Escherichia coli inactivation in water by sulfate radical-based oxidation process using FeCl₃-activated...

Pathogenic microbes in water present great risks to environments, water resources, and human health. In the present study, for the first time, a FeCl₃-activated bermudagrass-derived biochar (FA-BC) was applied to activate persulfate (PS) for E. coli inactivation. The PS activation was ascribed to the presence of Fe⁰ and Fe₃O₄ on the surface of FA-BC, and SO₄^·- radicals were proved to be the main role for E. coli inactivation using FA-BC activated PS system (FA-BC/PS). Decreasing the pH (5-9) and increasing the PS concentration (50-300 mg/L), reaction temperature (20-50 °C), and FA-BC dosage (100-500 mg/L) resulted in the enhancement of disinfection efficiency of E. coli using FA-BC/PS. 6.21 log reductions of E. coli were achieved within 20 min under the optimal conditions (500 mg/L FA-BC, 200 mg/L PS, pH 7, and 20 °C with 10⁷ CFU/mL E. coli in DI water). The FA-BC/PS effectively eliminated various initial concentrations of E. coli (10⁵-10⁸ CFU/mL). The E. coli inactivation rate decreased from 0.1426 min^-1 to 0.0883, 0.1268 min^-1, and 0.1093 min^-1 with the presence of 10 mg/L humic acid, 100 mg/L Cl^-, and 100 mg/L HCO₃^-, respectively. In addition, after three cycles of disinfection tests using FA-BC/PS, the E. coli inactivation rate only slightly decreased from 0.1426 to 0.1288 min^-1. The FA-BC/PS also effectively removed the E. coli in real stormwater with a 99.2 % inactivation efficiency within 180 min. The FA-BC/PS in fixed-bed column tests revealed the continuous and high inactivation of E. coli in water. Increasing the FA-BC amount (1.5 %-5 %) and PS concentration (50-200 mg/L) and decreasing the flow rate (2-4 mL/min) caused the lower E. coli concentration in effluent. Therefore, the FA-BC/PS can be considered as a promising and efficient technique for water disinfection.