Publication Abstract

Chlorination of indicator bacteria and viruses in primary sewage effluent

J. A. Tree, M. R. Adams and D. N. Lees

Wastewater disinfection is used in many countries for reducing faecal coliform levels in effluents impacting recreational bathing waters which do not comply with microbiological standards. Whether such treatments simultaneously inactivate human enteric viruses, which may be responsible for waterborne disease, however, remains unclear. This laboratory study focused on the chlorination of primary treated effluent with three doses (8, 16, and 30 mg/l) of free chlorine as sodium hypochlorite. Seeding experiments showed that inactivation (>5 log₁₀) of Escherichia coli and Enterococcus faecalis was rapid and complete but that poor inactivation (0.2-1.0 log₁₀) of FRNA bacteriophage (MS2) (a potential ‘virus indicator’), was recorded at all three doses. However, seeded poliovirus was significantly more susceptible (2.8 log₁₀) to inactivation by chlorine than was the FRNA bacteriophage. To ensure that these results were not artefacts of the seeding process, comparisons were made between inactivation rates of laboratory-seeded organisms in sterilised sewage and inactivation rates of organisms occurring naturally in sewage. Multifactorial ANOVA showed that there was no signficant 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.

Reference:

J. A. Tree, M. R. Adams and D. N. Lees, 2003. Chlorination of indicator bacteria and viruses in primary sewage effluent. Journal of Applied and Environmental Microbiology, 69(11): 2038-2043.