New Antimicrobially Amended Media for Improved Nonpoint Source Bacterial Pollution Treatment

Abstract

Nonpoint source pollution (NPS) such as stormwater runoff may introduce high loads of bacteria, impairing surface water bodies. The existing filter materials in stormwater best management practices (BMP) are typically not designed to inactivate bacteria. Herein, novel filtration media were extensively tested for microbial load reduction in stormwater runoff. Red cedar wood chips (RC) were amended with different loadings of either 3-(trihydroxysilyl) propyldimethyloctadecyl ammonium chloride (TPA) or silver nanoparticles (AgNP). Under batch conditions at 25 °C, log10 removal values (LRV) up to 3.71 ± 0.38 (mean ± standard error) for TPA-RC and 2.25 ± 1.00 for AgNP-RC were achieved for Escherichia coli (E. coli), whereas unmodified RC achieved less than 0.5 LRV. Similar trends were observed at 17.5 °C, however at low temperature (10 °C) no statistically significant difference in E. coli inactivation between modified and unmodified RC was detected. Inactivation kinetic studies show that TPA-RC has higher inactivation rate constants compared to AgNP-RC. Under dynamic flow conditions a mass balance approach indicates that even after remobilization up to 99.8% of E. coli removal using 9 mg/g TPA-RC compared to 64.8% for unmodified RC. This study demonstrates that RC wood chips amended with antimicrobial compounds show promising applications as filtration material for the reduction of microbiological contamination load in stormwater runoff.

Stormwater Biofilters as Barriers against Campylobacter jejuni, Cryptosporidium Oocysts and Adenoviruses; Results from a Laboratory Trial

“…For instance, vegetation with extensive root structures was shown to improve E. coli retention in stormwater biofilters [13]. Filter media modified with either antimicrobial compounds [14,15] or adsorption enhancements [16,17] were found to improve faecal indicator microorganism attenuation rates. Intermittent wetting/drying operation is generally associated with poor removal performances due to decreased microbial adsorption and increased microbial desorption [7,8,17].…”

Bacteria Removal from Stormwater Runoff Using Tree Filters: A Comparison of a Conventional and an Innovative System

“…However, recent studies on bacteria removal in a wide range of structural BMPs concluded that bacteria treatment was ineffective and unreliable, as the removal of pathogens primarily relied on attachment/collection and not inactivation [13,14]. This is because sorbed pathogens can remain viable during attachment [15][16][17] and therefore can be remobilized/detached during intermittent flow conditions. The ineffectiveness in inactivating bacteria is especially relevant in areas with shallow water tables, because not enough soil depth might be present to filter out pathogens effectively, therefore increasing the risk of bacterial contamination of groundwater [18].…”

“…Studies have shown that filter materials amended with antimicrobials can remove bacteria from aqueous solutions by inactivation processes that damage the cell [15,16,27,28] or permanently fixating bacteria on porous media [16]. For instance, in a previous study antimicrobially amended wood chips were tested with intentions for use in stormwater BMPs [15,29].…”

“…For instance, in a previous study antimicrobially amended wood chips were tested with intentions for use in stormwater BMPs [15,29]. The laboratory derived data indicate that red cedar wood chips loaded with 6 mg/g of 3-(trihydroxysilyl)propyldimethyloctadecyl ammonium chloride (TPA) effectively removed E. coli from aqueous solution by at least two Log 10 units (>99%).…”

“…In addition, studies have shown that wood is capable of almost quantitatively removing aqueous phase PAH [30][31][32][33], dissolved metals and other inorganic compounds [34]. While the E. coli removal rate of the amended wood is substantially greater than required by some states, the performance of the filter material was only tested under laboratory batch conditions [15]. Additional studies are therefore needed to evaluate the performance of this promising antimicrobial treatment approach under field conditions.…”