Enhancement of Surface Runoff Quality Using Modified Sorbents

Abstract

The objective of this study was to develop and test nanoparticle-and polymer-based bioactive amended sorbents to enhance stormwater runoff treatment in best management practices (BMPs). Red cedar wood and expanded shale were the sorbents tested. Red cedar wood chips (RC) were modified with 3-(trihydroxysilyl) propyldimethyloctadecyl ammonium chloride (TPA) and silver nanoparticles (AgNPs) at different mass loadings (0.36 mg/g, 0.67 mg/g, and 0.93 mg/g for TPA and 0.33 mg/g and 0.68 mg/g for AgNPs) to simultaneously improve the sorption of organic and inorganic contaminants and pathogenic deactivation in BMPs treating stormwater runoff. Unmodified expanded shale is often used as a filter material for stormwater treatment and was used as a base comparison. The results showed that TPA and AgNPs loading onto red cedar increased the Langmuir maximum sorption coefficient (Q) for polycyclic aromatic hydrocarbons, up to 35 fold and 29 fold, respectively, compared to unmodified red cedar. In the case of heavy metals, Q for lead increased with increased loading of TPA and AgNPs, whereas no significant change in the Q value for cadmium was observed, while zinc and nickel sorption slightly decreased. The Langmuir maximum sorption coefficient of copper was higher for modified red cedar; however, no correlation was observed with TPA or AgNP loadings. The log reduction value (LRV) for Escherichia coli using unmodified red cedar was <1 log, while modified red cedar exhibited LRV up to 2.90 ± 0.50 log for 0.67 mg/g TPA-RC and up to 2.10 ± 0.90 log for 0.68 mg/g AgNP-RC. Although AgNP-modified red cedar shows a comparable performance to TPA-RC, the high cost of production may limit the use of AgNP-amended materials. While TPA-modified red cedar has advantages of lower cost and lower toxicity, the fate, transport, and environmental implications of TPA in natural environments has not been fully evaluated. The findings from this study show that if BMPs were to incorporate the modified red cedar, stormwater treatment of PAH and E. coli could be enhanced, and the quality of the treated water will improve.

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

“…Following the procedures described by Kasaraneni et al, the red cedar wood chips were amended with 6 mg/g 3-(trihydroxysilyl)propyldimethyloctadecyl ammonium chloride (TPA), a quaternary ammonium compound [29]. Briefly, the red cedar was soaked in frequently exchanged clean water for a minimum of 2 weeks to leach out soluble matter and remove fines.…”

“…The E. coli removal during the field experiment was similar for both the tree filters, i.e., 99.2% and 99.1% for CTF and ITF, respectively. Although from preliminary batch tests it was expected that the ITF will have higher bacteria removal than the CTF system [29].Subsequent laboratory column experiments showed that a loading of greater than 6 mg/g of TPA to red cedar is required (i.e., 9 mg/g) to achieve measurable inactivation of bacteria under dynamic conditions [15]. Even though similar E. coli removal rates were found in the tracer experiments, the data suggest that when clean water is pumped following the tracer injection the E. coli concentration in the effluent of the ITF decreased more readily compared to CTF (Figure 2).…”

“…This may indicate that E. coli are indeed inactivated by the TPA amended wood chips in the ITF, compared to the CTF where E. coli only attach to the porous media temporarily and get transported out as viable cells when clean water gets flushed through the system. Even though E. coli removal was extensively and successfully tested in the laboratory [15,29], the laboratory results were difficult to replicate in the field. A major reason explaining the lower than expected performance of under field conditions is that not sufficient quantities of antimicrobially amended wood chips were added to the TF system.…”

“…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%).…”

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].…”