Water Treatment "Part 8": Hard water treatment.

Aerial groundwater is often very hard due to biological processes in calcium-rich soils. For drinking water, the hardness value (concentration of magnesium and calcium ions) should not exceed 1.5 mmol/litter; to produce potable water, softening can be done by using alkaline solutions (caustic soda). The softening reactants contain small grains of sand that are used to crystallize the nuclei during the calcium carbonate precipitation process.

Surface Aerator

Aeration is frequently used as the first step in the treatment of water that lacks free oxygen, followed by filtering using immersed granular components. Since oxygen is used to convert iron(II) ions to iron(III) ions, aeration is required to add oxygen and remove carbon dioxide. The aeration procedure can involve blowing tiny air bubbles into the water or dispersing thin droplets of water via the air.

A 1 horsepower paddlewheel aereator used in a shrimp pond in Indonesia.
After the aeration process, the dissolved groundwater components are oxidized through a variety of biological and chemical reactions that occur during the groundwater filtration stage through submerged sand. The filters consist of a sand bottom that is one to two meters high and allows water to pass through. As a result of a reaction between oxidized iron and hydroxide ions, flocculants are produced during the filtration process Fe(OH)3-. Additionally, partial chemical and biological transformations occur in manganese.

Fine Bubble Aeration

Iron oxidation and hydrolysis progress at different rates depending on pH. When the pH is high, the process is faster. Therefore, the aeration method is applied, in which most of the carbon dioxide gas remains, in order to raise the pH when groundwater is treated with a low pH.

References:

• 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.