Escherichia coli Reduction in Water by Zero-Valent Iron–Sand Filtration Is Based on Water Quality Parameters

Seongyun Kim,Katherine Eckart,Cheryl L East,Eric T Handy,Amy Rebecca Sapkota,Manan Sharma,Pei C Chiu,Sarah Sabet,Kalmia E Kniel

doi:10.3390/w13192702

Abstract

Improving the microbial quality of agricultural water through filtration can benefit small farms globally. The incorporation of zero-valent iron (ZVI) into sand filters (ZVI–sand) has been effective in reducing E. coli, Listeria spp., and viruses from agricultural water. This study evaluated ZVI–sand filtration in reducing E. coli levels based on influent water type and the percentage of ZVI in sand filters. A ZVI–sand filter (50% ZVI/50% sand) significantly (p < 0.001) reduced E. coli levels in deionized water by more than 1.5 log CFU/mL compared to pond water over six separate trials, indicating that water type impacts E. coli removal. Overall reductions in E. coli in deionized water and pond water were 98.8 ± 1.7% and 63 ± 24.0% (mean ± standard deviation), respectively. Filters constructed from 50% ZVI/50% sand showed slightly more reduction in E. coli in pond water than filters made from a composition of 35% ZVI/65% sand; however, the difference was not statistically significant (p = 0.48). Principal component analysis identified that the turbidity and conductivity of influent water affected E. coli reductions in filtered water in this study. ZVI–sand filtration reduces Escherichia coli levels more effectively in waters that contain low turbidity values.

Highlights

Rapid urbanization, climate change, population growth, and water scarcity have focused more attention on agricultural water quality, irrigation water intended for fresh fruits and vegetables that are to be consumed raw [1]
Kim et al (2011) found that inactivated E. coli through nano-zero-valent iron (ZVI) was greater under de-aerated conditions than under air-saturated conditions [35,44]. These results indicate that reductions in E. coli through ZVI–sand filtration can be improved if turbidity and conductivity levels are actively lowered and managed during the maintenance of ZVI filtration, and if water quality is characterized in advance of ZVI–sand filtration
E. coli populations were reduced by larger amounts in DI when filtered through 50% ZVI/sand columns compared to pond water

Summary

Introduction

Climate change, population growth, and water scarcity have focused more attention on agricultural water quality, irrigation water intended for fresh fruits and vegetables that are to be consumed raw [1]. Cooler seasons (lower water temperatures) were associated with a higher prevalence of L. monocytogenes compared to warmer seasons [4,6], and specific non-traditional water sources (ponds) had a lower prevalence of Salmonella enterica compared to rivers or creeks [6,7]. To prevent foodborne illness from the consumption of microbiologically contaminated produce, multiple criteria and standards for the microbiological quality of irrigation water have been established or recommended by multiple international, governmental, and industry organizations.

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