AWWA WQTC55005

The Second Taxing District Water Department (STDWD) of South Norwalk, Connecticut owns and operates a 10 mgd filtration plant located in Wilton, Connecticut. The plant, last upgraded in 1968, utilizes conventional treatment comprised of pre-aeration, rapid mix, flocculation, sedimentation and shallow-bed ABW sand filtration. Raw water for the filtration plant is drawn from City Lake Reservoir. The STDWD filtration plant produces high-quality drinking water that meets all current standards. Future regulatory requirements of the Enhanced Surface Water Treatment Rule and Disinfectant/Disinfection Byproducts Rule have compelled the utility to re-examine existing treatment processes and evaluate future treatment alternatives. The STDWD engaged Metcalf and Eddy, Inc. to conduct a feasibility and pilot study. A key objective of this pilot study was to determine if membrane ultrafiltration could effectively replace conventional treatment. A two season (winter and summer) pilot study was ultimately recommended to evaluate the following four process alternatives in parallel: dissolved air flotation (DAF) clarification, ozonation, with granular activated carbon filtration; micro-sand enhanced clarification, ozonation, with granular activated carbon (GAC) filtration; membrane ultrafiltration using immersed membranes; and, membrane ultrafiltration using pressurized membranes. This paper presents the results of the winter season of piloting with regard to DBP and NOM removal for the four pilot processes. Independent variables throughout the study included coagulant dose, intermediate ozone, pH adjustment, and hydraulic loading rates. Alum was used for coagulation for all four processes, and alum combined with powdered activated carbon (PAC) for the membrane processes. Includes tables, figures.