The City of Rushville, Indiana, had to remedy a consent order filed in 2007 for its untreated combined sewer overflow (CSO) discharges that were polluting the Flatrock River, a violation of the Clean Water Act. The city originally planned to install a 1 mgd stormwater storage tank, but was approached by Aqua-Aerobic representatives with a pilot test proposal utilizing a new technology.
The pilot proposal featured the AquaPrime Cloth Media Filter using 5-micron microfiber cloth media, which would be tested during five wet-weather events. This study captured events from May to July 2015, and produced impressive results.
The pilot test prompted the city to request a design for an AquaPrime filtration system in February 2016 with two stipulations: the filters were to treat both dry and wet weather conditions, and alum coagulant was to be injected upstream of the filters to meet future effluent phosphorus limits and eliminate fine CSO particles.
System startup
Startup of the 14-disk AquaPrime filtration system began in July 2017 with a design average flow rate of 1 mgd in dry conditions and peak wet weather flow rate of 12.6 mgd. Each cloth media disk is 6.6 feet in diameter and provides an effective filtration area of 53.8 feet squared, for a total filtration area of 1,506.4 feet squared.
The filters were retrofitted into the plant’s existing, abandoned sand media filter structures, saving the city considerable capital costs. In addition, the new filtration system cost $1 million less than the original, conventional storage tank design.
The AquaPrime cloth media filters experienced the first wet-weather events shortly after startup in October and November 2017. Due to the continuous treatment capacity, no untreated overflows have occurred.
Rushville’s new tertiary/wet-weather filtration system also included replacement of its existing gas chlorine disinfection system with a UV disinfection system. The UV system was installed in the existing tank, which also provided significant project cost savings.
Completion of the filtration/disinfection phase of the city’s upgrade project was achieved five years earlier than required by the state regulation agency. This project is the first AquaPrime filter installation in the nation for dual tertiary/wet-weather treatment and will keep approximately 50 million gallons of raw sewage from entering the nearby Flatrock River, annually.
“With the addition of the AquaPrime Filter System and new UV disinfection system, Rushville is discharging the best quality of water to our receiving stream, Flatrock River, than in years past,” says Les Day, utilities director.
AquaPrime filter process
The AquaPrime filter features a disk configuration and an outside-in flow path, which allows for three zones of solids removal. These zones are especially critical in wet-weather applications due to the high solids typically associated with the first flush after wet-weather events.
The top zone is the “floatable zone” where materials collect; the middle zone is the “filtration zone” where solids are removed; and the bottom zone is the “solids zone” where settling occurs.
Design characteristics
In order to remove 85 percent or more of TSS and CBOD5 in CSO discharges, the AquaPrime filters are designed for upstream alum addition. The system is also designed to treat for the duration of a wet-weather event, which can last for several days.
Aqua-Aerobic Systems Inc. services its customers around the world with products and systems that are adaptable to the changing demands of the water and wastewater treatment industry. Its markets range from small- and medium-sized municipalities to large metro areas around the world, treating both domestic and industrial waste streams.
815-654-2501 | www.aquaprimefiltration.com
