Introduction

Field testing has been performed on various storm events for an Aqua-Filter™ Model AF-4.2 at the University of New Hampshire (UNH) Stormwater Center in Durham, New Hampshire. This field data is used to determine the water quality removal efficiency of the Aqua-Filter™ stormwater treatment system for Total Suspended Solids (TSS).

Efficiency tests were conducted at various rainfall intensities, various flow rates, and various pollutant concentrations, all variables reflective of natural field performance conditions.

Test Facility Description

The UNH Stormwater Center studies stormwater-related water quality and quantity issues. The field facility is designed to evaluate and verify the performance of stormwater management devices and technologies in a parallel, event normalized setting. Fifteen different management systems are currently undergoing side-by-side comparison testing under strictly controlled natural conditions (Figure 1).

Figure 1. Plan view of the University of New Hampshire field research facility.	Figure 2. Cross section of Aqua-Filter

Description of the Unit

The Aqua-Filter™ Stormwater Filtration System is designed for sites that require advanced treatment of runoff stormwater that may discharge into sensitive receiving waters, is custom engineered, and utilizes a unique approach for pollutant removal. This patented configuration begins with the removal of gross pollutants by the Swirl Concentrator, followed by the removal of fine sediments and water-borne pollutants by the Filtration Chamber (See Figure 2).

The Aqua-Filter™ selected for evaluation at the UNH Test Facility is a Model AF-4.2. This model consists of a 4-foot inside diameter Swirl Concentrator and a Filter Chamber with an approximate diameter of 6.5 feet by 12 foot length. The storage volume of the treatment technology installed at the Test Facility is the combined storage volume of the Swirl Concentrator and the Filter Chamber. The storage capacity of the Swirl Concentrator and Filter Chamber is approximately 517 gallons (69 cubic feet) and 476 gallons (64 cubic feet), respectively. Thus, the total storage volume for the Aqua-Filter™ (the entire treatment train) is approximately 993 gallons (133 cubic feet).

The overall treatment capacity of the Aqua-Filter™ is defined by the maximum filtration rate for the Filter Chamber’s filter bed. The media installed in the Filter Chamber is an inorganic perlite media, which is enclosed in twenty four (24) filter containers aligned in two (2) rows on the Filter Chamber’s bed.

Testing Procedure

Eight storm events were sampled starting from September 2004 to October 2005. Samples were taken for influent and effluent waters by Teledyne ISCO 6712 Automated Samplers accompanied by Teledyne ISCO 730 Bubbler Flow Modules in combination with Thelmar compound weirs. The site orientation is illustrated by Figure 1.

During separate storm events, sediment concentration was taken from the influent waters and compared to the concentration of the effluent waters. The data was tested in accordance to EPA Method 160.2 and reported by an EPA certified laboratory.

Field Results

Each sample was taken from eight different storm events and labeled as shown in Table 1. For each sample, the influent and effluent concentrations were listed in mg/L. Then, the actual removal efficiency (ARE) of the Aqua-Fitler™ system was computed.

Equation 1. Actual Removal Efficiency

Conclusion

This removal efficiency is comparable to and within the same order of magnitude to full-scale laboratory testing of the Aqua-Filter™ models. The analysis of the field data reveals that the Aqua-Filter™ AS-4.2 has a mean TSS removal efficiency of 80.6%. The mean particle size was 49 microns, while the mean loading rate was 7.2 gpm/ft^2.