AWWA WQTC62464

The Swansea Water District (Massachusetts) is planning to construct a plant to treat ablend of water from the Palmer River and a groundwater wellfield. The river, approximately 5miles upstream of Narragansett Bay, is tidally influenced, and seawater from the bay will intrudeinto the planned river intakes during high tides. At high tide, when salinity is highest, the waterhas 21,300 mg/L of total dissolved solids, 14 mg/L total organic carbon (TOC), and 33 PCU ofcolor. To treat this water, a system comprising of coagulation-assisted membrane pretreatmentfollowed by reverse osmosis has been proposed. To determine the optimum coagulant type anddose for Palmer River pretreatment, a series of bench-scale jar tests was conducted using ferricchloride (FeCl₃) and a medium-basicity polyaluminum chloride (PACl) to simulate thecoagulation, sedimentation, and membrane filtration processes. Coagulant doses up to 150 mg/L(as coagulant) were tested at various pH levels to determine an optimum dose and pH. Differentpolymers and a powdered activated carbon (PAC) were then tested at the optimum coagulantdose and pH to determine if the pretreated water quality could be improved.FeCl₃ was found to be very effective at removing TOC and color and reducing ultraviolet (UV)absorbance. The optimum dose was 40 mg/L FeCl₃. Higher FeCl₃ doses produced water withbetter pre- and post-filtration quality, but the improved water quality was outweighed by thesubstantially higher chemical use and residuals solids handling. PACl was not effective; evendoses as high as 150 mg/L PACl failed to achieve results comparable to the optimum FeCl₃ dose.Decreasing the pH to as low as pH 5.0 offered substantial improvements to the water quality.Use of PAC and polymers did not improve the performance of the pretreatment step. Includes 4 references, table, figures.

Product Details

Edition:

Vol. - No.

Published:

11/01/2005

Number of Pages:

14

File Size:

1 file , 360 KB