US20130087509A1

US20130087509A1 - Filtration system and method for removing suspended solids and affiliated pollutants from stormwater runoff using a geosynthetic filter

Info

Publication number: US20130087509A1
Application number: US13/608,568
Authority: US
Inventors: Allen P. Davis; Ahmet H. Aydilek; David M. Ayres; Carmen Franks
Original assignee: University of Maryland at Baltimore
Current assignee: University of Maryland at Baltimore
Priority date: 2011-09-09
Filing date: 2012-09-10
Publication date: 2013-04-11

Abstract

A filtration system and method are provided for removing suspended solids and other affiliated pollutants from stormwater runoff and any other contaminated water. The filtration system and method utilize a filter having a geosynthetic material. By improving or replacing a conventional filtration system, such as a sand filtration system, with a geosynthetic material, the removal efficiency of suspended solids and affiliated pollutants is maintained or improved and the lifespan of the filtration system is lengthened due to simpler cleaning processes and a reduced need for material replacements. The filter can be a retrofit filter for fitting to existing storm drains for removing suspended solids and affiliated pollutants.

Description

PRIORITY CLAIM
The present application claims priority to and the benefit of the previously filed provisional application to Allen P. Davis et al. having U.S. Provisional Patent Application No. 61/533,050, entitled “Geosynthetic Filters for Water Quality Improvement of Urban Stormwater Runoff,” filed on Sep. 9, 2011, the entire contents thereof are incorporated herein by reference.

RELATED TO

The present application is related to a dissertation titled “Treatment of Stormwater Runoff by Geotextile Filters via Suspended Solids Capture,” by Carmen Ann Franks, 2012; the entire contents of which are incorporated herein by reference.

BACKGROUND

1. Technical Field
The present disclosure relates to an urban stormwater runoff filtration system and method. In particular, the present disclosure relates to a filtration system and method for removing suspended solids and affiliated pollutants from stormwater runoff utilizing a geosynthetic filter.
2. Description of Related Art
Stormwater runoff is rain that falls on streets, parking areas, sports fields, gravel lots, rooftops or other developed land and flows directly into nearby lakes, rivers and other water landforms. The drizzling or pounding rain picks up and mixes with what's on the ground, such as oil, grease, metals and coolants from vehicles; fertilizers, pesticides and other chemicals from gardens and homes; bacteria from pet wastes and failing septic systems; soil from construction sites and other bare ground; soaps from car or equipment washing; and accidental spills, leaky storage containers, and whatever else ends up on the ground. The polluted runoff then rushes into nearby gutters and storm drains and into streams, lakes, rivers and bays. In most areas, stormwater runoff enters these waters without being cleaned of pollutants.
Poorly managed stormwater runoff causes three big problems: (1) pollution from stormwater runoff contaminates waters, closes local businesses, and harms or kills fish and other wildlife. As stormwater passes over developed land, it picks up pollutants and transports them to the nearest storm drain and eventually rivers and bays. (2) Flooding harms streams and wetlands and destroys habitat needed for fish and other wildlife. Unable to soak into the ground, stormwater runoff quickly flows or floods downstream from developed land during the rainy season. As a result, floods can damage homes and businesses, flood septic system drain fields and overwhelm streams, wetlands and wildlife habitat. (3) Water shortages in growing communities may occur, especially in developed areas with impervious surfaces or areas where water cannot infiltrate through, such as roads, parking lots and rooftops. The impervious surfaces keep rainfall from soaking into the ground and replenishing groundwater and streams used for drinking water or fish habitat.
To solve these problems and other problems attributed stormwater runoff, filtration systems have been developed. These filtration systems, as shown by FIG. 4, receive runoff and debris at an inlet (A in FIG. 4), filter the runoff and capture suspended solids and affiliated pollutants (B in FIG. 4), and release the filtered runoff at an outlet (C in FIG. 4). Sand and other media are typically used to perform suspended solids and affiliated pollutants removal from urban stormwater runoff. However, filtration systems that use sand and other media, such as gravel, to filter stormwater runoff, as the filtration system shown by FIG. 4, clog frequently requiring replacement of media in order to restore the drainage capacity of the filtration systems.
There is therefore a need for a filtration system and method for removing suspended solids and affiliated pollutants from stormwater runoff which overcomes the drawbacks of conventional systems and methods.
There is also a need for a filter which can be retrofit unto existing storm drains and other discharge areas for removing suspended solids and affiliated pollutants.

SUMMARY

The present disclosure provides a filtration system and method for removing suspended solids and other affiliated pollutants from stormwater runoff or other contaminated water streams. The filtration system and method utilize a filter having a geosynthetic material. By improving or replacing a conventional filtration system, such as a sand filtration system, with a geosynthetic material, the removal efficiency of suspended solids and affiliated pollutants is maintained or improved and the lifespan of the filtration system is lengthened due to simpler cleaning processes and a reduced need for material replacements. The filter can be retrofit filter that can be employed along the fluid flow in existing storm filtration, drainage systems, and other fluid discharge areas.
A geosynthetic is a commercially available polymeric material, such as 1120 N available from Koninklijke Ten Cate nv. Geosynthetic materials are used in a variety of applications for reinforcement, separation, filtration, and drainage of soils, and containment of liquids and gases. The most commonly used form of geosynthetic is geotextile, a material of synthetic fibers either woven or matted together.
In an embodiment of the present disclosure, an urban stormwater runoff system utilizing a geosynthetic filter is provided for removing suspended solids and other pollutants from stormwater runoff. The geosynthetic filter can include a geocomposite or a nonwoven geotextile. The pore size heterogeneity of nonwovens is similar to that of the sand filters which are commonly used in conventional urban stormwater runoff filtration systems.
In an additional embodiment of the present disclosure, there is provided a method for removing suspended solids and other pollutants from stormwater runoff using a geosynthetic filter, such as a filter having a geocomposite or a nonwoven geotextile.
Therefore, in an aspect of the present disclosure there is provided a filter that can be used, for example, in a filtration or drainage system. The filter includes a geosynthetic material configured for being positioned along a fluid path of the filtration or drainage system. The suspended solids and other pollutants are carried along the fluid path by fluid flow and are removed from said fluid flow by the geosynthetic material. The geosynthetic material can be a geotextile or geocomposite. The geotextile can be a nonwoven geotextile.
The filter further can include a screen provided on a surface of the geosynthetic material. The system can also include at least one securing mechanism, such as a clamp, for securing the geosynthetic material to the filtration system. The fluid flow includes stormwater runoff or any other contaminated water. The filter can be a retrofit filter that is configured for placement in proximity to an opening of a drainage system and other areas receiving contaminated fluid flow, for removing suspended solids and other affiliated pollutants.
In another aspect of the present disclosure, there is provided a filtration system. The filtration system includes an inlet defining an opening for receiving fluid flow containing suspended solids and other pollutants. The system also includes a filter comprising a geonsynthetic material configured for being positioned along the fluid flow. The suspended solids and other pollutants are removed from said fluid flow by the geosynthetic material. The system also includes an outlet defining an opening for dispensing the fluid flow from the filtration system. The geosynthetic material can be a geotextile or geocomposite. The geotextile can be a nonwoven geotextile.
In another aspect of the present disclosure, there is provided a method for removing suspended solids and other pollutants from fluid flow, such as stormwater runoff. The method includes receiving fluid flow containing suspended solids and other pollutants; providing a filter comprising a geosynthetic material along the fluid flow; and removing the suspended solids and other pollutants from the fluid flow using the filter. The geosynthetic material can be a geotextile or geocomposite. The geotextile can be a nonwoven geotextile. The filter can be a retrofit filter configured for placement in proximity to an opening of a drainage system and other areas receiving contaminated fluid flow, for removing the suspended solids and other affiliated pollutants.
The method further includes securing the geosynthetic material within a chamber of a filtration system. The chamber receives the stormwater runoff or any other contaminated water. The method also includes dispensing the fluid flow after the suspended solids and other pollutants are removed. The method also includes cleaning the filter. The method also includes removing the geosynthetic material from the filtration system. The method also includes backwashing the filtration system to clean the geosynthetic material.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other advantages will become more apparent from the following detailed description of the various embodiments of the present disclosure with reference to the drawings wherein:

FIG. 1 is a graph showing concentration data for influent and effluent TSS as a function of time for geotextile 1 tests. Particle size range is 0.106 to 0.125 mm. Hydraulic loading is 0.25 mm/s (35 in/hr). Influent TSS concentrations were taken at an initial time and a final time. The dashed line indicates the target effluent TSS concentration.

FIG. 2 is a graph showing TSS concentration data plotted versus time for geotextile 2 tests. Particle size range is 0.106 to 0.125 mm. Hydraulic loading is 0.25 mm/s (35 in/hr). Influent TSS concentrations were taken at an initial time and a final time. The dashed line indicates the target effluent TSS concentration.

FIG. 3 is a graph showing concentration data as a function of time for geotextile 2 with particle size 0.075-0.106 mm. Influent TSS concentrations were taken at an initial time and a final time. Hydraulic loading is 0.25 mm/s (35 in/hr). The red line indicates the target effluent TSS concentration.

FIG. 4 illustrates a prior art subsurface sand filtration system for stormwater runoff.

FIG. 5 is a diagram illustrating a stormwater runoff filtration system in accordance with the present disclosure.

FIG. 6 is a schematic diagram of a retrofit filter having a geosynthetic material and configured for placement in proximity to an opening of a drainage system and other areas receiving contaminated fluid flow in accordance with the present disclosure.

DETAILED DESCRIPTION

In the Summary section above, in this Detailed Description, in the Claims below, and in the accompanying drawings, reference is made to particular features (including method steps or acts) of the present disclosure. It is to be understood that the disclosure in this specification includes combinations of parts, features, or aspects disclosed herein. For example, where a particular feature is disclosed in the context of a particular aspect or embodiment of the present disclosure, or a particular claim, that feature can also be used, to the extent possible, in combination with and/or in the context of other particular aspects and embodiments of the present disclosure, and in the disclosure generally.
The term “comprises” and grammatical equivalents thereof are used herein to mean that other components, ingredients, steps, acts, etc. are optionally present. For example, an article “comprising (or “which comprises”) component A, B, and C can consist of (i.e., contain only) components A, B, and C, or can contain not only components, A, B, and C but also one or more additional components, elements, features, ingredients, steps, acts, etc.
Where reference is made herein to a method comprising two or more defined steps or acts, the defined steps or acts can be carried out in any order or simultaneously (except where the context excludes that possibility); and the method can include one or more other steps or acts which are carried out before any of the defined steps or acts, between two of the defined steps or acts, or after all the defined steps or acts (except where the context excludes that possibility).
The term “at least” followed by a number is used herein to denote the start of a range beginning with that number (which may be a range having an upper limit or no upper limit, depending on the variable being defined). For example, “at least one” means one or more than one. The term “at most” followed by a number is used herein to denote the end of a range ending with that number (which may be a range having 1 or 0 as its lower limit, or a range having no lower limit, depending upon the variable being defined). For example “at most 40%” means 40% or less than 40%. When, in this specification, a range is given as “(a first number) to (a second number)” or “(a first number) (a second number),” this means a range whose lower limit is the first number and whose upper limit is the second number. For example, 25 to 100 mm means a range whose lower limit is 25 mm, and whose upper limit is 100 mm.
The present disclosure relates to an urban stormwater runoff filtration system and method. In particular, the present disclosure relates to a filtration system and method for removing suspended solids and affiliated pollutants from stormwater runoff, such as highway runoff, utilizing a geosynthetic filter. Suspended solids can block light, deposit on organisms and exert an oxygen demand. Also, suspended particles can often carry pollutants such as phosphorous, hydrocarbons, and metals, like lead, copper and zinc.
The present disclosure addresses the need to control, as a best management practice, the concentration of total suspended solids (TSS) and affiliated pollutants released into aquatic systems. Average TSS concentrations for highway stormwater runoff range from 50-400 mg/L. The filtration system of the present disclosure reduces reduce influent TSS concentrations to an effluent concentration of 30 mg/L or less. This is beneficial since typical TSS concentrations for release by point source dischargers range from 20-30 mg/L.
The urban stormwater runoff filtration system utilizes a geosynthetic filter. A geosynthetic is a commercial polymeric material, such as 1120 N available from Koninklijke Ten Cate nv. These materials are currently used in a variety of applications for reinforcement, separation, filtration, and drainage of soils, and containment of liquids and gases. The most commonly used form of geosynthetic is geotextile, a material of synthetic fibers either woven or matted together. The system of the present disclosure is designed for the use of a nonwoven geotextile to provide filtration of runoff. This is because the pore size heterogeneity of nonwovens is similar to that of the sand filters which are currently in common use for urban stormwater runoff filtration. However, in accordance with the present disclosure, other types of geosynthetic materials, such as geocomposites, can be used for the geosynthetic filter.
Research has been conducted using three types of nonwoven geotextiles made of polypropylene. The first geotextile tested has an apparent opening size (AOS) of 0.180 mm. The results of two tests on this geotextile (geotextile 1: 180 N available from Koninklijke Ten Cate nv) are given in FIG. 1. In both tests, the influent TSS concentration was approximately 225 mg/L. The diameters of the particles in the influent ranged from 0.106 mm to 0.125 mm, and the influent flow rate was approximately 3.14 mL/s for a circular geotextile filter with a diameter of 13.97 cm (5.5 in). This flow rate for the given filter area is equivalent to a loading rate of 0.25 mm/s (35 in/hr). If the runoff area to drainage area ratio is 50, this loading rate corresponds to an approximate rainfall rate of 1.8 cm/s, or 0.7 in/hr. From the data in FIG. 1, it is clear that geotextile 1 is capable of reducing the TSS concentration to less than half of the influent concentration for the duration of the first 60 minutes of a runoff event for this specific rainfall rate. Additionally, no accumulation of water head on the filter was observed throughout the duration of the test. This result shows that the insertion of geotextile 1 will not decrease drainage capacity for the treatment system.
While geotextile 1 removed a significant amount of suspended solids, it did not consistently reach the target effluent concentration of 30 mg/L. The tests were repeated for a second type of geotextile. The effluent TSS concentrations from this geotextile (geotextile 2: 1120 N available from Koninklijke Ten Cate nv) are much lower than those for geotextile 1. Geotextile 2 has an AOS of 0.150 mm. Due to the smaller opening size of the material, geotextile 2 has a lower permittivity than geotextile 1. Permittivity is equivalent to the permeability, normalized by the thickness of the material. Therefore, geotextile 2 is more likely to retain water, decreasing the drainage capacity. However, after performing the test with 3.14 mL/s flow and 170-240 mg/L influent TSS with particles in the size range of 0.106-0.125 mm on geotextile 2, no accumulation of water was detected. The results of the tests, shown in FIG. 2, indicate that geotextile 2 is able to reduce the influent TSS concentration to approximately the target concentration of 30 mg/L.
Tests were performed on geotextile 2 using a smaller particle size, 0.075-0.106 mm, as well. All other parameters were kept the same as the previous tests. The results of these tests shown in FIG. 3 show that the filter is able to reduce the TSS concentrations significantly, frequently below the target. Once again, no reduction of drainage capacity was detected.
Additional tests were performed to further validate the results of adequate filtration and drainage by these geotextiles. Higher flow rates, smaller suspended particle sizes and longer test durations were investigated. Additionally, a larger runoff area to drainage area ratio was explored which showed that the geotextile filters are able to function sufficiently in “worst case scenarios”. Some of the findings and additional tests are described in the dissertation titled “Treatment of Stormwater Runoff by Geotextile Filters via Suspended Solids Capture,” by Carmen Ann Franks, 2012; the entire contents of which are incorporated herein by reference.
Urban Stormwater Runoff Filtration System Design
The current physical design for the geotextile filtration system is shown in FIG. 5 and designated by reference numeral 500. A conventional sand filter design is shown in FIG. 4 and designated by reference numeral 400. The system 400 includes gravel 402 and sand 403 as the filter media. The system 500 includes a filter 502 having geosynthetic material 503, such as, for example, geotextile material as the filter media, and a screen 505. Captured suspended solids 507 are shown on top of the filter 502. These suspended solids 507 do not pass through the geotextile material 503, and if the suspended solids 507 are larger than the openings of the screen 505, they are blocked by the screen 505.
The filtration system 500 is provided underneath a surface 512, such as a highway, within a treatment chamber 508. Three manhole openings 514 and respective manhole covers 516 are shown by FIG. 5. The runoff enters the chamber 508 via an inlet 518. The inlet 518 is in fluid communication with a sewer system and other systems designed to capture stormwater and debris 515. The water level WL within the treatment chamber 508, as shown by the broken line in FIG. 5, is below the inlet 518 to prevent backflow. In case the water level WL rises above the inlet 518, a dewatering valve 517 is provided for releasing runoff from the chamber 508 to lower the water level WL.
Heavy particles and other debris coming into the chamber 508 from inlet 518, such as sediment 519, settle to the bottom of the chamber 508, whereas suspended solids and affiliated pollutants 507 remain suspended in the runoff before they are captured by the geotextile material 503 of the filter 502.
The runoff is filtered by the geotextile material 503 in which the suspended solids and affiliated pollutants 507 are captured. The runoff then flows through the screen 505 and is captured within a perforated underdrain, 520. The underdrain 520 can be manufactured from PVC. The filtered runoff flows through the underdrain 520 and exits the chamber 508 via outlet 522.
FIG. 5 illustrates two methods of cleaning the filter 502. The first is the inclusion of an outlet fitting 504 on outlet 522 which would allow the attachment of a hose (not shown). The hose will direct pressurized water flow into the system 500 to backwash the system 500 and clear the filter 502. The second method is represented by a means of securing the geotextile 503 in place such as with at least one securing mechanism, such as a clamp 506, which could easily release the geotextile 503 to allow for removal and thus cleaning the filter 502 outside of the treatment chamber 508. A self-cleaning, or other simple cleaning mechanism, may be added to the filtration system 500 to alleviate clogging of the filter 502.
FIG. 6 shows a schematic diagram of a retrofit filter 600 having a geosynthetic material 603 in accordance with the present disclosure. The filter 600 is configured for placement in proximity to an opening 605 of a drainage system 610 and other areas receiving contaminated fluid flow.
The opening 605 can be, for example, an opening of a storm drain. The metal cover of a typical storm drain can be replaced with the retrofit filter 600 for filtering the fluid flow, such as stormwater runoff, prior to the fluid flow entering the drainage system 610 and being received by a filtration system, such as the filtration system 500 or a conventional filtration system.
The filter 600 includes a metal casing 608 having a screen 612. The geosynthetic material 603 is positioned underneath the screen 612 for filtering fluid flow (shown by arrow “A”) which enters the filter 600 via openings 614 of the screen 612. The filtered fluid flow then enters the drainage system 610 from where it flows to the filtration system 500, or other filtration system.
While traditional sand filters can sufficiently perform the filtration functions necessary to remove suspended solids, they clog after some amount of time. After clogging, there is no method of cleaning the filter; instead the sand media must be fully or partially replaced in order to work properly again. This can be highly labor intensive. Replacing sand filters with geotextiles in the filtration system eliminates the need for compaction/vibration of the sand during its placement. Moreover, exchange of a sand filter with a geotextile will provide a filter with a much longer lifetime. When a geotextile material becomes clogged, a filter cake of particles has formed on the surface of the material. It is envisioned that this cake can be easily removed by a washing or backwashing process. As a result, the geotextile can be used for filtration repeatedly before needing to be replaced.
Although the present disclosure has been described in considerable detail with reference to certain preferred version thereof, other versions are possible and contemplated. Therefore, the spirit and scope of the appended claims should not be limited to the description of the preferred versions contained therein.
Any element in a claim that does not explicitly state “means for” performing a specified function or “step for” performing a specified function, is not to be interpreted as a “means” or “step” clause as specified in 35 U.S.C. §112, ¶6. In particular, the use of “step of” in the claims is not intended to invoke the provisions of 35 U.S.C. §112, ¶6.

Claims

What is claimed:

1. A filter comprising:

a geonsynthetic material configured for being positioned along a fluid path;

wherein suspended solids and other pollutants are carried along the fluid path by fluid flow and are removed from said fluid flow by said geosynthetic material.

2. The filter according to claim 1, wherein the geosynthetic material is a geotextile or geocomposite.

3. The filter according to claim 2, wherein the geotextile is a nonwoven geotextile.

4. The filter according to claim 1, further comprising a screen provided on a surface of the geosynthetic material.

5. The filter according to claim 1, further comprising at least one securing mechanism for securing the geosynthetic material to said filtration system.

6. The filter according to claim 1, wherein the fluid flow comprises stormwater runoff or any other contaminated water.

7. The filter according to claim 1, wherein the filter is configured for placement in proximity to an opening of a drainage system.

8. A filtration system comprising:

an inlet defining an opening for receiving fluid flow containing suspended solids and other pollutants;

a filter comprising a geonsynthetic material configured for being positioned along the fluid flow, wherein the suspended solids and pollutants are removed from said fluid flow by said geosynthetic material; and

an outlet defining an opening for dispensing the fluid flow from said filtration system.

9. The filtration system according to claim 8, wherein the geosynthetic material is a geotextile or geocomposite.

10. The filtration system according to claim 9, wherein the geotextile is a nonwoven geotextile.

11. The filtration system according to claim 8, further comprising a screen provided on a surface of the geosynthetic material.

12. The filtration system according to claim 8, further comprising at least one securing mechanism for securing the geosynthetic material within a chamber of said filtration system.

13. The filtration system according to claim 8, wherein the fluid flow comprises stormwater runoff or any other contaminated water.

14. A method for removing suspended solids and other pollutants from fluid flow, said method comprising:

receiving the fluid flow containing suspended solids and other pollutants;

providing a filter comprising a geonsynthetic material along the fluid flow; and

removing the suspended solids and other pollutants from the fluid flow using the filter.

15. The method according to claim 14, wherein the geosynthetic material is a geotextile or geocomposite.

16. The method according to claim 14, further comprising securing the geosynthetic material within a chamber of a filtration system receiving the fluid flow.

17. The method according to claim 14, further comprising dispensing the fluid flow after the suspended solids and other pollutants are removed.

18. The method according to claim 14, further comprising cleaning the filter.

19. The method according to claim 16, further comprising removing the geosynthetic material from the filtration system.

20. The method according to claim 16, further comprising backwashing the filtration system to clean the geosynthetic material.

21. The method according to claim 14, further comprising placing the filter in proximity to an opening of a drainage system.