Issue 12 and Volume 32.

WHEN SAND FILTRATION IS IMPOSSIBLE. In purifying water by sand filtration much depends upon the amount and nature of the matter held in suspension, as to the kind of treatment that will be successful in purification. If there is a large amount of very fine matter in suspension, a sand filtering apparatus will not do. Some of this suspended matter is smaller than bacteria. Now the presence of this matter will make it impossible, or at least very difficult, to purify by the sand filtration method. The matter will soon cover the sand in the filter beds and make it of no use until the beds are covered and cleaned. The cleaning will have to be done very frequently, and it is a costly process in both time and money. In all such cases mechanical filtration should be used instead. Over in eastern Ohio not long ago a city went…

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