Low-pH Ammonia Oxidation at a Biological Nutrient Removal Facility
Abstract:McAlpine Creek Wastewater Management Facility (MCWWMF), owned and operated by Charlotte Mecklenburg Utilities (CMU) of Charlotte, North Carolina, is permitted to treat 64 million gallons per day (mgd). Along with MCWWMF, three CMU treatment plants discharge effluent into the Catawba River just upstream of the South Carolina border. CMU worked with North and South Carolina regulators agreeing to accept a National Pollutant Discharge Elimination System (NPDES) permit limit for phosphorus set on the same basis as that for South Carolina dischargers: 1 mg/L TP. The same permit requires that the facility meet an ammonia- N limit of 1.0 mg/L in summer and 1.9 mg/L in winter months. The facility expansion and conversion to Enhanced Biological Phosphorus Removal (EBPR) is complete and the facility is operational at this time. The facility expansion also included real-time monitoring and feed-back loop control of the phosphate, nitrogen, DO, pH and solids, allowing the facility to add ferric chloride if needed to meet discharge requirements at all times. Monitoring data during startup showed that the pH values were much lower than typically needed for the ammonia oxidizing bacteria; i.e.; nitrifiers. Corresponding performance values were evaluated and the change in the population activity showed that even at pH values of less then 7.0, as low as 5.7, the system was able to continue to nitrify. EBPR functions were found to be more sensitive to low pH values. A short-term study was conducted to establish PO4-P, NH3-N, NO3-N, pH and DO profiles in the aeration basins. The results were then utilized to develop a control strategy for the daily operations, with the goal of maintaining sustainable ammonia and phosphorus removal.
Document Type: Research Article
Publication date: January 1, 2006
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