Fördjupad funktionsanalys av Uppsalaåsen : Avskiljning av organiskt material (NOM) vid konstgjord infiltration och kemisk fällning

Detta är en Uppsats för yrkesexamina på avancerad nivå från Uppsala universitet/Institutionen för geovetenskaper

Sammanfattning: Uppsala’s drinking water production is built around the Uppsala esker. Through managed aquifer recharge, surface water from Fyris river is infiltrated into the esker at several sites, in order to enhance the natural groundwater recharge. During 2017 more than 8 million m3 of water was artificially infiltrated, however, by 2100 the infiltration required is expected to increase to 28 million m3 per year. In the last 25 years, 3700 metric tons of dissolved organic carbon (DOC) have been added to the esker through managed aquifer recharge. In Sweden increasing trends of natural organic matter (NOM) in surface water have been observed, this may cause problems when producing drinking water. High concentration of NOM in drinking water can affect the taste and odor of the produced water as well as forming carcinogenic disinfection byproducts (DBPs). The purpose of this thesis was to investigate the fate of DOC within the esker in between the infiltration site at Tunåsen and the uptake site in Galgbacken. The natural removal of DOC was compared with the removal that could be achieved through chemical flocculation, specifically through jar tests with ferric chloride, FeCl3. Furthermore, another purpose was to evaluate whether or not pre- or post-flocculation should be implemented, in order to secure water availability in the future. Through groundwater sampling along the esker it can be concluded that the esker naturally removes up to 70 % of the DOC in theinfiltrated water, which can be replicated with chemical flocculation when 100 mg of FeCl3 is added per liter of water, when pH is set to 6,2. By characterizing the organic matter with spectrophotometry and liquid chromatography (LC-OCD) in the investigated groundwater wells, there is evidence that organic matter in the water that is pumped out of the esker mostly consists of high molecular-weight (HMW) compounds >600 Da on average. Through chemical flocculation a vast majority of the HMW compounds can be flocculated. Post flocculation, the largest fraction of organic matter consists of low molecular-weight compounds <500 Da on average. In the future, when larger volumes of water are expected to be infiltrated, a post flocculation step could be implemented after the managed aquifer recharge. This study highlights the ecosystem service that the esker provides to Uppsala, which is a great resource for Uppsalas drinking water production.

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