Pesticides are conventionally used to control weeds, plant pathogens, insects, and nematodes in soil. However, these chemicals may cause harm to humans and the environment. Biosolarization is a pesticide alternative that couples anaerobic soil fermentation to high Summer temperatures to treat soils for plant pathogens. In addition to controlling pathogens, biosolarization adds value to food wastes that are applied as organic amendments to stimulate anaerobic digestion. Biosolarization can potentially be applied to control soil-borne human pathogens such as Escherichia coli. In this study, the use of common agricultural residues — tomato and white grape pomace — to inactivate E. coli during biosolarization was evaluated. The effect of adding mature compost to the process was evaluated as well; compost is usually used to ensure that thermophilic microorganisms are available for the process. To simulate field conditions, 50 mL tubes were filled with amended soil. E.coli in phosphate-buffer saline was used to inoculate the bacteria (109 cells/ml) and wet the soil. Identical treatments amended with compost were used to evaluate the effect of compost on the process. Tubes were incubated on a 12hr 30-50 (Celsius) cycle for 8 days to mimic daily temperature conditions observed during biosolarization. E. coli reduction was calculated by subtracting the log of Colony forming units (CFUs) of a given treatment from the non-amended control. Tomato pomace did not show significant CFU reduction compared to the control, regardless of compost addition. However, for grape pomace, the number of CFUs fell below the detection limit after 3 days, and total inactivation of E.coli was achieved after 8 days. The combination of heating and bioactive compounds in grape pomace (i.e. polyphenols) and/or produced during soil fermentation of the residues (i.e. organic acids) may be responsible for the E. coli reduction. To test this hypothesis, two different batches of white grape pomaces were tested as amendment. Batch 2 had similar results to batch 1 used in figure 1. Batch 3 had a greater CFU count than the control showing a protective effect. Grape polyphenol and soil organic acid profiles were obtained using HPLC-UV for comparison; The most relevant polyphenols (e.g. gallic acid) were tested in isolation. Preliminary results suggest that biosolarization using abundant food processing residues can effectively eliminate human pathogens from soil.

Escherichia coli inactivation during biosolarization using tomato and grape pomaces as soil amendments

2019 Fall National Meeting

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