Optimising the Media of Next Generation Low Impact Designs for Phytoremediation and Bioremediation

Low impact designs (LID) such as raingardens treat stormwater runoff through a combination of physicochemical and biological processes, including filtration, adsorption, phytoremediation, and bioremediation. Some of the most common stormwater pollutants include suspended solids (TSS), heavy metals, nutrients, and dissolved organics such as polycyclic aromatic hydrocarbons. Phytoremediation and Bioremediation are processes that remove or transform such pollutants into nontoxic compounds through the use of plants and microorganisms, respectively.

The role of these processes in treating environmental pollutants has been well documented in the literature. Microorganisms and plants can uptake heavy metals and transform hydrocarbons into nontoxic compounds, thus decontaminating urban stormwater runoffs. These biological processes can also play a significant role in removing nutrients from stormwater. Despite these well-documented benefits, phytoremediation and bioremediation are not well studied and accounted for in designing of the LID media.

The current standards in New Zealand promote a ‘deemed to comply’ approach and use TSS removal as a sole measure of stormwater treatment. While this approach offers an easy and economical way to compliance, it has potentially led to reliance predominantly on the physicochemical processes for removal of stormwater contaminants.

Careful selection of plants and optimizing the LID media for microbial growth can boost its phytoremediation and bioremediation capabilities and enhance its overall treatment efficiency. Through such amendments leaching of nutrients can also be minimized and specific pollutants can be targeted for treatment.

This paper outlines the findings of the multi-stage research project being carried out at the University of Auckland, jointly by Opus International Consultants and the University of Auckland to enhance phytoremediation and bioremediation in Suspended Raingardens – a next generation LID for treating stormwater runoffs in urban catchments. It also outlines how the findings of this research can be applied to traditional LID for the treatment of pollutants beyond physicochemical processes.