Role of Biochar Surface Properties on the Removal of Waterborne Pathogenic Escherichia coli from Stormwater

The designing of biochars with surfaces that have an effect against leaching of bacteria from biochar-based biofilters is a promising approach for removing waterborne pathogens from storm-water. Consensus regarding the contribution of biochar surface properties (i.e. charge, roughness, and surface area) to pathogen deposition/removal is currently not definitive. The present study investigates the efficacy of biochar surface properties on the removal of Escherichia coli in biochar-augmented sand biofilters. We quantified the retention and transport of E. coli pathogenic O157:H7 and non-pathogenic K12 strains in water-saturated Quincy sand columns amended with 20 wt.% pine wood or pine bark biochar produced at 350oC and 600oC.  In this study, we utilized both heat treatment and post-pyrolysis oxidation procedures to modify the surface physicochemical characteristics of biochars used. Our results showed that (1) Oxidized biochar enhanced the transport of E. coli O157:H7 cells due to more repulsive forces and higher negative charge densities; (2) E. coli O157:H7 displayed higher retention then E. coli K12 in biochar-sand columns under experimental pH conditions tested; (3) increased biochar application rates (from 0 to 20%) led to a reduction in the transport of both bacterial strains from 95 to 35%; (4) pine bark biochar produced at 600^oC increased the  transport  of E. coli O157:H7 whereas pine wood biochar produced at the same pyrolysis temperature reduced the transport of the same bacterium. These results provide insight into pathogen removal mechanisms in biochar-based biofilters and the importance of biochar production and post-production conditions.