In order to evaluate the effectiveness and significance of Clostridiumperfringens as an indicator microorganism for fecal pollution, a series of field investigations were performed on the incidence of several indicator microorganisms as well as C.perfringens. Water samples were collected from several stages of wastewater and sludge treatment processes and natural environmental water bodies, such as rivers and lakes. Beside these field surveys, laboratory experiments were also performed to assess the chlorine resistance of these micrporganisms. Results obtained are as follows:

  1. The contact time required for 99% inactivation of C. perfringens with 0.1 mg/L free chlorine at pH 7 was 5 minutes for pure cultured cells. Chlorine resistance of C. perfringens indigenous in sewage was 3 to 5 times higher than that of pure cultured one.

  2. A proportional relationship was found between the density of C. perfringens and that of heterotrophic bacteria in environmental waters.

  3. C.perfringens was least reduced in almost all unit processes, compared with the other indicator microorganisms studied.

These results suggest that C.perfringens is an attractive indicator microorganism which is useful for the assessment of microbial removal in wastewater and sludge treatment, and for the evaluation of the quality of treated wastewater which is discharged to the rivers and/or reused for industrial purposes.

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