AERATION

B. Marangoly, Term Project, December 1994

(in Italian)

Water aerated naturally by flowing over sandy or pebbly beds or rocky falls has been acclaimed by writers of all ages and countries. Only a few of these enthusiasts realized that the waters they so highly praised were clear, bright, sparkling, tasteless and odorless when they reached the streams. In the eighteenth century, artificial aeration was directed at making up the oxygen deficiencies of distilled water and of rain water that had been stored up in household cisterns. Toward the end of the eighteenth century and early into the next century, aeration was applied to a few public water supplies carrying decomposed vegetatble or animal matter. Not until the last half of the nineteenth century did aeration become a marked feature of municipal supplies. Even then, the number of applications was small and pertained chiefly to stored surface waters subject to tastes and odors from algae growths. In this period, aeration was applied here and there, generallly to ground waters, for the removal of iron, and then of maganese, and also to eliminate malodorous gases from sulfur bearing ground waters.


Aeration in History Around the World

Obsessed by the notion that removal of organic matter was the chief end and aim of aeration, many inventors and promoters centered their energies there. Until near the close of the nineteenth century, confidence in the self purification of rivers continued widespread. After two thousand years of recognition of the good effects on water from natural aeration, experiments on artificial aeration were reported. The first of these that has been found was in a paper on blowing showers of air through water being distilled, read by Dr. Stephen Hales on December 18, 1755. 
  • Dr.Hales
  • Montbruel and Ferrand's Project
  • Quai des Celestins, Paris
  • Britain
  • Scotland
  • Russia 
  • Aeration in America

  • Elmira, N.Y. Water Works Company (1861)
  • Lawrence, Massachusetts (1875)
  • Utica, N.Y. Water Works Company (1890)
  • Hyatt Patent
  • Leeds Patent
  • Winchester Kentucky (1900)
  • South Norwalk, Connecticut (1940) 
  • Early Apparatus Used for Aeration

  • Aer-O-Mix 
  • Methods of Aeration

    From the examples of various aeration plants provided above, we can conclude that there are several different ways in which aeration can proceed. By causing the water to flow by gravity down an arrangement of steps, thus splashing and breaking up into films and drops; by causing it to flow downward through a vertically aranged series of trays containing beds of coke or gravel, it being pumped to the utmost tray; by throwing it into the air in a spray; and by blowing or drawing air bubbles through it, is some of the ways to bring the water into contact with the air. Pumping by air lift also has a partial aerating effect. 

    Mechanical Equipment Used in Aeration

    After discussing several accomplishments in the history of aeration, we can address the topic of present day mechanical equipment for aeration. It can be classified, for convenience into two basic categories, the diffusion type and the waterfall type. In the choice between waterfall and diffusion types of aerator units, theory strongly favors the latter. A diffusion unit wherein finely divided air bubbles are introduced over the bottom of a basin through which water is flowing, provides most adequately for all the factors that control the efficiency of aeration. Some authorities feel that the principal advantage arises from the fact that the velocity of bubbles ascending through the water is much lower than the velocity of free falling drops of water, thus affording a longer period of contact for an equal expenditure of energy. 
  • Air Diffusion Type
  • Waterfall Type
  • Spray Nozzle
  • Air Lift 
  • Uses of Aeration

  • Iron Removal
  • Organics Removal
  • Volatiles Organic Compounds Removal 
  • Concluding Statements on Aeration

    Aeration by spraying into the air takes too much energy. Other methods call for jets, pans showers through small, closely spaced perforations, coke trays and compressed air admitted to the water at the bottom of the basins. In no case reported is high pressure air used nor is there a single instance of compressed air admitted to a main tank.

    We thus conclude our study of aeration. Outlined above is the theory, history and practice behind this intimate mixing of air and water. As Theophrastus , an early Greek philosopher once explained, "running waters are generally better than standing water, and when aerated are still softer, or less harsh."


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