DETECTION OF INFECTIOUS ADENOVIRUS IN TERTIARY TREATED AND UV DISINFECTED WASTEWATER DURING A UV DISINFECTION PILOT STUDY
Abstract:A pilot study investigating the efficacy of low pressure, high intensity ultraviolet (UV) radiation for disinfection of urban wastewater was conducted. The pilot study utilized a small-scale version of the Ultra Guard UV treatment system provided by UV Systems Technology, Inc. (Burnaby, Canada). The primary objective was to determine whether low pressure, high intensity UV irradiation could potentially be used to meet the California Water Reclamation Criteria (CWRC) for total coliform bacteria in reclaimed water and to determine its potential for a 99.99% reduction of two model enteric viruses(MS2 coliphage and poliovirus). UV pilot unit inactivation of the total and fecal coliform bacteria, sewage indigenous F-specific coliphage, seeded F-specific coliphage (MS2), sewage indigenous enteric viruses, and seeded poliovirus type I in tertiary treated wastewater was investigated. During the course of the pilot study, an infectious adenovirus was isolated from UV disinfected tertiary and secondary treated wastewater. The virus was detected in 15 of 16 experiments involving large volume (352-697 L)sampling and analysis for indigenous enteric viruses and seeded poliovirus. The adenovirus was identified via electron microscopy and enzyme immunoassay after isolation using traditional cell culture based methods. Tertiary treated samples in which the adenovirus was detected received calculated UV doses in the range of 34-71 mW-sec/cm2. Turbidity and total coliform bacteria levels in these samples were within the CWRC standards of <2 NTU and no greater than 23 MPN/100 mL for a single sample(30 d sampling period), respectively. Overall, total coliform bacteria were effectively removed from UV disinfected tertiary effluent indicating that low pressure, high intensity UV irradiation could potentially be used to meet the stringent CWRC. Seven-day totalcoliform median values were not determined from the pilot unit data, however, a conservative estimate suggests that a dose of approximately 60 mW-sec/cm2 would be sufficient to meet the 7-d median concentration of no more than 2.2 MPN/100 mL for the last 7 samples taken. A 4-log10 removal of seeded MS2 and indigenous F-specific coliphage in the pilot unit experiments (tertiary effluent) was achieved at doses of 70 and 50 mW-sec/cm2, respectively. The seeded poliovirus was not detected in UV treated secondary or tertiary effluents, however, problems with the concentration protocol prevented documentation of a specific 4-log10 removal of the virus. Comparative collimated UV irradiation studies indicated that the isolated adenovirus was more UV resistant than MS2 coliphage and poliovirus type I. Doses of approximately 33, 112, and 183 mW-sec/cm2 were required to achieve a 4-log10 removal of poliovirus, MS2, and theisolated adenovirus, respectively. These findings indicate that UV doses found to be effective at meeting the stringent CWRC total coliform standards may not provide suitable reduction of some naturally occurring pathogenic viruses such as adenovirus. Further research is needed to determine appropriate doses for UV disinfection of pathogenic enteric viruses in wastewater.
Document Type: Research Article
Publication date: January 1, 2000
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