EVALUATION OF THE LONG-TERM POLLUTION REMOVAL PERFORMANCE OF ESTABLISHED BIORETENTION CELLS

Abstract

Over the last two decades bioretention (biofiltration) systems have been commonly
constructed in urban areas to manage stormwater runoff by moderating peak flows and reducing downstream
pollution loads. Bioretention systems are generally soil-plant based systems which typically include a filter
medium above a drainage layer. They are often either lined with a geofabric to support infiltration, or with an
impermeable membrane to prevent infiltration and/or to allow stormwater harvesting and reuse. Bioretention
systems are known to treat a range of stormwater pollutants through physical, chemical and biological
processes such as mechanical filtering, sedimentation, adsorption, and plant and microbial uptake. However,
the long-term pollution removal performance, particularly of heavy metals, remains largely unknown. It is
generally accepted that the filter media used in bioretention systems has a finite life span, after which time it
should be replaced. However, there is only very limited information available on when this should occur, or
how to assess this. It is also recognised that contaminated filter media may require regulated disposal. This
study presents results from a series of controlled field experiments conducted over two years which evaluated
the pollution removal performance of a series of 10 year old bioretention systems located in an industrial
estate in Australia.