Browsing by Author "Churn, C. Calvert"

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    Field and laboratory studies concerning the detection of enteric viruses in either settled or disinfected secondary sewage
    Churn, C. Calvert (Virginia Polytechnic Institute and State University, 1978)
    The demand for potable water may be culminating in a compromise on what constitutes a "safe" drinking water due to the rapidly approaching need to utilize recycled waters. The elimination of viruses pathogenic to humans from recycled waters will depend on the removal efficiencies of treatment processes and the sensitivity of detection methodologies. Enteric viruses can survive current wastewater treatment practices, and some even persist for long periods of time in natural waters. The objectives of this investigation were threefold: first, to construct a virus concentrator suitable for sampling secondary sewage treatment plant effluents; second, to sample the effluent of trickling filter sewage treatment plants prior to chlorination to determine the remaining amount of enteric viruses; third, to determine the virus removal efficiencies of a final settling and chlorination operation by using bench-scale simulations of the two units. Viruses were not detected in any of the secondary effluents of three trickling filter plants samples. However, these results may have been obtained because the level of viruses was below the minimum detection limits of the virus concentrator that was constructed. Also, if viruses were present, the high pH elution process may have been deleterious, or the BGM host cell was incompatible. Detention times in the model system studies of a final sedimentation basin and chlorine contact chamber were based on Rhodamine WT dye studies of plant-scale units. These studies suggested that 98.5 to 100 percent of the enteric viruses contained in the actual plant effluent would be removed or inactivated by the combination of final settling and chlorination.
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    A study of the kinetics and mechanism of inactivation of a DNA- containing enteric virus by chlorine
    Churn, C. Calvert (Virginia Polytechnic Institute and State University, 1982)
    A newly discovered enteric virus has recently been associated with large outbreaks of waterborne gastroenteritis. Most commonly referred to as the Norwalk agent, this virus appears to be morphologically and biophysically similar ·to the parvoviruses. Presently there is very little known about the fate of parvoviruses in environmental systems. In this study the parvovirus H-1, a putative human virus containing single-stranded DNA (ssDNA), was used as a model virus for chlorine inactivation experiments. The purpose of this research was two-fold: first, to investigate the kinetics of inactivation of parvovirus H-1 by low levels of free chlorine (0.05 - 0.20 mg L⁻¹) at pH 7 and at 5, 10, 20, and 30°C; and secondly, to determine the mechanism by which chlorine inactivates this virus. Inactivation occurred in the usual dose-response relationship, that is, increasing the chlorine dose caused an increase in the rate of inactivation. The results indicated that perhaps more than one reaction mechanism was responsible for inactivation, and the reaction mechanism was a function of temperature. The energy required for the inactivation reaction using 0.05 mg L⁻¹ free chlorine from 5 to 30°C was graphically determined to be 2.4 Kcal mole⁻¹. The change in entropy was calculated to be -52.34 entropy units. From the mechanism study it was concluded that the initial action of chlorine on parvovirus H-1 was on the capsid. Alterations in the two major capsid proteins caused the virion to rupture, and, as evidenced by electron microscopy the ssDNA was exposed. Also, the adsorption ability of the chlorine-treated virions to host cells was significantly inhibited. This was presumably due to the effect on the spatial arrangement of the capsid proteins in their entirety rather than a loss of, or change, in only one polypeptide. The sedimentation rate of the chlorine-treated whole virus decreased from 116S to 43S. The chlorine caused certain sites on the capsid proteins to become highly reactive which facilitated the formation of higher molecular weight aggregates as detected by fluorographs of electrophoretic protein patterns in polyacrylamide gels. Most significant was the discovery that the ssDNA remained undamaged and was still capable of in vitro replication even after 60 minutes of exposure to 5 mg L⁻¹ of sodium hypochlorite at pH 7.