Combined pretreatment using alkaline hydrothermal and ball milling to enhance enzymatic hydrolysis of oil palm mesocarp fiber

Enhancing thermophilic methane production from oil palm empty fruit bunches through various pretreatment methods: A comparative study

This study investigated the effects of various pretreatment methods on the anaerobic digestibility of oil palm empty fruit bunches (EFB) for methane production. Pretreatment methods included weak alkaline (2 % Ca(OH)2), weak acid (2 % acetic acid), acidified palm oil mill effluent (POME), biogas effluent, hydrothermal (180 °C, 190 °C, and 200 °C), and microwave pretreatments. All pretreatment methods enhanced methane yield compared to untreated EFB (189.45 mL-CH4/g-VS), with weak alkaline pretreatment being the most effective (277.11 mL-CH4/g-VS), followed by hydrothermal pretreatment at 180 °C (244.33 mL-CH4/g-VS) and biogas effluent pretreatment (238.32 mL-CH4/g-VS). The enhanced methane yield was attributed to increased cellulose content (45.5 % for weak alkaline pretreatment), reduced hemicellulose (18.0 % for hydrothermal pretreatment at 200 °C), and lignin contents (19.0 % for hydrothermal pretreatment at 200 °C), decreased crystallinity index (40.0 % for hydrothermal pretreatment at 200 °C), and increased surface area. Weak alkaline pretreatment also showed the highest net energy balance (8.73 kJ/g-VS) and a short break-even point (2 years). Microbial community analysis revealed that weak alkaline pretreatment favored the growth of syntrophic acetate-oxidizing bacteria and hydrogenotrophic methanogens, contributing to improved methane yield. This study demonstrates the potential of EFB pretreatment, particularly weak alkaline and biogas effluent pretreatment, for enhancing methane production and sustainable management of palm oil mill waste.

Investigating process parameters to enhance (hemi)cellulolytic enzymes activity produced by Trichoderma reesei RUT-C30 using deoiled oil palm mesocarp fiber in solid-state fermentation

This study investigates the synthesis of (hemi)cellulolytic enzymes, including endoglucanase (CMCase), xylanase, and β-glucosidase, employing Trichoderma reesei RUT-C30 and deoiled oil palm mesocarp fiber (OPMF) through solid-state fermentation (SSF). The objective was to determine the optimal process conditions for achieving high enzyme activities through a one-factor-at-a-time approach. The study primarily focused on the impact of the solid-to-liquid ratio, incubation period, initial pH, and temperature on enzyme activity. The effects of OPMF pretreatment, particularly deoiling and fortification, were explored. This approach significantly improved enzyme activity levels compared to the initial conditions, with CMCase increasing by 111.6 %, xylanase by 665.2 %, and β-Glucosidase by 1678.1 %. Xylanase and β-glucosidase activities, peaking at 1346.75 and 9.89 IU per gram dry substrate (GDS), respectively, under optimized conditions (1:4 ratio, pH 7.5, 20 °C, 9-day incubation). With lower moisture levels, CMCase reached its maximum activity of 227.84 IU/GDS. The study highlights how important it is for agro-industrial byproducts to support environmentally sustainable practices in the palm oil industry. It also emphasizes how differently each enzyme reacts to changes in process parameters.

Combined dilute alkali and milling process enhances the functionality and gut microbiota fermentability of insoluble corn fiber

In this study, we developed a process combining dilute alkali (NaOH or NaHCO3) and physical (disk milling and/or ball milling) treatments to improve the functionality and fermentability of corn fiber. The results showed that combining chemical with physical processes greatly improved the functionality and fermentability of corn fiber. Corn fiber treated with NaOH followed by disk milling (NaOH-DM-CF) had the highest water retention (19.5 g/g), water swelling (38.8 mL/g), and oil holding (15.5 g/g) capacities. Moreover, NaOH-DM-CF produced the largest amount (42.9 mM) of short-chain fatty acid (SCFA) during the 24-hr in vitro fermentation using porcine fecal inoculum. In addition, in vitro fermentation of NaOH-DM-CF led to a targeted microbial shifting to Prevotella (genus level), aligning with a higher fraction of propionic acid. The outstanding functionality and fermentability of NaOH-DM-CF were attributed to its thin and loose structure, decreased ester linkages and acetyl groups, and enriched structural carbohydrate exposure.

Thermoplastic starch composite with oil palm mesocarp fiber waste and its application as biodegradable seeding pot

Thermoplastic starch (TPS) composites with oil palm mesocarp fiber waste were prepared using compression molding. Oil palm mesocarp fiber (PC) was reduced to powder (MPC) by dry grinding in a planetary ball mill at various speeds and grinding times. It was found that fiber powder with the smallest particle size (33 μm) was obtained at a rotation speed of 200 rpm after milling for 90 min. A TPS composite with 50 wt% of MPC showed the highest tensile strength, thermal stability, and water resistance. A biodegradable seeding pot was produced from this TPS composite that was slowly degraded by microorganisms in the soil without releasing pollutants. The pot could support certain commercially and domestically grown plants for the duration of their growth period and showed potential as an innovative product that could replace existing non-biodegradable products.

Effect of Ball-Milling Pretreatment of Cellulose on Its Photoreforming for H2 Production

Photoreforming of cellulose is a promising route for sustainable H₂ production. Herein, ball-milling (BM, with varied treatment times of 0.5-24 h) was employed to pretreat microcrystalline cellulose (MCC) to improve its activity in photoreforming over a Pt/TiO₂ catalyst. It was found that BM treatment reduced the particle size, crystallinity index (CrI), and degree of polymerization (DP) of MCC significantly, as well as produced amorphous celluloses (with >2 h treatment time). Amorphous cellulose water-induced recrystallization to cellulose II (as evidenced by X-ray diffraction (XRD) and solid-state NMR analysis) was observed in aqueous media. Findings of the work showed that the BM treatment was a simple and effective pretreatment strategy to improve photoreforming of MCC for H₂ production, mainly due to the decreased particle size and, specifically in aqueous media, the formation of the cellulose II phase from the recrystallization of amorphous cellulose, the extent of which correlates well with the activity in photoreforming.

Hydrothermal Pretreatment of Lignocellulosic Feedstocks to Facilitate Biochemical Conversion

Biochemical conversion of lignocellulosic feedstocks to advanced biofuels and other bio-based commodities typically includes physical diminution, hydrothermal pretreatment, enzymatic saccharification, and valorization of sugars and hydrolysis lignin. This approach is also known as a sugar-platform process. The goal of the pretreatment is to facilitate the ensuing enzymatic saccharification of cellulose, which is otherwise impractical due to the recalcitrance of lignocellulosic feedstocks. This review focuses on hydrothermal pretreatment in comparison to alternative pretreatment methods, biomass properties and recalcitrance, reaction conditions and chemistry of hydrothermal pretreatment, methodology for characterization of pretreatment processes and pretreated materials, and how pretreatment affects subsequent process steps, such as enzymatic saccharification and microbial fermentation. Biochemical conversion based on hydrothermal pretreatment of lignocellulosic feedstocks has emerged as a technology of high industrial relevance and as an area where advances in modern industrial biotechnology become useful for reducing environmental problems and the dependence on fossil resources.

Preparation of Oil Palm Empty Fruit Bunch Hydrolysate

Malaysia is the second largest palm oil producer and exporter globally. When crude palm oil is produced in both plantations and oil processing mills, a large amount of oil palm empty fruit bunch (OPEFB) is simultaneously produced as a waste product. Here, we describe the preparation of hydrolysate from OPEFB. After OPEFB was hydrothermally treated at 180–200 °C, the resultant liquid phase was subjected to high-performance liquid chromatography analysis, while the solid phase was used for acidic and enzymatic hydrolysis. Hemicellulose yield from the acid-treated solid phase decreased from 153 mg/g-OPEFB to 27.5 mg/g-OPEFB by increasing the hydrothermal treatment temperature from 180 to 200 °C. Glucose yield from the enzyme-treated solid phase obtained after hydrothermal treatment at 200 °C was the highest (234 ± 1.90 mg/g-OPEFB, 61.7% production efficiency). In contrast, xylose, mannose, galactose, and arabinose yields in the hydrolysate prepared from the solid phase hydrothermally treated at 200 °C were the lowest. Thus, we concluded that the optimum temperature for hydrothermal pretreatment was 200 °C, which was caused by the low hemicellulose yield. Based on these results, we have established an effective method for preparing OPEFB hydrolysates with high glucose content.

Effects of insoluble dietary fiber from kiwi fruit pomace on the physicochemical properties and sensory characteristics of low-fat pork meatballs

ABSTRACT

As beverage industry by product, kiwi fruit pomace is potential but underutilized. In this study, insoluble dietary fiber from kiwi fruit pomace was modified via ultra-fine pulverization. The physicochemical and functional properties of kiwi fruit insoluble dietary fiber (KWIDF) superfine powder and its application in pork meatballs as a fat substitute were investigated. The SEM and droplet size measurement results revealed that the specific surface area of KWIDF increased from 44.4 to 192.9 m² kg^-1. The swelling capacity, water-, oil- and fat-holding capacities increased by 51.61%, 40.21%, 46.09% and 47.01%, respectively. The poisonous substances adsorbing abilities and the inhibition of enzyme activities were also improved. Similarly, KWIDF adsorbed cholesterol and glucose preferably. In addition, KWIDF revealed significant dose-response effects on the nutritional within a meat matrix, quality and sensory characteristics in meatballs (P < 0.05). The addition of 3% KWIDF superfine powder was found most suitable with high acceptability overall.

GRAPHIC ABSTRACT

Enhanced lignocellulosic component removal and biomethane potential from chestnut shell by a combined hydrothermal-alkaline pretreatment

This study proposes new perspectives for the management and biorefinery of wastes deriving from the agri-food sector such as chestnut shell (CS), which was here used as an organic feedstock for biomethane production through anaerobic digestion (AD). 1-5% alkaline (i.e. NaOH and KOH), hydrothermal (i.e. at 100 °C) and combined hydrothermal-alkaline pretreatments were employed to enhance the CS biodegradability prior to biochemical methane potential (BMP) tests conducted under mesophilic conditions. The hydrothermally-pretreated CS with 3% NaOH achieved the highest biomethane yield of 253 (±9) mL CH₄·g VS^-1 coupled to a volatile solid reduction of 48%. The hydrothermal-alkaline pretreatment positively affected both delignification and hemicellulose polymerization, promoting an approximately 2.4-fold higher substrate biodegradability compared to the untreated CS, which only reached a CH₄ production of 104 (±5) mL CH₄·g VS^-1. AD proceeded via volatile fatty acid accumulation, subsequently followed by methane production that was effectively simulated via the modified Gompertz kinetic having a R² of 0.974-0.999. Among the physical-chemical parameters characterizing the CS, the soluble chemical oxygen demand (sCOD) was highly correlated with the BMP showing a Pearson coefficient of 0.952. The cumulative biomethane yield, the sCOD and the cellulose, hemicellulose and lignin amount of CS were also processed through the least square method, obtaining a useful regression equation to predict the BMP. The economic assessment indicated that the hydrothermal-alkaline pretreatment is a cost-effective method to improve the BMP of CS, also for future full-scale applications.

The Utilisation of Palm Oil and Oil Palm Residues and the Related Challenges as a Sustainable Alternative in Biofuel, Bioenergy, and Transportation Sector: A Review

The importance of energy demands that have increased exponentially over the past century has led to the sourcing of other ideal power solutions as the potential replacement alternative to the conventional fossil fuel. However, the utilisation of fossil fuel has created severe environmental issues. The identification of other renewable sources is beneficial to replace the energy utilisation globally. Biomass is a highly favourable sustainable alternative to renewable resources that can produce cleaner, cheaper, and readily available energy sources in the future. The palm oil industry is essentially ideal for the availability of abundant biomass resources, where the multifaceted residues are vital for energy production through the conversion of biomass waste into value-added products simultaneously. This article discusses the utilisation of palm oil and its residues in the energy and transportation sector. Assessment and evaluation on the feasibility of palm oil and its residues were made on the current valorisation methods such as thermochemical and biochemical techniques. Their potential as transportation fuels were concurrently reviewed. This is followed by a discussion on future challenges of palm oil industries that will take place globally, including the prospects from government and nongovernment organisations for the development of palm oil as a sustainable alternative replacement to fossil fuel. Hence, this review aims to provide further insight into the possibilities of palm oil and its residues towards sustainable development with reduced environmental-related issues.

Steam explosion pretreatment improves acetic acid organosolv delignification of oil palm mesocarp fibers and sugarcane bagasse

Steam explosion can be used to pretreat lignocellulosic materials to decrease energy and chemical consumption during pulping to obtain environmentally friendly lignin and to improve lignin yield without changing its structure. The objective of this study was to evaluate the extraction of lignin from oil palm mesocarp fibers and sugarcane bagasse using steam explosion pretreatment followed by acetosolv. The biomasses were pretreated at 168 °C for a reaction time of 10 min. Steam explosion combined with acetosolv at lower severities was also carried out. Steam explosion followed by acetosolv increased the lignin yield by approximately 15% and 17% in oil palm mesocarp fibers and sugarcane bagasse, respectively. In addition, steam explosion decreased the reaction time of acetosolv four-fold while maintaining the lignin yield from sugarcane bagasse. Similar results were not obtained for oil palm mesocarp. High-purity and high-quality lignins were obtained using steam explosion pretreatment with structural characteristics similar to raw ones. Sugarcane bagasse lignin seems to be a better option for application in material science due its higher lignin yield and higher thermal stability. Our findings demonstrate that steam explosion is efficient for improving lignin yield and/or decreasing pulping severity.

Feasibility of Continuous Pretreatment of Corn Stover: A Comparison of Three Commercially Available Continuous Pulverizing Devices

We determined the potential of three mechanical pulverizers—a continuous ball mill (CBM), an air classifier mill (ACM), and a high-speed mill (HSM)—in the continuous pretreatment of corn stover. The mean diameters of the pulverized biomasses were not significantly different in the three cases, and the glucose yields from the CBM-, ACM-, and HSM-pulverized samples were 29%, 49%, and 44%, respectively. The energy requirements and process capacities for the ACM and HSM were similar. We conclude that the ACM and HSM could be used in the continuous pretreatment of corn stover and would be useful in biofuel production.

Mechanochemical-assisted hydrolysis of pretreated rice straw into glucose and xylose in water by weakly acidic solid catalyst

In this work, carbonaceous materials bearing only weakly acidic COOH and phenolic OH groups were directly prepared by the pyrolysis of lignin and KOH in black liquor generating from rice straw that was pretreated with KOH aqueous solution. The synthesized carbon materials were used for the hydrolysis of cellulose or the alkali pretreated rice straw in water, after mixed ball-milling pretreatment, and provided a high glucose yield of 76.3% for cellulose, high yields of 52.1% glucose and 66.5% xylose for alkali pretreated rice straw, respectively, in 0.015 wt% HCl aqueous solution at 200 °C for 60 min. The weakly acidic catalyst showed good stability and recyclability in the aqueous reaction system. This work provides an efficient process for the hydrolysis of lignocellulose by biomass-derived weakly acidic catalysts in water and should have wide applications in biomass utilization.

Combined Ball Milling and Ethanol Organosolv Pretreatment to Improve the Enzymatic Digestibility of Three Types of Herbaceous Biomass

A combined ball milling and ethanol organosolv process is proposed for the pretreatment of three types of herbaceous biomass, giant miscanthus, corn stover, and wheat straw. The combined pretreatment was effective at both removing lignin and increasing the glucan content. After 120 min pretreatment, the glucan content increased to 63.09%, and 55.89% of the acid-insoluble lignin was removed from the giant miscanthus sample. The removal of cellulose, hemicellulose, and acetyl groups were correlated with the removal of lignin. The pretreatment of corn stover showed the highest removal of cellulose, but this was dependent on the removal of acid-insoluble lignin. The slope of the regression lines, which shows the correlation between the removal of lignin and cellulose, was lower than other correlations. The changes in biomass size were analyzed using size distribution graphs. With increasing pretreatment time, the particle size reduction improved in the three types of herbaceous biomass. Because of the combined physicochemical pretreatment, the enzymatic digestibility improved, and a maximum of 91% glucan digestibility was obtained from the pretreated corn stover when 30 FPU/g-glucan enzyme was added. Finally, compositional analysis of the recovered lignin from the remaining black liquor was investigated.

Pre-treatment of Oil Palm Biomass for Fermentable Sugars Production

Malaysia is the second largest palm oil producer in the world and this industry generates more than 80 million tonnes of biomass every year. When considering the potential of this biomass to be used as a fermentation feedstock, many studies have been conducted to develop a complete process for sugar production. One of the essential processes is the pre-treatment to modify the lignocellulosic components by altering the structural arrangement and/or removing lignin component to expose the internal structure of cellulose and hemicellulose for cellulases to digest it into sugars. Each of the pre-treatment processes that were developed has their own advantages and disadvantages, which are reviewed in this study.

Subcritical Water-Carbon Dioxide Pretreatment of Oil Palm Mesocarp Fiber for Xylooligosaccharide and Glucose Production

The present work aimed to investigate the pretreatment of oil palm mesocarp fiber (OPMF) in subcritical H₂O-CO₂ at a temperature range from 150⁻200 °C and 20⁻180 min with CO₂ pressure from 3⁻5 MPa. The pretreated solids and liquids from this process were separated by filtration and characterized. Xylooligosaccharides (XOs), sugar monomers, acids, furans and phenols in the pretreated liquids were analyzed by using HPLC. XOs with a degree of polymerization X2⁻X4 comprising xylobiose, xylotriose, xylotetraose were analyzed by using HPAEC-PAD. Enzymatic hydrolysis was performed on cellulose-rich pretreated solids to observe xylose and glucose production. An optimal condition for XOs production was achieved at 180 °C, 60 min, 3 MPa and the highest XOs obtained was 81.60 mg/g which corresponded to 36.59% of XOs yield from total xylan of OPMF. The highest xylose and glucose yields obtained from pretreated solids were 29.96% and 84.65%, respectively at cellulase loading of 10 FPU/g-substrate.

Combination of Superheated Steam with Laccase Pretreatment Together with Size Reduction to Enhance Enzymatic Hydrolysis of Oil Palm Biomass

The combination of superheated steam (SHS) with ligninolytic enzyme laccase pretreatment together with size reduction was conducted in order to enhance the enzymatic hydrolysis of oil palm biomass into glucose. The oil palm empty fruit bunch (OPEFB) and oil palm mesocarp fiber (OPMF) were pretreated with SHS and ground using a hammer mill to sizes of 2, 1, 0.5 and 0.25 mm before pretreatment using laccase to remove lignin. This study showed that reduction of size from raw to 0.25 mm plays important role in lignin degradation by laccase that removed 38.7% and 39.6% of the lignin from OPEFB and OPMF, respectively. The subsequent saccharification process of these pretreated OPEFB and OPMF generates glucose yields of 71.5% and 63.0%, which represent a 4.6 and 4.8-fold increase, respectively, as compared to untreated samples. This study showed that the combination of SHS with laccase pretreatment together with size reduction could enhance the glucose yield.

Production of acetoin from hydrothermally pretreated oil mesocarp fiber using metabolically engineered Escherichia coli in a bioreactor system

Acetoin is used in the biochemical, chemical and pharmaceutical industries. Several effective methods for acetoin production from petroleum-based substrates have been developed, but they all have an environmental impact and do not meet sustainability criteria. Here we describe a simple and efficient method for acetoin production from oil palm mesocarp fiber hydrolysate using engineered Escherichia coli. An optimization of culture conditions for acetoin production was carried out using reagent-grade chemicals. The final concentration reached 29.9gL^-1 with a theoretical yield of 79%. The optimal pretreatment conditions for preparing hydrolysate with higher sugar yields were then determined. When acetoin was produced using hydrolysate fortified with yeast extract, the theoretical yield reached 97% with an acetoin concentration of 15.5gL^-1. The acetoin productivity was 10-fold higher than that obtained using reagent-grade sugars. This approach makes use of a compromise strategy for effective utilization of oil palm biomass towards industrial application.

Evaluating the effect of wood ultrastructural changes from mechanical treatment on kinetics of monomeric sugars and chemicals production in acid bisulfite treatment

Currently, various chemical-mechanical treatments were widely used in biofuel production to achieve high total sugar yields. However, the interaction between two treatments was scarcely investigated. In this study, we employed a ball milling process to create ultrastructural changes for Douglas-fir (Pseudotsuga menziesii) micronized wood powders. The 0, 30, and 60min ball milled wood powders resulted in a crystallinity index of 0.41, 0.21, and 0.10 respectively. It was found that the ultrastructural changes accelerate monomeric sugars production without influencing the yield of sugar degradation products. The optimal acid bisulfite treatment time was substantially decreased from 120min to 40min as the cellulose crystallinity decreased. Meanwhile, total sugar yield increased from 65% to 92% and had a linear relation with a decrease of the cellulose crystallinity.

Influence of a facile pretreatment process on lipid extraction from Nannochloropsis sp. through an enzymatic hydrolysis reaction

A wall-breaking technology for algal cell composed of swelling by weak alkali and decomposition by enzyme was developed.

Mechanical fragmentation of corncob at different plant scales: Impact and mechanism on microstructure features and enzymatic hydrolysis

In this work, corncob samples at different scales, i.e., plant scale (>1mm), tissue scale (500-100μm) and cellular scale (50-30μm), were produced to investigate the impact and mechanisms of different mechanical fragmentations on microstructure features and enzymatic hydrolysis. The results showed that the microstructure features and enzymatic hydrolysis of corncob samples, either at a plant scale or tissue scale, did not change significantly. Conversely, corncob samples at a cellular scale exhibited some special properties, i.e., an increase in the special surface area with the inner mesopores and macropores exposed to the surface; breakage of crystalline cellulose and linkages in polysaccharides; and a higher proportion of polysaccharides on the surface, which significantly enhanced enzymatic digestibility resulting in a 98.3% conversion yield of cellulose to glucose which is the highest conversion ever reported. In conclusion, mechanical fragmentation at the cellular scale is an effective pretreatment for corncob.

Soluble inhibitors generated during hydrothermal pretreatment of oil palm mesocarp fiber suppressed the catalytic activity of Acremonium cellulase

Oil palm mesocarp fiber was subjected to hydrothermal pretreatment under isothermal and non-isothermal conditions. The pretreated slurries were separated by filtration, pretreated liquids and solids were characterized. An enzymatic digestibility study was performed for both pretreated slurries and solids to understand the effect of soluble inhibitors generated during the pretreatment process. The highest glucose yield obtained from pretreated slurries was 70.1%, and gradually decreased with higher pretreatment severities. The highest glucose yield obtained in pretreated solids was 100%, after pretreatment at 210°C for 20min. In order to study the inhibitory effects of compounds generated during pretreatment with cellulase, technical grade solutions that mimic the pretreated liquid were prepared and their effect on Acremonium cellulase activity was monitored using Avicel. Xylo-oligomers and tannic acid were identified as powerful inhibitors of Acremonium cellulase, and the lowest hydrolysis rate of Avicel of 0.18g/g-glucose released/L/h was obtained from tannic acid.

Promise of combined hydrothermal/chemical and mechanical refining for pretreatment of woody and herbaceous biomass

Production of advanced biofuels from woody and herbaceous feedstocks is moving into commercialization. Biomass needs to be pretreated to overcome the physicochemical properties of biomass that hinder enzyme accessibility, impeding the conversion of the plant cell walls to fermentable sugars. Pretreatment also remains one of the most costly unit operations in the process and among the most critical because it is the source of chemicals that inhibit enzymes and microorganisms and largely determines enzyme loading and sugar yields. Pretreatments are categorized into hydrothermal (aqueous)/chemical, physical, and biological pretreatments, and the mechanistic details of which are briefly outlined in this review. To leverage the synergistic effects of different pretreatment methods, conducting two or more pretreatments consecutively has gained attention. Especially, combining hydrothermal/chemical pretreatment and mechanical refining, a type of physical pretreatment, has the potential to be applied to an industrial plant. Here, the effects of the combined pretreatment (combined hydrothermal/chemical pretreatment and mechanical refining) on energy consumption, physical structure, sugar yields, and enzyme dosage are summarized.

Physicochemical properties and intestinal protective effect of ultra-micro ground insoluble dietary fibre from carrot pomace

Carrot pomace is an abundant, but underutilized, byproduct from the juice industry.

Biological lignocellulose solubilization: comparative evaluation of biocatalysts and enhancement via cotreatment

BACKGROUND

Feedstock recalcitrance is the most important barrier impeding cost-effective production of cellulosic biofuels. Pioneer commercial cellulosic ethanol facilities employ thermochemical pretreatment and addition of fungal cellulase, reflecting the main research emphasis in the field. However, it has been suggested that it may be possible to process cellulosic biomass without thermochemical pretreatment using thermophilic, cellulolytic bacteria. To further explore this idea, we examine the ability of various biocatalysts to solubilize autoclaved but otherwise unpretreated cellulosic biomass under controlled but not industrial conditions.

RESULTS

Carbohydrate solubilization of mid-season harvested switchgrass after 5 days ranged from 24 % for Caldicellulosiruptor bescii to 65 % for Clostridium thermocellum, with intermediate values for a thermophilic horse manure enrichment, Clostridium clariflavum, Clostridium cellulolyticum, and simultaneous saccharification and fermentation (SSF) featuring a fungal cellulase cocktail and yeast. Under a variety of conditions, solubilization yields were about twice as high for C. thermocellum compared to fungal cellulase. Solubilization of mid-season harvested switchgrass was about twice that of senescent switchgrass. Lower yields and greater dependence on particle size were observed for Populus as compared to switchgrass. Trends observed from data drawn from six conversion systems and three substrates, including both time course and end-point data, were (1) equal fractional solubilization of glucan and xylan, (2) no biological solubilization of the non-carbohydrate fraction of biomass, and (3) higher solubilization for three of the four bacterial cultures tested as compared to the fungal cellulase system. Brief (5 min) ball milling of solids remaining after fermentation of senescent switchgrass by C. thermocellum nearly doubled carbohydrate solubilization upon reinnoculation as compared to a control without milling. Greater particle size reduction and solubilization were observed for milling of partially fermented solids than for unfermented solids. Physical disruption of cellulosic feedstocks after initiation of fermentation, termed cotreatment, warrants further study.

CONCLUSIONS

While the ability to achieve significant solubilization of minimally pretreated switchgrass is widespread, a fivefold difference between the most and least effective biocatalyst-feedstock combinations was observed. Starting with nature's best biomass-solubilizing systems may enable a reduction in the amount of non-biological processing required, and in particular substitution of cotreatment for pretreatment.

Combined pretreatment with hot compressed water and wet disk milling opened up oil palm biomass structure resulting in enhanced enzymatic digestibility

Combined pretreatment with hot compressed water and wet disk milling was performed with the aim to reduce the natural recalcitrance of oil palm biomass by opening its structure and provide maximal access to cellulase attack. Oil palm empty fruit bunch and oil palm frond fiber were first hydrothermally pretreated at 150-190° C and 10-240 min. Further treatment with wet disk milling resulted in nanofibrillation of fiber which caused the loosening of the tight biomass structure, thus increasing the subsequent enzymatic conversion of cellulose to glucose. The effectiveness of the combined pretreatments was evaluated by chemical composition changes, power consumption, morphological alterations by SEM and the enzymatic digestibility of treated samples. At optimal pretreatment process, approximately 88.5% and 100.0% of total sugar yields were obtained from oil palm empty fruit bunch and oil palm frond fiber samples, which only consumed about 15.1 and 23.5 MJ/kg of biomass, respectively.

Hydrothermal and wet disk milling pretreatment for high conversion of biosugars from oil palm mesocarp fiber

Eco-friendly pretreatment methods for lignocellulosic biomass are being developed as alternatives to chemical based methods. Superheated steam (SHS), hot compressed water (HCW) and wet disk milling (WDM) were used individually and with combination to partially remove hemicellulose and alter the lignin composition of recalcitrant structure of oil palm mesocarp fiber (OPMF). The efficiency of the pretreatment methods was evaluated based on the chemical compositions altered, SEM analysis, power consumption and degree of enzymatic digestibility. Hemicellulose removal (94.8%) was more pronounced under HCW compared to SHS, due to maximal contact of water and production of acetic acid which enhanced further degradation of hemicellulose. Subsequent treatment with WDM resulted in defibrillation of OPMF and expansion of the specific surface area thus increasing the conversion of cellulose to glucose. The highest glucose yield was 98.1% (g/g-substrate) when pretreated with HCW (200 °C, 20 min) and WDM which only consumed 9.6 MJ/kg of OPMF.

Hydrothermal pretreatment enhanced enzymatic hydrolysis and glucose production from oil palm biomass

The present works investigate hydrothermal pretreatment of oil palm empty fruit bunch and oil palm frond fiber in a batch tube reactor system with temperature and time range from 170 to 250°C and 10 to 20min, respectively. The behavior of soluble sugars, acids, furans, and phenols dramatically changed over treatment severities as determined by HPLC. The cellulose-rich treated solids were analyzed by SEM, WAXD, and BET surface area. Enzymatic hydrolysis was performed from both pretreated slurries and washed solid, and data obtained suggested that tannic acid derived from lignin degradation was a potential cellulase inhibitor. Both partial removal of hemicellulose and migration of lignin during hydrothermal pretreatment caused structural changes on the cellulose-hemicellulose-lignin matrix, resulting in the opening and expansion of specific surface area and pore volume. The current results provided important factors that maximize conversion of cellulose to glucose from oil palm biomass by hydrothermal process.