How to choose the right anti-scalant

Choosing the right anti-scalant is a crucial step in maintaining the efficiency and performance of water and heating systems. This process requires a good understanding of the water quality and potential problems that can result from scale buildup. Scale involves the accumulation of minerals such as calcium and magnesium in pipes and equipment, reducing their efficiency and increasing energy consumption. To determine the optimal anti-scalant, several factors must be considered, such as the composition of the water, the type of system used, and maintenance requirements. In addition, it is important to review the products available on the market and compare their characteristics and usage recommendations, to ensure that the most effective product that meets the specific needs of the system is chosen.

An article explaining the different types of anti-scalant

What is the scale or sedimentation process?

The term anti-scalant as a functional material in industrial systems to reduce the formation of sediments in industrial equipment such as reverse osmosis (RO) systems. Scale (scaling) means the deposition of inorganic or mineral fouling particles on the surface of membranes, which leads to the blockage of the membrane pores. Sedimentation is the deposition of low-solubility salts on the membrane surface and calcification is the accumulation of suspended solids and microorganisms on the membrane surface. Calcification in reverse osmosis systems is a natural phenomenon and can be controlled through proper filtration and chemical washing processes when needed.

Scaling caused by mineral compounds in solution in water such as sodium carbonate, calcium sulfate, silica, silicon dioxide, barium sulfate, can reduce the efficiency of membrane filtration systems and membrane filters, increase pressure and thus increase energy consumption and associated costs, reduce water quality, reduce washing operations and frequent breakdowns. It is worth noting that the useful life of the membrane filter may be reduced due to the phenomenon of chemical scaling.

Scaling begins when the salt concentration exceeds its solubility under solution conditions. Primary crystal nuclei play a catalytic role in the formation of larger salt crystals. These salt crystals emerge from the suspended state and begin to precipitate as long as they reach the required size and mass. The sedimentation process will continue until the ions that make up the salt in the solution are saturated.

Reason for the formation of deposits on the membrane filter

There are several reasons that lead to the formation of deposits on the surface of the reverse osmosis membrane, the most important of which are:

• Increased concentration of mineral materials in the solution in the water entering the membranes
• Increased pH
• Created and increased surfaces required for sedimentation (which will double with the continuous chemical scaling of mineral deposits to this required level)
• Increased water temperature

What is an anti-scalant?

An anti-scalant is used as an additive in the primary treatment process in reverse osmosis systems. An anti-scalant is used as an active substance to control the sedimentation in reverse osmosis membranes. Before transferring the water to reverse osmosis, an anti-scalant is injected with the appropriate concentration into the water feed flow. Injecting appropriate concentrations of anti-scalants leads to controlling the formation of types of mineral deposits such as calcium carbonate, calcium sulfate, iron deposits, etc. on the membrane surface.

The use of antiscalants in reverse osmosis systems can reduce the costs associated with the repair and maintenance of water purification systems. By continuously injecting antiscalants into the reverse osmosis system, the current of scale formation will be reduced rapidly. The amount of antiscalant used as a descaling agent depends on the concentration of soluble salts in the feed water or the place of use.

Due to the presence of inorganic and mineral salts in the solution of the water entering the reverse osmosis water purification system and the water desalination machine and the blockage and sedimentation in the polyamide or cellulose micropores of the reverse osmosis membranes, the phenomenon of scale occurs. The deposits on polyamide membranes include calcium carbonate, calcium sulfate, barium sulfate, and strontium sulfate. Silica and calcium fluoride deposits are less common but are a problem. To prevent these soluble salts on the membrane, antiscalants are injected into the water entering the reverse osmosis system.

Disadvantages of choose the right anti-scalant in reverse osmosis systems:

• Reduces the production capacity of water purification systems
• Increases the amount of soluble mineral salts in water
• Increases the pressure on the floor pumps and reduces the life of the pump
• Increases energy consumption during the reverse osmosis process
• Reduces the life of the membranes and their early replacement.

Mechanism of action of antiscalants

The mechanism of action of antiscalants is to disrupt the reactions of mineral deposits, through the materials that make up the antiscalant, the rate of reaction of the alkaline compound with all mineral ions in the water is reduced. In this case, while the water passes through the polyamide membrane. The possibility of deposit formation is eliminated.

In general, all systems that use membrane technology to treat water are subject to membrane pore clogging. The most important types are reverse osmosis water desalination systems.

Amount of antiscalant injection

The amount of antiscalant injection depends on various parameters such as water analysis, flow rate, temperature, pH, system recovery rate, water source, type of membranes, and how the membranes are arranged. The injection rate of antiscalants ranges from 1 to 6 ppm.

Problems due to improper choose the right anti-scalant

The problems that most often occur due to chemical scaling in membrane filters are as follows:

• Reduced quality and quantity of incoming water flow
• Increased pressure drop, required pressure, energy consumption and cost.
• Frequent washing with shorter intervals to improve the processes which leads to reduced useful life of membranes and increased costs
• Frequent and long-term failures
• Membrane dispersion when colliding with mineral deposit crystals

One of the useful ways to prevent the occurrence of the problems mentioned is to use an anti-scalant

Results of choosing a poor quality anti-scalant

Poor quality anti-scalant increases the need to wash the membrane filter, which is not good at all for water purification devices. In addition, the poor quality of the anti-scalant causes the membrane filter to be replaced quickly, which reduces the useful life of the filter and shortly after causes total damage to the device. The useful productive life of the pumps is also affected by this poor product and decreases.

More importantly, if this material is not of good quality, it is also harmful to the water and reduces the production and quality of pure water. As a result, low-quality anti-scalants cause many problems. Conversely, the higher the quality of the anti-fouling materials, the better the quality of the treated water.

Sedimentation and clogging of the membranes lead to a decrease in the effective area between the materials and reduce the flow turbulence and may result in concentration polarization on the membrane surface. The higher the concentration of the solution on the membrane surface, the greater the dissolution rate that passes through it. When the membrane efficiency level decreases, the turbulence will decrease and the cleaning of the membrane surface will be difficult, because the possibility of sending the chemical solution to the surfaces clogged with solids will decrease. It is possible to prevent the formation of scale by using the correct system efficiency and chemical injection.

Choose the right anti-scalant in seawater treatment

One of the most important points in seawater treatment is that the probability of boron (boron) in this type of feed water is high and it must be separated at a higher pH (around 9-11) with increasing pH. The probability of scale formation on the membrane surface is much higher. Since the pH should not change much, adding acid is never useful and the only solution would be to inject antiscalant. Most antiscalants are oxidized by strong oxidants such as chlorine and bromine, and not only lose their properties, but also cause biofouling by destroying the molecular structure. Therefore, these oxidants must be removed in the pretreatment system before the injection site (such as the carbon filter at the beginning of the line that absorbs chlorine).

The chemical structure of the antiscalant molecule cannot pass through the membrane. Therefore, no concentration of this solution enters the water produced by reverse osmosis. However, in terms of environmental impacts, the solution must be checked to exit the discharge stream. In this context, the amount of injection into the line must be controlled and the minimum possible injection rate is injected when the need is met.

Anti-scaling agent for seawater

Anti-scaling agents play a major role in seawater desalination. Due to the scarcity of water in recent years, desalination has become increasingly important. One of these solutions is the use of reverse osmosis devices, by which seawater is desalinated. The water entering the reverse osmosis system contains soluble salts of calcium, magnesium and other minerals. Anti-scaling agents for seawater are mainly based on polymers.