Special Issue "Bioconversion Processes"

A special issue of Fermentation (ISSN 2311-5637).

Deadline for manuscript submissions: closed (30 November 2017)

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

Special Issue Editor

Guest Editor
Prof. Dr. Christian Kennes

Department of Chemical Engineering, Faculty of Sciences, University of La Coruña, 15008—La Coruña, Spain
Website | E-Mail
Interests: waste gas treatment; wastewater treatment; fermentation technology; biodegradation; bioconversion; biofuels; biorefinery

Special Issue Information

Dear Colleagues,

Compared to conventional chemical technologies and other similar industrial processes, bioprocesses represent a more sustainable and environmentally-friendly alternative for the production of fuels and platform chemicals. In biorefineries, different kinds of feedstocks, such as biomass or lignocellulosic materials in general, can be used and fermented by microorganisms (e.g., bacteria, fungi, algae), after some pretreatment steps, to produce high added-value metabolites. More recently, wastes, wastewaters and also waste gases have been shown to be suitable for resource recovery or for their bioconversion to (bio)fuels (e.g., ethanol, butanol, hexanol, biodiesel, biohydrogen, biogas) or other commercial products (e.g., biopolymers). In this sense, much effort has also been made to bioconvert greenhouse gases, such as CO2, into useful products.

The goal of this Special Issue is to publish both recent innovative research data, as well as review papers on the fermentation of different types of substrates to commercial (bio)fuels and (bio)products, mainly focusing on the bioconversion of pollutants in solid, liquid, or gas phases (wastes, wastewaters, waste gases).

Prof. Dr. Christian Kennes
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. Fermentation is an international peer-reviewed open access quarterly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) is waived for well-prepared manuscripts submitted to this issue. 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

  • Acetogens
  • Algae
  • Bioalcohols
  • Biodiesel
  • Biogas
  • Biohydrogen
  • Bioreactor
  • Carbon dioxide (CO2)
  • Carbon monoxide (CO)
  • Clostridia
  • Fungi
  • Life cycle assessment (LCA)
  • Metabolic engineering
  • Methane (CH4)
  • Microbial electrosynthesis (MES)
  • Polyhydroxyalkanoates
  • Solid waste
  • Syngas
  • Waste gas
  • Wastewater

Published Papers (11 papers)

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Editorial

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Open AccessEditorial Bioconversion Processes
Fermentation 2018, 4(2), 21; https://doi.org/10.3390/fermentation4020021
Received: 10 March 2018 / Revised: 20 March 2018 / Accepted: 21 March 2018 / Published: 23 March 2018
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Abstract
Bioprocesses represent a promising and environmentally friendly option to replace the well-established chemical processes used nowadays for the production of platform chemicals, fuels, and other commercial products[...] Full article
(This article belongs to the Special Issue Bioconversion Processes) Printed Edition available

Research

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Open AccessFeature PaperArticle Integrated Process for Extraction of Wax as a Value-Added Co-Product and Improved Ethanol Production by Converting Both Starch and Cellulosic Components in Sorghum Grains
Fermentation 2018, 4(1), 12; https://doi.org/10.3390/fermentation4010012
Received: 18 January 2018 / Revised: 5 February 2018 / Accepted: 11 February 2018 / Published: 13 February 2018
Cited by 2 | PDF Full-text (529 KB) | HTML Full-text | XML Full-text
Abstract
Grain sorghum is a potential feedstock for fuel ethanol production due to its high starch content, which is equivalent to that of corn, and has been successfully used in several commercial corn ethanol plants in the United States. Some sorghum grain varieties contain
[...] Read more.
Grain sorghum is a potential feedstock for fuel ethanol production due to its high starch content, which is equivalent to that of corn, and has been successfully used in several commercial corn ethanol plants in the United States. Some sorghum grain varieties contain significant levels of surface wax, which may interact with enzymes and make them less efficient toward starch hydrolysis. On the other hand, wax can be recovered as a valuable co-product and as such may help improve the overall process economics. Sorghum grains also contain lignocellulosic materials in the hulls, which can be converted to additional ethanol. An integrated process was developed, consisting of the following steps: 1. Extraction of wax with boiling ethanol, which is the final product of the proposed process; 2. Pretreatment of the dewaxed grains with dilute sulfuric acid; 3. Mashing and fermenting of the pretreated grains to produce ethanol. During the fermentation, commercial cellulase was also added to release fermentable sugars from the hulls, which then were converted to additional ethanol. The advantages of the developed process were illustrated with the following results: (1) Wax extracted (determined by weight loss): ~0.3 wt % of total mass. (2) Final ethanol concentration at 25 wt % solid using raw grains: 86.1 g/L. (3) Final ethanol concentration at 25 wt % solid using dewaxed grains: 106.2 g/L (23.3% improvement). (4) Final ethanol concentration at 25 wt % solid using dewaxed and acid-treated grains (1 wt % H2SO4) plus cellulase (CTec2): 117.8 g/L (36.8% improvement). Full article
(This article belongs to the Special Issue Bioconversion Processes) Printed Edition available
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Open AccessFeature PaperArticle Green Biorefinery of Giant Miscanthus for Growing Microalgae and Biofuel Production
Fermentation 2017, 3(4), 66; https://doi.org/10.3390/fermentation3040066
Received: 13 November 2017 / Revised: 1 December 2017 / Accepted: 7 December 2017 / Published: 11 December 2017
Cited by 1 | PDF Full-text (1141 KB) | HTML Full-text | XML Full-text
Abstract
In this study, an innovative green biorefinery system was successfully developed to process the green biomass into multiple biofuels and bioproducts. In particular, fresh giant miscanthus was separated into a solid stream (press cake) and a liquid stream (press juice) using a screw
[...] Read more.
In this study, an innovative green biorefinery system was successfully developed to process the green biomass into multiple biofuels and bioproducts. In particular, fresh giant miscanthus was separated into a solid stream (press cake) and a liquid stream (press juice) using a screw press. The juice was used to cultivate microalga Chlorella vulgaris, which was further thermochemically converted via thermogravimetry analysis (TGA) and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) analysis, resulting in an approximately 80% conversion. In addition, the solid cake of miscanthus was pretreated with dilute sulfuric acid and used as the feedstock for bioethanol production. The results showed that the miscanthus juice could be a highly nutritious source for microalgae that are a promising feedstock for biofuels. The highest cell density was observed in the 15% juice medium. Sugars released from the miscanthus cake were efficiently fermented to ethanol using Saccharomyces cerevisiae through a simultaneous saccharification and fermentation (SSF) process, with 88.4% of the theoretical yield. Full article
(This article belongs to the Special Issue Bioconversion Processes) Printed Edition available
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Open AccessFeature PaperArticle Tuning of the Carbon-to-Nitrogen Ratio for the Production of l-Arginine by Escherichia coli
Fermentation 2017, 3(4), 60; https://doi.org/10.3390/fermentation3040060
Received: 6 October 2017 / Revised: 4 November 2017 / Accepted: 6 November 2017 / Published: 10 November 2017
Cited by 3 | PDF Full-text (1832 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
l-arginine, an amino acid with a growing range of applications within the pharmaceutical, cosmetic, food, and agricultural industries, can be produced by microbial fermentation. Although it is the most nitrogen-rich amino acid, reports on the nitrogen supply for its fermentation are scarce.
[...] Read more.
l-arginine, an amino acid with a growing range of applications within the pharmaceutical, cosmetic, food, and agricultural industries, can be produced by microbial fermentation. Although it is the most nitrogen-rich amino acid, reports on the nitrogen supply for its fermentation are scarce. In this study, the nitrogen supply for the production of l-arginine by a genetically modified Escherichia coli strain was optimised in bioreactors. Different nitrogen sources were screened and ammonia solution, ammonium sulphate, ammonium phosphate dibasic, and ammonium chloride were the most favourable nitrogen sources for l-arginine synthesis. The key role of the C/N ratio for l-arginine production was demonstrated for the first time. The optimal C/N molar ratio to maximise l-arginine production while minimising nitrogen waste was found to be 6, yielding approximately 2.25 g/L of l-arginine from 15 g/L glucose with a productivity of around 0.11 g/L/h. Glucose and ammonium ion were simultaneously utilized, showing that this ratio provided a well-balanced equilibrium between carbon and nitrogen metabolisms. Full article
(This article belongs to the Special Issue Bioconversion Processes) Printed Edition available
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Open AccessFeature PaperArticle Techno-Economic and Life Cycle Assessment of Wastewater Management from Potato Starch Production: Present Status and Alternative Biotreatments
Fermentation 2017, 3(4), 56; https://doi.org/10.3390/fermentation3040056
Received: 13 September 2017 / Revised: 13 October 2017 / Accepted: 16 October 2017 / Published: 23 October 2017
Cited by 2 | PDF Full-text (1118 KB) | HTML Full-text | XML Full-text
Abstract
Potato liquor, a byproduct of potato starch production, is steam-treated to produce protein isolate. The heat treated potato liquor (HTPL), containing significant amounts of organic compounds, still needs to be further treated before it is discarded. Presently, the most common strategy for HTPL
[...] Read more.
Potato liquor, a byproduct of potato starch production, is steam-treated to produce protein isolate. The heat treated potato liquor (HTPL), containing significant amounts of organic compounds, still needs to be further treated before it is discarded. Presently, the most common strategy for HTPL management is concentrating it via evaporation before using it as a fertilizer. In this study, this scenario was compared with two biotreatments: (1) fermentation using filamentous fungus R. oryzae to produce a protein-rich biomass, and (2) anaerobic digestion of the HTPL to produce biogas. Technical, economic and environmental analyses were performed via computational simulation to determine potential benefits of the proposed scenarios to a plant discarding 19.64 ton/h of HTPL. Fungal cultivation was found to be the preferred scenario with respect to the economic aspects. This scenario needed only 46% of the investment needed for the evaporation scenario. In terms of the environmental impacts, fungal cultivation yielded the lowest impacts in the acidification, terrestrial eutrophication, freshwater eutrophication, marine eutrophication and freshwater ecotoxicity impact categories. The lowest impact in the climate change category was obtained when using the HTPL for anaerobic digestion. Full article
(This article belongs to the Special Issue Bioconversion Processes) Printed Edition available
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Open AccessArticle Production of Fungal Biomass for Feed, Fatty Acids, and Glycerol by Aspergillus oryzae from Fat-Rich Dairy Substrates
Fermentation 2017, 3(4), 48; https://doi.org/10.3390/fermentation3040048
Received: 31 August 2017 / Revised: 16 September 2017 / Accepted: 19 September 2017 / Published: 22 September 2017
Cited by 4 | PDF Full-text (1347 KB) | HTML Full-text | XML Full-text
Abstract
Dairy waste is a complex mixture of nutrients requiring an integrated strategy for valorization into various products. The present work adds insights into the conversion of fat-rich dairy products into biomass, glycerol, and fatty acids via submerged cultivation with edible filamentous fungi. The
[...] Read more.
Dairy waste is a complex mixture of nutrients requiring an integrated strategy for valorization into various products. The present work adds insights into the conversion of fat-rich dairy products into biomass, glycerol, and fatty acids via submerged cultivation with edible filamentous fungi. The pH influenced fat degradation, where Aspergillus oryzae lipase was more active at neutral than acidic pH (17 g/L vs. 0.5 g/L of released glycerol); the same trend was found during cultivation in crème fraiche (12 g/L vs. 1.7 g/L of released glycerol). In addition to glycerol, as a result of fat degradation, up to 3.6 and 4.5 g/L of myristic and palmitic acid, respectively, were released during A. oryzae growth in cream. The fungus was also able to grow in media containing 16 g/L of lactic acid, a common contaminant of dairy waste, being beneficial to naturally increase the initial acidic pH and trigger fat degradation. Considering that lactose consumption is suppressed in fat-rich media, a two-stage cultivation for conversion of dairy waste is also proposed in this work. Such an approach would provide biomass for possibly feed or human consumption, fatty acids, and an effluent of low organic matter tackling environmental and social problems associated with the dairy sector. Full article
(This article belongs to the Special Issue Bioconversion Processes) Printed Edition available
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Open AccessFeature PaperArticle Optimization of the Enzymatic Saccharification Process of Milled Orange Wastes
Fermentation 2017, 3(3), 37; https://doi.org/10.3390/fermentation3030037
Received: 2 July 2017 / Revised: 18 July 2017 / Accepted: 30 July 2017 / Published: 1 August 2017
Cited by 1 | PDF Full-text (2463 KB) | HTML Full-text | XML Full-text
Abstract
Orange juice production generates a very high quantity of residues (Orange Peel Waste or OPW-50–60% of total weight) that can be used for cattle feed as well as feedstock for the extraction or production of essential oils, pectin and nutraceutics and several monosaccharides
[...] Read more.
Orange juice production generates a very high quantity of residues (Orange Peel Waste or OPW-50–60% of total weight) that can be used for cattle feed as well as feedstock for the extraction or production of essential oils, pectin and nutraceutics and several monosaccharides by saccharification, inversion and enzyme-aided extraction. As in all solid wastes, simple pretreatments can enhance these processes. In this study, hydrothermal pretreatments and knife milling have been analyzed with enzyme saccharification at different dry solid contents as the selection test: simple knife milling seemed more appropriate, as no added pretreatment resulted in better final glucose yields. A Taguchi optimization study on dry solid to liquid content and the composition of the enzymatic cocktail was undertaken. The amounts of enzymatic preparations were set to reduce their impact on the economy of the process; however, as expected, the highest amounts resulted in the best yields to glucose and other monomers. Interestingly, the highest content in solid to liquid (11.5% on dry basis) rendered the best yields. Additionally, in search for process economy with high yields, operational conditions were set: medium amounts of hemicellulases, polygalacturonases and β-glucosidases. Finally, a fractal kinetic modelling of results for all products from the saccharification process indicated very high activities resulting in the liberation of glucose, fructose and xylose, and very low activities to arabinose and galactose. High activity on pectin was also observed, but, for all monomers liberated initially at a fast rate, high hindrances appeared during the saccharification process. Full article
(This article belongs to the Special Issue Bioconversion Processes) Printed Edition available
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Open AccessArticle Codigestion of Untreated and Treated Sewage Sludge with the Organic Fraction of Municipal Solid Wastes
Fermentation 2017, 3(3), 35; https://doi.org/10.3390/fermentation3030035
Received: 5 June 2017 / Revised: 4 July 2017 / Accepted: 15 July 2017 / Published: 27 July 2017
Cited by 3 | PDF Full-text (1395 KB) | HTML Full-text | XML Full-text
Abstract
Disposal of biodegradable waste has become a stringent waste management and environmental issue. As a result, anaerobic digestion has become one of the best alternative technology to treat the organic fraction of municipal solid wastes and can be an important source of bioenergy.
[...] Read more.
Disposal of biodegradable waste has become a stringent waste management and environmental issue. As a result, anaerobic digestion has become one of the best alternative technology to treat the organic fraction of municipal solid wastes and can be an important source of bioenergy. This study focuses on the evaluation of biogas and methane yields from the digestion and co-digestion of mixtures of waste untreated sludge and the organic fraction of municipal solid wastes. These are compared with the results obtained from the digestion and codigestion of mixtures containing waste active sludge and the organic fraction of municipal solid wastes. The two types of substrates were used to perform biomethanation potential tests, in mesophilic conditions (35 °C) at lab scale. It was observed a maximum biogas yield for 100% of untreated sewage sludge, corresponding to 0.644 Nm 3 /kg VS and 0.499 Nm 3 /kg VS of biogas and methane production respectively. The study also demonstrates the possibility of increasing biogas production up to 36% and methane content up to 94% using waste untreated sludge substrate in both digestion and codigestion, compared to waste active sludge substrate. Full article
(This article belongs to the Special Issue Bioconversion Processes) Printed Edition available
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Open AccessFeature PaperArticle Engineering Yarrowia lipolytica for Enhanced Production of Lipid and Citric Acid
Fermentation 2017, 3(3), 34; https://doi.org/10.3390/fermentation3030034
Received: 2 May 2017 / Revised: 8 July 2017 / Accepted: 12 July 2017 / Published: 17 July 2017
Cited by 2 | PDF Full-text (2077 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Increasing demand for plant oil for food, feed, and fuel production has led to food-fuel competition, higher plant lipid cost, and more need for agricultural land. On the other hand, the growing global production of biodiesel has increased the production of glycerol as
[...] Read more.
Increasing demand for plant oil for food, feed, and fuel production has led to food-fuel competition, higher plant lipid cost, and more need for agricultural land. On the other hand, the growing global production of biodiesel has increased the production of glycerol as a by-product. Efficient utilization of this by-product can reduce biodiesel production costs. We engineered Yarrowia lipolytica (Y. lipolytica) at various metabolic levels of lipid biosynthesis, degradation, and regulation for enhanced lipid and citric acid production. We used a one-step double gene knock-in and site-specific gene knock-out strategy. The resulting final strain combines the overexpression of homologous DGA1 and DGA2 in a POX-deleted background, and deletion of the SNF1 lipid regulator. This increased lipid and citric acid production in the strain under nitrogen-limiting conditions (C/N molar ratio of 60). The engineered strain constitutively accumulated lipid at a titer of more than 4.8 g/L with a lipid content of 53% of dry cell weight (DCW). The secreted citric acid reached a yield of 0.75 g/g (up to ~45 g/L) from pure glycerol in 3 days of batch fermentation using a 1-L bioreactor. This yeast cell factory was capable of simultaneous lipid accumulation and citric acid secretion. It can be used in fed-batch or continuous bioprocessing for citric acid recovery from the supernatant, along with lipid extraction from the harvested biomass. Full article
(This article belongs to the Special Issue Bioconversion Processes) Printed Edition available
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Review

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Open AccessFeature PaperReview Biological Production of 3-Hydroxypropionic Acid: An Update on the Current Status
Fermentation 2018, 4(1), 13; https://doi.org/10.3390/fermentation4010013
Received: 22 January 2018 / Revised: 5 February 2018 / Accepted: 9 February 2018 / Published: 13 February 2018
Cited by 2 | PDF Full-text (2028 KB) | HTML Full-text | XML Full-text
Abstract
The production of high added-value chemicals from renewable resources is a necessity in our attempts to switch to a more sustainable society. 3-Hydroxypropionic acid (3HP) is a promising molecule that can be used for the production of an important array of high added-value
[...] Read more.
The production of high added-value chemicals from renewable resources is a necessity in our attempts to switch to a more sustainable society. 3-Hydroxypropionic acid (3HP) is a promising molecule that can be used for the production of an important array of high added-value chemicals, such as 1,3-propanediol, acrylic acid, acrylamide, and bioplastics. Biological production of 3HP has been studied extensively, mainly from glycerol and glucose, which are both renewable resources. To enable conversion of these carbon sources to 3HP, extensive work has been performed to identify appropriate biochemical pathways and the enzymes that are involved in them. Novel enzymes have also been identified and expressed in host microorganisms to improve the production yields of 3HP. Various process configurations have also been proposed, resulting in improved conversion yields. The intense research efforts have resulted in the production of as much as 83.8 g/L 3HP from renewable carbon resources, and a system whereby 3-hydroxypropionitrile was converted to 3HP through whole-cell catalysis which resulted in 184.7 g/L 3HP. Although there are still challenges and difficulties that need to be addressed, the research results from the past four years have been an important step towards biological production of 3HP at the industrial level. Full article
(This article belongs to the Special Issue Bioconversion Processes) Printed Edition available
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Open AccessReview Utilization of Volatile Fatty Acids from Microalgae for the Production of High Added Value Compounds
Fermentation 2017, 3(4), 54; https://doi.org/10.3390/fermentation3040054
Received: 9 September 2017 / Revised: 4 October 2017 / Accepted: 9 October 2017 / Published: 15 October 2017
Cited by 2 | PDF Full-text (430 KB) | HTML Full-text | XML Full-text
Abstract
Volatile Fatty Acids (VFA) are small organic compounds that have attracted much attention lately, due to their use as a carbon source for microorganisms involved in the production of bioactive compounds, biodegradable materials and energy. Low cost production of VFA from different types
[...] Read more.
Volatile Fatty Acids (VFA) are small organic compounds that have attracted much attention lately, due to their use as a carbon source for microorganisms involved in the production of bioactive compounds, biodegradable materials and energy. Low cost production of VFA from different types of waste streams can occur via dark fermentation, offering a promising approach for the production of biofuels and biochemicals with simultaneous reduction of waste volume. VFA can be subsequently utilized in fermentation processes and efficiently transformed into bioactive compounds that can be used in the food and nutraceutical industry for the development of functional foods with scientifically sustained claims. Microalgae are oleaginous microorganisms that are able to grow in heterotrophic cultures supported by VFA as a carbon source and accumulate high amounts of valuable products, such as omega-3 fatty acids and exopolysaccharides. This article reviews the different types of waste streams in concert with their potential to produce VFA, the possible factors that affect the VFA production process and the utilization of the resulting VFA in microalgae fermentation processes. The biology of VFA utilization, the potential products and the downstream processes are discussed in detail. Full article
(This article belongs to the Special Issue Bioconversion Processes) Printed Edition available
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