AWWA WQTC69315

The City of Gardner, Massachusetts, was the first community in the state to use ultrafiltration membranes with a 100,000 MWCO (~ 0.1 µm) using a polysulfone (PS)material on a surface water source. However, shortly after the new membrane system was installed, the system wasunable to pass the rated production capacity by the manufacture, with a particularproblem during the fall turnover period. An autopsy of themembrane surface suggested a thick silica fouling layer. Various acid, base, anddisinfectant schemes were tested along with increased backwashing capabilities, with no success. This left in questionwhether the issue was inherent with the membranes or rather, a function of the source water. Assuch, it was decided to rent a full scale microfiltration membrane unit with a differentmembrane material (Polyvinylidene di-fluoride or PVDF), but similar pore size (~ 0.1µm) and test the two systems side-by-side.It was determined that the PVDF membranes performed better than the PS membranes atthe full scale pilot test for the Crystal Lake source water. Generally the PS system lostproduction and became more fouled over time. The PVDF membranes, however,demonstrated a resilient system that had limited irreversible fouling and generally ahigher specific flux. The Unified Modified Fouling Index (UMFI) was implemented andprovided insight into the relative performance of the system, as operational changes weremade and could be used as an index that the operator could implement in determininghow a change in membrane operation affects membrane performance.In general, the following observations were made from the pilot testing results:dosing the raw water with an alum coagulant was essential for both membranesto obtain the higher flux rates; and,the PS membrane required approximately 10 square feet of membrane to produce1 gallon of water during a run, and as the membranes fouled, required upwards ofgreater than 20 square feet of membrane area. When alum was dosed, the PVDFmembranes required less than 5 square feet of membrane to produce 1 gallon ofwater. The PVDF membranes exhibited a similar trend as the PS membraneswhen the alum was turned off. Includes 3 references, tables, figures.

Product Details

Edition:

Vol. - No.

Published:

11/01/2008

Number of Pages:

20

File Size:

1 file , 1 MB