The Swansea Water District (Massachusetts) is planning to construct a plant to treat a
blend of water from the Palmer River and a groundwater wellfield. The river, approximately 5
miles upstream of Narragansett Bay, is tidally influenced, and seawater from the bay will intrude
into the planned river intakes during high tides. At high tide, when salinity is highest, the water
has 21,300 mg/L of total dissolved solids, 14 mg/L total organic carbon (TOC), and 33 PCU of
color. To treat this water, a system comprising of coagulation-assisted membrane pretreatment
followed by reverse osmosis has been proposed. To determine the optimum coagulant type and
dose for Palmer River pretreatment, a series of bench-scale jar tests was conducted using ferric
chloride (FeCl<sub>3</sub>) and a medium-basicity polyaluminum chloride (PACl) to simulate the
coagulation, 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. Different
polymers and a powdered activated carbon (PAC) were then tested at the optimum coagulant
dose and pH to determine if the pretreated water quality could be improved.
FeCl<sub>3</sub> was found to be very effective at removing TOC and color and reducing ultraviolet (UV)
absorbance. The optimum dose was 40 mg/L FeCl<sub>3</sub>. Higher FeCl<sub>3</sub> doses produced water with
better pre- and post-filtration quality, but the improved water quality was outweighed by the
substantially higher chemical use and residuals solids handling. PACl was not effective; even
doses as high as 150 mg/L PACl failed to achieve results comparable to the optimum FeCl<sub>3</sub> 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.
| Edition : | Vol. - No. |
| File Size : | 1
file
, 360 KB |
| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 14 |
| Published : | 11/01/2005 |
