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Applied and Environmental Microbiology, April 2003, p. 2038-2043, Vol. 69, No. 4
0099-2240/03/$08.00+0     DOI: 10.1128/AEM.69.4.2038-2043.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

Chlorination of Indicator Bacteria and Viruses in Primary Sewage Effluent

Julia A. Tree,^1, Martin R. Adams,² and David N. Lees^1*

Centre for Environment, Fisheries and Aquaculture Science, Weymouth, Dorset DT4 8UB,¹ School of Biological Sciences, University of Surrey, Guildford, Surrey GU2 5XH, United Kingdom²

Received 7 August 2002/ Accepted 11 January 2003

Wastewater disinfection is used in many countries for reducing fecal coliform levels in effluents. Disinfection is therefore frequently used to improve recreational bathing waters which do not comply with microbiological standards. It is unknown whether human enteric viruses (which are responsible for waterborne disease) are simultaneously inactivated alongside fecal coliforms. This laboratory study focused on the chlorination of primary treated effluent with three doses (8, 16, and 30 mg/liter) of free chlorine as sodium hypochlorite. Seeding experiments showed that inactivation (>5 log₁₀ units) of Escherichia coli and Enterococcus faecalis was rapid and complete but that there was poor inactivation (0.2 to 1.0 log₁₀ unit) of F⁺-specific RNA (FRNA) bacteriophage (MS2) (a potential virus indicator) at all three doses. However, seeded poliovirus was significantly more susceptible (2.8 log₁₀ units) to inactivation by chlorine than was the FRNA bacteriophage. To ensure that these results were not artifacts of the seeding process, comparisons were made between inactivation rates of laboratory-seeded organisms in sterilized sewage and inactivation rates of organisms occurring naturally in sewage. Multifactorial analysis of variance showed that there was no significant difference (P > 0.05) between the inactivation rates for seeded and naturally occurring FRNA bacteriophage. However, laboratory-grown poliovirus was inactivated much more rapidly than were naturally occurring, indigenous enteroviruses (P < 0.001). This may reflect differences in the way indigenous virus is presented to the disinfectant. Inactivation rates for indigenous enteroviruses were quite similar to those seen for FRNA bacteriophage at lower doses of chlorine. These results have significance for the effectiveness of chlorination as a sewage treatment process, particularly where virus contamination is of concern, and suggest that FRNA bacteriophage would be an appropriate indicator of such viral inactivation under field conditions.

Present address: Centre for Applied Microbiology and Research, Salisbury, Wiltshire SP4 0JG, United Kingdom.

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