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Simulating the hydraulic dynamics and treatment performance of a sequencing batch flow constructed wetland
KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Water and Environmental Engineering.ORCID iD: 0000-0002-8957-6772
KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Water and Environmental Engineering.ORCID iD: 0000-0001-6617-4001
KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Water and Environmental Engineering.
KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Resources, Energy and Infrastructure.ORCID iD: 0000-0003-2726-6821
(English)In: Article, book review (Refereed) Submitted
Abstract [en]

In a six-month field trial, the performance of a full-scale sequencing batch flow constructed wetland (SBCW) treating on-site wastewater was determined. The filling and draining periods lasted 5-9 days, depending on wastewater production by users (two households). The results indicated that the SBCW system efficiently removed ammonium-nitrogen (NH4-N, 76%) and Escherichia coli (89%). However, draining by pumping increased preferential water flow and considerably limited removal of dissolved phosphorus (PO4-P) in the filter bed. Analysis of water samples from nine points and three vertical levels of the wetland bed showed that pumping aerated the bed, resulting in removal of NH4-N being highest in the top 0-0.2 m layer (43%) intermediate in the 0.2-0.4 m layer (32%), and lowest in the deep (0.4-0.6 m) layer (4%). Complementary modeling using COMSOL Multiphysics software to predict the hydraulic dynamics for three different SBCW designs indicated that the drainage system of the present SBCW should be re-designed to increase contact time and aeration, for improved phosphorus and nitrogen removal.

Keywords [en]
Constructed wetland; Reactive Modeling; Phosphorus; Nitrogen; Design Optimization
National Category
Water Engineering
Research subject
Land and Water Resources Engineering
Identifiers
URN: urn:nbn:se:kth:diva-256495OAI: oai:DiVA.org:kth-256495DiVA, id: diva2:1346001
Funder
Lars Erik Lundberg Scholarship Foundation, 696881:2017/2018
Note

QC 20190903

Available from: 2019-08-26 Created: 2019-08-26 Last updated: 2019-09-03Bibliographically approved
In thesis
1. Filtration System For On-Site Wastewater Treatment: Experiences From Modelling and Experimental Investigations
Open this publication in new window or tab >>Filtration System For On-Site Wastewater Treatment: Experiences From Modelling and Experimental Investigations
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Many on-site wastewater treatment systems in Sweden are not sustainable in terms of treatment efficiency, nutrient recycling and economics. Achieving reliable and sustainable systems to meet on-site wastewater treatment demands requires comprehensive field investigations of the performance of novel technologies. This thesis investigated the performance of a new leading-edge technology for on-site wastewater treatment in a real field environment in northwest of Baltic Proper Sea, Sweden. The system integrates septic tank treatment technology with a package treatment plant (PTP) and a sequencing batch subsurface flow constructed wetland (SBCW). The investigation combined three approaches: field monitoring, laboratory-scale column experiments and process-based modelling, to provide a better understanding of system performance, predict contaminant retention and test system response to various environmental factors, design scenarios and operational conditions.

The overall results indicated that the entire system is efficient in removing total phosphorus (83%), biological oxygen demand (BOD7, 99%) and Escherichia coli bacteria (89%). It is less efficient in total inorganic nitrogen removal (22%). Mean concentration of phosphorus (0.96 mg/L) and pH (8.8) in effluent from the entire system were found to be below the Swedish threshold values for on-site wastewater discharge. This indicates that the system could be reliable and sustainable technology for on-site wastewater treatment in cold climate conditions.

A complementary three-dimensional (3D) model developed using COMSOL Multiphysics® software proved to be a useful and rapid tool for predicting the behaviour of complex hydraulic dynamics. It provided valuable insights into the spatial and temporal variability in sorption processes caused by changes in different wastewater treatment system design parameters, environmental factors and modes of operation. Through process-based modelling, a reactive filter material with longer lifetime and a SBCW design that improved the sustainability of on-site wastewater treatment system were successfully identified.

It was concluded that long-term performance of reactive filter materials in PTP systems can be achieved when the system is loaded intermittently with low influent contaminant concentrations (<3 mg/L). Optimum phosphorus and nitrogen removal in SBCW can be achieved by manipulating drainage pipe placement and feeding mode, to enable longer contact time and artificial aeration conditions.

Abstract [sv]

Många system för småskalig avloppsrening (OWT) i Sverige är inte hållbara när det gäller reningsseffektivitet, näringsåtervinning och ekonomi. Milstolpen för att uppnå pålitlig och hållbar teknik för OWT kräver noggranna undersökningar av prestandan för att en ny och förbättrad teknik ska kunna utvecklas inom området. Denna studie har syftat till att bidra med kunskap och erfarenhet genom att undersöka prestandan för en ny teknik för OWT genom undersökningar av funktionen i verklig fältmiljö. Det studerade systemet integrerar behandlingsteknik med klassisk slamavskiljning följt av minireningsverk med filtermaterial (PTP) och sist ett poleringssteg med våtmark som drivs med sekventiell påfyllnad av vatten (SBCW).

Studien kombinerade tre tillvägagångssätt: fältövervakning, kolonnexperiment i laboratorieskala och processbaserad modellering. Syftet var att ge bättre förståelse för systemets prestanda och förutsäga föroreningarnas avskiljning i olika delar av anläggningen samt testa svaren från systemet på olika miljöfaktorer, utförd konstruktion och driftsförhållanden under olika årstider. De sammanvägda resultaten indikerade att hela systemet är mer effektivt för behandling av total-fosfor (83%), biologiskt syretärande ämnen (BOD7 , 99%) och E. coli-bakterier (89%) och mindre effektiv för total borttagning av oorganiskt kväve (22%). Medelkoncentration av fosfor i det renade avloppsvattnet efter SBCW var 0,96 mg / L  och pH 8,8 vilket ligger under det svenska rekommenderade värdena för enskilda avlopp. Detta är en indikation på att denna systemlösning kan vara en tillförlitlig och hållbar teknik för OWT under kalla klimatförhållanden.

En kompletterande tredimensionell (3D) -modell som utvecklades med COMSOL Multiphysics®-programvara befanns vara ett användbart verktyg och snabb metod för att förutsäga beteendet hos komplex hydraulisk dynamik och insikter erhölls om den rumsliga och temporära variationen i sorptionsprocesser orsakade av förändring av olika designscenarier, miljöfaktorer och driftssätt. Genom processbaserad modellering identifierade studien framgångsrikt reaktiva filtermaterials (RFM) livslängd och konstruktionsscenarier där SBCW kan omformas för ökad hållbarhet i OWT-systemet. Denna studie drar slutsatsen att den långsiktiga prestandan och livslängden hos de reaktiva filtermaterialen i PTP-systemet kan uppnås om avloppsvattnen påfylls intermittent i en låg koncentration (<3 mg / L). Ett konstruktionsscenario visade att avskiljningen av fosfor och kväve i SBCW kan förbättras genom att dräneringsrör och tillförsel av avloppsvatten ändras i förhållande till befintlig lösning.

Place, publisher, year, edition, pages
Stockholm, Sweden: KTH Royal Institute of Technology, 2019. p. 83
Series
TRITA-ABE-DLT ; 1930
National Category
Environmental Engineering
Research subject
Land and Water Resources Engineering
Identifiers
urn:nbn:se:kth:diva-256487 (URN)978-91-7873-281-4 (ISBN)
Public defence
2019-09-20, Kollegiesalen, Brinellvägen 8, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
The Lars Erik Lundberg Foundation for Research and Education, (696881:2015-2019)
Available from: 2019-08-27 Created: 2019-08-26 Last updated: 2019-08-27Bibliographically approved

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