Can Reverse Osmosis Antisclants Cause Membrane Fouling?

Yes, Reverse Osmosis (RO) antiscalants can cause membrane fouling under certain conditions. While antiscalants are designed to prevent scale formation, improper selection, dosing, or formation can lead to performance issues. Common causes of membrane fouling due to antiscalants include:

1. Fungal Growth in the Antiscalant

Some antiscalants contain impurities that can provide the necessary nutrients and carbon for microbial growth. It is not uncommon to find fungal growth in polymer-based antiscalants. Growth in the drum can seed biofouling on the membrane surface. Reputable chemical manufacturers mitigate this risk by producing higher-purity products and using NSF-approved antifungal preservatives to prevent these issues.

2. Dosing Point Too Close to Acid Injection

pH is typically adjusted using concentrated sulfuric acid.  In the absence of good mixing, the acid will temporarily form a separate phase due to its very high density relative to water.  If the antiscalant is dosed immediately after the acid dosing point, it can be hydrolyzed by the strong acid.  Certain polymer-based antiscalants are very susceptible to this degradation.

3. Incompatibility with Water Quality

Some antiscalants lack good tolerance to iron and aluminum. Such antiscalants will form an insoluble complex with these metals and precipitate on the surface of the RO membrane.

4. High Hardness or Antiscalant Overdosing

Antiscalants carry a higher negative charge than typical scale-forming anions such as carbonate or phosphate; so they have a strong attraction to calcium and magnesium.  During threshold inhibition, this attraction to calcium and magnesium causes adsorption to form clusters, interfering with the formation of a stable nucleus. However, when hardness concentrations are very high, the antiscalant itself can form an insoluble calcium-antiscalant salt. This is problematic because once the active inhibitor precipitates, other scales will also precipitate. Hardness impacts all antiscalants, regardless of whether they are polymer or phosphonate-based. AWC’s Proton antiscalant projection software can predict this salt formation and, therefore, predict maximum recovery at a given temperature and pH.

5. Quality Control Issues

In some cases, manufacturing issues can cause certain polymer-based antiscalants to form insoluble gels on the membrane surface. It is therefore imperative to use antiscalants only from reputable suppliers.

Partnering for Long-Term Reliability

To avoid these challenges, it’s essential to partner with a chemical solutions provider that not only supplies high-quality antiscalants, but also offers

• In-depth understanding of your system and feedwater quality
• Predictive software to model scaling risks and optimize recovery
• Ongoing technical support and operator training
• Reliable quality control backed by proven performance

By choosing a knowledge partner like AWC, you gain confidence that your antisclant program is optimized for both performance and membrane longevity. To partner with AWC, contact us today!