Abstract
Chlorination and UV disinfection of untreated wastewater were compared, assuming that the activated sludge process is not functioning after disasters. Untreated wastewater samples were collected from a wastewater treatment plant that was severely damaged by the Great East Japan Earthquake in 2011, and the samples were subjected to chlorination or UV disinfection with or without preceding coagulation. Disinfection efficiency was evaluated based on the inactivation profiles of indigenous microorganisms: total coliforms, Escherichia coli, and somatic phages. Chlorination without coagulation was not effective for either microorganism regardless of the chlorine injection rate (5 mg/L or 10 mg/L) and contact time (up to 30 min), but the inactivation efficiency was improved when coagulation preceded chlorination. Meanwhile, UV disinfection was effective even without coagulation, and the UV inactivation rate constant was not significantly different between samples with and without coagulation for either microorganism (ANOVA, p > 0.10) under the experimental conditions adopted in this study. In conclusion, the direct chlorination of untreated wastewater, as conducted after the Great East Japan Earthquake, is not very effective and we recommend coagulation before chlorination if secondary wastewater treatment is unavailable after a disaster. Alternatively, UV irradiation would be an option for disinfecting untreated wastewater after disasters.
