Patent Application
20120134748
The present invention relates to an erosion barrier wastewater treatment system and in particular to a liner for a wastewater treatment lagoon. The lagoon may be any earthen basin for containing a body of water, for instance wastewater, and the liner is utilized mainly for reducing the erosion of the lagoon walls due to water turbulence.
Conventional lagoon based wastewater treatment systems rely generally on open air lagoons to permit aerobic and anaerobic treatment of wastewater. A lagoon is any earthen basin for containing a body of water, such as a treatment reactor cell. Lagoons and other wastewater treatment ponds or basins are typically constructed by excavating land to create a reservoir area. If desired, berms can then be built around the perimeter of the reservoir area to extend the walls of the reservoir above ground level. Quite often, a lagoon is lined with a layer of clay to serve as a barrier. For example, environmental regulations typically require a subgrade clay layer of uniform thickness, for example 5 feet thick and having uniform water content. Often times a plastic liner made of high-density polyethylene may be placed over the entire interior surface defined by the reservoir and the berm area. The liner is made of sheet strips of high density polyethylene (HDPE) which overlap in an abutting fashion and are then welded or cemented together to create a water impermeable and erosion control line.
Once the lagoon is constructed and lined the wastewater liquid or sludge material is then pumped into the lagoon on top of the liner and/or the clay which is lining the lagoon. This liner facilitates not only maintaining the wastewater in the reservoir or lagoon but also in maintaining any turbulent water flow in the surface from eroding the berm and banking of the lagoon. The lagoon or pond is the subject to water fluid level changes as well as a turbulence of the surface in particular from aeration of the wastewater which can erode the banking and the berm. The liner is instrumental in protecting the underlying clay and soil lining forming the lagoon particularly where the turbulent water contacts the berm and banking.
Lagoon based water treatment systems require a large amount of space, on the order of several acres and often necessitate the large interior encompassing liner in conjunction with the lagoon construction to facilitate containment of the wastewater and to prevent erosion of the banking around the lagoon. This is tremendously expensive where an entire lagoon system must be covered with a liner, not only upon initial construction but upon replacement or fixing of a compromised liner.
Such traditional lagoon-based liner systems have several shortcomings. Because of the large size of the liners where the liners cover the entire interior of the lagoon, the liners which are generally impermeable material must be constructed on-site usually in large strips, where the strips are heat sealed together along their edges after being placed in an empty a lagoon. This of course means that the lagoon must be emptied and cannot be used for the time period in which the new liner material is placed inside. It is tremendously labor intensive, time-consuming and expensive to assemble such liners and empty the lagoons if a liner needs to be fixed or replaced.
The liner system of the present invention is a significant savings in material and man-hours to implement because the lagoon does not need to be drained, or operation even interrupted in most cases to construct and implement the erosion liner system. The liner is in effect a skirt which entirely surrounds the lagoon but does not need to extend and cover throughout the entire interior surface area of the lagoon. However, it is to be appreciated that the liner may extend to any length necessary to cover an interior surface as required. The skirt may be placed around the outside edge, banking and berm of the lagoon so that the there is no down time for the wastewater treatment facility. Also, the panels of the skirt may be fit together by a simpler less labor intensive means because all the edges do not have to be sealed between all the panels such as in the prior art liners.
In general the skirt is manufactured in manageable sections for instance in 50×20 foot rectangular sections which can be manufactured off-site, brought to the site and connected together along their edges with stainless steel bolts. The side edges of each section do not need to be entirely sealed because the skirt is concerned mainly with preventing erosion and ensuring that such erosion does not occur along the top of the lagoon wall where turbulence from aeration or other mechanical processes to the wastewater may erode the lagoon banking or berm.
Several embodiments of the present invention will now be described by way of example only, with reference to the accompanying drawings in which:
In primary treatment 120 the wastewater generally flows into large tanks called clarifiers, or sedimentation tanks, and these are used to initially settle sludge and to allow grease and oil accumulating on the surface where it can be skimmed off. The primary treatment 120 can include settling tanks equipped with the mechanically driven scrapers to drive the sludge towards a hopper in the base of the tank and skimmers at the surface for collecting the grease and oil, often times referred to as sapofication.
The wastewater is then transferred generally via a pump to a secondary treatment process 130 which often entails a lagoon or pool where most conventional water treatment facilities use aerobic biological processes to break down the biological materials in the wastewater. These aerobic processes require sufficient oxygen and food so that this aeration can take place for example in the lagoon. The aerators are often motor driven aerators floating on the surface of the wastewater in the lagoon. This aeration often causes a significant turbulence on the surface of the water which then of course propagates outwards to the edges of the lagoon. Over time this turbulence if significant can wear away the banking and berm potentially compromising the lagoon. The liner and fasteners described in further detail below ensures that such turbulence does not erode the banking of the lagoon and that installation of this device does not impact the operation or efficiency of the lagoon.
An aerator 32 may be positioned in the lagoon 10 to supply oxygen to the wastewater 22. An ample oxygen supply in a wastewater lagoon is the key to rapid and effective wastewater treatment. Oxygen is needed by the bacteria to allow their respiration reactions to proceed rapidly. The oxygen is combined by the bacteria with carbon to form carbon dioxide. Without sufficient oxygen being present, bacteria are not able to quickly biodegrade the incoming organic matter. In the absence of dissolved oxygen, degradation must occur under septic conditions which are slow, odorous and yield incomplete conversions of pollutants. Under septic conditions without aeration, some of the carbon will react with hydrogen and sulfur to form sulfuric acid and methane. Other carbon will be converted to organic acids that create low pH conditions in the ponds and make the water more difficult to treat. For example, treated ponds designed to biodegrade wastewater pollutants without oxygen often must hold the incoming sewage for six months or longer to achieve acceptable levels of pollution removal. This is because the biodegradation of organic matter in the absence of oxygen is a very slow kinetic process.
Motor driven, mechanical aerators provide a combination of liquid aeration and mixing. Some mechanical aerators produce the gas-liquid interface by entraining air from the atmosphere and dispersing it into bubbles. Other types disperse liquid in the form of droplets or they produce jets or thin films as a spray that contact the ambient air. Some other types even generate both liquid droplets and air bubbles. Mechanical aerators create turbulence on the surface of the pond, this turbulence is beneficial in that turbulence facilities gas-liquid interface however, the turbulence has consequential side effects where the turbulence reaches to the banking and berms of the lagoon and creates erosion where no liner is utilized. Until now, the only solution to such erosion has been to ameliorate the effects by using a full lagoon liner as shown and described in
Turning to
Along the entire bottom edge 34 of the panel 30 is a pocket 40 sewn into the panel by overlapping the lowermost edge of the panel on itself and sewing the lowermost edge along a stitch line 41 to define the pocket 40. The overlap of the lowermost edge 34 can be in the range of about 1-3 inches so that the pocket 40 can accommodate a ½ to 1 inch chain or other ballast 42 inserted into the pocket 40 along the entire bottom edge 34 of the panel. The chain or ballast 42 is stretched through the pocket 40 so that the weight of the chain 42 is essentially uniform along the length of the panel 30 and so that the panel lies evenly and uniformly along the berm 18 and banking 16 of the lagoon 10 as described in further detail below. The reinforcing nylon webbing 44 at the bottom edge of the panel 30 is, in one embodiment, sewn in conjunction with the stitch line 41 which defines the overlap and joining of the lowermost edge of the panel 34 to the panel to define the pocket 40. Thus the pocket 40 actually hangs below the nylon webbing 44 at the bottom edge 34 of the panel 30. This arrangement of the lower reinforcing nylon webbing 44 is important because the panel 30 is most susceptible to failure along the stitch line 41 which defines the pocket 40. While there is some potential wear of the panel 30 material along the pocket portion of the panel 30, a hole or abrasion here which exposes the chain or ballast 42 will not cause failure of the panel 30. On the other hand failure of the stitching along the pocket 40 can compromise the entire pocket 40 and permit the chain or ballast 42 to fall entirely out of the pocket.
It is to be appreciated that lagoons may be of any size and shape, but are generally circular, square or rectangular. The size and shape of different lagoons may determine the specific size and shape of the panels used in a certain lagoon. For example as seen in
An alternative panel shape shown in
Separate panels are secured together along adjacent side edges by overlapping the side edges and aligning the respective grommets and holes in the adjacent panels. One manner of securing the side edges is the insertion of a bolt through each aligned hole and securing of the bolt in the hole by a nut. The bolt head and nut of course being larger than the hole in the side edge of the panel. Other methods of fastening the aligned side edges of the panels such as with clips or other fasteners are also contemplated.
It is an important aspect of the present invention that the liner system and panels can be placed in position and into operation without having to interrupt operation of the wastewater treatment system and lagoon. Because, while it is to be appreciated that the panels may extend to any length within the lagoon, the panels do not need extend entirely across and along the bottom of the lagoon, the entire circumferential ring of panels can be assembled around the edge of the lagoon and placed into position in the lagoon while the treatment plant or system continues to operate.
In
An embodiment of panel dimensions is shown in
In this way an erosion control lagoon liner can be constructed and implemented inexpensively and without interruption of facility operation for installation of the device. Additionally, a single panel can be easily replaced by disengaging the side edges removing the panel and replacing with a similar replacement panel, all without interruption of facility operation. One embodiment of the liner and panels involves the use of 3028 XR5® material a highly resistant, non-degradable membrane surface with extreme puncture and tear resistance as well as dimensional stability under high loads and extreme temperature fluctuations. Other containment and liner materials can be used as well.
The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.
