Types of Chemical Treatments Used in Wooden Cooling Towers
To enhance durability and resistance to rot, fungi, and insects, wooden cooling towers are often treated with preservatives. The most common treatments include:
1. Chromated Copper Arsenate (CCA)
◉ Best for: High rot & insect resistance (historically popular).
◉ Advantages:
- Extremely effective against termites, fungi, and marine borers.
- Long-lasting protection (20+ years in some cases).
◉ Disadvantages: - Contains arsenic, which can leach into water (banned in many countries for potable water applications).
- Environmental and health concerns (phased out in the EU and restricted in the U.S. for residential use).
Applications:
- Older cooling towers (now mostly replaced by safer alternatives).
- Industrial settings where leaching is less critical.
2. Alkaline Copper Quaternary (ACQ)
◉ Best for: Modern, arsenic-free wood treatment.
◉ Advantages:
- No arsenic or chromium (safer for water contact).
- Effective against fungi and termites.
- Approved for cooling towers in many regions.
◉ Disadvantages: - More corrosive to metal fasteners (requires stainless steel or galvanized hardware).
- Slightly higher cost than CCA.
Applications:
- Cooling towers in food processing, drinking water plants.
- Replacement for CCA in environmentally sensitive areas.
3. Copper Azole (CA-B & CA-C)
◉ Best for: Non-arsenic, long-lasting protection.
◉ Advantages:
- Similar performance to ACQ but with lower copper leaching.
- Good for high-moisture environments.
◉ Disadvantages: - Slightly less effective in marine environments compared to CCA.
Applications:
- Cooling towers in moderate-chemical water conditions.
- Used where ACQ is restricted.
4. Creosote (Coal Tar-Based)
◉ Best for: Heavy-duty industrial applications.
◉ Advantages:
- Excellent waterproofing & rot resistance.
- Long lifespan (30+ years in some cases).
◉ Disadvantages: - Toxic & carcinogenic (not suitable for water that contacts humans or animals).
- Strong odor and dark color (not aesthetically pleasing).
Applications:
- Industrial cooling towers (e.g., power plants, chemical factories).
- Not used in food, beverage, or potable water systems.
5. Borate Treatments (Disodium Octaborate Tetrahydrate – DOT)
◉ Best for: Non-toxic, eco-friendly protection.
◉ Advantages:
- Safe for humans and animals (used in organic farming).
- Effective against fungi and insects.
◉ Disadvantages: - Leaches out in water exposure (not ideal for constant wet conditions).
- Best for indoor or protected cooling tower components.
Applications:
- Secondary treatment for cooling tower wood.
- Used in hybrid designs where wood is not constantly submerged.
6. Pentachlorophenol (Penta)
◉ Best for: Extreme decay resistance (now largely obsolete).
◉ Advantages:
- Once a strong preservative for utility poles and industrial wood.
◉ Disadvantages: - Highly toxic (banned in many countries).
- Environmental persistence (not recommended for new installations).
Applications:
- Rarely used today due to health and environmental bans.
Comparison Table: Wood Treatment Types
| Treatment | Rot Resistance | Insect Resistance | Toxicity | Water Leaching Risk | Best For |
| CCA | ★★★★★ | ★★★★★ | High (As) | High | Old industrial towers |
| ACQ | ★★★★☆ | ★★★★☆ | Low | Moderate | Modern cooling towers |
| Copper Azole | ★★★★☆ | ★★★★☆ | Low | Low-Moderate | Eco-sensitive areas |
| Creosote | ★★★★★ | ★★★★★ | Very High | High (toxic) | Heavy industry |
| Borate | ★★★☆☆ | ★★★☆☆ | Very Low | High (leaches) | Indoor/low-water exposure |
| Penta | ★★★★★ | ★★★★★ | Extreme | High (banned) | Obsolete |
Best Practices for Treated Wood in Cooling Towers
- Avoid CCA & Penta if water contacts humans, animals, or food.
- Use ACQ or Copper Azole for safer, modern cooling towers.
- Seal cuts & drilled holes to prevent untreated wood exposure.
- Pair with stainless steel fasteners (ACQ corrodes regular steel).
- Monitor leaching if used in sensitive environments.
Alternative Solutions
- Switch to PVC/FRP fill for longer life and no chemical risks.
- Use hybrid designs (wood frame + plastic fill) for balance.