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Influence of environmental stress on the microalgal-bacterial process during nitrogen removal
Mälardalen University, School of Business, Society and Engineering, Future Energy Center. (ACWA)ORCID iD: 0000-0002-0137-2194
University of Massachusetts Amherst, US.
Mälardalen University, School of Business, Society and Engineering, Future Energy Center.ORCID iD: 0000-0002-5014-3275
Mälardalen University, School of Business, Society and Engineering, Future Energy Center. ABB AB Corporate Research, Sweden.
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(English)Manuscript (preprint) (Other academic)
National Category
Water Treatment
Research subject
Biotechnology/Chemical Engineering
Identifiers
URN: urn:nbn:se:mdh:diva-39155OAI: oai:DiVA.org:mdh-39155DiVA, id: diva2:1204240
Available from: 2018-05-07 Created: 2018-05-07 Last updated: 2018-05-15Bibliographically approved
In thesis
1. A passage to wastewater nutrient recovery units: Microalgal-Bacterial bioreactors
Open this publication in new window or tab >>A passage to wastewater nutrient recovery units: Microalgal-Bacterial bioreactors
2018 (English)Doctoral thesis, comprehensive summary (Other academic) [Artistic work]
Abstract [en]

In recent years, the microalgal–bacterial process has been considered to be a very attractive engineering solution for wastewater treatment. However, it has not been widely studied in the context of conventional wastewater treatment design under Swedish conditions. The technology holds several advantages: as a CO2 sink, ability to withstand cold conditions, ability to grow under low light, fast settling without chemical precipitation, and reducing the loss of valuable nutrients (CO2, N2, N2O, PO4). The process also provides the option to be operated either as mainstream (treatment of municipal wastewater) or side stream (treatment of centrate from anaerobic digesters) to reduce the nutrient load of the wastewater. Furthermore, the application is not only limited to wastewater treatment; the biomass can be used to synthesise platform chemicals or biofuels and can be followed by recovery of ammonium and phosphate for use in agriculture.

In the present study, the feasibility of applying the process in Swedish temperature and light conditions was investigated by implementing microalgae within the activated sludge process. In this context, the supporting operational and performance indicators (hydraulic retention time (HRT), sludge retention time (SRT) and nutrients removal) were evaluated to support naturally occurring consortia in photo-sequencing and continuous bioreactor configuration. Furthermore, CO2 uptake and light spectrum-mediated nutrient removal were investigated to reduce the impact on climate and the technical challenges associated with this type of system.

The results identified effective retention times of 6 and 4 days (HRT = SRT) under limited lighting to reduce the electrical consumption. From the perspective of nitrogen removal, the process demands effective CO2 input either in the mainstream or side stream treatment. The incorporation of a vertical absorption column demonstrated effective CO2 mass transfer to support efficient nitrogen and phosphorus removal as a side stream treatment. However, the investigation of a continuous single-stage process as the mainstream showed a requirement for a lower SRT in comparison to semi-continuous operation due to faster settlability, regardless of inorganic carbon. Furthermore, the process showed an effective reduction of influent phosphorus and organic compounds (i.e. COD/TOC) load in the wastewater as a result of photosynthetic aeration. Most importantly, the operation was stable at the temperature equivalent of wastewater (12 and 13 ˚C), under different lighting (white, and red-blue wavelengths) and retention times (6 and 1.5 d HRT) with complete nitrification. Additionally, the biomass production was stable with faster settling properties without any physiochemical separation.

The outcomes of this thesis on microalgal–bacterial nutrient removal demonstrates that (1) photosynthesis-based aeration at existing wastewater conditions under photo-sequential and continuous photobioreactor setup, (2) flocs with rapid settling characteristics at all studied retention times, (3) the possibility of increasing carbon supplementation to achieve higher carbon to nitrogen balance in the photobioreactor, and (4) most importantly, nitrification-based microalgal biomass uptake occurred at all spectral distributions, lower photosynthetic active radiation and existing wastewater conditions.

Place, publisher, year, edition, pages
Västerås: Mälardalen University, 2018. p. 66
Series
Mälardalen University Press Dissertations, ISSN 1651-4238 ; 263
Keywords
Microalgae, Bacteria, Carbon, Nitrogen, Light
National Category
Water Treatment Bioremediation Bioprocess Technology
Research subject
Energy- and Environmental Engineering
Identifiers
urn:nbn:se:mdh:diva-39158 (URN)978-91-7485-387-2 (ISBN)
Public defence
2018-06-19, Delta, Mälardalens högskola, Västerås, 09:00 (English)
Opponent
Supervisors
Funder
Knowledge Foundation
Available from: 2018-05-08 Created: 2018-05-07 Last updated: 2018-05-17Bibliographically approved

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Anbalagan, AnbarasanSchwede, Sebastian

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