Location: Microbial and Chemical Food Safety
2024 Annual Report
Objectives
Objective 1: To mitigate issues with bacterial pathogen-contaminated irrigation waters, examine the use of biochar as an antimicrobial and filtration intervention, for example, combining biochar filtration with ARS pre-existing zero-valent water filtration technology.
Objective 2: Examine the use of adding biochar to compost piles, in order to inactivate pathogens in the compost, but especially the problematic “toes” of manure piles.
Approach
The approach of project will follow two objectives. The first objective will evaluate the ability of biochar filters to remove pathogenic bacteria from surface irrigation waters with or without zero valent iron and sand-composite filtration. Biochar pyrolysis will be optimized for this purpose by altering the residence time, temperature and biofeedstock with an in-house biochar slow-pyrolysis reactor. The optimized water filtration units will then be scaled up to reduce pathogens in irrigation water, lowering the risk of foodborne illness from irrigated fresh produce. Second, pyrolysis will be further optimized for maximal antimicrobial efficacy of biochar. This biochar will then be utilized in lab-scale and field-trial dairy and poultry compost experiments with the goal of more rapidly inactivating EHEC and Salmonella. Successful results will allow for shorter composting times prior to field application, which will decrease the chances for pathogenic bacteria to survive the process and contaminate field crops. Stakeholders will be consulted and collaborated with for all objectives, and technology will be transferred to the appropriate entities. Overall, the results and outcomes from this project plan will increase the safety of fresh fruits and vegetables and lower the burden of human-related illnesses caused by foodborne pathogens by providing practical intervention solutions for farmers, packers, processors and distributers of fresh produce, related to foodborne pathogens.
Progress Report
Surface waters used for irrigating fruit and vegetable crops sometimes become contaminated with pathogens such as enterohemorrhagic, Shiga toxin-producing Escherichia coli (E. coli), Salmonella or Listeria monocytogenes, which has led to foodborne outbreaks in recent years. Microbial pathogens can also be transferred to produce in fields via composted dairy and poultry manures (biological soil amendments of animal origin [BSAAO]) applied to farmland. The resulting effect is potential contamination of fresh produce, which can lead to human foodborne illnesses from uncooked fruits and vegetables or due to cross-contamination from fresh produce to other foods and food preparation surfaces.
Previous studies have demonstrated that biochar may be an effective matrix for filtering E. coli from pathogen-contaminated water, as well as for inactivating foodborne pathogens in agricultural soils and compost. Under Objective 1, we previously examined optimal temperatures requisite to produce antimicrobial biochar, which would have utility in inactivating foodborne bacterial pathogens as soil amendments. In these studies, we demonstrated that the primary factor influencing the inactivation of bacterial pathogens by biochar is alkaline pH, which is enhanced at higher pyrolysis temperatures.
Recent experiments, related to Objective 1, have made significant progress in constructing sand:biochar irrigation water filters to test the filtration capacity of various types of biochar. Ten biochars were tested in irrigation water filters during FY 2024, including (1) those made in-house, (2) one biochar provided by a collaborator, and (3) one commercially produced and purchased biochar. These biochars were produced by the following organic feedstocks and temperatures: 700 C miscanthus straw, 750 and 800 C switchgrass, 600 C hardwood, 700 C hardwood pellets, 700 C softwood, 750 C cocoa shells, 700 C alkaline paper, a commercial fast-pyrolysis softwood, and an alkaline hardwood cyclone biochar provided by a collaborator. Reduction of E. coli in simulated irrigation water ranged from 0.07-4.47 log colony forming units (CFU) per ml of water. Optimization of biochar:sand filters was achieved by adjusting the following variables: (1) Increasing the filter matrix ratio to 50:50 biochar:sand, (2) increasing the length of the biochar:sand filters from 4.25 to 8.5 inches, and (3) pre-wetting biochar to ca. 78% moisture before constructing filters, in contrast to construction with dry biochar. Ongoing studies are being designed to further increase the E. coli-reducing capacity of biochar:sand filters, as well as adding antimicrobial zero valent iron to the optimized biochar:sand filters.
Under Objective 2, significant progress was made in determining the effects of adding optimized concentrations of antimicrobial alkaline biochar to crop soil on the seed germination and plant growth of vegetable and grain crops. Because alkaline hardwood biochar (AHB) has previously been shown to inactivate pathogenic bacteria, experiments were conducted to determine whether 2.5% of antimicrobial AHB affects vegetable and cereal plant seed germination and growth, in the presence or absence of arbuscular mycorrhizal fungi (AMF). Treatments consisted of five plant species (i.e., romaine lettuce [Lactuca sativa var. longifolia], grape tomato [Solanum lycopersicum], spinach [Spinacea oleracea], leek [Allium ampeloprasum] and wheat [Triticum vulgare]) and four AMF/AHB combinations (viz., -AHB/-AMF, +AMF/+AHB, -AMF/+AHB and +AMF/-AHB). Soil nutrient content, seed germination, plant height, and other growth parameters were assessed. The nutrient composition, cation exchange capacity, and organic matter content of the plant growth medium (soil, sand, vermiculite and turface [SSVT]) and SSVT + 2.5% AHB were characterized. Seed germination in +AMF/+AHB was greater than 90% and not statistically different from the control for all plants, except for leek. After six weeks of plant growth, variation in plant height was numerically similar across all treatments for all five plants, regardless of the presence or absence of AMF and AHB. Similar effects were observed for other plant growth parameters, indicating that 2.5% of antimicrobial alkaline hardwood biochar had no adverse effects on plant growth. Additional studies are required to assess the effects of varying the type of biochar, concentrations, and diversity of plant growth conditions.
Accomplishments
1. Reduction of Escherichia coli with biochar:sand filters. Foodborne pathogens, such as Shiga toxin-producing Escherichia coli (E. coli), are known to contaminate irrigation water, leading to contaminated fresh produce and human foodborne illnesses. ARS researchers in Wyndmoor, Pennsylvania, constructed b iochar:sand irrigation water filters to test multiple types of biochar (organic material, such as wood or agricultural waste, heated in the absence of oxygen) to reduce E. coli in irrigation water. Reductions of greater than 4.0 log CFU/ml of E. coli in irrigation water was achieved when biochar:sand filters were optimized by (1) using a softwood biochar that was heated at 700-1000 C, (2) construction with a 50:50 biochar:sand ratio, (3) pre-wetting biochar to approximately 78% moisture prior to mixing with sand, and (4) increasing the irrigation water filter length from 4.25 to 8.5 inches. These results may provide practical means for fresh produce growers to reduce bacterial foodborne pathogens in crop irrigation water to prevent contamination of fresh produce and human illnesses.
2. Addition of antimicrobial biochar to crop soil does not affect germination or growth of select vegetable and grain crops. Crop soil is occasionally contaminated with foodborne pathogens, such as Shiga toxin-producing E. coli, and must be rotated out of production or antimicrobially remediated before used to grow fresh produce. Previous studies have demonstrated that 2.5% of antimicrobial alkaline hardwood biochar (AHB) is capable of inactivating E. coli in crop soil, although its effects on crop production have not been determined. ARS researchers in Wyndmoor, Pennsylvania, conducted a study to assess whether adding 2.5% AHB to crop soil would affect seed germination and plant growth of five vegetable and grain crops. Results demonstrated that the addition of 2.5% AHB to crop soil had no significant effect on seed germination or plant growth (up to six weeks) for romaine lettuce, grape tomato, spinach, or wheat, and did not affect the growth of leek, compared with the control. These results reveal that up to 2.5% of antimicrobial alkaline hardwood biochar may be used to remediate soils contaminated with E. coli without negatively affecting the growth of these five vegetable and grain crops.
Review Publications
Fan, X., Gurtler, J. 2024. Depletion of free chlorine and generation of trichloromethane in the presence of pH control agents in chlorinated water at pH 6.5. Journal of Food Protection. 87(7):100296. https://doi.org/10.1016/j.jfp.2024.100296.
Gurtler, J., Garner, C.M., Mullen, C.A., Vinyard, B.T. 2023. Minimum concentrations of slow pyrolysis paper and walnut hull cyclone biochars needed to inactivate Escherichia coli O157:H7 in soil. Journal of Food Protection. 87:100210. https://doi.org/10.1016/j.jfp.2023.100210.
Gurtler, J., Garner, C.M., Grasso-Kelley, E., Fan, X., Jin, Z.T. 2024. Inactivation of desiccation-resistant salmonella on apple slices following treatment with e-polylysine, sodium bisulfate or peracetic acid and subsequent dehydration. Journal of Food Protection. 87:100297. https://doi.org/10.1016/j.jfp.2024.100297.
Olanya, O.M., Mukhopadhyay, S., Ukuku, D.O., Niemira, B.A., Uknalis, J. 2024. Attachment of Salmonella Typhimurium and survival on post-harvest produce and seed. Food Science and Technology Research. 2024(3):457-465. https://doi.org/10.3136/fstr.FSTR-D-24-00032.
