Final Report: Upflow Filters for the Rapid and Effective Treatment of Stormwater at Critical Source AreasEPA Contract Number: 68D02100
Title: Upflow Filters for the Rapid and Effective Treatment of Stormwater at Critical Source Areas
Investigators: Raghavan, Ramjee
Small Business: U.S. Infrastructure Inc.
EPA Contact: Manager, SBIR Program
Project Period: October 1, 2002 through July 31, 2003
Project Amount: $99,926
RFA: Small Business Innovation Research (SBIR) - Phase I (2002) RFA Text | Recipients Lists
Research Category: Water and Watersheds , SBIR - Water and Wastewater , Small Business Innovation Research (SBIR)
This Phase I research project was designed to develop and demonstrate the effectiveness of upflow filtration for the treatment of stormwater runoff. To demonstrate marked improvement in water quality in many urban areas, it will be necessary to either treat stormwater runoff in a central location, or install and maintain many small treatment devices throughout a watershed. The goal of this project was to develop an upflow filter that can be installed in-line that will effectively remove a broad range of pollutants. Secondary goals were low cost and low maintenance. The potential markets for these devices include owners of critical source areas (industrial facilities, municipalities, state transportation departments, service stations, etc.). Many of these people are small business owners without significant capital for investing in large-scale complex treatment facilities. A successful low-cost, low-maintenance upflow filter for stormwater treatment would allow these owners to meet the upcoming requirements for treating their runoff without incurring the tremendous financial burden that would result from the purchase of a complex treatment device/facility, in addition to the cost of maintaining it.
This research was conducted in three phases: (1) bench-scale tests to evaluate the potential of upflow filters to remove solids and dissolved pollutants, (2) pilot-scale tests to evaluate pollutant removal using real stormwater runoff, and (3) flow-rate testing of a prototype device. Test media in the laboratory and the field included two types of sand, a peat moss-sand mixture, and a compost-sand mixture.
Solids Removal in Laboratory-Scale Filters Operated in an Upflow Mode. The objectives of the first task of the research were to determine: (1) the optimum flow rate where there was no rising or separation of the media from the gravel layer of within media itself and where suspended solids removal was best; (2) the suspended solids loading on the media that will reduce the flow rate to certain endpoints; and (3) the breakthrough point (i.e., where the effluent concentration equaled the influent concentration) for different media filters. The laboratory testing for solids removal demonstrated that upflow filters operated in the flow rate range of rapid sand filters (but without the chemical addition that typically accompanies rapid downflow filtration) and were capable of removing 80 percent of the solids found in the influent water. Testing of these filters for dissolved pollutant removal showed that the organic filter media provided the best removals for most dissolved pollutants (metals and organics).
Laboratory-Scale Upflow Tests for Dissolved Pollutant Removal. The upflow column design functioned well during the column tests. Pumping the water allowed the contact time to be controlled. At residence times of 3-10 minutes, the compost and zeolite columns showed little sign of increased head loss during the runs, even when influent suspended solids concentrations were around 400 mg/L. At these lower flow rates, most of the suspended solids appeared to settle out in the sump area of the columns. Overall, peat had the best removal capabilities of the media in the column test, but also had the most detrimental impact on pH, the greatest head loss, and showed the most potential for clogging. Compost had the second-best metal removal capabilities, while zeolite had the lowest.
The TP 207 commercial ion-exchange resin had far better removal of zinc than any of the other media at high initial zinc concentrations, but had lower removal than many of the media at the low concentrations typically encountered in stormwater and it dramatically decreased the pH of the treated runoff. Conversely, the peat/sand mixture had a very low removal of zinc at high initial zinc concentrations, but had better removal than many of the media at the low concentrations typically encountered in stormwater.
The peat/sand mixture performed very well at the metal concentrations used in the column tests in this study. It appeared to remove dissolved metals from solution better than the other two column media during relatively low concentration conditions. However, if the runoff to be treated had higher metal concentrations, the sorption capacity of the peat/sand mixture could quickly be exhausted. Runoff with higher metal concentrations might be better treated with another media, such as compost. Another possibility is the use of multiple media. One example would be to use a compost filter followed by a peat/sand filter to treat runoff with high metal concentrations. The compost filter could remove the bulk of the metal load, reducing the metal concentrations down to the range where peat/sand works best, then the peat/sand could polish the runoff to lower metal concentrations than the compost could achieve.
Pilot-Scale Testing Using Detention Pond Water as an Influent. The pilot-scale testing was performed using presettled stormwater runoff, and the results were compared to prior downflow results obtained by the same research team. Pollutant removals were similar to downflow results. The benefits of upflow filtration primarily were seen in the delay in the onset of measurable head loss/pressure buildup in the filters. Substantially longer filter runs were seen with the upflow filters compared to the downflow filters with the same media.
Flow Testing of the Prototype. Flow testing of the prototype demonstrated that the prototype could be operated at flow rates significantly higher than those seen in rapid filtration. These tests were performed using clean water, and pollutant removal efficiencies were not evaluated. The Phase II testing has been designed to investigate pollutant removal efficiencies at one or more full-scale installations during 1 year of operation, which will help indicate the intervals for required maintenance. It also is designed to see if the prototype as developed will be effective in full-scale operation and provide opportunities for modifications of the prototype to improve operation during the Phase II period. In addition, Phase II testing has been designed to optimize the media selection and address media retention in the filter during high flow rate operation. The Phase I testing demonstrated the promise of this technology, and the Phase II proposal has been designed to allow for further testing in a real-world application.
Technical questions to be answered during Phase II include:
· How does the head loss change during filtration? How does the head loss recover between filtration events? Will a recovery in head loss be seen due to the removal of solids from the filter surface to the sump during the quiescent times?
· Is the pollutant removal "permanent" between events, or does the pore water chemistry change sufficiently that previously sorbed pollutants "leach" from the media?
· What is the effect of decreasing/increasing the flow rate through the filters on the treatment efficiency? What is the effect of natural aging on the filtration efficiency?
· Is the proposed setup configuration feasible for actual operation?
· Part of the benefit of the upflow design will be that the surface of the filter will strain out the larger particulates during operation. Between storms, the water in the system will be quiescent and a sump would be used to catch the particulates that fall off the filter’s surface. What size of sump would be required? How are the particulates collected in the sump managed efficiently?
Phase I testing demonstrated the promise of this technology, and the Phase II proposal has been designed to allow for further testing in a real-world application. The development of a marketable product has been pursued by US Infrastructure, Inc. (USI), with a third party, and a prototype device was built and tested as described above. The commercialization plan proposed in Phase II by USI, in conjunction with the third party, includes the following tasks:
· Obtain patent protection for the device (in progress).
· Work with the third party's designers to refine a cost-effective prototype of the system that can be easily installed in the field, fit into most storm drains and curb inlets, and allow easy access for changing out the media and for sediment removal.
· Complete testing on the removal efficiencies of the prototype full-scale device.
· Develop a sound marketing strategy in conjunction with the third-party investor.
· Establish production schedules for the device components.
· Introduce the product to the third party investor's national distribution network and train the distributors on the attributes of the upflow design.
USI believes that the Upflow Filter System is a distinct new technology that has the potential to meet the needs of municipalities and owners of critical sources areas for a low-cost, low-maintenance stormwater treatment system.