HOW LOW CAN YOU GO? PROVE IT! ENSURING HIGH NITROGEN REMOVAL PERFORMANCE OF UPFLOW DENITRIFICATION FILTERS

The Cheshire, CT Water Pollution Control Plant (WPCP) is required to meet stringent nitrogen discharge limits as a result of the Connecticut Department of Environmental Protection's (CTDEP) Total Maximum Daily Limit (TMDL) program. The Cheshire WPCP has an average day capacity of 3.5 MGD and employs advanced conventional secondary treatment to provide nitrification. A nitrogen removal study determined that separate stage denitrification (DN) filters were the most cost effective means to meet the CTDEP's nitrogen discharge limits at Cheshire (3.5 mg/l total nitrogen (TN) yearly average at design flows). This paper examines the pre-selection process and performance test developed for an upflow DN filter system to achieve the stringent nitrogen removal requirements at the Cheshire WPCP and presents an approach that could be used by other municipalities facing similar stringent effluent limits.