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Special Issue "Efficient Technology for the Pretreatment of Biomass"

A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Green Chemistry".

Deadline for manuscript submissions: closed (30 June 2018)

Special Issue Editors

Guest Editor
Dr. Helene Carrere

LBE, INRA Institut National de La Recherche Agronomique, Montpellier Université, Avenue des etangs, 11100 Narbonne, France
Website | E-Mail
Interests: physico–chemical and biological pretreatments; anaerobic digestion; dark fermentation; lignocellulosic biomass; agricultural residues; sludge; fatty residues
Guest Editor
Dr. Aline Carvalho da Costa

Faculdade de Engenharia Química, Universida de Estadual de Campinas, Campinas, Brazil
Website | E-Mail
Interests: biomass pretreatment; enzymatic hydrolysis; hexoses and pentoses fermentation; second generation ethanol; enzyme production
Guest Editor
Dr. Cigdem Eskicioglu

The University of British Columbia, UBC Bioreactor Technology Group, School of Engineering, Kelowna, Canada
Website | E-Mail
Interests: sludge pretreatment; advanced anaerobic digestion; nutrient removal/recovery from wastewater; odor minimization; fate of micropollutants
Guest Editor
Dr. Ivet Ferrer

Universitat Politecnica de Catalunya·BarcelonaTech, Department of Civil & Environmental Engineering, Group of Environmental Engineering and Microbiology, Barcelona, Spain
Website | E-Mail
Interests: microalgae; sludge; pretreatment techniques; anaerobic digestion; co-digestion; biogas; life-cycle assessment (LCA)

Special Issue Information

Dear Colleagues,

Biomass corresponds to organic matter of animal, vegetable, microbial, or algal origin. Biomass use as feedstock for biomaterial, chemicals, platform molecules, biofuel or bioenergy are the most reliable alternatives to limit fossil fuel consumption and to reduce greenhouse gas emissions. Resource recovery from different kinds of waste, such as sludge, food waste, municipal solid waste, and animal waste (manure and slaughterhouse waste) is particularly interesting from an environmental point of view, as it also reduces environmental pollution. In addition, lignocellulosic biomass and algae, which do not compete for food production, represent an important source of renewable resources (i.e., energy and other value-added products). However, a pretreatment step is generally required before biomass (bio)-conversion into valuable products in order to increase the process yield and/or productivity.

Pretreatmentsare applied upstream of various conversion processes of biomass into biofuel or biomaterial with valuable end products such as bioethanol, biohydrogen, biomethane, biomolecules or biomaterials. Pretreatments cover a wide range of processes that include mechanical, thermal, chemical and biological techniques. This step is recognized as crucial and cost intensive for the development of biorefineries. Thus, more research is necessary to identify the most effective and economical pretreatment options for different biomass sources.

This Special Issue aims to gather research papers on recent developments of biomass pretreatments for biomaterial, chemicals, biofuel or bioenergy production, in the fields of Chemistry Sciences, Process Engineering, Chemical Engineering, Modeling and Control, Energy and Fuels, and Bioprocesses. Papers describing new insights on pretreatment mechanisms, development of new and efficient pretreatment processes, environmental, energy or economical assessments and modeling of more conventional pretreatment processes are particularly expected. Review articles are also welcome.

Dr. Helene Carrere
Dr. Aline Carvalho da Costa
Dr. Cigdem Eskicioglu
Dr. Ivet Ferrer
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Molecules is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1800 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • New pretreatment process
  • Pretreatment mechanisms
  • Pretreatment modeling
  • Environmental assessment
  • Energy assessment
  • Economic assessment
  • Biomass fractionation for biorefinery
  • Life cycle assessment

Published Papers (13 papers)

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Research

Jump to: Review

Open AccessArticle Strategies to Optimize Microalgae Conversion to Biogas: Co-Digestion, Pretreatment and Hydraulic Retention Time
Molecules 2018, 23(9), 2096; https://doi.org/10.3390/molecules23092096
Received: 13 July 2018 / Revised: 9 August 2018 / Accepted: 16 August 2018 / Published: 21 August 2018
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Abstract
This study aims at optimizing the anaerobic digestion (AD) of biomass in microalgal-based wastewater treatment systems. It comprises the co-digestion of microalgae with primary sludge, the thermal pretreatment (75 °C for 10 h) of microalgae and the role of the hydraulic retention time
[...] Read more.
This study aims at optimizing the anaerobic digestion (AD) of biomass in microalgal-based wastewater treatment systems. It comprises the co-digestion of microalgae with primary sludge, the thermal pretreatment (75 °C for 10 h) of microalgae and the role of the hydraulic retention time (HRT) in anaerobic digesters. Initially, a batch test comparing different microalgae (untreated and pretreated) and primary sludge proportions showed how the co-digestion improved the AD kinetics. The highest methane yield was observed by adding 75% of primary sludge to pretreated microalgae (339 mL CH4/g VS). This condition was then investigated in mesophilic lab-scale reactors. The average methane yield was 0.46 L CH4/g VS, which represented a 2.9-fold increase compared to pretreated microalgae mono-digestion. Conversely, microalgae showed a low methane yield despite the thermal pretreatment (0.16 L CH4/g VS). Indeed, microscopic analysis confirmed the presence of microalgae species with resistant cell walls (i.e., Stigioclonium sp. and diatoms). In order to improve their anaerobic biodegradability, the HRT was increased from 20 to 30 days, which led to a 50% methane yield increase. Overall, microalgae AD was substantially improved by the co-digestion with primary sludge, even without pretreatment, and increasing the HRT enhanced the AD of microalgae with resistant cell walls. Full article
(This article belongs to the Special Issue Efficient Technology for the Pretreatment of Biomass)
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Open AccessArticle Comparison of Different Electricity-Based Thermal Pretreatment Methods for Enhanced Bioenergy Production from Municipal Sludge
Molecules 2018, 23(8), 2006; https://doi.org/10.3390/molecules23082006
Received: 30 June 2018 / Revised: 24 July 2018 / Accepted: 9 August 2018 / Published: 11 August 2018
Cited by 1 | PDF Full-text (3216 KB) | HTML Full-text | XML Full-text
Abstract
This paper presents results for a comprehensive study that compares the performance of three electricity-based thermal pretreatment methods for improving the effectiveness of anaerobic digestion (AD) to process municipal wastewater sludge. The study compares thermal pretreatment using conventional heating (CH), microwave (MW), and
[...] Read more.
This paper presents results for a comprehensive study that compares the performance of three electricity-based thermal pretreatment methods for improving the effectiveness of anaerobic digestion (AD) to process municipal wastewater sludge. The study compares thermal pretreatment using conventional heating (CH), microwave (MW), and radio frequency (RF) heating techniques. The effectiveness of the pretreatment methods was assessed in terms of chemical oxygen demand (COD) and biopolymers solubilization, AD bioenergy production, input electrical energy, and overall net energy production of the sequential pretreatment/AD process. The heating applicators for the bench-scale testing consisted of a custom-built pressure-sealed heating vessel for CH experiments, an off-the-shelf programmable MW oven operating at a frequency of 2.45 GHz for MW heating experiments, and a newly developed 1 kW RF heating system operating at a frequency of 13.56 MHz for RF heating experiments. Under identical thermal profiles, all three thermal pretreatment methods achieved similar sludge disintegration in terms of COD and biopolymer solubilization as well as AD bioenergy production (p-value > 0.05). According to the energy assessment results, the application of CH and MW pretreatments resulted in overall negative energy production, while positive net energy production was obtained through the sequential pretreatment/AD process utilizing RF pretreatment. Full article
(This article belongs to the Special Issue Efficient Technology for the Pretreatment of Biomass)
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Open AccessArticle Impact of Alkaline H2O2 Pretreatment on Methane Generation Potential of Greenhouse Crop Waste under Anaerobic Conditions
Molecules 2018, 23(7), 1794; https://doi.org/10.3390/molecules23071794
Received: 25 June 2018 / Revised: 15 July 2018 / Accepted: 16 July 2018 / Published: 20 July 2018
PDF Full-text (2004 KB) | HTML Full-text | XML Full-text
Abstract
This paper intended to explore the effect of alkaline H2O2 pretreatment on the biodegradability and the methane generation potential of greenhouse crop waste. A multi-variable experimental design was implemented. In this approach, initial solid content (3–7%), reaction time (6–24 h),
[...] Read more.
This paper intended to explore the effect of alkaline H2O2 pretreatment on the biodegradability and the methane generation potential of greenhouse crop waste. A multi-variable experimental design was implemented. In this approach, initial solid content (3–7%), reaction time (6–24 h), H2O2 concentration (1–3%), and reaction temperature (50–100 °C) were varied in different combinations to determine the impact of alkaline H2O2 pretreatment. The results indicated that the alkaline H2O2 pretreatment induced a significant increase in the range of 200–800% in chemical oxygen demand (COD) leakage into the soluble phase, and boosted the methane generation potential from 174 mLCH4/g of volatile solid (VS) to a much higher bracket of 250–350 mLCH4/gVS. Similarly, the lignocellulosic structure of the material was broken down and hydrolyzed by H2O2 dosing, which increased the rate of volatile matter utilization from 31% to 50–70% depending on selected conditions. Alkaline H2O2 pretreatment was optimized to determine optimal conditions for the enhancement of methane generation assuming a cost-driven approach. Optimal alkaline H2O2 pretreatment conditions were found as a reaction temperature of 50 °C, 7% initial solid content, 1% H2O2 concentration, and a reaction time of six h. Under these conditions, the biochemical methane potential (BMP) test yielded as 309 mLCH4/gVS. The enhancement of methane production was calculated as 77.6% compared to raw greenhouse crop wastes. Full article
(This article belongs to the Special Issue Efficient Technology for the Pretreatment of Biomass)
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Open AccessArticle Acid Assisted Organosolv Delignification of Beechwood and Pulp Conversion towards High Concentrated Cellulosic Ethanol via High Gravity Enzymatic Hydrolysis and Fermentation
Molecules 2018, 23(7), 1647; https://doi.org/10.3390/molecules23071647
Received: 19 June 2018 / Revised: 2 July 2018 / Accepted: 4 July 2018 / Published: 5 July 2018
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Abstract
Background: Future biorefineries will focus on converting low value waste streams to chemical products that are derived from petroleum or refined sugars. Feedstock pretreatment in a simple, cost effective, agnostic manner is a major challenge. Methods: In this work, beechwood sawdust was delignified
[...] Read more.
Background: Future biorefineries will focus on converting low value waste streams to chemical products that are derived from petroleum or refined sugars. Feedstock pretreatment in a simple, cost effective, agnostic manner is a major challenge. Methods: In this work, beechwood sawdust was delignified via an organosolv process, assisted by homogeneous inorganic acid catalysis. Mixtures of water and several organic solvents were evaluated for their performance. Specifically, ethanol (EtOH), acetone (AC), and methyl- isobutyl- ketone (MIBK) were tested with or without the use of homogeneous acid catalysis employing sulfuric, phosphoric, and oxalic acids under relatively mild temperature of 175 °C for one hour. Results: Delignification degrees (DD) higher than 90% were achieved, where both AC and EtOH proved to be suitable solvents for this process. Both oxalic and especially phosphoric acid proved to be good alternative catalysts for replacing sulfuric acid. High gravity simultaneous saccharification and fermentation with an enzyme loading of 8.4 mg/gsolids at 20 wt.% initial solids content reached an ethanol yield of 8.0 w/v%. Conclusions: Efficient delignification combining common volatile solvents and mild acid catalysis allowed for the production of ethanol at high concentration in an efficient manner. Full article
(This article belongs to the Special Issue Efficient Technology for the Pretreatment of Biomass)
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Open AccessFeature PaperArticle Lime Pretreatment of Miscanthus: Impact on BMP and Batch Dry Co-Digestion with Cattle Manure
Molecules 2018, 23(7), 1608; https://doi.org/10.3390/molecules23071608
Received: 18 May 2018 / Revised: 27 June 2018 / Accepted: 28 June 2018 / Published: 2 July 2018
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Abstract
In Europe, the agricultural biogas sector is currently undergoing fast developments, and cattle manure constitutes an important feedstock. Batch dry digester processes with leachate recirculation prove to be particularly interesting for small-scale plants. However, their startup being relatively slow, the process could be
[...] Read more.
In Europe, the agricultural biogas sector is currently undergoing fast developments, and cattle manure constitutes an important feedstock. Batch dry digester processes with leachate recirculation prove to be particularly interesting for small-scale plants. However, their startup being relatively slow, the process could be facilitated by co-digestion with energy crops. In this study, Miscanthus xgiganteus was chosen for its high biomass yields and low input requirements. The carbohydrate accessibility of this lignocellulosic biomass is limited but may be improved with alkali pretreatment. The efficiency of lime (CaO) pretreatment with low water addition on the biochemical methane potential (BMP) of miscanthus was investigated through two experimental designs (CaO concentrations ranged between 2.5 and 17.5% and pretreatment lasted 1, 3, or 5 days). The pretreated miscanthus was then co-digested with cattle manure in dry leach bed reactors. CaO pretreatments led to a 14–37% improvement of miscanthus BMP, and a 67–227% increase in the first-order kinetics constant; a high contact time was shown to favor methane production. According to these results and to industrial requirements, miscanthus was pretreated with 5 and 10% CaO for 5 days, then co-digested with manure in dry leach bed reactors. Nevertheless, the promising results of the BMP tests were not validated. This could be related to the high water absorption capacity of miscanthus. Full article
(This article belongs to the Special Issue Efficient Technology for the Pretreatment of Biomass)
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Open AccessArticle Subcritical Water-Carbon Dioxide Pretreatment of Oil Palm Mesocarp Fiber for Xylooligosaccharide and Glucose Production
Molecules 2018, 23(6), 1310; https://doi.org/10.3390/molecules23061310
Received: 24 April 2018 / Revised: 20 May 2018 / Accepted: 29 May 2018 / Published: 30 May 2018
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Abstract
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
[...] Read more.
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. Full article
(This article belongs to the Special Issue Efficient Technology for the Pretreatment of Biomass)
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Open AccessArticle Enhanced Enzymatic Hydrolysis and Structural Features of Corn Stover by NaOH and Ozone Combined Pretreatment
Molecules 2018, 23(6), 1300; https://doi.org/10.3390/molecules23061300
Received: 19 March 2018 / Revised: 19 April 2018 / Accepted: 8 May 2018 / Published: 29 May 2018
Cited by 1 | PDF Full-text (1946 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
A two-step pretreatment using NaOH and ozone was performed to improve the enzymatic hydrolysis, compositions and structural characteristics of corn stover. Comparison between the unpretreated and pretreated corn stover was also made to illustrate the mechanism of the combined pretreatment. A pretreatment with
[...] Read more.
A two-step pretreatment using NaOH and ozone was performed to improve the enzymatic hydrolysis, compositions and structural characteristics of corn stover. Comparison between the unpretreated and pretreated corn stover was also made to illustrate the mechanism of the combined pretreatment. A pretreatment with 2% (w/w) NaOH at 80 °C for 2 h followed by ozone treatment for 25 min with an initial pH 9 was found to be the optimal procedure and the maximum efficiency (91.73%) of cellulose enzymatic hydrolysis was achieved. Furthermore, microscopic observation of changes in the surface structure of the samples showed that holes were formed and lignin and hemicellulose were partially dissolved and removed. X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR) and Cross-Polarization Magic Angle Spinning Carbon-13 Nuclear Magnetic Resonance (CP/MAS 13C-NMR) were also used to characterize the chemical structural changes after the combined pretreatment. The results were as follows: part of the cellulose I structure was destroyed and then reformed into cellulose III, the cellulose crystal indices were also changed; a wider space between the crystal layer was observed; disruption of hydrogen bonds in cellulose and disruption of ester bonds in hemicellulose; cleavage of bonds linkage in lignin-carbohydrate complexes; removal of methoxy in lignin and hemicellulose. As a result, all these changes effectively reduced recalcitrance of corn stover and promoted subsequent enzymatic hydrolysis of cellulose. Full article
(This article belongs to the Special Issue Efficient Technology for the Pretreatment of Biomass)
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Open AccessArticle Effective Saccharification of Corn Stover Using Low-Liquid Aqueous Ammonia Pretreatment and Enzymatic Hydrolysis
Molecules 2018, 23(5), 1050; https://doi.org/10.3390/molecules23051050
Received: 27 March 2018 / Revised: 22 April 2018 / Accepted: 28 April 2018 / Published: 1 May 2018
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Abstract
Low-liquid aqueous ammonia (LLAA) pretreatment using aqueous ammonia was investigated to enhance enzymatic saccharification of corn stover. In this method, ground corn stover was simply contacted with aqueous ammonia mist (ammoniation step), followed by pretreatment at elevated temperature (90–150 °C) for an extended
[...] Read more.
Low-liquid aqueous ammonia (LLAA) pretreatment using aqueous ammonia was investigated to enhance enzymatic saccharification of corn stover. In this method, ground corn stover was simply contacted with aqueous ammonia mist (ammoniation step), followed by pretreatment at elevated temperature (90–150 °C) for an extended period (24–120 h) at different solid/liquid (S/L) ratios (0.29, 0.47 or 0.67), termed a pretreatment step. After that, excess (unreacted) ammonia was removed by evaporation, and the pretreated material was immediately saccharified by an enzyme without a washing step. The effects of key reaction parameters on both glucan digestibility and XMG digestibility were evaluated by analysis of variance (ANOVA). Under the best pretreatment conditions [S/L = 0.47, 0.16 (g NH3)/(g biomass), 90 °C, 24 h], LLAA pretreatment enhanced enzymatic digestibility from 23.1% for glucan and 11.3% for XMG (xylan + galactan + mannan) of untreated corn stover to 91.8% for glucan and 72.6% for XMG in pretreated solid. Full article
(This article belongs to the Special Issue Efficient Technology for the Pretreatment of Biomass)
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Open AccessArticle Combination of Superheated Steam with Laccase Pretreatment Together with Size Reduction to Enhance Enzymatic Hydrolysis of Oil Palm Biomass
Molecules 2018, 23(4), 811; https://doi.org/10.3390/molecules23040811
Received: 22 February 2018 / Revised: 20 March 2018 / Accepted: 23 March 2018 / Published: 2 April 2018
Cited by 1 | PDF Full-text (12033 KB) | HTML Full-text | XML Full-text
Abstract
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)
[...] Read more.
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. Full article
(This article belongs to the Special Issue Efficient Technology for the Pretreatment of Biomass)
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Open AccessArticle Mechano-Enzymatic Deconstruction with a New Enzymatic Cocktail to Enhance Enzymatic Hydrolysis and Bioethanol Fermentation of Two Macroalgae Species
Molecules 2018, 23(1), 174; https://doi.org/10.3390/molecules23010174
Received: 14 November 2017 / Revised: 19 December 2017 / Accepted: 7 January 2018 / Published: 17 January 2018
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Abstract
The aim of this study was to explore the efficiency of a mechano-enzymatic deconstruction of two macroalgae species for sugars and bioethanol production, by using a new enzymatic cocktail (Haliatase) and two types of milling modes (vibro-ball: VBM and centrifugal milling: CM). By
[...] Read more.
The aim of this study was to explore the efficiency of a mechano-enzymatic deconstruction of two macroalgae species for sugars and bioethanol production, by using a new enzymatic cocktail (Haliatase) and two types of milling modes (vibro-ball: VBM and centrifugal milling: CM). By increasing the enzymatic concentration from 3.4 to 30 g/L, the total sugars released after 72 h of hydrolysis increased (from 6.7 to 13.1 g/100 g TS and from 7.95 to 10.8 g/100 g TS for the green algae U. lactuca and the red algae G. sesquipedale, respectively). Conversely, total sugars released from G. sesquipedale increased (up to 126% and 129% after VBM and CM, respectively). The best bioethanol yield (6 geth/100 g TS) was reached after 72 h of fermentation of U. lactuca and no increase was obtained after centrifugal milling. The latter led to an enhancement of the ethanol yield of G. sesquipedale (from 2 to 4 g/100 g TS). Full article
(This article belongs to the Special Issue Efficient Technology for the Pretreatment of Biomass)
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Review

Jump to: Research

Open AccessReview An Overview of Current Pretreatment Methods Used to Improve Lipid Extraction from Oleaginous Microorganisms
Molecules 2018, 23(7), 1562; https://doi.org/10.3390/molecules23071562
Received: 7 June 2018 / Revised: 20 June 2018 / Accepted: 26 June 2018 / Published: 28 June 2018
Cited by 2 | PDF Full-text (652 KB) | HTML Full-text | XML Full-text
Abstract
Microbial oils, obtained from oleaginous microorganisms are an emerging source of commercially valuable chemicals ranging from pharmaceuticals to the petroleum industry. In petroleum biorefineries, the microbial biomass has become a sustainable source of renewable biofuels. Biodiesel is mainly produced from oils obtained from
[...] Read more.
Microbial oils, obtained from oleaginous microorganisms are an emerging source of commercially valuable chemicals ranging from pharmaceuticals to the petroleum industry. In petroleum biorefineries, the microbial biomass has become a sustainable source of renewable biofuels. Biodiesel is mainly produced from oils obtained from oleaginous microorganisms involving various upstream and downstream processes, such as cultivation, harvesting, lipid extraction, and transesterification. Among them, lipid extraction is a crucial step for the process and it represents an important bottleneck for the commercial scale production of biodiesel. Lipids are synthesized in the cellular compartment of oleaginous microorganisms in the form of lipid droplets, so it is necessary to disrupt the cells prior to lipid extraction in order to improve the extraction yields. Various mechanical, chemical and physicochemical pretreatment methods are employed to disintegrate the cellular membrane of oleaginous microorganisms. The objective of the present review article is to evaluate the various pretreatment methods for efficient lipid extraction from the oleaginous cellular biomass available to date, as well as to discuss their advantages and disadvantages, including their effect on the lipid yield. The discussed mechanical pretreatment methods are oil expeller, bead milling, ultrasonication, microwave, high-speed and high-pressure homogenizer, laser, autoclaving, pulsed electric field, and non-mechanical methods, such as enzymatic treatment, including various emerging cell disruption techniques. Full article
(This article belongs to the Special Issue Efficient Technology for the Pretreatment of Biomass)
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Open AccessReview Pre-treatment of Oil Palm Biomass for Fermentable Sugars Production
Molecules 2018, 23(6), 1381; https://doi.org/10.3390/molecules23061381
Received: 24 April 2018 / Revised: 31 May 2018 / Accepted: 31 May 2018 / Published: 7 June 2018
PDF Full-text (1014 KB) | HTML Full-text | XML Full-text
Abstract
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
[...] Read more.
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. Full article
(This article belongs to the Special Issue Efficient Technology for the Pretreatment of Biomass)
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Open AccessReview Efficient Anaerobic Digestion of Microalgae Biomass: Proteins as a Key Macromolecule
Molecules 2018, 23(5), 1098; https://doi.org/10.3390/molecules23051098
Received: 12 March 2018 / Revised: 3 May 2018 / Accepted: 3 May 2018 / Published: 6 May 2018
Cited by 2 | PDF Full-text (1140 KB) | HTML Full-text | XML Full-text
Abstract
Biogas generation is the least complex technology to transform microalgae biomass into bioenergy. Since hydrolysis has been pointed out as the rate limiting stage of anaerobic digestion, the main challenge for an efficient biogas production is the optimization of cell wall disruption/hydrolysis. Among
[...] Read more.
Biogas generation is the least complex technology to transform microalgae biomass into bioenergy. Since hydrolysis has been pointed out as the rate limiting stage of anaerobic digestion, the main challenge for an efficient biogas production is the optimization of cell wall disruption/hydrolysis. Among all tested pretreatments, enzymatic treatments were demonstrated not only very effective in disruption/hydrolysis but they also revealed the impact of microalgae macromolecular composition in the anaerobic process. Although carbohydrates have been traditionally recognized as the polymers responsible for the low microalgae digestibility, protease addition resulted in the highest organic matter solubilization and the highest methane production. However, protein solubilization during the pretreatment can result in anaerobic digestion inhibition due to the release of large amounts of ammonium nitrogen. The possible solutions to overcome these negative effects include the reduction of protein biomass levels by culturing the microalgae in low nitrogen media and the use of ammonia tolerant anaerobic inocula. Overall, this review is intended to evidence the relevance of microalgae proteins in different stages of anaerobic digestion, namely hydrolysis and methanogenesis. Full article
(This article belongs to the Special Issue Efficient Technology for the Pretreatment of Biomass)
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