What are the most common causes of membrane failure in industrial RO systems?

The operating system becomes less effective and functional as a result of fouling, which is the gradual accumulation of contributing deposits. Since membrane systems are mechanical, surface fouling is a possibility. The membranes eventually deteriorate due to this fouling. The performance of RO and NF membranes is affected by four key fouling factors: suspended particles, scaling, organic, and biological. There are three basic reasons of degradation—hydrolysis, oxidation brought on by pH extremes, and exceeding the maximum operating temperature.

Oxidation

Oxidizers like chlorine, ozone, chloramines, hydrogen peroxide, and other substances will damage the concentration layer of the membrane's structure. Some layers are more severely harmed by this than others, such as the thin film composite layer. You can take safety measures including keeping chlorine levels below 0.01 parts per million. When present in the input water, metals like iron and copper speed up the oxidation process. If oxidation-related damage is severe, salt rejection will decrease. When it reaches a certain level, the cost of operating the machinery and the ionic burden on downstream ion exchange machinery will be more than the price of repairing damaged membranes.

Floating Solids

In the feedwater, suspended particles build up on the membrane's surface. This obstructs feed channels and may be particularly problematic for lead membranes in a system. This can be brought on by suspended materials such silt, clay, iron, silica, manganese, and aluminium. Cleaning contaminated membranes can be done with dispersants and surfactants.

Scaling

A membrane's surface may become very saturated with materials like calcium, strontium, barium, and other salts, which reduces the quantity of water that can permeate through the membrane and flow through the feed channel. A typical cleaning method for this is to apply an acidic solution with a low pH to the membrane. It is not very frequent, but if silica fouling does happen, it will be considerably harder to clean and call for a new, more specialised approach.

Organic

Membrane fouling can be brought on by naturally occurring organics in surface water. Coagulants (also known as flocking agents) and incompatible pretreatment chemicals are other forms of fouling besides organic fouling. Organic materials are often cleaned by using a high pH solution. There are times when a more specialist cleaning technique may be required, however this depends on the foulants present.

 

 

pH Excessive

Extremes in pH balance can lead to hydrolysis, a chemical process that breaks down the membrane. The thin film composite layer of a membrane will function between 2 and 11 on the pH scale. The pH range of the cellulose acetate membrane is 5-8. According to both sources, hydrolysis takes place above this point. This results in damage to the feed channel spacer, glue joints on membrane leaves, and the polymeric structure of the membrane. The membrane won't function well in these circumstances.

Biological

It's possible for biological matter to accumulate on the membrane's surface, which would reduce the permeate and feed channel flows. Organic slimes and microorganisms are two examples of fouling components. To remove biological matter, use a high pH cleaner with dispersants at high temperatures and turbulent flow rates. If there is significant biofouling present, overnight soaking may be required.

Temperature

The membrane suffers heat degradation when its operating range is surpassed, rendering it typically unusable. The maximum temperature for most thin film composites is 45 degrees Celsius, compared to 35 degrees Celsius for cellulose acetate membranes. The membrane is completely destroyed if the temperature surpasses this.

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