Properties
- normally a gas - 100% available chlorine
- heavier than air
- is a hazardous gas
Sources of chlorine other than gas
- Sodium hypochlorite (NaOCl) (liquid - % available chlorine can vary)
- -ve shipping costs (mostly water)
- -ve pH is elevated
- +ve very safe to handle and store
- +ve excellent for chlorinating mains and reservoirs
- -ve loses strength with time and temperature
- 1% NaOCl = 10,000 mg/L as available chlorine
- 5% (Javex) = 50,000 mg/L as available chlorine
- 10% (commercial grade) = 100,000 mg/L as available chlorine
- 1 L of 10% = contains .10 Kg of available chlorine
Calcium hypochlorite Ca(OCl)2
- +ve shipping costs less than NaOCl
- -ve % of inert material
- +ve storage can be hazardous
fire gives off chlorine gas
reacts with organic material and becomes flammable
Method of Disinfection with chlorine
- inactivates key cell enzymes
Critical factors for disinfection by chlorine
- injection point - mixing with water
- contact time
- turbidity
- temperature
- type of residual
- pH
Chlorine residual = chlorine dos - chlorine demand
Total chlorine residual (mg/L) = free chlorine(mg/L) + combined chlorine(mg/L)
Breakpoint chlorination curve
Chlorine + water -> hypochlorous acid + hydrochloric acid
Cl2 + H2O -> HOCl + HCl (1) (lowers pH)
Hypochlorous acid <- -> hypochlorite ion + hydrogen ion
HOCl <- -> OCl- + H+ (2) (pH dependent)
Breakpoint phenomenon
- NH3 + HOCl -> NH2Cl monochloramine (3)
- NH2Cl + HOCl -> NHCl2 dichloramine (4)
- NHCl2 + HOCl -> NCl3 nitrogen trichloride (5)
