CENTRA-FLO™
Georgetown WWTP, CO - Phosphorus
and Zinc Removal
| Equipment: | Centra-flo™ Gravity Sand Filter with Blue PRO® Three (3) Model CF-64 |
System Size: |
0.88 MGD average flow, 1.2 MGD peak flow |
Deliverable: |
0.3 mg/L total phosphorus, 0.2 mg/L total zinc |
Installation Date: |
Construction in progress, start-up in June 2011 |
Location: |
City of Georgetown, Colorado |
Details
The City of Georgetown, Colorado wastewater
system is located in a historic mining district in the Colorado Rockies. The plant
receives a high amount of zinc in the influent and consequently has a zinc discharge
limit of 0.20 mg/L. Georgetown also has nutrient concerns, with a phosphorus limit
of 0.30 mg/L. Pilot studies of reactive filtration and membrane technology were conducted
in the summer of 2009 to find a technology that could meet both limits for reasonable capital
and operations and maintenance costs. Based on the pilot studies, reactive filtration was
selected for the plant.
In
reactive filtration, continuous backwash filters are used with a chemical process as tertiary treatment.
Ferric iron salts are added before the filters to generate a hydrous ferric
oxide (HFO) coating on the sand within the filter. The reactive filtration process is distinguished from
other processes by its multiple mechanisms of contaminant removal. Beyond co-precipitation and filtration,
the reactive filter system is designed for contaminant removal by adsorption via the continuous regeneration
of fresh, amorphous HFO-coated sand, rather than relying on coagulation-filtration. Additionally, the moving
sand bed itself helps overcome equilibrium limitations by acting as an adsorption column, and it helps overcome
diffusion limitations by forcing contaminants in the aqueous phase into contact with the solid phase HFO-coated
sand surface. Through these multiple removal mechanisms and characteristics of the moving sand bed environment,
the process is able to lower contaminants to extremely low concentrations by removing several chemical species
of the contaminant simultaneously.
In
reactive filtration, continuous backwash filters are used with a chemical process as tertiary treatment.
Ferric iron salts are added before the filters to generate a hydrous ferric
oxide (HFO) coating on the sand within the filter. The reactive filtration process is distinguished from
other processes by its multiple mechanisms of contaminant removal. Beyond co-precipitation and filtration,
the reactive filter system is designed for contaminant removal by adsorption via the continuous regeneration
of fresh, amorphous HFO-coated sand, rather than relying on coagulation-filtration. Additionally, the moving
sand bed itself helps overcome equilibrium limitations by acting as an adsorption column, and it helps overcome
diffusion limitations by forcing contaminants in the aqueous phase into contact with the solid phase HFO-coated
sand surface. Through these multiple removal mechanisms and characteristics of the moving sand bed environment,
the process is able to lower contaminants to extremely low concentrations by removing several chemical species
of the contaminant simultaneously.
System Design
The Georgetown wastewater treatment plant has 0.88 MGD average flow and
1.2 MGD peak flow. Three continuous backwash filters with 64 square feet of filtration area each were
installed, along with a chemical dosing system. Ferric chloride will be added for the continuous regeneration
of the HFO sand coating. Pilot studies showed that zinc removal at this location requires a slight pH adjustment,
only increasing by 0.5 pH units.
Installation of the reactive filtration system was complete in February, 2011. System startup is expected by late Spring 2011, pending other projects at the Georgetown plant.
Installation of the reactive filtration system was complete in February, 2011. System startup is expected by late Spring 2011, pending other projects at the Georgetown plant.