GB1294880A - - Google Patents

Abstract

1294880 Filters; dual granular-bed type GULF DEGREMONT Inc 17 Nov 1969 [10 March 1969] 56155/69 Heading B1D Liquid-to-be-filtered such as raw water, supplied through pipe 28, flows up pipe 26 to space 40 in the top of a filter-container whence the water flows downwardly through a bed of coarse-granular material 20 (e.g. gravel) resting on support 12 which has a plurality of nozzles 14 extending into intermediate space 38; the prefiltered water reaching space 38 is further treated in a bed of finegranular material 22 (e.g. sand) resting on support 16 which has nozzles 18. About half the flow of prefiltered water passes through pipe 54 to lower space 36 and then flows upwardly through the lower part 22b of bed 22 to outlet header 24. The remainder of the prefiltered water flows downwardly through the upper part 22a of bed 22 to outlet header 24. When the filter beds require backwashing, backwash water and air are introduced through pipes 42 and 46, respectively. The air and water collects in spaces 36 and 38 where separation occurs so that air occupies a layer of about 4" below each support 12 and 16. Nozzles 18 and 14 have slots, and air passes through the slots and becomes mixed with water flowing upward through the open bottom of the nozzles. Thus a mixture of air and water flows through bed 22 and then through bed 20. Some of the air flows directly from space 36 to space 38 through orifices 70, 72 in pipes 68. Dirty water and air reach space 40, and are discharged through pipes 26 and 32. After about 6 minutes, air-valve 48 is closed, and the beds are rinsed with water alone for 8 to 10 minutes. The filtration operation is then resumed. A plurality of filters can be operated under pressure in parallel, and the filtered water of one unit can be redirected to provide wash-rinse water for the unit being cleaned. Also described is a horizontal type filter wherein a gravel bed and a sand bed are located side-by-side (Fig. 3, not shown) there being a space between the two beds through which the prefiltered water from below the gravel bed flows upwardly to the top of the sand bed. The liquid flows in the reverse direction during backwashing. The invention is applicable to raw surface water, and to industrial wastes such as those from a steel mill scale pit, and to the tertiary treatment of sewage.