Chief Operator Level · Advanced Process Control · Plant Management · Regulatory Compliance
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Cl₂ residual = 1.5 mg/L, contact time = 40 min → CT = 60 mg/L·min
C = disinfectant residual (mg/L) at the outlet; T = theoretical detention time (min). For chlorine at pH 7 and 15°C, CT = 60 achieves 3-log Giardia inactivation.
HRT = 60 min, BF = 0.5 → T₁₀ = 30 min
BF = baffling factor (0.1–1.0 per regulatory tables). T₁₀ is the time for 10% of tracer to pass through. Use T₁₀ for CT credit calculations.
k = 0.02, C = 1 mg/L, n = 1, T = 30 min → log inactivation = 0.6
k = rate constant (varies by organism and disinfectant); n = dilution coefficient (typically 1 for chlorine). Used to calculate inactivation credit for regulatory compliance.
Ozone residual = 0.3 mg/L, T₁₀ = 3 min → CT = 0.9 > 0.63 ✓
Ozone is far more effective than chlorine. At 15°C, only 0.63 mg/L·min achieves 3-log Giardia inactivation vs. 60 mg/L·min for chlorine at pH 7.
3-log Giardia requires ≥5.8 mJ/cm²; 4-log Cryptosporidium requires ≥22 mJ/cm²
UV dose = irradiance (mW/cm²) × exposure time (s). UV provides no residual — must be combined with chemical disinfection for distribution system protection.
Higher NOM, higher Cl₂ dose, longer contact time, higher pH → higher THM formation
Simplified empirical relationship. Key levers: reduce NOM before chlorination (enhanced coagulation, GAC), minimize Cl₂ dose, lower pH, reduce contact time before distribution.
| Parameter | Typical Value / Limit | Regulatory Reference | Notes |
|---|---|---|---|
| Giardia CT (Cl₂, 15°C, pH 7) | 60 mg/L·min (3-log) | GUDI / Surface Water Regs | Use T₁₀ with baffling factor |
| Ozone CT (Giardia, 3-log) | 0.63 mg/L·min | GUDI | Far more efficient than Cl₂ |
| UV Dose (Giardia, 3-log) | 5.8 mJ/cm² | UV Disinfection Guidance | No residual — combine with Cl₂ |
| UV Dose (Crypto, 4-log) | 22 mJ/cm² | UV Disinfection Guidance | Crypto resistant to Cl₂ |
| Filtered turbidity (95th %ile) | ≤0.3 NTU | O. Reg. 170/03 / Prov. Regs | No single reading >1.0 NTU |
| THM MAC (RAA) | 100 μg/L | Health Canada GCDWQ | Running annual average |
| HAA MAC (RAA) | 80 μg/L | Health Canada GCDWQ | Running annual average |
| Lead MAC | 10 μg/L (90th %ile) | Health Canada GCDWQ | First-draw samples |
| Fluoride optimal | 0.7 mg/L | Health Canada | MAC = 1.5 mg/L |
| Chlorine residual (distribution) | ≥0.05 mg/L free Cl₂ | Provincial regulations | Minimum at all points |
| Notification of adverse result | Within 24 hours | O. Reg. 170/03 | To MOH and Director |
| Baffling factor (poor) | 0.1 | CT Guidance | Unbaffled tanks |
| Baffling factor (excellent) | 0.7–1.0 | CT Guidance | Plug flow / serpentine |
| Membrane flux (UF typical) | 20–80 LMH | Manufacturer guidance | Monitor for fouling |
| VFD power savings (20% speed reduction) | ~49% power reduction | Affinity laws | P ∝ N³ |