Final Report: Upflow Filter for Rapid and Effective Treatment of Stormwater at Critical Source AreasEPA Contract Number: 68D03068
Title: Upflow Filter for Rapid and Effective Treatment of Stormwater at Critical Source Areas
Investigators: Raghavan, Ramjee
Small Business: U.S. Infrastructure Inc.
EPA Contact: Richards, April
Project Period: October 1, 2003 through December 31, 2004
Project Amount: $225,000
RFA: Small Business Innovation Research (SBIR) - Phase II (2003) Recipients Lists
Research Category: Small Business Innovation Research (SBIR) , Water and Watersheds , SBIR - Water and Wastewater
This Phase II research project was conducted by USInfrastructure, Inc., to develop further the UpFlow™ filter for commercialization. The main objectives of this research project were to:
- design and construct a second-generation prototype UpFlow™ filter;
- conduct hydraulic evaluations of the prototype sizing options;
- select and modify a test location for field trials;
- install UpFlow™ filter and monitoring equipment at modified inlets and initiate evaluation testing;
- clarify approaches and initial development of an UpFlow™ filter module for the Source Loading and Management Model (WinSLAMM);
- acquire field test results for both controlled sediment capture tests and actual rain events;
- conduct detailed laboratory testing of alternative media for flow capacity and particle retention; and
- market the device through commercialization partner, Hydro-International, Inc.
This report summarizes most of the components of the research and contains detailed information regarding the UpFlow™ filter. Because USInfrastructure, Inc., is working closely with its marketing partners, design details are proprietary.
The UpFlow™ filter is basically a catchbasin insert. It is designed to be compact for installation and inexpensive to maintain. Figure 1 shows the side view of the filter. The heavier particles settle in the sump. Water enters the filter through the screen, leaving behind all the debris. Due to the available head, the water is pushed upwards through the filter media and then downwards, and finally, into the effluent pipe. The main advantage of this setup is that the stormwater passes through the filter media twice and the heavier particles settle in the sump at the bottom of the filter before they can enter the filter. Figure 2 shows the commercial unit under normal filter operation. Stormwater enters the filter through the grated inlet.
Figure 1. Side View of UpFlow™ Filter and Catchbasin system. 1 = Catchbasin; 2 = Grate inlet cover; 3 = Sump; 4 = Coarse screen; 5 = Fine screen; 6 and 7 = Filter media; 8 = Effluent pipe; a, b, and c = Filter path in the filter; and d and e = Overflow path.
Figure 2. UpFlow™ Filter Drawing Showing Normal Filtering Operation (Hydro-International, Ltd.)
As part of the research, samples were collected at various parking lots during a variety of storm events. The samples then were analyzed for common stormwater pollutants, such as suspended solids, turbidity, nutrients, chemical oxygen demand (COD), and heavy metals. All the sampling equipment has been tested in the laboratory for repeatability and consistency.
The rest of this report summarizes the main literature pertaining to stormwater behavior in storm drainage inlets and catchbasins and the reported performance of major categories of treatment units that can be used at these locations.
Like all treatment devices, the long-term performance of the UpFlow™ filter is highly dependent on the percentage of annual runoff treated by the unit. A series of calculations were made using WinSLAMM to determine the distribution of flows that could be expected for several sets of conditions. Sizing plots of 1 acre of paved parking or storage areas were examined. The plots had differing levels of rainfall and were located in various parts of the United States (Seattle, WA; Phoenix, AZ; Atlanta, GA; Milwaukee, WI; and Portland, ME). It is interesting to note that Seattle, typically known as a wet and rainy city, has the lowest flow rates for the probability points shown and the smallest required treatment flow rates for the different treatment objectives. In this sampling of cities, the needed treatment flow rates for the same treatment objectives are seen to range by a factor of about three or four. It would require four UpFlow™ filter modules per acre of paved drainage area to treat about 90 percent of the runoff in Atlanta (similar to what was found for the Tuscaloosa test site during the monitoring period). Only one or two modules would be needed for the same area and treatment level objective for Seattle.
Upflow filtration has many advantages over conventional downflow filtration. It can operate at much higher flow rates and is less susceptible to clogging. The UpFlow™ filter can be used as a catchbasin inset and provides moderate to high removals of stormwater pollutants. As the physical size of the filter decreases, however, the design becomes more critical. The UpFlow™ filter is intended to capture and retain litter and other large floatables, bedload material that settles in storm drainage, and a portion of conventional stormwater pollutants.
The performance of the UpFlow™ filter is dependent on many factors, including: (1) construction that allows the unit to fit into a variety of inlets; (2) overflow capacity to prevent any increased flooding, irrespective of operational conditions; (3) retention of floatables and other pollutants in the unit, preventing them from scouring or washing out during high flows; (4) provisions to drain the treatment media to minimize anaerobic conditions; and (5) a broad selection of treatment media to meet stormwater treatment objectives. There are some site limitations that define the performance of the UpFlow™ filter, mainly the amount and rate of runoff needing treatment and the quality of the runoff, in addition to the physical limitations of the inlet and whether the installation is a retrofit. Many of these limitations can be overcome through the use of an in-line unit that can be sized to accommodate best the flow conditions and treatment objectives.
The UpFlow™ filter has several removal mechanisms: sedimentation and screening, filtration, sorption, and ion exchange. The screening process is associated with the screen along the bottom of the UpFlow™ filter, preventing large material and other floatables from entering the filter. This material will be trapped in the inlet sump. During bypass flow conditions, the materials are retained in the inlet and hoods and other devices protect the bypass flow paths. Large debris and bedload material rapidly falls into the inlet sump and is retained by gravity. Sedimentation removes finer particulates from the flowing water, depending on the size of the sump and the flow rate. This material also will be retained in the inlet sump. The UpFlow™ filter will trap finer particulates, depending on the flow rate and the media characteristics. As the media drains through the weep tubes after each event, the downward counter currents tend to remove some of the particulates from the media and they settle in the inlet sump. This counter current also helps to remove any floatable material from the screen. The flow turbulence around the screen during runoff events also will help to keep material from clogging the submerged screen.
Basically, any water passing through a specific filtration material will be treated, resulting in an effluent of a reasonably predictable quality. Filters (and most other stormwater controls) do not operate to achieve a set percentage of reduction in a pollutant. If the influent concentrations are high, the percentage reductions also will be high. Similarly, if the influent concentrations are low, the percentage reductions also will be low. “Irreducible” concentrations are associated with different filtration media. Filtration media can have a wide range of performance capabilities. For the removal of particulate solids, usually the treatment effectiveness (the most obvious objective in a stormwater management plan) will be dependent on the particle size distribution in the stormwater and the size of the interstitial pores in the filtration material. Large stormwater particles are much more easily removed than smaller particles. On the other hand, small pores are more effective in capturing stormwater particulates (although this usually results in a slower treatment flow rate). The presence of chemically active filtration material enhances sorption and ion exchange, reducing the concentrations of a broad range of dissolved or colloidally bound pollutants. These media usually are organic-based and include many types of activated carbon, peats, and composts. Chemically treated sands and other minerals include iron-coated sand, manganese-coated zeolites, and organic resins; these also will be effective treatment media. Therefore, it is possible to select a combination of filtration media having the desired geomorphic characteristics (size and shape) and chemical treatment characteristics that will affect the flow capacity of the unit. The UpFlow™ filter can include a combination of media in the primary upflow filtration chamber and other media in the secondary treatment chamber. Water flowing through the secondary media will be pretreated by the prior processes (sedimentation and primary filtration) and can be selected to target additional contaminants.
The performance of an UpFlow™ filter is dependent on the fraction of water that is treated and the level of treatment provided to that water. A treatment unit that can remove almost all of the contaminants in the water, but has a very slow flow capacity, is not very useful for stormwater treatment. A device that is a balance between treatment and flow is needed. Modifications made to WinSLAMM enabled USInfrastructure, Inc., to calculate the trade-offs and prepare appropriate design curves for various locations with different rain and drainage conditions and treatment objectives.