A preparation of infectious human rotavirus, isolated from faeces and resuspended in wastewater effluent, was shown to be inactivated by chlorine, chlorine dioxide, ozone and peracetic acid. Infectivity was assayed in MA 104 cells by the detection of cell-associated viral antigen by immunofluorescence. The inactivation curves were similar to those reported for other enteric viruses. Human rotavirus was at least as resistant as poliovirus, coxsackievirus, echovirus and f2 coliphage and was strikingly less sensitive to inactivation than the simian rotavirus, SA11. The latter was generally the most sensitive of the six tested viruses yet is often taken as being representative of the human rotaviruses.

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The resistance of bacteria to antimicrobial agents could be influenced by growth environment. The susceptibility of two enteric bacteria, Yersinia enterocolitica and Klebsiella pneumoniae, to chlorine dioxide was investigated. These organisms were grown in a defined medium in a chemostat and the influence of growth rate, temperature, and cell density on the susceptibility was studied. All inactivation experiments were conducted with a dose of 0.25 mg of chlorine dioxide per liter in phosphate-buffered saline at pH 7.0 and 23°C. The results indicated that populations grown under conditions that more closely approximate natural aquatic environments, e.g., low temperatures and growth at submaximal rates caused by nutrient limitation, were most resistant. The conclusion from this study is that antecedent growth conditions have a profound effect on the susceptibility of bacteria to disinfectants, and it is more appropriate to use the chemostat-grown bacteria as test organisms to evaluate the efficacy of a certain disinfectant.

The virucidal efficacy of peracetic acid (PAA) was evaluated against poliovirus 1, echovirus 1, coxsackievirus B5, human rotavirus, simian rotavirus SA11 and bacteriophage f2 in a municipal sewage effluent. The results indicated relatively high concentrations of acid were required to achieve significant inactivation. Human rotavirus, which was the most resistant, required 140 ppm to achieve 99.99% inactivation. On the other hand, simian rotavirus SA11, which was the most sensitive, required only 20 ppm to achieve the same degree of inactivation. The three enteroviruses reacted similarly and the bacteriophage was slightly less resistant than the enteroviruses, especially at high concentrations of peracetic acid. The effluent did not exert a demand for peracetic acid. Temperature, organic matter and suspended solids had negligible effects on the virucidal efficacy of peracetic acid.

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The effects of the combination of any two of the following disinfectants: chlorine, chlorine dioxide, ozone and peracetic acid were investigated using poliovirus 1 as a model virus in a municipal sewage effluent. It was noted that the efficacy of chlorine was enhanced in the presence of either chlorine dioxide, ozone or peracetic acid. Maximum enhancement was achieved when peracetic acid was present with either chlorine or ozone and less enhancement was noted when the peracetic acid was added before chlorine dioxide. Similar results were noted when hydrochloric acid was used instead of peracetic acid. It may be concluded that the application of any two of the disinfectants studied were rarely synergistic but merely additive or complementary (i.e., one disinfectant provides the other with a medium in which it functions better).

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