WATER STREAMS

TECHNICAL FIELD

[0001] This invention relates an apparatus for the removal of solid particulates from water streams.

BACKGROUND

[0002] Recovery of floating solid particulates from water streams is a key step to treating wastewater, especially storm drainage. Stormwater runoff and other wastewater streams collect floating particulates such as wood and plastic as they run toward drains. The particulates that must be separated from the water before the water can be further treated or released into the environment.

[0003] Underflow baffles are an inexpensive means to gather the floating particulates for recovery. A solid baffle blocks the upper part of the stream, forcing water to flow down and under it. It is expected that floating particulates will continue to float and will be trapped against the upstream face of the baffle.

[0004] In actual practice, floating particulates are frequently carried down and under the underflow baffle by water flowing under the baffle. This problem is worse when the water flow velocity is high, such as after a storm. Many arrangements of underflow baffles and overflow weirs have been published to overcome this problem, with different sizes, spacings and angles of baffles and weirs. See, for example, US Patent Publications 2004/0074846 Al and 2013/0264258 Al. Still, underflow of floating particulates remains a problem.

[0005] It would be useful to identify simple modifications to the underflow baffle to reduce the flow of floating particulates under the baffle.

SUMMARY

[0006] We have determined that vortices at the upstream face of the underflow baffle play an important role in drawing floating particulates down to a level where they can flow under the baffle. Reducing the vortices can reduce the number of floating particulates that are carried under the baffle.

[0007] Our invention is an apparatus to separate floating particulates from a water stream comprising: a. A channel for water to flow which channel has two side walls, two end walls and a floor, with an inlet for water at or near one end wall and an outlet for water at or near the opposite end wall, all arranged so that water flows through the channel between the sidewalls from the inlet to the outlet without substantial loss of water, and in which the surface of the water in the channel rises to a certain waterline during ordinary use; b. At least one underflow baffle located between the inlet and the outlet which (1) has an upstream face, a downstream face and a bottom edge and (2) extends from one sidewall to the other sidewall and (3) extends down from above the waterline to a bottom edge depth that is under the waterline but above the floor, so that water flowing from the inlet to the outlet flows underneath the underflow baffle; c. At least one overflow weir located downstream from the underflow baffle which (1) has an upstream face, a downstream face and a top edge and (2) extends from one sidewall to the other sidewall and (3) extends up from the floor to the top edge, so that water flowing from the inlet to the outlet flows over the top of the overflow weir; and d. A device upstream from the underflow baffle to collect floating particulates captured by the underflow baffle, wherein at least one underflow baffle has at least one of the following antivortex features:

(i) The bottom edge of the underflow baffle is beveled at an angle from 15° to 60° from horizontal, with the higher side of the bevel on the upstream face and the lower side of the bevel on the downstream face of the baffle; or

(ii) The underflow baffle has vortex dampeners, which are plates that are fixed to and extend from both comers formed by the underflow baffle and the side walls below the waterline on the upstream face of the baffle, wherein the vortex dampeners (1) are oriented from 0° to 30° from horizontal; (2) are each independently located from 0.3 D to 1 D below the waterline; (3) each independently extend at least 0.2 D from the underflow baffle; and (4) each independently extend cross stream from the sidewall at least 10 percent of the width across the channel, wherein D is the depth from the ordinary waterline to the bottom of the underflow baffle; or

(iii) The underflow baffle has a shelf below the waterline that is fixed to the upstream face of the baffle and extends cross stream to both side walls, wherein the shelf (1) is oriented from 0° to 30° from horizontal; (2) is located from 0.5 D to 1.0 D below the waterline; (3) extends at least 0.25 D from the underflow baffle, wherein D is the depth from the waterline to the bottom of the underflow baffle.

[0008] The apparatus of the present invention is useful to recover floating particulates from water. For example, it may be used to recover plastic pellets. Plastic pellets may be spilled in a handling facility such as a fabricator shop or a loading facility and may get carried into wastewater streams and drains by rainwater or wash water.

BRIEF DESCRIPTION OF DRAWINGS

[0009] Drawing 1 shows a side view of an apparatus that has an underflow baffle to trap floating particulates and an overflow weir.

[0010] Drawing 2 shows a side view of an apparatus that has two underflow baffles to trap floating particulates separated by an overflow weir.

[0011] Drawing 3 shows the beveled bottom edge of an underflow baffle and the beveled top edge of an overflow weir.

[0012] Drawing 4 shows a side and top view of an underflow baffle with vortex dampeners.

[0013] Drawing 5 shows a side view of an underflow baffle with a vertical shelf and a side view of an underflow baffle with a tilted shelf.

[0014] Drawing 6 shows a side view of an underflow baffle with a vertical orientation and a side view of an underflow baffle with an orientation tilted from vertical in the upstream direction.

DETAILED DESCRIPTION

[0015] The apparatus of our invention comprises a channel for water to flow through. The channel has two sidewalls, two end walls and a floor. The channel also has an inlet for water at or near one end wall and an outlet for water at or near the opposite end wall. In many embodiments, the channel is essentially horizontal. The walls, floor, inlet and outlet are arranged so that water can flow from the inlet through the channel between the sidewalls to and out of the outlet without substantial loss of water. In many embodiments, the channel is essentially horizontal; a high level of pitch can interfere with water velocity in the channel.

[0016] Descriptions of the channel and objects in it may use some of the following terms:

• “Upstream” means in the direction from the outlet to the inlet.

• “Downstream” means in the direction from the inlet to the outlet.

• “Cross stream” means perpendicular to the flow of water in the channel.

• “Waterline” means the level that the surface of the water rises to above the floor of channel in ordinary use. It is known to manage the waterline by placement of overflow weirs and the outlet. By use of weirs, the waterline can be established at different levels in different sections of the channel. It is also known that the level of water may change when the flow of water is outside the design limits of the apparatus, but the “waterline” referred to in this application is the level of the water surface during ordinary use. • “Solid” means that an item is free of perforations that would allow substantial water to pass through the item.

• “Essentially” means that any deviation from a stated parameter is small enough that it does not materially change the functioning of the apparatus. In all cases where “essentially” is used, the stated parameter may meet the stated limit precisely so that “essentially” can be omitted.

[0017] Suitable channels have been known and in common use since prehistory. Many common variations are known and may be used in the present invention. In some embodiments, the sidewalls may be essentially vertical, and the floor may be essentially horizontal, so that the cross stream section of the channel is essentially square or essentially rectangular. In some embodiments, the floor may be essentially horizontal, and the side walls may slant outwards from the floor, so that the cross stream section of the channel appears trapezoidal. Other shapes may also be used in the present invention, as long as water flows under the underflow baffle(s) and over the overflow weir(s) without interfering with the function of the apparatus. In some embodiments, a rectangular cross section is easiest to work with.

[0018] The dimensions and placement of the underflow baffles and the overflow weirs are conveniently stated as a ratio based on the height of the waterline in the channel. For this application, the term “H” refers to the height of the waterline above the floor of the channel. H is generally controlled by the water flow velocity and the height of overflow weirs in the channel. In some embodiments, the width of the channel (in the cross stream direction) is at least equal to H. and in some embodiments the width of the channel is greater than H. In some embodiments, the width of the channel is at least 1.25 H or at least 1.5 H or at least 2 H.

[0019] The channel may optionally have a solid top attached to the top of the sidewalls.

[0020] In some embodiments, the sidewalls extend above the waterline of the apparatus, so there is an air-filled headspace above the waterline. In some embodiments, the waterline is at or near the solid top, so there is little or no headspace.

[0021] The channel has an inlet at or near one end and an outlet at or near the other end, disposed so that water flows from the inlet through the channel to the outlet. In some embodiments, the inlet is less than 1 H from an end wall or less than 0.5 H or less than 0.25 H; in some embodiments, the outlet is less than 1 H from the other end wall or less than 0.5 H or less than 0.25 H. Examples of suitable inlets include a pipe or an opening from another channel.

Examples of suitable outlets include a second pipe or a second opening into another channel. In some embodiments, the inlet and/or the outlet has a valve, sluice gate or other means to regulate flow of water into or out of the apparatus. In other embodiments, the inlet and/or the outlet have no such means to regulate the flow of water.

[0022] The apparatus contains at least one underflow baffle between the inlet and outlet. The underflow baffle runs from one sidewall to the other sidewall and extends from above the waterline to a depth that is under the waterline but above the floor, so that water flowing from the inlet to the outlet flows underneath the underflow baffle. In some embodiments, the underflow baffle is solid. The bottom edge of the underflow baffle may be horizontal in the cross-stream direction from sidewall to sidewall. Alternatively, the bottom edge of the baffle may have curves or notches in the cross-stream direction from sidewall to sidewall. In many embodiments, an essentially straight horizontal bottom edge is simpler to use.

[0023] The underflow baffle should extend low enough below the waterline so that a majority of floating particulates are retained upstream from the baffle, but end high enough above the floor of the channel so that water can flow readily under the baffle. In some embodiments, the underflow baffle extends below the waterline to a depth (£)) of at least 0.4 H or at least 0.45 H or at least 0.5 H. In some embodiments, the underflow baffle extends below the waterline to a depth (£>) of at most 0.8 H or at most 0.75 H or at most 0.7 H. Conversely, in some embodiments, the gap from the floor of the channel to the bottom of the underflow baffle is at least 0.2 H or at least 0.25 H or at least 0.3 H. In some embodiments, the gap from the floor of the channel to the bottom of the underflow baffle is at most 0.6 H or at most 0.55 H or at most 0.5 H.

[0024] In some embodiments, the underflow baffle is located at least 1.25 H downstream from the inlet to the channel, or at least 1.5 H or at least 1.75 H or at least 2 H. Location too close to the inlet can increase turbulence at the baffle and decrease its effectiveness. The maximum distance between the underflow baffle and the inlet is not important, but selecting a long distance may increase the size and cost of the apparatus without providing a corresponding benefit. In some embodiments, it will be desirable to keep the distance between the underflow baffle and the inlet at no more than 10 H.

[0025] The orientation of the underflow baffle as it extends down from above the waterline may be essentially vertical. ’Alternatively, part or all of the underflow baffle may be oriented at an angle to vertical. In some embodiments, the orientation of the underflow baffle is within 30° of vertical or within 20° of vertical or within 10° of vertical. In some embodiments, the orientation of the underflow baffle is essentially vertical (essentially 0° from vertical). In some embodiments where the underflow baffle is oriented at an angle from vertical, the bottom of the baffle is upstream from the top of the baffle. Figure 6(a) illustrates an essentially vertical baffle, and Figure 6(b) illustrates a baffle that is oriented at an angle from vertical in the upstream direction. [0026] The apparatus further contains at least one overflow weir downstream from the underflow baffle. The overflow weir runs from one sidewall to the other sidewall and extends from the floor, so that water flowing from the inlet to the outlet flows over the top of the overflow weir. In many embodiments, the overflow weir is solid. The top edge of the overflow weir may be essentially straight and horizontal from sidewall to sidewall. Alternatively, it may have curves or notches. In some embodiments, an essentially straight horizontal top edge is easier to work with.

[0027] The overflow weir should extend far enough above the floor of the channel so that the flow of water through the channel is slowed but not stopped. In some embodiments that contain a second underflow baffles, the overflow weir extends far enough above the floor of the channel, so that floating particulates that escape under the first underflow baffle are redirected to the surface to be trapped by the second underflow baffle. In some embodiments, the height of the overflow weir from the floor of channel is at least 0.2 H or at least 0.25 H or at least 0.3 H. In some embodiments, the height of the overflow weir from the floor of channel is at most 0.5 H or at most 0.45 H or at most 0.4 H. In some embodiments, the top of the overflow weir is at least even with the bottom of the underflow baffle or at least 0.1 H above the bottom of the underflow baffle or at least 0.15 H or at least 0.2 H. In some embodiments, the top of the overflow weir is at most 0.35 H above the bottom of the underflow baffle or at most 0.3 H or at most 0.25 H.

[0028] In some embodiments, the overflow weir is located at least 0.5 H downstream from the underflow baffle, or at least 0.6 H or at least 0.7 H. Again, the maximum distance between the overflow weir and the underflow baffle is not important, but selecting a long distance increases the size and cost of the apparatus without providing a corresponding benefit. In some embodiments, it will be desirable to keep the distance between the overflow weir and the underflow baffle at no more than 10 H.

[0029] The orientation of the overflow weir may be essentially vertical. Alternatively, part or all of the overflow weir may be oriented at an angle to vertical. In some embodiments, the orientation of the overflow weir is within 45° of vertical or within 30° of vertical or within 20° of vertical or within 10° of vertical. In some embodiments, the entire overflow weir is oriented essentially vertical (essentially 0° from vertical).

[0030] The apparatus optionally contains a second underflow baffle downstream from the overflow weir. The dimensions and orientation of the second underflow baffle meet the same broad description and exemplary embodiments as the first underflow baffle. In some embodiments, the second underflow baffle is located at least 0.9 H downstream from the overflow weir, or at least 1 H or at least 1.1 H or at least 1.25 H. The maximum distance between the second underflow baffle and the overflow weir is not important, but selecting a long distance increases the size and cost of the apparatus without providing a corresponding benefit. In some embodiments, it will be desirable to keep the distance between the second underflow baffle and the overflow weir at no more than 10 H.

[0031] In some embodiments, the outflow from the channel is at least 0.75 H downstream from the final weir or baffle, or at least 0.8 H or at least 1 H. The maximum distance between the final weir or baffle and the outlet to the channel is not important, but selecting a long distance increases the size and cost of the apparatus without providing a corresponding benefit. In some embodiments, it will be desirable to keep the distance between the final weir or baffle and outlet to the channel at no more than 10 H.

[0032] The apparatus may optionally have more overflow baffles and overflow weirs located upstream or downstream of the baffles and weirs previously discussed.

[0033] The channel, baffles and weirs may be made of any suitable strong, water-resistant and weatherable material. Examples of materials include concrete, plastic, fiberglass, steel and the like.

[0034] The size of the channel, baffles and weirs will vary depending on the intended use of the apparatus, and the expected volume of water and floating particulates that it must handle. Water flowing through the apparatus at velocity that is too high will carry floating particulates under the baffles regardless of any modification of the baffles. The channel should be sized to keep velocity low enough for the baffles to be effective, given the expected volume of water. In some embodiments, the dimensions of the channel are between 3 and 60 meters wide and between 1.5 to 2 meters deep and the channel is sized so that in ordinary use:

• the velocity of water under the underflow baffle is no more than 1 meter per second or no more than 0.5 meters per second or no more than 0.3 meters per second; or

• the bulk velocity of water after it has entered the channel from the inlet and flows toward the first underflow weir is no more than 0.5 m. second or no more than 0.25 m/second or no more than 1.5 m/second.

Minimum velocity is not critical as long as water flows with enough velocity to bring floating particulates to the upstream face of the underflow baffle. In some embodiments, the velocity of water under the underflow baffle during ordinary use is at least 0.01 m/second or at least 0.02 m/second or at least 0.05 m/second. Persons who design wastewater handling systems can readily calculate the proper flow velocity and sizing for specific apparatus.

[0035] The apparatus further contains one or more devices to collect floating particulates at the upstream face of each underflow baffle. The devices remove the accumulated floating particulates from the upstream face of the underflow baffles and dewater them. In various embodiments, the water removed from the dewatered particulates is added back into the stream upstream of the inlet or upstream of the underflow baffle, or is added back into the stream downstream of the underflow baffle or past the inlet, or is otherwise disposed of. The dewatered particulates may be reused, recycled or otherwise disposed of.

[0036] Suitable collection devices are known. They may include pumps, skimmers and strainers. For example,

• A pump-based collection device may have an inflow pipe that opens into the channel at the waterline near the face of the underflow baffle. The inflow pipe draws water with floating particulates from the waterline of the channel into a separation device, such as a dewatering hopper or a tank with a mesh screen, where floating particulates are separated from the water. Water from the separation device is drawn through a pump and expelled into an outflow pipe which carries the expelled water back to the channel. Particulates collected in the separation device are expelled into a container. In some embodiments, the inflow pipe may be flexible and mounted such that it remains at the waterline if the waterline moves.

• A skimmer system may have a mesh basket that travels cross stream in front of the underflow baffle with an opening partially above and partially below the waterline, so that floating particulates at the waterline are scooped into the mesh basket. At the end of the travel, the mesh basket may lift the collected particulates into a container.

[0037] In apparatus of the present invention, at least one underflow baffle has antivortex features to reduce formation of vortices at the upstream face of the underflow baffle. The antivortex features comprise one or more of the following: i. The bottom edge of the underflow baffle is beveled at an angle from 15° to 60° from horizontal in the downstream direction, with the higher side of the bevel on the upstream face and the lower side of the bevel on the downstream face; or ii. The underflow baffle has vortex dampeners, which are plates that are fixed to and extend from each corner formed by the underflow baffle and the side walls below the waterline on the upstream face of the baffle, wherein the vortex dampeners (1) are each independently oriented from 0° to 30° from horizontal; (2) are each independently located from 0.3 D to 1.0 D below the waterline; (3) each independently extend at least 0.2 D upstream from the underflow baffle; and (4) each independently extend crossstream from the sidewall for at least 10 percent of the width of the channel, wherein D is the depth from the waterline to the bottom of the underflow baffle; or iii. The underflow baffle has a shelf below the waterline that is fixed to the upstream face of the baffle and extends cross stream to both side walls, wherein the shelf (1) is oriented from 0° to 30° from horizontal; (2) is located from 0.5 to 1.0 D below the waterline; (3) extends at least 0.25 D upstream from the underflow baffle, wherein D is the depth from the waterline to the bottom of the underflow baffle.

[0038] A single underflow baffle may have one, two or all three of the antivortex features.

[0039] In apparatus that have more than one underflow baffle, one or multiple or all underflow baffles may have antivortex features. In some embodiments, at least the most upstream underflow baffle has an antivortex feature. In some embodiments the multiple underflow baffles may have the same antivortex feature(s), and in some embodiments the underflow baffles may have different antivortex feature(s).

Beveled Edge

[0040] In some embodiments of the antivortex feature, the bottom edge of the underflow baffle is beveled at an angle of 15° to 60° from horizontal in the downstream direction, with the higher side of the bevel on the upstream face and the lower side of the bevel on the downstream face. The beveled edge is illustrated in Figure 3 a, in which angle 0 shows the angle of the beveling from horizontal.

[0041] In some embodiments, the angle of the bevel (0) is at least 20° or at least 25° or at least 30° from horizontal. In some embodiments, the angle of the bevel (0) is at most 55° or at most 50° or at most 45° from horizontal.

[0042] In some embodiments, the bevel is an essentially straight line. In some embodiments, the bevel has a convex curve. In some embodiments with a convex bevel, the bevel is tangential to the vertical at the upstream face of the baffle and tangential to the horizontal at the downstream face of the baffle. For a convex bevel, the angle of the bevel (0) is the angle from the start of the bevel on the upstream face to the end of the bevel on the downstream face of the baffle.

[0043] In some embodiments in which the apparatus contains more than one underflow baffle, the bottom edges on more than one underflow baffles are beveled, or the bottom edges on all underflow baffles in the apparatus are beveled. When the apparatus contains more than one underflow baffle with beveled edges, the angles of beveling on each baffle may be the same or may be different.

[0044] In some embodiments, the top edges on one or more overflow weirs are beveled at an angle of 15° to 60° from horizontal in the downstream direction, with the lower side of the bevel on the upstream face and the higher side of the bevel on the downstream face. The beveled edge on the overflow weir(s) is illustrated in Figure 3b, in which angle cp shows the angle of the beveling from horizontal.

[0045] In some embodiments, the angle of the bevel on the top edge of the overflow weir(s) (cp) is at least 20° or at least 25° or at least 30° from horizontal. In some embodiments, the angle of the bevel (cp) is at most 55° or at most 50° or at most 45° from horizontal. In some embodiments, the apparatus contains multiple overflow weirs with beveled edges. When the apparatus contains more than one overflow weir with beveled edges, the angles of beveling on each weir may be the same or may be different. As with underflow baffles, some embodiments of the bevels on overflow weirs are essentially straight, and some embodiments of the bevels have a convex curve. [0046] Without intending to be bound, we hypothesize that the beveled bottom edge of the underflow baffles smooths the flow of water as it moves down in front of the baffle and under the baffle, reducing vortices in front of the baffle. In particular, vortices initiated on the bottom edge of the baffle are reduced. The reduction of vortices reduces floating particulates that are drawn under the baffle.

Vortex Dampeners

[0047] In some embodiments of the antivortex feature, the underflow baffle has vortex dampeners in the comers formed by the underflow baffle and the side walls. The vortex dampeners are located below the waterline on the upstream face of the baffle. The vortex dampener is a plate. In some embodiments, the vortex dampener is solid. An example of vortex dampeners is illustrated in Figure 4.

[0048] The vortex dampeners are each independently oriented from 0° to 30° from horizontal. In some embodiments, the vortex dampeners are no more than 20° or no more than 10° from horizontal. In some embodiments, the vortex dampeners are essentially horizontal (0° from horizontal).

[0049] It is convenient to express the size and location of the vortex dampeners in terms of the unit D, which is the distance from the waterline to the bottom of the underflow baffle. The vortex dampeners are each independently located from 0.3 D to 1 D below the waterline. In some embodiments, the vortex dampeners are each independently located at least 0.5 D or at least 0.6 D or at least 0.75 D below the waterline. In some embodiments, the vortex dampeners are each independently located at most 0.85 D or at most 0.8 D below the waterline.

[0050] The vortex dampeners extend at least 0.2 D upstream from the underflow baffle. In some embodiments, the vortex dampeners each independently extend at least 0.25 D or at least 0.35 D or at least 0.5 D upstream from the underflow baffle. In some embodiments, the vortex dampeners each independently extend at most 1 D or at most 0.75 D upstream from the underflow baffle.

[0051] The vortex dampeners each independently extend cross-stream from the sidewall to a distance at least 10 percent of the width of the channel. In some embodiments, the vortex dampeners each independently extend cross-stream from the sidewall to a distance at least 15 percent or 20 percent of the width of the channel. There is no maximum distance that the vortex dampeners should extend cross-stream from the sidewall; in some embodiments, the vortex dampeners can form a single shelf extending from one sidewall to the other. However, in some embodiments, there may be little value in extending each vortex dampener cross-stream from the sidewall to more than 30 percent or more than 25 percent of the width of the channel.

[0052] In some embodiments the vertical edge of the vortex dampener is squared, and in some embodiments the vertical edge of the vortex dampener is beveled. A beveled edge may be beveled toward the top side of the vortex dampener, or toward the bottom side of the vortex dampener (as illustrated the side view in Figure 4), or toward both sides to form a point facing the water. The bevel may be straight or convex (as illustrated in the side view in Figure 4) or concave.

[0053] The comers on each vortex dampener may form a 90° corner or a different angle or may be rounded (as illustrated the top view in Figure 4).

[0054] In some embodiments in which the apparatus contains more than one underflow baffle, more than one underflow baffle has vortex dampeners, or all underflow baffles have vortex dampeners. When the apparatus contains more than one underflow baffle with vortex dampeners, the size, location and orientation of vortex dampeners on each baffle may be the same or may be different.

[0055] In some embodiments, the underflow baffle has only one vortex dampener in each corner of the upstream face. In some embodiments, the underflow baffle has two or more vortex dampeners in each corner of the upstream face.

[0056] Without intending to be bound, we hypothesize that the vortex dampeners form horizontal vortices close to the water surface in the upstream corners of the underflow baffle; these horizontal vortices reduce the formation and intensity of vertical vortices formed on the water surface in the upstream corners of the underflow baffle, and thus reduce the ability of the vertical vortices to draw floating particulates down to a level where the particulates can be carried below the underflow baffle.

Upstream Shelf

[0057] In some embodiments of the antivortex feature, the underflow baffle has a shelf below the waterline. The shelf is fixed to the upstream face of the underflow baffle and extends crossll stream to both side walls. In some embodiments, the shelf is solid, and in some embodiments, it is perforated or a mesh. Examples of the shelf are illustrated in Figures 5(a) and (b).

[0058] The shelf is oriented from 0° to 30° from horizontal. In some embodiments, the shelf is no more than 20° or no more than 10° from horizontal. In some embodiments, shelf is essentially horizontal (0° from the horizontal plane of the channel).

[0059] It is convenient to express the size and location of the shelf in terms of the unit D, which is the distance from the waterline to the bottom of the underflow baffle. The shelf is located from 0.5 D to 1 D below the waterline. In some embodiments, the shelf is located at least 0.6 D or at least 0.7 D below the waterline. In some embodiments, the shelf is located at most 0.9 D or at most 0.8 D below the waterline.

[0060] The shelf extends at least 0.25 D upstream from the underflow baffle. In some embodiments, the shelf extends at least 0.3 D or at least 0.4 D or at least 0.6 D or at least 0.7 D upstream from the underflow baffle. In some embodiments, the shelf extends at most 1.3 D or at most 1.2 D or at most 1 D upstream from the underflow baffle.

[0061] The shelf extends cross-stream from one sidewall to the other sidewall. In some embodiments, the front edge is essentially straight in the cross-stream direction. In some embodiments, the front edge has a convex curve in the cross-stream direction. In some embodiments, the front edge may have a concave curve in the cross-stream direction, but too deep a curve may reduce the effectiveness of the shelf.

[0062] In some embodiments, the vertical edge of the shelf is squared (as illustrated in Figure 5) and in some embodiments it is beveled. A beveled edge may be beveled toward the top side of the shelf, or toward the bottom side of the shelf, or toward both sides to form a point facing the water. The bevel may be straight or convex or concave.

[0063] In some embodiments in which the apparatus contains more than one underflow baffle, more than one underflow baffle has a shelf, or all underflow baffles have a shelf. When the apparatus contains more than one underflow baffle with underwater shelves, the size, location and orientation of shelves on each baffle may be the same or may be different.

[0064] Without intending to be bound, we hypothesize that the shelf limits the depth that vortices can reach down the upstream face of the underflow baffle, which limits the ability of vortices to bring floating particulates to a level where they can be carried under the baffle. Ordinary Operation

[0065] In ordinary operation, water that contains floating particulates flows into inlet. In some embodiments, the floating particulates comprise plastic pellets having a size of 1 mm to 10 mm in each direction. [0066] The water flows through the channel until it encounters and flows under an underflow baffle. Examples of flow velocity are described previously.

[0067] At least some floating particulates are trapped near the upstream face of the underflow baffle. In some embodiments at least 90 percent of floating particulates are trapped at the upstream face, or at least 95 percent or at least 98 percent. The trapped floating particulates are removed from the water by the collection device. They are dewatered and are sent on for further processing. The removed water is optionally returned to the water stream upstream or downstream from the baffle.

[0068] The water that passes under the underflow baffle passes over an overflow weir. The water may optionally pass under more underflow baffles and over more overflow weirs. At the upstream face of each underflow baffle, trapped floating particulates are removed from the water as previously described.

[0069] Downstream of the last weir or baffle, the water flows or is pumped through the outlet.

In some embodiments, the apparatus removers at least 95% of the floating particulates before the water leaves the outlet, or at least 98% or at least 99% or at least 99.5% or at least 99.9%. Description of Drawings

[0070] Illustrative examples of the apparatus are shown in Figures 1 and 2. Illustrative examples of anti vortex features are shown in Figures 3, 4 and 5. Figure 6 illustrates two variations in how underflow baffles may be oriented.

[0071] Figure 1 illustrates the side view of an apparatus with a single underflow baffle. The apparatus has:

• A channel that has two end walls of the channel (16 and 17), floor (18), an inlet (11), and an outlet (14);

• A single underflow baffle (12);

• A single overflow weir (13); and

• A device (15) to collect floating particulates trapped at the front of the underflow baffle. The sidewalls of the channel are not illustrated and are perpendicular to the viewpoint.

Water flows from the inlet to the outlet in the direction shown and forms a waterline. The underflow baffle and the overflow weir have a beveled edge as described for this invention. The depth from the waterline to the floor of the channel (H) and the depth from the waterline to the bottom of the underflow baffle (£)) are identified.

[0072] Figure 2 illustrates the side view of an apparatus of the present invention with two underflow baffles. The apparatus has: • A channel that has two end walls of the channel (27 and 28), floor (29), an inlet (21), and an outlet (24);

• Two underflow baffles (22 and 25);

• A single overflow weir (23); and

• Two devices (26 and 27) to collect floating particulates trapped at the front of the underflow baffles.

Water flows from the inlet to the outlet in the direction shown and forms a waterline. The underflow baffles and the overflow weir have a beveled edge as described for this invention.

[0073] Figure 3(a) illustrates the bottom of an underflow baffle (31) having a straight beveled edge (32). The higher side of the bevel is on the upstream face of the baffle and the lower side of the bevel is on the downstream face of the bevel . The bevel forms an angle (0) from horizontal. Figure 3(b) illustrates the top of an overflow weir (33) having a straight beveled edge (34), as may optionally be used in the present invention. The lower side of the bevel is on the upstream face of the baffle and the higher side of the bevel is on the downstream face of the bevel . The bevel forms an angle (cp) from horizontal.

[0074] Figure 4 illustrates a side view and a top view of an underflow baffle (41) that has vortex dampeners (42) on the upstream face of the baffle. The width of the channel is illustrated. [0075] Figure 5(a) illustrates an underflow baffle (51) that has a horizontal shelf (52) attached to its upstream face. Figure 5(b) illustrates an underflow baffle (53) that has a tilted shelf (54), which forms an angle (p) from horizontal, attached to its upstream face.

[0076] Figure 6(a) illustrates an underflow baffle (61) that has an essentially vertical orientation. Figure 6(b) illustrates an underflow baffle (62) whose orientation is tilted from vertical in the upstream position.