| 1. |
- Millati, Ria, 1972, et al.
(författare)
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Ethanol production from xylose and wood hydrolyzate by Mucor indicus at different aeration rates
- 2008
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Ingår i: BioResources. - : North Carolina State University. - 1930-2126. ; 3:4, s. 1020-1029
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Tidskriftsartikel (refereegranskat)abstract
- The fungus Mucor indicus is able to produce ethanol from xylose as well as dilute-acid lignocellulosic hydrolyzates. The fungus completely assimilated 10 g/L xylose as the sole carbon and energy source within 32 to 65 h at an aeration rate of 0.1 to 1.0 vvm. The highest ethanol yield was 0.16 g/g at 0.1 vvm. Xylitol was formed intermediately with a maximum yield of 0.22 g/g at 0.5 vvm., but disappeared towards the end of experiments. During cultivation in a mixture of xylose and glucose, the fungus did not assimilate xylose as long as glucose was present in the medium. The anaerobic cultivation of the fungus in the hydrolyzate containing 20% xylose and 80% hexoses resulted in no assimilation of xylose but complete consumption of the hexoses in less than 15 h. The ethanol yield was 0.44 g/g. However, the xylose in the hydrolyzate was consumed when the media were aerated at 0.067 to 0.333 vvm. The best ethanol yield was 0.44 g/g at 0.067 vvm. The results of this study suggest that M. indicus hydrolyzate can be first fermented anaerobically for hexose assimilation and subsequently continued under oxygen-limited conditions for xylose fermentation.
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| 2. |
- Chandolias, Konstantinos, et al.
(författare)
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Protective effect of a reverse membrane bioreactor against toluene and naphthalene in anaerobic digestion
- 2022
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Ingår i: Biotechnology and Applied Biochemistry. - : Wiley. - 1470-8744 .- 0885-4513. ; 69:3, s. 1267 -1274
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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.
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| 3. |
- Ferreira, Jorge A., et al.
(författare)
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Spent sulphite liquor for cultivation of an edible Rhizopus sp.
- 2012
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Ingår i: BioResources. - : North Carolina State University: College of Natural Resources. - 1930-2126. ; 7:1, s. 173-188
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Tidskriftsartikel (refereegranskat)abstract
- Spent sulphite liquor, the major byproduct from the sulphite pulp production process, was diluted to 50% and used for production of an edible zygomycete Rhizopus sp. The focus was on production, yield, and composition of the fungal biomass composition. The fungus grew well at 20 to 40°C, but 32°C was found to be preferable compared to 20 and 40°C in terms of biomass production and yield (maximum of 0.16 g/g sugars), protein content (0.50-0.60 g/g), alkali-insoluble material (AIM) (ca 0.15 g/g), and glucosamine content (up to 0.30 g/g of AIM). During cultivation in a pilot airlift bioreactor, the yield increased as aeration was raised from 0.15 to 1.0 vvm, indicating a high demand for oxygen. After cultivation at 1.0 vvm for 84 h, high yield and production of biomass (up to 0.34 g/g sugars), protein (0.30-0.50 g/g), lipids (0.02-0.07 g/g), AIM (0.16-0.28 g/g), and glucosamine (0.22-0.32 g/g AIM) were obtained. The fungal biomass produced from spent sulphite liquor is presently being tested as a replacement for fishmeal in feed for fish aquaculture and seems to be a potential source of nutrients and for production of glucosamine.
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| 4. |
- Kurniawan, Tonny, et al.
(författare)
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Semi-continuous reverse membrane bioreactor in two-stage anaerobic digestion of citruswaste
- 2018
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Ingår i: Materials. - : MDPI AG. - 1996-1944. ; 11:8
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Tidskriftsartikel (refereegranskat)abstract
- The presence of an antimicrobial compound called D-Limonene in citrus waste inhibits methane production from such waste in anaerobic digestion. In this work, a two-stage anaerobic digestion method is developed using reverse membrane bioreactors (rMBRs) containing cells encased in hydrophilic membranes. The purpose of encasement is to retain a high cell concentration inside the bioreactor. The effectiveness of rMBRs in reducing cell washout is evaluated. Three different system configurations, comprising rMBRs, freely suspended cells (FCs), and a combination of both (abbreviated to rMBR-FCs), are incubated at three different organic loading rates (OLRs) each, namely 0.6, 1.2, and 3.6 g COD/(L cycle). Incubation lasts for eight feeding cycles at 55 °C. Methane yield and biogas composition results show that rMBRs perform better than rMBR-FCs and FCs at all three OLRs. Volatile fatty acid profiles and H2production show that the reactors are working properly and no upset occurs. Additionally, a short digestion time of 4 days can be achieved using the rMBR configuration in this study.
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| 5. |
- Millati, Ria, 1972, et al.
(författare)
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Anaerobic digestion of citrus waste using two-stage membrane bioreactor
- 2018
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Ingår i: IOP Conference Series: Materials Science and Engineering. - 1757-8981 .- 1757-899X. ; 316:1
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Konferensbidrag (refereegranskat)abstract
- Anaerobic digestion is a promising method to treat citrus waste. However, the presence of limonene in citrus waste inhibits anaerobic digestion process. Limonene is an antimicrobial compound and could inhibit methane forming bacteria that takes a longer time to recover than the injured acid forming bacteria. Hence, volatile fatty acids will be accumulated and methane production will be decreased. One way to solve this problem is by conducting anaerobic digestion process into two stages. The first step is aimed for hydrolysis, acidogenesis, and acetogenesis reactions and the second stage is aimed for methanogenesis reaction. The separation of the system would further allow each stage in their optimum conditions making the process more stable. In this research, anaerobic digestion was carried out in batch operations using 120 ml-glass bottle bioreactors in 2 stages. The first stage was performed in free-cells bioreactor, whereas the second stage was performed in both bioreactor of free cells and membrane bioreactor. In the first stage, the reactor was set into 'anaerobic' and 'semi-aerobic' conditions to examine the effect of oxygen on facultative anaerobic bacteria in acid production. In the second stage, the protection of membrane towards the cells against limonene was tested. For the first stage, the basal medium was prepared with 1.5 g VS of inoculum and 4.5 g VS of citrus waste. The digestion process was carried out at 55°C for four days. For the second stage, the membrane bioreactor was prepared with 3 g of cells that were encased and sealed in a 3×6 cm 2 polyvinylidene fluoride membrane. The medium contained 40 ml basal medium and 10 ml liquid from the first stage. The bioreactors were incubated at 55°C for 2 days under anaerobic condition. The results from the first stage showed that the maximum total sugar under 'anaerobic' and 'semi-aerobic' conditions was 294.3 g/l and 244.7 g/l, respectively. The corresponding values for total volatile fatty acids were 3.8 g/l and 2.9 g/l, respectively. Methane production of citrus waste taken from the first stage under 'anaerobic' condition in membrane and free-cells bioreactors was 11.2 Nml and 7.2 Nml, respectively. Whereas, methane production of citrus waste taken from the first stage under 'semi-aerobic' condition in membrane and free-cells bioreactors was 8.8 Nml and 5.7 Nml, respectively. It can be seen from the results of the first stage that volatile fatty acids from 'anaerobic' condition was higher than that of 'semi-aerobic' condition. The absence of oxygen provides the optimal condition for growth and metabolism of facultative and obligatorily anaerobic bacteria in the first stage. Furthermore, polyvinylidene fluoride membrane was able to protect the cells from antimicrobial compounds.
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| 6. |
- Millati, Ria, 1972, et al.
(författare)
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Ethanol from Oil Palm Empty Fruit Bunch via Dilute-Acid Hydrolysis and Fermentation by Mucor indicus and Saccharomyces cerevisiae
- 2011
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Ingår i: Agricultural Journal. - : Medwell Journals. - 1994-4616 .- 1816-9155. ; 6:2, s. 54-59
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Tidskriftsartikel (refereegranskat)abstract
- Oil Palm Empty Fruit Bunch (OPEFB) was hydrolyzed in a one-stage hydrolysis using dilute-sulfuric acid (0.2, 0.8%) at 170-230°C with a holding time of 5 and 15 min. The maximum yield of xylose was 135.94 g kg-1 OPEFB, obtained at 0.8% acid, 190°C and 5 min. The maximum yield of glucose was 62.70 g kg-1 OPEFB, obtained at 0.8% acid, 210°C and 5 min. Based on these results, two-stage hydrolysis was performed to produce hydrolyzates for the fermentation process. Hydrolyzate from the first stage was fermented by Mucor indicus while the hydrolyzate from the second stage was fermented by Saccharomyces cerevisiae. The corresponding ethanol yields were 0.45 and 0.46 g ethanol g-1 sugar consumed.
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| 7. |
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| 8. |
- Sárvári Horváth, Ilona, 1960, et al.
(författare)
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Effects of furfural on the respiratory metabolism of Saccharomyces cerevisiae in glucose-limited chemostats
- 2003
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Ingår i: Applied and Environmental Microbiology. - 0099-2240 .- 1098-5336. ; 69:7, s. 4076-4086
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Tidskriftsartikel (refereegranskat)abstract
- Effects of furfural on the aerobic metabolism of the yeast Saccharomyces cerevisiae were studied by performing chemostat experiments, and the kinetics of furfural conversion was analyzed by performing dynamic experiments. Furfural, an important inhibitor present in lignocellulosic hydrolysates, was shown to have an inhibitory effect on yeast cells growing respiratively which was much greater than the inhibitory effect previously observed for anaerobically growing yeast cells. The residual furfural concentration in the bioreactor was close to zero at all steady states obtained, and it was found that furfural was exclusively converted to furoic acid during respiratory growth. A metabolic flux analysis showed that furfural affected fluxes involved in energy metabolism. There was a 50% increase in the specific respiratory activity at the highest steady-state furfural conversion rate. Higher furfural conversion rates, obtained during pulse additions of furfural, resulted in respirofermentative metabolism, a decrease in the biomass yield, and formation of furfuryl alcohol in addition to furoic acid. Under anaerobic conditions, reduction of furfural partially replaced glycerol formation as a way to regenerate NAD+. At concentrations above the inlet concentration of furfural, which resulted in complete replacement of glycerol formation by furfuryl alcohol production, washout occurred. Similarly, when the maximum rate of oxidative conversion of furfural to furoic acid was exceeded aerobically, washout occurred. Thus, during both aerobic growth and anaerobic growth, the ability to tolerate furfural appears to be directly coupled to the ability to convert furfural to less inhibitory compounds.
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| 9. |
- Elena, Palmquist, et al.
(författare)
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Inlärning av tröskelbegreppen inom Bioreaktionsteknik - studentdriven utveckling av en webbaserad modul för självstudier
- 2016
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Abstrakt Självstudier utgör en stor del av lärandet vid högskolestudier, vilket gör det intressant och relevant att studera de pedagogiska utmaningarna inom detta område. I detta kandidatarbete har studenter i samarbete med erfarna lärare arbetat med kursutveckling med fokus på utveckling av en webbaserad modul för självstudier inom Chalmerskursen KKR090 Bioreaktionsteknik. Kursen uppfattas av studenter som svår då den kombinerar kunskap från tidigare lästa kurser och innehåller många komplicerade begrepp, vilka ibland benämns tröskelbegrepp. Ett tröskelbegrepp definieras som ett begrepp som är svårt för studenterna att ta till sig, är centralt för disciplinen och förändrar studenternas sätt att tänka (Perkins, 2006 & Burch, Burch, Bradley, & Heller, 2015). Genom att öka insikten för tröskelbegrepp kan en djupare förståelse öppnas upp även för andra områden och begrepp (Cousin, 2010 & Pettersson, 2011). I studien identifierades sex tröskelbegrepp genom djupintervjuer med både lärare och studenter. Med dessa som grund utvecklades ett innehåll av teori- och beräkningsuppgifter, uppdelade i veckoavsnitt och med progressivt anpassad svårighetsgrad, i Maple T.A. För att leda studenten i rätt riktning består beräkningsuppgifterna av flera, mindre deluppgifter och om ytterligare vägledning önskas finns det ledtrådar till varje deluppgift. Lösningsförslag med förklarande lösningsgång och teori finns att tillgå direkt efter att svar lämnats in. Det finns även möjlighet för studenten att genomföra övningstentamina.Utvärdering av modulen gjordes initialt genom ett alpha- och ett betatest. Det första utfördes av lärare och det senare av studenter. Under betatestet använde studenter modulen under uppsyn och information samlades in genom dialog på plats med studenterna samt genom en enkätstudie. Eftersom både studenter och lärare upplevde modulen användbar, givande och utmanande, förväntas modulen svara mot behovet av ett ökat stöd för självstudier och kommer därmed underlätta studierna.Modulen kommer att införas och utvärderas under Hösttermin 2015. En kort introduktion och demonstration ska genomföras, varefter modulen kommer att vara tillgänglig hela kursen. Schemalagda seminarier ska också genomföras, där studenten har möjlighet att träna på de identifierade tröskelbegreppen med handledning. Utvärderingen sker genom djupsamtal, statistik över hur studenterna jobbar med modulen samt en skriftlig enkät. Jämförelser av årets resultat med de från tidigare examina kan, trots begränsningar i det statistiska urvalet, indikera hur förståelsen av tröskelbegrepp ändrats jämfört med tidigare års kurser.Vi anser att modulens utformning skulle kunna förbättra studenternas självstudier även inom andra områden på Chalmers. Arbetsmetoden, att utgå från tröskelbegrepp, kan ses som den pedagogiska nyckeln för att låsa upp studenternas förståelse (Burch et al., 2015). Att använda nytänkande informations- och kommunikationsteknik som ett didaktiskt verktyg för att stimulera aktivt lärande och att involvera studenter i kursutvecklingsprocessen är ytterligare två intressanta perspektiv av studien. Den största vinsten med att modulen utformats från ett studentperspektiv är tillvaratagandet av aspekter som lärare ibland tar för självklart. Exempelvis kan det vara lättare för en student att specificera svårigheter i lärandeprocessen än för den ämneskunnige läraren.
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| 10. |
- Abtahi, Z., et al.
(författare)
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Ethanol production by Mucor indicus at high glucose and ethanol concentrations
- 2010
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Ingår i: Minerva Biotecnologica. - : Edizioni Minerva Medica. - 1120-4826 .- 1827-160X. ; 22:3-4, s. 83-89
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Tidskriftsartikel (refereegranskat)abstract
- Mucor indicus was cultivated under aerobic and anaerobic conditions to study its tolerance against high concentration of glucose up to 350 g/L and ethanol up to 120 g/L present in the medium. The fungus could grow well even in 350 g/L glucose and produce ethanol, but it was able to assimilate the entire glucose when its concentration was less than 200 g/L. On the other hand, M. indicus produced ethanol as the main product with yield and concentration up to 0.45 g/g and 73 g/L, respectively, while glycerol, its only major byproduct, was produced up to 24 g/L. However, the fungus was not so tolerant against exogenously added ethanol, and it could not grow with more than 40 g/L added ethanol to the culture. Under aerobic conditions, M. indicus displayed different morphology, switching from long filamentous to yeast-like growth forms by increasing initial glucose concentration. This implies that yeast-like growth can be induced by growing M. indicus at high glucose concentration. Under anaerobic conditions, only one yeast-like form was observed.
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