Reducing Effluent Total Nitrogen to 2.0 mg/L Using Conventional Nutrient Removal Strategies

Authors:

  • Katya Bilyk, Joe Rohrbacher, Paul Pitt, Ron Taylor, and Ron Latimer - Hazen and Sawyer

Introduction
The purpose of this paper is to document the performance of water reclamation facilities (WRFs) in the region that are achieving annual average effluent total nitrogen (TN) concentrations of 1.3 – 2.4 mg/L with the use of conventional technologies. This information will be beneficial to utilities (a) facing effluent TN limits at/below 3 mg/L as well as (b) planning for future BNR upgrades that want to gain a high level perspective on the technology choices available and how they perform.

Methodology
Four regional WRFs were selected for this study (Table 1). The operational characteristics of these facilities including influent wastewater composition, solids handling processes, secondary treatment efficiency, chemical usage and denitrification filter operation were evaluated. Historical data was evaluated and additional wastewater sampling was performed in order to characterize influent, solids recycle and operational impacts on plant performance, particularly in regards to TN removal.

Additionally, the following metrics for characterizing the reliability of treatment performance using percentile plots, developed by Bott, et. al., (2009), were used:

• The best 14-consecutive days of effluent quality represents the best achievable effluent quality
• The 50th percentile represents typical performance
• The 95th percentile represents how the plant may perform during a major process upset

Results
The percentile plots are very similar between plants, with a median effluent TN concentration between 1.9 and 2.2 mg/L. For comparison purposes, three regional plants that utilize 5-stage BNR but do not have denitrification filters were also plotted and their median effluent TN concentration ranged between 3.4 and 7.5 mg/L.

Conclusions
It appears that the dual-barrier approach to nutrient removal enhances the reliability of the process and is partly what has allowed many wastewater treatment facilities in the region to reliably reduce effluent TN below 3 mg/L and in some cases, achieve effluent TN concentrations below 2 mg/L on a regular basis. Influent wastewater characteristics, solids handling operations, inert organic nitrogen, supplemental carbon feed and solids handling will impact the level of total nitrogen removal achievable.

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

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