Biofiltration Technologies for Stormwater Quality Treatment
(2005 – 2010)
Godecke Blecken (Luleå University of Technology)
Biofilters have been mostly developed without specific consideration for their operation under varying climate conditions. The biofilter treatment efficiency depends on a range of physical, biological and chemical processes, which to unknown extend might be influenced by variations of the ambient environmental conditions.
Thus this thesis investigated the effects of :
- various ambient conditions (temperature and antecedent dry weather period),
- stormwater characteristics (stormwater or snowmelt of different pollutant concentrations), and
- modifications of filter design (coarse filter material, submerged anoxic zone and/or embedded carbon source to faciliate de-nitrification)
on the water quality treatment performance of biofilters using laboratory experiments to: clarify the roles of features of biofilters, elucidate pollutant removal processes inside them, and facilitate the design of effective biofilters. The main focus has been on the removal of metals and TSS. However, nutrient removal under varying temperatures has also been investigated.
The following points summarise the main conclusions of this PhD study:
- Given that the total TSS, metal and phosphorus outflow concentrations were, in all cases, far lower than those in the stormwater or snow, biofilters were shown to be appropriate treatment systems. However, metal outflow concentrations were significantly affected by extended dry periods and temperature changes, the factors representing the varying ambient conditions biofilters are exposed to.
- Concerns that use of coarse filter media with no significant clay and silt contents may impair metal removal were not confirmed. It was confirmed that the top layer is of prime importance for pollutant removal. Metal concentrations were found to be highest in the top layer and sediment accumulation resulted from effective TSS trapping on top of the filter. The deeper filter layers and plants retain pollutants as well, but to a minor degree.
- Embedding a submerged zone (SZ) in the filter combined with a solid organic matter carbon source (C: wood chips, pea straw) significantly enhanced metal removal; especially the comparatively poor Cu removal was considerably improved by a combination of SZ and C. In contrast, for Pb and Zn the statistically significant improvements were of little practicality.
- Adverse temperatures can lead to high nitrate production instead of removal (following a strong Arrhenius relationship), thus jeopardising total nitrogen removal. However, TSS, metal and P were removed reliably over a wide range of temperatures (2-20°C).
- Extended drying of the filter between two storm events increased outflow concentrations at the subsequent event significantly. However, a SZ helped to mitigate (Cu) or even eliminate (Pb) the negative effects of extended drying on metal removal.
Click here to read the abstract of this PhD – PDF (0.3MB)
Blecken, G.-T. (2010) Biofiltration technologies for stormwater quality treatment. Doctoral thesis, Luleå University of Technology. (link to PDF)
Other publications (link)