Purpose: To determine the influence of biochar on the survival of E. coli O157:H7 (EHEC) in crop soil.
Methods: Twelve types of biochar (slow pyrolysis or fast pyrolysis type) were generated in on-site reactors. A three-strain composite of EHEC (6 log CFU/g, final population) was added to autoclaved crop soil + 10% (final concentration) of one of 12 types of biochar. Samples were adjusted to a final moisture content of 17.6% and stored in sealed bags at 22 °C. Populations of EHEC were determined weekly up to five weeks.
Results: Fast pyrolysis-produced switchgrass (FP-SG) and FP horse litter (FP-HL) biochars inactivated 3.52 and 2.58 log CFU/g more EHEC than did control soil by day 14. By day 28, FP-SG, FP-HL, and FPpelleted-SG biochars all reduced EHEC to undetectable levels (< 1.2 log CFU/g) by direct plating versus control soil, which contained 5.45 log CFU/g of EHEC on day 28. FP oak biochar inactivated 3.1 log more EHEC than control soil on day 28, and at day 35, no EHEC was detected in FP-oak soil by direct plating. Four slow pyrolysis biochars all inactivated 2 log CFU/g more EHEC than the control soil by day 28, including SG (1 h at 500 °C), mixed hardwood pellets (MHP, 1 h at 500 °C), and MHP (30 min at 700 °C).
Significance: These results are the first to suggest that biochar amendments enhance the inactivation of EHEC in crop soil.