Public defence in Water and Environmental Engineering, M.Sc. Maija Jylhä-Ollila
Public defence from Aalto University School of Engineering, Department of Built Environment
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Title of the thesis: The long-term development of water quality in managed aquifer recharge – organic matter removal and related redox reactions
Doctoral student: Maija Jylhä-Ollila
Opponent: Associate Professor Daniele Pedretti, University of Milan (UNIMI), Italy
Custos: Professor Harri Koivusalo, Aalto University School of Engineering, Department of Built Environment
Reseach at Iso Tiilijärvi strengthens the understanding of managed aquifer recharge as a sustainable solution in drinking water production
The research objective was to investigate the long-term impact of managed aquifer recharge in terms of water quality development. At the research site at Lake Iso Tiilijärvi in Hollola, surface water naturally infiltrates in the ground, and the area can be used as a surrogate to built managed aquifer recharge plants. At the lake, infiltration has been ongoing for thousands of years—a much longer period than can be reached at built bank infiltration facilities.
The removal of organic matter and water quality changes related to the removal process were investigated from lake water and groundwater samples. The water quality development in the area was modeled with a reactive flow and transport model. FT-ICR MS was used to determine the molecular composition of the organic matter at the University of Eastern Finland. FT-ICR MS is a cutting-edge analytical approach for organic matter estimation and in this research it was applied to managed aquifer recharge for the first time.
The natural infiltration system from Lake Iso Tiilijärvi to the aquifer showed water quality development to be similar to built bank infiltration plants, with 80–90% removal of organic matter, and a temperature-mediated seasonal pattern in concentrations of oxygen, iron, and manganese. Based on FT-ICR MS results, the removal of organic matter in the aquifer was selective: the relative abundance of oxygen-containing species decreased, while the relative abundance of sulfur-containing species increased.
It was concluded that a lake-aquifer system can remove organic matter over the long term without losing its capacity. The results also revealed the seasonally dominating role of lake bottom sediments on water quality in bank infiltration. The modeling results highlighted the importance of good conceptual understanding and flow velocity estimation in field studies.
Managed aquifer recharge is widely used in drinking water production in Finland. From the 20 largest water intake plants, 14 are based on the method. The application of managed aquifer recharge is increasing worldwide. On the other hand, the method has sometimes received resistance from the public due to concerns about e.g. environmental impacts. The results gained from the water analyses and modeling give guidance to the design of new managed aquifer recharge plants. They also suggest that managed aquifer is a sustainable solution for water treatment for water supply.
Keywords: Managed aquifer recharge, groundwater modelling, NOM, FT-ICR MS, GLUE
Thesis available for public display 10 days prior to the defence at: https://aaltodoc.aalto.fi/doc_public/eonly/riiputus/
Contact information of doctoral student: maija.jylha-ollila@aalto.fi
Doctoral theses of the School of Engineering: https://aaltodoc.aalto.fi/handle/123456789/49
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