Table 1 Levels of free residual chlorine, trihalomethanes and Legionella isolation according to chlorination stage
Chlorination stage | Residual free chlorine mg/L | Trihalomethanes μg/L | Legionella spp. Samples without point of use filters | Legionella spp. Samples with point of use filters | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
Arithmetic mean | SD | Median | IQ Range | Arithmetic mean | SD | Median | IQ Range | Positive | Total | Positive | Total | |
Before hyperchlorination | 0.19 | 0.56 | 0.10 | 0.05 - 0.20 | 2.71 | 1.81 | 2.38 | 1.36 - 3.17 | 43 (21.1%) | 204 | 0 | 4 |
15 days after hyperchlorination | 0.34 | 0.73 | 0.18 | 0.10 - 0.25 | 8.70 | 6.61 | 7.50 | 3.95 - 12.5 | 15 (7.8%) | 193 | 0 | 18 |
30 days after hyperchlorination | 0.23 | 0.18 | 0.20 | 0.11 - 0.30 | 8.55 | 3.52 | 7.84 | 6.38 - 11.30 | 6 (3.5%) | 173 | 0 | 20 |
Continuous hyperchlorination | 0.61 | 0.34 | 0.60 | 0.40 - 0.79 | 10.7 | 23.8 | 5.50 | 2.76 - 10.01 | 23 (5.5%) | 416 | 0 | 222 |
No continuous hyperchlorination | 0.15 | 0.15 | 0.12 | 0.07 - 0.17 | 1.05 | 1.07 | 0.88 | 0.66 - 2.62 | 15 (27.8%) | 55 | 0 | 3 |
Total | 0.43 | 0.44 | 0.30 | 0.13 - 0.65 | 8.97 | 18.56 | 5.40 | 2.58 - 9.87 | 102 (9.8%) | 1041 | 0 | 267 |