Combining Proven Technologies to Increase Treatment Capacity and Enhance Nitrogen Removal

Combining Proven Technologies to Increase Treatment Capacity and Enhance Nitrogen Removal

JULY 07, 2016

In collaboration with a few of our colleagues from the Windsor Locks, Connecticut Water Pollution Control Facility (WPCF), we recently had an article published in the summer issue of the NEWEA Journal detailing a process improvement that simultaneously improved nitrogen removal and increased wet weather capacity of their biological treatment system. The approach taken at the Windsor Locks WPCF that we describe in the article involved making modest changes to the facility, which allowed for the use of two operating modes, combined with close cooperation with WPCF staff operators to define effective operating protocols to optimize process capabilities. Read on for a condensed synopsis, or find the full article here with a more detailed explanation of this project.

Solving wet weather-related nitrogen load issues

The Windsor Locks WPCF was upgraded to secondary treatment in 1982, using the complete-mix activated sludge process. One of the challenges the facility regularly faced was the intermittent increase in flow it experienced due to unknown I/I sources during wet weather events. Though the facility undertook interim upgrades in 2002 in response to Connecticut’s Nitrogen General Permit, which included converting its system to a serpentine-flow Modified Ludzack-Ettinger (MLE) configuration and adding Integrated Fixed Film Activated Sludge (IFAS) media to achieve nitrification and denitrification, the system wasn’t as effective as hoped.

The town decided to complete a comprehensive facilities plan that would identify short- and long-term wastewater collection and treatment needs. Part of this effort included identifying an alternative method to increase the WPCF’s wet weather capacity and improve nitrogen removal performance within the capacity of the existing process tanks. Since the flow increases from wet weather were generally short in duration, the facility realized a flexible operating approach might be the solution to minimize their impact. After thorough evaluations of the plant’s operations and available alternatives, modifications were completed that allowed use of a dual operating mode (DOM) process that involves switching from the facility’s MLE mode to a contact stabilization (C/S) mode when additional wet weather capacity is needed.

Since installing the MLE configuration and implementing the DOM process, effluent total nitrogen at the WPCF has been reduced by more than 75%, and the total nitrogen load has been decreased below its Annual Average Nitrogen General Permit target level. All of this has also allowed the operators to test the limits of the facility’s processes in ways that were previously not possible and has significantly improved wet weather capacity.

For more information on this or similar projects, contact me at


Chief Technologist
Municipal Wastewater

View All Posts

Enter your email address below for industry news and updates about Woodard & Curran.