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Biogeochemical Processes in Denitrifying Woodchip Bioreactors and their Application in the Mining Industry
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.ORCID iD: 0000-0002-0311-8368
2019 (English)Doctoral thesis, comprehensive summary (Other academic)Alternative title
Biogeokemiska processer i kvävebarriärer med tillämpning inom gruvindustrin (Swedish)
Abstract [en]

This thesis evaluates passive denitrifying woodchip bioreactors (DWBs) for the removal of nitrate (NO3-) in neutral pH mine drainage, where water is passed through a carbon-rich porous matrix (e.g. woodchips) for the reduction of NO3- to nitrogen gas. DWBs have been used for the removal of NO3- from water in various settings and are expected to operate with little maintenance for at least a decade; however, the processes controlling the emission of greenhouse gases and other undesirable by-products, as well as the magnitude and variability in NO3- removal rates and how these develop over time, are not completely understood and were the focus of this thesis.

Water treatment in DWBs was investigated in laboratory-scale column tests and in a pilot-scale bioreactor installed at the Kiruna iron ore mine, northern Sweden. Denitrification was the major pathway for NO3- removal in both experimental systems. Incoming NO3- concentrations (up to 30.0 mg N L-1) were removed to below detection limits at temperatures and hydraulic residence times (HRTs) between 5-22°C and ~1.9-2.6 days, respectively, without substantial production of nitrite or ammonium (NH4+). NO3- removal was incomplete in both systems when HRTs decreased to ~1 day, and/or as temperature decreased below 5°C in the pilot-scale bioreactor, under which conditions an increased production of nitrous oxide (N2O) and NH4+ was observed (relative to the NO3- reduced).

In the column tests, non-ideal flow was detected and solute transport was described using a dual-porosity model. Stagnant zones not transmitting flow did not participate in NO3- removal and the fraction of immobile water increased with increases in the advection velocity, suggesting that bioreactor performance could be enhanced by emphasizing design with low advection velocities.  

The study demonstrated that dominating biogeochemical processes varied with time in the pilot-scale bioreactor. There was a decline in organic carbon export and increase in pH and alkalinity that, based on a stoichiometric mass-balance, was suggested to be the result of a change in fermentation end-products that provided a carbon source to the denitrifying community. The decline in NO3- removal rates and biogeochemical process diversity, and the preferential selection of denitrifiers with the genetic capacity for reduction to N2O, but not N2, are hypothesized to arise from the temporal development of syntrophic structures between fermenters and denitrifiers.

Abstract [sv]

Denna avhandling utvärderar passiva kvävebarriärer (eng. denitrifying fixed-bed bioreactors) som en metod för att minska kvävehalter i gruvvatten (neutralt pH), där vattnet rinner genom en porös matris rik på kol (här träflis) för att omvandla nitrat (NO3-) till kvävgas. Kvävebarriärer har tidigare använts i olika miljöer för att minska nitrathalter i vatten och förväntas fungera med minimalt underhåll i upp till tio år. Dock så är de processer som kontrollerar utsläpp av växthusgaser och andra biprodukter, samt variabiliteten i nitratreduceringshastigheter och hur dessa förändras över tid, fortfarande relativt okända i dessa system och var fokus i denna avhandling.

Kvävereningen i kvävebarriärer utvärderades i kolonnstudier samt i en barriär i pilotskala som installerades vid Kirunagruvan i Kiruna. Denitrifikation var den huvudsakliga processen varmed NO3- reducerades i båda systemen. Inkommande NO3- koncentrationer (upp till 30.0 mg N L-1) reducerades till under detektionsgränsen vid temperaturer mellan 5-22°C och uppehållstider mellan ~1,9-2,6 dagar, utan betydande produktion av nitrit (NO2-) eller ammonium (NH4+). Då uppehållstiden minskades till ~1 dag förblev inkommande NO3- ofullständigt reducerat i båda systemen; vid låga temperaturer (<5°C) och/eller uppehållstider om ~1 dag i barriären så ökade produktionen av lustgas (N2O) och NH4+ (relativt den reducerade mängden NO3-).

Preferentiellt flöde i träflismatrisen påvisades i kolonnstudierna och ämnestransporten beskrevs med en ’dubbel-porositets’-modell. Zoner i träflismatrisen som inte deltog i flödet ökade tillsammans med flödeshastigheten i systemet och bidrog inte till att minska nitrathalter, vilket tydde på att reningskapaciteten i dessa system kan ökas genom att främja låga flödeshastigheter.

Den här studien demonstrerade att de dominerande biogeokemiska processerna i den pilotskaliga barriären förändrades med tid. Exporten av organisk kol minskade medan pH och alkalinitet ökade med tid vilket, baserat på en stökiometrisk mass-balans, kunde förklaras av en ändring i slutprodukten från fermentation. Minskningen i nitratreduceringshastigheter och mångfalden av biogeokemiska processer, samt främjandet av denitrifierare med N2O som slutprodukt, diskuterades utifrån en utveckling av syntrofi mellan fermenterare och denitrifierare.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2019. , p. 65
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1790
Keywords [en]
water treatment, mine drainage, nitrate, nitrous oxide, DNRA, fermentation, syntrophy, temperature
Keywords [sv]
kväverening, gruvvatten, nitrat, lustgas, DNRA, fermentation, syntrofi, temperatur
National Category
Oceanography, Hydrology and Water Resources Water Treatment
Research subject
Hydrology
Identifiers
URN: urn:nbn:se:uu:diva-380386ISBN: 978-91-513-0617-9 (print)OAI: oai:DiVA.org:uu-380386DiVA, id: diva2:1299616
Public defence
2019-05-17, Axel Hambergsalen, Geocentrum, Villavägen 16, Uppsala, 09:00 (English)
Opponent
Supervisors
Projects
miNing
Funder
Vinnova, 2014-01134Available from: 2019-04-24 Created: 2019-03-27 Last updated: 2019-06-18
List of papers
1. Denitrification in a low-temperature bioreactorsystem at two different hydraulic residence times: laboratory column studies
Open this publication in new window or tab >>Denitrification in a low-temperature bioreactorsystem at two different hydraulic residence times: laboratory column studies
2017 (English)In: Environmental technology, ISSN 0959-3330, E-ISSN 1479-487X, Vol. 38, no 11, p. 1362-1375Article in journal (Refereed) Published
Abstract [en]

Nitrate removal rates in a mixture of pine woodchips and sewage sludge were determined in laboratory column studies at 5°C, 12°C, and 22°C, and at two different hydraulic residence times (HRTs; 58.2–64.0 hours and 18.7–20.6 hours). Baffles installed in the flow path were tested as a measure to reduce preferential flow behavior, and to increase the nitrate removal in the columns. The nitrate removal in the columns was simulated at 5°C and 12°C using a combined Arrhenius-Monod equation controlling the removal rate, and a first-order exchange model for incorporation of stagnant zones. Denitrification in the mixture of pine woodchips and sewage sludge reduced nitrate concentrations of 30 mg N L−1 at 5°C to below detection limits at a HRT of 58.2–64.0 hours. At a HRT of 18.7–20.6 hours, nitrate removal was incomplete. The Arrhenius frequency factor and activation energy retrieved from the low HRT data supported abiochemically controlled reaction rate; the same parameters, however, could not be used to simulate the nitrate removal at high HRT. The results show an inversely proportional relationship between the advection velocity and the nitrate removal rate, suggesting that bioreactor performance could be enhanced by promoting low advection velocities.

National Category
Oceanography, Hydrology and Water Resources
Research subject
Hydrology
Identifiers
urn:nbn:se:uu:diva-303686 (URN)10.1080/09593330.2016.1228699 (DOI)000400464400004 ()27603564 (PubMedID)
Projects
MiNing
Funder
VINNOVA, P31054-1
Available from: 2016-09-22 Created: 2016-09-22 Last updated: 2019-03-27Bibliographically approved
2. Determination of major biogeochemical processes in a denitrifying woodchip bioreactor for treating mine drainage
Open this publication in new window or tab >>Determination of major biogeochemical processes in a denitrifying woodchip bioreactor for treating mine drainage
2018 (English)In: Ecological Engineering: The Journal of Ecotechnology, ISSN 0925-8574, E-ISSN 1872-6992, Vol. 110, p. 54-66Article in journal (Refereed) Published
Abstract [en]

At the Kiruna iron ore mine in northern Sweden, mine drainage and process water contain elevated concentrationsof nitrate (NO3−) from the use of ammonium nitrate fuel oil explosives. In order to investigate thetreatment capacity of a denitrifying woodchip bioreactor technique for the removal of NO3− through denitrification,a bioreactor was installed at the mine site in 2015 and operated for two consecutive years. Neutral-pHmine drainage and process water containing 22 mg NO3−-N and 1132 mg SO42− (average) was passed throughthe bioreactor which was filled with a reactive mixture of pine woodchips and sewage sludge, at treatmenttemperatures ranging between 0.8 and 17 °C. At bioreactor temperatures above ∼5 °C, NO3− removal proceededto below detection limits (0.06 mg N L−1) without substantial production of nitrite (NO2−), ammonium(NH4+), nitrous oxide (N2O), or methane (CH4). The relative production of NH4+ and N2O to the NO3− reducedincreased as bioreactor temperatures decreased below ∼5 °C. Based on the resultant changes in alkalinity andpH from the production of bicarbonate (HCO3−) and carbonic acid (H2CO3), a stoichiometric mass balancemodel indicated that denitrification, nitrate reduction to ammonium (DNRA), sulfate reduction, and fermentationwere the major biogeochemical processes controlling pH, alkalinity and nitrogen, sulfur and carbonconcentrations in the system. It is suggested that fermentation changed from being mainly butyrate producing toacetate producing with time, triggering a decline in biogeochemical process diversity and leaving denitrificationas the sole major electron accepting process.

Keywords
Denitrification, sulfate reduction, DNRA, woodchip bioreactor, temperature, biogeochemical processes, mine drainage, nitrogen, denitrifikation, sulfatreduktion, DNRA, bioreaktor med träflis, temperatur, biogeokemiska processes, gruvvatten, kväve
National Category
Geochemistry
Research subject
Hydrology
Identifiers
urn:nbn:se:uu:diva-331698 (URN)10.1016/j.ecoleng.2017.09.018 (DOI)000417048500007 ()
Projects
miNing
Funder
VINNOVA, 2014-01134
Available from: 2017-10-17 Created: 2017-10-17 Last updated: 2019-03-27Bibliographically approved
3. Identification of the temporal control on nitrate removal rate variability in a denitrifying woodchip bioreactor
Open this publication in new window or tab >>Identification of the temporal control on nitrate removal rate variability in a denitrifying woodchip bioreactor
2019 (English)In: Ecological Engineering: The Journal of Ecotechnology, ISSN 0925-8574, E-ISSN 1872-6992, Vol. 127, p. 88-95Article in journal (Refereed) Published
Abstract [en]

Nitrate (NO3) removal rates in a denitrifying woodchip bioreactor (DWB) removing NO3 from mine water in a subarctic climate was modeled with the purpose of determining the processes controlling variability in NO3 removal rates over time. The Eyring equation was used to define the temperature dependency, while a rate law was used to describe the NO3 concentration dependency of the NO3 removal rates. The results show that the temperature and NO3 concentration dependency of the NO3 removal rates changes over time in the DWB due to the preferential selection of conceptualized NO3 - reducing bacteria favoring low temperatures, with the mean temperature optimum of the NO3 reducing consortium decreasing from 24.2 °C to 16.0 °C following the first year of DWB operations. It is suggested that the selection of the low temperature NO3 reducers in the DWB represented an increased dependence on cross-feeding between a fermentative community, producing the reactive organic carbon substrate, and a denitrifying community, consuming the organic carbon substrate, with the temporal variability in NO3 removal rates being controlled by the stabilization of the microbial community structure. It is also suggested that the life expectancy of DWBs is more related to the stability of the cross-feeding between the fermenting microbial community and the denitrifying microbial community, than to the total carbon content.

Keywords
Woodchip bioreactor, Modeling, Macromolecular rate theory, Selection, Temperature, Longevity
National Category
Water Treatment
Identifiers
urn:nbn:se:uu:diva-366588 (URN)10.1016/j.ecoleng.2018.11.015 (DOI)000455632500009 ()
Funder
VINNOVA, 2014-01134
Available from: 2018-11-21 Created: 2018-11-21 Last updated: 2019-03-27Bibliographically approved
4. Microbial Controls on Net Production of NOx Species in a Denitrifying Woodchip Bioreactor
Open this publication in new window or tab >>Microbial Controls on Net Production of NOx Species in a Denitrifying Woodchip Bioreactor
(English)Manuscript (preprint) (Other academic)
National Category
Water Treatment
Identifiers
urn:nbn:se:uu:diva-380384 (URN)
Projects
miNing
Funder
Vinnova, 2014-011334
Available from: 2019-03-27 Created: 2019-03-27 Last updated: 2019-03-27

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