Communities must find a reliable and effective way to prevent weather-related combined sewer overflow (CSO) and sanitary sewer overflow (SSO) from spilling directly into nearby waterways. While a separate treatment system for CSO/SSO concerns is viable for some plants, others do not have the footprint or funding for a single-use system.
The WWETCO FlexFilter™ system meets both of these concerns with a simple, gravity-fed process that plants can use for both daily primary or tertiary treatment and unpredictable wet-weather treatment to remove total suspended solids (TSS).
The FlexFilter system is a high-rate filtration system that uses synthetic compressible media. Media compression is accomplished through the lateral hydraulic force applied by the head pressure of the influent. This unique method of compression eliminates mechanically actuated internal components and provides a tapered media compression.
The varied porosity of the compressed media bed allows for increased filtering capacity as well as the ability to treat flow streams with higher solids concentrations – all while minimizing backwash cycles. In addition to the filter's ability to handle higher solids to the filter, the backwash system with air scour and specialized backwash troughs minimizes the volume of backwash water needed.
This versatile system has no internal moving parts and is ideal for a variety of applications, including combined sewer overflow (CSO), sanitary sewer overflow (SSO), primary, enhanced primary, and tertiary treatment. It can also function as a dual-use system, providing both primary or tertiary and CSO/SSO treatment. Plants can implement it in both new systems and retrofits.
The influent liquid applies a hydrostatic force to the compression bladder causing the media to compress (1). The tapered compression provides for densely compressed media at the bottom that graduates to an expanded bed toward the surface (2).
As the liquid flows onto the top of the media, the larger particles are trapped in the upper portions of the filter. As the liquid works its way down, the smaller particles are captured. This porosity gradient within the filter bed allows for a more effective use of the entire media bed and allows for a higher mass load to the filter prior to backwash (3). As the filter bed becomes plugged, the influent level increases, signaling the need for a backwash (4).
For the backwash, the feed to the filter is stopped, allowing the media to decompress (5). The air scour is initiated along with a small amount of backwash water (6). When cleaned, the filter is put back into service or sits empty until the next event occurs.
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Cities across the country are struggling to find a reliable and effective way to prevent weather-related stormwater runoff and CSO/SSO from spilling directly into nearby waterways.
New Jersey is one state where CSOs are a priority concern. The Environmental Protection Agency (EPA) and New Jersey Department of Environmental Protection (NJDEP) collaborated on The Wet Weather Flow Treatment and Disinfection Demonstration Project. It was conducted over a two-year period, 2014 and 2015, at the Bayonne Municipal Utilities Authority's Oak Street facilities, which receives CSOs from the City of Bayonne.
The pilot treatment included high-rate and enhanced high-rate solids removal and disinfection. A total of six technologies were tested in 18 treatment process combinations over nine wet-weather events.
Results showed that WWETCO FlexFilter is capable of high performance total suspended solids (TSS) removal (up to 90 percent) and of allowing for disinfection – effluent UV (medium or low pressure) and peracetic acid (PAA).
After the demonstration project was complete, the NJDEP summarized the results in a report, with a goal of providing engineering practitioners with an improved understanding of wet-weather treatment technologies and their potential use as satellite end-of-the-pipe wet-weather CSO treatment.
The FlexFilter can easily take the place of a traditional primary clarifier. This creates a dual-use system, providing the additional capacity to handle wet-weather conditions while increasing primary-treatment capacity in dry weather.
Likewise, plants that require tertiary treatment can either choose the FlexFilter as their tertiary system or implement FlexFilter as a dual-use system. The FlexFilter can achieve low-level phosphorous removal, helping plants meet increasingly strict phosphorous-removal requirements for reuse-quality effluent.