Water Treatment "Part 12": Expulsion of gases and aeration.

Aeration is usually among the first steps to treat groundwater for the purpose of producing drinking water, and it aims to add oxygen (O2) and remove methane (CH4), carbon dioxide, hydrogen sulfide (H2S), and other volatile organic compounds such as dichloropropene, trichloromethane, etc. Moreover, the oxidation of iron(II), manganese (Mn2+) and ammonium (NH4+), depends mainly on the addition of oxygen.

Due to the damage that can be caused by those gases that are removed during the aeration process, this process is classified as very important in water treatment. Recognizing that volatile organic chemicals are often harmful and some of them are cancer-causing, they shouldn't be found in drinking water. As for hydrogen sulfide, it smells bad. Furthermore, bacteria overgrow during the filtering process if methane is present in the water.

Fine Bubble Aeration

The water is separated into thin layers in a variety of aeration systems, including waterfalls and aeration towers. Additionally, there is the spray ventilation technique, which disperses water droplets into the air. And the air bubble technique, which uses compressor or deep well aerators to blow air bubbles into the water.

Henry's law:

​Based on Henry's law; in a closed vessel holding both gas and water, the concentration of volatile components in the gas phase will eventually converge on the concentration in the water phase. This is because water includes dissolved gases. The following application of Henry's law can be used to get the equilibrium concentration:

Cs= Kh. Cg

Cs: Gas equilibrium concentration in water (g/m³).
Kh: Henry's constant (distribution coefficient).
Cg: Gas concentration in the air (g/m³).

It should be noted that the equilibrium concentration is greatly affected by pollution and the presence of impurities in the water. As that, the type of gas and temperature affect distribution coefficient value, whereas, gases that dissolve easily in water have high distribution coefficient values, and vice versa.

References:

• Taparhudee, Wara (2002). "Applications of Paddle Wheel Aerators and Diffused-Air System in Closed Cycle Shrimp Farm System" (PDF). Witthayasan Kasetsart (Sakha Witthayasat). 36: 408–419. Retrieved 26 April 2020.
• Unsafe water kills more people than war, Ban says on World Day". UN News. 22 March 2010. Retrieved 10 May 2018
• Raymond Desjardins- Livre: Le traitement des eaux- 2éme edition- Ecole Polytechnique de Montréal- 1997- ISBN 2-553-00643-8
• Drinking Water Treatment- EDX- Delft University of Technology.
• Book- Drinking Water: Principles and Practices- by Hans J C Van Dijk (Author), Jasper Q J C Verberk (Author), Peter J De Moel.