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Efficient Technology for the Pretreatment of Biomass

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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) | Viewed by 62053

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Special Issue Editors

Dr. Helene Carrere

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Guest Editor

LBE, INRA Institut National de La Recherche Agronomique, Montpellier Université, Avenue des etangs, 11100 Narbonne, France
Interests: physico–chemical and biological pretreatments; anaerobic digestion; dark fermentation; lignocellulosic biomass; agricultural residues; sludge; fatty residues

Dr. Aline Carvalho Da Costa

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Guest Editor

Faculdade de Engenharia Química, Universida de Estadual de Campinas, Campinas, Brazil
Interests: biomass pretreatment; enzymatic hydrolysis; hexoses and pentoses fermentation; second generation ethanol; enzyme production

Dr. Cigdem Eskicioglu

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Guest Editor

UBC Bioreactor Technology Group, School of Engineering, The University of British Columbia, Kelowna, BC, Canada
Interests: sludge pretreatment; advanced anaerobic digestion; nutrient removal/recovery from wastewater; odor minimization; fate of micropollutants
Special Issues, Collections and Topics in MDPI journals

Dr. Ivet Ferrer

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Guest Editor

Department of Civil & Environmental Engineering, Universitat Politecnica de Catalunya, Barcelona, Spain
Interests: biodegradable waste; microalgae, sewage sludge, biogas; anaerobic digestion; co-digestion; biomass pretreatment; life cycle assessment (LCA); low-tech digesters
Special Issues, Collections and Topics in MDPI journals

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

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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 semimonthly 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 2700 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

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16 pages, 13239 KiB

Open AccessArticle

Strategies to Optimize Microalgae Conversion to Biogas: Co-Digestion, Pretreatment and Hydraulic Retention Time

by Maria Solé-Bundó, Humbert Salvadó, Fabiana Passos, Marianna Garfí and Ivet Ferrer

Molecules 2018, 23(9), 2096; https://doi.org/10.3390/molecules23092096 - 21 Aug 2018

Cited by 47 | Viewed by 3892

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 (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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15 pages, 3216 KiB

Open AccessArticle

Comparison of Different Electricity-Based Thermal Pretreatment Methods for Enhanced Bioenergy Production from Municipal Sludge

by E. Hosseini Koupaie, T. Johnson and C. Eskicioglu

Molecules 2018, 23(8), 2006; https://doi.org/10.3390/molecules23082006 - 11 Aug 2018

Cited by 24 | Viewed by 3032

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 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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17 pages, 2004 KiB

Open AccessArticle

Impact of Alkaline H₂O₂ Pretreatment on Methane Generation Potential of Greenhouse Crop Waste under Anaerobic Conditions

by N. Altınay Perendeci, Sezen Gökgöl and Derin Orhon

Molecules 2018, 23(7), 1794; https://doi.org/10.3390/molecules23071794 - 20 Jul 2018

Cited by 23 | Viewed by 3326

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), 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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18 pages, 2680 KiB

Open AccessArticle

Acid Assisted Organosolv Delignification of Beechwood and Pulp Conversion towards High Concentrated Cellulosic Ethanol via High Gravity Enzymatic Hydrolysis and Fermentation

by Konstantinos G. Kalogiannis, Leonidas Matsakas, James Aspden, Angelos A. Lappas, Ulrika Rova and Paul Christakopoulos

Molecules 2018, 23(7), 1647; https://doi.org/10.3390/molecules23071647 - 05 Jul 2018

Cited by 44 | Viewed by 4875

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 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/g_solids 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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13 pages, 1649 KiB

Open AccessFeature PaperArticle

Lime Pretreatment of Miscanthus: Impact on BMP and Batch Dry Co-Digestion with Cattle Manure

by Hélène Laurence Thomas, Jordan Seira, Renaud Escudié and Hélène Carrère

Molecules 2018, 23(7), 1608; https://doi.org/10.3390/molecules23071608 - 02 Jul 2018

Cited by 19 | Viewed by 3600

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 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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14 pages, 3693 KiB

Open AccessArticle

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

by Norlailiza Ahmad, Mohd Rafein Zakaria, Mohd Zulkhairi Mohd Yusoff, Shinji Fujimoto, Hiroyuki Inoue, Hidayah Ariffin, Mohd Ali Hassan and Yoshihoto Shirai

Molecules 2018, 23(6), 1310; https://doi.org/10.3390/molecules23061310 - 30 May 2018

Cited by 21 | Viewed by 4264

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 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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13 pages, 1946 KiB

Open AccessArticle

Enhanced Enzymatic Hydrolysis and Structural Features of Corn Stover by NaOH and Ozone Combined Pretreatment

by Wenhui Wang, Chunyan Zhang, Shisheng Tong, Zhongyi Cui and Ping Liu

Molecules 2018, 23(6), 1300; https://doi.org/10.3390/molecules23061300 - 29 May 2018

Cited by 25 | Viewed by 3244

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 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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15 pages, 1641 KiB

Open AccessArticle

Effective Saccharification of Corn Stover Using Low-Liquid Aqueous Ammonia Pretreatment and Enzymatic Hydrolysis

by Nguyen Phuong Vi Truong and Tae Hyun Kim

Molecules 2018, 23(5), 1050; https://doi.org/10.3390/molecules23051050 - 01 May 2018

Cited by 9 | Viewed by 4743

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 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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14 pages, 12033 KiB

Open AccessArticle

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

by Nur Fatin Athirah Ahmad Rizal, Mohamad Faizal Ibrahim, Mohd Rafein Zakaria, Ezyana Kamal Bahrin, Suraini Abd-Aziz and Mohd Ali Hassan

Molecules 2018, 23(4), 811; https://doi.org/10.3390/molecules23040811 - 02 Apr 2018

Cited by 17 | Viewed by 4177

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) 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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11 pages, 2348 KiB

Open AccessArticle

Mechano-Enzymatic Deconstruction with a New Enzymatic Cocktail to Enhance Enzymatic Hydrolysis and Bioethanol Fermentation of Two Macroalgae Species

by Sameh Amamou, Cecilia Sambusiti, Florian Monlau, Eric Dubreucq and Abdellatif Barakat

Molecules 2018, 23(1), 174; https://doi.org/10.3390/molecules23010174 - 17 Jan 2018

Cited by 35 | Viewed by 4936

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 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 g_eth/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

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22 pages, 652 KiB

Open AccessReview

An Overview of Current Pretreatment Methods Used to Improve Lipid Extraction from Oleaginous Microorganisms

by Alok Patel, Fabio Mikes and Leonidas Matsakas

Molecules 2018, 23(7), 1562; https://doi.org/10.3390/molecules23071562 - 28 Jun 2018

Cited by 91 | Viewed by 7389

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 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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14 pages, 1014 KiB

Open AccessReview

Pre-treatment of Oil Palm Biomass for Fermentable Sugars Production

by Nur Fatin Athirah Ahmad Rizal, Mohamad Faizal Ibrahim, Mohd Rafein Zakaria, Suraini Abd-Aziz, Phang Lai Yee and Mohd Ali Hassan

Molecules 2018, 23(6), 1381; https://doi.org/10.3390/molecules23061381 - 07 Jun 2018

Cited by 44 | Viewed by 6929

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 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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16 pages, 1140 KiB

Open AccessReview

Efficient Anaerobic Digestion of Microalgae Biomass: Proteins as a Key Macromolecule

by Jose Antonio Magdalena, Mercedes Ballesteros and Cristina González-Fernandez

Molecules 2018, 23(5), 1098; https://doi.org/10.3390/molecules23051098 - 06 May 2018

Cited by 54 | Viewed by 6558

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 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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