liu.seSearch for publications in DiVA
Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • oxford
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Diluting the evidence? How residence time analyses can influence your results
Linköping University, Department of Physics, Chemistry and Biology, Biology. Linköping University, The Institute of Technology.
Department of Landscape Architecture, Planning and Management, Swedish University of Agricultural Sciences, Alnarp, Sweden.
Department of Biosystems and Technology, Swedish University of Agricultural Sciences, Alnarp, Sweden.
Linköping University, Department of Physics, Chemistry and Biology, Biology. Linköping University, The Institute of Technology.ORCID iD: 0000-0001-6128-1051
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Hydraulic tracer studies are frequently used to estimate wetland residence time distributions (RTDs) and ultimately pollutant removal. However, there is no consensus on how to analyse these data. We set out to (i) review the different methods used and (ii) use simulations to explore how the data analysis method influences the quantification of wetland hydraulics and pollutant removal. The results showed that the method influences the water dispersion (N) most strongly and the removal least strongly. The influence increased with decreasing effective volume ratio (e) and N, indicating a greater effect of the method in wetlands with low effective volume and high dispersion. The method of moments with RTD truncation at 3 times the theoretical residence time (tn) and tracer background concentration  produced the most dissimilar parameters. The most similar parameters values were those for gamma modelling and the method of moments with RTD truncation at tracer background concentration. For correct removal estimates, e was more important than N. However, the results from the literature review and simulations indicated that previously published articles may contain overestimated e and underestimated N values as a result of frequent RTD truncations at 3tn when using the method of moments. As a result, the removal rates may also be overestimated by as much as 14% compared to other truncation methods or modelling. Thus, it is recommended that wetland hydraulic tracer studies should use the same method, specifically, RTD truncation. We conclude that the choice of tracer data analysis method can greatly influence the quantifications of wetland hydraulics and removal rate.

Keyword [en]
Gamma model, removal rate, residence time analysis, tracer, trapezoid rule, wetland hydraulics
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:liu:diva-91401OAI: oai:DiVA.org:liu-91401DiVA: diva2:617651
Available from: 2013-04-24 Created: 2013-04-24 Last updated: 2014-10-08
In thesis
1. Wastewater treatment in constructed wetlands: Effects of vegetation, hydraulics and data analysis methods
Open this publication in new window or tab >>Wastewater treatment in constructed wetlands: Effects of vegetation, hydraulics and data analysis methods
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Degradation of water resources has become one of the most pressing global concerns currently facing mankind. Constructed Wetlands (CWs) represent a concept to combat deterioration of water resources by acting as buffers between wastewater and receiving water bodies. Still, constructing wetlands for the sole purpose of wastewater treatment is a challenging task. To contribute to this research area, the fundamental question raised in this doctorate thesis was: how do factors such as vegetation and residing water movements (hydraulics) influence wastewater treatment in CWs? Also, effects of different data analysis methods for results of CW hydraulics and wastewater treatment were investigated. Research was focused on  phosphorus (P), ammonium-nitrogen (NH4+-N) and solids (TSS) in wastewater and o n P in macrophyte biomass. Studies were performed in pilot-scale free water surface (FWS) CW systems in Kenya (Chemelil) and Sweden (Halmstad) and as computer simulations.

Results from the Chemelil CWs demonstrated that meeting effluent concentration standards simultaneously for all water quality parameters in one CW was difficult. Vegetation harvest, and thus nutrient uptake by young growing macrophytes, was important for maintaining low effluents of NH4+-N and P, especially during dry seasons. On the other hand, mature and dense vegetation growing for at least 4 months secured meeting TSS standards. Phosphorus in above-ground green biomass accounted for almost 1/3 of the total P mass removal, demonstrating high potential for P removal through macrophyte harvest in CWs. Also, results suggested that harvest should be species-specific to achieve high P removal by macrophytes and overall acceptable wastewater treatment in CWs. Still, different methods to estimate evapotranspiration (ET) from the Chemelil CWs showed that water balance calculations greatly impacted estimations of wastewater treatment results.

Hydraulic tracer studies performed in the Chemelil and Halmstad CWs showed that mature and dense emergent vegetation in CWs could reduce effective treatment volumes (e-values), which emphasized the importance of regulating this type of vegetation. Also, it was shown that hydraulic tracer studies with lithium chloride performed in CWs with dense emergent vegetation had problems with low tracer recoveries. This problem could be reduced by promoting the distribution of incoming tracer solution into the CW using a barrier near the CW inlet pipe. Computer simulation results showed that the choice of tracer data analysis method greatly influenced quantifications of CW hydraulics and pollutant removal. The e-value could be 50% higher and the pollutant removal 13% higher depending upon used method. Moreover, unrealistic evalues (above 100%) in published literature could to some extent be explained by tracer data analysis method. Hence, to obtain more reliable hydraulic data and wastewater treatment results from CWs, more attention should be paid to the choice of tracer data analysis method.

Abstract [sv]

Konstruerade våtmarker representerar ett koncept för möjligheten att nå en hållbar vattenresurshantering genom att agera som ”filter” mellan föroreningskälla och viktiga vattenresurser såsom sjöar och hav. Mycket kunskap saknas däremot om hur man konstruerar våtmarker med en optimal och pålitlig vattenreningskapacitet. Den här avhandlingen undersöker därför hur vegetation och vattnets väg genom våtmarken (hydrauliken) påverkar avloppsvattenrening i våtmarker. Dessutom undersöktes hur valet av dataanalysmetod av insamlad data påverkar resultaten. Studier genomfördes i Kenya och Sverige i experimentvåtmarker (ca. 40-60 m2) och inkluderadedatainsamling av vattenkvalité, hydraulik (spårämnesexperiment) samt biomassa och fosfor i biomassan av två olika våtmarksväxter. Dessutom genomfördes datorsimuleringar.

Resultaten från Kenya visade att växtskörd och efterföljande näringsupptag av nyskördade växter var viktig för att uppnå låga utgående koncentrationer av fosfor och ammonium i en tropisk våtmark, speciellt under torrsäsongen. Däremot var en välutvecklad och tät vegetation viktig för reningen av partiklar. Fosfor i grön växtbiomassa representerade cirka 1/3 av våtmarkernas totala fosforrening, vilket påvisade potentialen i att genom skörd ta bort fosfor från avloppsvatten m.h.a. konstruerade våtmarker. Resultaten pekade också på att skörden bör vara art-specifik för att uppnå en hög fosforrening och generellt bra vattenreningsresultat. Dock visade olika beräkningsmetoder att vattenbalansen i en tropisk våtmark markant kan påverka vattenreningsresultaten.

Resultaten från spårämnesexperimenten demonstrerade att den effektiva våtmarksvolymen för vattenrening blev mindre vid hög täthet av övervattensväxter. Detta pekade på att regelbunden växtskörd var viktig för att uppnå god vattenrening i våtmarker. Experiment med spårämnet litium visade att man kan få felaktiga resultat p.g.a. att en del spårämne fasthålls på botten i våtmarken om denna har mycket övervattensväxter. Därför bör spridningen av spårämnet i sådana våtmarker underlättas m.h.a. en spridningsbarriär nära inloppsröret. Simuleringar visade också att valet av dataanalysmetod av spårämnesdata starkt kan påverka resultaten och därmed också vår tolkning av en våtmarks hydraulik och reningskapacitet. Den effektiva volymen kunde vara 50% högre och reningseffekten 13% högre beroende på vilken metod som användes. Likaså kan valet av dataanalysmetod ha bidragit till överskattade och orealistiska effektiva volymer (över 100%) i artiklar publicerade de senaste 25 åren. Genom att fokusera mer på valet av dataanalysmetod och t.ex. jämföra resultaten från två olika metoder kan man minimera risken för bristfälliga resultat och därmed felaktiga slutsatser om en våtmarks vattenreningskapacitet.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2013. 59 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1509
Keyword
constructed wetland, free water surface flow, wastewater treatment, Kenya, Sweden, vegetation, harvest, Cyperus papyrus, Echinochloa pyramidalis, mass load, phosphorus, ammonium, suspended solids, pollutant removal, hydraulics, residence time distribution, data analysis methods, Konstgjorda våtmarker, avloppsvatten, vattenrening, fosfor, ammonium, partiklar, Kenya, Sverige, växter, Cyperus papyrus, Echinochloa pyramidalis, skörd, hydraulik, dataanalysmetod
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-91402 (URN)978-91-7519-649-7 (ISBN)
Public defence
2013-05-30, Planck, Physics House, Campus Valla, Linköpings universitet, Linköping, 13:00 (English)
Opponent
Supervisors
Available from: 2013-04-24 Created: 2013-04-24 Last updated: 2014-10-08Bibliographically approved

Open Access in DiVA

No full text

Authority records BETA

Bodin, HristinaMilberg, Per

Search in DiVA

By author/editor
Bodin, HristinaMilberg, Per
By organisation
BiologyThe Institute of Technology
Natural Sciences

Search outside of DiVA

GoogleGoogle Scholar

urn-nbn

Altmetric score

urn-nbn
Total: 90 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • oxford
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf