Achieving BNR with Bioaugmentation and High Purity Oxygen: Rigorous Technology Review and Process Modeling Leads to Successful Startup of the Harrisburg AWTF BNR Retrofit

Bioaugmentation strategies are generally categorized as one of two types of systems where (1) little or no mainstream RAS is incorporated into the sidestream treatment system or (2) a large majority of the mainstream RAS is integrated into the sidestream treatment system. These two strategies were evaluated with the development and application of a calibrated and validated process model of the Harrisburg Advanced Wastewater Treatment Facility (AWTF) which was a non-nitrifying high purity oxygen (HPO) plant. The maximum specification nitrification growth rates were lowered from the default values of 0.9 and 1.0d-1 for AOBs and NOBs, respectively, to 0.59 and 0.69d-1 to account for the pH suppression effects of accumulated CO2 commonly observed in closed-vessel HPO systems. Following calibration and validation, the process model was modified to investigate the performance and robustness of both of strategies. The strategy that employed RAS integration exceeded the performance of the strategy where no RAS was integrated. Superior nitrification was evident, TN removal was limited only by denitrification, and it was found more robust due to its ability to operate at a greater aerobic solids retention time (aSRT). Following design and construction of the upgrade to a RAS Regeneration configuration, the process was started up in late April 2016. Full nitrification was realized in early May of the same year. Methanol addition to the post-anoxic zone commenced in late May. The process has been performing admirably and better than the process modeling predictions; the effluent ammonia, nitrite + nitrate, and TN have respectively come down to 0.1 mg/L, 1.0 mg/L, and 2.0 mg/L.