Population and commercial growth put stress on Folkston, Ga.'s wastewater treatment plant.
The city had
expanded the facility a decade ago by adding a storage pond, land application
system and three-cell constructed wetland system. During the drier periods in
the summer, the land system and discharge to the Spanish Creek can handle the
flows from the wetlands, but during wetter periods, the two systems cannot
treat the increased flow. Also, the plant had to contend with expansion of a
nearby prison that added to the wastewater plan's load.
solution was a moving-bed biological reactor (MBBR) system to upgrade the
lagoon. The MBBR is a once-through system that incorporates a biofilm process
in a completely stirred reactor, with no sludge recirculation required.
develops on the inside of plastic carriers, which move freely in suspension in
the reactor tank, oxidizing ammonia nitrogen in the wastewater. Oxygen is
delivered to the carriers through coarse bubble aeration which also keeps the
carriers mixed and in suspension. Media is retained in the tank via stainless
steel cylindrical retention screens.
Each MBBR train has
three individual MBBR reactors or stages. Staging facilitates high-rate ammonia
removal in the first stage, where the bulk ammonia concentration was highest,
and low-rate polishing in the third stage. Staging allows for a smaller
footprint and less media volume to help minimize equipment costs. Each stage
contains one 10" dia wedge-wire retention screen, sized for peak hydraulic
flows with minimal head loss. The screen is kept free of debris by aeration
headers located directly underneath that also keep carriers from continually
knocking into the screen. Airflow to the MBBR is controlled by a control system
After the wastewater leaves the MBBR system,
it flows to the newly installed effluent pump station where the water is pumped
into existing constructed wetlands, then to ultraviolet disinfection and
The MBBR system began meeting the
effluent ammonia limit of 5 mg/l less than two weeks after startup. Influence
and effluent samples were analyzed regularly for the first four months and the
average ammonia discharge from the MBBR was <1 mg/l.
removal for the MBBR occurs within the biomass carrier and is measured in a g
NH3-N/m2/d. The specific removal rate across the entire
MBBR at Folkston averaged 0.05 g/m2/d up to a maximum of
For more information on
Siemens Water Technologies and to view this case study video, go to www.siemens.com/water, type
"Georgia town" in the search box, then click on "Georgia Town
Meets Regulations and Increases Capacity with MBBR System."