Optimization through Design: Implementing Full-Scale Carbon Addition to 700 mgd of WWTP

Authors:

  • Mark Supplee PE, Sarah Galst PE, Robert Frost PE, Tom Sadick PE, Matthew Osit PE, Sue Liu PE., Sal Scapelito PE

The process configuration of the NYC BNR WWTP aeration tanks consist of four-pass aeration; each pass configured with anoxic zones followed by aerobic zones. PE is fed to the head of each pass, where anoxic conditions are present, to support denitrification. Supplemental carbon is fed to achieve the overall level of TN removal required to meet the regulatory limit.

Further complicating supplemental carbon demand, NYC’s WWTPs have diurnal variability in the carbon and nitrogen content of the influent. This variability increases/reduces the supplemental carbon demand at different times of the day, as the ratio of carbon to nitrogen changes.

Glycerol is fed “neat” (70% glycerol) to carbon supply control stations (CSCS) that act as flow splitters. CSCSs meter flow to the various dose injection points at each aeration tank.

A 20-day study was conducted at the 26th Ward WWTP running side-by-side aeration tanks under two different glycerol control strategies to compare overall glycerol addition with denitrification. The control strategies tested were manual control, with settings based on achieving TN removal goals regardless of diurnal fluctuations in influent, and nitrate analyzer control.

As a final step in the implementation of their 20-year plan for Biological Nitrogen Removal (BNR), the New York City (NYC) Department of Environmental Protection (DEP) has installed and is initiating operation of supplemental carbon facilities to meet total nitrogen (TN) discharge limitations.

The DEP facilities are configured to make use of the readily biodegradable carbon present in the primary effluent (PE) for denitrification via a step-feed process approach, however there is insufficient carbon in the PE to support the needed denitrification to comply with permit limits. To overcome this limitation and improve nitrogen removal, supplemental carbon is being added to several of NYC’s BNR plants. DEP contracted with the joint venture of CH2M and Hazen to design supplemental carbon (glycerol) addition facilities at the Wards Island, Tallman Island, 26th Ward, Bowery Bay and Jamaica Wastewater Treatment Plants (WWTPs). The construction of the designs is complete and all facilities are online with carbon addition being optimized. Optimization features were incorporated into the design of the carbon addition strategies to enhance overall TN removal while minimizing glycerol usage.

This paper will:
a) Summarize the existing step feed BNR process
b) Summarize the new glycerol addition systems’ process-mechanical and instrumentation features as they pertain glycerol dosing control strategies
c) Review glycerol system control strategies
d) Present comparative control strategy performance data from one of the operational full-scale systems.
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For more information, please contact the author at rfrost@hazenandsawyer.com.

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