FULL-SCALE BIOFILTER DEMONSTRATION TESTING IN NEW YORK CITY

The New York City Department of Environmental Protection (NYCDEP) conducted a full-scale demonstration test of biofilter technologies at the Newtown Creek Water Pollution Control Plant (WPCP) in two phases between 1997 and 2002. The purpose of the demonstration was to evaluate BOD polishing, nitrification and denitrification performance of biofilters as well as demonstrate their reliability and operability for potential use at one of the City's 14 WPCPs.The demonstration facility included four 1-mgd units (two Biostyr biofilters from US Filter - Krüger and two Biofor biofilters from Ondeo Degremont Inc.) and a Tetra Technologies denitrification sand filter pilot unit. The biofilters were treating high-rate activated sludge effluent from Newtown Creek WPCP. While biofilters were operating in nitrification mode most of the time, some denitrification data were also obtained from both biofilters and the Tetra sand filter.The first demonstration in 1997-1998 focused on process performance and evaluation of design parameters for both biofilter technologies. The units produced excellent process results but showed questionable reliability (instrumentation and control as well as equipment reliability, particularly valves). The demonstration plant was reactivated in 2001 to further evaluate the reliability and operability of biofilters. The two demonstration periods yielded over 27 months of process data and an extensive operations database recording backwash sequences and parameters, valve opening and closures, alarms and significant operational events.Reliability significantly improved and was adequate during the demonstration reactivation. Even with improved reliability, both biofilter providers lacked the process expertise to successfully set up or troubleshoot the units at some point during startup and testing. Biofilter units were prone to clogging if backwashed inadequately or too highly loaded, highlighting the importance of hydraulic and mass design loads as well as adequate backwash flow rate control and parameter settings. Altogether, both biofilter technologies demonstrated excellent nitrification capabilities in a predictable fashion and could operate successfully in automatic mode.