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Laboratory evaluation of coagulants for treatment of urban snowmelt
Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Arkitektur och vatten. (Urban Water Engineering)ORCID-id: 0000-0003-3580-8715
Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Arkitektur och vatten. (Urban Water Engineering)
Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Arkitektur och vatten.ORCID-id: 0000-0001-9541-3542
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(Engelska)Manuskript (preprint) (Övrigt vetenskapligt)
Abstract [en]

The treatment effect and process characteristics of coagulation were investigated in urban snow at laboratory scale using jar tests. An initial screening of twelve coagulants and flocculant aids was carried out to find a selection of chemicals that efficiently reduced turbidity and suspended solids. Five coagulants were then further investigated and additional parameters measured (conductivity, alkalinity and ζ-potential). The urban snowmelt mixture was characterized by high, but variable, particle content and low alkalinity. In the jar tests, high treatment efficiency (>90% reduction of both turbidity and suspended solids) was achieved for all coagulants. For very low alkalinity waters, the use of a biopolymer such as chitosan may be advantageous due to minimal alkalinity consumption. Based on the occurrence of charge reversal for all chemicals investigated, the mechanism for coagulation was likely charge neutralization. Treatment effect occurred in the ζ-potential range of -14 to +1 mV depending on the coagulant used. Initial turbidity and the ζ-potential are interesting parameter candidates for dosing control in stormwater treatment applications.

Nyckelord [en]
Stormwater, treatment, coagulation mechanism, sweep floc, charge neutralization, zeta potential
Nationell ämneskategori
Vattenteknik
Forskningsämne
VA-teknik
Identifikatorer
URN: urn:nbn:se:ltu:diva-73088OAI: oai:DiVA.org:ltu-73088DiVA, id: diva2:1292991
Tillgänglig från: 2019-03-01 Skapad: 2019-03-01 Senast uppdaterad: 2019-03-01
Ingår i avhandling
1. Coagulation process characteristics and pollutant removal from urban runoff
Öppna denna publikation i ny flik eller fönster >>Coagulation process characteristics and pollutant removal from urban runoff
2019 (Engelska)Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

Many different stormwater control measures (SCMs) can be implemented in order to mitigate issues with polluted stormwater flows into receiving water bodies.  The treatment function of  SCMs is commonly based on the removal of particles by sedimentation, thereby also removing pollutants associated with particles. In recent years, more attention has been given to characterizing and understanding of different particle size fractions and their association with pollutants commonly found in stormwater. It has become increasingly clear that the smaller sized particles are very important pollutant transporters and should be considered when designing and implementing SCMs. However, the settling velocities for smaller sized particles are very low and may not be effectively removed in existing SCMs. One treatment process with a proven ability to enhance sedimentation is coagulation/flocculation, widespread in water and wastewater treatment, but with very few accounts of it being used in a stormwater context. This thesis aims to investigate the treatability of stormwater with a coagulation/flocculation process. This includes the determination of operating conditions, the dominating coagulation mechanism and the reduction efficiency of stormwater related pollutants. The objectives of the thesis were achieved in laboratory tests treating stormwater in a jar-testing procedure.

An initial screening of primary coagulants and flocculant aids was conducted using an urban snowmelt mixture. Five of the chemicals were then selected for an extended testing regime which was setup up to determine the operating conditions where maximal turbidity reduction was attained by measuring the pH, conductivity, alkalinity and zeta-potential over the tested doses for each coagulant. Criteria used for chemical selection included high turbidity reduction, low dose requirement and low pH/alkalinity impacts.

Charge reversal was observed at positive zeta-potential indicating that the dominating coagulation mechanism was charge neutralization. The content of turbidity/total suspended solids, total organic carbon, total metals and hydrocarbons by >90%. Dissolved copper was reduced by 40% on average, and the reduction rates for dissolved zinc were varying with up to a 300% increase, presumably due to changes in pH, leading to a higher mobility. Changes in the particle size distribution after coagulation/flocculation as compared to sedimentation indicated an effect on the size fraction corresponding to smaller particles.

The performance of the coagulation/flocculation process was also tested on road runoff collected from a central road in Luleå with a high traffic intensity. Two coagulants were tested, iron chloride and pre-hydrolyzed aluminum chloride. Reduction rates for the total metal fraction were >90% on average for both coagulants, but for the dissolved metal fractions differences could be observed between the coagulants with the iron chloride resulting in higher reductions for dissolved chrome (57% compared to 34%) and copper (47% compared to 30%). Both products increased the dissolved fractions of nickel and zinc due to lower final pH.

Ort, förlag, år, upplaga, sidor
Luleå: Luleå University of Technology, 2019
Serie
Licentiate thesis / Luleå University of Technology, ISSN 1402-1757
Nyckelord
stormwater, urban snowmelt, road runoff, coagulation/flocculation/sedimentation, coagulation characteristics, coagulation mechanism, treatment efficiency
Nationell ämneskategori
Vattenteknik
Forskningsämne
VA-teknik
Identifikatorer
urn:nbn:se:ltu:diva-73091 (URN)978-91-7790-322-2 (ISBN)978-91-7790-323-9 (ISBN)
Presentation
2019-04-26, F231, VR-Studion, Laboratorievägen 10, Luleå, 09:00 (Engelska)
Opponent
Handledare
Tillgänglig från: 2019-03-04 Skapad: 2019-03-01 Senast uppdaterad: 2019-04-09Bibliografiskt granskad

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Herrmann, IngaHedström, AnnelieViklander, Maria

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Nyström, FredrikHerrmann, IngaHedström, AnnelieViklander, Maria
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