Patent Application
20170252673
This invention concerns wastewater treatment plants, particularly clarifiers, and is directed to an improved clarifier launder construction that eliminates algae buildup and the need for algae sweeps, launder covers or frequent cleaning.
Clarifier launders typically are formed by a shelf of concrete, L-shaped in cross section and integral with the wall, on the inside or the outside of the clarifier wall. They can also be of other materials such as steel or FRP (fiberglass reinforced plastic). If inside, the conventional launder provides with its vertical leg a weir for overflow of effluent liquid into the launder with a weir plate attached to the top of the vertical leg. In an external concrete launder the top edge of the clarifier with weir plate attached provides the overflow weir.
Algae growth is a recurrent problem in conventional clarifier effluent launders. The launders are exposed to daylight, promoting algae growth, and must be cleaned frequently to remove the algae growth. Sometimes effluent launder algae sweeps have been installed, at significant capital and operational costs. Without these sweeps, plant operators must frequently clean the launders. In some cases effluent launder covers have been used to eliminate light and prevent algae growth.
The following documents have some relevance to the current invention: U.S. Pat. Nos. 8,220,644, 8,083,075, 7,416,662, 7,243,802, 6,712,222, 6,193,888, 5,597,483, 5,252,205, 5,277,077, 4,059,529 and 4,009,106, U.S. Pub. No. 2012/0248036 and British Patent No. GB 2115304. Of these references, U.S. Pat. No. 8,220,644, shows a somewhat typical inboard launder construction with density current baffle and scum baffle.
The present invention differs from previously known solutions to these problems by eliminating costs associated with effluent launders, weir plates and scum baffle plates, launder covers and/or algae sweeps. The current design requires fewer components to perform the same functions, while also eliminating the problem of algae buildup that required periodic cleaning of the launders by plant operators or continual cleaning by algae sweeps installed in the launders.
In one preferred form the submerged effluent launder of the invention comprises a modified density current baffle. A density current baffle in conventional construction is typically attached to the clarifier tank wall about one-half to two-thirds of the side water depth from the tank floor or to the bottom corner of the launder. In conversion of the density current baffle to a submerged effluent launder in this embodiment of the invention, the inwardly/downwardly angled density current baffle is extended and elevated such that the highest point of the angled plate is attached to the tank wall below the clarifier liquid level. A vertical mounting plate at top of the angled plate extends up to or above liquid level and is attached to the wall. Also, the density current baffle is modified by adding a horizontal shelf that extends from the clarifier tank wall to the inside of the density current baffle, thus defining a triangular cross section submerged effluent launder. Orifices are formed in the angled wall of the density current baffle, at an elevation below the liquid level and preferably just above the horizontal shelf of the submerged launder. The submerged effluent exit minimizes or eliminates sun exposure and prevents algae growth.
In another embodiment a clarifier with existing internal launder is modified by removing the vertical leg of the L-shaped launder, and the remaining shelf becomes the bottom horizontal leg of the triangular cross section launder as described above. Brackets secure the angled launder top/density current baffle to the clarifier wall at top and to the edge of the shelf.
The submerged effluent launder operates hydraulically as a substantially or completely full conduit, with liquid level in the clarifier controlled by monitoring plant influent flow rate or monitoring liquid level in the clarifier and controlling the level by an automatic weir elsewhere in the launder, or by an automatic valve in the effluent pipe. For all iterations of the submerged effluent launder a level monitoring/control system must be in place. An example of this is by monitoring the flow into the clarifier and adjusting an effluent weir or valve. Another example of this is to have sensors monitoring the liquid level that again would adjust an effluent weir or valve to control water level elevations.
Accordingly, the submerged clarifier launder of the invention can be in several forms, some of which involve an existing internal launder and others not, such as in new construction. One embodiment employs a submerged pipe with openings that admit effluent, the pipe secured to a mounting structure that includes a density current baffle. The need for a scum baffle is eliminated in most cases, in that the liquid exits not over a weir but via submerged openings into the launder, while scum remains on the liquid surface.
Significant construction and maintenance costs are eliminated with the submerged clarifier launder embodiments of the invention, and the algae buildup problem is overcome. These and other objects, advantages and features of the invention will be apparent from the following description of a preferred embodiment, considered along with the accompanying drawings.
The plate 24 preferably comprises an integral plate that includes a downwardly/inwardly sloping density current baffle 30, as shown. Proportions can be different than illustrated in
The plate unit 24 extends around the entire periphery of the clarifier, assembled in sections. It is attached via integral vertical and horizontal plates indicated at 34 and 36, to the wall and shelf of the clarifier, using bolts such as indicated at 38 and 40. Access to the shelf bolt 40 would be difficult or impossible, but effluent holes into the launder are provided through the plate at 42. These can be, for example, two inch diameter holes through the plate, approximately two to three inches above the shelf, spaced at 30 inches from hole to hole. Each shelf bolt 40 is at the same position as the effluent hole 42, so that tool access to the bolt 40 is provided, for securing the brackets 36.
Preferably a vent hole is included near the top of the plate, approximately at the position 44 shown in the drawing, so that rising of the liquid level inside the launder will not be inhibited. In addition, the vent hole(s) will assist in draining the launder when clarifier is taken down for servicing.
As indicated in
A series of liquid entry orifices 68 in the unit 60 are positioned just below the existing shelf 16 or at a level as desired in the launder unit. These orifices also serve as vents to facilitate draining when needed for service.
The conduit or pipe 70 has orifices positioned as desired, such as at locations indicated at 74 (which can be about 2 inch diameter) in
This embodiment includes a density current baffle 76, similar to those discussed above, but the baffle 76 is a part of a mounting structure 78 for the pipe 70. This structure 78 preferably is continuous from the clarifier wall 80 to the lower end of the baffle 76, for function as a density current baffle, which should not allow throughflow except that vents can be included at the top of the density current baffle (near the wall 80) to prevent gas buildup. This structure is secured to the clarifier wall by bolts as indicated at 81, and includes or supports a pipe saddle 82 that firmly retains the pipe 70 to the mounting structure 78. One or more vent holes preferably are located at top of the pipe so that a rising level of liquid inside the launder will not be inhibited, and the vent will facilitate draining the launder pipe when taken down for service.
In this form of submerged launder, a gap may be provided between the pipe 70 and the angled platform structure 78, to allow the settling solids to pass through and slide down the angled platform 78.
In this form of submerged launder of the invention a top plate 86 is affixed at the top of the existing launder as shown, in sealed relationship. Typically neoprene material is engaged between the cover 86 and the existing concrete surfaces (and the same or similar sealing material can be used for sealing purposes in the earlier-described embodiments). The plate preferably is angled as shown, declining inwardly so as not to trap rain, etc. The top plate 86 forms a closed conduit, i.e. a fully or partly submerged effluent launder, preferably positioned about at or close to the liquid surface 22 in the clarifier. At least part of the launder must be submerged. As shown, the added plate 86 can have vertical plates, preferably integral, at both inner and outer sides. At the outer side is a continuous plate or flange 88 that engages with the tank wall 12, for bolting at intervals to the wall, and at the inner side is a depending plate 90 that laps over and against the existing concrete launder leg 59. This vertical plate 90 provides a closure, provides for affixing the top plate to the leg via bolts 91, and also acts an integral scum surface, i.e. a smooth surface for the skimming mechanism to ride against in order to efficiently remove scum from the surface. The preferred clarifier liquid level is indicated at 22, and the plate 90 preferably extends about four inches above the existing liquid level.
Effluent liquid enters the launder 85 via openings 92 through the vertical leg 59 as shown. These orifices can be about 2 inches in diameter, for example, formed by drilling, and spaced apart at appropriate intervals such as every 2 to 3 feet, depending in part on orifice size. The depth location of the orifices 92 can vary, and the orifices could be through the bottom 16, but that is not preferred.
The plate or flange 88 at the upper/outer end of the sloped top cover 86 provides for mounting that side of the cover plate 86 to the clarifier wall 12 (with bolts 94). A vent orifice 96 can be formed (at intervals) through the plate 86 near the upper side, the orifice oriented at an angle (up and to right in the drawing) so that any sunlight will only enter high in the launder. A downwardly extending vertical plate 98 can be included, extending down against the wall 12, for any sunlight contact. The plate if a smooth surface of FRP discourages algae growth.
In this embodiment the launder 85 will typically be partially submerged in the clarifier, not fully. The liquid level in the clarifier (and in the launder) can be about as shown so that the surface 90 acts as a scum cleaning surface. In all forms of the invention the launder is fully or partially submerged. The forms shown in
Note that the
The submerged pipe launder 102, as shown in
The open channel 108 has another purpose as well; the maximum design liquid level is shown at 22 in the drawing, with the sides of the open channel 108 being an inch or two higher than the maximum liquid level. This provides an overflow to withdraw clarifier water in the event of a failure in the system, such as failure of the valve 106 (which is an automatically controlled valve) to allow the proper amount of effluent out of the clarifier. The clarifier liquid level will then rise beyond the design level 22, but would flow into the open channel 108 for withdrawal.
It should be understood that the effluent viewer channel 108 can be provided outside the clarifier instead of inside the clarifier, and can be included with the other embodiments. For example, an open channel such as that shown at 108 can be just outside the clarifier tank wall, receiving effluent that has been collected any of the launders described. The open channel allows inspection such as by an operator on the top of the tank wall. An automatic control valve can be downstream of the open channel, and if that level control valve should fail, the open channel, with its walls an inch or two above maximum design liquid level, would overflow outwardly. A basin below the channel can catch the overflow and can conduct it through a pipe to join the rest of the effluent, at a lower elevation. Note that if the viewer channel is not to serve also as an emergency overflow weir, it can have a removable cover, or it could be covered but with an openable viewing port.
The several embodiments of submerged clarifier launders described above eliminated algae problems, the cost of cleaning or algae sweeps, and reduce capital expense in forming a conventional clarifier launder in a newly-constructed clarifier.
The above described preferred embodiments are intended to illustrate the principles of the invention, but not to limit its scope. Other embodiments and variations to these preferred embodiments will be apparent to those skilled in the art and may be made without departing from the spirit and scope of the invention as defined in the following claims.
