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Filtration System For On-Site Wastewater Treatment: Experiences From Modelling and Experimental Investigations
KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering. (Vatten- och miljöteknik, Water and Environmental Engineering)ORCID iD: 0000-0002-8957-6772
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: urn:nbn:se:kth:diva-256487ISBN: 978-91-7873-281-4 (electronic)OAI: oai:DiVA.org:kth-256487DiVA, id: diva2:1345945
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
List of papers
1. Modelling phosphorus sorption kinetics and the longevity of reactive filter materials used for on-sitewastewater treatment
Open this publication in new window or tab >>Modelling phosphorus sorption kinetics and the longevity of reactive filter materials used for on-sitewastewater treatment
2019 (English)In: Water, ISSN 2073-4441, E-ISSN 2073-4441, Vol. 11, no 4, article id 811Article in journal (Refereed) Published
Abstract [en]

Use of reactive filter media (RFM) is an emerging technology in small-scale wastewater treatment to improve phosphorus (P) removal and filter material longevity for making this technology sustainable. In this study, long-term sorption kinetics and the spatial dynamics of sorbed P distribution were simulated in replaceable P-filter bags filled with 700 L of reactive material and used in real on-site treatment systems. The input data for model calibration were obtained in laboratory trials with Filtralite P®, Polonite® and Top16. The P concentration breakthrough threshold value was set at an effluent/influent (C/C 0 ) ratio of 1 and simulations were performed with P concentrations varying from 1 to 25 mg L -1 . The simulation results showed that influent P concentration was important for the breakthrough and longevity, and that Polonite performed best, followed by Top16 and Filtralite P. A 100-day break in simulated intermittent flow allowed the materials to recover, which for Polonite involved slight retardation of P saturation. The simulated spatial distribution of P accumulated in the filter bags showed large differences between the filter materials. The modelling insights from this study can be applied in design and operation of on-site treatment systems using reactive filter materials.

Place, publisher, year, edition, pages
MDPI AG, 2019
Keywords
Breakthrough, COMSOL modelling, P-filter bags, Phosphorus saturation, Solute transport, Effluents, Filtration, Phosphorus, Wastewater treatment, Design and operations, Emerging technologies, Filter bags, Phosphorus sorption, Reactive materials, Small scale wastewater treatment, Passive filters
National Category
Water Treatment
Identifiers
urn:nbn:se:kth:diva-255943 (URN)10.3390/w11040811 (DOI)2-s2.0-85065037122 (Scopus ID)
Note

QC 20190815

Available from: 2019-08-15 Created: 2019-08-15 Last updated: 2019-08-27Bibliographically approved
2. Performance of an On-Site Wastewater Treatment System Using Reactive Filter Media and a Sequencing Batch Constructed Wetland
Open this publication in new window or tab >>Performance of an On-Site Wastewater Treatment System Using Reactive Filter Media and a Sequencing Batch Constructed Wetland
2019 (English)In: Sustainability, ISSN 2071-1050, E-ISSN 2071-1050, Vol. 11, no 11, article id UNSP 3172Article in journal (Refereed) Published
Abstract [en]

Many on-site wastewater treatment systems, such as soil treatment systems, are not sustainable in terms of purification efficiency, nutrient recycling potential, and economics. In this case study, a sequencing batch constructed wetland (SBCW) was designed and added after a package treatment plant (PTP) using reactive filter media for phosphorus (P) removal and recycling. The treatment performance of the entire system in the start-up phase and its possible applicability in rural areas were investigated. Raw and treated effluents were sampled during a period of 25 weeks and analyzed for nitrogen, phosphorus, BOD7, and bacteria. Field measurements were made of wastewater flow, electrical conductivity, oxygen, and temperature. The entire system removed total-P and total inorganic nitrogen (TIN) by 83% and 22%, respectively. High salt concentration and very low wastewater temperature were possible reasons for these unexpectedly low P and TIN removal efficiencies. In contrast, removal rates of bacteria (Escherichia coli, enterococci) and organic matter (as BOD) were high, due to filtration in the alkaline medium Polonite((R)) (Ecofiltration Nordic AB, Stockholm, Sweden) and the fine sand used as SBCW substrate. High pH in effluent from the PTP was efficiently reduced to below pH 9 in the SBCW, meeting recommendations by environmental authorities in Sweden. We concluded that treating cold on-site wastewater can impair treatment performance and that technical measures are needed to improve SBCW performance.

Place, publisher, year, edition, pages
MDPI, 2019
Keywords
add-on unit, biofiltration, nitrogen, package treatment plant, phosphorus, Polonite, sand
National Category
Other Environmental Engineering
Identifiers
urn:nbn:se:kth:diva-255445 (URN)10.3390/su11113172 (DOI)000472632200177 ()2-s2.0-85067278721 (Scopus ID)
Note

QC 20190820

Available from: 2019-08-20 Created: 2019-08-20 Last updated: 2019-10-09Bibliographically approved
3. Simulating the hydraulic dynamics and treatment performance of a sequencing batch flow constructed wetland
Open this publication in new window or tab >>Simulating the hydraulic dynamics and treatment performance of a sequencing batch flow constructed wetland
(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
Constructed wetland; Reactive Modeling; Phosphorus; Nitrogen; Design Optimization
National Category
Water Engineering
Research subject
Land and Water Resources Engineering
Identifiers
urn:nbn:se:kth:diva-256495 (URN)
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
4. Phosphorus sorption and leaching in sand filters used for onsite wastewater treatment - a column experiment
Open this publication in new window or tab >>Phosphorus sorption and leaching in sand filters used for onsite wastewater treatment - a column experiment
(English)In: Article, book review (Refereed) Submitted
Abstract [en]

The sorption capacities of filter sands used for onsite wastewater treatment and their associated risks of phosphorus (P) leakage on contact with rainwater were investigated in column experiments and modelling studies. Columns packed with sand were exposed to real domestic wastewater of different characteristics and hydraulic loading modes. The wastewater fed into the columns was effluent collected from three different treatment units in the field: a septic tank (ST), biofiltration tank (BF) and Polonite® filter bag (PO). The risk of P leaching to groundwater and surface water was also assessed, by exposing the same sand columns to artificial rainwater. The results indicated that sand columns can exhibit different adsorption capacities for Total-P, phosphate-P and total suspended solids, depending on the characteristics of influent wastewater. The adsorption capacity increased in the order ST > BF > PO, based on availability of organic matter to form biofilm. Effluent from Pol columns was significantly clearer, indicating lower organics content, than effluent from ST and BF columns. The modelled breakthrough curves for Total-P desorption agreed satisfactorily with the measured values, but further model improvement is needed.

Keywords
Adsorption; Constructed wetlands; Leaching; Phosphorus; Sand Column; Suspended solids
National Category
Civil Engineering
Research subject
Land and Water Resources Engineering
Identifiers
urn:nbn:se:kth:diva-256499 (URN)
Funder
Lars Erik Lundberg Scholarship Foundation, 696881:2017/201
Note

QC 20190903

Available from: 2019-08-26 Created: 2019-08-26 Last updated: 2019-09-03Bibliographically approved

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