Chlorine Dosing Rate for Water Disinfection
Chlorine Dosing Rate for Water Disinfection
Disinfecting a water supply with chlorine requires feeding it in at a mass rate that matches both the desired concentration (dose) and how fast the water is flowing — feed too little and the water is under-disinfected, feed too much and taste, odor, and disinfection byproduct problems follow.This calculation converts a target dose in mg/L directly into the mass feed rate a chemical feed pump must deliver, which is the number an operator actually sets on the dosing equipment.
The feed rate is dose_rate = C·Q, the target dose concentration times the flow rate. where C is the target chlorine dose (concentration) and Q is the water flow rate being treated.
Inputs
C_dose := 2 mg/L=2e-03 kg/m^3
Q_flow := 100 L/s=0.1 m^3/s
Multiplying the target concentration by the flow rate converts a dose target into the actual mass of chlorine that must be fed per unit time.
dose_rate := C_dose·Q_flow=2e-04 kg/s
Results
A feed rate on the order of 200 mg/s (about 0.2 g/s, or roughly 17 kg/day) is a realistic dosing rate for a moderate-size supply at a 2 mg/L target dose. Because dose and flow both scale the feed rate linearly, any surge in plant flow requires a proportional increase in feed rate to hold the same residual concentration downstream.
Assumptions & limitations
- Instantaneous, complete mixing at the dose point assumed.
- Chlorine demand (consumption by organics/ammonia) not separately subtracted.
- Steady-state flow and dose; transient surges not modeled.