SUCCESS STORIES

Impact of Ferrous Ion Oxidation on Silica Scaling in RO Systems

Severe Membrane Fouling

A 23 ML/day reverse osmosis plant in South Texas that was using chlorine to oxidize arsenic for improved membrane rejection was experiencing severe membrane fouling.

ISSUE

The ferrous ions in the well water were being oxidized by the chlorine, resulting in ferric hydroxide fouling of the cartridge filters and membranes throughout the system. The RO facility did not have an acid dosing system and the antiscalant in use was not designed for such high ferric concentrations.

APPLICATION

A cleaning study was performed in AWC’s labs to determine the best cleaning chemicals and methodology for recouping the membranes’ performance. Lab simulations were then performed to determine the optimal product and dosage for inhibiting scale. The normalized data showed excellent control of the scaling and significantly extended times between cleaning using AWC A-108FE.

CONCLUSION

The use of an antiscalant that was capable of inhibiting ferric hydroxide precipitation resulted in
significant improvement in performance and reduced cleaning times. Normalized data from a 90 day full scale trial on the existing membrane elements operating at 75% recovery found the use of a novel antiscalant for ferric ion control to be highly effective at maintaining system productivity.

An autopsy on a newly installed membrane after 6 months of continuous operation at 80% recovery revealed that there was no recurrence of silica fouling while the ferric hydroxide was being controlled, despite operation at higher recovery and lower cross-flow.

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