Water Treatment "Part 7": Treatment of aggressive water.

One of the advantages of groundwater is that most of the time it is drinkable even without treatment, and at other times it only needs simple and inexpensive treatment. However, the process of extracting this water must be subject to specific proportions, so that the extraction process does not harm the environment and agriculture in the surrounding area; this is what makes some countries, such as the Netherlands, seek to limit the extraction of groundwater and replace it with surface water, although the cost of treatment is higher.

According to the source and the way it reaches the surface, groundwater is classified, and according to this classification, the treatment method is determined to obtain potable water.

Aquifer water:

The water of the aquifer is connected to the atmosphere, and therefore oxygen is not lost when the organic matter is limited in the soil, which makes the dissolution of iron from the soil not possible.
The majority of the essential standards are met by the water from the aquifer, but some treatment is typically necessary to change the pH, saturation index, bicarbonate, and calcium levels.

Station for complex water treatment SKO-10K

When the element calcium is missing in the ground, the value of the saturation index becomes less than zero and the concentration of carbon dioxide in the water rises. In this case, for the purpose of making this water's distribution achievable, the value of the saturation index must be raised. This type is called corrosive water and it is very aggressive on limestone.

Increasing the value of the PH is necessary to treat this type of water to make it less acidic, and for this purpose, the method of aeration/ gas transfer, limestone filtration, or the addition of small doses of an alkaline solution is used. The last method is used only as a final correction for the pH, where the concentration of carbon dioxide must be completely identical to the concentration of the dose. This process leads to the conversion of carbon dioxide into bicarbonate according to the following equation:

NaOH + CO2 ==== HCO(3-) + Na(+)

Precipitation of calcium carbonate occurs in the event that the dose is in excess of what is required, but in the case of a decrease in the dose, the water remains acidic.

Corrosive water is forced through calcium carbonate granules at the filter's bottom during the limestone filtering process, this causes the granules to slowly disintegrate and reduce in size before being eliminated by backwashing. During this process, aggressive carbon dioxide gas is removed according to the following equation:

CaCO3+ CO2+ H2O ====== Ca(HCO3)2

With a height of 2 meters and a saturation index of -0,3, the filter's bottom is employed. However, if iron, manganese, and ammonium are to be removed, a filter bottom with a height of more than two meters is necessary.

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.