Full Scale Evaluation, Modeling, and Optimization of Nitrate Removal through Continuously Backwashing Denitrification Filter

There are two basic types of denitrification filters being used in the Chesapeake Bay region to meet enhanced nutrient removal (ENR) level effluent requirements: continuously backwashing upflow sand filters (herein called “continuously backwashing denitrification filters”) (CBDF) and intermittent backwashing downflow sand filters (herein called “downflow denitrification filters”) (DDF). These types of filters can also be used as conventional effluent filters – in fact, there is little difference between the physical design of a denitrification filter and a conventional effluent filter. Primary differences are hydraulic loading rates and bed depths and in some cases media size, backwash rates, and control sequences.Although there is limited performance data for denitrification filters operating in the Chesapeake Bay watershed, common operation problems such as high influent DO levels and low influent phosphorus levels have been experienced at several facilities and have resulted in reduced treatment performance. The requirement to achieve very low total nitrogen (TN) and total phosphorus (TP) levels in the same filter requires a tool for operations staff to predict how changes in operating parameters will impact performance, especially as the flows and loads increase from startup conditions to design conditions at these facilities. A CBDF has been online at the 2.0 mgd Aberdeen Area Wastewater Treatment Plant of the Aberdeen Proving Grounds (AAWWTP-APG) since March 2006. While this facility has achieved excellent nutrient removal since startup, it is apparent that more precise process control will be required as the WWTP approaches design conditions.Additionally, CBDF equipment manufacturers propose filter sizing without providing kinetic calculations to demonstrate the performance of the filter under varying operating conditions. A modeling tool would be beneficial as more CBDFs are utilized to meet ENR level treatment.