Attenuation of Escherichia Coli In a Biochar-Amended Soil.

Advances in research on biochar have highlighted its tremendous potential for mitigating climate change, improving soil properties, and reducing chemical pollution of soils and groundwater.  However, studies that evaluate its potential in treating bacterial contaminants are lacking. This study evaluated the attenuation of Escherichia coli in soils amended with various rates of biochars  that were produced by high temperature and by low temperature pyrolysis. Biochars from poultry litter pyrolyzed at 700^oC and at 350^oC were separately mixed with a loamy sand to produce 2% and 10% biochar-soil mixtures. Along with an unamended loamy sand control, the mixtures were packed in separate 2.5 cm-diameter by 15 cm-high glass columns and saturated with 1mM KCl. Roughly a pore volume of bacterial suspension (10⁷ cell mL^-1) of two E. coli isolates with contrasting surface properties were then separately injected into the saturated columns and leached with ~3 pore volumes of 1mM KCl. Effluent bacterial concentrations reveal that mixing biochar pyrolyzed at 350^oC to loamy sand at rates of 2% and 10% did not result in significant attenuation of  E. coli.  The same was observed for the 2% mixture using biochar pyrolyzed at 700^oC. However, the 10% mixture using 700^oC biochar resulted in at least five orders of magnitude reduction in effluent bacterial concentration compared to the control. Surface properties seemed to influence the degree of sorption of E. coli in the 2% biochar-soil mixture wherein the strain with lower hydrophobicity and a zeta potential closer to neutral were attenuated more effectively. In contrast, the difference in surface properties did not lead to any difference in attenuation of E coli in the 10% biochar-soil mixture.  The pyrolysis temperature employed in biochar production significantly influences its efficacy in treating bacteria.