Enhanced Nutrient Removal Strategies: Approaches and Case Studies Demonstrating Nutrient Removal Success

A greater burden is placed on municipalities to comply with more stringent water quality requirements as an increasing number of lakes, rivers, and streams are being classified as impaired or nutrient sensitive. Flexible design of a wastewater treatment plant is critical to meeting nutrient limits under changing regulations and in some cases, changing influent wastewater characteristics. The challenge for meeting these stringent limits is selecting the nutrient removal process that optimizes existing infrastructure, allows operator flexibility, accommodates moving nutrient limit targets as flows increase, and is economically affordable. This paper examines several approaches and strategies for enhanced nitrogen and phosphorus removal. Four case studies are presented that examine the conversion of existing wastewater treatment facilities to enhanced nutrient removal facilities. The cost per gallon of nutrient removal upgrades will be dependent on the amount of reliability and redundancy built into the new process design as well as the target or permit limit concentration. Variability in process performance is an unavoidable outcome from the operation of any wastewater treatment plant; however, reliability and redundancy in process design may yield a more consistent plant performance and may eliminate or reduce the need for advanced tertiary or supplemental treatment measures.