A municipality in Texas had been operating its new reverse osmosis (RO) trains for only a few months when it started experiencing severe decline in flux and an increase in salt passage. Membrane cleaning did not restore performance. Cartridge filter analysis found heavy iron loading. Membrane autopsies revealed heavy iron hydroxide fouling across the entire length of the system, with the concentrate elements experiencing the worst flux decline and severe surface abrasion. The plant was designed with the RO system being fed from a 50,000 gal (189 m3) storage tank. The feedwater contained a significant concentration of iron which was completely soluble under anoxic conditions but oxidized to insoluble ferric hydroxide in the atmospheric feed tank. The concentrations of iron exiting the feed tank were highly variable as precipitated iron sludge would slough off from the bottom of the tank. While bypassing the feed tank and installing a VFD on the well pump would have been the ideal solution, the plant needed to operate, and such a major undertaking could not be performed overnight. A chemical solution was therefore needed to resolve the issue. After verifying the cause of the fouling by membrane autopsy, an iron-specific CIP chemical was used to restore performance. A novel iron-control antiscalant was then put online, upstream of the feed tank, resulting in stable normalized performance for a full year, and eliminating the need for further cleaning. This case study describes how the owner, the consulting engineer and the chemical solutions provider worked together to troubleshoot, select and validate the optimal chemistry, and most importantly, make changes in the process to allow for the correct application of the chemistry and restore system performance.
This presentation is available to AMTA Members only.
- Mo Malki
- American Water Chemicals
- AMTA/AWWA Membrane Technology Conference, West Palm Beach, FL
- AMTA/AWWA Membrane Technology Conference
- Brackish Water, Novel Antiscalant, Iron Fouling