Fluidized ion exchange (FIX) to control NOM fouling in ultrafiltration

To control NOM fouling, either NOM or hardness ions can be (partly) removed before membrane filtration. In this work, anion Fluidized Ion Exchange (FIX) is used to remove NOM from untreated surface water and cation FIX is used to remove calcium and magnesium ions from untreated surface water. The effect of calcium and magnesium removal by cation FIX is studied in lab-scale ultrafiltration (UF). FIX was successful in treating untreated surface water containing high loads of suspended solids (33 mg/L). No problems have been observed with clogging of the resin bed during operation. NOM was successfully removed (60%) using anion FIX during 1 month without regeneration. Calcium and magnesium were also successfully removed using cation FIX during the first day of operation. A significant difference in UF fouling was found after treatment of untreated surface water with cation FIX. Reversible fouling increased after cation FIX treatment, it was hypothesized that this was due to more open NOM fouling layers on the UF membrane. Irreversible fouling decreased after cation FIX treatment, it was hypothesized that this was due to less calcium-NOM complex formation.

Treatment of raw surface water using fluidized ion exchange (FIX) is feasible. No problems have been observed with clogging of the resin bed during operation, despite high loads of suspended solids in the feed water. NOM was successfully removed (60%) using anion FIX during 1 month without regeneration. Calcium and magnesium were also successfully removed (respectively 80% and 40%) using cation FIX during the first three days of operation. After this, calcium and magnesium removal decreased to almost zero within 1–2 weeks. A significant difference in UF fouling was found after treatment of raw surface water with cation FIX. UF fouling after FIX and batch type cation IEX treatment was found significantly lower than fouling with untreated water. Reversible fouling increased after FIX treated and batch type IEX treatment, it was hypothesized that this was due to more open NOM fouling layers on the UF membrane. Irreversible fouling decreased after FIX and batch type IEX treatment, it was hypothesized that this was due to less calcium–NOM complex formation.