Zero-valent iron-sand filtration reduces Escherichia coli in surface water and leafy green growing environments

Authors: KIM, SEONGYUN - University Of Maryland; BRADSHAW, RHODEL - University Of Maryland; KULKARNI, PRACHI - University Of Maryland; ALLARD, SARAH - University Of Maryland; CHIU, PEI - University Of Maryland; SAPKOTA, AMY - University Of Maryland; KNIEL, KALMIA - University Of Maryland; NEWELL, MICAHEL - University Of Maryland; Handy, Eric; East, Cheryl - Roberts; Sharma, Manan

Submitted to: Frontiers in Sustainable Food Systems
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/22/2020
Publication Date: 7/31/2020
Citation: Kim, S., Bradshaw, R., Kulkarni, P., Allard, S., Chiu, P.C., Sapkota, A.R., Kniel, K.E., Newell, M.J., Handy, E.T., East, C.L., Sharma, M. 2020. Zero-valent iron-sand filtration reduces Escherichia coli in surface water and leafy green growing environments. Frontiers in Sustainable Food Systems. https://doi.org/10.3389/fsufs.2020.00112.
DOI: https://doi.org/10.3389/fsufs.2020.00112

Interpretive Summary: Surface waters, like rivers and ponds, have been known to harbor foodborne pathogens like Escherichia coli O157:H7 and Salmonella, which can contaminate raw produce. Previous outbreaks of E. coli O157:H7 traced back to contaminated Romaine lettuce originated from irrigation water. Small-scale fruit and vegetable growers require a cost-effective filtration technology to remove potential pathogenic bacteria from irrigation water intended for produce. As water becomes a more critical resource, it may require mitigation strategies to improve the microbial quality of this potential irrigation water. Zero-valent iron, combined with sand, may provide a filtration technique that can remove and / or inactivate E. coli in water. Pond water collected on a research farm was contaminated with non-pathogenic E. coli and filtered through either a sand or Zero-valent iron (ZVI) filter. Laboratory studies shows that ZVI filtration was more effective than sand filtration in reducing E. coli populations in pond water. Six trials were performed, and ZVI-filtration was much more effective than sand filtration in the first three trials. In field trials were ZVI- or sand-filtered water was irrigated on to growing spinach plants, both soils and spinach plants irrigated with ZVI water had lower E. coli levels than those irrigated with sand-filtered water. These results show that ZVI-filtration is more effective than sand filtration in reducing E. coli inoculated into pond water and can reduce E. coli levels transferred to spinach plants and soils. This work benefits farmers and growers by designing and evaluating cost-effective filtration strategies that can reduce E. coli in irrigation waters.

Technical Abstract: Surface water may provide an additional source of irrigation water for growers of fruits and vegetables. However, surface waters can be a source of bacterial foodborne pathogens that can contaminate fresh produce intended for human consumption. The risk of foodborne illness, along with proposed standards for microbial quality of irrigation water through the Produce Safety Rule (PSR) of the Food Safety Modernization Act (FSMA), have placed emphasis on the need for effective mitigation of bacterial fecal indicator and pathogens in surface water intended to be used on fruit and vegetable crops. This study evaluated of a zero-valent iron (ZVI) sand filtration system to reduce inoculated E. coli populations in pond water. Six replicate filtration events were conducted in ZVI-sand (ZVI) and Sand (S) filtration systems. In each replicate, pond water (PW) inoculated with E. coli was pumped through each filter followed by uninoculated PW with samples taken throughout filtering process for enumeration of E. coli populations. For ZVI-filtered water, there was a statistically significant (p < 0.05) difference of E. coli removal from early trials (trials 1-3, average removal 96%) than in later trials (trial 4-6, average removal 44%), suggesting that the age of the ZVI filter may influence the efficacy of E. coli inactivation in water. Overall, ZVI and sand filtration reduced E. coli populations by 70% and -10%, respectively. Most of the microbial reduction was attributed to reductions in populations from the initial effluent volumes (0-8 L) from each trial. A field study was also conducted to evaluate the effectiveness of ZVI, S, and control pond water (no filtration) on the inactivation of E. coli in irrigation water. Soils and spinach plant samples irrigated with ZVI-filtered water had significantly lower E. coli TVS 353 levels than soils irrigated with either sand-filter water or unfiltered control water.