Escherichia coli reductions in water by zero valent iron sand filtration is based on water quality parameters

Authors: KIM, SEONGYUN - US Department Of Agriculture (USDA); ECKART, KATHERINE - University Of Maryland; SABET, SARAH - University Of Maryland; CHIU, PEL - University Of Delaware; SAPKOTA, AMY - University Of Maryland; HANDY, ERIC - US Department Of Agriculture (USDA); East, Cheryl - Roberts; KNIEL, KALMIA - University Of Delaware; Sharma, Manan

Submitted to: Water
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/25/2021
Publication Date: 9/29/2021
Citation: Kim, S., Eckart, K., Sabet, S., Chiu, P., Sapkota, A.R., Handy, E., East, C.L., Kniel, K.E., Sharma, M. 2021. Escherichia coli reductions in water by zero valent iron sand filtration is based on water quality parameters. Water. 13(19):2702.

Interpretive Summary: Improving the microbial quality of agricultural water through filtration can benefit small farmers globally. Surface irrigation water may contaminate fresh fruits and vegetables with bacterial pathogens that can cause foodborne illness. Cost-effective, simple filtration systems, using a mixture of zero-valent iron (ZVI) and sand – can reduce pathogens and improve the microbial quality of irrigation water. Sand filtration is used in various agricultural applications. Research presented here shows that influent water quality parameters can influence the amount of Escherichia coli, an indicator of water quality, removed or inactivated during the filtration process. ZVI-sand filtration reduced E. coli levels to a greater extend in deionized water from the laboratory compared to pond (surface) water. Higher levels of turbidity and oxygen reduction potential in the surface water reduced the amount of E. coli inactivated or removed compared to deionized water, which had extremely low levels of turbidity. Filters made with 50% ZVI – 50% sand were slightly more effective in reducing E. coli than 35% ZVI-sand filters. Overall, our results show that higher levels of turbidity and oxygen reduction in water potential limit the ability of zero-valent iron sand filtration to reduce E. coli. This work benefits small farmers by providing them a cost-effective method to improve irrigation water quality.

Technical Abstract: Improving the microbial quality of agricultural water through filtration can benefit small farmers globally. The effectiveness of reducing of pathogenic bacteria through filtration is dependent upon the filter (composition, design, particle composition of the filter, size, contact time) and influent water quality, which may include conductivity, dissolved oxygen, pH, redox state, and turbidity. 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 the efficacy of ZVI sand filtration on reduction of E. coli levels based on influent water type and percentage of ZVI in sand filters. The water quality (conductivity, dissolved oxygen, pH, ORP, and turbidity) of pond water and deionized water were measured before ZVI-sand or sand filtration events. ZVI sand filtration reduced E. coli levels in deionized water by more than 2 log CFU/ml compared to in pond water, indicating that water quality impacts E. coli removal as evaluated over six separate trials. Overall reductions of E. coli in deionized water (DI) 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 of E. coli in pond water than filters made from a composition of 35% ZVI / 65% sand but not at a statistically significant (p=0.48) level. The main factors influencing different levels of removal of E. coli in deionized water and pond water were evaluated with principal component analysis, including conductivity, dissolved oxygen, pH, oxygen reduction potential (ORP) and turbidity. Turbidity and ORP played a fundamental role in determining the inactivation of E. coli in filtered water in this study.