Patent Description:
Grit is one of the most unpredictable and difficult materials a sewage treatment plant must handle. Grit can be defined as the heavy mineral matter present in sewage. It is principally made up of sand, gravel, and inorganic material with a specific gravity of <NUM> which reaches a sewage disposal plant. It is desirous to remove this material as it cannot be treated, reduced in size, or eliminated by treatment methods. It presents a problem to waste treatment as it is hard and abrasive. It wears pumps and other mechanical devices. It is heavy and accumulates in clarifiers, treatment basins, digesters, etc., where it must sometimes be removed manually.

Grit removal devices of various designs have been proposed to remove grit from a flowing stream of water. For example, inclined flat plate separators known as lamella units have been used in various types of equipment for separating solids from liquid and in other separation applications. See, e.g., <CIT> and <CIT>.

Other devices remove grit from the waste water as the water flows from an influent channel around a round chamber creating a circular flow stream which causes the grit to settle near the bottom center of the round chamber before exits through an effluent channel. The grit in the injected liquid is removed from the liquid stream and collected in the storage chamber for relatively easy removal (see, e.g., <CIT> and U. <CIT><CIT><CIT><CIT><CIT><CIT> and <CIT>).

<CIT> includes an upper settling chamber and a lower grit storage chamber. The settling chamber, being of large diameter, communicates with the storage chamber through a relatively small opening in a substantially flat transition surface therebetween. Rotating paddles positioned within the settling chamber, a short distance above the transition surface, can enhance the natural rotational flow of liquid entering the settling chamber adjacent the outer periphery to rotate about the chamber as a forced vortex resulting in an upward spiral flow which urges the settled particles across the transition surface towards the opening. The heavier settled particles fall through the opening into the storage chamber and the lighter organic particles rise in the spiral flow. The contents in the storage chamber are lightly air scoured prior to removal to cause any organics therein to be lifted out of the storage chamber and returned to the settling chamber.

A similar type of grit removal device is disclosed in <CIT>, in which a ramp is in communication with the flume portion of the inlet trough to cause grit to follow the ramp down towards the transition surface. A baffle is also positioned in the settling chamber against which the rotating liquid impinges to deflect the liquid downwardly into a generally toroidal flow pattern that spirals around the periphery of the settling chamber. The toroidal motion of the liquid moves the grit on the transition surface towards the center opening.

<CIT> and <CIT> also disclose vortex-type grit extractor apparatuses. <CIT>, for example, discloses an apparatus for removing grit in which a grit storage chamber is provided beneath the center of the round chamber of the grit removal system. A removable plate substantially aligned with the floor of the round chamber generally separates the two chambers, with a central opening through the plate permitting communication between the chambers. A cylindrical shaft is rotatably supported on its upper end above the round chamber and extends down through the round chamber through the plate central opening. Liquid flow in the round chamber forces grit particles to settle toward the chamber floor, where they are urged radially inwardly so as to drop through the plate central opening into the grit storage chamber. A multi-bladed propeller is mounted on that shaft above the plate, and rotates with the shaft to assist in the liquid flow to move the grit toward the plate center opening. A pipe also extends down through the cylindrical shaft into the grit storage chamber, and a pump is provided on the upper end of the pipe to allow grit in the bottom of the storage chamber to be removed by pumping up through the pipe.

The above-described prior art devices operate on the forced vortex principle. In these devices the head at the periphery of the settling chamber is higher than at the center of the settling chamber. This causes liquid to flow down the wall of the settling chamber to the bottom thereof and across the bottom to the point of lower head at the center thereof. It is this transverse circulatory flow pattern which permits the device to work. The particulate matter in suspension must follow this path to reach the bottom of the settling chamber and be carried to the center of the transition surface to the storage chamber. This takes some time and some of the particulate matter may not travel the full circuit before it is caught in the flow passing out the effluent, which results in a lowering of grit removal efficiency.

In still other grit removal devices such as shown in <CIT><CIT>and <CIT>, flow toward the center of a chamber is facilitated by a rotating propeller or paddle. <CIT> also includes a ring around the interior periphery of the settling chamber blocking fluid flowing around the outside of the chamber from rising up to the level of the chamber outlet. <CIT> discloses a settler for liquids to be purified comprising a tank which embodies a plurality of hollow truncated-cone shaped elements stacked coaxially with their minimum diameter facing the tank bottom and delimiting intermediate passages which extend conically from the element centre holes towards the periphery of the tank. In proximity to the lower truncated-cone shaped element, an intermediate horizontal partition is provided, which divides the tank into a lower chamber, to which an inlet duct for the delivery of dirty liquid is connected, and an upper chamber, to which an outlet duct for purified liquid is connected.

Grit removal devices as described above, whether operating by settling or vortex action, require a relatively large footprint, presenting space problems in designing overall treatment facilities in which the grit removal devices are only a part. Of course, larger devices are inherently more costly, and can use more energy. Further, such devices are not as well adapted as might be desired to operate efficiently in environments in which the flow rate varies widely. Still further, the ability of the devices to efficiently remove grit can always be improved.

The present invention is directed toward, inter alia, one or more of the problems set forth above.

In one aspect, a grit removal unit for a wastewater system for removing grit from a fluid includes a grit removal chamber cylindrical about a center vertical axis with a grit storage chamber disposed below the grit removal chamber, and at least one opening through the bottom of the grit removal chamber. At least one layer plate which is an inverted truncated cone around the center axis is spaced from the grit removal chamber vertical wall to allow fluid flow between the at least one layer plate and the grit removal chamber vertical wall. A plurality of concentric inverted truncated cone lamella plates are also in the grit removal chamber around the center axis and above the at least one layer plate, the lamella plates being radially spaced from one another relative to the center axis wherein the spacings between adjacent lamella plates define flow paths through which wastewater flows upwardly. An influent opening in the grit removal chamber vertical wall below the layered plates allows fluid and grit into the grit removal chamber, and an effluent opening in the grit removal chamber vertical wall above the lamella plates allows fluid to exit the grit removal chamber.

In one form, a center shaft is substantially coaxial with the center axis and rotatable around the central vertical axis, and blades projecting from and rotatable with the center shaft are disposed above the opening through the grit removal chamber bottom surface. In a further form, the blades are configured to direct flow of the fluid up around the center shaft and assist with forcing grit toward the grit storage chamber. In a further form, the grit removal chamber vertical wall is substantially annular about the center axis.

In another form, an enclosed influent channel is adapted to direct wastewater into the grit removal chamber beneath the layered plates. In a further form, the enclosed influent channel is adapted to direct wastewater into the grit removal chamber adjacent the grit removal chamber bottom surface and substantially tangential to the grit removal chamber vertical wall.

In still another form, the at least one layer plate is a substantially flatter truncated cone than the lamella plates.

In yet another form, the at least one layer plate has a center opening larger than the center shaft.

In another form, a FOG removal system is in the grit removal chamber above the lamella plates and beneath the effluent opening.

In a still further form, the at least one layer plate includes a first layer plate, and second and third layer plates vertically spaced from the first layer plate. The second layer plate is between the first and third layer plates and is substantially adjacent the grit removal chamber vertical wall to substantially block fluid flow between the second layer plate and the grit removal chamber wall. The third layer plate is spaced from the grit removal chamber vertical wall to allow fluid flow between the third layer plate and the grit removal chamber vertical wall.

In another aspect, a grit removal unit for removing grit from a fluid includes a grit removal chamber with a vertical wall which is annular about a central vertical axis, with a grit storage chamber disposed below the grit removal chamber, and at least one opening through the grit removal chamber bottom surface through which grit from the grit removal chamber may pass into the grit storage chamber. A center shaft is coaxial with, and rotatable around, the center axis. Blades project from, and rotate with, the center shaft, with the blades disposed above the grit storage chamber and configured to direct flow of fluid up around the center shaft. At least one layer plate is in the grit removal chamber in the shape of inverted truncated cones annular around the center axis. The at least one layer plate is spaced from the grit removal chamber annular vertical wall to allow fluid flow between it and the annular vertical wall. A plurality of concentric inverted truncated cone lamella plates are supported in the grit removal chamber around the center shaft and above the at least one layer plate. An influent opening in the grit removal chamber vertical wall below the layer plate allows the fluid and grit to enter the grit removal chamber through the influent opening. An effluent opening in the grit removal chamber vertical wall above the lamella plates allows fluid and grit to exit the grit removal chamber above the lamella plates.

In one form, an enclosed influent channel is adapted to direct wastewater into the grit removal chamber beneath the layered plates. In another form, the enclosed influent channel is adapted to direct wastewater into the grit removal chamber adjacent the grit removal chamber bottom surface and substantially tangential to a grit removal chamber substantially annular vertical wall.

In another form, an effluent channel is adapted to direct fluid from the grit removal chamber above the lamella plates.

According to the invention there are at least three layer plates in the grit removal chamber, with the three layer plates being inverted truncated cones annular around the central vertical axis. The layer plates are vertically spaced from one another wherein a middle one of the three layer plates is substantially adjacent the grit removal chamber annular vertical wall to substantially block fluid flow between the middle layer plate and the annular vertical wall, and the layer plates above and below the middle layer plate are spaced from the grit removal chamber vertical wall to allow fluid flow between the grit removal chamber vertical wall and the layer plates above and below the middle layer plate.

In still another aspect, the grit removal unit includes an annular grit removal chamber with a bottom surface and a grit storage chamber disposed below the grit removal chamber and at least one opening through the bottom surface through which grit may pass into the grit storage chamber. A center shaft is rotatable around a vertical center axis and blades project from, and are rotatable with, the center shaft adjacent and above the bottom surface opening to direct flow of the fluid up around the center shaft. At least three layered plates which are inverted truncated cones annular around the center axis are vertically spaced from one another with a middle one of the three layered plates being substantially adjacent the grit removal chamber vertical wall to substantially block fluid flow between the middle layered plate and the annular vertical wall. The layered plates have center openings larger than the center shaft. A plurality of concentric inverted truncated cone lamella plates are in the grit removal chamber around the center shaft and above the layered plates. An enclosed influent channel is connected to an influent opening through the grit removal chamber annular vertical wall below the layered plates, whereby wastewater is directed into the grit removal chamber in a direction substantially tangential to the grit removal chamber vertical wall. An effluent channel is connected to an effluent opening in the grit removal chamber annular vertical wall above the lamella plates and allows fluid to exit. A FOG removal system is in the grit removal chamber above the lamella plates and beneath the effluent opening.

In one form, the wastewater flows through the layered plates in a substantially serpentine path.

In another form, the layered plates are substantially flatter truncated cones than the lamella plates.

Other objects, features, and advantages of the grit removal unit in its various forms will become apparent from a review of the entire specification, including the appended claims and drawings.

A grit removal unit <NUM> is variously shown in <FIG>.

The grit removal unit <NUM> includes a grit removal chamber <NUM> including a vertical wall <NUM> which is substantially annular or cylindrical about a central axis <NUM> and extending upwardly from a bottom surface <NUM>.

Beneath the bottom surface <NUM> is a hopper or grit storage chamber <NUM>, where grit removed from fluid in the grit removal chamber <NUM> is directed and captured (collected) for periodic removal for dewatering and disposal. The grit removal chamber bottom surface <NUM> includes one or more openings <NUM> therethrough toward which wastewater (fluid with grit) is directed for passage down into the grit storage chamber <NUM>.

Three layered plates 40a, 40b, 40c are in the grit removal chamber <NUM> spaced above the grit removal chamber bottom surface <NUM> (the multiple plates 40a, 40b, 40c are "layered" and referred to as such, but individual plates are also referred to herein as "layer" plates). The layered plates 40a-c are relatively flat inverted truncated cones - that is, they are annular around the central axis <NUM> with their wide end above the narrow end 42a-c, where the narrow ends 42a-c each have a central opening <NUM> therethrough.

The layered plates 40a-c are vertically spaced from one another, with the middle layered plate 40b extending outwardly to the grit storage chamber vertical wall <NUM> where a suitable seal or gasket <NUM> preventing wastewater from passing between the vertical wall <NUM> and the middle layered plate 40b may be advantageously provided. The gasket <NUM> also helps for proper fit if any components are out of tolerance The top and bottom layered plates 40a, 40c are, by contrast, spaced from the grit storage chamber vertical wall <NUM> and extend further toward the central axis <NUM> than the middle layered plate 40b so that, as described in greater detail hereafter in connection with <FIG>, wastewater will flow up from the bottom of the grit removal chamber <NUM> and between the layered plates 40a-c in a serpentine manner.

While three layered plates 40a-c are disclosed herein, it should be understood that it would be within the scope of the advantageous structure disclosed herein to have more than three layered plates.

A plurality of concentric inverted truncated cone lamella-style (lamella) plates <NUM> are disposed above the layered plates 40a-c in the grit removal chamber <NUM> and centered around the central axis <NUM>. (Eight lamella plates <NUM> are illustrated in the Figures, though more or less could be used depending on the design requirements - for example, <FIG> shows twelve lamella plates). The outermost lamella plate 50a, like the middle layered plate 40b, extends outwardly to the grit storage chamber vertical wall <NUM> with a suitable seal or gasket <NUM> preventing wastewater from passing between the vertical wall <NUM> and the outside of the outermost lamella plate 50a. It should be appreciated that the gaskets <NUM>, <NUM> will avoid and/or correct for field construction mistakes which can result in improper diameters and/or concentricity of the grit removal chamber <NUM>. That is, flexible/compressible gaskets <NUM>, <NUM> allow elimination of gaps around the outside of the grit removal chamber <NUM> through which grit particles may short cut through the unit <NUM> and decrease grit particle capture efficiency.

The inclined configuration of the layered plates 40a-c and lamella plates 50a-h provide a self-cleaning mechanism which prevents excessive buildup of the solids and clogging.

As noted, the layered plates 40a-c and lamella plates <NUM> may advantageously be in the shape of inverted truncated cones, with the layered plates 40a-c substantially flatter cones than the lamella plates <NUM>. However, it should be understood that the plates may in some forms have flat rather than curved sides, with pyramidal flat sides approximating a truncated cone, such as a four sided pyramid or octagonal pyramid. As used herein, such shapes are to be considered to be truncated cones.

A suitable bracket structure <NUM> may be secured to the grit removal chamber <NUM> (see <FIG>) for supporting the described plates 40a-c, <NUM> and other components. For example, circumferentially spaced radial supports <NUM>, <NUM> are disposed at the top and bottom of the lamella plates <NUM> with slots <NUM>, <NUM> therein receiving the top and bottom lips of the lamella plates <NUM> to thereby support the lamella plates <NUM> in concentric spaced locations.

The bracket structure 60a may further function to support a center shaft <NUM> which may be rotatably driven (see drive <NUM> in <FIG>) about the center axis <NUM> to drive propeller blades <NUM> near the bottom surface <NUM> of the grit removal chamber <NUM> to direct the flow of wastewater and hydraulically forced grit toward the grit storage chamber <NUM> as desired and described in further detail hereafter, and drive fluidizing vanes <NUM> near the bottom surface of the grit storage chamber <NUM> to stir settled grit. A top bracket 60a across the top of the grit removal chamber <NUM> may similarly support a suitable drive to rotate the center shaft <NUM> as desired.

An enclosed influent channel <NUM> is connected to an influent opening through the grit removal chamber vertical wall <NUM> beneath the layered plates 40a-c and generally tangentially to the grit removal chamber annular vertical wall <NUM>. Wastewater thus enters the grit removal chamber <NUM> at its outer perimeter where the vertical wall <NUM> directs the flow toward circling around the outer perimeter - that is, in a vortex movement.

An effluent channel <NUM> is connected to an effluent opening <NUM> in the grit removal chamber vertical wall <NUM> above the lamella plates <NUM>. The input wastewater minus the removed grit passes out of the grit removal unit <NUM> to allow for further processing where necessary.

A fat, oil and grease ("FOG" as used herein) removal system <NUM> (see <FIG>) with a skimmer arm may also be included above the lamella plates <NUM> and below the effluent channel <NUM>. FOG particles flow with and float on the wastewater due to lower density. The FOG removal system <NUM> may include static and/or dynamic FOG capturing media allowing constant contact with the everchanging water height for continuous capturing of FOG particles. A skimmer arm may also be advantageously included to accumulate and drain a small depth of the water stream height to facilitate acquiring floating FOG particles. The FOG removal system <NUM> helps collect (capture) and remove (dispose of) any greases, oils and fats which might become nuisances in apparatuses such as may be downstream of the grit removal unit <NUM> which further treat the effluent from the grit removal unit <NUM>. Thus, creation of odor emitting bacteria which can occur with coagulation and collection of FOG particles in no-flow areas of the equipment downstream from the grit removal unit <NUM> may be avoided.

Operation of the grit removal unit <NUM> may thus be best understood by reference to the schematic view of <FIG>. As is known for vortex type grit removal units, wastewater flow in the grit removal chamber <NUM> enters tangentially to the annular vertical wall <NUM> and then swirls around the bottom of the grit removal chamber <NUM> to create a vortex in which grit falls down toward the bottom surface <NUM> and is drawn to the center where such grit may fall through the openings <NUM> and into the grit storage chamber <NUM>.

In addition to the vortex movement of the fluid, the propeller blades <NUM> propel wastewater near the center of the grit removal chamber <NUM> up to also add a donut-like flow element such as shown by arrows <NUM>. Along with the propeller blades <NUM> and vortex movement, such flow element also facilitates the settling or falling out of the grit particles as well as the movement of such particles toward the center where they may fall into the grit storage chamber <NUM>.

As more wastewater enters the unit <NUM>, flow additionally occurs up (see arrows <NUM> and <NUM>) from the bottom portion of the grit removal chamber <NUM> and through the layered plates 40a-c in a serpentine manner (i.e., [i] around the outside of the bottom layered plate 40a, then [ii] radially inwardly between the bottom and middle layered plates 40a, 40b [arrows <NUM>, <NUM>], then [iii] up [arrows <NUM>] through the gap between the middle layered plate 40b and center shaft <NUM>, and then [iv] between the middle layered plate 40b and the top layered plate 40c [arrows <NUM>].

It should be appreciated that during this flow through the layered plates 40a-c, some of the remaining grit particles will settle out due to the large effective settling area, which settled grit settles onto the bottom and middle layered plates 40a, 40b and then slides down the layered plates 40a, 40b and ultimately through the gap between the bottom and middle layered plates 40a, 40b and the center shaft <NUM>.

Further, wastewater exiting from the channel between the middle layered plate 40b and top layered plate 40c (arrows <NUM>) will continue to flow upwards, this time through the spaces between the lamella plates <NUM> (arrows <NUM>). As with the flow through the layered plates 40a-c, grit particles still remaining in the wastewater passing through the lamella plates <NUM> will settle out due to the large effective settling area of the lamella plates <NUM>, which settled grit will slide down the lamella plates <NUM> (dotted arrows <NUM>) onto the top layered plate 40c, then sliding down the top layered plate 40c and ultimately through the gap between the layered plates 40a-c and the center shaft <NUM>.

In short, flow of wastewater through the layered plates 40a-c and the lamella plates <NUM> will settle out remaining grit particles which will slide over the plates 40a-c, <NUM> to the center, and then down around the center shaft <NUM> (dotted arrows <NUM>, <NUM>) back into the bottom of the grit removal chamber <NUM> where the grit particles may also ultimately pass through the openings <NUM> into the grit storage chamber <NUM> (dotted arrows <NUM>). Wastewater which has passed through the layered plates 40a-c and lamella plates <NUM> will exit the grit removal chamber through the effluent opening <NUM> into the effluent channel <NUM>.

Claim 1:
A grit removal unit (<NUM>) for a wastewater system for removing grit from a fluid, comprising:
a grit removal chamber (<NUM>) defined by a bottom surface (<NUM>) and a vertical wall (<NUM>) extending up from said bottom surface (<NUM>), said grit removal chamber (<NUM>) having a substantially central vertical axis (<NUM>);
a grit storage chamber (<NUM>) disposed below said grit removal chamber (<NUM>), and at least one opening (<NUM>) through said grit removal chamber bottom surface (<NUM>) through which grit from said grit removal chamber (<NUM>) may pass into said grit storage chamber (<NUM>);
first, second and third layer plates (40a, 40b, 40c) in said grit removal chamber (<NUM>), said layer plates (40a, 40b, 40c) being inverted truncated cones annular around said central vertical axis (<NUM>) and vertically spaced from one another, wherein
said first and third layer plates (40a, 40c) are spaced from the grit removal chamber vertical wall (<NUM>) to allow fluid flow between the first and third layer plates (40a, 40c) and the grit removal chamber vertical wall (<NUM>), and
said second layer plate (40b) is between said first and third layer plates (40a, 40c) and is substantially adjacent the grit removal chamber vertical wall (<NUM>) to substantially block fluid flow between the second layer plate (40b) and the grit removal chamber wall (<NUM>);
lamella settlers in said grit removal chamber (<NUM>) around said central vertical axis (<NUM>) and above said layer plates (40a, 40b, 40c);
an influent opening in said grit removal chamber vertical wall (<NUM>) below said layer plates (40a, 40b, 40c) wherein fluid and grit enters said grit removal chamber (<NUM>) through said influent opening; and
an effluent opening (<NUM>) in said grit removal chamber vertical wall (<NUM>) above said lamella settlers wherein said fluid exits said grit removal chamber (<NUM>) through said effluent opening (<NUM>).