Background
The present disclosure relates to media filtration systems and in particular embodiments, techniques for enhancing movement of influent through the media bed. Media filtration systems have become increasingly used in aquaculture, wastewater treatment, and other water treatment areas. In particular, air charged backwashing bioclarifiers employing floating media such as disclosed in U.S. Pat. No. 6,517,724 have proven to be a cost-effective system for treating water used in the above industries. However, the usefulness of such systems may be enhanced further with continued improvements, including enhancing movement of influent through the media bed.
SUMMARY OF SELECTED EMBODIMENTS
One embodiment is a floating media filter including a filter housing having an influent inlet and an effluent outlet. A floating media is positioned in the housing and forms a static media bed when the filter is in a filtration stage. A diffuser trough is positioned in the filter housing such that the lower surface of the media bed, when the filter is in the filtration stage, is below the upper edge of the diffuser trough. A backwashing mechanism causes dispersion of the media bed during the backwashing stage. Another embodiment is a method of directing influent through a floating media filter.
The floating media filter includes a filter housing having an influent inlet and an effluent outlet, floating media positioned in the filter housing, and a diffuser trough positioned in the filter housing. The method includes the steps of: (a) positioning a sufficient volume of floating media in the housing such that a media bed, formed when the filter is in a filtration stage, has a lower surface below an upper edge of the diffuser trough; (b) dispersing the media bed during a backwashing operation; and (c) continuing the filtration stage after the media bed has reformed with its lower surface below the upper edge of the diffuser trough.
Other embodiments are described or are apparent in the following disclosure and their omission from this Summary section should not be interpreted as a limitation on the scope of the present invention.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 illustrates a prior art media filter employing a double plate diffuser.
FIG. 2 illustrates a side sectional view of one floating media filter of the present invention.
FIG. 3 illustrates the FIG. 1 view rotated 90°.
FIG. 4 illustrates the media bed at a lower level during the backwashing stage.
FIG. 5 illustrates the filter refilling and the media bed rising during the backwashing stage.
FIG. 6 illustrates the media bed reforming at the end of the backwashing stage and in the early phase of the filtration stage.
FIG. 7 illustrates the media bed in a later phase of the filtration stage.
FIGS. 8a to 8f illustrate alternative diffuser trough configurations.
FIG. 9 illustrates a modified diffuser trough arrangement.
FIG. 10 illustrates a pipe based diffuser trough arrangement.
FIG. 11 illustrates a diffuser trough in an “hour-glass” type floating media filter.
FIG. 12 illustrates multiple diffuser troughs in a “propeller-wash” type floating media filter.
FIG. 13 illustrates a peripheral diffuser trough arrangement.
DETAILED DESCRIPTION OF SELECTED EMBODIMENTS
FIG. 1 shows a prior art floating media filter 1 which is generally formed of a filter housing 2 having an influent inlet 10, an effluent outlet 11, a volume constituting a filter chamber 3, and a volume constituting a drop zone 9. A mass of floating media pellets or “beads” 14 form a floating media bed 12 in the space defining filter chamber 3. In many embodiments, a screen 8 is positioned below effluent outlet 11 to prevent beads 14 from moving with the effluent out of filter chamber 3 and escaping through outlet 11.
As is well known in the art, the general operational principle of floating media filters is to introduce influent beneath the media bed and allow the influent to pass upward through the media bed 12 to the outlet 11. The FIG. 1 example includes an inlet extension pipe 36 which carries influent to a double plate diffuser 65 positioned below a lower surface 13 of media bed 12. The double plate diffuser 65 will introduce influent in a 360° radial pattern below media bed 12. Typically, this introduction of influent will create various eddy currents 66 beneath media bed 12 and into drop zone 9. Often the eddy currents 66 have the undesirable effect of keeping small solids, which would settle in more quiescent conditions, entrained in the drop zone 9. These entrained solids form a volume of “cloudy” water which tends to co-mingle with influent water under media bed 12.
After influent is introduced below the media bed 12, it will begin moving in a path through media bed 12. While passing through the media bed, the influent is subject to both physical solids filtration and biological treatment from micro-organisms adhering to the beads 14. During treatment, biological growth forms a film on and between the beads in media bed 12. Suspended solids being strained by media bed 12, as well as biomass, form a “floc” on the beads. During the filtration stage, the floc will over a period of time, tend to bridge from bead to bead, requiring periodic agitation of the media bed 12 (referred to as “dispersion” or “”fluidization“) to loosen floc and other solids for removal from the media bed. Such fluidization is achieved during a backwashing stage of operation using one of many different types of backwashing mechanisms.
FIG. 1 illustrates a filter with one backwashing mechanism 15. The backwashing mechanism of the FIG. 1 example is an air-washed, dropping bed mechanism described in U.S. Pat. No. 6,517,724, which is incorporated by reference herein in its entirety. In this backwashing mechanism, air accumulates in charge chamber 4 by the slow injection of air through air inlet 6. At some point, the air in charge chamber 4 will reach the bottom of siphon 5, which will then be “triggered” and rapidly release air into the filter chamber 3. As air leaves charge chamber 4, water in drop zone 9 fills the charge chamber, causing media bed 12 to “drop” into the area of drop zone 9 while air is bubbling through the beads, thereby dispersing or fluidizing the media bed and dislodging accumulated floc. Thereafter, as influent replaces the water which has moved into charge chamber 4, the beads will rise back into filter chamber 3, as limited by screen 8, and reform the media bed 12.
One undesirable effect observed in many prior art filters relates to the movement of the cloud of entrained solids mentioned above during the backwashing stage. At the beginning of the backwashing stage, the dropping media bed creates the cloudy volume as both the beads and released solids move downward together. At the end of the backwash stage, the beads float upward reforming the media bed. As the bed moves upward toward the screen, the influent waters move downward filling the voids left by the rising beads. The volume of cloudy water remains in drop zone. Thus, at the end of each backwash cycle, the now static bead bed is underlain by an observable volume of “dirty” appearing water. The relatively clean water now continues to enter the upper reaches of drop zone through the diffuser placed just below the media bed. The influent waters then mix with dirty waters in the upper reaches of the drop zone prior to entering the bed, creating a dirty “burp” of cloudy water as the fine solids capture abilities of the media bed are overwhelmed. The finer solids escape the bed creating a noticeably “dirty burp.” With a well-designed double plate diffuser the cloudiness in the effluent passes in less than a minute as the fine solids in the upper portion of the drop zone are diluted by the co-mingling influent waters. Although these short “burps” of “dirty” water are typically not significant from the standpoint of overall water quality performance in many applications, such as ornamental pond and aquaculture, they are considered very undesirable aesthetically. Additionally, the “dirty burp” phenomenon prevents expansion of these filtration technologies into many applications requiring a consistently pristine effluent, such as swimming pools, subsurface micro-irrigation and drinking water treatment applications.
When media bed 12 has fully reformed against screen 8 and influent is flowing through the media bed, this may be referred to as the filtration stage or sometimes, the “steady-state” filtration stage. While some filtration effect may occur shortly prior to the media bed completely reforming, the “filtration stage” for purposes of this description begins when the media bed becomes substantially stationary against screen 8 in filter chamber 3. The filtration stage terminates when the backwash cycle begins. As referenced above, in the filtration stage, the media bed 12 has a lower surface 13. It will be understood that lower surface 13 is not necessarily a perfectly flat and stationary surface, but may have small irregularities depending on how individual media beads “stack” as the media bed reforms after backwashing and how the lower beads may discretely shift due to currents and other factors occurring below the media bed. Nevertheless, the bottom area of the media bed 12 will form a reasonably well defined lower surface during the filtration stage.
FIGS. 2 and 3 illustrate one embodiment of the present invention. FIG. 2 shows a floating media filter 1 that generally operates as described in reference to FIG. 1. However, in the FIG. 2 embodiment, media filter 1 includes a diffusor trough 20 extending across the width of filter chamber 3. An inlet extension pipe 36 is positioned in diffuser trough 20 and, in this embodiment, is co-extensive with diffusor trough 20. FIG. 3 is a section view rotated 90° from FIG. 2 and better shows the shape and position of diffusor trough 20. In this embodiment, diffuser trough 20 is V-shaped with an upper edge 21, a midpoint 22, and a bottom edge 23. The inlet extension pipe 36 includes a series of apertures 38 which discharge influent against the inner surfaces of diffuser trough 20. In the FIGS. 2-3 embodiment, the lower surface 13 of media bed 12 (denoted schematically with a light dashed line in FIGS. 2 and 3) is at about the midpoint 22 of diffuser trough 20. Although FIG. 2 shows the diffuser trough 20 extending the entire width of filter housing 2, this is not necessary in all embodiments. The diffuser trough may extend less than the entire width of the filter housing. Likewise, many embodiments may not include influent extension pipe 36.
FIGS. 4-7 suggests the flow of influent in the filter during both the filtration stage and during backwash and bed reformation. These figures show a modified embodiment where the extension pipe 36 seen in FIGS. 2 and 3 has been removed. However, the influent flow characteristics described herein relative to the media bed are substantially the same with or without extension pipe 36.
FIG. 4 shows the media beads 14 well into the backwash cycle when the fluid level and the media beads have lowered into the drop chamber 9 below diffuser trough 20. At this point, influent flowing into the diffuser trough 20 quickly fills the trough and spills over onto the dispersed media beads 14. This downward flow of influent will further clean the media beads and tend to push floc particles 60 downward as the fluid level rises. FIG. 5 shows the rising level of the media beads 14 as inflowing influent continues to raise the fluid level in the filter and continues to produce downward flow currents urging floc particles 60 downward.
FIG. 6 shows the media bed 12 substantially reformed in an early filtration stage subsequent to backwashing. The illustrated flow arrows suggests how influent from diffusor trough 20 follows various paths through the media bed to the effluent outlet. At this early filtration stage, the flow path to effluent outlet 11 is fairly direct since the biofilm and solids have not yet accumulated sufficiently in the media bed so as to impede fluid flow. Likewise, heavier solids below the media bed are beginning to settle into sludge 61. Because influent is being directed from the inlet along the interior space of diffuser trough 20 and because of the upward projecting walls of the diffuser trough, it can be seen that the influent's path into the media bed is in the predominantly upward direction, i.e., “upward” being the direction opposing gravitational force. “Predominantly upward” means that at least a majority of the influent volume exits diffuser trough 20 at an angle of 45° or less relative to the vertical. However, this does not mean that the walls of diffuser trough 20 are necessarily at 45°, just that a majority of the flow is generally upward. Moreover, the eddy currents seen in FIG. 1 below the media bed in the prior art example are not present since virtually all flow is upward. Further, the buoyancy of beads lying between the upper edge 21 of the diffuser trough 20 and the lower surface 13 of the media bed 12 is sufficient to dampen any turbulence induced by the influent waters.
FIG. 7 shows the media bed 12 later in the filtration stage. FIG. 7 suggests how the sludge at the bottom of the filter has become more consolidated. Likewise, floc and other particulate matter 60 begin accumulating in the space between media beads. As a result, the flow paths through the media bed become more indirect, including some flows 63 near diffuser trough 20 which move downward out the bottom of the bed before re-entering the media bed along the sides of the filter housing. However, even where flows 63 move out of the media bed, the flow velocity is not sufficient to produce substantial eddy currents. Thus, this media filter design does not tend to entrain solids below the media bed and as a result, does not produce the above described “burp” of “dirty” water as in certain prior art filters. FIG. 7 also shows the lower surface 13 of media bed 12 is at the bottom edge 23 of diffuser trough 20. However, in other embodiments the lower surface 13 is at the midpoint 22 of diffuser trough 20 (see FIG. 3) or just below upper edge 21 of diffuser trough 20 or well below the bottom edge 23 of the diffuser trough 20.
FIGS. 8a to 8f illustrate a few nonlimiting examples of diffuser trough cross-sectional shapes. FIG. 8a shows the V-shaped cross-section 30 seen in earlier figures. The legs of the “V” seen in FIG. 8a are at approximately 45° from the vertical. However, in other embodiments, the legs could be at shallower angles (e.g., 60° from vertical) or steeper angles (e.g., 30° from vertical). FIG. 8a shows the diffuser trough having a height “H,” which in certain embodiments may be between about 3″ and about 12,″ but in other embodiments could be less than or greater than this range depending on the scale and flow requirements of the unit. FIG. 8b shows a rectangular cross-section 31 while FIG. 8c shows a curved or semi-circular shaped cross-section 35. Either of cross-sections 31 or 35 may be considered “U-shaped.” In FIG. 8b, it is not necessary for the cross-section to be square, and the base segment of the trough could be shorter or longer than the upstanding leg segments of the trough. Likewise, the FIG. 8c cross-section need not be perfectly semicircular (i.e., have a constant radius), but could be parabolic in shape. The common feature in the cross-sections 30, 31, and 35 is that they will be oriented in the filter housing in a manner to direct influent flow in a predominantly upward direction into the media bed. The cross-sectional area of the trough is adjusted with flowrate such that the trough velocities are low enough to avoid fluidization of the overlying beads. Inlet trough horizontal velocities (typically in the range of 0.5 to 3 feet per sec) are also dependent on trough length. It is observed that the trough horizontal velocity falls with length as water moves vertically into the media bed. Longer troughs are less susceptible to momentum induced turbulence at the trough's terminal end, and can tolerate higher initial horizontal trough velocities.
FIG. 8d suggests how the diffuser trough may be a pipe 33 with apertures 38 formed in the upper half of the pipe wall. Again, this will tend to direct influent in an upward orientation toward the media bed. Naturally, the orientation and spacing of the apertures in the upper half of the pipe wall can vary considerably from one embodiment to another. FIG. 8e shows how the diffuser trough may take an irregular shape or a shape that is a combination of earlier described shapes. FIG. 8f illustrates that certain embodiments of the diffuser trough will have baffles 25 along its length converting the velocity driven momentum to a localized pressure to encourage vertical flow into the media bed near the baffle's location. It is often advantageous to avoid having the influent stream reach the housing wall opposite inlet 10 with too much velocity. Excessive water velocity at this location could be disruptive to the media bed at this locality. Baffles have been found to be effective at mitigating high horizontal inlet trough velocities particularly for short troughs that are prone to momentum induced erosion on the terminal end. The baffles 25 could take on any number of shapes, including upstanding legs 26. Baffles 25 could also take the shape of surface irregularities 27 on the inner wall of the diffuser trough. Virtually any structure along the surface of or in the cross-sectional area of the diffuser trough may serve as baffles as long as the structure slows the velocity of influent (along the length of the diffuser) while increasing the tendency of the influent waters to flow vertically without eroding the media bed.
FIG. 9 suggests how different embodiments could have multiple diffuser troughs 20, typically one trough being associated with each influent inlet opening into the filter housing. FIG. 10 shows a side sectional view of a media filter having a diffuser trough formed of circular pipe 33 with upwardly directed apertures 38 and baffles 25. The lower surface 13 of the media bed is shown just below circular pipe 33, but lower surface 13 could be as high as just beneath apertures 38 (or perhaps somewhat above the apertures or upper trough edge in certain specialized embodiments). FIG. 11 illustrates an “hour-glass” type floating media filter such as disclosed in U.S. Pat. No. 5,232,586, which is incorporated by reference herein in its entirety. As explained in U.S. Pat. No. 5,232,586, the backwashing principle operates through the constricted throat 46 in the filter housing below the media bed and a valve allowing discharge of sufficient liquid to cause a rapid drop of the media bed into the throat. The FIG. 11 embodiment shows the lower surface 13 of the media bed (during the filtration stage) just above the bottom edge of diffuser trough 20. FIG. 12 shows two diffuser troughs 20 positioned in a “propeller wash” type of floating media filter such as disclosed in U.S. Pat. No. 5,126,042 which is incorporated by reference herein in its entirety. The backwash mechanism in propeller wash filters involves at least one propeller 51 positioned in the filter housing and rotated with sufficient speed to disperse the media bed. Although not shown in the figures, a related backwash mechanism is a “paddle wash” floating media filter such as seen in U.S. Pat. No. 5,445,740, which is incorporated by reference herein in its entirety.
FIG. 13 illustrates a propeller wash type media filter having a peripheral diffuser trough 55. It can be envisioned how peripheral diffuser tough 55 forms a conical frustum shape with an open center portion. The filter housing will include the exterior circumferential feed channel 56 which receives influent flow and distributes the influent to a series of filter housing inlet apertures 57, which are also formed around the circumference of the filter housing. The open center portion of the peripheral diffuser trough enhances backwashing in propeller wash embodiments allowing the extension of propellers at or below the diffuser trough and lessening interference with the movement of media beads in response to propeller generated dispersion forces.
Although many aspects of the invention have been described in terms of certain specific embodiments illustrated above, many modifications and variations will be obvious to those skilled in the art to which the invention pertains. All such modifications and variations are intended to come within the scope of the following claims.
Patent Application
20160354711
