Achieving Low Nutrient Residuals with BAF In West Warwick, Rhode Island

Biological nitrification and denitrification filters were initially started up in the Spring of 2005 at the Regional Wastewater Treatment Facility in West Warwick Rhode Island. These were the first large scale biological filters installed in the Northeast. The West Warwick plant is a 10.5 MGD facility serving the communities of West Warwick, Warwick, East Greenwich, Cranston and Coventry. The West Warwick plant was recently expanded and upgraded, with new headworks, advanced treatment processes for nutrient removal, ultraviolet disinfection, odor control and plant wide SCADA systems. The advanced treatment processes are designed to meet newly adopted RIDEM effluent requirements for discharges into the Pawtuxet River and ultimately Narragansett Bay. The permit requirements for West Warwick are seasonal and include stringent requirements for BOD, Total Suspended Solids, Ammonia, Total Nitrogen and Phosphorus.The West Warwick plant has very limited area and is surrounded by wetlands. There was insufficient land area to expand the existing activated sludge process into a configuration suitable for biological nutrient removal. Biological activated filters (BAF's) were installed to remove ammonia and total nitrogen on a footprint of only 25,000 square feet. The biological filters operate at comparatively high hydraulic loading rates and make very efficient use of land area. Phosphorus removal is achieved by the addition of alum at the plant headworks. Hydrated lime storage and feed facilities have been provided to replace alkalinity lost in the phosphorus removal and nitrification processes.The nutrient removal processes are housed in two compact structures, one a former pair of treatment tanks converted into a building housing chemical storage tanks, backwash pumps and backwash blowers. The second is the new BAF Building that houses the BAF influent pump station, four nitrification filters, four denitrification filters, the clearwell and the mudwell.Construction started in the Fall of 2002 and was completed in October 2004. The process was started up in the Spring of 2005 and was required to meet permit requirements by July 2005. Thirty day acceptance testing of the nitrification and denitrification filters was completed in October and November 2005, during one of the wettest Octobers on record. Despite influent flows that approached the design peak for the facility, the system passed its performance tests with flying colors.The poster will include an interesting, easily understood description of the process including graphics and photos. It will also discuss the effluent quality obtained and lessons learned during the start up the plant.