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Alkalinity Lowered by Filtration

Issue 16 and Volume 64.

Alkalinity Lowered by Filtration According to Charles P. Hoover, chemist in charge of the filtration plant of the Columbus, Ohio, water department, the alkalinity or temporary hardness of softened settled water is lowered by filtration through sand; therefore filtration is necessary as a final or finishing step in the softening process. A possible explanation of this reduction of hardness by filtration is that the lime and soda ash combine with the magnesium and form a colloidal precipitate of basic carbonate of magnesium, which is removed or retained by the filters. Although the removal of this colloidal material from the water by retaining it on the sand beds results in filter difficulties, it is advisable to remove it before the water is pumped into the distribution system, because if it were not removed by the filters it would very probably be deposited on the walls of the distribution system and in…

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