Meeting Stringent Phosphorus Limits Within Tight Footprint Constraints

Challenge

Originally constructed in 1966, the Billerica, Massachusetts wastewater treatment facility primarily processes residential wastewater.  However, alum sludge from Billerica’s drinking water treatment facility makes up a significant portion of the solids loading at the plant with the treated effluent discharged to the Concord River.

Solution

​To meet a new total phosphorus (TP) limit of 0.2 mg/L, as well as future TP limits that could be even lower, the town of Billerica considered several options. The CoMag® system was an ideal solution due to its small footprint.

In order to reduce upgrade costs, the town of Billerica needed to fit tertiary clarifiers within the walls of two existing concrete tanks, however reusing the existing tankage eliminated demolition and excavation costs. The CoMag® System was ideal for this configuration because it requires significantly smaller clarifiers than conventional systems to treat equivalent flow rates.  The design only required two 23-ft. (7-m.) circular clarifiers, which easily fit in the existing concrete tanks.

Results

Initial Pilot Testing

In 2007,  the CoMag​® system was initially piloted and proven to meet the new TP limit with alum, polyaluminum chloride (PACL), ferric chloride or sodium aluminate coagulants.  Additionally, the pilot demonstrated that future permit limits as low as 0.05 g/L could also be met without the need for a polishing filter by simply increasing the coagulant dose.  

Full-Scale Installation Results

Since installation at the Billerica Wastewater Treatment plant in 2010, the CoMag® system has proven to be a reliable and versatile tertiary treatment process with the capability to achieve any effluent TP target down to less than 0.05 mg/L, while also achieving significant reductions in total suspended solids (38 percent), BOD (59 percent) and other contaminants.

“The CoMag® system’s quick learning curve and reliability make it a great system for tertiary treatment with only a few simple parameters to monitor that make for easy operation,” said Jeff Kalmes, Billerica’s plant supervisor. The CoMag® system allowed the facility to meet stringent TP limits within challenging footprint limitations, while coping with wide fluctuations in feed flow, TP and TSS concentrations.