Descriptive statistics using uncensored and modeled left-censored values for concentrations of coliphage and E. coli indicators in pre- and post-disinfection effluent, Ontario, Canada, 2014–2017
| . | Plants B, D, and E combined, n = 34 (providing secondary treatment) . | Plants A and C combined, n = 24 (providing tertiary treatment) . | Secondary vs. tertiary plant differences in LR means; p-value; 0.95 CI . | ||||
|---|---|---|---|---|---|---|---|
| Indicator organism . | d (%) . | nd (%) . | mean (±SE) . | d (%) . | nd (%) . | mean (±SE) . | Welch two-sample t-test . |
| F+ (male-specific), coliphage, PFU/L | |||||||
| Pre-disinfection | 34 (100) | 0 | 2.6 × 10+3 (4.6 × 10+2) | 24 (100) | 0 | 2.9 × 10+2 (4.4 × 10+1) | |
| Post-disinfection | 27 (79) | 7 (21) | 3.9 × 10+2 (1.3 × 10+2) | 11 (46) | 13 (54) | 1.5 × 100 (6.8 × 10−1) | |
| Mean LR | 0.8 (0.05) | 2.3 (0.2) | p < 0.001; 1.1–1.9 | ||||
| Somatic coliphage, PFU/L | |||||||
| Pre-disinfection | 34 (100) | 0 | 2.9 × 10+4 (5.2 × 10+3) | 24 (100) | 0 | 9.2 × 10+3 (1.6 × 10+3) | |
| Post-disinfection | 29 (85) | 5 (15) | 5.2 × 10+2 (1.9 × 10+2) | 12 (50) | 12 (50) | 8.8 × 100 (5.4 × 100) | |
| Mean LR | 1.8 (0.1) | 3.0 (0.4) | p < 0.001; 0.6–2.0 | ||||
| E. coli, CFU/100 mL | |||||||
| Pre-disinfection | 33 (100) | 0 | 4.7 × 10+4 (1.3 × 10+4) | 24 (100) | 0 | 1.0 × 10+3 (2.0 × 10+2) | |
| Post-disinfection | 29 (88) | 4 (12) | 1.6 × 10+2 (8.4 × 10+1) | 18 (75) | 6 (25) | 3.0 × 100 (3.0 × 10−1) | |
| Mean LR | 2.5 (0.3) | 2.5 (0.1) | p = 0.8 (NS); (–)0.4–0.5 | ||||
| . | Plants B, D, and E combined, n = 34 (providing secondary treatment) . | Plants A and C combined, n = 24 (providing tertiary treatment) . | Secondary vs. tertiary plant differences in LR means; p-value; 0.95 CI . | ||||
|---|---|---|---|---|---|---|---|
| Indicator organism . | d (%) . | nd (%) . | mean (±SE) . | d (%) . | nd (%) . | mean (±SE) . | Welch two-sample t-test . |
| F+ (male-specific), coliphage, PFU/L | |||||||
| Pre-disinfection | 34 (100) | 0 | 2.6 × 10+3 (4.6 × 10+2) | 24 (100) | 0 | 2.9 × 10+2 (4.4 × 10+1) | |
| Post-disinfection | 27 (79) | 7 (21) | 3.9 × 10+2 (1.3 × 10+2) | 11 (46) | 13 (54) | 1.5 × 100 (6.8 × 10−1) | |
| Mean LR | 0.8 (0.05) | 2.3 (0.2) | p < 0.001; 1.1–1.9 | ||||
| Somatic coliphage, PFU/L | |||||||
| Pre-disinfection | 34 (100) | 0 | 2.9 × 10+4 (5.2 × 10+3) | 24 (100) | 0 | 9.2 × 10+3 (1.6 × 10+3) | |
| Post-disinfection | 29 (85) | 5 (15) | 5.2 × 10+2 (1.9 × 10+2) | 12 (50) | 12 (50) | 8.8 × 100 (5.4 × 100) | |
| Mean LR | 1.8 (0.1) | 3.0 (0.4) | p < 0.001; 0.6–2.0 | ||||
| E. coli, CFU/100 mL | |||||||
| Pre-disinfection | 33 (100) | 0 | 4.7 × 10+4 (1.3 × 10+4) | 24 (100) | 0 | 1.0 × 10+3 (2.0 × 10+2) | |
| Post-disinfection | 29 (88) | 4 (12) | 1.6 × 10+2 (8.4 × 10+1) | 18 (75) | 6 (25) | 3.0 × 100 (3.0 × 10−1) | |
| Mean LR | 2.5 (0.3) | 2.5 (0.1) | p = 0.8 (NS); (–)0.4–0.5 | ||||
PFU, plaque forming units; CFU, colony forming units; d, number detected (percent); nd, number of non-detects (percent) that were modeled; SE, standard error; LR, log10 reduction; CI, confidence interval; NS, not significant (p > 0.05); counts are unadjusted for recovery – see the text.