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Microbial population dynamics in a microalgae-based municipal wastewater treatment photobioreactor located in Northern Sweden
Umeå University, Faculty of Science and Technology, Department of Chemistry.
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

A pilot-scale high-rate algal pond (HRAP) located in Northern Sweden was inoculated with the collection strain S. dimorphus UTEX 417 in spring and operated until autumn. The microbial diversity of eukaryotic and prokaryotic communities and their seasonal dynamics over time were revealed by high-throughput metabarcoding of 18S and 16S rRNA genes and correlated with various environmental factors. S. dimorphus was initially stable in the culture, but other microalgae appeared later and co-dominate the system as a consequence of predation by zooplankton. Desmodesmus, Pseudocharaciopsis, Chlorella, Characium and Oocystis were the main competing algal species. Proteobacteria, Firmicutes, Bacteroidetes and Actinobacteria were the most abundant bacterial phyla in the HRAP. The bacterial and zooplanktonic communities changed with seasonal variation, correlation not only with changes in light and temperature, but also with abiotic factors (pH and nutrients) were observed.

National Category
Microbiology
Identifiers
URN: urn:nbn:se:umu:diva-156465OAI: oai:DiVA.org:umu-156465DiVA, id: diva2:1289198
Funder
Swedish Energy Agency, 38239-1Swedish Research Council Formas, 942-2015-92Available from: 2019-02-15 Created: 2019-02-15 Last updated: 2019-02-19
In thesis
1. Wastewater treatment and biomass generation by Nordic microalgae: growth in subarctic climate and microbial interactions
Open this publication in new window or tab >>Wastewater treatment and biomass generation by Nordic microalgae: growth in subarctic climate and microbial interactions
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Nordic native microalgal strains were isolated, genetically classified and tested for their ability to grow in municipal wastewater. Eight of the isolated strains could efficiently remove nitrogen and phosphate in less than two weeks. Two of these strains, Coelastrella sp. and Chlorella vulgaris, were found to have high biomass concentration and total lipid content; also two Desmodesmus sp. strains showed desirable traits for biofuel-feedstock, due to their fast growth rates and high oil content.

The adaptation to subarctic climate was comparatively evaluated in three Nordic strains (C. vulgaris, Scenedesmus sp. and Desmodesmus sp.) and a collection strain (S. obliquus). Their growth performance, biomass composition and nutrients removal was investigated at standard (25°C) or low temperature (5°C), under continuous light at short photoperiod (3 h light, 25°C) or moderate winter conditions (6 h light, 15°C). Only the Nordic strains could grow and produce biomass at low temperature, and efficiently removed nitrogen and phosphate during both cold- and dark-stress. Phenotypic plasticity was observed in Scenedesmus and Desmodesmus under different growth conditions, adaptation to low temperature increased their carbohydrate content. Short photoperiod strongly reduced growth rates, biomass and storage compounds in all strains and induced flocculation in C. vulgaris, which, however, performed best under moderate winter conditions.

The symbiotic relationships between the Nordic microalga C. vulgaris and the naturally co-occurring bacterium Rhizobium sp. were investigated batchwise under photoautotrophic, heterotrophic and mixotrophic conditions, comparing the co-culture to the axenic cultures. The photoautotrophic algal growth in BG11 medium mainly supported Rhizobium activity in the co-culture, with no significant effects on C. vulgaris. In synthetic wastewater, a synergistic interaction only occurred under mixotrophic conditions, supported by CO2/O2 exchange and a lower pH in the culture, resulting in higher biomass and fatty acids content and more efficient wastewater treatment in the co-culture. Under heterotrophic conditions, the lower biomass production in the co-culture suggested a competition for nutrients, although nutrients removal remained efficient.

A pilot-scale high rate algal pond (HRAP) located in Northern Sweden was inoculated with the collection strain Scenedesmus dimorphus UTEX 417 and operated from spring to autumn. Using metabarcoding of 18S and 16S rRNA genes, the microbial diversity of eukaryotic and prokaryotic communities was revealed. S. dimorphus was initially stable in the culture, but other microalgal species later colonized the system, mainly due to parasitic infections and predation by zooplankton in summer. The main competitor algal species were Desmodesmus, Pseudocharaciopsis, Chlorella, Characium and Oocystis. Proteobacteria, Firmicutes, Bacteroidetes and Actinobacteria were the most abundant bacterial phyla in the HRAP. The structure of the microbial communities followed a seasonal variation and partially correlated to environmental factors such as light, temperature and nutrients concentrations.

Overall, these results contribute with new knowledge on the establishment and optimization of microalgal-based wastewater treatment systems coupled with biomass generation in Nordic areas. The use of native microalgal species is proposed as a potential strategy to overcome the limitations posed to algal cultivation in subarctic regions.

Place, publisher, year, edition, pages
Umeå: Umeå University, 2019. p. 75
Keywords
Microalgae, Wastewater, Nitrogen, Phosphate, Biomass, Lipids, Subarctic Climate, Light, Temperature, Bacteria, Photoautotrophy, Heterotrophy, Mixotrophy, HRAP, Metabarcoding, Microbial Communities, Alpha-diversity, Environmental Factors
National Category
Microbiology Other Biological Topics Biochemistry and Molecular Biology Chemical Sciences
Research subject
Biochemistry; Microbiology
Identifiers
urn:nbn:se:umu:diva-156470 (URN)978-91-7855-014-2 (ISBN)
Public defence
2019-03-15, Carl Kempe salen (KB.E3.03), KBC-huset, Umeå, 10:00 (English)
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Supervisors
Available from: 2019-02-22 Created: 2019-02-15 Last updated: 2019-02-21Bibliographically approved

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Ferro, LorenzaFunk, Christiane

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