The Chesapeake Bay Agreement of 1987 calls for an overall reduction in nutrient loading of forty percent of 1985 levels by the year 2000. Signatories to the agreement include the states located in the Bay's watershed and the District of Columbia. The District's 16.2 m3/sec (370 mgd) Blue Plains Regional Wastewater Treatment Plant is the single, largest point source of nitrogen load to the Bay, discharging approximately 18 metric tons per day. In an effort toward meeting the nitrogen reduction goal, a post-denitrification demonstration study was recently begun to access its potential for long-term implementation.
The denitrification demonstration project involves operating half of the nitrification facilities in a nitrification-denitrification mode using methanol as a carbon source for post-denitrification. The other half continues operation in a nitrification-only mode as a control. The post-denitrification process was selected for demonstration because it utilizes existing facilities and may offer substantial long-term cost savings. Objectives of the study are to demonstrate the process without a negative impact on effluent quality, to verify performance and capacity, to determine the stability and limitations of the project, and to compare the process to other nitrogen-removal technologies.
Thus far, the process has been successful in removing nitrogen despite problems with phosphorus limitation and with the settling characteristics of the denitrification sludge. It is believed that insufficient phosphorus availability has been responsible for problems associated with settling, sludge yield, methanol use, and denitrification rates. Recently, phosphorus input to the denitrification process has been increased by reducing metal salt addition in upstream processes and preliminary results have been promising. If performance criteria are achieved without sacrificing plant capacity, the process will be continued at full scale.