The Journal of Hazardous Materials (Volume 429, 5 May 2022, 128309) released a new article, “Natural Aging of ESCS Amendment with Heavy Metals in Stormwater Increases its Antibacterial Properties: Implications on Biofilter Design.”
Expanded shale, clay and slate lightweight aggregate media can make stormwater biofilters bactericidal. It can adsorb large amounts of heavy metals, and hence, can be used to kill off pathogens as heavy metals are toxic to pathogens.
• Expanded shale, clay, and slate (ESCS) media adsorb metals irreversibly.
• Heavy metals bind with -OH groups on ESCS and lower surface charge.
• Adsorbed metals increased E. coli attachment sites and lower mobilization.
• Increased attachment sites could lower the exhaustion rate of filter media.
• Adsorbed metals on ESCS, not leached metals, inactivated E. coli in biofilters.
Aging is often expected to decrease the pathogen removal capacity of media because of exhaustion of attachment sites by adsorption of co-contaminants and dissolved organics. In contrast, the adsorption of metals naturally present in stormwater during aging could have a positive impact on pathogen removal. To examine the effect of adsorbed metals on pathogen removal, biofilter media amended with expanded clay, shale, and slate (ESCS) aggregates, a lightweight aggregate, were exposed to metals by intermittently injecting natural stormwater spiked with Cu, Pb, and Zn, and the capacity of aged and unaged media to remove Escherichia coli (E. coli), a pathogen indicator, were compared. Metal adsorption on ESCS media decreased their net negative surface charge and altered the surface properties as confirmed by zeta potential measurement and Fourier-Transform Infrared Spectroscopy (FTIR) analysis. These changes increased the E. coli adsorption capacity of aged media compared with unaged media and decreased overall remobilization of attached E. coli during intermittent infiltration of stormwater. A live-dead analysis confirmed that the adsorbed metals inactivated attached E. coli, thereby replenishing the adsorption capacity. Overall, the results confirmed that natural aging of biofilter media with adsorbed metals could indeed have a net positive effect on E. coli removal in biofilters and therefore should be included in the conceptual model predicting long-term removal of pathogens from stormwater containing mixed pollutants.
Reprinted from Journal of Hazardous Materials, Volume 429, 5 May 2022, 128309, Annesh Borthakur, Kristida L. Chhour, Hannah L. Gayle, Samantha R. Prehn, Michael K. Stenstrom, Sanjay K. Mohanty, “Natural Aging of ESCS Amendment with Heavy Metals in Stormwater Increases its Antibacterial Properties: Implications on Biofilter Design,” pgs. 1-10, Copyright 2022, with permission from Elsevier.
By Abigail Gabbard | March 3, 2022 | New report release