Evaluation of carbon sources for biodenitrification of concentrated nitrate wastewater generated at the Y-12 plant

The Y-12 West End Treatment Facility (WETF) currently treats concentrated nitrate wastewater (1-5% nitrate) generated at the Oak Ridge Y-12 plant. The facility contains 500,000 gallon tanks equipped with mixers that are used as batch suspended growth biodenitrification reactors. Acetic acid neutralized with hydrated lime (calcium acetate) is used as the carbon source for the biodenitrification process. However, partly due to the amount of lime required to neutralize the acetic acid, substantial amounts of sludge are produced that will require dewatering and disposal, possibly at a mixed waste disposal facility. Stoichiometric calculations indicate that the quantity of sludge could be reduced by 23% if a carbon source not requiring neutralization was used resulting in annual WETF storage/disposal cost savings of $250,000 to $1,250,000.

Denitrification data was obtained from WETF, and a laboratory study of the denitrification process was performed to determine and compare denitrification rates and sludge production of batch reactors fed with calcium acetate, methanol, and sucrose at nitrate concentrations ranging from 1% to 5%. Denitrification rates of 810 to 9000 mg/1 NO₃/day were determined for WETF Tanks fed with calcium acetate at nitrate concentrations up to 36,000 mg/1. A laboratory reactor fed with acetate had a denitrification rate of 700 mg/1 NO₃/day or .060 NO₃-N/MLVSS/day; sucrose fed reactors had denitrification rates ranging from 570 to 2030 mg/1 NO₃/day or .039 to 0.19 NO₃-N/MLVSS/day. Denitrification rates and order of reaction for the concentrated nitrate wastewater were comparable with similar data found in literature for wastewater with lower concentrations of nitrates.