Scale Control Methods

There are generally three methods used to control scaling:

1. Acidification:
   The presence of acids leads to the breakdown of carbonate ions. This eliminates one of the reactants required for the formation of calcium carbonate scale.
2. Ion Exchange Reduction:
   In this method, sodium ions are used to exchange with calcium and magnesium ions. Once all sodium ions are replaced by calcium and magnesium, the resin must be regenerated with a saline solution. Ion exchange resins typically require acid injection.
3. Use of Antifouling or Antiscalant Agents:
   Antifouling agents are surfactants. Antiscalants stabilize supersaturated solutions against water-soluble salts, thereby preventing scale formation.

How Antifouling Works

Antifouling operates in two main ways:

• Adsorption Effects
• Deformation of Crystal Growth Sites

Adsorption occurs when antifouling agents cover the nucleation sites, preventing crystals from finding active bonding points and thus halting crystal formation.
Other antifouling mechanisms rely on deformation, which inhibits crystal development even in the presence of supersaturation.

Antifouling Properties

An ideal antifouling product should have the following characteristics:

1. Effective scale control at the lowest concentration
2. Compatibility with seawater
3. Balanced adsorption and desorption behavior
4. High thermal stability
5. Low toxicity and biodegradability
6. Cost-effective and economical

Antiscalant Ingredients

Antiscalants are generally divided into two main categories based on their chemical nature:

• Organic compounds
• Inorganic compounds

Inorganic types include phosphates such as polymetaphosphate and phosphate salts.
Organic antifouling agents include polyacrylic acids, phosphino-carboxylic acids, sulfonated polymers, and phosphonates.

• Phosphonates are highly effective at high temperatures.
• Sulfonated polymers are more effective at lower temperatures.
• Copolymers that contain both phosphonates and sulfonated polymers can function across a wide range of temperatures.
• Copolymers containing phosphonates, combined with acrylic acid and vinyl sulfonic acid, are particularly used in water-based systems to prevent barium sulfate scaling.

Acidic Antiscalants

These products contain scale inhibitors that prevent scaling on membranes of reverse osmosis (RO) and nanofiltration systems.
They play an important role in inhibiting inorganic scale formation such as calcium carbonate and iron.
These agents are particularly effective in preventing calcium carbonate precipitation.

Chemical Properties:
They can effectively prevent calcium carbonate scaling up to an LSI (Langelier Saturation Index) of around 2.
However, their use is not recommended in situations where the raw water contains high levels of sulfate, silica, or barium.

Alkaline Antiscalants

These alkaline antifouling agents act based on the composition of scale inhibitors.
They are used to prevent scale formation on RO and nanofiltration membranes and are commonly utilized in this field.