Benedict R. Schwegler, Jr., Michael A. Langston, Gregg Harkness, and Bob Kirkpatrick
Proceedings of the 72nd annual conference and exposition of the Water Environment Federation (WEFTEC '99), New Orleans, LA. October 9-13, 1999.
ABSTRACT: The Reedy Creek Improvement District's (RCID) wastewater treatment facility is a five-stage modified-Bardenpho process comprised of four parallel trains each designed to treat 6 MGD. Due to innovative procedures implemented by the engineering and operational staff, the bioreactor has been operating at near 200% of its design treatment capacity, which has led to substantial cost savings. While nitrogen removal is satisfactory under current loading rates, our experience with this facility suggests that a lack of carbon in the second anoxic zone will limit denitrification and become a bottleneck to increased treatment capacity in the future. We believe that if we can develop an effective control strategy for adding a carbon source to optimize denitrification at higher flows, a single bioreactor train could treat up to 15 MGD. External carbon sources, such as methanol, are commonly used to enhance denitrification in advanced wastewater treatment facilities.
Despite the financial and compliance implications, there exist few good options for metering carbon additions. For this study we evaluated the effectiveness of using on-line data from a "Biological Activity Meter" (BAM) to establish a protocol for adding ethanol into the second anoxic zones of the RCID bioreactor and a pilot-scale version of the bioreactor. The addition of ethanol increased the denitrification rates in both plants, and the BAMs were able to detect subtle changes in these rates. By using the BAM data to guide manual addition of ethanol, we reduced consumption significantly over using a constant addition rate (25% and 17% in the full-scale and pilot-scale plants, respectively) while maintaining very low effluent nitrate concentrations in both plants.
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