Plenty of Room for Carbon on the Ground: Bacterial Removal from Stormwater Using Biochar.

Fecal indicator bacteria in stormwater may cause widespread contamination of surface waters and groundwater, because traditional stormwater biofilter or bioinfiltration systems have limited capacity to remove bacteria. To improve bacterial removal, biofilter can be augmented with geomedia including biochar.  We examine the potential of biochar to remove a model bacterium (E. coli) under complex conditions relevant to stormwater infiltration: presence of natural organic matter (NOM), intermittent flow of stormwater, high flow rates, and high bacterial loading. Experiments were designed to examine how biochar weathering affects bacterial removal. Addition of small quantity of biochar to biofilter media not only enhanced E. coli removal, but also decreased the mobilization of attached E. coli during intermittent flow of stormwater. Biochar consistently removed more than 90% of injected E. coli in the presence of NOM—a condition that typically lowers bacterial removal in a traditional biofilter. The removal capacity of biochar-augmented biofilter remained high with increases in bacterial loading. Biochar-augmented biofilters weathered under dry-wet cycles removed more E. coli than the biofilters exposed to the same volume of stormwater without intermediate drying, which indicates that biochar weathering may benefit bacterial removal. Because biochar is expected to last for years, increasing use of biochar in biofilter and other stormwater management systems could potentially alleviate water contamination issue in urban area and provide an alternative source for non-portable water, in addition to the added benefit of sequestering carbon in ground.