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. Here, 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 attenuationmore » 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.« less

Authors:

Delaire, Caroline ^[1]; van Genuchten, Case M. ^[2]; Amrose, Susan E. ^[1]; Gadgil, Ashok J. ^[3]

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+ Show Author Affiliations

1. Univ. of California, Berkeley, CA (United States)
2. Univ. of Utrecht (Netherlands)
3. Univ. of California, Berkeley, CA (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)

Publication Date:

Mon Jul 11 00:00:00 EDT 2016

Research Org.:

Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES); United States Agency for International Development (USAID)

OSTI Identifier:

1828154

Alternate Identifier(s):

OSTI ID: 1397363

Grant/Contract Number:  

AC02-05CH11231; AID-OAA-A-13-00002

Resource Type:

Accepted Manuscript

Journal Name:

Water Research

Additional Journal Information:

Journal Volume: 103; Journal ID: ISSN 0043-1354

Publisher:

Elsevier

Country of Publication:

United States

Language:

English

Subject:

59 BASIC BIOLOGICAL SCIENCES; Iron electrocoagulation; Bacteria attenuation; Bacterial surface functional groups; Specific interactions; Bivalent cations; Oxyanions