Summary of Awards to Date

Use of zero valent iron (ZVI) in irrigation of tomatoes with manure-contaminated water at varying E. coli levels


Jul. 1, 2013 - Jun. 30, 2014

Award Number


Amount Awarded



Kalmia Kniel, Ph.D.
University of Delaware


Zero-valent iron (ZVI) has been shown to reduce pathogenic bacteria in water used for drinking or irrigation. Overhead irrigation water was treated with ZVI and successfully reduced E.coli subsequently found on spinach leaves. The initial amount of microbial contamination in water may directly affect the final amount of contamination on produce at harvest. In this proposed study we will further assess the ability of ZVI to reduce microbial contamination and nitrate levels from irrigation water contaminated with  bovine manure, with a high organic load, and known amount of E. coli. Filtered water  will be tested for nitrates and other minerals. Water will be filtered using varying levels  of ZVI and sand or sand only and then used for overhead irrigation of tomato plants ten days prior to harvest. Water and fruit samples will be tested for mineral composition and bacterial load. This project will provide insight into how varying levels of ZVI are affected by the presence of manure-contaminated water. We will also assess the effect of ZVI treatment on bacterial indicators and total microflora in irrigation water and on tomatoes. The shelf-life of tomatoes with presumably lower total and fecal coliform populations will also be assessed.

Technical Abstract

Zero-valent ion treatment may be a cost-effective mitigation step to help small to mid-sized farmers reduce the risk of foodborne illness associated with contamination of raw agricultural products.  Zero-valent iron (ZVI) filters may provide an efficient method to mitigate the contamination of produce crops through irrigation water. This research team has previously showed that ZVI could remove the surrogate pathogen E. coli O157:H12 from irrigation water applied to spinach using a field-scale system compared to a bio-sand filter, and a no-treatment control. In this study ZVI filters inactivated 6 log CFU/100 ml E. coli O157:H12 during filtration on day zero, which was significantly (p < 0.05) more than E. coli populations removed by the sand filter or no control. Treatment of irrigation water is an increasingly important means to reduce the risk of foodborne illness associated with raw agricultural commodities. The Proposed Produce Rule announce by the US Food and Drug Administration, following guidelines set by the  Food Safety Modernization Act states that surface water must be tested and all water must meet specific microbiological standards. In some cases, ZVI may be a viable mitigation strategy to reduce pathogenic bacterial loads in surface water when its use is required (e.g., in the case of a drought where surface water must be used or when surface water must be used for frost protection). This study will determine the efficacy of ZVI for use in reducing microbial indicator populations in surface water with a high organic load (containing bovine manure). Water will be contaminated with bovine manure at four different E. coli levels (0, 100, 1000, 10000 cfu/ml) prior to filtration through ZVI or sand filtration units. Total coliforms, fecal coliforms and E. coli will be enumerated in post-treatment water and on tomatoes (variety BHN 602) harvested from field plots irrigated overhead with the treated and untreated water at days 0,1,3,5,7,and 10. Upon completion of these field trials, surface water will be contaminated with Salmonella enterica, subjected to ZVI filtration and used for irrigation with tomato varietals grown in greenhouse conditions. This water will be assessed for pathogen and nitrate removal. The removal of nitrates and potential pathogens from surface or tail water by ZVI treatment would provide small growers with an efficient and simple process to comply with the FDA Proposed Produce Rule.