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 was unable to pass the rated production capacity by the manufacture, with a particular problem during the fall turnover period. An autopsy of the membrane surface suggested a thick silica fouling layer. Various acid, base, and disinfectant schemes were tested along with increased backwashing capabilities, with no success. This left in question whether the issue was inherent with the membranes or rather, a function of the source water. As such, it was decided to rent a full scale microfiltration membrane unit with a different membrane material (Polyvinylidene di-fluoride or PVDF), but similar pore size (~ 0.1 µm) and test the two systems side-by-side. It was determined that the PVDF membranes performed better than the PS membranes at the full scale pilot test for the Crystal Lake source water. Generally the PS system lost production and became more fouled over time. The PVDF membranes, however, demonstrated a resilient system that had limited irreversible fouling and generally a higher specific flux. The Unified Modified Fouling Index (UMFI) was implemented and provided insight into the relative performance of the system, as operational changes were made and could be used as an index that the operator could implement in determining how 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 membranes to obtain the higher flux rates; and, the PS membrane required approximately 10 square feet of membrane to produce 1 gallon of water during a run, and as the membranes fouled, required upwards of greater than 20 square feet of membrane area. When alum was dosed, the PVDF membranes required less than 5 square feet of membrane to produce 1 gallon of water. The PVDF membranes exhibited a similar trend as the PS membranes when the alum was turned off. Includes 3 references, tables, figures.