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Online-instrumentering på avloppsreningsverk: status idag och effekter av givarfel på reningsprocessen
Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology.
2018 (Swedish)Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesisAlternative title
Online sensors in wastewater treatment plants : status today and the effects of sensor faults on the treatment process (English)
Abstract [sv]

Effektiviteten av automatiserade reningsprocesser inom avloppsreningsverk beror ytterst på kvaliteten av de mätdata som fås från installerade instrument. Givarfel påverkar verkens styrning och är ofta anledningen till att olika reglerstrategier fallerar. Idag saknas standardiserade riktlinjer för hur instrumenteringsarbetet på svenska reningsverk bör organiseras vilket ger begränsade förutsättningar för reningsverken att resurseffektivt nå sina utsläppskrav. Mycket forskning har gjorts på att optimera olika reglerstrategier men instrumentens roll i verkens effektivitet har inte givits samma uppmärksamhet. Syftet med detta examensarbete har varit att undersöka hur instrumentering på reningsverk kan organiseras och struktureras för att säkerställa mätdata av god kvalitet och att undersöka effekter av givarfel på reningsprocessen.

Inom arbetet genomfördes en litteraturstudie där instrumentering på reningsverk under-söktes. Effekter av givarfel på reningsprocessen undersöktes genom att simulera en fördenitrifikationsprocess i Benchmark Simulation Model no. 2 där bias och drift implementerades i olika givare. Simuleringar visade att positiva bias (0,10–0,50 mg/l) i en ammoniumgivare inom en kaskadreglering bidrar till att öka luftförbrukningen med cirka 4–25 %. Vidare resulterade alla typer av fel i DO-givare i den sista aeroba bassängen i en markant större påverkan på reningsprocessen än samma fel i DO-givare i någon av de tidigare aeroba bassängerna. Om den sista aeroba bassängen är designad för att hålla lägre syrehalter är DO-givaren i den bassängen den viktigaste DO-givaren att underhålla. Positiva bias (200–1 000 mg/l) i TSS-givare som används för att styra uttaget av överskottsslam bidrog till kraftiga ökningar av mängden ammonium med cirka 29–464 % i utgående vatten. Negativ drift i DO-givare visade att stora besparingar i luftningsenergi, cirka 4 %, var möjliga genom ett mer frekvent underhåll av DO-givarna.

Huruvida ett instrument lider av ett positivt eller negativt givarfel, bias eller drift, kommer att påverka hur mycket och i vilken mån reningsprocessen påverkas. Studien av givarfel visade att effekten av ett positivt eller ett negativt fel varierade och att effekten på reningsprocessen inte var linjär. Effekten av givarfel på reningsprocessen kommer i slutändan att bero på den implementerade reglerstrategin, inställningar i regulatorerna och på den styrda processen.

Abstract [en]

The effectiveness of automated treatment processes within wastewater treatment plants ultimately depend on the quality of the measurement data that is given from the installed sensors. Sensor faults affect the control of the treatment plants and are often the reason different control strategies fail. Today there is a lack of standardized guidelines for how to organize and work with online sensors at Swedish wastewater treatment plants which limits the opportunities for treatment plants to reach their effluent criteria in a resource efficient manner. Much research has been done on ways to optimize control strategies but the role of sensors in the efficiency of the treatment plants has not been given the same level of attention. The purpose of this thesis has been to examine how instrumentation at wastewater treatment plants can be organized and structured to ensure good quality measurement data and to examine how sensor faults affect the treatment process.

Within the thesis a literature study was conducted where instrumentation at wastewater treatment plants was examined. The effects of sensor faults were examined by simulating a pre-denitrification process in Benchmark Simulation Model no. 2 where off-sets (biases) and drift where added to measurements from different implemented sensors. The simulations showed that positive off-sets (0.10–0.50 mg/l) in an ammonium sensor within a cascaded feedback-loop adds to the energy consumption used for aeration by roughly 4-25%. It could further be shown that all types of faults in a DO sensor in the last aerated basin had significantly larger effect on the treatment process than the same fault in any of the other DO sensors in the preceding basins. If the last aerated basin is designed to have low DO concentrations the DO sensor in that basin is the most important DO sensor to maintain. Positive off-sets (200–1 000 mg TSS/l) in suspended solids sensors used for control of waste activated sludge flow contributed to large increases of ammonia, by 29-464%, in effluent waters. Negative drift in DO sensors showed that significant savings in aeration energy, roughly 4%, was possible to achieve with more frequent maintenance.

Whether a sensor is affected by a positive or a negative fault, be it off-set or drift, will affect how much and in what way the treatment process will be affected. The study of sensor faults showed that the effect of a positive or a negative fault varied and that the effect on the treatment process was not linear. The effect of a sensor fault on the treatment process will ultimately depend on the implemented control strategy, settings in the controllers and on the controlled process.

Place, publisher, year, edition, pages
2018. , p. 60
Series
UPTEC W, ISSN 1401-5765 ; 18 013
Keywords [en]
Sensor faults, off-set, bias, drift, sensor, instrument, instrumentation, Benchmark Simulation Model no. 2, BSM2, activated sludge process, pre-denitrification, wastewater, wastewater treatment
Keywords [sv]
Givarfel, bias, drift, givare, instrument, instrumentering, Benchmark Simulation Model no. 2, BSM2, aktivslamprocess, fördenitrifikation, avloppsvatten, avloppsrening
National Category
Water Treatment Water Engineering Engineering and Technology
Identifiers
URN: urn:nbn:se:uu:diva-351372OAI: oai:DiVA.org:uu-351372DiVA, id: diva2:1209864
External cooperation
IVL Svenska Miljöinstitutet
Educational program
Master Programme in Environmental and Water Engineering
Presentation
2018-03-08, Skåne, Geocentrum, Villavägen 16, Uppsala, 10:15 (Swedish)
Supervisors
Examiners
Available from: 2018-05-25 Created: 2018-05-24 Last updated: 2018-05-25Bibliographically approved

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