Improving Nitrogen Removal without Significant Capital Expenditures
- Brian Book - Hazen and Sawyer
The University Area Joint Authority’s (UAJA) Spring Creek Pollution Control Facility (SCPCF) is a 10.34 million gallon per day (mgd) treatment facility located in State College, Pennsylvania, which currently discharges 4.5-5.5 mgd into Spring Creek, a High Quality, Cold Water Trout Fishery and tributary to the Chesapeake Bay. The treatment facility was upgraded between 2000 and 2003 primarily to address additional capacity requirements while being non-degrading to the fishery (i.e. Water Reuse). In anticipation of the PA DEP’s Chesapeake Bay Tributary Strategy (CBTS), the upgrade included the A2O activated sludge process with treatment goal of 8 mg/L total nitrogen (TN). This case study documents a series of pilot and full-scale trials which have resulted in the reduction of the TN discharge by 3-4 mg/L.
Beginning in March 2011 a supplemental carbon source, MicroCglycerinTM, was used to enhance nitrogen removal at the SCPCF over a six-month operating period. Several different supplemental carbon feed locations and scenarios were evaluated, including adjusting feed rates concurrent with influent load conditions to maximize nitrogen removal efficiency. In addition the use of online nitrate analyzers is being studied to improve the overall nutrient removal process.
After the preliminary work associated with carbon addition strategies, sampling by UAJA showed that nitrate levels were reduced to approximately 1.0 mg/L at the end of the anoxic zone, but that 8-11 mg/L of nitrate remained in the biological process effluent. By reviewing an uncalibrated BioWin model it was believed that the internal nitrogen recycle (NRCY) could be increased, and additional nitrogen could be removed.
To date, the plant has increased the NRCY to 450% of forward flow and achieved a reduction of 3-4 mg/L TN. The BioWin model is being calibrated with a sampling program of the entire treatment train, focusing on the secondary treatment system. The calibrated BioWin model results will then be used to make further adjustments to the NRCY rate and returned activated sludge (RAS) feed rate.
The paper will present the final results of all trials, developing recommendations for application of Carbon Feed, the chemicals used, and the controls implemented. Additionally, the paper will present the results of full scale operational changes to NRCY, RAS and MLSS operational settings as they relate to total nitrogen removal. Finally, the related operational issues of dissolved oxygen carryover in the NRCY and related processes will be discussed.
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