Wednesday, June 22, 2011

Water aerated naturally by flowing over sandy or pebbly beds

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. Towards the end of the eighteenth century and early into the next century, aeration was applied to a few public water supplies carrying decomposed vegetable 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, generally to ground waters, for the removal of iron, and then of manganese, and also to eliminate malodorous gases from sulphur bearing ground waters.


As suggested, the basic purpose of aeration is the improvement of the physical and chemical characteristics of waters for public supply. Primarily, this improvement involves the reduction of objectionable tastes and odors, but some additional benefits of aeration, as a preliminary step to other purification processes have also been noted.
In the cool stagnant bottoms of lakes and reservoirs during late summer and late winter, in deep wells and in the dry-weather flow of some sluggish rivers are found natural waters which are so deficient in oxygen that they are objectionable in both taste and odor. Aeration of such waters improves their tastes by supplying the deficient oxygen, rescuing the free carbon dioxide and eliminating much of the hydrogen sulphide and other odorous constituents present. Removal of iron and manganese from such oxygen deficient waters also usually requires aeration as an initial step. This initial step allows for the lower oxides of these minerals that are dissolved in the water and combined with carbon dioxide to be converted to higher insoluble oxides and in turn removed by subsequent sedimentation, contact or filtration.
is the process by which air is circulated through, mixed with or dissolved in a liquid or substance. In its broadest sense, aeration is the process by which the area of contact between water and air is increased, either by natural methods or by mechanical devices. Ordinary usage in water works practice has however, been given the term in the more limited sense referring specifically to use of mechanical devices or procedures. In this limited sense aeration clearly defines itself as a method of treatment rather than merely a modification of natural conditions at the source of supply. The terms ‘natural aeration’ or ‘reaeration’ are used to represent non-mechanical procedures or slower aeration of large bodies of water under natural conditions. In the progress of water from source to consumer, aeration is one of the most elemental techniques frequently employed in the improvement of the physical and chemical characteristics of water.