Feedstock Pretreatment Research Articles

Deep eutectic solvents in the pretreatment of feedstock for efficient fractionation of polysaccharides: current status and future prospects

Deep eutectic solvents in the pretreatment of feedstock for efficient fractionation of polysaccharides: current status and future prospects

Sustainable Second-Generation Ethanol Production from Switchgrass Biomass via Co-fermentation of Pentoses and Hexoses Using Novel Wild Yeasts

The production of second-generation (2G) ethanol remains an interesting proposition for the implementation of sustainable and net carbon–neutral energy systems. To be economically viable, 2G biorefineries must make use of all processing streams, including the less desirable pentose (C5) sugar stream. In this work, a strategy of sequential dilute acid and alkaline pretreatment of the lignocellulosic feedstock, switchgrass, was implemented for improving the fermentable sugar yield. The hemicellulose-enriched hydrolysate obtained after dilute acid pretreatment was fermented by a newly isolated wild Scheffersomyces parashehatae strain—UFMG-HM-60.1b; the corresponding ethanol yield (YPS) and volumetric productivity (QP) were 0.19 g/g and 0.16 g/L h, respectively. The remaining switchgrass cellulignin fraction was subjected to optimized alkaline delignification at 152 ºC for 30 min. Then, the delignified solid fraction was subjected to contiguous enzymatic saccharification and fermentation releasing a glucose (C6) sugar stream. The control yeast strain, Saccharomyces cerevisiae 174, displayed an ethanol YPS of 0.46 g/g and QP of 0.70 g/L h for the C6 sugar stream, whereas the above-mentioned wild strain presented YPS and QP of 0.29 g/g and 0.38 g/L h, respectively. Upon combining the conversion of hemicellulose (37%) and cellulose-derived sugars (57%), the wild S. parashehatae strain provided higher yield (94%) than the generic S. cerevisiae (90%). Henceforth, our sequential two-stage pretreatment and fermentation of C5 and C6 sugar streams provides a pathway for maximum utilization of switchgrass carbohydrates for 2G ethanol production.

Prediction of three-phase product distribution and bio-oil heating value of biomass fast pyrolysis based on machine learning

In this work, by mining the experimental data of fast pyrolysis of lignocellulosic biomass in bubbling fluidized bed in previous literature, regression prediction models were established for three-phase product distribution and bio-oil heating value (HHV) based on gradient boosting, random forest, support vector machine, and multilayer perceptron algorithms. Comprehensive feedstock characteristics and pyrolysis conditions were considered and compared as input features. Among the several algorithms, random forest is most suitable for the prediction of three-phase product yields and bio-oil HHV with the benefits of high accuracy and good generalization ability. Visual analysis of the model shows that pyrolysis temperature is the most critical factor affecting three-phase product distribution, while bio-oil HHV is more affected by the feedstock characteristics such as the contents of C and H. The highest yield and HHV of bio-oil is obtained at about 480 °C, suggesting 480 °C as the optimum pyrolysis temperature of fast pyrolysis of biomass in a bubbling fluidized bed. As for the feedstock characteristics, high contents of C and H and low content of O are favorable to the enhancement of bio-oil HHV, indicating the crucial importance of feedstock pretreatment such as torrefaction to the quality improvement of bio-oil.

Enhanced Hydrothermal Carbonization of Spent Coffee Grounds for the Efficient Production of Solid Fuel with Lower Nitrogen Content

As an increasingly abundant lignocellulosic biomass with high moisture content, spent coffee grounds (SCG) are an ideal feedstock for hydrothermal carbonization (HTC). The few examples that have converted SCG into a solid fuel hydrochar have yet to address the char’s prohibitively high nitrogen content (∼3 wt %)–a barrier to commercialization due to NOx emission regulations. In this work, an alkaline pretreatment is presented that reduces the N content prior to carbonization under regimes optimized for maximum calorific value (HHV), energy yield, and a conflation of both fuel properties. Characterization of hydrochars and secondary chars, the extractable volatile phase, revealed the highest calorific value for the secondary chars (max HHV = 40.69 MJ/kg) and a minimum N content of 0.1 wt % in hydrochars derived from the alkali pretreated feedstock. Char thermal stability and oxidative reactivity were also determined, with pretreated primary chars exhibiting superior combustion reactivities, ignition, and burnout temperatures. Management of HTC process water is both an environmental and operational challenge due to the presence of phytotoxic organic components and the energy expenditure associated with heating large volumes of water. To this end, the process water was recirculated for up to five cycles resulting in an increase in HHV, energy, and solid yield as well as compositional change of the char products.

Effective water/wastewater treatment methodologies for toxic pollutants removal: Processes and applications towards sustainable development

Release of pollutants due to inflating anthropogenic activities has a conspicuous effect on the environment. As water is uniquely vulnerable to pollution, water pollution control has received a considerable attention among the most critical environmental challenges. Diverse sources such as heavy metals, dyes, pathogenic and organic compounds lead to deterioration in water quality. Demand for the pollutant free water has created a greater concern in water treatment technologies. The pollutants can be mitigated through physical, chemical and biological methodologies thereby alleviating the health and environmental effects caused. Diverse technologies for wastewater treatment with an accentuation on pre-treatment of feedstock and post treatment are concisely summed up. Pollutants present in the water can be removed by processes some of which include filtration, reverse osmosis, degasification, sedimentation, flocculation, precipitation and adsorption. Membrane separation and adsorption methodologies utilized to control water pollution and are found to be more effective than conventional methods and established recovery processes. This audit relatively features different methodologies that show remarkable power of eliminating pollutants from wastewater. This review describes recent research development on wastewater treatment and its respective benefits/applications in field scale were discussed. Finally, the difficulties in the enhancement of treatment methodologies for pragmatic commercial application are recognized and the future viewpoints are introduced.

Effect of acid treatment and Na2CO3 as a catalyst on the quality and quantity of bio-products derived from the pyrolysis of granular bacteria biomass

The intense growth rate of granular bacteria biomass (GB) in anaerobic wastewater treatment units has made environmental problems with its disposal. In this research the potential of pyrolysis method to convert granular bacteria biomass to biofuels was completely investigated. The non-catalytic experiments were performed in a temperature range of 400 to 700 °C and the maximum liquid product yield on dry ash-free basis (55.0 %wt.) was obtained at optimum temperature of 550 °C. Pyrolysis of pretreated granular bacteria with 5 wt% HCl (PGB) and then impregnation with Na2CO3 (IPGB) was studied to improve the bio-oil quality as well as higher amount of synthesis gas. Feedstock pretreatment with acid decreased the gas yield in 550 °C while Na2CO3 pretreatment had reverse effect, with H2 yield (mmol/g feed) of 2.9, 2.4 and 1.8 for IPGB, GB and PGB respectively. It means Na2CO3 exhibited excellent catalytic activity toward producing hydrogen-rich hydrocarbons. Acid treatment increased bio-oil weight percent with little effect on the quality, while the IPGB pyrolysis resulted 8.3% and 8.6% decrease in the oxygenates and nitrogenates respectively and 19.5% increase in the hydrocarbons which improved the higher heating value (HHV) from 32.6 MJ/kg to 33.7 MJ/kg in comparison with GB. The raw and treated biomass was characterized by using thermogravimetric analysis (TGA-DTG), X-ray fluorescence (XRF), elemental analyses (CHNS), field emission scanning electron microscope (FESEM) and scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDS). The bio-products were analyzed by a gas chromatography-thermal conductivity detector (GC-TCD), a gas chromatography-mass spectrometry (GC–MS) and CHNS.

Base activation of persulfate: an effective pretreatment method to enhance glucose production from lignocellulosic biomass

Pretreatment is a necessary process in biorefineries to overcome recalcitrance of biomass and enhance its conversion efficiency for further transformation. NaOH activation of Na2S2O8, which merges alkaline pretreatment and advanced oxidation processes (AOPs) into one process, was performed at room temperature (25 °C) within a short duration (60 min). High concentration of NaOH plays a critically important role in NaOH–Na2S2O8 pretreatment, which not only selectively removed hemicellulose in the lignocellulosic feedstock, but also activated Na2S2O8 to produce strong oxidative radicals, leading to disruption of lignin matrix. The surface area and porosity for the pretreated feedstock were significantly increased compared with those of the pristine counterpart. After pretreatment by 5.12 M NaOH and 0.85 M Na2S2O8, the maximum glucose yield of the feedstock was increased by 47.4% compared with that of pristine counterpart (60.3% vs. 40.9%). This study provides an effective and easily-realizable pretreatment method for the utilization of lignocellulosic biomass.

Pretreatment of second and third generation feedstock for enhanced biohythane production: Challenges, recent trends and perspectives

In the context of biofuel production and achieving sustainable bioeconomy, the use of lignocellulosic and algae biomass in anaerobic fermentation processes yields biohythane that has a typical composition of 10–15% H2, 50–55% CH4 and 30–40% CO2. Using organic biomass-based substrates has been shown to minimize environmental impacts due to the versatile production of high-value products under normal operating conditions that are practically achievable. However, the biohythane yield depends on different factors such as the biomass type, the organic loading rate, soluble metabolic products formed, the type of fermentation (single/dual stage) and the pretreatment strategy adopted for the biomass. Different pretreatment strategies based on physical, chemical and biological processes have been proposed in the literature. In this review, improvements in biohythane yield as a result of these pretreatment strategies, the need/effect of inoculum enrichment, the effects of pH, temperature, trace element addition and organic loading rate has been reviewed. Finally, the major developments of improving biohythane yield due to the addition of co-substrates and the current trends are discussed.

Novel Process Simulation of Biodiesel Production from Crude Castor Oil

A continuous process flowsheet for biodiesel production from crude castor oil and methanol was developed on Aspen HYSYS simulation environment. It consists of an acid-catalysed sub-process for pre-treatment of the crude feedstock and a base-catalysed one for trans-esterification of treated oil. Reactions involved were defined using kinetic parameters obtained from lab-scale experiments for increased realism, and reactor setup was decided based on basic technological and economical assessments. Specifications of other unit operations and flows were obtained from different approximation methods, literature adaptation and trade-off consideration. Input and output quality controls were achieved via simple adjustments with tight tolerances. The use of crude feedstock reduced the cost of raw material while expanding the scale of the process, which managed to produce 8000 tons of biodiesel having purity of over 99 % a year. Specifically, the process could remove up to 90.83 % amount of free fatty acids in the crude oil and convert up to 93.82 % of oil to biodiesel.

Expired food products and used disposable adult nappies mesophilic anaerobic co-digestion: Biochemical methane potential, feedstock pretreatment and two-stage system performance

Used absorbent hygiene products are complex materials (only partially biodegradable) that constitute a significant percentage of municipal solid wastes ending up in landfills. At the same time, food wastes disposed of in landfills have a major contribution to greenhouse gas emissions. In this study, the authors propose the separation of the biodegradable part of used disposable adult nappies and its co-digestion with expired food products, originating from supermarkets. Three different pretreatment schemes were examined, with the meat waste pasteurization treatment scenario leading to the recovery of 427 kJ/Lfeed, while acid hydrolysis and intense thermal treatment led to a reduction of the recovered energy by 25.5 and 49.4% respectively, even though the hydrogen production, after acid hydrolysis, is almost 2 times higher compared to the other pretreatment schemes. This was caused by impeded methanogenic reactor operation, probably triggered by inhibitory cation concentrations and complex compounds. Finally, the methanogenic reactor during two-stage system operation, with meat pasteurization, was capable of operating with an HRT of 10.6 d, with 67% COD reduction, from an initial feedstock COD of 42 g/L. The reduction of HRT from 20 to 10.6 d exhibited an insignificant effect in specific (per LFeed) methane production.

The Effects of Hot Water and Ultrasonication Pretreatment of Microalgae (Nannochloropsis oculata) on Biogas Production in Anaerobic Co-Digestion with Cow Manure

Anaerobic co-digestion provides a promising solution for converting inexpensive carbon from wastes to biogenic methane. We used microalgae (Nannochloropsis oculata) with cow manure and sludge to produce a better quantity and quality of biogas. To further improve the gas production, microalgae were pretreated with ultrasonication, hot water, and a combination of both. Interestingly, the results showed that the pretreatment of microalgae decreased biogas production by 5 to 30%. The no-pretreatment runs produced a maximum of 118 L of biogas. The relative content of biogenic methane was higher in the pretreated feedstock (48 to 52%) in comparison with the no-pretreatment runs (44%). The conversion of volatile suspended solids present in the feedstock to total biogenic methane production was highest in hot-water-treated runs. The carbon content in the gas produced by the pretreated microalgae peaked (38%) in the middle of the experiment (i.e., at 45 days), whereas for no-pretreatment runs, the content remained constant from the start to the middle and declined (from 36 to 34%) at the end of the experiment (i.e., at 90 days). We also report the chemical structure of microalgae with and without pretreatments.

Improving the Efficiency of Oil Treating and Refining Processes (Review)

Basic technologies for crude oil conditioning and transportation and the processing of various petroleum feedstocks are considered from the viewpoint of methods for their improvement, energy saving, increasing the feedstock pretreatment efficiency, optimization of stream heat recovery schemes, improvement of hardware design, etc.

Fuel-specific devolatilization parameters for detailed comparison of pulverized biomass fuels

Low-grade biomass feedstocks are sustainable alternatives for pulverized fuel applications in the energy industry. Adverse fuel properties can make their adoption challenging due to operational issues such as flame ignition problems and high emissions. These issues can be potentially resolved by Computational Fluid Dynamics (CFD) simulations, where a submodel is needed to describe the fuel devolatilization behavior. In this work, the devolatilization parameters are reported for three pulverized biomass fuels: high-quality industrial wood pellet, lower-grade spruce bark, and steam-explosion pretreated spruce bark. The parameters are determined with a combination of high heating-rate drop-tube reactor experiments and CFD-coupled optimization algorithm. Comprehensive analysis is conducted to examine how the devolatilization reactivity and steam-explosion pretreatment affect the industrially relevant fuel properties. The functionality of the drop-tube devolatilization parameters is further demonstrated in larger-scale combustion simulations of a 120 kW pulverized fuel test rig. The simulations are able to capture the more challenging ignition behavior of the lower-grade bark fuels, and give detailed insight on the phenomenological side of solid fuel ignition. The fuel devolatilization reactivity is shown to have a strong impact on highly nonlinear flame characteristics, such as NO formation. Most importantly, the presented characterization, simulation and analysis methods can be applied to other biomass feedstocks to better understand how reactivity is altered by feedstock pretreatment, and how the process characteristics are influenced by fuel devolatilization reactivity.

Recent development and challenges in extraction of phytonutrients from palm oil.

Phytonutrients are plant-derived bioactives which are widely utilized as colorants or supplements in food, cosmetic, and pharmaceutical products. To meet the global demand for phytonutrients, oil palm has emerged as a promising source of phytonutrients on account of its large-scale plantation worldwide and high oil productivity. Phytonutrients including carotenoids, tocols, sterols, squalene, phospholipids, coenzyme Q10, and polyphenols can be found in crude palm oil as well as in the byproducts (e.g. palm oil mill effluent and palm-pressed fiber oil) generated from the palm oil milling process. However, the high viscosity and semisolid properties of palm oil are problematic in phytonutrient extraction. Another major challenge is the retention of the sensitive phytonutrients during the extraction process. Over the years, the advances in the extraction methods have improved the extractability of phytonutrients. The emerging extraction methods can operate under mild conditions to mitigate the risk of phytonutrient degradation. This review outlines the types of phytonutrient in palm oil and their extraction strategies. The working principles and operating conditions of extraction methods are discussed along with their potential and limitations in terms of extraction efficiency and practicability. The methods for pretreatment of feedstocks for improving extraction efficiency are also highlighted. The challenges in the extraction of phytonutrient from palm oil feedstock are summarized. Lastly, we provide suggestions for overcoming the limitations and improving the performances of phytonutrient extraction.

Fungal Pretreatments on Non-Sterile Solid Digestate to Enhance Methane Yield and the Sustainability of Anaerobic Digestion

Fungi can run feedstock pretreatment to improve the hydrolysis and utilization of recalcitrant lignocellulose-rich biomass during anaerobic digestion (AD). In this study, three fungal strains (Coprinopsis cinerea MUT 6385, Cyclocybe aegerita MUT 5639, Cephalotrichum stemonitis MUT 6326) were inoculated in the non-sterile solid fraction of digestate, with the aim to further (re)use it as a feedstock for AD. The application of fungal pretreatments induced changes in the plant cell wall polymers, and different profiles were observed among strains. Significant increases (p < 0.05) in the cumulative biogas and methane yields with respect to the untreated control were observed. The most effective pretreatment was carried out for 20 days with C. stemonitis, causing the highest hemicellulose, lignin, and cellulose reduction (59.3%, 9.6%, and 8.2%, respectively); the cumulative biogas and methane production showed a 182% and 214% increase, respectively, compared to the untreated control. The increase in AD yields was ascribable both to the addition of fungal biomass, which acted as an organic feedstock, and to the lignocellulose transformation due to fungal activity during pretreatments. The developed technologies have the potential to enhance the anaerobic degradability of solid digestate and untap its biogas potential for a further digestion step, thus allowing an improvement in the environmental and economic sustainability of the AD process and the better management of its by-products.

Bioconversion in batch bioreactor of olive-tree pruning biomass optimizing treatments for ethanol production

Processes efficiency for second-generation ethanol production depends mainly on the type of lignocellulosic raw material. Therefore, the optimization (considering a central composite design) for each step involved in olive-tree pruning biomass valorization was studied: (1) alkaline pretreatment of the original feedstock, (2) diluted acid hydrolysis of pretreated solids and (3) fermentation of the hemicellulosic hydrolyzates for ethanol production by Scheffersomyces stipitis. The recommended alkaline pretreatment conditions were 30 min, 90 °C and 0.5% w/v NaOH, with losses of 88.3% of acetyl groups from starting biomass, but only 6.9% of D-xylose. Comparing both, in natura and previously treated acid hydrolyzates at the most effective conditions (2.0% w/v H2SO4 and 60 min) revealed more inhibitory effect for non-treated liquor, with 4.8, 2.1 and 1.6 times higher concentrations of acetic acid, furans and phenolic compounds, respectively. A significant improvement in ethanol production was observed in treated hemicellulose liquor (20.4 g dm−3, YP/S = 0.20 g g−1 and QP = 0.21 g dm−3 h−1). In contrast, the yeast could not satisfactorily ferment the reference hydrolyzate. Biomass pretreatment with alkali previously to dilute acid hydrolysis was a suitable strategy for olive-tree pruning biomass biotransformation, substantially decreasing the hydrolyzate toxicity, without requiring an additional detoxification step.

Effect of thermal pretreated organic wastes on the dark fermentative hydrogen production using mixed microbial consortia

The present study investigates the effect of thermal pretreated organic waste as a feedstock for the dark fermentative hydrogen (H2) production. Acidogenic mixed consortia was used for H2 production from starchy wastewater supplemented with groundnut de-oiled cake (GDOC). Physicochemical changes in GDOC after pretreatment were analyzed by using SEM, XRD and FTIR spectra. Maximum cumulative H2 production and H2 yield of 3.24 L L−1 and 12.05 mol H2 kg−1 CODremoved, respectively were achieved using the pretreated feedstock, which is 20% higher than that of the untreated one. Several kinetic models such as Logistic model, first order reaction kinetics, Pirt model, modified Gompertz model and Luedeking–Piret model were used to find out the effect of pretreatment on the kinetic parameters. Material analysis indicated that the fermentation was dominated by butyric acid pathway. Gaseous energy recovery was improved by two folds after the pretreatment. This is the first attempt to analyze the effect of thermal pretreatment of feedstock on different kinetic parameters associated with dark fermentation.

The effect of torrefaction pre-treatment on the pyrolysis of corn cobs

Production of green fuels and chemicals from non-edible corn cob residues presents an excellent opportunity to produce sustainable low carbon energy vectors as an alternative to fossil fuels. The objective of this study was to optimize the fuel physical and chemical properties of torrefied corn cobs bio-oil by investigating the relationship between feedstock pre-treatment (torrefaction) temperatures (240, 260, 280 and 300 ​°C), and subsequent pyrolysis temperatures (400, 450, 500 and 550 ​°C). This experimental methodology aimed to improve both yields and properties of bio-oils from corn cobs. Torrefaction was first carried out as a pre-treatment step using a custom-built torrefaction reactor followed by pyrolysis using a continuous fluidized bed reactor. Torrefaction was found to be a promising pre-treatment step because it had the effect of reducing the water content and viscosity within the bio-oil. Corn cobs grinding energy requirements could be reduced by 69% when torrefaction was applied from 240 ​°C to 260 ​°C. A maximum bio-oil yield of 51.7% was achieved when the optimal temperatures (torrefaction 260 ​°C and pyrolysis 450 ​°C) was applied. Overall, using torrefaction as a pre-treatment step before pyrolysis was shown to be a promising approach for improving some physiochemical properties of bio-oil for its application as a fuel.

Surface states of gas-atomized Al 6061 powders – Effects of heat treatment

Surface oxides formed on powder feedstocks used for cold spray deposition can play an important role in the bonding of the particles and in the development of defects in the deposit. A combination of scanning transmission electron microscopy and x-ray photoelectron spectroscopy was used to investigate the oxides formed on gas-atomized Al 6061 alloy feedstock powders. The powders were studied in the as-atomized condition and after two different thermal exposures that correspond to typical feedstock pre-treatment conditions. The surface features and internal microstructures are consistent with those reported previously for these powders. The as-atomized powders have 5.2 nm thick amorphous oxide layers, with an outer Mg-rich sub-layer and an inner Mg-lean sub-layer. Powders heat-treated at 230 °C in air exhibit slightly thicker oxide layers with a crystalline MgAl2O4 spinel outer sub-layer and an amorphous aluminum oxide inner sub-layer. Powders homogenized under Ar at 400 and 530 °C have significantly thicker (8.9 nm) oxide layers with evidence for a defect inverse spinel Al(Mg,Al)2O4 inner sub-layer between the MgAl2O4 spinel outer sub-layer and the alloy. Differences between these observations and those reported previously for oxidation of bulk alloys are explained on the basis of Mg surface segregation during the gas atomization process.

The Effects of Alkaline Pretreatment on Agricultural Biomasses (Corn Cob and Sweet Sorghum Bagasse) and Their Hydrolysis by a Termite-Derived Enzyme Cocktail

Sweet sorghum bagasse (SSB) and corncob (CC) have been identified as promising feedstocks for the production of second-generation biofuels and other value-added chemicals. In this study, lime (Ca(OH)2) and NaOH pretreatment efficacy for decreasing recalcitrance from SSB and CC was investigated, and subsequently, the pretreated biomass was subjected to the hydrolytic action of an in-house formulated holocellulolytic enzyme cocktail (HEC-H). Compositional analysis revealed that SSB contained 29.34% lignin, 17.75% cellulose and 16.28% hemicellulose, while CC consisted of 22.51% lignin, 23.58% cellulose and 33.34% hemicellulose. Alkaline pretreatment was more effective in pretreating CC biomass compared to the SSB biomass. Both Ca(OH)2 and NaOH pretreatment removed lignin from the CC biomass, while only NaOH removed lignin from the SSB biomass. Biomass compositional analysis revealed that these agricultural feedstocks differed in their chemical composition because the CC biomass contained mainly hemicellulose (33–35%), while SSB biomass consisted mainly of cellulose (17–24%). The alkaline pretreated SSB and CC samples were subjected to the hydrolytic action of the holocellulolytic enzyme cocktail, formulated with termite derived multifunctional enzymes (referred to as MFE-5E, MFE-5H and MFE-45) and exoglucanase (Exg-D). The HEC-H hydrolysed NaOH pretreated SSB and CC more effectively than Ca(OH)2 pretreated feedstocks, revealing that NaOH was a more effective pretreatment. In conclusion, the HEC-H cocktail efficiently hydrolysed alkaline pretreated agricultural feedstocks, particularly those which are hemicellulose- and amorphous cellulose-rich, such as CC, making it attractive for use in the bioconversion process in the biorefinery industry.