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Anhydrous vs Dihydrate in Water Treatment Chemicals: What’s the Difference?

In the water treatment industry, the choice between anhydrous and dihydrate chemical forms can significantly impact treatment efficiency, cost, and handling procedures. Longorder, a trusted supplier of water treatment chemicals such as Polyaluminium Chloride (PAC), Calcium Chloride, Magnesium Chloride, Poly Ferric Sulfate, Ferrous Sulfate, Polyacrylamide (PAM), Magnesium Sulfate, and Aluminium Sulfate, offers both forms for multiple compounds. Understanding the difference between these two hydration states helps you choose the right chemical for your specific application.

What Are Anhydrous and Dihydrate Forms?

  • Anhydrous chemicals are compounds without water molecules in their crystalline structure. They are typically more concentrated, react quickly upon contact with water, and require careful storage to avoid moisture absorption.
  • Dihydrate chemicals contain two water molecules per formula unit. They are less concentrated by weight but often easier to handle and more stable in humid environments.
Anhydrous chemicals
Dihydrate chemicals

Product-Wise Comparison: Anhydrous vs Dihydrate

1. Calcium Chloride (CaCl₂)

  • Anhydrous CaCl₂: Used in desiccation and rapid de-icing. In water treatment, it provides a fast reaction for hardness removal but must be stored carefully due to high hygroscopicity.
  • Dihydrate CaCl₂·2H₂O: Commonly used for dust control and water stabilization, easier to handle and dissolve, slightly lower active ingredient by weight.
Calcium Chloride (CaCl₂) 2

Calcium Chloride Anhydrous Powder

Calcium Chloride (CaCl₂)

Calcium Chloride Dihydrate Powder

2. Magnesium Chloride (MgCl₂)

  • Anhydrous MgCl₂: Offers high concentration and better performance in cold brine formulations. More suitable for high-efficiency applications but less stable under humid storage.
  • Hexahydrate MgCl₂·6H₂O: Widely used in municipal and industrial water softening, easier to handle, cost-effective for standard operations.

Magnesium chloride Anhydrous Powder

Magnesium chloride hexahydrate Powder 46%

Magnesium chloride hexahydrate Powder 46%

3. Aluminium Sulfate (Al₂(SO₄)₃)

  • Anhydrous Form: Rare in practical use due to its reactivity; higher aluminum content per gram.
  • Octadecahydrate Al₂(SO₄)₃·18H₂O: The common industry standard. Used extensively as a coagulant in drinking water and wastewater treatment.
Aluminium Sulfate Low Iron Granule

Aluminium Sulfate Low Iron Granule

Aluminium Sulfate Iron Free Granule

Aluminium Sulfate Iron Free Granule

4. Magnesium Sulfate (MgSO₄)

  • Anhydrous MgSO₄: Provides maximum magnesium concentration, ideal for high-precision chemical dosing.
  • Heptahydrate MgSO₄·7H₂O (Epsom salt): Used in biological wastewater treatment, cost-effective, readily dissolves.
Magnesium Sulphate Anhydrous

Magnesium Sulphate Anhydrous

Magnesium sulfate Heptahydrate

5. Ferrous Sulfate (FeSO₄)

  • Anhydrous FeSO₄: Unstable in air, oxidizes quickly; rarely used in water treatment.
  • Heptahydrate FeSO₄·7H₂O: The most common form in water treatment plants, effective for phosphate removal and odor control in wastewater.

6. Poly Ferric Sulfate (PFS)

  • Typically used in liquid form, but when powdered, it may come in different hydration states.
  • Lower hydration levels (quasi-anhydrous) may improve storage efficiency but require care during dissolution.
  • Hydrated PFS is more stable and easier to dose, widely used for coagulation in municipal and industrial wastewater.
Poly Ferric Sulfate (PFS)

7. Polyaluminium Chloride (PAC)

  • PAC is commonly categorized by basicity and aluminium content, but water content also matters.
  • Low-moisture/high-Al PAC (quasi-anhydrous) is used for high-demand coagulation processes with compact storage needs.
  • Hydrated PAC (standard powder or liquid) is easier to handle and widely used in municipal water treatment due to cost-effectiveness.

8. Polyacrylamide (PAM)

  • Though PAM is a polymer and not salt-based, its water content affects storage and application.
  • Dry powder PAM (anhydrous-like) has higher concentration, longer shelf life, but requires dilution before use.
  • Emulsion PAM contains water/oil and is ready-to-use, suitable for continuous dosing systems.

Performance Comparison

Feature

Anhydrous

Dihydrate

Concentration

Higher (more active ingredient)

Lower

Reactivity

Faster dissolution, more reactive

Slower but controlled release

Storage Sensitivity

High (moisture-sensitive)

More stable

Handling

Requires more care

Easier

Transportation Cost

Lower per active unit

Higher per ton due to water content

Price per kg

Higher unit price, but more effective

Lower unit price, may need more volume

How to Choose Between Anhydrous and Dihydrate Forms?

Consider the following factors:

  • Treatment Scale: For large-scale industrial systems, the efficiency of anhydrous products may outweigh handling complexity.
  • Storage Conditions: If humidity control is poor, dihydrate forms offer better stability.
  • Budget Constraints: Dihydrate forms are usually cheaper, though more material might be required to achieve the same result.
  • Dosing Equipment: Ensure compatibility—some dosing systems are optimized for hydrated or liquid forms.

Conclusion

Choosing between anhydrous and dihydrate forms in water treatment chemicals is not a one-size-fits-all decision. It depends on your treatment goals, operational setup, and budget. Longorder offers a full range of water treatment chemicals—including both anhydrous and hydrated forms—to meet various municipal, industrial, and commercial water treatment needs.

Visit www.mingchuanpac.com or contact Longorder’s technical team to get expert advice tailored to your application.

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