On-site wastewater treatment in Northern conditions – Real world performance, pollutant load and fate
Thesis event information
Date and time of the thesis defence
Place of the thesis defence
ROM Rantsila – Wanha Meijeri, Paavolantie 10A, Rantsila
Topic of the dissertation
On-site wastewater treatment in Northern conditions – Real world performance, pollutant load and fate
Doctoral candidate
MSc. Tech. Juho Kinnunen
Faculty and unit
University of Oulu Graduate School, Faculty of Technology, Water, Energy and Environmental Engineering Research Unit
Subject of study
Environmental engineering
Opponent
Associate professor Fasil Ejigu Eregno, UiT the Arctic University of Norway
Custos
Docent Elisangela Heiderscheidt, University of Oulu
On-site wastewater treatment in Northern conditions – Real world performance, pollutant load and fate
Decentralised sanitation offers a flexible means of improving global sanitation. In Nordic
countries, on-site wastewater treatment systems (OWTS), common in sparsely populated areas,are regulated for the removal of phosphorus (P), organic matter (biological oxygen demand, BOD7) and nitrogen (N). OWTS efficiency is reported to vary, but information is scattered and the cold condition effects on real-world performance have not been satisfactorily explored. Furthermore, the transport and fate of contaminants discharged from OWTSs under Nordic climate and geological conditions have not been efficiently examined. To address the
knowledge gap, a 3 phase research plan was developed.
In phase 1, effluent water quality from 395 OWTSs located in Finland and Sweden was
statistically analysed to review performance, compliance with regulations and possible affecting factors. Overall, BOD7 removal met requirements, 10% of units exceeded Tot-N, and 25%
exceeded Tot-P limits. Air temperature and precipitation were not strong factors explaining
effluent quality. The results highlighted data biases, such as a lack of samples during cold
periods, indicating the need for additional data collection. The package plants efficiency was
studied via the field monitoring of nine units in phase 2. High BOD7 removal was observed
with no effect from air temperature on treatment performance. Effluent pharmaceutical
concentrations were within or above ranges reported for large treatment plants, while plastic
originated phthalate ester concentrations, originating from, for example, plastics, were below
those commonly reported. In phase 3, contaminant (N, P, micropollutants) load and fate from a
household infiltration field were studied. Soil iron and aluminium content, porosity, and a lack
of pH buffering provided a favourable environment for P precipitation, and over 90% dilution-
corrected retention was observed. The results suggest that in suitable conditions, soil infiltration can be a viable septic tank effluent treatment, especially in P-limited environments.
Information of this thesis supports the development of guidelines and regulations for
decentralized sanitation facilities. It highlights the need for randomized national OWTS
sampling to improve knowledge of system performance, pollutant load and the effect of
environmental conditions.
countries, on-site wastewater treatment systems (OWTS), common in sparsely populated areas,are regulated for the removal of phosphorus (P), organic matter (biological oxygen demand, BOD7) and nitrogen (N). OWTS efficiency is reported to vary, but information is scattered and the cold condition effects on real-world performance have not been satisfactorily explored. Furthermore, the transport and fate of contaminants discharged from OWTSs under Nordic climate and geological conditions have not been efficiently examined. To address the
knowledge gap, a 3 phase research plan was developed.
In phase 1, effluent water quality from 395 OWTSs located in Finland and Sweden was
statistically analysed to review performance, compliance with regulations and possible affecting factors. Overall, BOD7 removal met requirements, 10% of units exceeded Tot-N, and 25%
exceeded Tot-P limits. Air temperature and precipitation were not strong factors explaining
effluent quality. The results highlighted data biases, such as a lack of samples during cold
periods, indicating the need for additional data collection. The package plants efficiency was
studied via the field monitoring of nine units in phase 2. High BOD7 removal was observed
with no effect from air temperature on treatment performance. Effluent pharmaceutical
concentrations were within or above ranges reported for large treatment plants, while plastic
originated phthalate ester concentrations, originating from, for example, plastics, were below
those commonly reported. In phase 3, contaminant (N, P, micropollutants) load and fate from a
household infiltration field were studied. Soil iron and aluminium content, porosity, and a lack
of pH buffering provided a favourable environment for P precipitation, and over 90% dilution-
corrected retention was observed. The results suggest that in suitable conditions, soil infiltration can be a viable septic tank effluent treatment, especially in P-limited environments.
Information of this thesis supports the development of guidelines and regulations for
decentralized sanitation facilities. It highlights the need for randomized national OWTS
sampling to improve knowledge of system performance, pollutant load and the effect of
environmental conditions.
Last updated: 9.9.2024