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A passage to wastewater nutrient recovery units: Microalgal-Bacterial bioreactors
Mälardalens högskola, Akademin för ekonomi, samhälle och teknik, Framtidens energi. (ACWA)ORCID-id: 0000-0002-0137-2194
2018 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt) [Forskning på konstnärlig grund]
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.

Ort, förlag, år, upplaga, sidor
Västerås: Mälardalen University , 2018. , s. 66
Serie
Mälardalen University Press Dissertations, ISSN 1651-4238 ; 263
Nyckelord [en]
Microalgae, Bacteria, Carbon, Nitrogen, Light
Nationell ämneskategori
Vattenbehandling Biosanering Bioprocessteknik
Forskningsämne
energi- och miljöteknik
Identifikatorer
URN: urn:nbn:se:mdh:diva-39158ISBN: 978-91-7485-387-2 (tryckt)OAI: oai:DiVA.org:mdh-39158DiVA, id: diva2:1204277
Disputation
2018-06-19, Delta, Mälardalens högskola, Västerås, 09:00 (Engelska)
Opponent
Handledare
Forskningsfinansiär
KK-stiftelsenTillgänglig från: 2018-05-08 Skapad: 2018-05-07 Senast uppdaterad: 2019-10-01Bibliografiskt granskad
Delarbeten
1. Influence of hydraulic retention time on indigenous microalgae and activated sludge process
Öppna denna publikation i ny flik eller fönster >>Influence of hydraulic retention time on indigenous microalgae and activated sludge process
2016 (Engelska)Ingår i: Water Research, ISSN 0043-1354, E-ISSN 1879-2448, Vol. 91, s. 277-284Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Integration of the microalgae and activated sludge (MAAS) process in municipal wastewater treatment and biogas production from recovered MAAS was investigated by studying the hydraulic retention time (HRT) of semi-continuous photo-bioreactors. An average total nitrogen (TN) removal efficiency (RE) of maximum 81.5 ± 5.1 and 64.6 ± 16.2% was achieved at 6 and 4 days HRT. RE of total phosphorous (TP) increased slightly at 6 days (80 ± 12%) HRT and stabilized at 4 days (56 ± 5%) and 2 days (55.5 ± 5.5%) HRT due to the fluctuations in COD and N/P mass ratio of the periodic wastewater. COD and organic carbon were removed efficiently and a rapidly settleable MAAS with a sludge volume index (SVI_10) of less than 117 mL g-1 was observed at all HRTs. The anaerobic digestion of the untreated MAAS showed a higher biogas yield of 349 ± 10 mL g VS-1 with 2 days HRT due to a low solids retention time (SRT). Thermal pretreatment of the MAAS (120 °C, 120 min) did not show any improvement with biogas production at 6 days (269 ± 3 (untreated) and 266 ± 16 (treated) mL gVS-1), 4 days (258 ± 11(untreated) and 263 ± 10 (treated) mL gVS-1) and 2 days (308 ± 19 mL (treated) gVS-1) HRT. Hence, the biogas potential tests showed that the untreated MAAS was a feasible substrate for biogas production. Results from this proof of concept support the application of MAAS in wastewater treatment for Swedish conditions to reduce aeration, precipitation chemicals and CO2 emissions. 

Nyckelord
Activated sludge process, Anaerobic digestion, Hydraulic retention time, Microalgae, Nutrient removal, Thermal pretreatment
Nationell ämneskategori
Miljöbioteknik
Identifikatorer
urn:nbn:se:mdh:diva-31345 (URN)10.1016/j.watres.2016.01.027 (DOI)000371189100028 ()26803263 (PubMedID)2-s2.0-84960332248 (Scopus ID)
Tillgänglig från: 2016-03-24 Skapad: 2016-03-24 Senast uppdaterad: 2018-10-16Bibliografiskt granskad
2. Influence of iron precipitated condition and light intensity on microalgae activated sludge based wastewater remediation
Öppna denna publikation i ny flik eller fönster >>Influence of iron precipitated condition and light intensity on microalgae activated sludge based wastewater remediation
2017 (Engelska)Ingår i: Chemosphere, ISSN 0045-6535, E-ISSN 1879-1298, s. 1523-1530Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

The indigenous microalgae-activated sludge (MAAS) process during remediation of municipal wastewater was investigated by studying the influence of iron flocculation step and light intensity. In addition, availability of total phosphorous (P) and photosynthetic activity was examined in fed-batch and batch mode under northern climatic conditions and limited lighting. This was followed by a semi-continuous operation with 4 d of hydraulic retention time and mean cell residence time of 6.75 d in a photo-bioreactor (PBR) with varying P availability. The fed-batch condition showed that P concentrations of 3–4 mg L−1 were effective for photosynthetic chl. a development in iron flocculated conditions. In the PBR, the oxygen evolution rate increased with increase in the concentration of MAAS (from 258 to 573 mg TSS L−1) at higher surface photosynthetic active radiation (250 and 500 μmol m−2 s−1). Additionally, the rate approached a saturation phase at low MAAS (110 mg L−1) with higher light intensities. Semi-continuous operation with luxury P uptake and effective P condition showed stable average total nitrogen removal of 88 and 92% respectively, with residual concentrations of 3.77 and 2.21 mg L−1. The corresponding average P removal was 68 and 59% with residual concentrations of 2.32 and 1.75 mg L−1. The semi-continuous operation produced a rapidly settleable MAAS under iron flocculated condition with a settling velocity of 92–106 m h−1 and sludge volume index of 31–43 ml g−1 in the studied cases.

Ort, förlag, år, upplaga, sidor
Elsevier, 2017
Nyckelord
Iron flocculation; Microalgae-activated sludge flocs; Nitrogen; Photosynthetic active radiation; Phosphorous; Settling velocity
Nationell ämneskategori
Naturresursteknik
Forskningsämne
energi- och miljöteknik
Identifikatorer
urn:nbn:se:mdh:diva-34244 (URN)10.1016/j.chemosphere.2016.11.161 (DOI)000400879900074 ()27939662 (PubMedID)2-s2.0-85006761788 (Scopus ID)
Projekt
Wastewater treatment; Algae Cultivation
Tillgänglig från: 2016-12-15 Skapad: 2016-12-15 Senast uppdaterad: 2018-10-16Bibliografiskt granskad
3. Continuous photosynthetic abatement of CO2 and volatile organic compounds from exhaust gas coupled to wastewater treatment: Evaluation of tubular algal-bacterial photobioreactor
Öppna denna publikation i ny flik eller fönster >>Continuous photosynthetic abatement of CO2 and volatile organic compounds from exhaust gas coupled to wastewater treatment: Evaluation of tubular algal-bacterial photobioreactor
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2017 (Engelska)Ingår i: Journal of CO2 Utilization, ISSN 2212-9820, E-ISSN 2212-9839, Vol. 21, s. 353-359Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

The continuous abatement of CO2 and toluene from the exhaust gas by an indigenous microalgal-bacterial consortium was investigated in a pilot tubular photobioreactor interconnected to an absorption column using diluted centrate in seawater as a free nutrient source. The removal efficiency of CO2 and toluene was maximised in the vertical absorption column by identifying an optimum liquid to gas (L/G) ratio of 15. The photobioreactor supported steady-state nitrogen and phosphorus removals of 91 ± 2% and 95 ± 4% using 15% diluted centrate at 14 and 7 d of hydraulic retention time (HRT), respectively. A decrease in the removal efficiencies of nitrogen (36 ± 5%) and phosphorus (58 ± 10%) was recorded when using 30% diluted centrate at 7 d of HRT. The volumetric biomass productivities obtained at an HRT of 7 d accounted for 42 ± 11 and 80 ± 3 mg TSS L-1 d-1 using 15 and 30% centrate, respectively. Stable CO2 (76 ± 7%) and toluene removals (89 ± 5%) were achieved at an L/G ratio of 15 regardless of the HRT or centrate dilution. Hence, this study demonstrated the potential of algal-bacterial systems for the continuous removal of CO2 and volatile organic compounds from exhaust gas coupled with the simultaneous treatment of centrate. 

Ort, förlag, år, upplaga, sidor
Elsevier Ltd, 2017
Nationell ämneskategori
Vattenbehandling Förnyelsebar bioenergi
Identifikatorer
urn:nbn:se:mdh:diva-36676 (URN)10.1016/j.jcou.2017.07.016 (DOI)000411443200040 ()2-s2.0-85029771500 (Scopus ID)
Tillgänglig från: 2017-10-06 Skapad: 2017-10-06 Senast uppdaterad: 2018-05-07Bibliografiskt granskad
4. Continuous microalgae-activated sludge flocs for remediation of municipal wastewater under low temperature
Öppna denna publikation i ny flik eller fönster >>Continuous microalgae-activated sludge flocs for remediation of municipal wastewater under low temperature
2017 (Engelska)Ingår i: / [ed] Peter Van der Steen, 2017, s. 1-8Konferensbidrag, Poster (med eller utan abstract) (Refereegranskat)
Abstract [en]

The operational performance of indigenous microalgae-activated sludge was evaluated regarding the nutrient removal efficiency using raw wastewater collected from Västerås wastewater treatment plant, Sweden at limited artificial surface lighting (290 μmol m-1 sec-1) and Nordic wastewater conditions (13°C). Additionally, the oxygen production and consumption, biomass concentration and its settling was evaluated during the symbiotic algal-bacterial interaction. The results confirmed oxygenic organic compound removal (COD removal of 65-94%) at higher (31-45 d) and lower (13-18 d) sludge retention time (SRT). Also, a complete removal of ammonium throughout the process and partial nitrite-nitrate removal at all SRTs (total nitrogen removal of 41- 62%) were observed. Likewise, a partial phosphorus (P)removal was observed in the effluent which provides an opportunity to capture free P fromthe effluent for recovery as fertiliser. Further, the microalgal growth was slower due to lightor inorganic carbon limitation or ammonium repression caused by higher internal recirculationas observed from ammonium and nitrite-nitrate levels in the PBR. Most importantly, effectivePBR biomass concentration based nutrient removal and relative sludge recirculation have tobe considered in the PBR design to avoid light limitation and activate symbiosis.

Nyckelord
Indigenous microalgae-activated sludge, Lighting, Nordic wastewater condition; Sludge retention time; Sludge recirculation
Nationell ämneskategori
Naturresursteknik
Forskningsämne
bioteknik/kemiteknik
Identifikatorer
urn:nbn:se:mdh:diva-38020 (URN)
Konferens
1st IWA Conference on Algal Technologies for Wastewater Treatment and Resource Recovery
Tillgänglig från: 2018-01-12 Skapad: 2018-01-12 Senast uppdaterad: 2018-05-07Bibliografiskt granskad
5. Influence of environmental stress on the microalgal-bacterial process during nitrogen removal
Öppna denna publikation i ny flik eller fönster >>Influence of environmental stress on the microalgal-bacterial process during nitrogen removal
Visa övriga...
(Engelska)Manuskript (preprint) (Övrigt vetenskapligt)
Nationell ämneskategori
Vattenbehandling
Forskningsämne
bioteknik/kemiteknik
Identifikatorer
urn:nbn:se:mdh:diva-39155 (URN)
Tillgänglig från: 2018-05-07 Skapad: 2018-05-07 Senast uppdaterad: 2018-05-15Bibliografiskt granskad

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