New technology for cleaning municipal wastewater also to be used in Finland soon
Membrane technology is currently undergoing testing in several places in Finland for the cleaning of municipal wastewater. LUT membrane technology research group is involved in four different projects which are researching the cleaning of wastewater using a membrane bioreactor and tertiary membrane filtration.
Over one hundred membrane bioreactors (MBR) are being used in municipal wastewater cleaning in Europe and the world's largest membrane bioreactor process is currently being built in Stockholm. At the moment, there is no full-scale plant operating in Finland.
More efficient cleaning method
A membrane bioreactor process differs from a traditional municipal wastewater cleaning process in that instead of a settler and sand filtration, the waste water in the aeration tank is led through a semi-permeable membrane. The membrane has tiny pores which remove bacteria and solids from the water. The membranes are fastened in cubicle-like modules which are immersed directly into the aeration tank. The MBR process is not only more efficient than the current method, but also more compact.
"It does not require the vast settling tanks needed by the traditional approach to water purification so a membrane bioreactor plant can be built cost effectively in a smaller area", explains Kimmo Arola, a researcher at LUT's department of Chemical Engineering.
Water cleaned by a membrane bioreactor is also of a more even quality than that from a traditional wastewater cleaning plant. In the traditional process not all the substances are necessarily removed as high levels of impurities get out of the settler from time to time and pass into watercourses. All bacteria and solids are removed from water cleaned in a membrane bioreactor. That is why water cleaned in an MBR is easier to process further than water cleaned traditionally.
Contaminants are the challenge of the future
Kimmo Arola sees the MBR process as an investment in the future. For example, in the future contaminants will become a challenge on a European and world scale because various hormones and drug residues will accumulate in watercourses over time.
The traditional process does not remove all contaminants effectively enough. Harmful drugs and other compounds that are difficult to destroy in a biological process can be removed from the cleaned water produced by the MBR process more easily than from water cleaned in the traditional process.
"Monitoring values and permit conditions are expected in the near future for various contaminants, particularly for large treatment plants. That is why the old technology is automatically in trouble," Mr Arola believes.
People in Finland have not completely woken up to how critical the issue is because there is plenty of land and water that is regarded as clean. The traditional water treatment method has been able to function because it has worked well enough. However, Finland is waking up to the opportunities the new technology can bring. Parikkala has taken a preliminary decision to build a new treatment plant using membrane bioreactor-based technology. The Council will take the final construction decision in December.
Membrane technology is being tested in four municipalities at the moment in Finland: Parikkala, Vihti, Mikkeli and Savitaipale. Under the direction of Professors Mika Mänttäri and Mika Sillanpää, LUT's Chemical Engineering department is involved in all the projects. If Parikkala's Council make a positive decision on the construction of a membrane bioreactor process in December, interest in the subject will probably increase, argues Mr Arola.
Professor Mika Mänttäri
tel. +358 407342192
Researcher Kimmo Arola
tel. +358 503734447