Your comprehensive guide to choose Suitable antiscalant for your water treatment plant

Choosing the Suitable antiscalant for your water treatment plant goes beyond knowledge and familiarity with its different types. It reaches an understanding of the causes of calcification and its various damages and risks, not only to public health. But also from an economic point of view such as cost, reducing the time of stopping the plant and many other important matters. Therefore, we have developed this comprehensive guide to help those responsible for various industrial and commercial applications in choosing the appropriate anti-scalant.

What is calcification

It is the deposition of inorganic or mineral dirt particles on the surface of the membranes, which leads to the blockage of the membrane pores. Another definition of calcification is the accumulation of suspended solids and microorganisms on the surface of the membrane. Calcification in reverse osmosis systems is a natural phenomenon and can be controlled through appropriate filtration and chemical washing processes when necessary.

The harms of scale

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

You can read more about The stages of scale formation and the reason for its formation in this article

Mechanism of action of antiscalants:

Antiscalants work to disrupt the chemical reactions that lead to the formation of mineral deposits. These materials contain compounds in their chemical composition that reduce the rate of reaction of mineral ions with alkaline compounds in water. As a result, when water passes through the polyamide membrane, the formation of deposits is effectively prevented.

How antiscalants work:

Antiscalants slow down the sedimentation process by inhibiting the growth of mineral salt crystals. These substances work by adsorbing on the surfaces of salt crystals and on the polyamide membrane, preventing the accumulation of saturated ions on the crystal surfaces. This inhibition reduces the growth rate of salt crystals, preventing them from reaching the size or concentration required for precipitation.

In addition, most antiscalants have dispersing and suspension properties. These properties trap suspended particles of salts, iron or solid organic matter, causing them to be repelled by other ions in the solution. This process prevents the aggregation of small particles and the formation of larger particles capable of precipitation, which keeps the system clean and prevents blockages.

How to calculate the dosage of antiscalant:

After determining the required amount of antiscalant chemicals used in reverse osmosis (RO) systems, they are added to the system via a dosing pump connected to the equipment pipeline. These chemicals can be used either in their original form or after dilution, taking into account that the dilution should not be more than 10 times, i.e. the concentration should not be less than 10%.

The recommended concentration of antiscalants is usually between 5 to 20 parts per million (ppm), which means adding 5 to 20 grams of antiscalant per ton of water in the reverse osmosis system. The weekly dosage is determined based on the usage rate of the device, and the size of the dosing tank is selected accordingly. The dosing pump is then adjusted to ensure continuous and smooth injection of the antiscalant into the reverse osmosis system.

Read more about: Monthly Dosage Calculation Formula

Importance of Calculating Antiscalant Dosing:

Antiscalant chemicals are used to prevent the formation of deposits and fouling in reverse osmosis membranes. These deposits may consist of mineral impurities such as calcium sulfate, calcium carbonate, barium sulfate, silica, calcium fluoride, and strontium sulfate. The antiscalant must be injected before the water reaches the membranes to break up these deposits and prevent their buildup.

Antiscalants are considered one of the best pretreatment methods for water systems because of their high effectiveness in reducing membrane fouling. These materials are particularly used in the treatment of feed water of low quality or at high extraction rates. When used properly, antiscalants help extend the intervals between membrane cleanings from a few weeks to several years in some cases. Without them, reverse osmosis systems may fail to achieve the desired results, affecting the efficiency of the water treatment industry as a whole.

Different types of antiscalants

There are a large number of types of antiscalants, which are chemicals that can be used as antiscalants or as dispersants to improve the operation of reverse osmosis and nanofiltration (NF) systems. Antiscalants are a family of chemicals designed to prevent the formation and precipitation of crystalline mineral salts that form scales. Most antiscalants are man-made organic polymers (e.g., polyacrylic acids, carboxylic acids, polymaleic acids, organophosphates, polyphosphates, phosphonates, anionic polymers, etc.). The molecular weight of these polymers can range from 2000 to 10000.

Reason for the variety of antiscalants

The antiscalant technology for reverse osmosis (RO) systems was initially derived from chemicals used in cooling water and boiler water applications. It is worth noting that the large number of different antiscalant chemistries that have been developed have produced a wide range of results and effectiveness depending on the application and the organic polymer used. However, they should be used with caution.

Read more about: Different types of antiscalants

The importance of the role of Suitable antiscalant in maintaining the valves of water treatment plants

As mentioned earlier, the role of antiscalants in maintaining the valves water treatment plants play an important and vital role. As calcification is the deposition of salts in the source water, it leads to the appearance of scaling on the surface of the membranes, and if the situation worsens, it can reach the rest of the plant.

The role of anti-scalants is to prevent the deposition of salts and is injected in the pretreatment stage, before the water enters the R.O membranes. Its function is to delay the reaction between calcium magnesium and bicarbonate. Thus preventing the appearance and formation of scaling on the surface of the membranes.

Specific guidelines or criteria for selecting Suitable antiscalant for water treatment plants

There are a set of specific guidelines and criteria that must be taken into account when selecting appropriate anti-scalants for water treatment plants. By following these guidelines and criteria, the most appropriate anti-scalant can be selected for the specific water treatment plant and ensuring its effectiveness and efficiency in preventing calcification:

• Analyzing the concentration of minerals and dissolved materials in raw water.
• Determining the degree of water hardness (calcium and magnesium content).
• Knowing the acidity (pH) of the water.
• Knowing the water flow rate and the size of the plant.
• Determine the type of scale expected (carbonate, sulfate, silicate, etc.).
• Know the points of adding the antiscalant in the process.
• Ensure that the antiscalant is compatible with the materials used in the plant (pipes, tanks, etc.).
• Ensure that it does not react with other materials used in the treatment.
• Ensure that the antiscalant is safe for the environment and public health.
• Comply with local standards and legislation related to the chemicals used.
• Consider the capital and operating costs of the antiscalant.
• Evaluate the economic return from using the antiscalant versus the costs.
• Select the most appropriate antiscalant for local conditions and operational requirements.
• Adjust the antiscalant dosage accurately according to changes in water characteristics.
• Monitor the antiscalant consumption rates and adapt it to changing needs.
• Store in suitable conditions to protect the antiscalant from damage or reaction.
• Periodic maintenance: Inspect and clean the equipment regularly to prevent blockages and deposits.
• Search for opportunities for improvement and development in the future.

Read more about: The importance of using anti-scaling agents in water treatment plants

The 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
• Creating and increasing the surfaces required for sedimentation (which will double with the continuous chemical scaling of mineral deposits to this required level)
• Increased water temperature

Problems resulting from not using Suitable antiscalant agents:

The problems that most often occur due to chemical scaling in membrane filters are the following:

• Reduced quality and quantity of flowing water
• Increased pressure drop and required pressure, energy consumption and cost.
• Frequent washing with shorter time intervals to improve operations that lead to reducing the useful productive life of the membranes and increasing costs
• Recurring and long-term malfunctions
• Dispersion of the membrane when colliding with mineral deposit crystals

One of the useful ways to prevent the occurrence of the problems mentioned is to use anti-scaling agents.

Read more about The different mechanisms of action of antiscalants

Advantages of using Suitable antiscalant for reverse osmosis systems

• Effective control of inorganic pollution in a wide concentration range.
• Does not combine with iron oxides, aluminum oxides and silicon compounds to form insoluble substances.
• Effectively prevents silicon aggregation and precipitation, and the SiO2 concentration on the concentrated water side can reach 290ppm.
• Can be used in CA and TFC reverse osmosis membranes, nanofiltration membranes and ultrafiltration membranes.
• Excellent solubility and stability.
• Effective in the pH range of feed water from 5 to 10.

Read more about: Why should anti-scaling be added to reverse osmosis systems

Video showing the appearance of deposits in water when using anti-scaling agent and not using it

Disadvantages of choosing substandard anti-scaling agents in reverse osmosis systems:

• Reduces the production capacity of water purification systems
• Increases the amount of soluble mineral salts in the 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.

Consequences of choosing a poor quality anti-scaling agent

Poor quality anti-scaling agent increases the frequency of washing the membrane filter, which is never good for water purification devices. In addition, the poor quality of the anti-scaling agent causes the membrane filter to be replaced quickly. That reduces the useful life of the filter and shortly thereafter causes total damage to the device. The useful life of the pumps is also affected by this poor product and decreases.

More importantly, if this agent 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 antiscalants cause many problems. Conversely, the higher the quality of the anti-fouling agent, the better the quality of the treated water.

Sedimentation and clogging of membranes reduce 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 solute concentration that passes through it. When the effective membrane level decreases, the turbulence decreases and the cleaning of the membrane surface becomes more difficult, because the ability to send the chemical solution to the surfaces clogged with solids will be reduced. It is possible to prevent the formation of sedimentation by using the correct system efficiency and chemical injection.

This article will help you Choose the right antiscalant