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Utilization of food waste-derived volatile fatty acids for production of edible Rhizopus oligosporus fungal biomass
University of Borås, Faculty of Textiles, Engineering and Business.
Universitas Gadjah Mada.
Universitas Gadjah Mada.
Universitas Gadjah Mada.
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2020 (English)In: Bioresource Technology, ISSN 0960-8524, E-ISSN 1873-2976Article in journal (Refereed) Published
Sustainable development
According to the author(s), the content of this publication falls within the area of sustainable development.
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.

Place, publisher, year, edition, pages
2020.
Keywords [en]
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: urn:nbn:se:hb:diva-23158DOI: 10.1016/j.biortech.2020.123444ISI: 000539712800009Scopus ID: 2-s2.0-85083785704OAI: oai:DiVA.org:hb-23158DiVA, id: diva2:1426878
Funder
Swedish Agency for Economic and Regional GrowthAvailable from: 2020-04-28 Created: 2020-04-28 Last updated: 2021-10-21Bibliographically approved
In thesis
1. Developing a food waste-based volatile fatty acids platform using an immersed membrane bioreactor
Open this publication in new window or tab >>Developing a food waste-based volatile fatty acids platform using an immersed membrane bioreactor
2020 (English)Doctoral thesis, comprehensive summary (Other academic)
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
food waste, anaerobic digestion, volatile fatty acids, immersed membrane bioreactor, edible filamentous fungi
National Category
Environmental Biotechnology
Research subject
Resource Recovery
Identifiers
urn:nbn:se:hb:diva-23251 (URN)978-91-88838-76-6 (ISBN)978-91-88838-77-3 (ISBN)
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

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Wainaina, StevenTaherzadeh, Mohammad J

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