WC128 JanFeb2023 - Magazine - Page 33
A. J. Blackburn
Top and bottom: Bench-scale biofilter experimental
set-up for investigation of biofiltration resilience in
wildfire-prone systems, with close-up of filter media
and biofilm.
Biofiltration technologies
More and more, nature-based solutions (NBS) are proposed
and implemented to respond to climate change threats to the
water industry. This is especially evident in management of
urban flooding by harnessing the natural infiltration properties of vegetated landscapes (e.g. rain gardens or bioswales).
Although less common, similar approaches can be integrated
into drinking water treatment.
Biofiltration technologies are a great example of this. They
include a range of biologically mediated treatment processes, ranging from slow sand filtration to classical biofiltration
WAT E R C A N A D A . N E T
in which conventional rapid rate granular media filters are
operated without chlorine in the filter influent and sometimes
preceded by oxidation to enhance removal. In biofiltration processes, natural microbial communities develop on and within
filter media and contribute to treatment by degrading contaminants, including NOM. Because these processes can be relatively passive, some types of biofiltration offer low energy and low
maintenance alternatives to some conventional technologies,
which can be especially valuable for smaller drinking water
treatment plants. Of course, as process performance requires
control and monitoring to ensure sufficient treatment, biologically mediated treatment processes are more aptly described as
“techno-ecological NBS”.
Biofiltration processes are especially promising to address
NOM-related treatment concerns post-watershed disturbance.
Conventional treatment technologies rely on coagulation for
NOM removal. However, changes in concentration and character of NOM in source water following watershed disturbances can challenge coagulation processes because NOM exerts coagulant demand and can compromise coagulation effectiveness.
Although NOM itself is not a health concern nor a regulated
contaminant, it can react with disinfection chemicals like chlorine to produce potentially harmful disinfection by-products.
NOM in finished water can also create biological instability in
the distribution system, providing the nutrients necessary for
opportunistic pathogens like Legionella to proliferate. Biofiltration could be a treatment solution to address elevations
and shifts in source water NOM post-watershed disturbance,
although it has not yet been systematically investigated in this
context.
Biofiltration in wildfire-prone regions
After severe wildland fire, vegetation is reduced or absent so that
more precipitation reaches the land surface, typically leading to
increased erosion and solids runoff. Pyrogenic materials that are
episodically delivered to receiving waters can release nutrients
