THE IMPORTANCE OF MEMBRANE AUTOPSY

Membrane autopsy is performed to identify fillings and deposits formed on the membrane surface and chemical and mechanical damage to the membranes during the operation. Data and results obtained from autopsy tests lead to causation and thus provide solutions to reduce or eliminate operational problems.

A membrane autopsy involves several tests, and each test provides data and results to identify and quantify the filling and deposition or mechanical and chemical damage. The results of various tests are collected by experienced engineers for inference. Autopsy tests can be performed on high pressure membranes such as RO and NF as well as low pressure membranes such as MF and UF. Performing autopsies on cartridge filter pre-filters and even SDI filters provides useful information about contaminants entering the membrane system.

Identifying the problem in the early stages, before serious damage to the membranes, can be very cost-effective and prevent irreversible membrane problems and shorten their useful life.

Problems due to the presence of sediment in the membrane of the membrane

Most natural waters contain high amounts of calcium, sulfate and bicarbonate ions. In membrane purification operations with high recovery ratios, the solubility range of gypsum and calcite exceeds the saturation surfaces, which leads to the formation of sediment in the form of crystallization on the membrane surfaces. Sediment blockage reduces permeability acceleration, reduces process efficiency, and increases operating costs. It is economically best to prevent scaling of the membrane, even if effective cleaners are available to remove scale. In fact, membrane scaling occurs when particles accumulate in the membrane and connect the pores of the membrane, which increases the cost of production.

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Sediment control methods

Three methods are commonly used to control sediment:

Acidification: The presence of acids causes the destruction of carbonate ions. Destroys one of the reactants required to load calcium carbonate deposits.
Reduce ion exchange: This method uses sodium to exchange ions with calcium and magnesium. When all the sodium ions have been replaced by calcium and magnesium, the resin must be reduced with a saline solution. Ion exchange resins require acid injection.
Tendency to use anti-fouling or anti-scaling materials: Anti-fouling agents are surfactants. Antiscalant ability to hold supersaturated solution against water-soluble salts.

How anti-fouling works

Anti-fouling works in two ways:

Absorption effects
Deformation of growth sites
Absorption effects occur when antifouling occupies the nucleation sites and the crystals do not find active sites to adhere to the surface, thus stopping the crystalline nucleation. Other anti-fouling mechanisms are based on deformation, which prevents the formation of crystals in the presence of anti-fouling.

Anti-fouling feature

Ideal anti-fouling has the following features:

1. Effective sediment control with the lowest concentration
2. Adaptable to seawater
3. Balanced adsorption and desorption properties
4. High thermal stability
5. Low toxicity and biodegradability
6. to be cheap

Anti-scalant ingredients

Anti-sediments are divided into two main categories based on their nature: organic and inorganic compounds:

Their mineral types include phosphates such as polymethaphosphate and phosphate salts.

Organic antifouling agents include polyacrylic acids, phosphinocarbolic acids, sulfonated polymers, and phosphonates. Phosphonates are very effective at high temperatures while sulfone polymers are effective at low temperatures. Copolymers, which include phosphonates and sulfonated polymers, can be effective over a wide range of temperatures. Phosphonate-containing copolymers in combination with acrylic acids and vinyl sulfonic acid are specifically used as barium sulfate antifouling in water-based systems.

Acidic anti-scalant
These products contain sediment inhibitors and prevent the formation of sediment on the membranes of the reverse osmosis system RO and nanofiltration systems, which play an important role in preventing the formation of inorganic sediments such as carbonate – calcium and iron. These materials specifically prevent the deposition of calcium carbonate.

Chemical properties of acidic scalants:
Up to the LSI index of about 2, this material effectively prevents the deposition of calcium carbonate, which is not recommended for use in situations where the amount of sulfate, silica or barium in raw water is high.

Alkaline anti-scalant
These alkaline anti-fouling agents are effective based on the composition of the sediment inhibitors. These products can prevent the formation of sediment on the membranes of RO reverse osmosis devices and nanofiltration systems and are used in this field.