Removal of Escherichia coli from lake water in a biochar-amended biosand filtering system

Abstract A point-of-use household water treatment technology, the biosand filter (BSF), has been widely adopted across over 180 countries (CAWST, 2020). However, it has a poor Escherichia coli (E. coli) removal efficiency during the first few weeks of its use. This study investigated the potential of biochar on E. coli removal in a laboratory-modified biosand filtering system. Two biochars, produced from wheat straw and willow wood feedstocks, were used and their effects were compared. Only the coarser fraction of both biochars (1–4 mm) was used in order to minimize its impact on the filtration rate. It was observed that the filter amended with wheat straw biochar exhibited a higher mean E. coli removal rate (84%) than the filter amended with willow wood biochar (79%); however, both biochar-amended filters had lower mean E. coli removal rates than the sand-only control filter (88%), over a 5-week filtration experiment. The E. coli adsorption of biochar and sand were examined at the end of the filtration experiment. Both biochars were shown to have a larger total amount of E. coli adsorption (7.4 log10) than sand (6.8 log10). The two biochars showed comparable E. coli adsorption capacities of 5.7 log10 CFU/g, although their specific surface areas varied greatly (55.24 m2/g for wheat straw biochar and 380.00 m2/g for willow wood biochar). The discrepancy between the results of E. coli removal and E. coli adsorption might indicate the importance of biochar straining; the absence of fine biochar particles (