Question

Q2.

Chlorine gas is the main disinfectant used at a particular WWTP for pathogen removal. A spill has occurred within the plant that is some 15 ft below ground level.

a)What symptoms would you expect persons in close proximity to the plant to experience?

b)What safety precautions would you recommend in the event of a chlorine gas leak given it’s properties?

c)Explain the concept of breakpoint chlorination paying close attention to free and combined residuals at each stage of the process? (Chemical Equations are needed.)

Answer 1

A)

Symptoms:-

Excessive coughing

There will be difficulty in breathing or shortness of breathe

Eyes will be watery

Vomiting

burning sensation will be there in nose, throats and eyes.

B)

Properties of chlorine:-

Chlorine is heavier than air, Chlorine reacts with moisture in air to form HCl, Chlorine has a pungent smell and it is soluble in water

Precautions in an event of chlorine leak:

In case of chlorine gas leak, reach to the highest possible level from the ground as chlorine is heavier than air it will sink to lower level.

Immediately wash the body with soap and water.

eyes should be rinsed for around 10 minutes with plain water

Victime should be moved to a place where plenty of fresh air is available

Chlorine gas should be mitigated using water sprays.

Use available breathing apparatus

C)

Breakpoint chlorination

It is point beyond which the chlorine addition is unfruitful that means the disinfection demand is met or we can say all the undesirable componenets are oxidized and no further addition of chlorine is required.

Free Residual:-

It is a residual chlorine present in the water in form of hypochlorous acid ( HOCL ), or as dissolved Cl2 gas, or as a hypochlorite ion.

Cl₂ + H₂O = HOCL + HCl

HOCL = OCl^- + H⁺

Combined Residual.

It is a chlorine present in the water in combination with ammonia or amines which can be present in a polluted water.

NH₃ + HOCL = H₂O + NH₂CL

NH₃ + 2HOCL = 2H₂O + NHCl₂

NH₃ + 3HOCL = 3H₂O + NCl₃

This is a Breakpoint Chlorination curve with combined and free residual mentioned on the curve.