Abstract:
A level control device for constructed wetlands which is suitable for use in cold climates. The device comprises an outer casing with an inner diameter at least about 4 inches and less than about 18 inches with an overflow weir, in fluid communication with the constructed wetland, located inside the outer casing.

Description:
FIELD OF THE INVENTION 
     This invention relates to constructed wetlands that are used to treat wastewater, more particularly, for the control of the water level of such wetlands. 
     BACKGROUND OF THE INVENTION 
     Constructed wetlands are artificial wastewater treatment systems consisting of shallow (usually less than 1 m deep) ponds or channels which have been planted with aquatic plants, and which rely upon natural microbial, biological, physical and chemical processes to treat wastewater. They typically have impervious clay or synthetic liners, and engineered structures to control the flow direction, liquid detention time and water level. Depending on the type of system, they may or may not contain an inert porous media such as rock, gravel or sand. 
     Constructed wetlands have been used to treat a variety of sources of wastewater including urban runoff, municipal, industrial, agricultural and acid mine drainage. While some degree of pre- or post-treatment may be required in conjunction with the wetland to treat wastewater to meet stream discharge or reuse requirements, the wetland will be the central treatment component. 
     For some applications, wetlands are an excellent option because they are low in cost and in maintenance requirements, offer good performance, and provide a natural appearance, if not more beneficial ecological benefits. However, because they require large land areas, 4 to 25 acres per million gallons of flow per day, wetlands are not appropriate for some applications. Constructed wetlands are especially well suited for wastewater treatment in small communities where inexpensive land is available and skilled operators are hard to find. 
     Constructed wetlands have been classified by the literature and practitioners into two types. Free water surface (FWS) wetlands (also known as surface flow wetlands) closely resemble natural wetlands in appearance because they contain aquatic plants that are rooted in a soil layer on the bottom of the wetland and water flows through the leaves and stems of plants. Vegetated submerged bed (VSB) systems (also known as subsurface flow wetlands) do not resemble natural wetlands because they have no standing water. They contain a bed of media (such as crushed rock, small stones, gravel, sand or soil) which has been planted with aquatic plants. When properly designed and operated, wastewater stays beneath the surface of the media, flows in contact with the roots and rhizomes of the plants, and is not visible or available to wildlife. 
     The term “vegetated submerged bed” is used herein instead of subsurface flow wetland because it is a more accurate and descriptive term. Some VSBs may meet the strict definition of a wetland, but a VSB does not support aquatic wildlife because the water level stays below the surface of the media, and is not conducive to many of the biological and chemical interactions that occur in the water and sediments of a wetland with an open water column. VSBs have historically been characterized as constructed wetlands in the literature, and so they are included in this application. 
     Constructed wetlands were first developed in the relatively warm climate of Tennessee. As use of these constructed wetlands spread northwards, concerns arose over the possibility of the wetlands freezing thereby disabling the water treatment system. The largest concern is that the level control system will freeze thereby flooding the wetland. Solutions that have been tried to maintain the function of a wetland during cold temperatures include massive amounts of insulation and/or provision of heating elements to maintain the temperature of the level control device. Grove et al. (U.S. Pat. No. 5,951,866) discloses a cold climate wetland wastewater treatment system in which the hydraulic level control structure is positioned entirely within the rear end of the containment area. These solutions add to the expense of the wetlands wastewater treatment system and the inconvenience of servicing the wetlands. 
     Therefore, it would be desirable to have a wetlands level control device that solves the aforementioned problems. 
     SUMMARY OF THE INVENTION 
     The present invention provides an improved level control device for wetland wastewater treatment facilities that overcomes the aforementioned problems. The device comprising: an outer casing with an open top, the outer casing having an inner diameter at least about 4 inches and less than about 18 inches; an overflow weir in fluid communication with the constructed wetlands, wherein the overflow weir is located within the outer casing; a cap removably attached in a closing position over the open top of the outer casing; and an outlet in fluid communication with the overflow weir wherein the outlet provides a fluid flow path through the outer casing. 
     An improved device for controlling the level of a constructed wetlands wastewater treatment system, the device comprising: an outer casing with an open top, the outer casing having an outer surface and an inner surface and an inner diameter at least about 4 inches and less than about 18 inches; an overflow weir comprising an overflow pipe in fluid communication with the constructed wetlands, wherein the overflow pipe is located within the outer casing and has an outer diameter at least about 2 inches less than the inner diameter of the outer casing; a cap removably attached in a closing position over the open top of the outer casing; and an outlet in fluid communication with the overflow weir wherein the outlet extends through the outer casing from the inner surface to the outer surface providing a fluid flow path through the outer casing. 
    
    
     Various other features, objects and advantages of the present invention will be made apparent from the following detailed description and the drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Preferred embodiments of the invention are described below with reference to the following accompanying drawings, which are for illustrative purposes only. Throughout the following views, reference numerals will be used in the drawings, and the same reference numerals will be used throughout the several views and in the description to indicate same or like parts. 
     In the drawings: 
     FIG. 1 shows a section view of a prior art flow control device for wetlands wastewater treatment. 
     FIG. 2 shows a section view of the level control device of one embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In the following detailed description, references made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that structural changes may be made without departing from the spirit and scope of the present invention. 
     FIG. 1 shows a wetlands with a typical prior art water level control device. Water floods wetlands  1  and is discharged via wetlands drainage pipe  5  which is often embedded in cobbles  3 . Wetlands drainage pipe  5  passes under a berm  11 . Drainage pipe  5  is supported by pea gravel  7  and protected from the cold by rigid insulation  9  and the earth in berm  11 . The level of water in wetlands  1  is controlled by level control device  31 . Level control device  31  consists of a manhole casing  23  which is puddled into a concrete slab  27  and closed with a manhole cover  25 . In a typical prior art application, manhole casing  23  is at least two feet in diameter, frequently three to four feet in diameter. Manhole casing  23  is frequently four to six feet tall. Drainage pipe  5  enters level control device  31  and is connected to flexible hose  15  via rubber boot  13 . Typically, band clamps  17  fasten rubber boot  13  to drainage pipe  5  and flexible hose  15  to rubber boot  13 . Another stainless steel clamp  17  connects flexible hose  15  to chain  19 . Chain  19  is attached to hook  21  thereby holding the discharge end  33  of flexible hose  15  in the desired position. The height of the discharge end  33  may be adjusted by changing which link of chain  19  is attached to hook  21 . Water from the wetlands  1  flows through discharge pipe  5  and flexible hose  15  and discharges through the discharge end  33 . As such, the water level in wetlands  1  is the same as the height of discharge end  33 . Water outflowing from discharge end  33  pools on the concrete slab  27  and overflows through outlet pipe  29 . Similar to discharge pipe  5 , outlet pipe  29  is surrounded by pea gravel  7  and covered by rigid insulation  9 . 
     In typical installations drainage pipe  5 , flexible hose  15  and outlet pipe  29  are all at least three inches in diameter. These dimensions are typically regulated by state or local codes. 
     A number of common variations to level control device  31  are known in the prior art. In one such variation, rubber boot  13  and flexible hose  15  are attached to outlet pipe  29  rather than to wetlands drainage pipe  5 . In this variation, water from the wetlands fills manhole casing  23  up to the level of discharge end  33  of flexible hose  15 . The water then overflows into discharge end  33  of flexible hose  15  and passes out through outlet pipe  29 . 
     Another common variation of level control device  31 , rubber boot  13  is replaced with a rotatable 90° elbow. Flexible hose  15  is replaced with a rigid pipe and clamps  17 , chain  19  and hook  21  are eliminated. The water level is controlled by rotating the 90° elbow such that the discharge end of the rigid pipe travels upward or downward along a circular arc. 
     The prior art has made adaptations to level control device  31  in order to adjust to cold weather conditions. Such adaptations usually consist of heavily insulating manhole casing  23  and burying the casing  23  deep in berm  11 . Another such adaptation is to position level control device  31  within the wetlands  1  thereby using the water and vegetation of wetlands  1  for insulation. 
     FIG. 2 shows a preferred embodiment of the level control device of the current invention. Level control device  101  is positioned within a berm  103 . Level control device  101  consists of a casing  105  and a pipe cap  107 . Casing  105  and pipe cap  107  may be made out of any suitable material, preferably PVC (polyvinyl chloride) pipe. Rigid insulation  109  is installed around casing  105  and rigid insulation  111  is installed within pipe cap  107 . Preferably, pipe cap  107 , when attached in a closing position over the top of the casing  105 , forms a windproof seal. Casing  105  has a diameter ranging from about 4-18 inches, typically about 12 inches. Pipe cap  107  has a diameter corresponding to the diameter of casing  105 . The bottom of case  105  may be filled with grout  113 . Wetlands drainage pipe  115  enters casing  105  through a reducer  117 . In a typical application wherein the materials of construction are PVC, the reducer  117  and wetlands drainage pipe  115  are solvent welded at all connection services. Wetlands drainage pipe  115  extends upward through the center of casing  105  to an elevation  121 . Typically, wetland drainage pipe  115  is installed with its center line coincident with the center line of casing  105 , although this alignment is not critical. Elevation  121  is the same as the elevation of the liner (floor) of the wetland (not shown). Coupling  119  is affixed to overflow pipe  123 . Coupling  119  is slidably attached to wetland drainage pipe  115  at elevation  121 . The length of overflow pipe  123  defines a weir  131  which in turn defines the level of the wetland. The height of weir  131  may be adjusted by using different length overflow pipe  123 . Water discharging from the wetland overflows weir  131  into casing  105  and pools on the floor defined by grout  113  or reducer  117  The water in casing  105  overflows through a tee  125  into a outlet pipe  129 . Typically, the center line of outlet pipe  129  is coincident with the elevation  127  of the top of the sand within the wetland (not shown). Effluent from outlet pipe  129  typically flows to either another wetland cell or a disposal system (not shown). 
     The diameter of wetlands drainage pipe  115  and overflow pipe  123  is varied as desired or limited by ordinance. Typically, wetland drainage pipe  115  and overflow pipe  123  have the same diameters and the diameter ranges from about two inches to about six inches with a typical value of about four inches. The diameter of wetland drainage pipe  115  and overflow pipe  123  should be at least two inches less than the diameter of casing  105 . Again, any similar material of construction may be used for wetland drainage pipe  115  and overflow pipe  123  and coupling  119  but preferably, the material is PVC. 
     EXAMPLES 
     Several wetlands according to the present invention have been installed and are being operated within the State of Wisconsin. The level control devices are constructed out of PVC piping wherein the casing is 12″ schedule 40 PVC pipe and the wetlands drainage pipe and overflow pipes are 4″ schedule 40 PVC pipe. In the first installation, the State of Wisconsin required that a source of electrical power be available at the level control device in order to be able to install a heating device should the level control device freeze. This level control device surprisingly functioned throughout a Wisconsin winter without freezing and without requiring any external heat sources. Based on the successful operation of the first level control device, the State of Wisconsin allowed the second level control device to be installed without an electrical power source. The first installation is operating in a peak capacity of 5,900 gallons per day distributed through 4 cells each with a separate level control structure while the second installation operates at a peak capacity of 450 gallons per day. Both installations have been able to function throughout Wisconsin winters without freezing and without requiring external heat. 
     In comparison, a wetlands was constructed with accordance with the prior art as shown in FIG.  1 . Water within the flexible holes would freeze during the Wisconsin winters without external heat supplied by an electric heater installed within the casing. 
     In compliance with the statute, the invention has been described in language more or less specific as to structural and methodical features. It is to be understood, however, that the invention is not limited to the specific features shown and described, since the means herein disclosed comprise preferred forms of putting the invention into effect. The invention is, therefore, claimed in any of its forms or modifications within the proper scope of the appended claims appropriately interpreted in accordance with the doctrine of equivalents.