Apparatus and method for continuous froth flotation

A method for the treatment of raw water by use of an apparatus for the continuous flotation and separation of froth comprising

• 1. a vertically elongate column,
• 2. a plurality of shelves vertically spaced in said column and dividing the interior of said column into a plurality of vertically offset zones,
• a. said shelves each defining a plurality of unobstructed passages, each passage consisting of an upper part of fixed width and a lower part contiguous with said upper part, flaring outwardly and defined by faces inclined by an angle of at least 3.degree. with reference to the horizontal, the passages constituting the only interconnection between two of the offset zones adjacent each shelf,
• b. respective ones of said unobstructed passages in the plurality of shelves being vertically aligned to define continuous vertical spaces extending from a head portion to the bottom of the interior of the column, and
• c. the total area occupied by said unobstructed passages in each of said shelves being no less than 3 percent and no more than 30 percent of the total cross-sectional area of the column,
• 3. a froth separator disposed in the head portion of the column,
• 4. a raw water inlet pipe opening on an upper one of the zones,
• 5. a treated water outlet pipe disposed at the bottom of the column, and
• 6. a gas dispersing unit disposed below a lowermost one of said shelves,
• which method comprises the steps of continuously introducing the raw water subjected to treatment into said vertically elongate column through the raw water inlet pipe and continuously feeding air under pressure into said column through the gas dispersing unit, whereby the raw water continuously descending through the unobstructed passages in the successively lower shelves and the air continuously ascending in the form of bubbles through the unobstructed passages in the successively higher shelves come into countercurrent contact with each other so that substances contained in the raw water are now deposited on or adsorbed on said bubbles, and the bubbles on which the substancees formerly contained in the raw water are now deposited or adsorbed are discharged to the froth separator and the water which has been stripped of said substances is discharged through the treated water outlet pipe.