GB754544A - Apparatus and method for purification of liquids - Google Patents

Abstract

754,544. Filters; gravity-separation apparatus; purifying liquids; softening and imparting special properties to water. DORR-OLIVER, Inc., [formerly DORR CO.]. Feb. 22, 1954, No. 5103/54. Class 46. Liquid, for example water for domestic or industrial purposes, to which treatment chemicals, for example lime for softening, may have been added, is introduced through a valve V and a pipe 13, Fig. 1, into hollow rotating arms 18 carrying a cylindrical baffle 27; the water emerges from openings 30 in the parts of the arms outside the baffle 27 into a "sludgeblanket" treatment f section T bounded on the outside by a partition wall 15. The top of the blanket lies just above the upper edge of the baffle 27, and chemicals to aid flocculation and the like may be fed into the blanket from feed boxes supported by the tank superstructure. Rotation of the blanket by movement of the arms 18 is prevented by radial baffles 27a. Heavier flocs settling on the base of the tank are moved by scrapers 32 towards an annular slot formed by the outside of the cylindrical baffle 27 and the inside of the wall of a sump 14 in which collected solids are thickened by rotary members 33 depending from arms 18 and cylinder 27. Excess sludge from the blanket top also descends inside the cylinder 27 to the sump 14. Lighter flocs are conveyed by the supernatant liquid outwards to a filtration section F over the partition wall 15, maintained sufficiently submerged to ensure a low rate of flow thereover, and thus, in turn, no break-up of flocs. The level is maintained by a levelsensing device connected to the valve V and by adopting a suitable rate of filtration of the supernatant liquid. The latter is preferably maintained constant by a flow controller connected to the filtrate effluent valve 29a which progressively increases the filtrate flow as the sand filter bed 41 becomes progressively clogged. Prior to filtration, the pH of water which has been dosed with an excess of lime may be lowered by introduction of carbon dioxide through a perforate annular pipe 46. .Where the lime is not in excess the carbon dioxide is still added to render soluble, as bicarbonate, any calcium or magnesium carbonate present in the supersaturated state and liable to clog the filter bed. On cleaning of the filter bed becoming necessary the valve V is closed and a discharge valve 40 on a pipe 39 leading from an annular backwash-water channel G is opened. When the water level outside the partition 15 has fallen to that of the upper surface of the bed 41 the filtrate outlet valve 29a is closed. The level within the partition 15 falls to, and remains at, that of the top of the partition, the sludge discharge valve (not shown) on a pipe 33a being preferably closed. Wash water is now supplied through a valve 45 and pipe 44 and, after passing upwards through the bed 41, overflows the wall 37 forming the outside of the channel G and flows to waste through the still open valve 40. In Fig. 2 water is introduced through a valve W into a hollow rotary shaft 57 carrying scrapers 66a and emerges through openings 69 in the upper end of the shaft and openings 69a in the upper end of a surrounding rotary shaft 57a carrying arms 57b bearing upstanding paddles 57c interengaging with stationary paddles 57d. The paddles occupy a coagulating zone K defined by a cylindrical partition 70 supported from a bridge structure 59, and by an inwardly-extending annular shelf 71 at the lower end of the partition. Suspended solids are coagulated by the interaction of the paddles in the zone K and the mixture passes downwards through an opening I in the shelf 71 and radially outwards between the shelf and the tank bottom, heavier flocs settling and being scraped to a sump 53 by the scrapers 66a on the shaft 57 which rotates more slowly than the shaft 57a. Lighter solids are conveyed with the supernatant liquid over the partition 15 and the perforate pipe 81 into the filter, which is constructed as before. In each case, the pipe 81 may be used to introduce, instead of carbon dioxide, a chlorinating agent, or a thin slurry of activated carbon for taste or odour removal, or a suspension of lime. to raise the pH of the water.