Table 3.

Decimal reductiona of the numbers of different microbial parameters after chlorination of sewage

Experiment no.Chlorination conditionsDecimal reduction of the no. of:
Total residual chlorine (mg/liter)Time (min)E. colib CFUE. coliO157:H7c CFUSomatic coliphages (PFU)Phages infecting O157:H7 (PFU)Phages infecting O157:H7 and carrying the Stx2 gene (MPN)
110203.>0.3, <0.8d
210203.>0.4, <0.6
310204.>0.3, <0.8
  • a Decimal reduction calculated as the decrease in log units.

  • b Naturally occurring E. coli.

  • c Seeded E. coli O157:H7. NT, not tested.

  • d Decimal reduction was between the indicated values. When the result of one of the triplicates of one of the volumes was missing, the inactivation was considered to be between the MPN values calculated considering the missing value as positive or negative.