Gas Transfer

Gas Transfer  Some important examples of gas transfer in water

and wastewater treatment. 1. Oxygen transfer to biological processes. 2. Stripping of volatile toxic organics (solvents). 3. CO2 exchange as it relates to pH control. 4. Ammonia removal by stripping. 5. Odor removal –  removal –  volatile  volatile sulfur compounds 6. Chlorination, ozonation for disinfection and odor control. soluble in  in water and The materials of interest are soluble volatile volatile (i.e.  (i.e. they exert a significant vapor pressure).

Equilibrium and Solubility: 

For such materials there is an equilibrium equilibriu m established  between the liquid phase phase and  and the gaseous phase phase if  if there is enough time allowed and if the environmental conditions are held constant. This equilibrium is usually modeled, for dilute solutions, as Henry's Law. There are various forms of Henry's law as shown in the table below. below. In general saturation satu ration goes up as T goes down and as TDS goes down.

Form of equation

H

Liquid  phase conc.

Gas  phase

mol/m3

atm

unitless

mol/m3

mol/m3

atm

mol/mol

atm

atm m3

P  HC

Cg



Hc Cl 

P  Ha  X

conc.

moll mo

Some typical “H” values:  values:  gas

Ha

O2

4 x104

He CH4

12 x104  3.76 x104  4

CO2 H2S

0.14 x10   4.83 x104 

Volatile

Hc

H

Carbon tetrachloride

1.24

0.0304

Chloroform

0.15

0.00367

Vinyl chloride

1.14

0.0278

compound