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Special Issue "Bioenergy and Biorefining"

A special issue of Energies (ISSN 1996-1073).

Deadline for manuscript submissions: closed (30 April 2015)

Special Issue Editor

Guest Editor
Prof. Dr. Thomas E. Amidon

Department of Paper and Bioprocess Engineering, College of Environmental Science and Forestry, State University of New York, 1 Forestry Drive, Syracuse, NY 13210, USA
Website | E-Mail
Interests: biorefineries; biofuels; bioenergy; bio-based materials and chemicals; nanocellulose; pulp and paper; pellets; forest and biomass resources; process development; novel bio-based products; cell wall deconstruction; hot water extraction; cellulosic bioproducts; improved fiber-based products; biomass productivity

Special Issue Information

Dear Colleagues,

We would like to see articles in the intellectual space from raw materials (any form of biomass), to extraction and separation into components, to conversion of intermediates into final products. The products do not have to be biofuels if the products are renewable in origin and substitute for fossil fuel derived products. Engineering work applicable to any of the component operations is also appreciated. We would also be interested in articles showing that multiple products and more sophistication in product development could lead to greater returns. An example here might be furfural production from xylose as a more valuable product than fermentation of xylose to ethanol, as well as showing that this might be an energetically preferable way to produce furfural.

Prof. Dr. Thomas E. Amidon
Guest Editor

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. Energies 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 1600 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

  • biomass
  • biofuels
  • biorefinery
  • extraction
  • component separation
  • conversion
  • novel biobased products
  • biorefinery engineering
  • biomass and biorefinery policy
  • fossil fuel substitution

Related Special Issue

Published Papers (20 papers)

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Research

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Open AccessArticle Eicosapentaenoic Acid from Porphyridium Cruentum: Increasing Growth and Productivity of Microalgae for Pharmaceutical Products
Energies 2015, 8(9), 10487-10503; https://doi.org/10.3390/en80910487
Received: 16 June 2015 / Revised: 1 September 2015 / Accepted: 15 September 2015 / Published: 22 September 2015
Cited by 3 | PDF Full-text (457 KB) | HTML Full-text | XML Full-text
Abstract
An alternative source of eicosapentaenoic acid (EPA) or omega-3 could be microalgae lipids instead of fish oils. However, EPA and lipid contents extracted from microalgae vary at different growth conditions. Therefore, it is of paramount importance to optimize the growth conditions of microalgae
[...] Read more.
An alternative source of eicosapentaenoic acid (EPA) or omega-3 could be microalgae lipids instead of fish oils. However, EPA and lipid contents extracted from microalgae vary at different growth conditions. Therefore, it is of paramount importance to optimize the growth conditions of microalgae to maximize EPA production. In this paper, the effects of temperature (16 °C and 20 °C), light intensity (140 µE m−2 s−1 and 180 µE m−2 s−1) and nitrate level (0.075, 0.3, 0.5, and 0.7 g/L) on the cell growth, lipid productivity, and omega-6/omega-3 ratio of Porphyridium cruentum, one of the most promising oil-rich species of microalgae, are investigated. The ratio of the fatty acids with omega-6 and omega-3 groups at various growth conditions were compared, since an appropriate proportion of ω-6 (arachidonic acid (ARA)) to ω-3 (EPA) is vital for healthy nutrition. Lower EPA production and consequently a higher ARA/EPA ratio occurred when 5% CO2/air was utilized as CO2 supplementation compared to pure CO2. The highest EPA (13.08% (w/w) of total fatty acids) and biomass productivity (143 mg L−1 day−1) was achieved at 140 µE m−2 s−1, 20 °C, and 0.3 g/L nitrate, while lipid content was the lowest (0.5% w/w) at this condition. The optimal condition with minimum ARA/EPA ratio (2.5) was identified at 20 °C, 140 µE m−2 s−1, and 0.5 g/L nitrate concentration. Full article
(This article belongs to the Special Issue Bioenergy and Biorefining)
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Open AccessArticle Chemical Composition of Apricot Pit Shells and Effect of Hot-Water Extraction
Energies 2015, 8(9), 9640-9654; https://doi.org/10.3390/en8099640
Received: 25 May 2015 / Revised: 1 August 2015 / Accepted: 20 August 2015 / Published: 3 September 2015
Cited by 8 | PDF Full-text (581 KB) | HTML Full-text | XML Full-text
Abstract
Agricultural residues, such as corn stover, wheat straw, and nut shells show promise as feedstocks for lignocellulosic biorefinery due to their relatively high polysaccharide content and low or no nutritional value for human consumption. Apricot pit shells (APS) were studied in this work
[...] Read more.
Agricultural residues, such as corn stover, wheat straw, and nut shells show promise as feedstocks for lignocellulosic biorefinery due to their relatively high polysaccharide content and low or no nutritional value for human consumption. Apricot pit shells (APS) were studied in this work to assess their potential for use in a biorefinery. Hot water extraction (HWE; 160 °C, 2 h), proposed to remove easily accessible hemicelluloses, was performed to evaluate the susceptibility of APS to this mild pretreatment process. The chemical composition of APS before and after HWE (EAPS) was analyzed by standard methods and 1H-NMR. A low yield of the remaining HW-extracted APS (~59%) indicated that APS are highly susceptible to this pretreatment method. 1H-NMR analysis of EAPS revealed that ~77% of xylan present in raw APS was removed along with ~24% of lignin. The energy of combustion of APS was measured before and after HWE showing a slight increase due to HWE (1.61% increase). Near infrared radiation spectroscopy (NIRS), proposed as a quick non-invasive method of biomass analysis, was performed. NIRS corroborated results of traditional analysis and 1H-NMR. Determination of antioxidizing activity (AOA) of APS extracts was also undertaken. AOA of organic APS extracts were shown to be more than 20 times higher than that of a synthetic antioxidizing agent. Full article
(This article belongs to the Special Issue Bioenergy and Biorefining)
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Open AccessArticle Lignin-Furfural Based Adhesives
Energies 2015, 8(8), 7897-7914; https://doi.org/10.3390/en8087897
Received: 27 May 2015 / Revised: 14 July 2015 / Accepted: 15 July 2015 / Published: 30 July 2015
Cited by 17 | PDF Full-text (873 KB) | HTML Full-text | XML Full-text
Abstract
Lignin recovered from the hot-water extract of sugar maple (Acer saccharum) is used in this study to synthesize adhesive blends to replace phenol-formaldehyde (PF) resin. Untreated lignin is characterized by lignin content and nuclear magnetic resonance (NMR) analysis. The molecular weight
[...] Read more.
Lignin recovered from the hot-water extract of sugar maple (Acer saccharum) is used in this study to synthesize adhesive blends to replace phenol-formaldehyde (PF) resin. Untreated lignin is characterized by lignin content and nuclear magnetic resonance (NMR) analysis. The molecular weight distribution of the lignin and the blends are characterized by size exclusion chromatography (SEC). The effect of pH (0.3, 0.65 and 1), ex situ furfural, and curing conditions on the tensile properties of adhesive reinforced glass fibers is determined and compared to the reinforcement level of commercially available PF resin. The adhesive blend prepared at pH = 0.65 with no added furfural exhibits the highest tensile properties and meets 90% of the PF tensile strength. Full article
(This article belongs to the Special Issue Bioenergy and Biorefining)
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Open AccessArticle Bio-Refining of Carbohydrate-Rich Food Waste for Biofuels
Energies 2015, 8(7), 6350-6364; https://doi.org/10.3390/en8076350
Received: 1 March 2015 / Revised: 14 May 2015 / Accepted: 9 June 2015 / Published: 25 June 2015
Cited by 7 | PDF Full-text (541 KB) | HTML Full-text | XML Full-text
Abstract
The global dependence on finite fossil fuel-derived energy is of serious concern given the predicted population increase. Over the past decades, bio-refining of woody biomass has received much attention, but data on food waste refining are sorely lacking, despite annual and global deposition
[...] Read more.
The global dependence on finite fossil fuel-derived energy is of serious concern given the predicted population increase. Over the past decades, bio-refining of woody biomass has received much attention, but data on food waste refining are sorely lacking, despite annual and global deposition of 1.3 billion tons in landfills. In addition to negative environmental impacts, this represents a squandering of valuable energy, water and nutrient resources. The potential of carbohydrate-rich food waste (CRFW) for biofuel (by Rhodotorulla glutinis fermentation) and biogas production (by calculating theoretical methane yield) was therefore investigated using a novel integrated bio-refinery approach. In this approach, hydrolyzed CRFW from three different conditions was used for Rhodotorulla glutinis cultivation to produce biolipids, whilst residual solids after hydrolysis were characterized for methane recovery potential via anaerobic digestion. Initially, CRFW was hydrolysed using thermal- (Th), chemical- (Ch) and Th-Ch combined hydrolysis (TCh), with the CRFW-leachate serving as a control (Pcon). Excessive foaming led to the loss of TCh cultures, while day-7 biomass yields were similar (3.4–3.6 g dry weight (DW) L−1) for the remaining treatments. Total fatty acid methyl ester (FAME) content of R. glutinis cultivated on CRFW hydrolysates were relatively low (~6.5%) but quality parameters (i.e., cetane number, density, viscosity and higher heating values) of biomass extracted biodiesel complied with ASTM standards. Despite low theoretical RS-derived methane potential, further research under optimised and scaled conditions will reveal the potential of this approach for the bio-refining of CRFW for energy recovery and value-added co-product production. Full article
(This article belongs to the Special Issue Bioenergy and Biorefining)
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Open AccessArticle Energy Crop-Based Biogas as Vehicle Fuel—The Impact of Crop Selection on Energy Efficiency and Greenhouse Gas Performance
Energies 2015, 8(6), 6033-6058; https://doi.org/10.3390/en8066033
Received: 11 May 2015 / Revised: 29 May 2015 / Accepted: 11 June 2015 / Published: 18 June 2015
Cited by 14 | PDF Full-text (350 KB) | HTML Full-text | XML Full-text
Abstract
The production of biogas from six agricultural crops was analysed regarding energy efficiency and greenhouse gas (GHG) performance for vehicle fuel from a field-to-tank perspective, with focus on critical parameters and on calculation methods. The energy efficiency varied from 35% to 44%, expressed
[...] Read more.
The production of biogas from six agricultural crops was analysed regarding energy efficiency and greenhouse gas (GHG) performance for vehicle fuel from a field-to-tank perspective, with focus on critical parameters and on calculation methods. The energy efficiency varied from 35% to 44%, expressed as primary energy input per energy unit vehicle gas produced. The GHG reduction varied from 70% to 120%, compared with fossil liquid fuels, when the GHG credit of the digestate produced was included through system expansion according to the calculation methodology in the ISO 14044 standard of life cycle assessment. Ley crop-based biogas systems led to the highest GHG reduction, due to the significant soil carbon accumulation, followed by maize, wheat, hemp, triticale and sugar beet. Critical parameters are biogenic nitrous oxide emissions from crop cultivation, for which specific emission factors for digestate are missing today, and methane leakage from biogas production. The GHG benefits were reduced and the interrelation between the crops changed, when the GHG calculations were instead based on the methodology stated in the EU Renewable Energy Directive, where crop contribution to soil carbon accumulation is disregarded. All systems could still reach a 60% GHG reduction, due to the improved agricultural management when digestate replaces mineral fertilisers. Full article
(This article belongs to the Special Issue Bioenergy and Biorefining)
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Open AccessArticle Oxygen-Containing Fuels from High Acid Water Phase Pyrolysis Bio-Oils by ZSM−5 Catalysis: Kinetic and Mechanism Studies
Energies 2015, 8(6), 5898-5915; https://doi.org/10.3390/en8065898
Received: 24 March 2015 / Revised: 2 June 2015 / Accepted: 9 June 2015 / Published: 17 June 2015
Cited by 2 | PDF Full-text (898 KB) | HTML Full-text | XML Full-text
Abstract
This study developed an upgrading process focusing on acid transformations of water phase pyrolysis bio-oils to esters of oxygen-containing fuels via ZSM−5 catalyst. Temperature was set as a factor with five levels ranging from 60 to 135 °C with reaction time from 1
[...] Read more.
This study developed an upgrading process focusing on acid transformations of water phase pyrolysis bio-oils to esters of oxygen-containing fuels via ZSM−5 catalyst. Temperature was set as a factor with five levels ranging from 60 to 135 °C with reaction time from 1 to 8 h. The results showed that 89% of high acid conversion and over 90% of ester selectivity was obtained from the feedstock via 2 wt % ZSM−5 catalysts in a fixed feedstock to methanol ratio analyzed by HPLC and GC–MS. The upgrading process followed Langmuir–Hinshelwood and reaction constants were calculated to build a practical upgrading model for bio-oil compounds. Thermodynamics of the process showed endothermic properties during the breaking bonds’ reaction on carbonyl of acid while the reaction between the carbon in methanol and electrophile acid intermediate demonstrated exothermic performance. The optimum reaction conditions for the process was at a temperature of 100.1 °C with catalyst loading of 3.98 wt %. Full article
(This article belongs to the Special Issue Bioenergy and Biorefining)
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Open AccessArticle A Medium-Scale 50 MWfuel Biomass Gasification Based Bio-SNG Plant: A Developed Gas Cleaning Process
Energies 2015, 8(6), 5287-5302; https://doi.org/10.3390/en8065287
Received: 11 February 2015 / Revised: 4 May 2015 / Accepted: 27 May 2015 / Published: 3 June 2015
Cited by 3 | PDF Full-text (371 KB) | HTML Full-text | XML Full-text
Abstract
Natural gas is becoming increasingly important as a primary energy source. A suitable replacement for fossil natural gas is bio-SNG, produced by biomass gasification, followed by methanation. A major challenge is efficient gas cleaning processes for removal of sulfur compounds and other impurities.
[...] Read more.
Natural gas is becoming increasingly important as a primary energy source. A suitable replacement for fossil natural gas is bio-SNG, produced by biomass gasification, followed by methanation. A major challenge is efficient gas cleaning processes for removal of sulfur compounds and other impurities. The present study focuses on development of a gas cleaning step for a product gas produced in a 50 MWfuel gasification system. The developed gas cleaning washing process is basically a modification of the Rectisol process. Several different process configurations were evaluated using Aspen plus, including PC-SAFT for the thermodynamic modeling. The developed configuration takes advantage of only one methanol wash column, compared to two columns in a conventional Rectisol process. Results from modeling show the ability of the proposed configuration to remove impurities to a sufficiently low concentrations - almost zero concentration for H2S, CS2, HCl, NH3 and HCN, and approximately 0.01 mg/Nm3 for COS. These levels are acceptable for further upgrading of the gas in a methanation process. Simultaneously, up to 92% of the original CO2 is preserved in the final cleaned syngas stream. No process integration or economic consideration was performed within the scope of the present study, but will be investigated in future projects to improve the overall process. Full article
(This article belongs to the Special Issue Bioenergy and Biorefining)
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Open AccessArticle Fast Pyrolysis of Four Lignins from Different Isolation Processes Using Py-GC/MS
Energies 2015, 8(6), 5107-5121; https://doi.org/10.3390/en8065107
Received: 6 April 2015 / Accepted: 22 May 2015 / Published: 1 June 2015
Cited by 15 | PDF Full-text (710 KB) | HTML Full-text | XML Full-text
Abstract
Pyrolysis is a promising approach that is being investigated to convert lignin into higher value products including biofuels and phenolic chemicals. In this study, fast pyrolysis of four types of lignin, including milled Amur linden wood lignin (MWL), enzymatic hydrolysis corn stover lignin
[...] Read more.
Pyrolysis is a promising approach that is being investigated to convert lignin into higher value products including biofuels and phenolic chemicals. In this study, fast pyrolysis of four types of lignin, including milled Amur linden wood lignin (MWL), enzymatic hydrolysis corn stover lignin (EHL), wheat straw alkali lignin (AL) and wheat straw sulfonate lignin (SL), were performed using pyrolysis gas-chromatography/mass spectrometry (Py-GC/MS). Thermogravimetric analysis (TGA) showed that the four lignins exhibited widely different thermolysis behaviors. The four lignins had similar functional groups according to the FTIR analysis. Syringyl, guaiacyl and p-hydroxyphenylpropane structural units were broken down during pyrolysis. Fast pyrolysis product distributions from the four lignins depended strongly on the lignin origin and isolation process. Phenols were the most abundant pyrolysis products from MWL, EHL and AL. However, SL produced a large number of furan compounds and sulfur compounds originating from kraft pulping. The effects of pyrolysis temperature and time on the product distributions from corn stover EHL were also studied. At 350 °C, EHL pyrolysis mainly produced acids and alcohols, while phenols became the main products at higher temperature. No obvious influence of pyrolysis time was observed on EHL pyrolysis product distributions. Full article
(This article belongs to the Special Issue Bioenergy and Biorefining)
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Open AccessArticle Techno-Economic Analysis of Bioethanol Production from Lignocellulosic Biomass in China: Dilute-Acid Pretreatment and Enzymatic Hydrolysis of Corn Stover
Energies 2015, 8(5), 4096-4117; https://doi.org/10.3390/en8054096
Received: 23 December 2014 / Revised: 28 April 2015 / Accepted: 1 May 2015 / Published: 8 May 2015
Cited by 12 | PDF Full-text (1677 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Lignocellulosic biomass-based ethanol is categorized as 2nd generation bioethanol in the advanced biofuel portfolio. To make sound incentive policy proposals for the Chinese government and to develop guidance for research and development and industrialization of the technology, the paper reports careful techno-economic
[...] Read more.
Lignocellulosic biomass-based ethanol is categorized as 2nd generation bioethanol in the advanced biofuel portfolio. To make sound incentive policy proposals for the Chinese government and to develop guidance for research and development and industrialization of the technology, the paper reports careful techno-economic and sensitivity analyses performed to estimate the current competitiveness of the bioethanol and identify key components which have the greatest impact on its plant-gate price (PGP). Two models were developed for the research, including the Bioethanol PGP Assessment Model (BPAM) and the Feedstock Cost Estimation Model (FCEM). Results show that the PGP of the bioethanol ranges $4.68–$6.05/gal (9,550–12,356 yuan/t). The key components that contribute most to bioethanol PGP include the conversion rate of cellulose to glucose, the ratio of five-carbon sugars converted to ethanol, feedstock cost, and enzyme loading, etc. Lignocellulosic ethanol is currently unable to compete with fossil gasoline, therefore incentive policies are necessary to promote its development. It is suggested that the consumption tax be exempted, the value added tax (VAT) be refunded upon collection, and feed-in tariff for excess electricity (byproduct) be implemented to facilitate the industrialization of the technology. A minimum direct subsidy of $1.20/gal EtOH (2,500 yuan/t EtOH) is also proposed for consideration. Full article
(This article belongs to the Special Issue Bioenergy and Biorefining)
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Open AccessArticle Comprehensive Characterization of Napier Grass as a Feedstock for Thermochemical Conversion
Energies 2015, 8(5), 3403-3417; https://doi.org/10.3390/en8053403
Received: 18 March 2015 / Revised: 3 April 2015 / Accepted: 16 April 2015 / Published: 24 April 2015
Cited by 27 | PDF Full-text (1162 KB) | HTML Full-text | XML Full-text
Abstract
Study on Napier grass leaf (NGL), stem (NGS) and leaf and stem (NGT) was carried out. Proximate, ultimate and structural analyses were evaluated. Functional groups and crystalline components in the biomass were examined. Pyrolysis study was conducted in a thermogravimetric analyzer under nitrogen
[...] Read more.
Study on Napier grass leaf (NGL), stem (NGS) and leaf and stem (NGT) was carried out. Proximate, ultimate and structural analyses were evaluated. Functional groups and crystalline components in the biomass were examined. Pyrolysis study was conducted in a thermogravimetric analyzer under nitrogen atmosphere of 20 mL/min at constant heating rate of 10 K/min. The results reveal that Napier grass biomass has high volatile matter, higher heating value, high carbon content and lower ash, nitrogen and sulfur contents. Structural analysis shows that the biomass has considerable cellulose and lignin contents which are good candidates for good quality bio-oil production. From the pyrolysis study, degradation of extractives, hemicellulose, cellulose and lignin occurred at temperature around 478, 543, 600 and above 600 K, respectively. Kinetics of the process was evaluated using reaction order model. New equations that described the process were developed using the kinetic parameters and data compared with experimental data. The results of the models fit well to the experimental data. The proposed models may be a reliable means for describing thermal decomposition of lignocellulosic biomass under nitrogen atmosphere at constant heating rate. Full article
(This article belongs to the Special Issue Bioenergy and Biorefining)
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Open AccessArticle Life-Cycle Energy and GHG Emissions of Forest Biomass Harvest and Transport for Biofuel Production in Michigan
Energies 2015, 8(4), 3258-3271; https://doi.org/10.3390/en8043258
Received: 1 December 2014 / Revised: 16 March 2015 / Accepted: 15 April 2015 / Published: 22 April 2015
Cited by 16 | PDF Full-text (679 KB) | HTML Full-text | XML Full-text
Abstract
High dependence on imported oil has increased U.S. strategic vulnerability and prompted more research in the area of renewable energy production. Ethanol production from renewable woody biomass, which could be a substitute for gasoline, has seen increased interest. This study analysed energy use
[...] Read more.
High dependence on imported oil has increased U.S. strategic vulnerability and prompted more research in the area of renewable energy production. Ethanol production from renewable woody biomass, which could be a substitute for gasoline, has seen increased interest. This study analysed energy use and greenhouse gas emission impacts on the forest biomass supply chain activities within the State of Michigan. A life-cycle assessment of harvesting and transportation stages was completed utilizing peer-reviewed literature. Results for forest-delivered ethanol were compared with those for petroleum gasoline using data specific to the U.S. The analysis from a woody biomass feedstock supply perspective uncovered that ethanol production is more environmentally friendly (about 62% less greenhouse gas emissions) compared with petroleum based fossil fuel production. Sensitivity analysis was conducted with key inputs associated with harvesting and transportation operations. The results showed that research focused on improving biomass recovery efficiency and truck fuel economy further reduced GHG emissions and energy consumption. Full article
(This article belongs to the Special Issue Bioenergy and Biorefining)
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Open AccessArticle The Impact of a Mild Sub-Critical Hydrothermal Carbonization Pretreatment on Umbila Wood. A Mass and Energy Balance Perspective
Energies 2015, 8(3), 2165-2175; https://doi.org/10.3390/en8032165
Received: 8 October 2014 / Revised: 24 December 2014 / Accepted: 3 March 2015 / Published: 19 March 2015
Cited by 1 | PDF Full-text (419 KB) | HTML Full-text | XML Full-text
Abstract
Over the last years, the pretreatment of biomass as a source of energy has become one of the most important steps of biomass conversion. In this work the effect of a mild subcritical hydrothermal carbonization of a tropical woody biomass was studied. Results
[...] Read more.
Over the last years, the pretreatment of biomass as a source of energy has become one of the most important steps of biomass conversion. In this work the effect of a mild subcritical hydrothermal carbonization of a tropical woody biomass was studied. Results indicate considerable change in carbon content from 52.78% to 65.1%, reduction of oxygen content from 41.14% to 28.72% and ash slagging and fouling potential. Even though decarboxylation, decarbonylation and dehydration reactions take place, dehydration is the one that prevails. The mass and energy balance was affected by the treatment conditions than the severity of the treatment. Full article
(This article belongs to the Special Issue Bioenergy and Biorefining)
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Open AccessArticle Changes in Carbon Electrode Morphology Affect Microbial Fuel Cell Performance with Shewanella oneidensis MR-1
Energies 2015, 8(3), 1817-1829; https://doi.org/10.3390/en8031817
Received: 19 November 2014 / Revised: 8 January 2015 / Accepted: 11 February 2015 / Published: 4 March 2015
Cited by 8 | PDF Full-text (2262 KB) | HTML Full-text | XML Full-text
Abstract
The formation of biofilm-electrodes is crucial for microbial fuel cell current production because optimal performance is often associated with thick biofilms. However, the influence of the electrode structure and morphology on biofilm formation is only beginning to be investigated. This study provides insight
[...] Read more.
The formation of biofilm-electrodes is crucial for microbial fuel cell current production because optimal performance is often associated with thick biofilms. However, the influence of the electrode structure and morphology on biofilm formation is only beginning to be investigated. This study provides insight on how changing the electrode morphology affects current production of a pure culture of anode-respiring bacteria. Specifically, an analysis of the effects of carbon fiber electrodes with drastically different morphologies on biofilm formation and anode respiration by a pure culture (Shewanella oneidensis MR-1) were examined. Results showed that carbon nanofiber mats had ~10 fold higher current than plain carbon microfiber paper and that the increase was not due to an increase in electrode surface area, conductivity, or the size of the constituent material. Cyclic voltammograms reveal that electron transfer from the carbon nanofiber mats was biofilm-based suggesting that decreasing the diameter of the constituent carbon material from a few microns to a few hundred nanometers is beneficial for electricity production solely because the electrode surface creates a more relevant mesh for biofilm formation by Shewanella oneidensis MR-1. Full article
(This article belongs to the Special Issue Bioenergy and Biorefining)
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Open AccessArticle Analysis on Storage Off-Gas Emissions from Woody, Herbaceous, and Torrefied Biomass
Energies 2015, 8(3), 1745-1759; https://doi.org/10.3390/en8031745
Received: 26 November 2014 / Revised: 9 February 2015 / Accepted: 12 February 2015 / Published: 2 March 2015
Cited by 9 | PDF Full-text (680 KB) | HTML Full-text | XML Full-text
Abstract
Wood chips, torrefied wood chips, ground switchgrass, and wood pellets were tested for off‑gas emissions during storage. Storage canisters with gas‑collection ports were used to conduct experiments at room temperature of 20 °C and in a laboratory oven set at 40 °C. Commercially-produced
[...] Read more.
Wood chips, torrefied wood chips, ground switchgrass, and wood pellets were tested for off‑gas emissions during storage. Storage canisters with gas‑collection ports were used to conduct experiments at room temperature of 20 °C and in a laboratory oven set at 40 °C. Commercially-produced wood pellets yielded the highest carbon monoxide (CO) emissions at both 20 and 40 °C (1600 and 13,000 ppmv), whereas torrefied wood chips emitted the lowest of about <200 and <2000 ppmv. Carbon dioxide (CO2) emissions from wood pellets were 3000 ppmv and 42,000 ppmv, whereas torrefied wood chips registered at about 2000 and 25,000 ppmv, at 20 and 40 °C at the end of 11 days of storage. CO emission factors (milligrams per kilogram of biomass) calculated were lowest for ground switchgrass and torrefied wood chips (2.68 and 4.86 mg/kg) whereas wood pellets had the highest CO of about 10.60 mg/kg, respectively, at 40 °C after 11 days of storage. In the case of CO2, wood pellets recorded the lowest value of 55.46 mg/kg, whereas switchgrass recorded the highest value of 318.72 mg/kg. This study concludes that CO emission factor is highest for wood pellets, CO2 is highest for switchgrass and CH4 is negligible for all feedstocks except for wood pellets, which is about 0.374 mg/kg at the end of 11-day storage at 40 °C. Full article
(This article belongs to the Special Issue Bioenergy and Biorefining)
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Open AccessArticle Biohydrogen Fermentation from Sucrose and Piggery Waste with High Levels of Bicarbonate Alkalinity
Energies 2015, 8(3), 1716-1729; https://doi.org/10.3390/en8031716
Received: 24 November 2014 / Revised: 15 January 2015 / Accepted: 23 January 2015 / Published: 2 March 2015
Cited by 4 | PDF Full-text (750 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
This study examined the influence of biohydrogen fermentation under the high bicarbonate alkalinity (BA) and pH to optimize these critical parameters. When sucrose was used as a substrate, hydrogen was produced over a wide range of pH values (5–9) under no BA supplementation;
[...] Read more.
This study examined the influence of biohydrogen fermentation under the high bicarbonate alkalinity (BA) and pH to optimize these critical parameters. When sucrose was used as a substrate, hydrogen was produced over a wide range of pH values (5–9) under no BA supplementation; however, BA affected hydrogen yield significantly under different initial pHs (5–10). The actual effect of high BA using raw piggery waste (pH 8.7 and BA 8.9 g CaCO3/L) showed no biogas production or propionate/acetate accumulation. The maximum hydrogen production rate (0.32 L H2/g volatile suspended solids (VSS)-d) was observed at pH 8.95 and 3.18 g CaCO3/L. BA greater than 4 g CaCO3/L also triggered lactate-type fermentation, leading to propionate accumulation, butyrate reduction and homoacetogenesis, potentially halting the hydrogen production rate. These results highlight that the substrate with high BA need to amend adequately to maximize hydrogen production. Full article
(This article belongs to the Special Issue Bioenergy and Biorefining)
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Open AccessArticle Hot Water Pretreatment of Boreal Aspen Woodchips in a Pilot Scale Digester
Energies 2015, 8(2), 1166-1180; https://doi.org/10.3390/en8021166
Received: 26 November 2014 / Revised: 23 January 2015 / Accepted: 27 January 2015 / Published: 3 February 2015
Cited by 3 | PDF Full-text (891 KB) | HTML Full-text | XML Full-text
Abstract
Hot water extraction of aspen woodchips was treated at about 160 °C for 2 h with a liquor-to-solid ratio of 4.76:1 in a 1.84 m3 batch reactor with external liquor circulation. Both five-carbon and six-carbon sugars are obtained in the extraction liquor.
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Hot water extraction of aspen woodchips was treated at about 160 °C for 2 h with a liquor-to-solid ratio of 4.76:1 in a 1.84 m3 batch reactor with external liquor circulation. Both five-carbon and six-carbon sugars are obtained in the extraction liquor. Xylose and xylooligomers are the main five-carbon sugar in the hot water extract, which reached a maximum concentration of 0.016 mol/L, and 0.018 mol/L, respectively. Minor monosaccharides including galactose, mannose, rhamnose, glucose, and arabinose are also obtained during the hot water extraction. Rhamnose is the main six-carbon sugar in the extraction liquor, which has a maximum concentration of 0.0042 mol/L. The variations of acetyl groups and formic acid are investigated due to their catalytic effect on the extraction reactions. Zeroth-order kinetics models are found to be adequate in describing the dissolved solids, acids, xylose, and xylooligomers. Full article
(This article belongs to the Special Issue Bioenergy and Biorefining)
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Open AccessArticle Determination of Methane and Carbon Dioxide Formation Rate Constants for Semi-Continuously Fed Anaerobic Digesters
Energies 2015, 8(1), 645-655; https://doi.org/10.3390/en8010645
Received: 3 December 2014 / Accepted: 13 January 2015 / Published: 16 January 2015
Cited by 5 | PDF Full-text (511 KB) | HTML Full-text | XML Full-text
Abstract
To optimize commercial-scale biogas production, it is important to evaluate the performance of each microbial step in the anaerobic process. Hydrolysis and methanogenesis are usually the rate-limiting steps during digestion of organic waste and by-products. By measuring biogas production and methane concentrations on-line
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To optimize commercial-scale biogas production, it is important to evaluate the performance of each microbial step in the anaerobic process. Hydrolysis and methanogenesis are usually the rate-limiting steps during digestion of organic waste and by-products. By measuring biogas production and methane concentrations on-line in a semi-continuously fed reactor, gas kinetics can be evaluated. In this study, the rate constants of the fermentative hydrolysis step (kc) and the methanogenesis step (km) were determined and evaluated in a continuously stirred tank laboratory-scale reactor treating food and slaughterhouse waste and glycerin. A process additive containing Fe2+, Co2+ and Ni2+ was supplied until day 89, after which Ni2+ was omitted. The omission resulted in a rapid decline in the methanogenesis rate constant (km) to 70% of the level observed when Ni2+ was present, while kc remained unaffected. This suggests that Ni2+ mainly affects the methanogenic rather than the hydrolytic microorganisms in the system. However, no effect was initially observed when using conventional process monitoring parameters such as biogas yield and volatile fatty acid concentration. Hence, formation rate constants can reveal additional information on process performance and km can be used as a complement to conventional process monitoring tools for semi-continuously fed anaerobic digesters. Full article
(This article belongs to the Special Issue Bioenergy and Biorefining)
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Open AccessArticle Anaerobic Digestion and Biogas Potential: Simulation of Lab and Industrial-Scale Processes
Energies 2015, 8(1), 454-474; https://doi.org/10.3390/en8010454
Received: 2 October 2014 / Accepted: 31 December 2014 / Published: 13 January 2015
Cited by 6 | PDF Full-text (1416 KB) | HTML Full-text | XML Full-text
Abstract
In this study, a simulation was carried out using BioWin 3.1 to test the capability of the software to predict the biogas potential for two different anaerobic systems. The two scenarios included: (1) a laboratory-scale batch reactor; and (2) an industrial-scale anaerobic continuous
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In this study, a simulation was carried out using BioWin 3.1 to test the capability of the software to predict the biogas potential for two different anaerobic systems. The two scenarios included: (1) a laboratory-scale batch reactor; and (2) an industrial-scale anaerobic continuous lagoon digester. The measured data related to the operating conditions, the reactor design parameters and the chemical properties of influent wastewater were entered into BioWin. A sensitivity analysis was carried out to identify the sensitivity of the most important default parameters in the software’s models. BioWin was then calibrated by matching the predicted data with measured data and used to simulate other parameters that were unmeasured or deemed uncertain. In addition, statistical analyses were carried out using evaluation indices, such as the coefficient of determination (R-squared), the correlation coefficient (r) and its significance (p-value), the general standard deviation (SD) and the Willmott index of agreement, to evaluate the agreement between the software prediction and the measured data. The results have shown that after calibration, BioWin can be used reliably to simulate both small-scale batch reactors and industrial-scale digesters with a mean absolute percentage error (MAPE) of less than 10% and very good values of the indexes. Furthermore, by changing the default parameters in BioWin, which is a way of calibrating the models in the software, as well, this may provide information about the performance of the digester. Furthermore, the results of this study showed there may be an over estimation for biogas generated from industrial-scale digesters. More sophisticated analytical devices may be required for reliable measurements of biogas quality and quantity. Full article
(This article belongs to the Special Issue Bioenergy and Biorefining)
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Review

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Open AccessReview Combined Biogas and Bioethanol Production: Opportunities and Challenges for Industrial Application
Energies 2015, 8(8), 8121-8144; https://doi.org/10.3390/en8088121
Received: 8 May 2015 / Revised: 3 July 2015 / Accepted: 21 July 2015 / Published: 5 August 2015
Cited by 17 | PDF Full-text (402 KB) | HTML Full-text | XML Full-text
Abstract
In the last decades the increasing energy requirements along with the need to face the consequences of climate change have driven the search for renewable energy sources, in order to replace as much as possible the use of fossil fuels. In this context
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In the last decades the increasing energy requirements along with the need to face the consequences of climate change have driven the search for renewable energy sources, in order to replace as much as possible the use of fossil fuels. In this context biomass has generated great interest as it can be converted into energy via several routes, including fermentation and anaerobic digestion. The former is the most common option to produce ethanol, which has been recognized as one of the leading candidates to substitute a large fraction of the liquid fuels produced from oil. As the economic competitiveness of bioethanol fermentation processes has to be enhanced in order to promote its wider implementation, the most recent trends are directed towards the use of fermentation by-products within anaerobic digestion. The integration of both fermentation and anaerobic digestion, in a biorefinery concept, would allow the production of ethanol along with that of biogas, which can be used to produce heat and electricity, thus improving the overall energy balance. This work aims at reviewing the main studies on the combination of both bioethanol and biogas production processes, in order to highlight the strength and weakness of the integrated treatment for industrial application. Full article
(This article belongs to the Special Issue Bioenergy and Biorefining)
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Open AccessReview Engineering Plant Biomass Lignin Content and Composition for Biofuels and Bioproducts
Energies 2015, 8(8), 7654-7676; https://doi.org/10.3390/en8087654
Received: 2 June 2015 / Revised: 10 July 2015 / Accepted: 20 July 2015 / Published: 27 July 2015
Cited by 19 | PDF Full-text (606 KB) | HTML Full-text | XML Full-text
Abstract
Lignin is an aromatic biopolymer involved in providing structural support to plant cell walls. Compared to the other cell wall polymers, i.e., cellulose and hemicelluloses, lignin has been considered a hindrance in cellulosic bioethanol production due to the complexity involved in its
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Lignin is an aromatic biopolymer involved in providing structural support to plant cell walls. Compared to the other cell wall polymers, i.e., cellulose and hemicelluloses, lignin has been considered a hindrance in cellulosic bioethanol production due to the complexity involved in its separation from other polymers of various biomass feedstocks. Nevertheless, lignin is a potential source of valuable aromatic chemical compounds and upgradable building blocks. Though the biosynthetic pathway of lignin has been elucidated in great detail, the random nature of the polymerization (free radical coupling) process poses challenges for its depolymerization into valuable bioproducts. The absence of specific methodologies for lignin degradation represents an important opportunity for research and development. This review highlights research development in lignin biosynthesis, lignin genetic engineering and different biological and chemical means of depolymerization used to convert lignin into biofuels and bioproducts. Full article
(This article belongs to the Special Issue Bioenergy and Biorefining)
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