediate separation of fiber cells (ISFC) (1.1 Mpa/4 min-ISFC-1.2 MPa/4 min) can increase enzymatic hydrolyzation by 12.82%, reduce inhibitor conversion by 33%, and increase fermentation product (2,3-butanediol) conversion by 209%. Thus, the two-step steam explosion with ISFC process is proposed to optimize the hydrolysis process of lignocellulose by modifying the raw material from the origin. This novel process reduces the inhibitor content, promotes the biotransformation of lignocellulose, and simplifies the process of excluding the detoxification unit operation.

Effect of water extraction on sugars recovery from steam exploded olive tree pruning

Biomass of olive tree pruning can be considered a suitable raw material for the production of ethanol due to its high content of potentially fermentable carbohydrates. However its high extractives content could cause condensation reactions between extractives and acid insoluble lignin during pretreatment, hindering the enzymatic hydrolysis of pretreated material. In this work, the effect of extractives removal before steam explosion of olive tree pruning was evaluated. The objectives are to recover as much glucose as possible in the extraction stage and to avoid the condensation reactions. The effect of temperature and time of water extracted material on sugars recovery was studied using a response surface method according to a central composite design. Extractive removal previous to steam explosion resulted in 20% more total sugars recovery in comparison to a material without water extraction stage.