Review of subsurface flow treatment wetland feasibility in Finland
Horváth, Gábor (2012)
Tampereen ammattikorkeakoulu
2012
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Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:amk-201205107365
https://urn.fi/URN:NBN:fi:amk-201205107365
Tiivistelmä
Constructed wetlands are engineered systems for treating wastewater. They have normally been used only as secondary treatment systems. However, over the last five decades, they have started to be utilized more extensively, as problems with operation and maintenance are gradually being solved. In Finland, treatment wetland is still ignored as a way to replace expensive chemicals for wastewater treatment purposes. The wetland system is rejected partly because the biological and chemical processes are temperature dependent, and secondly, there are concerns about ice formation and its effect on hydraulic flow, hydrology and hydraulics. Thermal consequences for biologically or microbiologically mediated treatment processes are the main constraints. Constructed wetland systems in Finland have commonly failed because the temperature coefficient has not been designed carefully, and clogging by organic matter has occurred in the inlet of the pool. Therefore, energy and water balance calculations as well as thermal modeling are useful tools to prevent design, operation and maintenance failure.
Studies of constructed wetlands have shown less sensitivity to temperature swings in full-scale experiments than laboratory-scale ones. The lab-scale results should not prevent a full-scale trial because biological living beings in the nature interact with and affect the environment in ways which cannot be predicted in laboratory-scale testing. The wetland treatment method relies on anaerobic and partly aerobic conditions, which are essential for the transformation of nutrients and organic pollution to take place.
A common problem with treating wastewater with an SSF wetland system is clogging failure. Also, oxygen transfer is reduced significantly by the need to use an insulating mulch layer, compared with situations where a mulch layer is unnecessary. Nitrogen removal is low due to the lack of oxygen availability, but this can be increased by artificial aeration.
Studies of constructed wetlands have shown less sensitivity to temperature swings in full-scale experiments than laboratory-scale ones. The lab-scale results should not prevent a full-scale trial because biological living beings in the nature interact with and affect the environment in ways which cannot be predicted in laboratory-scale testing. The wetland treatment method relies on anaerobic and partly aerobic conditions, which are essential for the transformation of nutrients and organic pollution to take place.
A common problem with treating wastewater with an SSF wetland system is clogging failure. Also, oxygen transfer is reduced significantly by the need to use an insulating mulch layer, compared with situations where a mulch layer is unnecessary. Nitrogen removal is low due to the lack of oxygen availability, but this can be increased by artificial aeration.