1d0 NEW WATER SUPPLY SYSTEM AT TAMPA, FLORIDA.

 different waters, together with all intermediate gradations, are met with
 at Tampa. This requires what amounts practically to two treatment
 plants in one.
 Decolorizing. The most important treatment is that for color re-
 moval. Aluminum sulphate and sulphurous acid are used to accomplish
 this. Heretofore' aluminum sulphate alone generally has been used for the
 purpose. However, this chemical is expensive and when color, ranging
 from 100 to 200 parts per million is to be combated, the cost is almost pro-
 hibitive. By the addition of sulphurous acid, the alkalinity may be.neu-
 tralized and the hydrogen ion concentration raised to a point where the
 most complete precipitation of the aluminum sulphate as aluminum hy-
 droxide takes place. As a result, a much smaller amount of aluminum
 sulphate is required for the complete removal of color than when aluminum
 sulphate is used alone. Lime or, soda ash, added after filtration, again
 lowers the hydrogen ion concentration and cuts down the amount of free
 carbon dioxide in the water to a point where the water can be distributed
 safely without danger of corroding the distribution system.
 Softening. During a portion of the year softening is required in
 addition to the decolorizing treatment. The flexibility provided in the
 design of the sedimentation basins makes it possible to change readily from
 a decolorizing to a decolorizing-and-softening plant. By the use f hy-
 drated lime the carbonate hardness is thrown down. If, in addition, the
 .water has a sulphate hardness, soda ash is added to reduce it. The water
 then passes to decolorizing tanks and basins where aluminum sulph4te is
 added. The aluminum sulphate lowers the causticity due to the addition
 of the lime, and removes the color. The water then passes to a carbonkting
 chamber. i
 Recarbonization. It is believed that in recarbonization has been found
 the solution of one of the most perplexing problems in modem water puri-
 fication. The demand for soft water has reached such proportions that
 it cannot be ignored by those responsible for the design of present-day
 purification systems. This has been recognized in the Tampa plant where,
 by the introduction of recarbonization, the evils of the usual softening plant
 have been avoided. Recarbonization eliminates the reprecipitatioh of
 calcium carbonate in filter underdrains, distribution system and meters and
 the so-called sand growth, and gives a more palatable water. The amount
 of carbon dioxide introduced can be regulated accurately by the chemist
 in charge, so that the water, as delivered to the consumer, has the pfede- |
 termined content necessary to give the most satisfactory water.
 Pumping Plant. The pumping plant, of 25 million gal. instilled
capacity, consists of an intake and a steam-pumping station containing a
boiler room and two-level pump room.
 Intake Works. A concrete intake chamber, 31 ft. in height was pl ced
in the center of the river channel, in approximately 25 ft. of water. It has
three openings controlled by 48-in. sluice gates, and protected by $.in.