Hydrophobic biochar enhances Escherichia coli retention in a sandy loam soil influenced by irrigation management

Microbial pollution of the groundwater and surface waters could endanger animal and human health as a serious environmental issue. Escherichia coli retention was investigated in the sandy loam columns amended with biochar under deficit irrigation (60%, 80%, 100%, and 120% of the field capacity). A pulse of bacteria (1.00 × 10 8 CFU ml –1 ) was poured on the soil surface. Two scenarios were conducted using HYDRUS-1D. The retention rate in all treatments at 0–10 cm was higher than the depths of 10–30. This was more significant in amended soil compared to the control soils. The first scenario (attachment, k att or straining, k str ) showed that k att values were at least 25 times greater than the k str values, indicating that the physico-chemical process was dominant compared to the physical retention in both biochar treated and the control soils. The k att values calculated for the biochar-treated columns were increased as the deficit irrigation increased. The second scenario (physico-chemical, k det 2 or physical, k det1 detachment) illustrated no significant difference between the k det values in both sites, while the k det2 values of the amended soil were less than the controls, indicating the contribution of biochar in cell attachment. Obvious greater values of k att compared to k str approved the first scenario determining the fact that biochar's land application under deficit irrigation most probably enhances cell retention via attachment than straining.