BI-PHASIC BIORETENTION SYSTEM

Inventors: Parwinder S. Grewal Edward L. McCoy Warren A. Dick Hanbae Yang

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This non-provisional patent application claims the benefit of priority to

U.S. Provisional Patent Application No. 61/045,974, filed April 18, 2008, which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

[0002] The disclosed embodiments of this application relate generally to the treatment of storm water runoff, and more particularly to the treatment of storm water runoff via bioretention systems.

BACKGROUND OF THE ART

[0003] Urban and suburban homeowners and business owners are increasingly interested in developing rain garden (bioretention) systems that can enhance the overall pleasant look of their landscapes. At the same time there is an increasing awareness of environmental stewardship. However, there is still a need for systems and methods that are aesthetically pleasing and efficient at cleaning storm water runoff. This and other unmet needs of the prior art are met by a system and device as described in more detail below.

SUMMARY OF THE INVENTION

[0004] Chemicals associated with, for example, transportation, lawn care and other activities, often make their way into urban/suburban storm-water runoff. Many of these chemicals have been found to be harmful to the environment and to humans, especially when concentrated in storm-water runoff. This contaminated

runoff makes its way into the groundwater supply, making treatment necessary. One potential approach to treating this runoff is a low impact rain garden. Rain gardens are small, landscaped storm-water bioretention areas that promote infiltration of "remediated" storm-water into the ground. Rain gardens have become increasingly popular in urban and suburban areas due to the fact that they are designed to reduce runoff quantity and improve water quality in a natural and aesthetically pleasing manner. In spite of the increasing use of rain gardens, they are often limited in the integration of hydrology, soil, plant, and microbial components to optimize water flow, groundwater recharge and pollutant removal. An embodiment of the present application provides a modified design of the rain garden system which increases both retention time and treatment efficiency of runoff pollutants by creating a novel anaerobic to aerobic sequence. [0005] Embodiments disclosed herein may be located in or adjacent to residential units, commercial buildings, and parking lots or roadsides in commercial and residential settings. Embodiments can be used as a total rain garden package for commercial use that will include design for storm-water flow control and pollutant removal.

[0006] The invention may be developed as a total rain garden package for commercial use that will include design for storm water flow control and pollutant removal. By creating a biphasic system in rain gardens, the hydrologic conditions (e.g. saturated and unsaturated conditions, water infiltration, and retention time) can be optimized to remove common pollutants such as hydrocarbons, nitrates, phosphorus and heavy metals from storm water runoff. Bioretention systems of the past utilize a single aerobic or anaerobic phase or an aerobic to anaerobic sequence in their bi-phasic system. However, unless specifically referring to systems of the

past, when used in this application, the terms "bi-phasic system," "bi-phasic bioretention conditions," and "novel bi-phasic system" refers to the sequence of anaerobic to aerobic conditions disclosed in this application. [0007] An anaerobic to aerobic sequence enhances biological degradation of many organic pollutants due to the fact that the bi-phasic bioretention conditions support a diversity of electron acceptors and environmental conditions, thus supporting a much wider range of degrading microorganisms than the aerobic to anaerobic sequences of conventional bioretention systems. Alternatively, this technology can be applied to design a system that will remediate a specific pollutant of interest at a specific site. The market for this invention is broad and includes individual residence to commercial/retail outfits to cities, and farms. [0008] Exemplary embodiments provide a method for effective treatment of storm-water runoff pollutants such as hydrocarbons, nitrates, phosphorus, and heavy metals using sediment filtration and adsorption, and biochemical processes under bi-phasic bioretention conditions. By integrating these pollution cleanup pro- usages into a single unit, this apparatus optimizes retention time of the runoff through the system and maximizes removal rates of runoff pollutants, resulting in more reliable and efficient treatment mechanism than previous systems.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] A better understanding of the exemplary embodiments of the invention will be had when reference is made to the accompanying drawings, wherein identical parts are identified with identical reference numerals, and wherein: [0010] FIGURE 1 is a plan view of an embodiment of the present system with the anaerobic zone positioned substantially in the center and the aerobic zone around it. The embodiment depicted in Figure 1 represents one arrangement for a

roadway rain garden. Figure 1 shows an outlet from the roadway to direct water from the roadway into a designated micropooling location in the bioretention system. [0011] FIGURE 2 is a cross-section view of the embodiment depicted in

Figure 1 showing an embodiment of the present system including plant life, the anaerobic zone A, the aerobic zone B, the reverse drainage system, and an optional overflow drainage pipe among others.

[0012] FIGURE 3 is a schematic of the embodiment depicted in Figure 1 including the anaerobic zone, the aerobic zone and the reverse drainage system. [0013] Figure 4 is an alternative embodiment of the system positioned adjacent to a roadway.

[0014] Figure 5 is a cross-section view of the embodiment illustrated in

Figure 4.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT [0015] Exemplary embodiments incorporate a sequence from anaerobic to aerobic conditions which enhance organic pollutant removal by microorganisms due to the fact that the bi-phasic bioretention conditions support a diversity of electron acceptors and environmental conditions, thus supporting a much wider range of degrading microorganisms. The embodiment shown in Figure 1 includes an anaerobic zone 200, an aerobic zone 300. The size (i.e., surface area and medium depth) of each zone is determined based on the drainage area and the desired runoff volume to be caught and treated. In this embodiment, the storm-water runoff is directed to a micropooling area 100 in the anaerobic zone by an influent pipe 110. [0016] Figure 2 further illustrates the composition of Figure 1 . In an embodiment, the anaerobic zone comprises plastic liners 2, drainage pipes (further illustrated in Figure 3), an underdrainage layer 3, a mulch layer 8, herbaceous

plants 9, and a mixture of sand, topsoil, and compost collectively 7. In the anaerobic zone, a first flush (1/2 to 1 in.) of the runoff is captured and remediated through sediment filtration and adsorption and/or anaerobic biochemical degradation of pollutants by creating water saturated conditions. The remediated water (overflow) from the anaerobic zone is directed into the aerobic zone 200 through reverse drainage pipes (alternatively depicted in Figure 3). In this way retention times within the anaerobic zone may increase, providing increased biochemical degradation opportunities.

[0017] The aerobic zone, 300, where the water may be further treated through sediment infiltration and adsorption, and aerobic biochemical processes, comprises an underdrainage layer 13, a mulch layer 18, herbaceous plants 19, and a mixture of sand, topsoil, and compost collectively 17. With a high infiltration rate (2 in/hr and above), aerobic conditions are maintained in this zone. The treated water may be discharged to the recharge zone and/or drainage system. Alternatively, the anaerobic zone may include an overflow treatment bypass 10. The overflow treatment bypass allows for quick drainage of either excess rainwater or remediated water from the anaerobic zone. The overflow treatment bypass will allow excess water to drain directly to the recharge and or drainage system in order to maintain aerobic conditions.

[0018] The reverse drainage system for transporting treated runoff from the anaerobic zone to the aerobic zone enables longer storage of storm-water runoff for more effective treatment of pollutants. Additionally, by setting up the level of reverse drainage pipes below the medium layer in the anaerobic zone, it decreases the formation of ponds on the top of the anaerobic zone. An exemplary embodiment may therefore reduce the opportunity for mosquitoes to breed (a common drawback

for many conventional bioretention systems). Moreover, the creation of bi-phasic bioretention conditions in the embodiment can mineralize many organic pollutants which cannot be mineralized in either condition alone. Furthermore, the system lends for the inclusion and replacement of growing media carrying specific pollutant degrading microorganisms.

[0019] Figure 3 is a schematic depiction of an embodiment of a novel bi- phasic bioretention system with the components of the anaerobic and anaerobic zones removed for illustration of an exemplary drainage system. In this embodiment, the anaerobic zone is in the interior and the aerobic zone is depicted as wrapping around the anaerobic zone on three sides, this depiction is not intended to limit the present application to this arrangement of anaerobic and aerobic zones, it is merely intended to illustrate one embodiment of the reverse drainage system. [0020] Initially, untreated storm-water runoff is directed into the anaerobic zone, it passes via gravity through the mulch layer 8 and the sand, topsoil and compost mixture 7. After passing through these layers, the runoff filters through a layer of inorganic aggregate material (such as sand or gravel) to reach at least one horizontal pipe 120 from the reverse drainage system running along the lower interior of the anaerobic zone. The horizontal pipes are positioned to allow water that has passed through the anaerobic zone to enter the reverse drainage system. The horizontal pipe is in communication with the at least one vertical pipe 130. The vertical pipes will reach from the horizontal pipes to a height at least above the top of the aerobic zone. The at least one vertical pipe may further include, at its peak, a second horizontal pipe 140, in communication with the vertical pipe. This second horizontal pipes serve to deliver the water from the vertical pipes to the aerobic zone. When the water level in the anaerobic zone increases and reaches the height

of the top of the at least one vertical pipe, the remediated water may then flow from the reverse drainage pipe into the aerobic zone. This configuration increases the time that runoff water spends in the anaerobic zone as only treated water passes through the reverse drainage system to reach the aerobic zone. Additionally, embodiments of the system may incorporate a bypass drainage pipe 210. The bypass drainage pipe is in communication with the anaerobic zone and allows excess water that has passed through the anaerobic zone to pass out of the system. [0021] After the runoff water has passed from the second horizontal pipe 140, it enters the aerobic zone. The water will then filter through the layers of the aerobic zone via gravity, being remediated as it falls. Much like the anaerobic zone, the aerobic zone has at least one horizontal pipe adjacent to the bottom of the zone. When the runoff water has been treated by passing through the layers of the aerobic zone it will again pass through a layer of inorganic aggregate material at the bottom of the aerobic zone. Once the water has passed through the aggregate it will enter another horizontal pipe 320 and out a final effluent pipe 350 into a discharge zone or to the general groundwater supply.

[0022] Additionally, embodiments of the present system may include at least one bypass drain 331. The bypass drain 331 may include an inlet 332 (seen in Figure 5) that sits above the top level of the aerobic zone and is in communication with the horizontal pipe at the bottom of the aerobic zone. This alternative bypass drain serves to prevent excess water (either rainwater or water that has passed from the anaerobic zone) from pooling on the surface of the aerobic zone. This bypass drain allows the excess water to drain directly out of the system if the water level should reach a predetermined height.

[0023] Figure 4 depicts an alternative embodiment of the system positioned next to a roadway. In this embodiment, the anaerobic zone 200 is positioned on the left and the aerobic zone on the right. The runoff from the roadway will pass through the inlet 100 and into the bioretention system.

[0024] Figure 5 is a cross-section view of the embodiment of the Figure 4.

The water impermeable liner 2 defines the bottom and sides of the anaerobic zone. A section of the reverse drainage system including a vertical pipe 130 and a second horizontal pipe 140 can be viewed. Additionally, figure 5 displays the inlet 332 for the optional bypass drain.

[0025] The illustrated embodiments depict the system as having one anaerobic zone and one aerobic zone. Alternatively, the system may include many single anaerobic to aerobic systems arranged in parallel, one anaerobic zone feeding a plurality of aerobic zones, or a plurality of anaerobic zones feeding one aerobic zone. The nature and amount of contaminants will determine the overall design of the specific bioretention system and the plants and microorganisms employed in it.

[0026] The choice of plant species to be included in the rain garden is important due to species susceptibility and the different remediation and soil tolerances of different plant species. In an embodiment of the present application, at least four species of plants are employed in each zone of the system. [0027] The following is a non-exhaustive list of potential plant species for use in an embodiment of the anaerobic zone: Spirea alba; Asclepias incarnate; Eupatorium perfoliatum; Verbena hastate; Iris shrevei; liatris pycnostachya; Lobelia siphilitica, Tradescantia ohiensis; Lobelia cardinalis; Pycnanthemum virginianum; Monarda fistulosa; Veronicastrum virginicum; Zizia aurea.

[0028] The following is a non-exhaustive list of potential plant species for use in an embodiment of the aerobic zone: Echinacea pallida; Sorghastrum nutans; Demodium canadense; Rudbeckia triloba; Helianthus mollis; Aster novae-angliae; Liatris aspera; Asclepias syriaca; Aquilegia canadensis; Penstemon digitalis; Rudbeckia hirta; Aster sericeus; Ceanothus americanus; Echinacea purpurea; Liatrus aspera; Verbena stricta; Allium cernuum; Amorphae cansecens; Viola pedeta; Petalostum umpurpureum; Aster azureus; Campanula rotundiflolia; Geum triflorum; Sporobolus heterolepsis.

[0029] Having shown and described various embodiments of the invention, those skilled in the art will realize that many variations and modifications may be made to the described invention and still be within the scope of the claimed invention. Additionally, many of the elements indicated above may be altered or replaced by different elements which will provide the same result and fall within the spirit of the claimed invention. It is the intention, therefore, to limit the invention only as indicated by the scope of the claims.