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Developing a food waste-based volatile fatty acids platform using an immersed membrane bioreactor
University of Borås, Faculty of Textiles, Engineering and Business.
2020 (English)Doctoral thesis, comprehensive summary (Other academic)
Sustainable development
According to the author(s), the content of this publication falls within the area of sustainable development.
Abstract [en]

Approximately 1.3 billion tons of food waste is produced globally every year. In principle, all the resources in the supply chain are lost (e.g. land, energy, and water) when the food is not consumed as intended. Anaerobic digestion is an established biological technology to treat food waste, and is mainly employed for recovery of energy in the form of biogas. Volatile fatty acids (VFAs) are formed as intermediate products of the anaerobic digestion process, and can be applied as precursors for various essential biomaterials. The manipulation of the anaerobic digestion process to synthesize these intermediates instead of biogas is considered to recover more value from food waste. However, some bottlenecks that prevent large-scale production and application of VFAs still exist. Among the key issues to be addressed are the difficulty in recovering the VFAs from the fermentation medium and the overall low product yields. The goals of the present thesis were: 1) to investigate methods to boost the production of VFAs from food waste; 2) to continuously recover VFAs from food waste fermentation medium; 3) to determine the changes in the microbial structure during high organic loading of food waste in membrane bioreactors; and 4) to study a novel approach for applying food waste-derived VFAs for cultivating edible filamentous fungi.

For continuous product recovery at high yields, an immersed membrane bioreactor was constructed with robust cleaning capabilities to withstand the complex anaerobic digestion medium. The membrane bioreactor was first operated without pH control and a yield of 0.54 g VFA/g VSadded was achieved when an organic loading rate of 2 gVS/L/d was applied. Moreover, only a 16.4% reduction in the permeate flux during a 40-day operation period was recorded. In the second experimental work, the immersed membrane bioreactor system was subjected to high organic loading rates of 4, 6, 8, and 10 g VS/L/d as a tool of manipulating the anaerobic digestion process towards high VFAs and hydrogen production. The highest yield of VFAs was attained at 6 g VS/L/d (0.52 g VFA/gVSadded), while at 8 g VS/L/d, a maximal hydrogen yield of 14.7 NmL/gVSadded was obtained. An analysis of the microbial structure revealed that the presence of Clostridium resulted in high production of acetate, butyrate and caproate. On the other hand, the relative abundance of Lactobacillus was found to influence lactate biosynthesis.

Cultivation of edible filamentous fungi presents a novel possibility for application of food waste-derived VFAs. Due to the growing demand of single-cell protein, one of the potential uses for the fungal biomass is the production of animal feed. In this thesis, an edible filamentous fungus, Rhizopus oligosporus was grown solely on the VFAs recovered from the membrane bioreactors. It was revealed that high concentrations could inhibit fungal growth; thus, the dilution of the VFAs solution used as substrate was necessary. Furthermore, when a fed-batch cultivation technique was applied, a four-fold improvement in the biomass production relative to standard batch cultivation was realized. A maximum biomass yield of 0.21 ± 0.01g dry biomass/ g VFAs COD eq. consumed, containing 39.28 ± 1.54% crude protein, was obtained. With further improvements in the VFAs uptake and the biomass yield, this novel concept could be a fundamental step in converting anaerobic digestion facilities into biorefineries.

Place, publisher, year, edition, pages
Borås: Högskolan i Borås, 2020.
Series
Skrifter från Högskolan i Borås, ISSN 0280-381X ; 107
Keywords [en]
food waste, anaerobic digestion, volatile fatty acids, immersed membrane bioreactor, edible filamentous fungi
National Category
Environmental Biotechnology
Research subject
Resource Recovery
Identifiers
URN: urn:nbn:se:hb:diva-23251ISBN: 978-91-88838-76-6 (print)ISBN: 978-91-88838-77-3 (electronic)OAI: oai:DiVA.org:hb-23251DiVA, id: diva2:1434348
Public defence
2020-09-18, M402, Allégatan 1, Borås, 10:00 (English)
Opponent
Available from: 2020-08-24 Created: 2020-06-03 Last updated: 2020-08-25Bibliographically approved
List of papers
1. Food waste-derived volatile fatty acids platform using an immersed membrane bioreactor
Open this publication in new window or tab >>Food waste-derived volatile fatty acids platform using an immersed membrane bioreactor
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2018 (English)In: Bioresource Technology, ISSN 0960-8524, E-ISSN 1873-2976, article id S0960-8524(18)31650-XArticle in journal (Refereed) Published
Abstract [en]

Volatile fatty acids (VFAs) are the key intermediates from anaerobic digestion (AD) process that can be a platform to synthesize products of higher value than biogas. However, some obstacles still exist that prevent large-scale production and application of VFAs, key among them being the difficulty in recovering the acids from the fermentation medium and low product yields. In this study, a novel anaerobic immersed membrane bioreactor (iMBR) with robust cleaning capabilities, which incorporated frequent backwashing to withstand the complex AD medium, was designed and applied for production and in situ recovery of VFAs. The iMBR was fed with food waste and operated without pH control, achieving a high yield of 0.54 g VFA/g VSadded. The continuous VFA recovery process was investigated for 40 days at OLRs of 2 gVS/L/d and 4 gVS/L/d without significant change in the permeate flux at a maximum suspended solids concentration of 31 g/L.

Keywords
Food waste, Fouling control, Immersed membrane bioreactor, In situ recovery, Volatile fatty acids
National Category
Engineering and Technology
Research subject
Resource Recovery; Resource Recovery
Identifiers
urn:nbn:se:hb:diva-15420 (URN)10.1016/j.biortech.2018.11.104 (DOI)000454610900041 ()2-s2.0-85057618430 (Scopus ID)
Available from: 2018-12-04 Created: 2018-12-04 Last updated: 2020-12-01Bibliographically approved
2. Bioengineering of anaerobic digestion for volatile fatty acids, hydrogen or methane production: A critical review
Open this publication in new window or tab >>Bioengineering of anaerobic digestion for volatile fatty acids, hydrogen or methane production: A critical review
2019 (English)In: Bioengineered, ISSN 2165-5979, E-ISSN 2165-5987, ISSN 2165-5979Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
Taylor & Francis Group, 2019
Keywords
Anaerobic digestion, Metabolic pathways, Volatile fatty acids, Hydrogen, Biorefineries, Process parameters, Mixed culture fermentation, Inhibiting methanogens
National Category
Natural Sciences
Identifiers
urn:nbn:se:hb:diva-21807 (URN)10.1080/21655979.2019.1673937 (DOI)000490056900001 ()000490056900001 (PubMedID)2-s2.0-85073183117 (Scopus ID)
Funder
Swedish Research CouncilMoRe ResearchSwedish Agency for Economic and Regional Growth
Available from: 2019-10-03 Created: 2019-10-03 Last updated: 2022-01-20Bibliographically approved
3. Anaerobic digestion of food waste to volatile fatty acids and hydrogen at high organic loading rates in immersed membrane bioreactors
Open this publication in new window or tab >>Anaerobic digestion of food waste to volatile fatty acids and hydrogen at high organic loading rates in immersed membrane bioreactors
2020 (English)In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682Article in journal (Refereed) Published
Abstract [en]

The organic loading rate (OLR) is an essential parameter that controls the anaerobic digestion process. This work investigated the performance of immersed membrane bioreactors operated at high OLRs of 4, 6, 8 and 10 g volatile solids (VS)/L/d regarding the fermentation behavior, product recovery and microbial dynamics during the acidogenic fermentation of food waste to volatile fatty acids (VFAs) and hydrogen. The highest yield of 0.52 g VFA/ gVSadded was attained at 6 g VS/L/d, while an optimal hydrogen yield of 14.7 NmL/ gVSadded was obtained at 8 g VS/L/d. The bacterial populations, analyzed using 16S rRNA gene amplicon sequencing, consisted mainly of Firmicutes and Actinobacteria at OLRs 4 and 8 g VS/L/d while Firmicutes, Actinobacteria and Proteobacteria phyla dominated at 6 and 10 g VS/L/d. Moreover, the presence of Clostridium and Lactobacillus genera correlated with the acetate, butyrate, caproate and lactate production.

Keywords
In-situ product recovery Immersed membrane bioreactor High organic loading rate Volatile fatty acids Microbial dynamics
National Category
Engineering and Technology
Research subject
Resource Recovery
Identifiers
urn:nbn:se:hb:diva-22766 (URN)10.1016/j.renene.2020.01.138 (DOI)000536949600094 ()2-s2.0-85078880176 (Scopus ID)
Funder
Swedish Agency for Economic and Regional GrowthMoRe ResearchSwedish Research Council
Available from: 2020-02-03 Created: 2020-02-03 Last updated: 2024-02-01Bibliographically approved
4. Utilization of food waste-derived volatile fatty acids for production of edible Rhizopus oligosporus fungal biomass
Open this publication in new window or tab >>Utilization of food waste-derived volatile fatty acids for production of edible Rhizopus oligosporus fungal biomass
Show others...
2020 (English)In: Bioresource Technology, ISSN 0960-8524, E-ISSN 1873-2976Article in journal (Refereed) Published
Abstract [en]

Rhizopus oligosporus is an edible filamentous fungus that can contribute to meet the growing demand for single-cell protein. Volatile fatty acids (VFAs) are favorable potential substrates for producing R. oligosporus biomass due to their capacity to be synthesized from a wide range of low-value organic solid wastes via anaerobic digestion. The goal of this work was to cultivate R. oligosporus using food waste-derived VFAs as the sole carbon source. To maintain the requisite low substrate concentrations, the fed-batch cultivation technique was applied. This resulted in a four-fold improvement in biomass production relative to standard batch cultivation. Maximum biomass yield of 0.21 ± 0.01 g dry biomass/g VFAs COD eq. consumed, containing 39.28 ± 1.54% crude protein, was obtained. In the bubble-column bioreactors, the complete uptake of acetic acid was observed, while the consumptions of caproic and butyric acids reached up to 97.64% and 26.13%, respectively.

Keywords
Food waste; Anaerobic digestion; Volatile fatty acids; Fed-batch cultivation; Edible filamentous fungal biomass; Rhizopus oligosporus
National Category
Engineering and Technology
Research subject
Resource Recovery
Identifiers
urn:nbn:se:hb:diva-23158 (URN)10.1016/j.biortech.2020.123444 (DOI)000539712800009 ()2-s2.0-85083785704 (Scopus ID)
Funder
Swedish Agency for Economic and Regional Growth
Available from: 2020-04-28 Created: 2020-04-28 Last updated: 2021-10-21Bibliographically approved

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