Saving Carbon with SND Using Ammonia-Based DO Control

Authors:

  • Katya Bilyk PE, David Wankmuller PE, Paul Pitt PE, PhD, Dana Fredericks, Ron Latimer PE, Chris Tabor PE, James Grandstaff, Perry

The objective of this presentation is to summarize results from an SND pilot at a 75 mgd BNR facility (TN limit of 5 mg/L) in Virginia. A nutrient optimization projected was completed in early 2015, which determined that operating in SND mode offers the plant operational savings around $500,000 per year. A low influent BOD:TKN ratio requires the facility to use a significant amount of supplemental carbon for denitrification to meet their effluent TN limit.

The facility has eight ENR tanks configured in a six-stage process. One tank was used for the SND pilot, and an identical tank was used for the control. The control tank was operated with the typical DO strategy of maintaining a 2.0 mg/L DO in the aerobic zone and tapering oxygen to 1 mg/L in the final aerobic cell.

During the pilot the ammonia-based DO control mode was implemented, where DO in each zone was controlled within a user-specified range to achieve an ammonia setpoint at the end of the SND tank aerobic zone. A total of four DO probes, three nitrate probes, and one ammonia probe were used for controlling and monitoring the SND pilot and control tank. The goal of the pilot was to have no ammonia and equal or less nitrate leaving the SND tank compared to the control while using less carbon. The most effective DO control strategy in the SND tank was keeping the DO lowest in the first DO control zone and gradually increasing DO downstream.

During the pilot, nitrification was maintained in the SND tank and on average the SND tank used 40% less carbon than the control tank. This presentation will present detailed results from the pilot, which will restart in Spring 2016.

For more information, please contact the author at dwankmuller@hazenandsawyer.com.

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