What causes the loss of effectiveness of reverse osmosis membranes and how to fix it

Membrane reverse osmosis

Membrane fouling is still the major problem to overcome in seawater reverse osmosis plants, because it is the most important cause of the loss of effectiveness of this type of facility.

The loss of performance of reverse osmosis membranes is mainly caused by four types of fouling:

scaling and fouling by metals and insoluble salts, caused by precipitation of inorganic salts of low solubility and metal oxides/hydroxides in rejection

adsorption of organic matter

microbiological contamination due to the growth of microorganisms and biofilm formation on the membrane surface

-clogging of the membrane surface due to the deposition of colloidal and particulate material

Scaling and fouling by metals and insoluble salts in reverse osmosis systems

Due to the concentration of salinity process that takes place inside the reverse osmosis membranes, there is the possibility of exceeding the solubility limit of insoluble inorganic compounds.

The rejection of the reverse osmosis is where the solubility limits of the compounds can be exceeded and precipitate on the membrane surface. The precipitation is due to the high concentration of the components of insoluble salts in the concentrate.

The most common scaling and fouling by metals and insoluble salts are the following:

– calcium carbonate
– calcium sulfate
– calcium fluoride
– calcium phosphate
– strontium sulfate
– barium sulfate
– iron
– aluminum
– manganese
– silica

Reverse osmosis plant

Colloidal origin fouling

Colloidal origin fouling is an important type of contamination in reverse osmosis processes. The origin of colloidal material is diverse and may be composed of the following:

– organic colloids
– bacteria
– clay
– colloidal silica
– algae
– small size particulate matter
– corrosion products

How to prevent colloidal fouling

Fouling by colloidal origin material can be prevented using filter media, coagulation-flocculation, microfiltration and ultrafiltration. However, these pre-treatments do not completely remove colloids from feed water. Colloids smaller than 2 µm in diameter can reach the membrane system and cause fouling, depositing on the membrane surface.

This type of fouling is progressively deposited along the entire membrane system, however, it is more noticeable in the first elements of the pressure tube.

The dosage of an effective antiscalant with dispersant properties in the pre-treatment of desalination plants improves operating conditions by minimizing fouling by colloidal material.

Fouling

Product to prevent scale formation and disperse colloidal material in seawater desalination plants

Adic RO-20B is a highly effective antiscalant which has been used in desalination plants for 10 years. It presents an anti-scaling/dispersing duality:

– Prevents premature collapse of filters
– Delays its fouling
– Reduces the amount of colloids
– Reduces iron and manganese precipitate on the filters surface
– Prevents scaling formation in the rejection
– Prevents membranes fouling by colloids in desalination plants

The software AdicRO, a tool that has evolved over 20 years, complements the treatment and allows optimizing the operation of reverse osmosis plants by maximizing their conversion and minimizing both operating costs and environmental impact. Its main features include the following:

It accurately models water composition and behavior inside the membranes
It predicts very accurately the formation of scales
It calculates the optimal dose of antiscalant in order to ensure a complete protection of the membranes.

Study of the effectiveness of the product Adic RO-20B

If you are interested in preventing reverse osmosis membranes fouling, check this paper published in Industria Quimica named “Prevenir la formación de incrustaciones y para dispersar el material coloidal en desaladoras de agua de mar“.

The study evaluated the effectiveness of the antiscalant ADIC RO-20B to prevent the formation of scales in the rejection of reverse osmosis systems and effective to disperse colloidal material in all types of seawater desalination plants.

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