Enhancing Escherichia coli removal in stormwater biofilters with a submerged zone: balancing the impact of vegetation, filter media and extended dry weather periods

ABSTRACT

Stormwater biofilters have shown promising yet variable removal of faecal microorganisms. The effects of vegetation, filter media and extended drying on the removal of Escherichia coli are investigated in the current study. Semi-synthetic stormwater was applied to 25 biofilters representing five different design configurations, all of which contained a submerged zone (SZ). The influence of extended dry periods on E. coli removal depended on the presence/absence of vegetation. Uptake of SZ water by plants with extensive roots during the dry periods lead to deterioration of the subsequent outflow water quality compared to unvegetated biofilters. Without a significant loss of SZ volume, a loamy sand biofilter planted with either Carex appressa or Leptospermum continentale can achieve a higher removal performance than an unvegetated washed sand biofilter. However, in warmer climates that experience long dry weather periods, and inability to control SZ volumes, un-vegetated columns may result in lower effluent E. coli concentrations.

KEYWORDS:

• Bacteria
• Escherichia coli
• extended drying
• stormwater biofilter
• submerged zone
• vegetation

Acknowledgements

The support of the Commonwealth of Australia through the Cooperative Research Centre Programme (data collection, experimental design, etc.) and Australian Research Council-Discovery Early Career Researcher Award (grant number DE140100524; data analysis and paper writing) is acknowledged. Support from Yali Li, Minna Tom, Anthony Brosinsky, Christelle Schang, Peter Kolotelo, Kun Kim, Ashley Connelly and Ben Evans during the experimental duration is also gratefully acknowledged.

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplementary material

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Additional information

Funding

This work was supported by the Australian Research Council-Discovery Early Career Researcher Award [DE140100524];Commonwealth of Australia [Cooperative Research Centre Programme (CRC) for Water Sensitive Cities].