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Modelling phosphorus dynamics in constructed wetlands upgraded with reactive filter media
KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering. (Environmental Geochemistry Group)
2017 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Developing low-cost and effective technologies to upgrade phosphorus (P) removal from the catchment runoffs and rural wastewater treatment facilities is one of the main research agendas to save the Baltic Sea from eutrophication. In Sweden, the construction of the constructed wetlands has been one of the environmental objectives for wastewater quality improvement in the small communities. However, the insufficiently understanding of the mechanisms underlying the process of phosphorus mobility and sorption in the constructed wetlands has limited design of the effective constructed wetlands. To provide the better understanding of sorption process in the catchment and constructed wetland system, this thesis used the GIS-based Soil and Water Assessment Tool (SWAT) to predict phosphorus mobility and identify the critical diffusing sources of phosphorus loss in the Oxunda catchment (Paper I). Then, the study developed the three-dimensional numerical Reactive TRAnsPort Model (RETRAP - 3D) in the COMSOL Multiphysics® for evaluating the long - term sorption processes and removal efficiencies of the porous reactive media for upgrading the performance of constructed wetlands (Paper II and III). The latter model coupled many physics equations to solve process of water flow, reaction kinetics and solute transport in the porous reactive adsorbent media for application in the constructed wetlands. The data from the field measurements and column experiments have been used to demonstrate the model simulation accuracy to capture the process of phosphorus sorption in the real environment. Modeling results ranked the phosphorus removal efficiency of the adsorbent media as follows: Polonite® (88 %), Filtralite P® (85%), BFS (62%), Wollastonite (57 %). The satisfactory agreement which obtained between the simulated outputs and measured data confirmed that the SWAT and RETRAP-3D are useful tools for describing various processes in the complicated system. However, further study is required to generate and validate more experimental data to evaluate the sensitivity of local parameters.

Place, publisher, year, edition, pages
KTH: KTH Royal Institute of Technology, 2017. , 35 p.
Series
TRITA-LWR. LIC, ISSN 1650-8629 ; 2017:02
Keyword [en]
Constructed Wetland, COMSOL, Modelling, Reactive Solute Transport, Sorption Process
National Category
Water Engineering
Research subject
Land and Water Resources Engineering
Identifiers
URN: urn:nbn:se:kth:diva-207613ISBN: 978-91-7729-436-8 (print)OAI: oai:DiVA.org:kth-207613DiVA: diva2:1097305
Presentation
2017-06-12, V1, Teknikringen 76, KTH, STOCKHOLM, 13:00 (English)
Opponent
Supervisors
Note

This reserch project was finacially supported by Lars Erik Lundberg scholarship foundation for projectnumber (2015/34 and 2016/12), ÅkeochGreta Lissheds Stiftelsen for project number (2015-00026), J.Gust. Richert Stiftelsen and Ecopool researchproject for smart and sustainable environment. QC 20170523

Available from: 2017-05-23 Created: 2017-05-22 Last updated: 2017-06-02Bibliographically approved
List of papers
1. A new modelling approach for phosphorus mobility and retention processes in the Oxundaån catchment, Sweden
Open this publication in new window or tab >>A new modelling approach for phosphorus mobility and retention processes in the Oxundaån catchment, Sweden
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Eutrophication is the most significant threat towater quality in the entire Baltic Sea region. Its causes are nutrientover-enrichment from diffuse and point sources. Thematic strategies forsustainable mitigation of phosphorus loss from sewage drainage systems andrunoffs from arable land require a holistic approach to identify the criticalpolluting sources and implement relevant policy for adaptive water qualitymanagement. The use of constructed wetlands constitutes one such strategy thatcan mitigate phosphorus loss. However, insufficient understanding about phosphorusmobility and retention in catchments significantly hinders efforts to identifysuitable sites for constructed wetlands and implement alternative, adaptive andeffective management actions. This study aims to evaluate the long-termphosphorus mobility and retention in the Oxudaån catchment in Sweden, andthereby propose suitable sites to localize constructed wetlands. The Soil andWater Assessment watershed model was applied to map and quantify the phosphorusloading from diffuse and point sources under the scenarios of land usemanagement practices. Simulation results have demonstrated the positivecorrelation between the phosphorus concentration with the surface runoffs andnegative correlation with the pH. Overall, Oxundaån catchment indicates a decreasingtrend of phosphorus loading in the Verkaån and Oxundaån riverine of around 2.1% and 1.3 % per year, respectively. The present study suggests the suitablesites for localizing constructed wetlands in the south-west and north-east ofOxundaån lake based on the factor of low slope topography and soilpermeability. The simulation results from the SWAT model offer evidence thatcan guide the localization and choice of management interventions to achieve asustainable mitigation of phosphorus loss. This study concludes that, while singlemanagement actions can help solve the problem of eutrophication, a moreeffective and sustainable mitigation of eutrophication will require the integrationof multiple adaptive land use management approaches.

Keyword
Sediment erosion; Constructed wetlands; Phosphorus retentions;Adaptive management; Watershed modelling
National Category
Water Engineering
Identifiers
urn:nbn:se:kth:diva-207829 (URN)
Note

QC 20170529

Available from: 2017-05-24 Created: 2017-05-24 Last updated: 2017-05-29Bibliographically approved
2. Modelling phosphorus recovery by reactive adsorbent in a vertical subsurface flow constructed wetland
Open this publication in new window or tab >>Modelling phosphorus recovery by reactive adsorbent in a vertical subsurface flow constructed wetland
Show others...
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Phosphorus removal efficiencies by four low - costsreactive adsorbent media were evaluated in the long - time period using thethree - dimensional model of the vertical subsurface flow constructed wetlandsin the COMSOL Multiphysics® software. Evaluations were made for Polonite,Filtralite P, Sorbulite and Wollastonite adsorbent media with the aims ofpredicting their long - term sorption capacity and describing the phenomena ofsorption mechanisms when applied in the vertical subsurface flow constructedwetlands for wastewater purification. The 3D model of the vertical flowconstructed wetlands were dimensioned to Swedish EPA guidelines for small scalewastewater treatment, and calibrated at saturated media using the breakthroughdata derived from the column experiments of similar adsorbent mediaapplication, and the local sensitivity analysis were performed for waterquality and hydraulic loading parameters. It was observed that the breakthroughcurves developed by model were significantly correlated to the experimentaldata. The overall findings showed that Polonite® could be the potentialreactive adsorbent for phosphorus removal in the VF-CWs application, and itsremoval efficiency was discovered to last for 5 years. The large variation ofmedia sorption capacities discovered to be affected more by factor of pH andhydraulic loading rates than the particle size. High degree of predictionaccuracy which is demonstrated by this model suggest that the proposed model isa useful tool for predicting pollutants removal in various reactive porousmedia.

Keyword
Constructed wetlands, COMSOL, Phosphorus, Residence Time, Reactive Media
National Category
Water Engineering
Research subject
Land and Water Resources Engineering
Identifiers
urn:nbn:se:kth:diva-207827 (URN)
Funder
StandUp
Note

QC 20170529

Available from: 2017-05-24 Created: 2017-05-24 Last updated: 2017-05-29Bibliographically approved
3. Reactive transport modelling of long-term phosphorus dynamic in the compact constructed   wetland using COMSOL Multiphysics
Open this publication in new window or tab >>Reactive transport modelling of long-term phosphorus dynamic in the compact constructed   wetland using COMSOL Multiphysics
(English)In: Ecological Engineering JournalArticle in journal (Other academic) Submitted
Abstract [en]

A three-dimensional reactive transport model (RETRAP-3D) was developed by this study in the COMSOL Multiphysics®software to evaluate the long-term sorption capacity and mechanisms of dissolved reactive phosphorus removal in reactive adsorbent. The model coupledphysics interfaces for water flow, transport of reactive species, reaction kinetics for chemical compositions and biofilm development. Simulations were conducted for Polonite®, Filtralite P®, and Blast Furnace Slag mediaat fully saturated media, equilibrium miscible solution and isothermal heat transfer conditions. The model was validated using column experimental data ofsimilar media for application in constructed filter beds. The general modelling results showed good agreement with the measured breakthrough data. The most significant DIP retention capacity (P < 0.02) and longest residence time(1250 days) has been found for Polonite® and the most insignificant DIP retention for blast furnace slag (P > 0.54). The DIP removal was significantly correlated to factors of pH change, media characteristics, hydraulic dosage and retention times. These results demonstrate the reliability of the model as aflexible tool to predict the long-term performance of filter media and better understand processes within the system under various operational, weather and wastewater conditions.

Keyword
Adsorption; Phosphorus retention; Compact Reactive Filter; COMSOL; Porous Reactive Media; Reactive Solute Transport
National Category
Water Engineering
Identifiers
urn:nbn:se:kth:diva-207828 (URN)
Funder
StandUp
Note

QC 20170529

Available from: 2017-05-24 Created: 2017-05-24 Last updated: 2017-05-29Bibliographically approved

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