The Coeburn-Norton-Wise (CNW) Regional Wastewater Treatment Plant in Coeburn, VA upgraded its 6.5 MGD oxidation ditch using Entex’s IFAS Webitat system to meet ammonia effluent limits of 2.2 mg/L in summer and 4.7 mg/L in winter.
In 2014, eight Webitat modules with BioWeb fixed media were installed in the anoxic outer ring of the ditch, totaling 64,000 ft² of surface area. Each unit is aerated at approximately 40 SCFM to support effective ammonia oxidation. Prior to installation, effluent ammonia frequently exceeded seasonal permit limits, especially during peak summer months. After startup in spring 2015, ammonia levels dropped sharply and consistently remained well below permit thresholds.
Performance data from 2017–2018 demonstrates the long-term reliability of the system. Effluent ammonia averaged under 0.3 mg/L throughout both years, with most months below 0.1 mg/L—offering a significant margin of safety against discharge limits.
Application
6.5 MGD Oxidation Ditch Retrofit for Ammonia Removal
Entex Solution
Eight Webitat modules installed in the anoxic outer ring
Startup: Spring 2015
Results
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Met seasonal ammonia limits every year since installation
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2017–2018 effluent ammonia levels consistently below 0.3 mg/L
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System provides stable, long-term nitrification performance