Balancing yield, kinetics and cost for three external carbon sources used for suspended growth post-denitrification Y. Mokhayeri, R. Riffat, S. Murthy, W. Bailey, I. Takacs and C. Bott ABSTRACT Y. Mokhayeri R. Riffat Civil and Environmental Engineering Department, The George Washington University, Washington, DC 20052, USA E-mail: yalda@gwu.edu; riffat@gwu.edu S. Murthy W. Bailey DC Water and Sewer Authority, 5000 Overlook Ave, SW, Washington, DC 20032, USA E-mail: SudhirMurthy@dcwasa.com; wbailey@dcwasa.com I. Takacs EnviroSim Associates, Ltd., 15 Impasse Faure, 33000 Bordeaux, France E-mail: imre@envirosim.com C. Bott Civil and Environmental Engineering, Virginia Military Institute, Lexington, Virginia, USA E-mail: BottCB@vmi.edu Facilities across North America are designing plants to meet stringent limit of technology (LOT) treatment for nitrogen removal. In the Mid-Atlantic region of the United States, this is in response to the Chesapeake Bay Agreement, which limit effluent total nitrogen discharges from wastewater treatment plants to between 3–5 mg/L. Since denitrification is crucial for the removal of nitrogen, maximizing this process step will result in a decrease in nutrient load to the receiving waters. Of particular interest is the use of an alternate external carbon source to replace the most commonly used carbon, methanol. Three external carbon sources were evaluated in this study including: methanol, ethanol and acetate at 138C. The aim of this study was to evaluate the relative benefits and constraints for using these three carbon types. Laboratory scale Sequencing Batch Reactors (SBRs) were set up to grow and acclimate carbon free biomass to the specified substrate while in-situ Specific Denitrification Rates (SDNRs) were conducted concurrently. The results suggest that the SDNRs for acetate (31.0 ^ 4.6 mgNO 3 -N/gVSS/hr) and ethanol (29.6 ^ 5.6 mgNO 3 -N/gVSS/hr) are higher than that for methanol (10.1 ^ 2.5 mgNO 3 -N/ gVSS/hr). The yield coefficients in g COD/g COD were observed to follow a similar trend with values of 0.45 ^ 0.05 for methanol, 0.53 ^ 0.06 for ethanol and 0.66 ^ 0.06 for acetate. Key words | acetate, denitrification, ethanol, methanol, sequencing batch reactor, yield INTRODUCTION Wastewater treatment plants in the Chesapeake Bay region are interested in improving performance of their existing denitrification processes. This is in response to the Chesapeake Bay Agreement, which will limit effluent total nitrogen to between 3 – 5 mg/L. An important step for nitrogen elimination in wastewater treatment is hetero- trophic denitrification. In this process, organic substrates are utilized as electron donors by denitrifying bacteria, and the electron acceptor (nitrate and/or nitrite) in the anoxic reactor is converted to nitrogen gas. When essentially complete nitrogen removal is required, an external source of carbon containing no nitrogen will be used. External carbon addition typically is needed to attain low effluent nitrate concentrations because of carbon limitations/availability in the wastewater. Blue Plains Advanced Wastewater Treatment Plant (AWTP) in Washington, DC is the largest point source wastewater treatment plant discharging into the Potomac River that makes its many to the Chesapeake Bay. The plant is one of the many wastewater treatment plants evaluating its ability to meet future discharge limits and is specifically interested in assessing the use of external sources of organic carbon. The plant currently uses methanol as an external carbon source in a post denitrification process. Methanol is commonly used for denitrification because of its low cost and ability to denitrify without leaving a residual doi: 10.2166/wst.2009.623 2485 Q IWA Publishing 2009 Water Science & Technology—WST | 60.10 | 2009 Downloaded from https://iwaponline.com/wst/article-pdf/60/10/2485/447279/2485.pdf by guest on 11 June 2020