Chlorine Residual

Question 1

Residual Chlorine

Answer 1

The amount of active chlorine left in water after the demand has been satisfied

Question 2

Disinfection

Answer 2

Killing pathogens such as bacteria, viruses, and parasites

Question 3

What three reactions take place when chlorine is applied to wastewater?

Answer 3

1. Chlorine reacts with substances and is neutralized (Chlorine demand)
2. Chlorine reacts with ammonia to form chloramines (combined residual)
3. Chlorine reacts with water to form hypochlorite/hypochlorous acid. (Free residual)

Question 4

Total residual

Answer 4

A measure of the chloramines and the hypochlorite ions/hypochlorous acid

Question 5

Free residual

Answer 5

Measure of just the hypochlorite ion and hypochlorous acid

Question 6

Methods of disinfection

Answer 6

Chlorination
Ozone
UV
Hydrogen peroxide
Paracetic acid

Question 7

Sodium Hypochlorite, NaOCl

Answer 7

Liquid form of chlorine

Household at 8% concentration, industrial 12-15%

Question 8

Calcium Hypochlorite, Ca(OCl)2

Answer 8

Solid form of chlorine
Stored dry
Strong oxidant

Question 9

Are chloramines still disinfecting?

Answer 9

Yes, much weaker than hypochlorous acid and hypochlorite. Mono and Di will still perform some disinfection.

Question 10

When are chloramines formed?

Answer 10

When chlorine reacts with ammonia/nitrogen containing compounds

Question 11

DPD Chlorine Residual Test Procedure

Answer 11

1) Place 5 mL of buffer reagent and 5 mL of DPD reagent into a 250 mL Erlenmeyer flask
2) Add 100mL of sample and mix.
3) Add 1g potassium iodide. Allow to stand for 2 minutes.
4) Titrate with standard ferrous ammonium sulfate until the red color is discharged to colorless
5) If standard procedures are used, the amount of FAS used is the total chlorine residual