Virus removal by iron coagulation–microfiltration

This study was undertaken to determine virus removal efficiency by iron coagulation followed by microfiltration (MF) in water treatment using the MS2 bacteriophage (∼25 nm diameter) as a tracer virus. Results from these bench-scale studies were used to propose a mechanism for virus removal by iron coagulation–MF. Ferric chloride was used as coagulant, and the dosages were 0, 2, 5, and 10 mg/L as Fe(III) with pH adjusted during mixing to 6.3, 7.3 and 8.3. In the absence of iron-coagulation and with less than 2 mg/L Fe, MF alone achieved less than a 0.5 log removal of MS2 virus. However, iron-coagulation pretreatment dramatically improved virus removal, especially in the 5–10 mg/L Fe dose range, ultimately achieving more than 4-log removal at pH 6.3 with 10-mg/L Fe dose. For the 5 and 10 mg/L Fe dosages, decreasing pH in the 8.3–6.3 range resulted in significantly greater virus removal. For 0 and 2 mg/L iron dosages, decreasing pH in the 8.3–6.3 range also improved virus removal, but to a lesser extent. The experimental data indicates negatively charged MS2 viruses first adsorbed onto the positively charged iron oxyhydroxide floc particles before being removed by MF. MS2 viruses were not inactivated in iron or aluminum coagulation as evidenced by the fact that their concentrations before and after coagulation, settling, and re-suspension of the coagulated sludge were not statistically different.