Elimination of Complex Process Control Strategies in Single-Stage Deammonification

Abstract

A full-scale ANITAMox deammonification system was commissioned by Metro Wastewater Reclamation District at the Robert W. Hite Treatment Facility in Denver, Colorado for sidestream treatment of recycle nitrogen loads in the centrate stream. The single-stage partial nitritation anammox process has operated for over three years, with an average of 60% total ammonia removal. The facility eliminated the complex pH-based cascade control strategy after 16 months of operation, opting for simplified feedback control of volumetric airflow rates. The impacts of airflow and biomass concentration on nitrogen removal capacity were unclear. Bench-scale studies investigated the effects of surface area loading rate of ammonia (SALR), bulk dissolved oxygen (DO), and aeration rate on total ammonia nitrogen (TAN) and total inorganic nitrogen (TIN) removal capacity. Bulk DO between 1.0 and 2.0 mg/L did not impact the surface area removal rate (SARR) of TAN. Analysis of full-scale data did not reveal correlations between SARR-TAN and pH or DO. Biofilm concentration, estimated by total solids attached to the media, accumulated until October 2018. After the first year of operation, SARR-TIN did not increase accordingly, with respect to biofilm concentration. Average TAN removal was 60%, despite variable nitrogen loading, pH, and dissolved oxygen concentrations in the ANITAMox reactors and fixed airflow at operator-defined set points. Stable performance was observed and more robust than expected, considering variations in pH, DO, and airflow rates.