Counter-Current Suspension Extraction Process of Lignocellulose in Biorefineries to Reach Low Water Consumption, High Extraction Yields, and Extract Concentrations

The processing of large quantities of water in biorefining processes can lead to immense costs for heating, evaporation, and wastewater disposal. These costs may prohibit the exploitation of alternative products, e.g., xylooligosaccharides from straw, which are regarded as too costly. A new counter-current extractions method is proposed that aims at low solvent (water) consumption, as well as high yields and extract concentrations. This process was evaluated with suspension extraction experiments with steam pretreated wheat straw and the process window analysis based on a mass balance for a washing and a leaching scenario. The latter was conducted with two other suspension extraction processes as a comparison. The equilibration time was found to be well below 10 min. While the suspension extraction with and without recycling need to be designed to achieve a high yield or a high concentration and low solvent consumption, the proposed extraction method can reach all three simultaneously. Thus, this new process is evaluated as a potential method to spare water and downstream costs and allow new processing pathways in second-generation biorefineries.

Using electrical resistance tomography to measure the yield stress of pretreated wheat straw and wheat straw slurries

Wheat straw is a low-cost feedstock for production of biofuels as a viable alternative to fossil -based fuels. Pretreatment process is an important stage in producing biofuels. Pretreated wheat straw slurries (PWS) are non-Newtonian fluids with yield stress. In mixing operations, the presence of yield stress creates a region of active motion (cavern) around the impeller and stagnant zones elsewhere which causes difficulties in the production of biofuels. In this study, for the first time electrical resistance tomography (ERT) was utilized to measure the cavern dimensions as a function of the impeller type (A200, A100, and A315), impeller speed (20 to 110 rpm), fiber size (≤ 2 and ≤ 6 mm), and PWS concentration (6, 8, and 10 wt%). The cavern sizes were used to measure the yield stress of PWS slurries as a function of fiber size and fiber concentration. The average yield stresses of 6, 8, and 10 wt% PWS slurries with the fiber sizes of ≤ 2 mm were 2.00, 5.43, and 8.51 Pa, respectively, and 4.26, 9.30, and 13.84 Pa for the fiber sizes of ≤ 6 mm.

Using electrical resistance tomography to measure the yield stress of pretreated wheat straw and wheat straw slurries

Wheat straw is a low-cost feedstock for production of biofuels as a viable alternative to fossil -based fuels. Pretreatment process is an important stage in producing biofuels. Pretreated wheat straw slurries (PWS) are non-Newtonian fluids with yield stress. In mixing operations, the presence of yield stress creates a region of active motion (cavern) around the impeller and stagnant zones elsewhere which causes difficulties in the production of biofuels. In this study, for the first time electrical resistance tomography (ERT) was utilized to measure the cavern dimensions as a function of the impeller type (A200, A100, and A315), impeller speed (20 to 110 rpm), fiber size (≤ 2 and ≤ 6 mm), and PWS concentration (6, 8, and 10 wt%). The cavern sizes were used to measure the yield stress of PWS slurries as a function of fiber size and fiber concentration. The average yield stresses of 6, 8, and 10 wt% PWS slurries with the fiber sizes of ≤ 2 mm were 2.00, 5.43, and 8.51 Pa, respectively, and 4.26, 9.30, and 13.84 Pa for the fiber sizes of ≤ 6 mm.

Production of a β-Glucosidase-Rich Cocktail From Talaromyces Amestolkiae Using Raw Glycerol: Its Role for Lignocellulose Wastes Valorization

As β-glucosidases represent the major bottleneck for industrial degradation of plant biomass, great efforts are being devoted both to discover novel and robust versions of these enzymes, as well as to develop efficient and inexpensive ways to produce them. In this work, raw glycerol from chemical production of biodiesel was tested as carbon source for the fungus Talaromyces amestolkiae with the aim of producing enzyme cocktails rich in this activity. Approximately 11 U/mL β-glucosidase were detected in these cultures, constituting the major cellulolytic activity. Proteomic analysis revealed BGL-3 as the most abundant protein and the main β-glucosidase. This enzyme crude was successfully used to supplement a basal commercial cellulolytic cocktail (Cellu-clast 1.5L) for saccharification of pretreated wheat straw, corroborating that even hardly exploitable industrial wastes, such as glycerol, can be used as secondary raw materials to produce valuable enzymatic preparations in a framework of circular economy

Pilot Scale Elimination of Phenolic Cellulase Inhibitors From Alkali Pretreated Wheat Straw for Improved Cellulolytic Digestibility to Fermentable Saccharides

Depleting supplies of fossil fuel, regular price hikes of gasoline and environmental deterioration have necessitated the search for economic and eco-benign alternatives of gasoline like lignocellulosic biomass. However, pre-treatment of such biomass results in development of some phenolic compounds which later hinder the depolymerisation of biomass by cellulases and seriously affect the cost effectiveness of the process. Dephenolification of biomass hydrolysate is well cited in literature. However, elimination of phenolic compounds from pretreated solid biomass is not well studied. The present study was aimed to optimize dephenoliphication of wheat straw using various alkalis i.e., Ca(OH)2 and NH3; acids i.e., H2O2, H2SO4, and H3PO4; combinations of NH3+ H3PO4 and H3PO4+ H2O2 at pilot scale to increase enzymatic saccharification yield. Among all the pretreatment strategies used, maximum reduction in phenolic content was observed as 66 mg Gallic Acid Equivalent/gram Dry Weight (GAE/g DW), compared to control having 210 mg GAE/g DW using 5% (v/v) combination of NH3+H3PO4. Upon subsequent saccharification of dephenoliphied substrate, the hydrolysis yield was recorded as 46.88%. Optimized conditions such as using 1%+5% concentration of NH3+ H3PO4, for 30 min at 110°C temperature reduced total phenolic content (TPC) to 48 mg GAE/g DW. This reduction in phenolic content helped cellulases to act more proficiently on the substrate and saccharification yield of 55.06% was obtained. The findings will result in less utilization of cellulases to get increased yield of saccharides by hydrolyzing wheat straw, thus, making the process economical. Furthermore, pilot scale investigations of current study will help in upgrading the novel process to industrial scale.

Production of a β-glucosidase-Rich Cocktail from Talaromyces Amestolkiae using Raw Glycerol: Its Role for Lignocellulose Wastes Valorization

Background: As β-glucosidases represent the major bottleneck for industrial degradation of plant biomass, great efforts are being devoted both to discover novel and robust versions of these enzymes, as well as to develop efficient and inexpensive ways to produce them. In this work, raw glycerol from chemical production of biodiesel was tested as carbon source for the fungus Talaromyces amestolkiae with the aim of producing enzyme cocktails rich in this activity. Results: When using raw glycerol as sole carbon source, approximately 11 U/mL β-glucosidase were detected in these cultures, constituting the major cellulolytic activity. Besides, it was detected that the enzymatic production started when glycerol was completely depleted, which implicates that it was produced under carbon starvation stimuli. Proteomic analysis of the produced crudes revealed BGL-3 as the most abundant protein and the main b-glucosidase. This enzymatic cocktail was successfully used to supplement a basal commercial cellulolytic cocktail (Celluclast 1.5L) for saccharification of different pretreated wheat straw, and improving the yield that the commercial preparation can reach alone.Conclusions: This study corroborates that even hardly exploitable industrial wastes, such as glycerol, can be used by Talaromyces amestolkiae as carbon sources to produce very valuable enzymatic preparations for the production of biofuels and other bioproducts in a framework of circular economy.

Thermal Decomposition and Combustion of Microwave Pre-Treated Biomass Pellets

The objective of the study was to investigate a more effective use of commercially available biomass pellets (wheat straw, wood, peat) using microwave pretreatment to improve heat production. Pellets were pretreated using the originally designed microwave torrefaction device. The effects of microwave (mw) pretreatment were quantified, providing measurements of the weight loss and elemental composition of pellets and estimating the effect of mw pretreatment on their porosity, surface area and calorific values at pretreatment temperatures of T = 448–553 K. Obtained results show that the highest structural variations and elemental composition during mw pretreatment were obtained for wheat straw pellets, with an increase in reactivity, a decreasing in the duration of the thermal decomposition by about 40% and an increase in the yield of combustible volatiles. Increased reactivity of pretreated pellets enhanced the ignition and burnout of volatiles, decreasing the duration of the burnout of pretreated wheat straw, wood and peat pellets by 40%, 24% and 9%, respectively, and increasing the peak and average values of the flame temperature, heat output, and produced heat energy by 40–50%, with a correlating increase of combustion efficiency and the mass fraction of carbon-neutral CO2 emission. Thus, the applicability of microwave pretreatment for the control and improvement of heat production was confirmed.

Methane Production Potential of Rumen Pretreated Lignocellulosic Wastes

Bioenergy production from lignocellulosic biomass is challenging due to its structure and a pretreatment is required before methane production. In this study, biological pretreatment by using rumen microorganisms was applied for different types of lignocellulosic wastes: wheat straw, cotton stalk, reeds and sunflower stalk. The reactors were pretreated for 2, 5, 10, 15 and 20 days. After the pretreatment stages and gas measurements were done, reactors were separated into two phases as lower solid phase and upper liquid phase. The reactors were installed for the methanation stage, gas measurements were made at regular intervals and graphs were drawn using the cumulative results. Modified Gompertz equation was used to estimate potential biogas production. According to the results, the reactor containing 5 days pretreated wheat straw became prominent among the other reactors in terms of biogas and methane production with 163 ml and 102 ml, respectively. It was followed by 20 days pretreated reeds with 104 ml biogas and 80 ml methane, 2 days pretreated sunflower stalk with 88 ml biogas and 52 ml methane, and 2 days pretreated cotton stalk with 87 ml biogas and 50 ml methane.

Storage and handling of pretreated lignocellulose affects the redox chemistry during subsequent enzymatic saccharification

The decomposition of lignocellulose in nature, as well as when used as feedstock in industrial settings, takes place in a dynamic system of biotic and abiotic reactions. In the present study, the impact of abiotic reactions during the storage of pretreated lignocellulose on the efficiency of subsequent saccharification was investigated. Abiotic decarboxylation was higher in steam-pretreated wheat straw (SWS, up till 1.5% CO2) than in dilute-acid-catalysed steam-pretreated forestry residue (SFR, up till 3.2% CO2) which could be due to higher iron content in SFR and there was no significant CO2 production in warm-water-washed slurries. Unwashed slurries rapidly consumed O2 during incubation at 50 °C; the behaviour was more dependent on storage conditions in case of SWS than SFR slurries. There was a pH drop in the slurries which did not correlate with acetic acid release. Storage of SWS under aerobic conditions led to oxidation of the substrate and reduced the extent of enzymatic saccharification by Cellic® CTec3. Catalase had no effect on the fractional conversion of the aerobically stored substrate, suggesting that the lower fractional conversion was due to reduced activity of the lytic polysaccharide monooxygenase component during saccharification. The fractional conversion of SFR was low in all cases, and cellulose hydrolysis ceased before the first sampling point. This was possibly due to excessive pretreatment of the forest residues. The conditions at which pretreated lignocellulose are stored after pretreatment significantly influenced the extent and kind of abiotic reactions that take place during storage. This in turn influenced the efficiency of subsequent saccharification. Pretreated substrates for laboratory testing must, therefore, be stored in a manner that minimizes abiotic oxidation to ensure that the properties of the substrate resemble those in an industrial setting, where pretreated lignocellulose is fed almost directly into the saccharification vessel.

Production of Cellulosic Ethanol from Enzymatically Hydrolysed Wheat Straws

The aim of this study is to find the optimal pretreatment conditions and hydrolysis in order to obtain a high yield of bioethanol from wheat straw. The pretreatments were performed with different concentrations of sulphuric acid 1, 2 and 3% (v/v), and were followed by an enzymatic hydrolysis that was performed by varying the solid-to-liquid ratio (1/20, 1/25 and 1/30 g/mL) and the enzyme dose (30/30 µL/g, 60/60 µL/g and 90/90 µL/g Viscozyme® L/Celluclast® 1.5 L). This mix of enzymes was used for the first time in the hydrolysis process of wheat straws which was previously pretreated with dilute sulfuric acid. Scanning electron microscopy indicated significant differences in the structural composition of the samples because of the pretreatment with H2SO4 at different concentrations, and ATR-FTIR analysis highlighted the changes in the chemical composition in the pretreated wheat straw as compared to the untreated one. HPLC-RID was used to identify and quantify the carbohydrates content resulted from enzymatic hydrolysis to evaluate the potential of using wheat straws as a raw material for production of cellulosic ethanol in Romania. The highest degradation of lignocellulosic material was obtained in the case of pretreatment with 3% H2SO4 (v/v), a solid-to-liquid ratio of 1/30 and an enzyme dose of 90/90 µL/g. Simultaneous saccharification and fermentation were performed using Saccharomyces cerevisiae yeast, and for monitoring the fermentation process a BlueSens equipment was used provided with ethanol, O2 and CO2 cap sensors mounted on the fermentation flasks. The highest concentration of bioethanol was obtained after 48 h of fermentation and it reached 1.20% (v/v).