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Biofuel and Bioenergy Technology

A special issue of Energies (ISSN 1996-1073). This special issue belongs to the section "A: Sustainable Energy".

Deadline for manuscript submissions: closed (20 November 2018) | Viewed by 132121

Printed Edition Available!
A printed edition of this Special Issue is available here.

Special Issue Editors

Prof. Dr. Wei-Hsin Chen

grade E-Mail Website
Guest Editor
Department of Aeronautics and Astronautics, National Cheng Kung University, Tainan 701, Taiwan
Interests: bioenergy; hydrogen energy; clean energy; thermoelectric generation; environmental engineering; AI & machine leaning for energy
Special Issues, Collections and Topics in MDPI journals
Prof. Dr. Keat Teong Lee

E-Mail Website
Guest Editor
School of Chemical Engineering, Universiti Sains Malaysia, 14300 Nibong Tebal, Pulau Pinang, Malaysia
Interests: energy environment; renewable energy; reaction engineering
Dr. Hwai Chyuan Ong

E-Mail Website
Guest Editor
School of Information, Systems, and Modelling, Faculty of Engineering and Information Technology, University of Technology, Sydney, Ultimo, NSW, Australia
Interests: energy and fuel; renewable energy; environmental sustainability; biomass energy; thermal engineering; green technology
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Biomass is considered as a renewable resource because of its short life cycle, and biomass-derived biofuels are potential substitutes to fossil fuels. When biomass grows, all carbon in biomass comes from the atmosphere and is liberated into the environment when it is burned. Therefore, biomass is thought of as a carbon-neutral fuel. For these reasons, the development of bioenergy is an effective countermeasure to elongate diminishing fossil fuel reserves, lessen greenhouse gas (GHG) emissions, and mitigate global warming and climate change. Biomass can be converted into biofuels through a variety of routes such as physical, thermochemical, chemical, and biological methods. The common and important biofuels for bioenergy include charcoal, biochar, biodiesel, bioethanol, biobutanol, pyrolysis and liquefaction bio-oils, synthesis gas (syngas), biogas, and biohydrogen.  On account of the merit of bioenergy for environmental sustainability, biofuel and bioenergy technology plays a crucial role for renewable energy development. This Special Issue aims to publish high-quality research and review papers addressing recent advances in bioenergy. Studies of advanced techniques and biorefinery for biofuel production are also welcomed. Research involving experimental and numerical studies, recent developments, and novel and emerging technologies in this field are highly encouraged.

Prof. Dr. Wei-Hsin Chen
Prof. Dr. Keat Teong Lee
Prof. Dr. Hwai Chyuan Ong
Guest Editors

Manuscript Submission Information

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Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 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

  • biofuel
  • bioenergy
  • biorefinery
  • physical conversion
  • thermochemical conversion
  • chemical conversion
  • biological conversion
  • production optimization
  • process design
  • thermodynamic analysis

Published Papers (28 papers)

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Editorial

Jump to: Research, Review

12 pages, 201 KiB  
Editorial
Biofuel and Bioenergy Technology
by Wei-Hsin Chen, Keat Teong Lee and Hwai Chyuan Ong
Energies 2019, 12(2), 290; https://doi.org/10.3390/en12020290 - 18 Jan 2019
Cited by 13 | Viewed by 4009
Abstract
Biomass is considered as a renewable resource because of its short life cycle, and biomass-derived biofuels are potential substitutes to fossil fuels [...] Full article
(This article belongs to the Special Issue Biofuel and Bioenergy Technology)

Research

Jump to: Editorial, Review

10 pages, 1369 KiB  
Article
Variation in the Distribution of Hydrogen Producers from the Clostridiales Order in Biogas Reactors Depending on Different Input Substrates
by Martin Černý, Monika Vítězová, Tomáš Vítěz, Milan Bartoš and Ivan Kushkevych
Energies 2018, 11(12), 3270; https://doi.org/10.3390/en11123270 - 23 Nov 2018
Cited by 31 | Viewed by 3445
Abstract
With growing demand for clean and cheap energy resources, biogas production is emerging as an ideal solution, as it provides relatively cheap and clean energy, while also tackling the problematic production of excessive organic waste from crops and animal agriculture. Behind this process [...] Read more.
With growing demand for clean and cheap energy resources, biogas production is emerging as an ideal solution, as it provides relatively cheap and clean energy, while also tackling the problematic production of excessive organic waste from crops and animal agriculture. Behind this process stands a variety of anaerobic microorganisms, which turn organic substrates into valuable biogas. The biogas itself is a mixture of gases, produced mostly as metabolic byproducts of the microorganisms, such as methane, hydrogen, or carbon dioxide. Hydrogen itself figures as a potent bio-fuel, however in many bioreactors it serves as the main substrate of methanogenesis, thus potentially limiting biogas yield. With help of modern sequencing techniques, we tried to evaluate the composition in eight bioreactors using different input materials, showing shifts in the microbial consortia depending on the substrate itself. In this paper, we provide insight on the occurrence of potentially harmful microorganisms such as Clostridium novyi and Clostridium septicum, as well as key genera in hydrogen production, such as Clostridium stercorarium, Mobilitalea sp., Herbinix sp., Herbivorax sp., and Acetivibrio sp. Full article
(This article belongs to the Special Issue Biofuel and Bioenergy Technology)
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13 pages, 3343 KiB  
Article
Simultaneous Extraction and Emulsification of Food Waste Liquefaction Bio-Oil
by David Längauer, Yu-Ying Lin, Wei-Hsin Chen, Chao-Wen Wang, Michal Šafář and Vladimír Čablík
Energies 2018, 11(11), 3031; https://doi.org/10.3390/en11113031 - 05 Nov 2018
Cited by 10 | Viewed by 3178
Abstract
Biomass-derived bio-oil is a sustainable and renewable energy resource, and liquefaction is a potential conversion way to produce bio-oil. Emulsification is a physical upgrading technology, which blends immiscible liquids into a homogeneous emulsion through the addition of an emulsifier. Liquefaction bio-oil from food [...] Read more.
Biomass-derived bio-oil is a sustainable and renewable energy resource, and liquefaction is a potential conversion way to produce bio-oil. Emulsification is a physical upgrading technology, which blends immiscible liquids into a homogeneous emulsion through the addition of an emulsifier. Liquefaction bio-oil from food waste is characterized by its high pour point when compared to diesel fuel. In order to partially replace diesel fuel by liquefaction bio-oil, this study aimed to develop a method to simultaneously extract and emulsify the bio-oil using a commercial surfactant (Atlox 4914, CRODA, Snaith, UK). The solubility and stability of the emulsions at various operating conditions such as the bio-oil-to-emulsifier ratio (B/E ratio), storage temperature and duration, and co-surfactant (methanol) addition were analyzed. The results demonstrate that higher amounts of bio-oil (7 g) and emulsifier (7 g) at a B/E ratio = 1 in an emulsion have a higher solubility (66.48 wt %). When the B/E ratio was decreased from 1 to 0.556, the bio-oil solubility was enhanced by 45.79%, even though the storage duration was up to 7 days. Compared to the emulsion stored at room temperature (25 °C), its storage at 100 °C presented a higher solubility, especially at higher B/E ratios. Moreover, when methanol was added as a co-surfactant during emulsification at higher B/E ratios (0.714 to 1), it rendered better solubility (58.83–70.96 wt %). Overall, the emulsified oil showed greater stability after the extraction-emulsification process. Full article
(This article belongs to the Special Issue Biofuel and Bioenergy Technology)
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25 pages, 4118 KiB  
Article
Mathematical Modeling of Non-Premixed Laminar Flow Flames Fed with Biofuel in Counter-Flow Arrangement Considering Porosity and Thermophoresis Effects: An Asymptotic Approach
by Mehdi Bidabadi, Peyman Ghashghaei Nejad, Hamed Rasam, Sadegh Sadeghi and Bahman Shabani
Energies 2018, 11(11), 2945; https://doi.org/10.3390/en11112945 - 29 Oct 2018
Cited by 5 | Viewed by 3076
Abstract
Due to the safe operation and stability of non-premixed combustion, it can widely be utilized in different engineering power and medical systems. The current paper suggests a mathematical asymptotic technique to describe non-premixed laminar flow flames formed in organic particles in a counter-flow [...] Read more.
Due to the safe operation and stability of non-premixed combustion, it can widely be utilized in different engineering power and medical systems. The current paper suggests a mathematical asymptotic technique to describe non-premixed laminar flow flames formed in organic particles in a counter-flow configuration. In this investigation, fuel and oxidizer enter the combustor from opposite sides separately and multiple zones including preheating, vaporization, flame and post-flame zones were considered. Micro-sized lycopodium particles and air were respectively applied as a biofuel and an oxidizer. Dimensionalized and non-dimensionalized mass and energy conservation equations were determined for the zones and solved by Mathematica and Matlab software by applying proper boundary and jump conditions. Since lycopodium particles have numerous spores, the porosity of the particles was involved in the equations. Further, significant parameters such as lycopodium vaporization rate and thermophoretic force corresponding to the lycopodium particles in the solid phase were examined. The temperature distribution, flame sheet position, fuel and oxidizer mass fractions, equivalence ratio and flow strain rate were evaluated for the counter-flow non-premixed flames. Ultimately, the thermophoretic force caused by the temperature gradient at different positions was computed for several values of porosity, fuel and oxidizer Lewis numbers. Full article
(This article belongs to the Special Issue Biofuel and Bioenergy Technology)
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20 pages, 4196 KiB  
Article
A Systematic Multivariate Analysis of Carica papaya Biodiesel Blends and Their Interactive Effect on Performance
by Mohammad Anwar, Mohammad G. Rasul and Nanjappa Ashwath
Energies 2018, 11(11), 2931; https://doi.org/10.3390/en11112931 - 26 Oct 2018
Cited by 24 | Viewed by 4359
Abstract
This paper investigates the interactive relationship between three operating parameters (papaya seed oil (PSO) biodiesel blends, engine load, and engine speed) and four responses (brake power, BP; torque; brake specific fuel consumption, BSFC; and, brake thermal efficiency, BTE) for engine testing. A fully [...] Read more.
This paper investigates the interactive relationship between three operating parameters (papaya seed oil (PSO) biodiesel blends, engine load, and engine speed) and four responses (brake power, BP; torque; brake specific fuel consumption, BSFC; and, brake thermal efficiency, BTE) for engine testing. A fully instrumented four cylinder four-stroke, naturally aspirated agricultural diesel engine was used for all experiments. Three different blends: B5 (5% PSO biodiesel + 95% diesel), B10 (10% PSO biodiesel + 90% diesel), and B20 (20% PSO biodiesel + 80% diesel) were tested. Physicochemical properties of these blends and pure PSO biodiesel were characterised, and the engine’s performance characteristics were analysed. The results of the engine performance experiments showed that, in comparison with diesel, the three PSO biodiesel blends caused a slight reduction in BP, torque, and BTE, and an increase in BSFC. The analysis of variance and quadratic regression modelling showed that both load and speed were the most important parameters that affect engine performance, while PSO biodiesel blends had a significant effect on BSFC. Full article
(This article belongs to the Special Issue Biofuel and Bioenergy Technology)
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17 pages, 2579 KiB  
Article
Electrochemical Hydrogenation of Acetone to Produce Isopropanol Using a Polymer Electrolyte Membrane Reactor
by Chen Li, Ashanti M. Sallee, Xiaoyu Zhang and Sandeep Kumar
Energies 2018, 11(10), 2691; https://doi.org/10.3390/en11102691 - 10 Oct 2018
Cited by 12 | Viewed by 6363
Abstract
Electrochemical hydrogenation (ECH) of acetone is a relatively new method to produce isopropanol. It provides an alternative way of upgrading bio-fuels with less energy consumption and chemical waste as compared to conventional methods. In this paper, Polymer Electrolyte Membrane Fuel Cell (PEMFC) hardware [...] Read more.
Electrochemical hydrogenation (ECH) of acetone is a relatively new method to produce isopropanol. It provides an alternative way of upgrading bio-fuels with less energy consumption and chemical waste as compared to conventional methods. In this paper, Polymer Electrolyte Membrane Fuel Cell (PEMFC) hardware was used as an electrochemical reactor to hydrogenate acetone to produce isopropanol and diisopropyl ether as a byproduct. High current efficiency (59.7%) and selectivity (>90%) were achieved, while ECH was carried out in mild conditions (65 °C and atmospheric pressure). Various operating parameters were evaluated to determine their effects on the yield of acetone and the overall efficiency of ECH. The results show that an increase in humidity increased the yield of propanol and the efficiency of ECH. The operating temperature and power supply, however, have less effect. The degradation of membranes due to contamination of PEMFC and the mitigation methods were also investigated. Full article
(This article belongs to the Special Issue Biofuel and Bioenergy Technology)
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13 pages, 2426 KiB  
Article
Effects of Organosolv Pretreatment Using Temperature-Controlled Bench-Scale Ball Milling on Enzymatic Saccharification of Miscanthus × giganteus
by Tae Hoon Kim, Dongjoong Im, Kyeong Keun Oh and Tae Hyun Kim
Energies 2018, 11(10), 2657; https://doi.org/10.3390/en11102657 - 05 Oct 2018
Cited by 17 | Viewed by 3505
Abstract
The effect of organosolv pretreatment was investigated using a 30 L bench-scale ball mill reactor that was capable of simultaneously performing physical and chemical pretreatment. Various reaction conditions were tried in order to discover the optimal conditions for the minimal cellulose loss and [...] Read more.
The effect of organosolv pretreatment was investigated using a 30 L bench-scale ball mill reactor that was capable of simultaneously performing physical and chemical pretreatment. Various reaction conditions were tried in order to discover the optimal conditions for the minimal cellulose loss and enhanced enzymatic digestibility of Miscanthus × giganteus (MG), with conditions varying from room temperature to 170 °C for reaction temperature, from 30 to 120 min of reaction time, from 30% to 60% ethanol concentration, and a liquid/solid ratio (L/S) of 10–20 under non-catalyst conditions. The pretreatment effects were evaluated by chemical compositional analysis, enzymatic digestibility test and X-ray diffraction of the treated samples. The pretreatment conditions for the highest glucan digestibility yield were determined as 170 °C, reaction time of 90 min, ethanol concentration of 40% and L/S = 10. With these pretreatment conditions, the XMG (xylan + mannan + galactan) fractionation yield and delignification were 84.4% and 53.2%, respectively. The glucan digestibility of treated MG after the aforementioned pretreatment conditions was 86.0% with 15 filter paper units (FPU) of cellulase (Cellic® CTec2) per g-glucan enzyme loading. Full article
(This article belongs to the Special Issue Biofuel and Bioenergy Technology)
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18 pages, 2533 KiB  
Article
Optimisation of Second-Generation Biodiesel Production from Australian Native Stone Fruit Oil Using Response Surface Method
by Mohammad Anwar, Mohammad G. Rasul, Nanjappa Ashwath and Md Mofijur Rahman
Energies 2018, 11(10), 2566; https://doi.org/10.3390/en11102566 - 26 Sep 2018
Cited by 66 | Viewed by 4934
Abstract
In this study, the production process of second-generation biodiesel from Australian native stone fruit have been optimised using response surface methodology via an alkali catalysed transesterification process. This process optimisation was performed varying three factors, each at three different levels. Methanol: oil molar [...] Read more.
In this study, the production process of second-generation biodiesel from Australian native stone fruit have been optimised using response surface methodology via an alkali catalysed transesterification process. This process optimisation was performed varying three factors, each at three different levels. Methanol: oil molar ratio, catalyst concentration (wt %) and reaction temperature were the input factors in the optimisation process, while biodiesel yield was the key model output. Both 3D surface plots and 2D contour plots were developed using MINITAB 18 to predict optimum biodiesel yield. Gas chromatography (GC) and Fourier transform infrared (FTIR) analysis of the resulting biodiesel was also done for biodiesel characterisation. To predict biodiesel yield a quadratic model was created and it showed an R2 of 0.98 indicating the satisfactory performance of the model. Maximum biodiesel yield of 95.8% was obtained at a methanol: oil molar ratio of 6:1, KOH catalyst concentration of 0.5 wt % and a reaction temperature of 55 °C. At these reaction conditions, the predicted biodiesel yield was 95.9%. These results demonstrate reliable prediction of the transesterification process by Response surface methodology (RSM). The results also show that the properties of the synthesised Australian native stone fruit biodiesel satisfactorily meet the ASTM D6751 and EN14214 standards. In addition, the fuel properties of Australian native stone fruit biodiesel were found to be similar to those of conventional diesel fuel. Thus, it can be said that Australian native stone fruit seed oil could be used as a potential second-generation biodiesel source as well as an alternative fuel in diesel engines. Full article
(This article belongs to the Special Issue Biofuel and Bioenergy Technology)
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11 pages, 696 KiB  
Article
Biodiesel Production from a Novel Nonedible Feedstock, Soursop (Annona muricata L.) Seed Oil
by Chia-Hung Su, Hoang Chinh Nguyen, Uyen Khanh Pham, My Linh Nguyen and Horng-Yi Juan
Energies 2018, 11(10), 2562; https://doi.org/10.3390/en11102562 - 26 Sep 2018
Cited by 29 | Viewed by 5089
Abstract
This study investigated the optimal reaction conditions for biodiesel production from soursop (Annona muricata) seeds. A high oil yield of 29.6% (w/w) could be obtained from soursop seeds. Oil extracted from soursop seeds was then converted into [...] Read more.
This study investigated the optimal reaction conditions for biodiesel production from soursop (Annona muricata) seeds. A high oil yield of 29.6% (w/w) could be obtained from soursop seeds. Oil extracted from soursop seeds was then converted into biodiesel through two-step transesterification process. A highest biodiesel yield of 97.02% was achieved under optimal acid-catalyzed esterification conditions (temperature: 65 °C, 1% H2SO4, reaction time: 90 min, and a methanol:oil molar ratio: 10:1) and optimal alkali-catalyzed transesterification conditions (temperature: 65 °C, reaction time: 30 min, 0.6% NaOH, and a methanol:oil molar ratio: 8:1). The properties of soursop biodiesel were determined and most were found to meet the European standard EN 14214 and American Society for Testing and Materials standard D6751. This study suggests that soursop seed oil is a promising biodiesel feedstock and that soursop biodiesel is a viable alternative to petrodiesel. Full article
(This article belongs to the Special Issue Biofuel and Bioenergy Technology)
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10 pages, 1167 KiB  
Article
Combined Ball Milling and Ethanol Organosolv Pretreatment to Improve the Enzymatic Digestibility of Three Types of Herbaceous Biomass
by Seong Ju Kim, Byung Hwan Um, Dong Joong Im, Jin Hyung Lee and Kyeong Keun Oh
Energies 2018, 11(9), 2457; https://doi.org/10.3390/en11092457 - 16 Sep 2018
Cited by 20 | Viewed by 3573
Abstract
A combined ball milling and ethanol organosolv process is proposed for the pretreatment of three types of herbaceous biomass, giant miscanthus, corn stover, and wheat straw. The combined pretreatment was effective at both removing lignin and increasing the glucan content. After 120 min [...] Read more.
A combined ball milling and ethanol organosolv process is proposed for the pretreatment of three types of herbaceous biomass, giant miscanthus, corn stover, and wheat straw. The combined pretreatment was effective at both removing lignin and increasing the glucan content. After 120 min pretreatment, the glucan content increased to 63.09%, and 55.89% of the acid-insoluble lignin was removed from the giant miscanthus sample. The removal of cellulose, hemicellulose, and acetyl groups were correlated with the removal of lignin. The pretreatment of corn stover showed the highest removal of cellulose, but this was dependent on the removal of acid-insoluble lignin. The slope of the regression lines, which shows the correlation between the removal of lignin and cellulose, was lower than other correlations. The changes in biomass size were analyzed using size distribution graphs. With increasing pretreatment time, the particle size reduction improved in the three types of herbaceous biomass. Because of the combined physicochemical pretreatment, the enzymatic digestibility improved, and a maximum of 91% glucan digestibility was obtained from the pretreated corn stover when 30 FPU/g-glucan enzyme was added. Finally, compositional analysis of the recovered lignin from the remaining black liquor was investigated. Full article
(This article belongs to the Special Issue Biofuel and Bioenergy Technology)
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17 pages, 3185 KiB  
Article
A Study of the Production and Combustion Characteristics of Pyrolytic Oil from Sewage Sludge Using the Taguchi Method
by Guan-Bang Chen, Jia-Wen Li, Hsien-Tsung Lin, Fang-Hsien Wu and Yei-Chin Chao
Energies 2018, 11(9), 2260; https://doi.org/10.3390/en11092260 - 28 Aug 2018
Cited by 31 | Viewed by 3586
Abstract
Sewage sludge is a common form of municipal solid waste, and can be utilized as a renewable energy source. This study examines the effects of different key operational parameters on sewage sludge pyrolysis process for pyrolytic oil production using the Taguchi method. The [...] Read more.
Sewage sludge is a common form of municipal solid waste, and can be utilized as a renewable energy source. This study examines the effects of different key operational parameters on sewage sludge pyrolysis process for pyrolytic oil production using the Taguchi method. The digested sewage sludge was provided by the urban wastewater treatment plant of Tainan, Taiwan. The experimental results indicate that the maximum pyrolytic oil yield, 10.19% (18.4% on dry ash free (daf) basis) by weight achieved, is obtained under the operation conditions of 450 °C pyrolytic temperature, residence time of 60 min, 10 °C/min heating rate, and 700 mL/min nitrogen flow rate. According to the experimental results, the order of sensitivity of the parameters that affect the yield of sludge pyrolytic oil is the nitrogen flow rate, pyrolytic temperature, heating rate and residence time. The pyrolysis and oxidation reactions of sludge pyrolytic oil are also investigated using thermogravimetric analysis. The combustion performance parameters, such as the ignition temperature, burnout temperature, flammability index and combustion characteristics index are calculated and compared with those of heavy fuel oil. For the blend of sludge pyrolytic oil with heavy fuel oil, a synergistic effect occurs and the results show that sludge pyrolytic oil significantly enhances the ignition and combustion of heavy fuel oil. Full article
(This article belongs to the Special Issue Biofuel and Bioenergy Technology)
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13 pages, 2368 KiB  
Article
Biodiesel by Transesterification of Rapeseed Oil Using Ultrasound: A Kinetic Study of Base-Catalysed Reactions
by José María Encinar, Ana Pardal, Nuria Sánchez and Sergio Nogales
Energies 2018, 11(9), 2229; https://doi.org/10.3390/en11092229 - 25 Aug 2018
Cited by 65 | Viewed by 5152
Abstract
The objective of this work was to study the acceleration that ultrasound causes in the rate of biodiesel transesterification reactions. The effect of different operating variables, such as ultrasound power, catalyst (KOH) concentration and methanol:oil molar ratio, was studied. The evolution of the [...] Read more.
The objective of this work was to study the acceleration that ultrasound causes in the rate of biodiesel transesterification reactions. The effect of different operating variables, such as ultrasound power, catalyst (KOH) concentration and methanol:oil molar ratio, was studied. The evolution of the process was followed by gas chromatography, determining the concentration of methyl esters at different reaction times. The biodiesel was characterized by its density, viscosity, saponification and iodine values, acidity index, water content, flash and combustion points, cetane index and cold filter plugging point (CFPP), according to EN 14214 standard. High methyl ester yield and fast reaction rates were obtained in short reaction times. Ultrasound power and catalyst concentration had a positive effect on the yield and the reaction rate. The methanol:oil molar ratio also increased the yield of the reaction, but negatively influenced the process rate. The reaction followed a pseudo-first order kinetic model and the rate constants at several temperatures were determined. The activation energy was also determined using the Arrhenius equation. The main conclusion of this work is that the use of ultrasound irradiation did not require any additional heating, which could represent an energy savings for biodiesel manufacture. Full article
(This article belongs to the Special Issue Biofuel and Bioenergy Technology)
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20 pages, 5667 KiB  
Article
Bamboo Fiber and Sugarcane Skin as a Bio-Briquette Fuel
by Anna Brunerová, Hynek Roubík and Milan Brožek
Energies 2018, 11(9), 2186; https://doi.org/10.3390/en11092186 - 21 Aug 2018
Cited by 27 | Viewed by 7164
Abstract
The present study deals with the issue of bio-briquette fuel produced from specific agriculture residues, namely bamboo fiber (BF) and sugarcane skin (SCS). Both materials originated from Thừa Thiên Huế province in central Vietnam and were subjected to analysis of their suitability for [...] Read more.
The present study deals with the issue of bio-briquette fuel produced from specific agriculture residues, namely bamboo fiber (BF) and sugarcane skin (SCS). Both materials originated from Thừa Thiên Huế province in central Vietnam and were subjected to analysis of their suitability for such a purpose. A densification process using a high-pressure briquetting press proved its practicability for producing bio-briquette fuel. Analysis of fuel parameters exhibited a satisfactory level of all measured quality indicators: ash content Ac (BF—1.16%, SCS—8.62%) and net calorific value NCV (BF—16.92 MJ∙kg−1, SCS—17.23 MJ∙kg−1). Equally, mechanical quality indicators also proved satisfactory; bio-briquette samples’ mechanical durability DU occurred at an extremely high level (BF—97.80%, SCS—97.70%), as did their bulk density ρ (BF—986.37 kg·m−3, SCS—1067.08 kg·m−3). Overall evaluation of all observed results and factors influencing the investigated issue proved that both waste biomass materials, bamboo fiber and sugarcane skin, represent suitable feedstock materials for bio-briquette fuel production, and produced bio-briquette samples can be used as high-quality fuels. Full article
(This article belongs to the Special Issue Biofuel and Bioenergy Technology)
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17 pages, 1590 KiB  
Article
Nitric Acid Pretreatment of Jerusalem Artichoke Stalks for Enzymatic Saccharification and Bioethanol Production
by Urszula Dziekońska-Kubczak, Joanna Berłowska, Piotr Dziugan, Piotr Patelski, Katarzyna Pielech-Przybylska and Maria Balcerek
Energies 2018, 11(8), 2153; https://doi.org/10.3390/en11082153 - 17 Aug 2018
Cited by 41 | Viewed by 5049
Abstract
This paper evaluated the effectiveness of nitric acid pretreatment on the hydrolysis and subsequent fermentation of Jerusalem artichoke stalks (JAS). Jerusalem artichoke is considered a potential candidate for producing bioethanol due to its low soil and climate requirements, and high biomass yield. However, [...] Read more.
This paper evaluated the effectiveness of nitric acid pretreatment on the hydrolysis and subsequent fermentation of Jerusalem artichoke stalks (JAS). Jerusalem artichoke is considered a potential candidate for producing bioethanol due to its low soil and climate requirements, and high biomass yield. However, its stalks have a complexed lignocellulosic structure, so appropriate pretreatment is necessary prior to enzymatic hydrolysis, to enhance the amount of sugar that can be obtained. Nitric acid is a promising catalyst for the pretreatment of lignocellulosic biomass due to the high efficiency with which it removes hemicelluloses. Nitric acid was found to be the most effective catalyst of JAS biomass. A higher concentration of glucose and ethanol was achieved after hydrolysis and fermentation of 5% (w/v) HNO3-pretreated JAS, leading to 38.5 g/L of glucose after saccharification, which corresponds to 89% of theoretical enzymatic hydrolysis yield, and 9.5 g/L of ethanol. However, after fermentation there was still a significant amount of glucose in the medium. In comparison to more commonly used acids (H2SO4 and HCl) and alkalis (NaOH and KOH), glucose yield (% of theoretical yield) was approximately 47–74% higher with HNO3. The fermentation of 5% nitric-acid pretreated hydrolysates with the absence of solid residues, led to an increase in ethanol yield by almost 30%, reaching 77–82% of theoretical yield. Full article
(This article belongs to the Special Issue Biofuel and Bioenergy Technology)
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19 pages, 3370 KiB  
Article
Enhancing Biochemical Methane Potential and Enrichment of Specific Electroactive Communities from Nixtamalization Wastewater using Granular Activated Carbon as a Conductive Material
by David Valero, Carlos Rico, Blondy Canto-Canché, Jorge Arturo Domínguez-Maldonado, Raul Tapia-Tussell, Alberto Cortes-Velazquez and Liliana Alzate-Gaviria
Energies 2018, 11(8), 2101; https://doi.org/10.3390/en11082101 - 13 Aug 2018
Cited by 24 | Viewed by 4164
Abstract
Nejayote (corn step liquor) production in Mexico is approximately 1.4 × 1010 m3 per year and anaerobic digestion is an effective process to transform this waste into green energy. The biochemical methane potential (BMP) test is one of the most important [...] Read more.
Nejayote (corn step liquor) production in Mexico is approximately 1.4 × 1010 m3 per year and anaerobic digestion is an effective process to transform this waste into green energy. The biochemical methane potential (BMP) test is one of the most important tests for evaluating the biodegradability and methane production capacity of any organic waste. Previous research confirms that the addition of conductive materials significantly enhances the methane production yield. This study concludes that the addition of granular activated carbon (GAC) increases methane yield by 34% in the first instance. Furthermore, results show that methane production is increased by 54% when a GAC biofilm is developed 10 days before undertaking the BMP test. In addition, the electroactive population was 30% higher when attached to the GAC than in control reactors. Moreover, results show that electroactive communities attached to the GAC increased by 38% when a GAC biofilm is developed 10 days before undertaking the BMP test, additionally only in these reactors Geobacter was identified. GAC has two main effects in anaerobic digestion; it promotes direct interspecies electron transfer (DIET) by developing an electro-active biofilm and simultaneously it reduces redox potential from −223 mV to −470 mV. These results suggest that the addition of GAC to biodigesters, improves the anaerobic digestion performance in industrial processed food waste. Full article
(This article belongs to the Special Issue Biofuel and Bioenergy Technology)
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13 pages, 1085 KiB  
Article
Thermophilic Anaerobic Digestion: Enhanced and Sustainable Methane Production from Co-Digestion of Food and Lignocellulosic Wastes
by Aditi David, Tanvi Govil, Abhilash Kumar Tripathi, Julie McGeary, Kylie Farrar and Rajesh Kumar Sani
Energies 2018, 11(8), 2058; https://doi.org/10.3390/en11082058 - 08 Aug 2018
Cited by 46 | Viewed by 6934
Abstract
This article aims to study the codigestion of food waste (FW) and three different lignocellulosic wastes (LW) (Corn stover (CS), Prairie cordgrass (PCG), and Unbleached paper (UBP)) for thermophilic anaerobic digestion to overcome the limitations of digesting food waste alone (volatile fatty acids [...] Read more.
This article aims to study the codigestion of food waste (FW) and three different lignocellulosic wastes (LW) (Corn stover (CS), Prairie cordgrass (PCG), and Unbleached paper (UBP)) for thermophilic anaerobic digestion to overcome the limitations of digesting food waste alone (volatile fatty acids accumulation and low C:N ratio). Using an enriched thermophilic methanogenic consortium, all the food and lignocellulosic waste mixtures showed positive synergistic effects of codigestion. After 30 days of incubation at 60 °C (100 rpm), the highest methane yield of 305.45 L·kg−1 volatile solids (VS) was achieved with a combination of FW-PCG-CS followed by 279.31 L·kg−1 VS with a mixture of FW-PCG. The corresponding volatile solids reduction for these two co-digestion mixtures was 68% and 58%, respectively. This study demonstrated a reduced hydraulic retention time for methane production using FW and LW. Full article
(This article belongs to the Special Issue Biofuel and Bioenergy Technology)
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13 pages, 1179 KiB  
Article
Prospecting for Oleaginous and Robust Chlorella spp. for Coal-Fired Flue-Gas-Mediated Biodiesel Production
by Bohwa Kim, Ramasamy Praveenkumar, Eunji Choi, Kyubock Lee, Sang Goo Jeon and You-Kwan Oh
Energies 2018, 11(8), 2026; https://doi.org/10.3390/en11082026 - 03 Aug 2018
Cited by 13 | Viewed by 2955
Abstract
Prospecting for robust and high-productivity strains is a strategically important step in the microalgal biodiesel process. In this study, 30 local strains of Chlorella were evaluated in photobioreactors for biodiesel production using coal-fired flue-gas. Three strains (M082, M134, and KR-1) were sequentially selected [...] Read more.
Prospecting for robust and high-productivity strains is a strategically important step in the microalgal biodiesel process. In this study, 30 local strains of Chlorella were evaluated in photobioreactors for biodiesel production using coal-fired flue-gas. Three strains (M082, M134, and KR-1) were sequentially selected based on cell growth, lipid content, and fatty acid composition under autotrophic and mixotrophic conditions. Under autotrophic conditions, M082 and M134 showed comparable lipid contents (ca. 230 mg FAME [fatty acid methyl esters derived from microalgal lipids]/g cell) and productivities (ca. 40 mg FAME/L·d) versus a reference strain (KR-1) outdoors with actual flue-gas (CO2, 13%). Interestingly, under mixotrophic conditions, M082 demonstrated, along with maximal lipid content (397 mg FAME/g cell), good tolerance to high temperature (40 °C). Furthermore, the fatty acid methyl esters met important international standards under all of the tested culture conditions. Thus, it was concluded that M082 can be a feedstock of choice for coal-fired, flue-gas-mediated biodiesel production. Full article
(This article belongs to the Special Issue Biofuel and Bioenergy Technology)
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17 pages, 731 KiB  
Article
Design, Construction, and Testing of a Gasifier-Specific Solid Oxide Fuel Cell System
by Alvaro Fernandes, Joerg Brabandt, Oliver Posdziech, Ali Saadabadi, Mayra Recalde, Liyuan Fan, Eva O. Promes, Ming Liu, Theo Woudstra and Purushothaman Vellayan Aravind
Energies 2018, 11(8), 1985; https://doi.org/10.3390/en11081985 - 31 Jul 2018
Cited by 13 | Viewed by 3679
Abstract
This paper describes the steps involved in the design, construction, and testing of a gasifier-specific solid oxide fuel cell (SOFC) system. The design choices are based on reported thermodynamic simulation results for the entire gasifier- gas cleanup-SOFC system. The constructed SOFC system is [...] Read more.
This paper describes the steps involved in the design, construction, and testing of a gasifier-specific solid oxide fuel cell (SOFC) system. The design choices are based on reported thermodynamic simulation results for the entire gasifier- gas cleanup-SOFC system. The constructed SOFC system is tested and the measured parameters are compared with those given by a system simulation. Furthermore, a detailed exergy analysis is performed to determine the components responsible for poor efficiency. It is concluded that the SOFC system demonstrates reasonable agreement with the simulated results. Furthermore, based on the exergy results, the components causing major irreversible performance losses are identified. Full article
(This article belongs to the Special Issue Biofuel and Bioenergy Technology)
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12 pages, 1056 KiB  
Article
Biogas Quality across Small-Scale Biogas Plants: A Case of Central Vietnam
by Hynek Roubík, Jana Mazancová, Phung Le Dinh, Dung Dinh Van and Jan Banout
Energies 2018, 11(7), 1794; https://doi.org/10.3390/en11071794 - 09 Jul 2018
Cited by 47 | Viewed by 6729
Abstract
Production of bioenergy by the fermentation reaction is gaining attraction due to its easy operation and the wide feedstock selection. Anaerobic fermentation of organic waste materials is generally considered a cost-effective and proven technology, allowing simultaneous waste management and energy production. Small-scale biogas [...] Read more.
Production of bioenergy by the fermentation reaction is gaining attraction due to its easy operation and the wide feedstock selection. Anaerobic fermentation of organic waste materials is generally considered a cost-effective and proven technology, allowing simultaneous waste management and energy production. Small-scale biogas plants are widely and increasingly used to transform waste into gas through anaerobic fermentation of organic materials in the developing world. In this research, the quality of biogas produced in small-scale biogas plants was evaluated, as it has a direct effect on its use (as fuel for biogas cookers), as well as being able to influence a decision making process over purchasing such technology. Biogas composition was measured with a multifunctional portable gas analyser at 107 small-scale biogas plants. Complementary data at household level were collected via the questionnaire survey with the owners of biogas plants (n = 107). The average daily biogas production equals 0.499 m3, not covering the demand of rural households which are using other sources of energy as well. Related to the biogas composition, the mean content of methane (CH4) was 65.44% and carbon dioxide (CO2) was 29.31% in the case of biogas plants younger than five years; and CH4 was 64.57% and CO2 was 29.93% for biogas plants older than five years. Focusing on the age of small-scale biogas plants there are no, or only minor, differences among tested values. In conclusion, the small-scale biogas plants are sustaining a stable level of biogas quality during their life-span. Full article
(This article belongs to the Special Issue Biofuel and Bioenergy Technology)
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10 pages, 1957 KiB  
Article
Valorization of Waste Wood as a Solid Fuel by Torrefaction
by Jeeban Poudel, Sujeeta Karki and Sea Cheon Oh
Energies 2018, 11(7), 1641; https://doi.org/10.3390/en11071641 - 23 Jun 2018
Cited by 31 | Viewed by 4203
Abstract
The aim of this study was to investigate the optimal temperature range for waste wood and the effect torrefaction residence time had on torrefied biomass feedstock. Temperature range of 200–400 °C and residence time of 0–50 min were considered. In order to investigate [...] Read more.
The aim of this study was to investigate the optimal temperature range for waste wood and the effect torrefaction residence time had on torrefied biomass feedstock. Temperature range of 200–400 °C and residence time of 0–50 min were considered. In order to investigate the effect of temperature and residence time, torrefaction parameters, such as mass yield, energy yield, volatile matter, ash content and calorific value were calculated. The Van Krevelen diagram was also used for clarification, along with the CHO index based on molecular C, H, and O data. Torrefaction parameters, such as net/gross calorific value and CHO increased with an increase in torrefaction temperature, while a reduction in energy yield, mass yield, and volatile content were observed. Likewise, elevated ash content was observed with higher torrefaction temperature. From the Van Krevelen diagram, it was observed that at 300 °C the torrefied feedstock came in the range of lignite. With better gross calorific value and CHO index, less ash content and nominal mass loss, 300 °C was found to be the optimal torrefaction temperature for waste wood. Full article
(This article belongs to the Special Issue Biofuel and Bioenergy Technology)
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12 pages, 2917 KiB  
Article
Liquid Lipase-Catalyzed Esterification of Oleic Acid with Methanol for Biodiesel Production in the Presence of Superabsorbent Polymer: Optimization by Using Response Surface Methodology
by Hoang Chinh Nguyen, Dinh Thi My Huong, Horng-Yi Juan, Chia-Hung Su and Chien-Chung Chien
Energies 2018, 11(5), 1085; https://doi.org/10.3390/en11051085 - 28 Apr 2018
Cited by 27 | Viewed by 4385
Abstract
Liquid lipase-catalyzed esterification of fatty acids with methanol is a promising process for biodiesel production. However, water by-product from this process favors the reverse reaction, thus reducing the reaction yield. To address this, superabsorbent polymer (SAP) was used as a water-removal agent in [...] Read more.
Liquid lipase-catalyzed esterification of fatty acids with methanol is a promising process for biodiesel production. However, water by-product from this process favors the reverse reaction, thus reducing the reaction yield. To address this, superabsorbent polymer (SAP) was used as a water-removal agent in the esterification in this study. SAP significantly enhanced the conversion yield compared with the reaction without SAP. The lipase-catalyzed esterification in the presence of SAP was then optimized by response surface methodology to maximize the reaction conversion. A maximum conversion of 96.73% was obtained at a temperature of 35.25 °C, methanol to oleic acid molar ratio of 3.44:1, SAP loading of 10.55%, and enzyme loading of 11.98%. Under these conditions, the Eversa Transform lipase could only be reused once. This study suggests that the liquid lipase-catalyzed esterification of fatty acids using SAP as a water-removal agent is an efficient process for producing biodiesel. Full article
(This article belongs to the Special Issue Biofuel and Bioenergy Technology)
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18 pages, 2376 KiB  
Article
Analysis of Syngas Production from Biogas via the Tri-Reforming Process
by Rei-Yu Chein and Wen-Hwai Hsu
Energies 2018, 11(5), 1075; https://doi.org/10.3390/en11051075 - 27 Apr 2018
Cited by 16 | Viewed by 5133
Abstract
The tri-reforming process was employed for syngas production from biogas at elevated pressures in this study. In the tri-reforming process, air and water were added simultaneously as reactants in addition to the main biogas components. The effects of various operating parameters such as [...] Read more.
The tri-reforming process was employed for syngas production from biogas at elevated pressures in this study. In the tri-reforming process, air and water were added simultaneously as reactants in addition to the main biogas components. The effects of various operating parameters such as pressure, temperature and reactant composition on the reaction performance were studied numerically. From the simulated results, it was found that methane and carbon dioxide conversions can be enhanced and a higher hydrogen/carbon monoxide ratio can be obtained by increasing the amount of air. However, a decreased hydrogen yield could result due to the reverse water–gas shift reaction. A higher level of methane conversion and hydrogen/carbon monoxide ratio can be obtained with increased water addition. However, negative carbon dioxide conversion could result due to the water–gas shift and reverse carbon dioxide methanation reactions. The dry reforming reaction resulting in positive carbon dioxide conversion can only be found at a high reaction temperature. For all cases studied, low or negative carbon dioxide conversion was found because of carbon dioxide production from methane oxidation, water–gas shift, and reverse carbon dioxide methanation reactions. It was found that carbon dioxide conversion can be enhanced in the tri-reforming process by a small amount of added water. It was also found that first-law efficiency increased with increased reaction temperature because of higher hydrogen and carbon monoxide yields. Second-law efficiency was found to decrease with increased temperature because of higher exergy destruction due to a more complete chemical reaction at high temperatures. Full article
(This article belongs to the Special Issue Biofuel and Bioenergy Technology)
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9 pages, 900 KiB  
Article
Microbial Biodiesel Production by Direct Transesterification of Rhodotorula glutinis Biomass
by I-Ching Kuan, Wei-Chen Kao, Chun-Ling Chen and Chi-Yang Yu
Energies 2018, 11(5), 1036; https://doi.org/10.3390/en11051036 - 24 Apr 2018
Cited by 24 | Viewed by 5008
Abstract
(1) Background: Lipids derived from oleaginous microbes have become promising alternative feedstocks for biodiesel. This is mainly because the lipid production rate from microbes is one to two orders of magnitude higher than those of energy crops. However, the conventional process for converting [...] Read more.
(1) Background: Lipids derived from oleaginous microbes have become promising alternative feedstocks for biodiesel. This is mainly because the lipid production rate from microbes is one to two orders of magnitude higher than those of energy crops. However, the conventional process for converting these lipids to biodiesel still requires a large amount of energy and organic solvents; (2) Methods: In this study, an oleaginous yeast, Rhodotorula glutinis, was used for direct transesterification without lipid pre-extraction to produce biodiesel, using sulfuric acid or sodium hydroxide as a catalyst. Such processes decreased the amount of energy and organic solvents required simultaneously; (3) Results: When 1 g of dry R. glutinis biomass was subject to direct transesterification in 20 mL of methanol catalyzed by 0.6 M H2SO4 at 70 °C for 20 h, the fatty acid methyl ester (FAME) yield reached 111%. Using the same amount of biomass and methanol loading but catalyzed by 1 g/L NaOH at 70 °C for 10 h, the FAME yield reached 102%. The acid-catalyzed process showed a superior moisture tolerance; when the biomass contained 70% moisture, the FAME yield was 43% as opposed to 34% of the base-catalyzed counterpart; (4) Conclusions: Compared to conventional transesterification, which requires lipid pre-extraction, direct transesterification not only simplifies the process and shortens the reaction time, but also improves the FAME yield. Full article
(This article belongs to the Special Issue Biofuel and Bioenergy Technology)
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11 pages, 18178 KiB  
Article
Effect of Wall Boundary Layer Thickness on Power Performance of a Recirculation Microbial Fuel Cell
by Yan-Ming Chen, Chin-Tsan Wang and Yung-Chin Yang
Energies 2018, 11(4), 1003; https://doi.org/10.3390/en11041003 - 20 Apr 2018
Cited by 17 | Viewed by 4844
Abstract
Hydrodynamic boundary layer is a significant phenomenon occurring in a flow through a bluff body, and this includes the flow motion and mass transfer. Thus, it could affect the biofilm formation and the mass transfer of substrates in microbial fuel cells (MFCs). Therefore, [...] Read more.
Hydrodynamic boundary layer is a significant phenomenon occurring in a flow through a bluff body, and this includes the flow motion and mass transfer. Thus, it could affect the biofilm formation and the mass transfer of substrates in microbial fuel cells (MFCs). Therefore, understanding the role of hydrodynamic boundary layer thicknesses in MFCs is truly important. In this study, three hydrodynamic boundary layers of thickness 1.6, 4.1, and 5 cm were applied to the recirculation mode membrane-less MFC to investigate the electricity production performance. The results showed that the thin hydrodynamic boundary could enhance the voltage output of MFC due to the strong shear rate effect. Thus, a maximum voltage of 22 mV was obtained in the MFC with a hydrodynamic boundary layer thickness of 1.6 cm, and this voltage output obtained was 11 times higher than that of MFC with 5 cm hydrodynamic boundary layer thickness. Moreover, the charge transfer resistance of anode decreased with decreasing hydrodynamic boundary layer thickness. The charge transfer resistance of MFC with hydrodynamic boundary layer of thickness 1.6 cm was 39 Ω, which was 0.79 times lesser than that of MFC with 5 cm thickness. These observations would be useful for enhancing the performance of recirculation mode MFCs. Full article
(This article belongs to the Special Issue Biofuel and Bioenergy Technology)
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11 pages, 3003 KiB  
Article
Treatment of Oily Wastewater by the Optimization of Fe2O3 Calcination Temperatures in Innovative Bio-Electron-Fenton Microbial Fuel Cells
by Jung-Chen Wu, Wei-Mon Yan, Chin-Tsan Wang, Chen-Hao Wang, Yi-Hao Pai, Kai-Chin Wang, Yan-Ming Chen, Tzu-Hsuan Lan and Sangeetha Thangavel
Energies 2018, 11(3), 565; https://doi.org/10.3390/en11030565 - 06 Mar 2018
Cited by 13 | Viewed by 3694
Abstract
Due to the fact that Iron oxide (Fe2O3) is known to have a good effect on the photochemical reaction of catalysts, an investigation in this study into the enhancement of the degradation performance of bio-electro-Fenton microbial fuel cells (Bio-E-Fenton [...] Read more.
Due to the fact that Iron oxide (Fe2O3) is known to have a good effect on the photochemical reaction of catalysts, an investigation in this study into the enhancement of the degradation performance of bio-electro-Fenton microbial fuel cells (Bio-E-Fenton MFCs) was carried out using three photocatalytic cathodes. These cathodes were produced at different calcination temperatures of Fe2O3 ranging from 500 °C to 900 °C for realizing their performance as photo catalysts within the cathodic chamber of an MFC, and they were compared for their ability to degrade oily wastewater. Results show that a suitable temperature for the calcination of iron oxide would have a significantly positive effect on the performance of Bio-E-Fenton MFCs. An optimal calcination temperature of 500 °C for Fe2O3 in the electrode material of the cathode was observed to produce a maximum power density of 52.5 mW/m2 and a chemical oxygen demand (COD) degradation rate of oily wastewater (catholyte) of 99.3% within one hour of operation. These novel findings will be useful for the improvement of the performance and applications of Bio-E-Fenton MFCs and their future applications in the field of wastewater treatment. Full article
(This article belongs to the Special Issue Biofuel and Bioenergy Technology)
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13085 KiB  
Article
Numerical Investigation of the Air-Steam Biomass Gasification Process Based on Thermodynamic Equilibrium Model
by Qitai Eri, Wenzhen Wu and Xinjun Zhao
Energies 2017, 10(12), 2163; https://doi.org/10.3390/en10122163 - 18 Dec 2017
Cited by 17 | Viewed by 4418
Abstract
In the present work, the air-steam biomass gasification model with tar has been developed based on the equilibrium constants. The simulation results based on two different models (with and without tar) have been validated by the experimental data. The model with tar can [...] Read more.
In the present work, the air-steam biomass gasification model with tar has been developed based on the equilibrium constants. The simulation results based on two different models (with and without tar) have been validated by the experimental data. The model with tar can well predict the tar content in gasification; meanwhile, the predicted gas yield (GY), based on the model with tar, is much closer to the experimental data. The energy exchange between the gasifier and the surrounding has been studied based on the dimensionless heat transfer ratio (DHTR), and the relationship between DHTR and the process parameters is given by a formula. The influence of process parameters on the syngas composition, tar content, GY, lower heating value (LHV), and exergy efficiency have been researched. Full article
(This article belongs to the Special Issue Biofuel and Bioenergy Technology)
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Review

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14 pages, 1458 KiB  
Review
A Critical Analysis of Bio-Hydrocarbon Production in Bacteria: Current Challenges and Future Directions
by Ziaur Rahman, Javed Nawab, Bong Hyun Sung and Sun Chang Kim
Energies 2018, 11(10), 2663; https://doi.org/10.3390/en11102663 - 06 Oct 2018
Cited by 12 | Viewed by 4074
Abstract
As global fossil reserves are abruptly diminishing, there is a great need for bioenergy. Renewable and sustainable bioenergy products such as biofuels could fulfill the global energy demand, while minimizing global warming. Next-generation biofuels produced by engineered microorganisms are economical and do not [...] Read more.
As global fossil reserves are abruptly diminishing, there is a great need for bioenergy. Renewable and sustainable bioenergy products such as biofuels could fulfill the global energy demand, while minimizing global warming. Next-generation biofuels produced by engineered microorganisms are economical and do not rely on edible resources. The ideal biofuels are alcohols and n-alkanes, as they mimic the molecules in fossil fuels and possess high energy densities. Alcohols and n-alkane hydrocarbons (C2 to C18) have been produced using engineered microorganisms. However, it is difficult to optimize the complex metabolic networks in engineered microorganisms to obtain these valuable bio-hydrocarbons in high yields. Metabolic engineering results in drastic and adverse cellular changes that minimize production yield in microbes. Here, we provide an overview of the progress in next-generation biofuel (alcohols and n-alkanes) production in various engineered microorganisms and discuss the latest tools for strain development that improve biofuel production. Full article
(This article belongs to the Special Issue Biofuel and Bioenergy Technology)
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24 pages, 539 KiB  
Review
Wastewater Treatment and Biogas Recovery Using Anaerobic Membrane Bioreactors (AnMBRs): Strategies and Achievements
by Mohammed Ali Musa, Syazwani Idrus, Hasfalina Che Man and Nik Norsyahariati Nik Daud
Energies 2018, 11(7), 1675; https://doi.org/10.3390/en11071675 - 27 Jun 2018
Cited by 41 | Viewed by 6167
Abstract
Anaerobic digestion is one of the most essential treatment technologies applied to industrial and municipal wastewater treatment. Membrane-coupled anaerobic bioreactors have been used as one alternative to the conventional anaerobic digestion process. They are presumed to offer the advantage of completely reducing or [...] Read more.
Anaerobic digestion is one of the most essential treatment technologies applied to industrial and municipal wastewater treatment. Membrane-coupled anaerobic bioreactors have been used as one alternative to the conventional anaerobic digestion process. They are presumed to offer the advantage of completely reducing or minimizing the volume of sludge and increasing biogas production. However, researchers have consistently reported different kinds of fouling that resulted in the reduction of membrane life span. Depending on the strength of the effluent, factors such as high suspended and dissolved solids, fats, oil and grease, transmembrane pressure (TMP) and flux were reported as major contributors to the membrane fouling. Moreover, extracellular polymeric substances (EPSs) are an important biological substance that defines the properties of sludge flocs, including adhesion, hydrophobicity and settling and have been found to accelerate membrane fouling as well. Extensive studies of AnMBR have been done at laboratory while little is reported at the pilot scale. The significance of factors such as organic loading rates (OLRs), hydraulic retention time (HRT), pH and temperature on the operations of AnMBRs have been discussed. Microbial environmental conditions also played the most important role in the production of biogas and the chemical oxygen demand (COD) removal, but adverse effects of volatile fatty acids formation were reported as the main inhibitory effect. Generally, evaluating the potential parameters and most cost effective technology involved in the production of biogas and its inhibitory effects as well as the effluent quality after treatment is technically challenging, thus future research perspectives relating to food to microorganism F/M ratio interaction, sufficient biofilm within the reactor for microbial attachment was recommended. For the purpose of energy savings and meeting water quality discharge limit, the use of micro filtration was also proposed. Full article
(This article belongs to the Special Issue Biofuel and Bioenergy Technology)
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