| 1. |
- Chandolias, Konstantinos, et al.
(författare)
-
Protective effect of a reverse membrane bioreactor against toluene and naphthalene in anaerobic digestion
- 2022
-
Ingår i: Biotechnology and Applied Biochemistry. - : Wiley. - 1470-8744 .- 0885-4513. ; 69:3, s. 1267 -1274
-
Tidskriftsartikel (refereegranskat)abstract
- Raw syngas contains tar contaminants including toluene and naphthalene, which inhibit its conversion to methane. Cell encasement in a hydrophilic reverse membrane bioreactor (RMBR) could protect the cells from hydrophobic contaminants. This study aimed to investigate the inhibition of toluene and naphthalene and the effect of using RMBR. In this work, toluene and naphthalene were added at concentrations of 0.5–1.0 and 0.1–0.2 g/L in batch operation. In continuous operation, concentration of 0–6.44 g/L for toluene and 0–1.28 g/L for naphthalene were studied. The results showed that no inhibition was observed in batch operation for toluene and naphthalene at concentrations up to 1 and 0.2 g/L, respectively. In continuous operation of free cell bioreactors (FCBRs), inhibition of toluene and naphthalene started at 2.05 and 0.63 g/L, respectively. When they were present simultaneously, inhibition of toluene and naphthalene occurred at concentrations of 3.14 and 0.63 g/L, respectively. In continuous RMBRs, no inhibition for toluene and less inhibition for naphthalene were observed, resulting in higher methane production from RMBR than that of FCBR. These results indicated that RMBR system gave a better protection effect against inhibitors compared with FCBR.
|
|
| 2. |
- Lennartsson, Patrik, et al.
(författare)
-
Growth tolerance of Zygomycetes Mucor indicus in orange peel hydrolysate without detoxification
- 2012
-
Ingår i: Process Biochemistry. - : Elsevier Ltd. - 1359-5113 .- 1873-3298. ; 47:5, s. 836-842
-
Tidskriftsartikel (refereegranskat)abstract
- The capability of two zygomycetes strains, Mucor indicus and an isolate from tempeh (Rhizopus sp.), to grow on orange peel hydrolysate and their tolerance to its antimicrobial activity, was investigated. Both fungi, in particular M. indicus, tolerated up to 2% d-limonene in semi-synthetic media during cultivation in shake flasks, under aerobic as well as anaerobic conditions. The tolerance of M. indicus was also tested in a bioreactor, giving rise to varying results in the presence of 2% limonene. Furthermore, both strains were capable of consuming galacturonic acid, the main monomer of pectin, under aerobic conditions when no other carbon source was present. The orange peel hydrolysate was based on 12% (dry w/v) orange peels, containing d-limonene at a concentration of 0.6% (v/v), which no other microorganism has been reported to be able to ferment. However, the hydrolysate was utilised by M. indicus under aerobic conditions, resulting in production of 410 and 400 mg ethanol/g hexoses and 57 and 75 mg fungal biomass/g sugars from cultivations in shake flasks and a bioreactor, respectively. Rhizopus sp., however, was slow to germinate aerobically, and neither of the zygomycetes was able to consistently germinate in orange peel hydrolysate, under anaerobic conditions. The zygomycetes strains used in the present study demonstrated a relatively high resistance to the antimicrobial compounds present in orange peel hydrolysate, and they were capable of producing ethanol and biomass in the presence of limonene, particularly when cultivated with air supply.
|
|
| 3. |
- Westman, Johan, 1983, et al.
(författare)
-
Effects of encapsulation of microorganisms on product formation during microbial fermentations
- 2012
-
Ingår i: Applied Microbiology and Biotechnology. - : Springer Science and Business Media LLC. - 1432-0614 .- 0175-7598. ; 96:6, s. 1441-1454
-
Forskningsöversikt (refereegranskat)abstract
- This paper reviews the latest developments in microbial products by encapsulated microorganisms in a liquid core surrounded by natural or synthetic membranes. Cells can be encapsulated in one or several steps using liquid droplet formation, pregel dissolving, coacervation, and interfacial polymerization. The use of encapsulated yeast and bacteria for fermentative production of ethanol, lactic acid, biogas, l-phenylacetylcarbinol, 1,3-propanediol, and riboflavin has been investigated. Encapsulated cells have furthermore been used for the biocatalytic conversion of chemicals. Fermentation, using encapsulated cells, offers various advantages compared to traditional cultivations, e.g., higher cell density, faster fermentation, improved tolerance of the cells to toxic media and high temperatures, and selective exclusion of toxic hydrophobic substances. However, mass transfer through the capsule membrane as well as the robustness of the capsules still challenge the utilization of encapsulated cells. The history and the current state of applying microbial encapsulation for production processes, along with the benefits and drawbacks concerning productivity and general physiology of the encapsulated cells, are discussed.
|
|
| 4. |
- Ylitervo, Päivi
(författare)
-
Concepts for improving ethanol productivity from lignocellulosic materials : encapsulated yeast and membrane bioreactors
- 2014
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Lignocellulosic biomass is a potential feedstock for production of sugars, which can be fermented into ethanol. The work presented in this thesis proposes some solutions to overcome problems with suboptimal process performance due to elevated cultivation temperatures and inhibitors present during ethanol production from lignocellulosic materials. In particular, continuous processes operated at high dilution rates with high sugar utilisation are attractive for ethanol fermentation, as this can result in higher ethanol productivity. Both encapsulation and membrane bioreactors were studied and developed to achieve rapid fermentation at high yeast cell density. My studies showed that encapsulated yeast is more thermotolerant than suspended yeast. The encapsulated yeast could successfully ferment all glucose during five consecutive batches, 12 h each at 42 °C. In contrast, freely suspended yeast was inactivated already in the second or third batch. One problem with encapsulation is, however, the mechanical robustness of the capsule membrane. If the capsules are exposed to e.g. high shear forces, the capsule membrane may break. Therefore, a method was developed to produce more robust capsules by treating alginate-chitosan-alginate (ACA) capsules with 3-aminopropyltriethoxysilane (APTES) to get polysiloxane-ACA capsules. Of the ACA-capsules treated with 1.5% APTES, only 0–2% of the capsules broke, while 25% of the untreated capsules ruptured within 6 h in a shear test. In this thesis membrane bioreactors (MBR), using either a cross-flow or a submerged membrane, could successfully be applied to retain the yeast inside the reactor. The cross-flow membrane was operated at a dilution rate of 0.5 h-1 whereas the submerged membrane was tested at several dilution rates, from 0.2 up to 0.8 h-1. Cultivations at high cell densities demonstrated an efficient in situ detoxification of very high furfural levels of up to 17 g L-1 in the feed medium when using a MBR. The maximum yeast density achieved in the MBR was more than 200 g L-1. Additionally, ethanol fermentation of nondetoxified spruce hydrolysate was possible at a high feeding rate of 0.8 h-1 by applying a submerged membrane bioreactor, resulting in ethanol productivities of up to 8 g L-1 h-1. In conclusion, this study suggests methods for rapid continuous ethanol production even at stressful elevated cultivation temperatures or inhibitory conditions by using encapsulation or membrane bioreactors and high cell density cultivations.
|
|
| 5. |
- Ylitervo, Päivi, et al.
(författare)
-
Continuous Ethanol Production with a Membrane Bioreactor at High Acetic Acid Concentrations
- 2014
-
Ingår i: Membranes. - : MDPI. - 2077-0375. ; 4:3, s. 372-387
-
Tidskriftsartikel (refereegranskat)abstract
- The release of inhibitory concentrations of acetic acid from lignocellulosic raw materials during hydrolysis is one of the main concerns for 2nd generation ethanol production. The undissociated form of acetic acid can enter the cell by diffusion through the plasma membrane and trigger several toxic effects, such as uncoupling and lowered intracellular pH. The effect of acetic acid on the ethanol production was investigated in continuous cultivations by adding medium containing 2.5 to 20.0 g•L−1 acetic acid at pH 5.0, at a dilution rate of 0.5 h−1. The cultivations were performed at both high (~25 g•L−1) and very high (100–200 g•L−1) yeast concentration by retaining the yeast cells inside the reactor by a cross-flow membrane in a membrane bioreactor. The yeast was able to steadily produce ethanol from 25 g•L−1 sucrose, at volumetric rates of 5–6 g•L−1•h−1 at acetic acid concentrations up to 15.0 g•L−1. However, the yeast continued to produce ethanol also at a concentration of 20 g•L−1 acetic acid but at a declining rate. The study thereby demonstrates the great potential of the membrane bioreactor for improving the robustness of the ethanol production based on lignocellulosic raw materials.
|
|
| 6. |
- Ylitervo, Päivi, 1983, et al.
(författare)
-
Ethanol production at elevated temperatures using encapsulation of yeast
- 2011
-
Ingår i: Journal of Biotechnology. - : Elsevier BV. - 1873-4863 .- 0168-1656. ; 156:1, s. 22-29
-
Tidskriftsartikel (refereegranskat)abstract
- The ability of macroencapsulated Saccharomyces cerevisiae CBS 8066 to produce ethanol at elevated temperatures was investigated in consecutive batch and continuous cultures. Prior to cultivation yeast was confined inside alginate-chitosan capsules composed of an outer semi-permeable membrane and an inner liquid core. The encapsulated yeast could successfully ferment 30 g/L glucose and produce ethanol at a high yield in five consecutive batches of 12 h duration at 42 degrees C, while freely suspended yeast was completely inactive already in the third batch. A high ethanol production was observed also through the first 48 h at 40 degrees C during continuous cultivation at D = 0.2 h(-1) when using encapsulated cells. The ethanol production slowly decreased in the following days at 40 degrees C. The ethanol production was also measured in a continuous cultivation in which the temperature was periodically increased to 42-45 degrees C and lowered to 37 degrees C again in periods of 12 h. Our investigation shows that a non-thermotolerant yeast strain improved its heat tolerance upon encapsulation, and could produce ethanol at temperatures as high as 45 degrees C for a short time. The possibility of performing fermentations at higher temperatures would greatly improve the enzymatic hydrolysis in simultaneous saccharification and fermentation (SSF) processes and thereby make the bioethanol production process more economically feasible.
|
|
| 7. |
- Ylitervo, Päivi, et al.
(författare)
-
Fermentation of lignocellulosic hydrolyzate using a submerged membrane bioreactor at high dilution rates
- 2014
-
Ingår i: Bioresource Technology. - : Elsevier. - 0960-8524 .- 1873-2976.
-
Tidskriftsartikel (refereegranskat)abstract
- A submerged membrane bioreactor (sMBR) was developed to ferment toxic lignocellulosic hydrolyzate to ethanol. The sMBR achieved high cell density of Saccharomyces cerevisiae during continuous cultivation of the hydrolyzate by completely retaining all yeast cells inside the sMBR. The performance of the sMBR was evaluated based on the ethanol yield and productivity at the dilution rates 0.2, 0.4, 0.6, and 0.8 h-1 with the increase of dilution rate. Results show that the yeast in the sMBR was able to ferment the wood hydrolyzate even at high dilution rates, attaining a maximum volumetric ethanol productivity of 7.94 ± 0.10 g L-1 h-1 at a dilution rate of 0.8 h-1. Ethanol yields were stable at 0.44 ± 0.02 g g-1 during all the tested dilution rates, and the ethanol productivity increased from 2.16 ± 0.15 to 7.94 ± 0.10 g L-1 h-1. The developed sMBR systems running at high yeast density demonstrates a potential for a rapid and productive ethanol production from wood hydrolyzate.
|
|
| 8. |
- Ylitervo, Päivi, 1983, et al.
(författare)
-
Impact of Furfural on Rapid Ethanol Production Using a Membrane Bioreactor
- 2013
-
Ingår i: Energies. - : MDPI AG. - 1996-1073 .- 1996-1073. ; 6:3, s. 1604-1617
-
Tidskriftsartikel (refereegranskat)abstract
- A membrane bioreactor was developed to counteract the inhibition effect of furfural in ethanol production. Furfural, a major inhibitor in lignocellulosic hydrolyzates, is a highly toxic substance which is formed from pentose sugars released during the acidic degradation of lignocellulosic materials. Continuous cultivations with complete cell retention were performed at a high dilution rate of 0.5 h(-1). Furfural was added directly into the bioreactor by pulse injection or by addition into the feed medium to obtain furfural concentrations ranging from 0.1 to 21.8 g L-1. At all pulse injections of furfural, the yeast was able to convert the furfural very rapidly by in situ detoxification. When injecting 21.8 g L-1 furfural to the cultivation, the yeast converted it by a specific conversion rate of 0.35 g g(-1) h(-1). At high cell density, Saccharomyces cerevisiae could tolerate very high furfural levels without major changes in the ethanol production. During the continuous cultures when up to 17.0 g L-1 furfural was added to the inlet medium, the yeast successfully produced ethanol, whereas an increase of furfural to 18.6 and 20.6 g L-1 resulted in a rapidly decreasing ethanol production and accumulation of sugars in the permeate. This study show that continuous ethanol fermentations by total cell retention in a membrane bioreactor has a high furfural tolerance and can conduct rapid in situ detoxification of medium containing high furfural concentrations.
|
|
| 9. |
- Ylitervo, Päivi, et al.
(författare)
-
Mechanically robust polysiloxane : ACA capsules for prolonged ethanol production
- 2013
-
Ingår i: Journal of chemical technology and biotechnology (1986). - : John Wiley & Sons Ltd.. - 0268-2575 .- 1097-4660. ; 88:6, s. 1080-1088
-
Tidskriftsartikel (refereegranskat)abstract
- Fermentation using encapsulated yeast leads to more robust ethanol production from lignocellulose hydrolyzates. Encapsulated yeast is much more tolerant to inhibitors present in hydrolyzates, and fermentation is faster due to increased total cell density. For industrial applications, capsules must be made robust enough to endure long periods and numerous cultivations without breaking. Liquid core alginate–chitosan–alginate (ACA) capsules containing Saccharomyces cerevisiae were produced by the liquid-droplet-forming method and treated with hydrolyzed 3-aminopropyltrietoxysilane (hAPTES) forming very glossy capsules. Capsules produced with 3.0% hAPTES showed the best mechanical robustness but no ethanol could be produced in dilute-acid spruce hydrolyzate using these capsules. Untreated ACA capsules gave the highest ethanol production but demonstrated poor mechanical robustness. 25% of the ACA capsules ruptured within 6 h in the shear test. Capsules treated with 1.5% hAPTES were significantly stronger, since only 0–2% of these capsules broke. Moreover, the ethanol production in the fifth consecutive cultivation in lignocellulose hydrolyzate was nearly as high as for untreated ACA capsules. The mechanical robustness of ACA capsules can be easily improved by treating the capsules with hAPTES. ACA capsules treated with 1.5% hAPTES showed excellent mechanical robustness and a similar ethanol production profile to untreated ACA capsules. © 2012 Society of Chemical Industry
|
|
| 10. |
- Ylitervo, Päivi, 1983, et al.
(författare)
-
Membrane bioreactors' potential for ethanol and biogas production: a review
- 2013
-
Ingår i: Environmental Technology (United Kingdom). - : Informa UK Limited. - 1479-487X .- 0959-3330. ; 34:13-14, s. 1711-1723
-
Tidskriftsartikel (refereegranskat)abstract
- Companies developing and producing membranes for different separation purposes, as well as the market for these, have markedly increased in numbers over the last decade. Membrane and separation technology might well contribute to making fuel ethanol and biogas production from lignocellulosic materials more economically viable and productive. Combining biological processes with membrane separation techniques in a membrane bioreactor (MBR) increases cell concentrations extensively in the bioreactor. Such a combination furthermore reduces product inhibition during the biological process, increases product concentration and productivity, and simplifies the separation of product and/or cells. Various MBRs have been studied over the years, where the membrane is either submerged inside the liquid to be filtered, or placed in an external loop outside the bioreactor. All configurations have advantages and drawbacks, as reviewed in this paper. The current review presents an account of the membrane separation technologies, and the research performed on MBRs, focusing on ethanol and biogas production. The advantages and potentials of the technology are elucidated.
|
|
