Inter-storm dissolved organic matter variability and its role in microbial transport during urban runoff events

At present major challenges in stormwater harvesting and reuse remain on the characterization of non-point source pollutants, especially microbial pathogens, and the associated public health risks due to the intrinsic short-term acute health risks. Due to the negative surface charge of most microbes, their transport in urban stormwater often relies on the attachment to particulate matter, suspended solids and organic matter. In this study, the transport behavior of two microbes, Escherichia coli and Enterococcus spp. and their relationship with dissolved organic matter present in stormwater were investigated over five stormwater runoff events collected from a medium density residential urban catchment in South East Queensland. Analyses on organic matter included hydrophobic and hydrophilic fractions. The hydrophillic substances were further fractionated into humic substances, building blocks and low molecular weight organics. Escherichia coli numbers of 3.6x10 ³ cfu 100mL ^-1were detected in the stormwater runoff, while Enterococcus spp. numbers as high as 3x 10 ⁴ cfu 100mL ^-1 were detected. The mean dissolved organic carbon in the stormwater samples was 5.1±1.9 mg/L in which hydrophilic constituted the highest mass fraction (60-80%). Results showed that microbial transport was hindered by an increase of the hydrophilic organics fraction, especially the humic fraction.