title: Bacteria attenuation by iron electrocoagulation governed by interactions between bacterial phosphate groups and Fe(III) precipitates.
abstract: Iron electrocoagulation (Fe-EC) is a low-cost process in which Fe(II) generated from an Fe(0) anode reacts with dissolved O2 to form (1) Fe(III) precipitates with an affinity for bacterial cell walls and (2) bactericidal reactive oxidants. Previous work suggests that Fe-EC is a promising treatment option for groundwater containing arsenic and bacterial contamination. However, the mechanisms of bacteria attenuation and the impact of major groundwater ions are not well understood. In this work, using the model indicator Escherichia coli (E. coli), we show that physical removal via enmeshment in EC precipitate flocs is the primary process of bacteria attenuation in the presence of HCO3(-), which significantly inhibits inactivation, possibly due to a reduction in the lifetime of reactive oxidants. We demonstrate that the adhesion of EC precipitates to cell walls, which results in bacteria encapsulation in flocs, is driven primarily by interactions between EC precipitates and phosphate functional groups on bacteria surfaces. In single solute electrolytes, both P (0.4 mM) and Ca/Mg (1-13 mM) inhibited the adhesion of EC precipitates to bacterial cell walls, whereas Si (0.4 mM) and ionic strength (2-200 mM) did not impact E. coli attenuation. Interestingly, P (0.4 mM) did not affect E. coli attenuation in electrolytes containing Ca/Mg, consistent with bivalent cation bridging between bacterial phosphate groups and inorganic P sorbed to EC precipitates. Finally, we found that EC precipitate adhesion is largely independent of cell wall composition, consistent with comparable densities of phosphate functional groups on Gram-positive and Gram-negative cells. Our results are critical to predict the performance of Fe-EC to eliminate bacterial contaminants from waters with diverse chemical compositions.
authors.affiliation: Department of Civil and Environmental Engineering, University of California, Berkeley, CA 94720-1710, United States. Electronic address: caroline.delaire@orange.fr.
authors.forename: Caroline
authors.initials: C
authors.lastname: Delaire
authors.affiliation: Department of Earth Sciences - Geochemistry, Faculty of Geosciences, Utrecht University, Utrecht 3508TA, The Netherlands.
authors.forename: Case M
authors.initials: CM
authors.lastname: van Genuchten
authors.affiliation: Department of Civil and Environmental Engineering, University of California, Berkeley, CA 94720-1710, United States.
authors.forename: Susan E
authors.initials: SE
authors.lastname: Amrose
authors.affiliation: Department of Civil and Environmental Engineering, University of California, Berkeley, CA 94720-1710, United States; Energy Technologies Area, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, United States.
authors.forename: Ashok J
authors.initials: AJ
authors.lastname: Gadgil
mesh_terms: D001151:Arsenic / Q000737:chemistry; D004564:Electrocoagulation; D004926:Escherichia coli; D007501:Iron / Q000737:chemistry*; D010710:Phosphates; D018508:Water Purification
chemical_list: D010710:Phosphates; D007501:Iron; D001151:Arsenic
keywords: Bacteria attenuation; Bacterial surface functional groups; Bivalent cations; Iron electrocoagulation; Oxyanions; Specific interactions