Role of Environmental Variables in the Transport of Microbes in Stormwater

Rupak Aryal,Jatinder Sidhu,Meng Chong,Wolfgang Gernjak,Simon Toze,Bandita Mainali

doi:10.3390/w13091146

Abstract

Microbial pathogens present in stormwater, which originate from human sewage and animal faecal matters, are one of the major impediments in stormwater reuse. The transport of microbes in stormwater is more than just a physical process. The mobility of microbes in stormwater is governed by many factors, such as dissolved organic matter, cations, pH, temperature and water flow. This paper examined the roles of three environmental variables, namely: dissolved organic matter, positive cations and stormwater flow on the transport of two faecal indicator bacteria (FIB), Enterococcus spp. and Escherichia coli. Stormwater runoff samples were collected during twelve wet weather events and one dry weather event from a medium density residential urban catchment in Brisbane. Enterococcus spp. numbers as high as 3 × 104 cfu/100 mL were detected in the stormwater runoff, while Escherichia coli numbers up to 3.6 × 103 cfu/100 mL were observed. The dissolved organic carbon (DOC) in the stormwater samples was in the range of 2.2–5.9 mg/L with an average concentration of 4.5 mg/L in which the hydrophilic carbon constituted the highest mass fraction of 60–80%. The results also showed that the transport of FIB in stormwater was reduced with an increasing concentration of the hydrophilic organic fraction, especially the humic fraction. On the contrary, the concentration of trivalent cations and stormwater flow rate showed a positive correlation with the FIB numbers. These findings indicated the potentiality to make a good use and measurement of simple environmental variables to reflect the degree of microbe transport in stormwater from residential/suburban catchments.

Highlights

The aims of this study were to evaluate the possible relationships and usefulness of environmental parameters such as dissolved organic matter, metal ions and stormwater flow to the transport of faecal indicator bacteria (FIB) of E. coli and Enterococcus spp. that could be useful as indicators of microbial pathogen presence or prevalence in a semi-urban watershed
High FIB numbers observed after the rain events were similar to what had been previously reported in the literature
Stormwater samples collected from a medium-density residential urban catchment in

Summary

Introduction

A wide range of pollutants, such as pathogens and chemicals from non-point sources, are the major challenges posed for its treatment and reuse [1] and may cause serious health risks to human beings [2,3,4]. Microbes in urban stormwater originate from both point and diffuse sources, including those from animal and human faecal pollution [2,5,6]. The urban stormwater runoff can mobilise and transport microbial pathogens from various non-point sources to surface water bodies, such as rivers, lakes and creeks. The transport of microbes involves several environmental factors, such as dissolved organic matter, cations, pH and temperature, while the hydrological processes include rainfall intensity, duration and flow rate [8,9]

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