Can we Avoid Nitrification? Tracking the In-Plant Fate of Nitrogen at the Hopewell Regional Wastewater Treatment

The allowable nutrient discharge loading for a publicly owned industrial treatment works (POITW) with high industrial loading treating approximately 27 million gallons per day (mgd) is being capped based on the Chesapeake Bay and its tributaries nutrient control regulations adopted by the Virginia Department of Environmental Quality. Based on an analysis of historical data, the facility has experienced an increase in effluent total nitrogen between 2000 and 2004 such that it cannot meet its proposed waste load allocation (WLA) at current flow conditions, without implementing source controls or in-plant nitrogen removal. Approximately one-half of this increase is the result of an increase in influent organic-N loading to the plant from both domestic and industrial sources. The other one-half is attributed to expected variability in the amount of TKN (organic-N and ammonia-N) that the treatment facility removed. To explain this variability and to identify plant practices or in-plant sources that may contribute to periodic lower nitrogen removal, the POITW initiated development of an optimization study for TKN removal. The objectives of the study were to determine fate of nitrogen species through the plant, and identify in-plant sources of nitrogen or possible operational practices that could be addressed to reduce effluent nitrogen. The study developed historical mass balances to track the fate of nitrogen within the plant by combining historical data with more detailed results from a short-term intense sampling effort. Tracking internal nitrogen sources, such as high-TKN solids recycle streams, provided a clearer picture of the uncontrollable variability in TKN removal that was observed in the plant's past performance. Understanding the causes of this variability will enable the facility to optimize TKN removal such that the plant removes the maximum amount of nitrogen possible for the system without nitrification, which may help the POITW to meet its proposed WLA at current flow conditions.