In-Depth Analysis of Changes Restores System Optimization
A brackish water reverse osmosis (BWRO) plant had been operating effectively, applying Avista antiscalant and cleaners for about a year. Increased water production demand has led to the addition of new water resources and a higher recovery operation at the plant. The change in feedwater quality led to increased stress on the pretreatment system and rapid membrane fouling. The existing membrane cleaning regime was reviewed to increase the time between cleans. Working with the site operator Avista Technologies assisted in re-optimizing the cleaning.
The RO system replaced a dealkalization (ion exchange) plant. At RO startup, the feedwater bypassed the ion-exchange filters, and the impact of bypassing the filters was experienced a few months later. At the same time, another borehole source was added – doubling the feed conductivity and introducing a higher level of iron to the feed. The first sign of the change was rapid clogging of cartridge filters on the feed to the RO system. On inspection, the filters were coated heavily in reddish slimy material. As the site team struggled to improve the feedwater quality to the RO units, the first stage differential pressure (dP) increased to the point where it required cleaning. The heavily fouled cartridge filter and the increase in normalized dP triggered the initial cleaning attempt. The slimy substance was suspected to be biological in nature, and the standard cleaning was performed using:
- RoClean P111 – good biological and colloidal fouling removal product.
- Citric acid – generic chemical used for sterilization and iron removal.
While the clean was in progress, analysis of the cartridge filter foulant revealed a mixture of iron and organic matter from bacterial growth.