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Viral and Bacterial Removal Efficiencies in Different Wastewater Treatment Processes for Various Types of Reclamation Purposes


Water reclamation has been used as an alternative to supplement the traditional water resource to meet the increasing demand owing to population growth and economic growth. However viruses and bacteria in wastewater can be a potential safety hazard for the public health in water reuse practices if are not effectively removed during water reclamation process. This research utilized a rapid flow cytometry (FCM) method to detect total viruses and total bacteria in each unit process of four different treatment process trains for water reclamation purposes, aiming at understanding their viral and bacterial removal efficiencies, which could provide a reference for the application of various treatment processes into water reclamation in the aspect of protecting public health. Multiple samplings was taken at four treatment processes trains over a half-year period, including activated sludge process (ASP) and membrane bioreactor (MBR) process of Michelson Water Reclamation Plant (MWRP), ASP of Chiquita Water Recycling Plant (CWRP), and microfiltration-reverse osmosis (MF-RO) process of Edward C. Little Water Recycling Facility (ECLWRF). The results showed viral removal in the ASP of MWRP was 4.6log10, with 4.4log10 at chlorine disinfection tank (CD); total bacterial removal in the ASP was 5.9log10, with 1.7log10 achieved at secondary clarifier (SC), 0.2log10 at DMF, and 3.8log10 at CD respectively; in the MBR train, viruses and bacteria were reduced by 4.3log10 and 5.9log10 respectively in MBR. In the ASP train of CWRP, only 1.4log10 reduction of bacteria achieved through out the whole process train at SC, which indicate undesired removal towards viruses and bacteria. This result may be due to a rapid conversion of chlorine to chloramine in the presence of high ammonia concentration in the influent water. Many gram-positive bacteria and viruses are more resistant to chloramine disinfection than indicator E. coli. In the MF-RO train of ECLWRF, viruses and bacteria were reduced by 4.5log10 and 5.1log10 as a consequence, with mainly reduction achieved at MF. This result indicates high efficiency of microbial removal capability of the advanced treatment train. However, the viral reduction rate by MF can vary significantly, the removal efficiency may be improved as the MF is clogged with reduced physical pore-size. This study contributes to our understanding of current wastewater treatment technology for virus and bacteria removal and offer insight to the policy decision for water reuse.

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