Chemically Enhanced High Rate Clarification for Phosphorus Removal – A Long Term Solution
The City of Jeffersonville’s Downtown WWTP uses a closed loop reactor type oxidation ditch system with
an anoxic zone to treat a design average flow of 9.0 MGD and a peak daily flow of 50.0 MGD. The new
NPDES permit requires the plant to meet a total phosphorus (TP) limit of 1.0 mg/L. The City’s long term
approach evaluated two Chemically Enhanced High Rate Clarification Systems (CEHRC) for tertiary
treatment to potentially meet low level total phosphorus in the long term.
The two CEHRC systems, including Veolia’s Actiflo and Evoqua’s CoMag systems, were pilot tested for
three weeks to determine the raw wastewater characteristics, coagulant dose, polymer dose, ballasting
material dose and surface overflow rates suited for different levels of TP removal. Raw wastewater and
secondary effluent were tested for CBOD, TSS and different forms of phosphorus including total
phosphorus, soluble total phosphorus, soluble reactive phosphorus and ortho-P. The influent total
phosphorus averaged 6.0 mg/L with a maximum value of 9.0 mg/L. 70% of influent phosphorus are
readily available for chemical precipitation in ortho-P form. In the secondary effluent, ortho-P
contributed to about 95% of total phosphorus, indicating the feasibility of chemical precipitation. The
secondary system with an anoxic zone currently results in 30% TP reduction and effluent TSS less than
20 mg/L.
Veolia’s Actiflo system is comprised of a coagulation tank, injection tank and a maturation tank with
lamella plates. The blasting material micro sand is induced in the injection tank for ballasting the floc.
Evoqua’s Comag system is comprised of a coagulation tank, ballasting tank, polymer tank and
maturation tank. Comag system uses magnetite material for ballasting the floc. Both the systems recycle
the ballasted sludge from the clarifier to a ballasting material separating hydro cyclones or magnetic
drum to separate the ballast material, which then is recycled back to the system. Pilot tests used
Aluminum Sulfate and Ferric Chloride as coagulants and anionic polymer for flocculation. The results
showed the two CEHRC systems will be able to achieve TP levels between 0.1 and 1.0 mg/L based on the
coagulant dose. The two systems responded to the phosphorus loading and chemical dosing in a similar
fashion. An Alum dose between 30-60 mg/L and a Ferric Chloride dose between 45-60 mg/L are required
to meet TP less than 1.0 mg/L. To achieve a very low TP levels (<0.1 mg/L), 90 mg/L of Alum and Ferric
are required. Polymer dose ranged between 0.5 and 1.0 mg/L to target less than 0.5 mg/L TP levels.
Hydraulic loading rate for the two high rate clarification system ranged between 30-40 GPM/SF during
both Alum and Ferric Addition in the two pilot systems. The total suspended solids in the effluent is
expected to be less than 5 mg/L.
Additional sludge production was estimated to determine the impacts on the sludge processing units.
The existing infrastructure, including aerobic sludge holding tanks and dewatering belt filter press units,
will be able to process the additional sludge from the tertiary system. Hydraulic calculations showed the
two CEHRC systems would fit within the head available between the secondary clarifiers and UV system,
eliminating the need for an intermediate 50 MGD pump station. The study concluded that chemically
enhanced high rate clarification is the best suited tertiary treatment technology for the Downtown
WWTP in the long term to meet potential stringent phosphorus limits.
61 Quartermaster Court
Jeffersonville, Indiana 47130
PHONE: 812.725.7900
61 Quartermaster Court
Jeffersonville, Indiana 47130
PHONE: 812.725.7900