Epsilon Archive for Student Projects

Abstract

Climate change will lead to more extreme rain events in parts of Sweden resulting in sewage overflows and thus more contamination of surface water, leading to an increased risk of waterborne infections. Swedish and Norwegian surface waters are rich in humic substances with high organic carbon content that interferes with disinfection, the most important barrier to viruses in the water treatment plant. Therefore the disinfection potential of free chlorine was evaluated for a number of viruses: canine adenovirus (CAdV), murine norovirus (MNV), mammalian orthoreovirus (MRV) and porcine enterovirus (PEV), and model viruses (MS2, 28B, ФX174 and Ф6 bacteriophages) on different water qualities (pH, turbidity and organic carbon content).
Viruses were enumerated by end-point titration and bacteriophages with plaque assay. The inactivation studies were done by chlorination (The amount of sodium hypochlorite added was 30–60 ml/L based on the types of water) at 5°C and the chlorine values were in between 0.12–0.2 mg/l range. Virus inactivations were determined for the initial reduction (IR) when the chlorine is consumed and further during the contact time within the test tube. During the later part, the chlorine contact time (CT) for one log reduction was determined (CT-1). The initial reduction was in between 3.18–3.94 logs for viruses (Adenovirus > Orthoreovirus > Norovirus > Enterovirus) and for bacteriophages it was in between 0.34–4.89 (ΦX174 > Φ6 > 28B > MS2). Due to high initial reduction the number of results used for determination of CT for one log reduction were limited. The CT-1 were around 0.5 mg*min/L for all the viruses. For a certain CT-1 time was more important than the chlorine concentration for MNV, PEV and MRV. The CT-1 for the bacteriophages MS2, 28B and фX174 were 12.6, 3.44 and 0.79 mg*min/L respectively. The CT values for ф6 bacteriophage could not be calculated because of its fast inactivation. MS2 and 28B bacteriophages were persistent to free chlorine and can preferably be used in larger scale pilot studies to better determine the effect of water quality parameters. The ΦX174 had a similar CT-1 as viruses, however the high initial reduction requires that it is added after the initial consumption to be used as a model organism. The fact that time seems to be more important than chlorine concentration for virus inactivation indicates that the design of contact reactors are important to provide as long minimum contact time for the water to react with free chlorine.