Pretreated Slurry Research Articles

Harnessing Ulva ohnoi for eco-friendly bioethanol production via hydrothermal pretreatment

BackgroundThe increasing demand for renewable energy sources has sparked interest in biofuels derived from green seaweeds, owing to their abundance and high carbohydrate content. Ulva ohnoi, harvested from Taiwan's shores, presents a promising candidate for bioethanol production due to its favorable characteristics. MethodsIn this study, Ulva ohnoi underwent hydrothermal pretreatment at temperatures of 120 °C, 150 °C, and 180 °C for 20 min. The pretreated slurry obtained at 180 °C was subjected to enzymatic saccharification at pH 4.8 and 50 °C for 72 h. This process resulted in the production of 5.8 g/L of glucose, which was subsequently concentrated to 18.86 g/L. Significant FindingsFermentation of the concentrated sugar fractions using Saccharomyces cerevisiae WLP 300 at 30 °C for 24 h yielded remarkable ethanol yields of 0.39 and 0.43 g/g of sugar. These yields approached the maximum theoretical values of 76.1% and 84.58%, respectively. Additionally, the study reported a maximum ethanol productivity of 0.54 g/L/h in the 12th hour in the concentrated fraction. These findings underscore the potential of Ulva ohnoi as a sustainable biofuel and clean energy source, aligning with Sustainable Development Goal 7 (SDG 7) of ensuring access to affordable, reliable, sustainable, and modern energy for mankind.

Enhancing the valorization efficiency of Camellia oil extraction wastes through sequential green acid pretreatment and solid-state fermentation-based enzymatic hydrolysis

This study focuses on the underutilized Camellia oleifera oil extraction wastes, namely C. oleifera shell (COS) and cake (COC), which are often overlooked due to their high recalcitrance and antimicrobial properties. COS was found to be an ideal substrate for producing on-site enzymes through solid-state fermentation (SSF) that can be used for lignocellulosic biomass degradation. Additionally, pretreating COS with 2 % (w/v) oxalic acid greatly enhanced sugar production, achieving 9.22 and 5.24 times more sugar compared to room temperature and thermal pretreatment methods, respectively. The highest sugar of 28 g/L was achieved by utilizing a mixture of COS and COC. Enzymatic hydrolysis performance was evaluated through three routes. In the first two routes, the whole pretreated slurry was employed, except the pH was adjusted in route 2. In route 3, the pretreated hydrolysate was recovered, while the solid residue underwent further enzymatic hydrolysis. Ultimately, route 3 resulted in the highest sugar of 20.58 g/L, using SSF enzymes and oxalic acid pretreated solid residues of COS and COC mixture. This value is twice the performance achieved using a single substrate of COS. The fine-tuning strategy employed in route 3 led to (1) achieving high sugar recovery from pretreatment and enzymatic hydrolysis, (2) minimizing water and alkaline regulator consumption, and (3) optimizing resource utilization efficiency. The effectiveness of this approach was also attributed to the synergistic effect of oxalic acid pretreatment and the use of mixed substrate. The possible mechanisms underlying these processes were discussed, offering potential directions for future studies aimed at developing even more efficient approaches.

Tailoring whole slurry bioprocessing for sugary stovers to augment sugar production by integrating soluble and insoluble carbohydrates

Obtaining sufficient concentrations of fermentable sugars from the polysaccharides of lignocellulosic materials represents a long-term challenge in achieving sustainable biorefineries. This work aimed to enhance sugar titers by employing high sugar-containing stovers (HSS) and combining its intrinsic soluble sugars with the two insoluble carbohydrates, namely cellulose and hemicellulose. Whole-slurry hydrolysis (WSH) was performed under low-to-high solid conditions using non-detoxified pretreated slurry, which exhibited a decrease in cellulose hydrolysis efficiency (CHE) from 89.08% to 42.1% as the solid loadings increased from 7% to 20%. A further WSH with detoxified slurry showed a significant increase in CHE from 42.1% to 59.52% at 20% solid loading, indicating that inhibitors present in the pretreated slurry had negative effects on CHE. Lower CHE with non-detoxified slurry accompanied by higher losses of cellulase and β-glucosidase activities, particularly at higher solid loadings. Therefore, systematic modification of WSH was performed by incorporating 2% syringic acid during pretreatment and 0.4% polyethylene glycol during saccharification, reformulating enzyme cocktails, and implementing a fed-batch experiment. These modifications resulted in a notable improvement in sugar production under high-solid loading (20%) and non-detoxified conditions, reaching 142.87 g/L total sugars with a CHE of 90.7%. These findings have revealed the potential of integrating soluble sugars with holocellulose for obtaining high-titer fermentable sugars in lignocellulosic biorefineries.

In situ saccharification of metal-containing ionic liquid pretreated (ligno)cellulose via alginate encapsulated cellulase@functionalized ZIF-8

The present work aimed to develop mixed-metal salts (MMs) assisted ionic liquid (IL) pretreatment for efficient in situ saccharification of (ligno)cellulose. To accommodate MMs-IL involved in situ saccharification, a novel immobilized cellulase based on amine-functionalized ZIF-8 and calcium alginate beads (Ce@ZIF-8-A/CA) was established. XRD, FT-IR and SEM were employed to characterize the immobilization carrier and immobilized cellulase. Compared to free cellulase, Ce@ZIF-8-A/CA showed enhanced tolerance to IL, MMs and temperature. Ce@ZIF-8-A/CA preserved more than 80% of original activity at a wide temperature range (40–70 °C) in 30% 1-butyl-3-methylpyridinium chloride ([BMPy]Cl), and retained 73.0% of initial activity in 1% MMs (FeCl3/LiCl) assisted 30% [BMPy]Cl. After pretreatment with MMs assisted [BMPy]Cl, 40%-60% (ligno)cellulose was decomposed into soluble lower-molecular-weight fragments without regeneration of cellulose after adding buffer. After in situ saccharification of pretreated slurries with Ce@ZIF-8-A/CA, total reducing sugars yields of 84.7% and 71.3% from cellulose and bagasse were obtained during 12 h, saving at least 12 h compared to traditional enzymatic in situ saccharification of (ligno)cellulose in IL.

Optimizing monosaccharide production from liquid hot water pretreatment and enzymatic hydrolysis of grass-clover press cake

In the present study, clover-grass press cake was treated by liquid hot water at temperatures of 180–200 °C for a reaction time of 5–10 min. Evaluation of pretreatments was based on the monosaccharide yield after enzymatic hydrolysis of the pretreated slurry and solid fraction, respectively. Extraction of up to 48% hemicellulose and 4% cellulose was observed during pretreatment. The optimal pretreatment conditions were identified as 190 °C and 10 min resulting in monosaccharide yields of 90% and 73% of the theoretical maximum by slurry and solid conversion, respectively. At optimal conditions, the C6 monosaccharide yield (83–90%) was fairly equal compared to the C5 monosaccharide yield (56–89%), which increased by slurry conversion due to near-complete monomerization of soluble xylo-oligosaccharides. In this study, we showed that clover-grass press cake possesses considerable potential as feedstock for production of fermentable sugars in a biorefinery context.

Saccharification of starchy food waste through thermochemical and enzymatic pretreatment, towards enhanced bioethanol production via newly isolated non-conventional yeast strains

A starchy food waste containing mainly cooked wasted rice (WR) was exploited for bioethanol production using novel yeast strains was investigated. Different pretreatment schemes of the waste at solids loading 10%–30% TS WR (w/v) i.e. enzymatic, thermochemical and combined thermochemical/enzymatic pretreatment, were evaluated aiming to the maximum liberation of fermentable carbohydrates and their subsequent bioconversion to ethanol. Fermentation tests of the whole pretreated slurries were initially performed with the yeasts strains that were identified as Kluyveromyces marxianus isolate V3-19,Pichia kudriavzevii strain YF1702 and K. marxianus strain TTG-428, and their fermentation efficiencies (FE) were comparatively assessed. It was shown that the combined pretreatment led to the maximum saccharification, whereas FEs were higher for K. marxianus, V3-19, exceeding 90% of the theoretical maximum. In the case of the highest organic loading of WR, though, up to 25% of soluble carbohydrates remained unexploitable after 72 h of fermentation, indicating that kinetic restrictions occurred in the process. Further experiments with the hydrolysates that were recovered after combined pretreatment, revealed that the removal of solids enhances the consumption of sugars and leads to complete uptake for the loading 20% TS WR (w/v).

Pretreatment of sugarcane postharvest leaves by γ-valerolactone/water/FeCl3 system for enhanced glucan and bioethanol production

The potential of sugarcane postharvest leaves for fermentable sugar yield and bioethanol production was analyzed using FeCl3 catalyzed γ-valerolactone/water pretreatment in the present study. Widely cultivated Indian cane variety Co 86032 (Nayana) was selected for the analysis. Cellulose (52.7 ± 5%), hemicellulose (33.9 ± 3.5%) and lignin (18 ± 0.3%) were estimated in postharvest leaves. Optimized GVL/water/FeCl3 pretreatment (70% GVL/300 mM FeCl3 in 30% water at 120 °C for 3 h) resulted in high delignification (74%) and hemicellulose dissolution (85.6%). Extensive removal of ester-linked ferulic acid (94.2%) and p-coumaric acid (84.4%) was also observed after pretreatment. The pretreatment-induced changes were visualized through FESEM, FTIR, XRD and confocal imaging. Only trace amounts of furfural and HMF were detected in the pretreated slurry. At 96 h of saccharification, 82.5% glucose was yielded. Fermentation of enzymatic hydrolyzate using S. cerevisiae MTCC-36 resulted in ethanol yield of 0.434 g/g glucose at 21 h. Current study revealed that, FeCl3 catalyzed GVL/water pretreatment causes effective deconstruction of cane leaves for bioethanol production.

A Critical Review on Water Overconsumption in Lignocellulosic Biomass Pretreatment for Ethanol Production through Enzymic Hydrolysis and Fermentation

Global demand for renewable and sustainable energy fostered the considerable development of biomass-to-ethanol valorization strategies. Thermochemical pretreatment methods have been proposed to render biomass more amenable to enzymatic and microbial digestion. However, the efforts have not led to its industrial-scale worldwide realization. One of the obstacles to commercialization could be related to water overconsumption, as excessive water washing of the pretreated slurry is often performed to remove inhibitory compounds and residual chemicals after biomass pretreatment. Only increasing solid loading for biomass pretreatment results in ineffective pretreatment performance, more inhibitors formation, and high viscosity, which in turn necessitates the water washing step. A number of physicochemical and biological methods are applied to detoxify the acid-pretreated liquid fraction for enzymatic hydrolysis and fermentation. Among them, alkaline neutralization and liquid–liquid extraction are preferred because of their simple operation and low cost. Seemingly, recycling black liquor for alkali pretreatment offers a pathway to reduce water and chemical consumption, but alkali replenishment and inhibitor accumulation significantly weaken this technology. Interestingly, quite a few studies have removed the water washing and even solid–liquid separation steps after (liquid hot water, Tween 40, and CaO) pretreatment. There is still much room for future studies to render biomass pretreatment more feasible in terms of economic and environmental points of view. This review provides a deep understanding of wastewater generation during biomass upgrading and discusses the solutions to reduce water consumption critically.

Efficient co-production of fermentable sugars and biobutanol from corn stover based on a novel butyric acid pretreatment strategy

Efficient deconstruction of lignocellulosic biomass by pretreatment is important for the production of fermentable sugars and biofuels. This study used butyric acid as a novel catalyst for corn stover pretreatment. The effects of butyric acid pretreatments on chemical composition and enzymatic digestibility were systematically investigated. The results indicate that a high linear correlation between xylan removal and fermentable sugars yield (r2 = 0.91) was found. Pretreatment of corn stover with 50 g/L butyric acid at 180 °C for 0.5 h removed 83.17% of xylan and recovered 86.99% of glucan, and fermentable sugars yield of pretreated corn stover reached 97.16%. The physiochemical characterization results show that crystalline index (CrI) of corn stover was increased from 30.13% to 45.04%−48.38% after pretreatments, and the chemical structure and morphological features also exhibited positive changes for enhancing enzymatic hydrolysis. Meanwhile, the liquid fraction of pretreated slurry can be used for recycled pretreatment with 73.81% of fermentable sugars yield after four cycles. Additionally, the residual butyric acid was re-utilized as the co-substrate for Clostridium acetobutylicum ATCC 824 to produce biobutanol via acetone-butanol-ethanol (ABE) fermentation. The final production of butanol and solvents reached 8.38 g/L and 12.63 g/L under an optimized intermittent feeding strategy with a higher butanol/acetone ratio of 2.40 g/g. Overall, this work presents a novel pretreatment strategy to co-produce fermentable sugars and advanced biofuel from abundant lignocellulosic biomass.

Subcritical Water Pretreatment for the Efficient Valorization of Sorghum Distillery Residue for the Biorefinery Platform.

The depletion of fossil fuels is resulting in an increased energy crisis, which is leading the paradigm shift towards alternative energy resources to overcome the issue. Lignocellulosic biomass or agricultural residue could be utilized to produce energy fuel (bioethanol) as it can resolve the issue of energy crisis and reduce environmental pollution that occurs due to waste generation from agriculture and food industries. A huge amount of sorghum distillery residue (SDR) is produced during the Kaoliang liquor production process, which may cause environmental problems. Therefore, the SDR generated can be utilized to produce bioethanol to meet current energy demands and resolve environmental problems. Using a central composite experimental design, the SDR was subjected to hydrothermal pretreatment. The conditions selected for hydrothermal pretreatment are 155 °C, 170 °C, and 185 °C for 10, 30, and 50 min, respectively. Based on the analysis, 150 °C for 30 min conditions for SDR hydrothermal pretreatment were selected as no dehydration product (Furfural and HMF) was detected in the liquid phase. Therefore, the pretreated slurry obtained using hydrothermal pretreatment at 150 °C for 30 min was subjected to enzymatic hydrolysis at 5% solid loading and 15 FPU/gds. The saccharification yield obtained at 72 h was 75.05 ± 0.5%, and 5.33 g/L glucose concentration. This non-conventional way of enzymatic hydrolysis eliminates the separation and detoxification process, favoring the concept of an economical and easy operational strategy in terms of biorefinery.

Valorization of Pineapple Leaves Waste for the Production of Bioethanol.

Being a lignocellulose-rich biomass, pineapple leaves waste (PL) could be a potential raw material for the production of biofuel, biochemicals, and other value-added products. The main aim of this study was to investigate the potential of pineapple leaves in the sustainable production of bioethanol via stepwise saccharification and fermentation. For this purpose, PL was subjected to hydrothermal pretreatment in a high-pressure reactor at 150 °C for 20 min without any catalyst, resulting in a maximum reducing sugar yield of 38.1 g/L in the liquid fraction after solid-liquid separation of the pretreated hydrolysate. Inhibitors (phenolics, furans) and oligomers production were also monitored during the pretreatment in the liquid fraction of pretreated PL. Enzymatic hydrolysis (EH) of both pretreated biomass slurry and cellulose-rich solid fraction maintained at a solid loading (dry basis) of 5% wt. was performed at 50 °C and 150 rpm using commercial cellulase at an enzyme dose of 10 FPU/gds. EH resulted in a glucose yield of 13.7 and 18.4 g/L from pretreated slurry and solid fractions, respectively. Fermentation of the sugar syrup obtained by EH of pretreated slurry and the solid fraction was performed at 30 °C for 72 h using Saccharomyces cerevisiae WLP300, resulting in significant ethanol production with more than 91% fermentation efficiency. This study reveals the potential of pineapple leaves waste for biorefinery application, and the role of inhibitors in the overall efficiency of the process when using whole biomass slurry as a substrate.

High-titer lactic acid production from pilot-scale pretreated non-detoxified rice straw hydrolysate at high-solid loading

Lignocellulosic biomasses are promising feedstocks for the production of high-value chemicals because they are abundant, inexpensive, renewable, sustainable, environmentally friendly, and can potentially reduce pollution. Furthermore, lignocellulose biomass is non-edible and a source of fermentable sugars, which makes it ideal for the fermentation of various biochemicals, such as bio-based lactic acid (LA). Furthermore, it contributes to the economic sustainability of biorefineries. LA is an industrially significant product with a large and rapidly growing market due to its attractive features and benefits. The current study demonstrates high-titer lactic acid (LA) fermentation from pretreated rice straw using co-fermenting (C5 & C6 sugars) Lactobacillus lactis 2369. Rice straw (RS) was chemically pretreated with mild acid additive in a pilot-scale (250 Kg day–1) steam-explosion unit. At first, the crude dilute acid pretreated slurry was enzymatically hydrolyzed using commercial cellulases (1.5–10 FPUg−1 residue) at 50 °C for 48 h followed by LA production for 96–140 h. In the current study high titer, LA production (82.2 gL−1) as well as higher conversion yield (87.2%) with the productivity of 0.61 gL−1h−1 were obtained with high substrate solid loading (20% wv−1) and low enzyme dose (5 FPU g−1) at 42 °C.

Optimization of Pretreatment Conditions and Enzymatic Hydrolysis of Corn Cobs for Production of Microbial Lipids by Trichosporon oleaginosus

Microbial lipids produced from lignocellulosic biomass are sustainable alternative feedstock for biodiesel production. In this study, corn cobs were used as a carbon source for lipid production and growth of oleaginous yeast Trichosporon oleaginosus. Lignocellulosic biomass was subjected to alkali and acid pretreatment using sulfuric acid and sodium hydroxide under different temperatures, catalyst concentrations and treatment times. Pretreatment of corn cobs was followed by cellulase hydrolysis. Hydrolysis of alkali pretreated (2% NaOH at 50 °C for 6 h, 1% NaOH at 50 °C for 16 h, 2% NaOH at 121 °C for 1 h, 1% NaOH at 121 °C for 2 h) and acid pretreated (1% H2SO4 120 °C for 20 min, and 2% H2SO4 120 °C for 10 min) corn cobs resulted in more than 80% of the theoretical yield of glucose. The effect of substrate (5, 10, 15 and 20%, g g−1) and cellulase loading (15 and 30 Filter Paper Units per gram of glucan, FPU g−1) on fermentable sugar yield was also studied. The maximal glucose concentration of 81.64 g L−1 was obtained from alkali-pretreated corn cobs (2% NaOH at 50 °C for 6 h) at 20% substrate loading and 30 FPU of Cellic CTec2 g−1 of glucan. Enzymatic hydrolysates of pretreated biomasses and filtrates of lignocellulosic slurries obtained after pretreatment were used for growth and lipid synthesis by T. oleaginosus. The highest lipid concentration of 18.97 g L−1 was obtained on hydrolysate of alkali-pretreated corn cobs (with 1% NaOH at 50 °C for 16 h) using a 15% (g g−1) substrate loading and 15 FPU g−1 of cellulase loading. Significant lipid accumulation was also achieved using undetoxified filtrates of pretreated slurries as substrates. Results showed that pretreated corn cobs and undetoxified filtrates are suitable carbon sources for the growth and efficient accumulation of lipids in T. oleaginosus.

Tamarind extract pretreatment: Valorization of sugarcane bagasse for cellulase production by Aspergillus flavus

Effective pretreatment is crucial for cellulase production from sugarcane bagasse. Pretreatment with tamarind extract could reduce the hazardous effect associated with chemical pretreatment. The present work investigated tamarind (Tamarindus indica) extract in combination with H2SO4 and thermal pretreatment of sugarcane bagasse for cellulase production by Aspergillus flavus. The sugarcane bagasse was pretreated with tamarind extract pH 2 and pH 4, followed by 1% H2SO4 and thermal treatment at 121°C for 15 min. The pretreatment slurry was analysed for reducing sugar while solid bagasse was analysed for weight loss. Aspergillus flavus grew on sugarcane bagasse under solid state fermentation and the Carboxy Methyl Cellulase (CMCase) and Filter Paper Assay (FPA) activities were compared on the various pretreatments. The pretreatments changed the visible morphology of the sugarcane bagasse observed by the swelling, fibrous appearance and colour change. Pretreatment slurry yielded highest soluble reducing sugar at 60.01 mg/ml in tamarind extract (pH 4/1% H2SO4 ) and highest weight loss of solids at 73.70% in tamarind extract (pH 2/1% H2SO4 /thermal 121°C). Aspergillus flavus performed better on tamarind extract (pH 2/1% H2SO4 ) by producing optimal CMCase and FPA activities at 0.100 U/ml and 0.409 U/ml respectively after 3 days of fermentation. Cellulase was maximally active at temperature of 50 °C. The tamarind extract pretreatment successfully proved to be an alternative organo-chemical pretreatment of sugarcane bagasse as evidenced by the physical properties, soluble reducing sugars and cellulase activities.
 Keywords: Aspergillus flavus, Cellulase, Pretreatment, Sugarcane bagasse, Tamarind extract

Biomethane enhancement from corn straw using anaerobic digestion by-products as pretreatment agents: A highly effective and green strategy

The development of biogas projects feed by lignocellulosic biomass has been constrained by the high cost of pre- and post-treatment. In this study, a novel strategy for pretreatment by using two by-products, i.e., CO2 and liquid digestate (LD), generated from anaerobic digestion (AD) was developed to overcome these shortcomings. Results showed that corn straw pretreated in LD pressurized under 1 Mpa CO2 at 55 ℃ resulted in increased glucose and xylose contents and a 9.80% decrease in cellulose crystallinity. After 45 days of AD conversion, the methane yield increased by 50.97% compared with untreated straw. However, pretreatment in LD pressurized under 1 Mpa CO2 at 170 ℃ produced 5-hydroxymethylfurfural and furfural, which led to a decrease in methane production from the straw in the subsequent AD conversion. The alteration of the microbial community in the pretreated slurry at 55 °C was another potential contributor to the enhanced performance of AD.

High solid loading and multiple-fed simultaneous saccharification and co-fermentation (mf-SSCF) of rice straw for high titer ethanol production at low cost

Efficient ethanol production using dilute acid pretreated rice straw was investigated in multiple-fed simultaneous saccharification and co-fermentation (mf-SSCF) for producing high titer ethanol at a low cost. The mf-SSCF was performed at very high solid loading (29.5% w/v) by multiple feeding of dilute acid pretreated rice straw without any detoxification, solid-liquid separation, and sterilization. After 72 h, an ethanol titer of 68.72 g L−1 was attained with higher ethanol yield (0.42 g g−1) and productivity (0.95 g L−1 h−1). Only magnesium sulfate (6 g L−1) was added as nutrient component and aqueous ammonia was used for pH adjustment of pretreated slurry to 5, which also provides ammonium ions as a nitrogen source for yeast during ethanol fermentation. Almost no water was added in the mf-SSCF process; therefore, higher ethanol titer (8.7 % v/v) was achieved, which further reduce distillation, water input, and treatment cost. These results suggest that the mf-SSCF process has great potential for the production of high titer ethanol on a commercial scale due to the consolidation and simplification of the process at a low cost.

Optimization of Thermal Pretreatment of Food Waste for Maximal Solubilization

Food waste has become an increasing concern across the globe. Anaerobic digestion (AD) has been recognized as an effective approach for handling this waste while generating biogas. AD’s performance could be enhanced by improving the carbon conversion efficiency and leading to the lowest amount of residuals possible. For this purpose, various pretreatment approaches have been investigated. This study focuses on optimizing thermal pretreatment of food waste. In particular, three parameters, namely temperature, treatment time, and total solid content, were evaluated statistically for their effects on the increase of soluble chemical oxygen demand (SCOD). It was found that temperature and time had statistically significant impacts on the SCOD increase compared with the untreated controls. The optimal condition of 170°C, 60 min, and 118 g/L solid content led to a 1.92-fold increase of SCOD. After a 5-day fermentation, the pretreated slurries produced 17.1 g/L of volatile fatty acids. Results from this study could be used at large scale for pretreating food waste before AD for producing biogas or other valuable products.

Steam Explosion Pretreatment of Beechwood. Part 1: Comparison of the Enzymatic Hydrolysis of Washed Solids and Whole Pretreatment Slurry at Different Solid Loadings

Steam explosion is a well-known process to pretreat lignocellulosic biomass in order to enhance sugar yields in enzymatic hydrolysis, but pretreatment conditions have to be optimized individually for each material. In this study, we investigated how the results of a pretreatment optimization procedure are influenced by the chosen reaction conditions in the enzymatic hydrolysis. Beechwood was pretreated by steam explosion and the resulting biomass was subjected to enzymatic hydrolysis at glucan loadings of 1% and 5% employing either washed solids or the whole pretreatment slurry. For enzymatic hydrolysis in both reaction modes at a glucan loading of 1%, the glucose yields markedly increased with increasing severity and with increasing pretreatment temperature at identical severities and maximal values were reached at a pretreatment temperature of 230 °C. However, the optimal severity was 5.0 for washed solids enzymatic hydrolysis, but only 4.75 for whole slurry enzymatic hydrolysis. When the glucan loading was increased to 5%, glucose yields hardly increased for pretreatment temperatures between 210 and 230 °C at a given severity, and a pretreatment temperature of 220 °C was sufficient under these conditions. Consequently, it is important to precisely choose the desired conditions of the enzymatic hydrolysis reaction, when aiming to optimize the pretreatment conditions for a certain biomass.

Investigation of Rheological Behavior of Untreated and Microwave-Assisted Alkaline Pretreated Sugarcane Straw for Biofuel Production

Biomass slurries, such as those subjected to microwave-assisted alkaline (MAA) pretreatment, will become common substrates for the production of biofuels in the future. While the rheology of acid and ionic liquid pretreated biomass is known, the rheology of alkaline pretreated biomass is not yet reported; hence, the goal of this study was to establish the rheological characteristics of untreated and MAA pretreated sugarcane straw (SC). Using rotational rheometry and rheological models, the rheology of SC slurries was assessed as a function of particle size and insoluble solids concentration. In the range of 5–17% insoluble solids concentration, the slurries were consistently pseudo-plastic (n = 0.33 ± 0.02), possessed yield stress with their flow accurately described by the Casson rheological model (R2 = 0.98–0.99). The apparent viscosity and yield stress increased by two orders of magnitude with an increase in insoluble solids concentration. Essentially, MAA pretreated slurries exhibited significantly higher values of apparent viscosity and yield stress than the untreated ones, in the range of 55–80% and 21–63% for particle sizes of < 63 µm (P63) and 90–180 µm (P90), respectively. Pretreated P63 samples exhibited higher apparent viscosity and yield stress than the P90. On the other hand, for untreated samples, P63 samples had a reduced apparent viscosity than P90 samples. The results of this study definitively reveal that MAA significantly increases the shear rate dependent shear viscosity values along with the yield stress of biomass slurries. This will, therefore, serve as a benchmark for characterizing other MAA pretreated biomass slurries to guide the design of industrial-scale production equipment.

Designing Efficient Processes for Sustainable Bioethanol and Bio-Hydrogen Production from Grass Lawn Waste.

The effect of thermal, acid and alkali pretreatment methods on biological hydrogen (BHP) and bioethanol production (BP) from grass lawn (GL) waste was investigated, under different process schemes. BHP from the whole pretreatment slurry of GL was performed through mixed microbial cultures in simultaneous saccharification and fermentation (SSF) mode, while BP was carried out through the C5yeast Pichia stipitis, in SSF mode. From these experiments, the best pretreatment conditions were determined and the efficiencies for each process were assessed and compared, when using either the whole pretreatment slurry or the separated fractions (solid and liquid), the separate hydrolysis and fermentation (SHF) or SSF mode, and especially for BP, the use of other yeasts such as Pachysolen tannophilus or Saccharomyces cerevisiae. The experimental results showed that pretreatment with 10 gH2SO4/100 g total solids (TS) was the optimum for both BHP and BP. Separation of solid and liquid pretreated fractions led to the highest BHP (270.1 mL H2/g TS, corresponding to 3.4 MJ/kg TS) and also BP (108.8 mg ethanol/g TS, corresponding to 2.9 MJ/kg TS) yields. The latter was achieved by using P. stipitis for the fermentation of the hydrolysate and S. serevisiae for the solid fraction fermentation, at SSF.