A low-cost solution for ever-tightening phosphorus limits at the Concord, MA WWTP

Challenge

Prior to 2007, the Concord, Massachusetts wastewater treatment plant operated under a NPDES permit that allowed a seasonal phosphorus limit of 0.7 mg/L.  However, with the issuance of a new five-year permit with a phosphorus limit of 0.2 mg/L and the probability that future limits could reach as low as 0.05 mg/L, the city of Concord needed a treatment solution that would be reliable and cost-effective over the long term.

Flexibility and Operational Reliability in a Small Footprint 

​When compared to dissolved air floatation, media filtration and sand ballasted technologies, Concord’s consulting engineers recommended the CoMag® System​ from Evoqua Water Technologies. Key benefits include:

• Ability to provide effluent TP values from 0.2 mg/L to ≤ 0.05 mg/L simply by adjusting the flocculent dose.

• Reliability of operation — conventional flocculation and coagulation coupled with high rate clarification and no filters to clog or backwash.

• Capital cost savings given its small clarifiers and footprint.

The CoMag® System Overview

Simple, reliable and proven, the CoMag® System from Evoqua uses magnetite to ballast conventional chemical floc, enhancing settling rates to dramatically increase the performance of wastewater treatment facilities. Primarily used to improve primary and/or tertiary treatment, the CoMag System easily integrates with planned or existing facilities, making it easier than ever to solve today’s operational and environmental challenges.

At the Concord WWTP, the CoMag System includes six steps:

• Conventional chemical flocculation with Ferric, Alum or PAC
• Infusion of the floc with fully inert, finely ground, nonabrasive magnetite
  (Fe3O4) to increase the specific gravity of the floc
• Coagulation to bind the floc together
• High rate clarification in traditional but smaller clarifiers
• Sludge recycled for stable operation, upset prevention and pin floc capture
• 99+% recycle and reuse of magnetite for low operating costs

Results

Installed in 2007, the CoMag® System exceeded all performance parameters — achieving TP down to 0.2 mg/L, with daily capacity of 1.25 (4.73)/4.4 (16.7) MGD(MLD).



The system now plays an integral role in a larger facility upgrade that includes improvements to the headworks, disinfection system, plant utilities, controls and other processes. Additionally, its high-quality effluent enables the facility to utilize smaller, more cost-effective UV disinfection system.​