Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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BACKGROUND OF THE INVENTION
2 1. Field of the Invention
3 This application relates to systems and methods for clarifying liquids,
4 especially water. More particularly, it concerns such systems and methods
wherein a liquid stream is passed first upwardly through a non-fluidized,
6 non-buoyant filter media and then sequentially passing the partially clarified
7 liquid downward through a second filter media.
8 2. D~.,,i~lion of the PriorArt
g Although conventional sand filters are relatively inexpensive and
effective in removing solid i~ u-ilies from liquids, their capacity for solids
11 retention is limited. Thus, the actual size of the pore spaces between the12 sand grains must be small to ~r~vent passage of objectionable solids into the
effluent and this limits the capacity of sand filters for storing solids.
4 Accordingly, conventional clarifying systems using such filters have included
sedimentation devices to protect the sand filters from rapid clogging by
16 removing the bulk of the solids from the liquid being treated before being7 passed to the sand filter (see U.S. 4,051,039).
8 Instead of sedimentation devices, two stage filter systems have been
19 developed. One class of the two stage systems uses upflow contact filtration
in the both the first stage and the second stage (see U.S. 3,623,978). A
21 second class of the two stage systems uses upflow contact filtration in the
22 first stage and downflow contact filtration in the second stage. (see U.S.23 4,547,286 and 4,793,934).
24 Difficulties have been encountered in the two stage filter systems that
have limited their utility, namely, difficulty in stabilizing the upflow filter to
26 achieve the required water quality and in plevelltillg breakthrough of
27 collected solids. Expensive components such as media screens, grids and
28 buoyant media have been employed in attempts to stabilize the upflow
29 operation. The present invention provides i~ lovenlents in such second
class of two stage filter systems without need to utilize such expensive
31 components.
32 OBJECI`S
33 A principal object of the invention is the provision of iml~lov~d
34 systems and methods for clarifying liquids, especially water.
Another object is the provision of improved two stage filter systems
36 of the upflow/downflow class that exhibit stabilized upflow and lack of
37 breakthrough of collected solids in the first stage.
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Other objects and further scope of applicability of the present
2 invention will become apparent from the detailed descriptions given herein;
3 it should be understood, however, that the detailed descriptions, while
4 indicating ~refel,ed embodiments of the invention, are given by way of
illustration only, since various changes and modifications within the spirit
6 and scope of the invention will become apparent from such descriptions.
7 SUMMARY OF THE INVENTION
8 The objects are accomplished, in part, in accordance with the
g invention by the provision, in a system for clarifying liquids, especially water,
0 coll~ ing a first chamber con~ail~ g first particulate filter media consisting
of solid particles with a density of between 3.5 and 4.4 and a size between 1.5
12 and 4 mm. and a second chamber containing second particulate filter media,13 the first chamber having an inlet to admit a liquid stream to pass upwardly
4 through such first filter media and then sequentially pass downward through
the second filter media. The system further colllplises backwash means in
16 both the first and second chambers to purge accumulated solids from the
7 filter media contained therein. Advantageously, the second filter media
8 chamber contains solid particles having densities of between 1.5 and 4.0 and
19 a size of between 0.3 and 1.5 mm.
The objects are further accomplished by the provision of a method
21 for clarifying a liquid colllprising p~ing influent liquid upwardly in a first
2 2 zone through first particulate filter media consisting of solid particles with a
2 3 density of between 3.5 and 4.4 and a size between 1.5 and 4 mm and then
24 sequentially passing the effluent from the first zone downward in a second2 5 zone through second particulate filter media.
2 6 In some embodiments, the first filter media is capped by a quantity of
2 7 particulate filter media of density less than 3.5 and/or size less than 1.5 mm.
2 8 In such embodiments, the lighter or smaller media does not become
2 9 unstable as the bulk of removed solids are collected in the lower, first media
3 o layer.
31 The use of coarse, dense filter media in accordance with the
32 invention has been discovered to remain stable even under high upflow
3 3 rates, i.e., 10 - 15 gpm/sq. ft. and to be capable of being purged of collected
3 4 solids by being fluidized by simultaneous flow of backwash liquid and air or
equivalent gas upwardly therethrough during a flush mode or backwash
3 6 mode.
3 7 Filter systems in accordance with the invention have several
noteworthy advantages as compared with prior two stage filter systems.
2 Thus, they are compact, with the application rate of the upflow clarification
3 first stage exceeding prior clarification rates by a factor of four.
4 Also, these new systems produce effluents with exceptional clarity
because the second stage polishing stage, while having very small pores, is
6 not subject to rapid plugging because the upflow first stage removes all large
7 particles.
8 Further, the new systems are reliable because they do not rely on
g screens, grids or like retaining devices which are subject to plugging.
Finally, the new systems are economical to construct and operate by
11 reason of their compactness, simplicity and lack of expensive retainer
12 components.
13 BRIEF DESCRIPTION OF THE DRAWINGS
14 A more complete understanding of the invention can be obtained by
1 s rererence to the accompanying drawings in which:
16 FIG. 1 is a lateral, sectional, diagr~mm~tic view of a two stage
17 filtration system in accordance with the invention operating in a filtering18 mode.
19 FIG. 2 is a lateral, sectional, diagr~mm~tic view of a two stage
filtration system of FIG. 1 operating in a first stage flush mode.
21 FIG. 3 is a lateral, sectional, diagr~mmz~tic view of a two stage
22 filtration system of FIG. 1 operating in a two stage backwash mode.
23 DESCRIPTION OF THE PREFERRED EMBODIMENTS
24 With reference in detail to the drawings, a filter system 2 of the
invention for clarifying liquids COlllpliscs a first chamber 4 having an
26 influent inlet 6 equipped with valve 8 and a second chamber 10 with
27 underdrain 12 connected to filter effluent line 14 containing valve 16 and
2 8 backwash inlet line 18 containing valve 20.
29 The first chamber 4 contains first particulate filter media 22 consist-
ing of solid particles with a density of between 3.5 and 4.4 and a size between
31 l.S and 4 mm. Also, the second chamber 10 contains second particulate
32 filter media 24 in the form of solid particles having densities of between 1.5
33 and 4.0 and a size of between 0.3 and 1.5 mm.
34 The system 2 has backwash means 24 in first chamber 4 to purge
accumulated solids from the filter media 22 coll.plising line 28, valve 30 and
36 ported underlay 32. It also includes waste removal means 34 comprising
37 tank 36, outlet line 38 and weir 40. The backwash means for chamber 10
comprises the underdrain 12, line 18 and valve 20.
2 In the filtration mode as shown in FIG. 1, valves 8 and 16 are open
3 and valves 20 and 30 are closed. Influent from line 6 enters chamber 4, flows
4 upward through packed filter media 22, typically at a rate of about 10 gals.
per minute per square foot cross-section of the packed filter media 22. It
6 then flows over the top of wall 42 into chamber 10, downward through filter
7 media 24 into underdrain 12 to exit via valve 16 and line 14. The water level
8 during the filtration mode is indicated by the wave line 44.
g In the chamber 4 flush mode as shown in FIG. 2, valves 8 and 30 are
open and valves 16 and 20 are closed. Influent via line 6 enters chamber 4,
flows upward through filter media 22 and over the weir 40 into tank 36 to
2 exit via line 38. At the same time, compressed air enters the chamber 4 via
13 line 28 and underlay 32 to cause filter media 22 to fluidize and thereby assist
14 in purging media 22 of accumulated solid material. The water level during the flush mode is indicated by the wave line 44a.
16 In the backwash mode as shown in FIG. 3, valves 8, 20 and 30 are
17 open and valve 16 is closed. Liquid flow in chamber 4 duplicates the flow of
18 the flush mode as explained above. Liquid flow in chamber 10 is from line19 18 through underdrain 12 upward through filter media 24 and over the top
2 o edge 46 of chamber 10 into a launder (not shown) for discharge to waste or
2 1 the like as indicated by the arrows. The water level during the backwash
22 mode is indicated by the wave line 44b. During the backwash mode, the
2 3 upward flow of liquid in chamber 10 serves to fluidize the filter media 24 to
2 4 assist in purging of accumulated solid particles therefrom.
