| 1. |
- Eryildiz, B, et al.
(author)
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Effect of pH, substrate loading, oxygen, and methanogens inhibitors on volatile fatty acid (VFA) production from citrus waste by anaerobic digestion
- 2020
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In: Bioresource Technology. - : Elsevier Ltd. - 0960-8524 .- 1873-2976. ; 302
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Journal article (peer-reviewed)abstract
- Citrus waste from e.g., juice production is a potential substrate for anaerobic digestion (AD). However, due to the toxic citrus peel oil content, citrus waste has several challenges in biogas production. Hence, volatile fatty acids (VFAs) are very interesting intermediate products of AD. This paper was aimed to investigate VFA production from citrus wastes by boosting its production and inhibiting methane formation. Therefore, the effects of inoculum to substrate ratio (ISR), O2 presence, pH, and inhibitor for methanogens, in VFA production from citrus waste through acidification process were studied. The addition of 2 g/L methanogens inhibitor and the presence of O2 in the reactors were able to reduce methane production. The highest yield of VFA (0.793 g VFA/g VSadded) was achieved at controlled pH at 6 and low substrate loading (ISR 1:1). Acetic acid (32%), caproic acid (21%), and butyric acid (15%) dominate the VFA composition in this condition. © 2020 Elsevier Ltd
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| 2. |
- Kurniawan, Tonny, et al.
(author)
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Semi-continuous reverse membrane bioreactor in two-stage anaerobic digestion of citruswaste
- 2018
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In: Materials. - : MDPI AG. - 1996-1944. ; 11:8
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Journal article (peer-reviewed)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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| 3. |
- Lukitawesa, Lukitawesa, et al.
(author)
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Effect of effluent recirculation on biogas production using two-stage anaerobic digestion of citrus waste
- 2018
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In: Molecules. - : MDPI AG. - 1420-3049 .- 1420-3049 .- 1431-5157. ; 23:12
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Journal article (peer-reviewed)abstract
- Citrus waste is a promising potential feedstock for anaerobic digestion, yet the presence of inhibitors such as D-limonene is known to limit the process. Effluent recirculation has been proven to increase methane yield in a semi-continuous process for recalcitrant material, but it has never been applied to toxic materials. This study was aimed to investigate the effect of recirculation on biogas production from citrus waste as toxic feedstock in two-stage anaerobic digestion. The first digestion was carried out in a stirred tank reactor (STR). The effluent from the first-stage was filtered using a rotary drum filter to separate the solid and the liquid phase. The solid phase, rich in hydrophobic D-limonene, was discarded, and the liquid phase containing less D-limonene was fed into the second digester in an up-flow anaerobic sludge bed (UASB) reactor. A high organic loading rate (OLR 5 g VS/(L·day)) of citrus waste was fed into the first-stage reactor every day. The effluent of the first-stage was then fed into the second-stage reactor. This experiment was run for 120 days. A reactor configuration without recirculation was used as control. The result shows that the reactor with effluent recirculation produced a higher methane yield (160–203 NmL/g·VS) compared to that without recirculation (66–113 NmL/g·VS). More stable performance was also observed in the reactor with recirculation as shown by the pH of 5–6, while without recirculation the pH dropped to the range of 3.7–4.7. The VS reduction for the reactor with recirculation was 33–35% higher than that of the control without recirculation. Recirculation might affect the hydrolysis-acidogenesis process by regulating pH in the first-stage and removing most of the D-limonene content from the substrate through filtration.
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| 4. |
- Lukitawesa, Lukitawesa, et al.
(author)
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Inhibition of patchouli oil for anaerobic digestion and enhancement in methane production using reverse membrane bioreactors.
- 2017
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In: Renewable energy. - : Elsevier Ltd.. - 0960-1481 .- 1879-0682.
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Journal article (peer-reviewed)abstract
- Patchouli oil is an essential oil extd. from arom. crop Pogostemon cablin and is widely used in perfumery industry, food industry, and/or even as medicine. The leaves have 4.6% oil that is extd. by steam, but remains an enormous amt. of wastes contg. ca 0.8% oil. Patchouli waste is an interesting substrate for methane prodn. However, the oil has been found to have antibacterial activity. The inhibition of patchouli oil on anaerobic digestion was investigated in this study under thermophilic conditions (55 °C). The patchouli oil showed antibacterial effect, where addn. of 0.05, 0.5 and 5 g/L patchouli oil reduced biogas prodn. by 16.2%, 27.2% and 100% resp. As patchouli oil is a lipophilic compd., hydrophilic polyvinylidene difluoride (PVDF) membrane was used to protect the microorganisms against this inhibitor in a reverse membrane bioreactor (rMBR) system. The methane yield of fresh plant and waste were 86 and 179 NmL CH4/gVS, resp. when using free cells. Although using solely an rMBR did not give significant rise to methane yield, the combination rMBR and free cell strategy to protect part of the digesting microorganisms against this inhibitor considerably enhanced the methane prodn. by 73% for fresh patchouli plant, compared to digestion using free cells. [on SciFinder(R)]
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| 5. |
- Lukitawesa, Lukitawesa, et al.
(author)
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Semi-continuous production of volatile fatty acids from citrus waste using membrane bioreactors
- 2021
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In: Innovative Food Science & Emerging Technologies. - : Elsevier BV. - 1466-8564 .- 1878-5522.
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Journal article (peer-reviewed)abstract
- In the production of volatile fatty acids (VFAs) from citrus waste, organic loadings rates (OLR) from 1 to 8 g VS/L·d were applied in semi-continuous anaerobic fermentation using a tubular membrane bioreactor (MBR). Filtration fluxes of the membrane were in the range of 7.9–8.5 L/m2·h. trans-Membrane pressure (TMP) revolved around 24.1–67.5 mbar. No obvious fouling and clogging occurred. The highest yield of VFAs 0.67 g VFA/g VS (volatile solids) was achieved at OLR 4 g VS/L·d. When citrus waste was pretreated to remove D-limonene using an airlift reactor, the highest yield of VFAs 0.84 g VFA/g VS was also obtained at OLR 4 g VS/L·d. A further increase in OLR of up to 8 g VS/L·d caused a sharp decrease in yield for the untreated citrus waste and only marginal changes were observed for the pretreated citrus waste. The main composition of VFAs was acetate, butyrate, caproate, and propionate. © 2020 Elsevier Ltd
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| 6. |
- Millati, Ria, 1972, et al.
(author)
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Anaerobic digestion of citrus waste using two-stage membrane bioreactor
- 2018
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In: IOP Conference Series: Materials Science and Engineering. - 1757-8981 .- 1757-899X. ; 316:1
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Conference paper (peer-reviewed)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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| 7. |
- Mukesh Kumar, Awasthi, et al.
(author)
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Bacterial dynamics during the anaerobic digestion of toxic citrus fruit waste and semi-continues volatile fatty acids production in membrane bioreactors
- 2022
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In: Fuel. - : Elsevier. - 0016-2361 .- 1873-7153. ; 319
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Journal article (peer-reviewed)abstract
- Citrus wastes (CW) are normally toxic to anaerobic digestion (AD) because of flavors such as D-limonene. In this study, bacterial community was evaluated during volatile fatty acids (VFAs) production from CW inoculated by sludge in a membrane bioreactor (MBR) using semi-continuous AD with different organic loading rates (OLR). Four treatments including untreated CW filled with 4 and 8 g center dot VS center dot L(-1)d(-1) OLR (UOLR4 and UOLR8), pretreated Dlimonene-free CW filled with 4 and 8 g center dot VS center dot L(-1)d(-1) OLR (POLR4 and POLR8). The initial inoculum and the CW mixture (DAY0) was used as control for comparison. There was an obviously higher bacterial diversity in raw material (66848 sequences in DAY0), while decreased after AD and higher in POLR4 and POLR8 (65239 and 63916) than UOLR4 and UOLR8 (49158 and 51936). The key bacterial associated with VFAs production mainly affiliated to Firmicutes (37.35-84.73%), Bacteroidetes (0.48-36.87%), and Actinobacteria (0.35-29.38%), and the key genus composed of Lactobacillus, Prevotella, Bacillus, Bacteroides and Olsenella which contributed in VFA generation by degradable complex organic compounds. Noticeably, methanogen completely suppressed after MBR-AD and UOLR4 has greater acid utilizing bacteria (70.09%).
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| 8. |
- Rousta, Neda, et al.
(author)
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Filamentous Fungus Aspergillus oryzae for Food : From Submerged Cultivation to Fungal Burgers and Their Sensory Evaluation – A Pilot Study
- 2021
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In: Foods. - : MDPI AG. - 2304-8158. ; 10:11
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Journal article (peer-reviewed)abstract
- New food sources are explored to provide food security in sustainable ways. The submerged fermentation of edible filamentous fungi is a promising strategy to provide nutritious and affordable food that is expected to have a low environmental impact. The aim of the current study was to assess the novel use of Aspergillus oryzae cultivated in submerged fermentation on oat flour as a source for food products that do not undergo secondary fermentation or significant downstream processing. The fungus was cultivated in a pilot-scale airlift bioreactor, and the biomass concentration and protein content of the biomass were assessed. A tasting with an untrained panel assessed consumer preferences regarding the taste and texture of minimally processed vegetarian and vegan burger patties made from the biomass, and how the patties fared against established meat-alternative-based patties. The cultivation of Aspergillus oryzae resulted in a yield of 6 g/L dry biomass with a protein content of 37% on a dry weight basis. The taste and texture of the minimally processed fungal burger patties were to the liking of some participants. This was also reflected in diverse feedback provided by the participants. The cultivation of the fungus on oat flour and its utilization in developing burger patties shows its promising potential for the production of nutritious food. The applications of the fungus can be further developed by exploring other favorable ways to texture and season this relatively new functional food source to the preferences of consumers.
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| 9. |
- Wainaina, Steven, et al.
(author)
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Bioengineering of anaerobic digestion for volatile fatty acids, hydrogen or methane production: A critical review
- 2019
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In: Bioengineered. - : Taylor & Francis Group. - 2165-5979 .- 2165-5987.
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Journal article (peer-reviewed)abstract
- Anaerobic digestion (AD) is a well-established technology used for producing biogas or biomethane alongside the slurry used as biofertilizer. However, using a variety of wastes and residuals as substrate and mixed cultures in the bioreactor makes AD as one of the most complicated biochemical processes employing hydrolytic, acidogenic, hydrogen-producing, acetate-forming bacteria as well as acetoclastic and hydrogenoclastic methanogens. Hydrogen and volatile fatty acids (VFAs) including acetic, propionic, isobutyric, butyric, isovaleric, valeric and caproic acid and other carboxylic acids such as succinic and lactic acids are formed as intermediate products. As these acids are important precursors for various industries as mixed or purified chemicals, the AD process can be bioengineered to produce VFAs alongside hydrogen and therefore biogas plants can become biorefineries. The current critical review paper provides the theory and means to produce and accumulate VFAs and hydrogen, inhibit their conversion to methane and to extract them as the final products. The effects of pretreatment, pH, temperature, hydraulic retention time (HRT), organic loading rate (OLR), chemical methane inhibitions, and heat shocking of the inoculum on VFAs accumulation, hydrogen production, VFAs composition, and the microbial community were discussed. Furthermore, this paper highlights the possible techniques for recovery of VFAs from the fermentation media in order to minimize product inhibition as well as to supply the carboxylates for downstream procedures.
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| 10. |
- Lukitawesa, -
(author)
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Methane and Volatile Fatty Acids Production from Toxic Substrate
- 2020
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Doctoral thesis (other academic/artistic)abstract
- Challenges caused by climate change and global warming have created a demand for improvements in resource recovery and the promotion of a circular economy. Waste management is one such challenge for which more recycling options are required for producing materials and energy sources from wastes. Toxic organic waste such as fruit waste has been conventionally disposed into landfills; however, anaerobic digestion can be performed to produce biogas or volatile fatty acids (VFAs) from these wastes.The main objective of this research was to develop an anaerobic digestion method for patchouli oil distillery waste and citrus processing residuals for biogas and VFA production using a membrane bioreactor and two-stage digestion system. To this end, a reverse membrane bioreactor with a membrane-encased mixed culture was used for both one-stage and two-stage digestion. The membrane encasement was used to protect the microorganisms from toxic compounds (e.g., D-limonene or patchouli alcohol). The membrane improved the methane yield of patchouli oil distillery waste (73%) and filtrate from citrus waste digestate from the acidification reactor (50%). Two-stage digestion of citrus waste was improved by performing effluent recirculation from the second-stage reactor into first-stage reactor (79% increase in methane yield).In addition to biogas, VFAs, as intermediate products of anaerobic digestion, are considered as valuable products. A two-stage digestion experiment showed that citrus waste can also be converted into VFAs. However, several factors influencing biogas and VFA production differed between the two processes. Batch experiments of anaerobic digestion were performed to investigate important factors affecting VFA production from citrus waste and food waste (as an example of a non-toxic substrate). The results showed that pH, moderate substrate loading, and inoculum adaptation were significant factors affecting VFA production, whereas additions of a methanogen inhibitor and the presence of oxygen did not significantly affect the VFA yield. At high citrus waste loading, D-limonene loading was also high and negatively impacted the VFA yield.To reduce product inhibition in the anaerobic digestion of citrus waste, a tubular membrane as a cross-flow filtration device was used for downstream processing of VFAs. Continuous extraction of VFAs from the reactor improved the VFA yield by two-fold compared with the reactor in which the membrane was not used. The cross-flow filtration allows the system to remain stable during continuous cake-layer removal, as the highest trans-membrane pressure detected was below 67.5 mbar.
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