Submitted to: International Association for Food Protection
Publication Type: Abstract Only
Publication Acceptance Date: March 6, 2012
Publication Date: July 25, 2012
Citation: Banerjee, R., Singh, A., Callahan, M.L., Roberts, C.L., Ingram, D.T., Patel, J.R., Hoover, D., Kniel, K., Sharma, M. 2012. The use of zero-valent iron filtration to reduce Escherichia coli and Listeria innocua in irrigation water. [abstract] International Association for Food Protection. P3-32. p.182.
Introduction: Irrigation water can be a source of contamination in outbreaks associated with produce. Zero-valent iron (ZVI) filtration has been effective in E. coli O157:H12 in irrigation water, but has not been evaluated against Listeria spp.
Purpose: To 1) determine effectiveness of ZVI filters against L. innocua and E. coli O157:H12 in contaminated irrigation water, and 2) determine residual ZVI antimicrobial activity in filtered water inoculated with E. coli.
Methods: HydrAid biosand filters were built containing gravel and coarse sand. Two columns were then modified to contain fine sand only (S), and two columns contained a mixture of ZVI and fine sand at a 1:1 ratio. L. innocua and E. coli O157:H12 were cultured separately in bovine manure slurry and then inoculated in water at between 6 and 8 log CFU/100 ml, respectively, on three separate occassions. Contaminated water was filtered through either S or ZVI columns and collected for analysis of bacterial populations. To determine residual antimicrobial activity of ZVI, water filtered through S- or ZVI-columns was inoculated with populations of three E. coli strains at populations between 6.5–8 log CFU/ml.
Results: ZVI columns reduced L. innocua and E. coli O157:H12 populations in water by 6.5 –6.9 and 6.8 –7.4 log CFU/100ml, respectively. S columns were less effective, reducing L. innocua and E. coli by 0.8–2.2 and 0.8 –2.7 log CFU/100ml, respectively. E. coli O157 strains declined more rapidly (6.5–8 log CFU/ml) in ZVI-filtered water than in S-filtered water (2.9-3.3 log CFU/ml), over 8 days, while non-O157 E. coli declined less rapidly in ZVI- and S-filtered compared to O157 strains.
Significance: ZVI columns were effective in reducing L. innocua and E. coli populations in irrigation water, and showed residual activity against E. coli populations after filtration. ZVI filtration may provide more effective mitigation treatment for irrigation water compared to sand filtration.