PAHs
What are PAHs ?
Polycyclic Aromatic Hydrocarbons (PAHs) are a group of organic compounds formed during the incomplete combustion of carbon-containing materials. They are among the most common contaminants found in industrial soils and sediments.
Typical sources include:
- Former gasworks and manufactured gas plants (MGPs)
- Coking plants
- Steel and metallurgical industries
- Creosote treatment facilities
- Oil refineries and petrochemical sites
- Waste incineration facilities
- Fuel spills and historical industrial activities
The most common PAHs are the following :
| Light PAHs | Medium PAHs | Heavy PAHs | Priority Carcinogenic PAHs |
| Naphthalene | Fluoranthene | Benzo(b)fluoranthene | Benzo(a)pyrene |
| Acenaphthylene | Pyrene | Benzo(k)fluoranthene | Dibenzo(a,h)anthracene |
| Acenaphthene | Benzo(a)anthracene | Indeno(1,2,3-cd)pyrene | Chrysene |
| Fluorene | Phenanthrene | Benzo(g,h,i)perylene | Anthracene |
Why are PAHs a concern?
PAHs strongly adsorb to soil organic matter, making natural degradation slow and often incomplete.
Potential impacts include:
🧬 Mutagenic and carcinogenic risks
🌱 Ecotoxicity affecting plants and wildlife
💧 Groundwater contamination
⚠️ Long-term environmental liabilities
Because of their persistence and toxicity, PAHs are among the most regulated contaminants at industrial brownfield sites.
Remediation Strategies - State of the Art
Historically, PAH-contaminated soils have been managed through excavation and disposal, bioremediation or containment measures. While these approaches can reduce risk, they often require long treatment periods or leave residual contamination behind.
Thermal desorption has become one of the most effective remediation technologies for PAH-contaminated soils because it physically removes contaminants from the soil matrix and significantly reduces long-term liabilities.
| Technology | PAH Removal | Speed | Long-Term Liability | Main Limitations |
| Landfilling / Disposal | 🔴 No | 🟢 Fast | 🔴 High | Transfers contamination elsewhere |
| Bioremediation | 🟠 Partial | 🔴 Slow | 🟠 Medium | Limited effectiveness for heavy PAHs |
| Soil Washing | 🟠 Partial | 🟢 Fast | 🟠 Medium | Generates secondary waste streams |
| Chemical Oxidation | 🟠 Partial | 🟠 Medium | 🟠 Medium | Variable site performance |
| Thermal Desorption | 🟢 Yes | 🟢 Fast | 🟢 Low | Requires thermal and vapor treatment systems |
Thermal Desorption with Haemers Technologies
PAHs are semi-volatile organic compounds whose volatility increases significantly with temperature.
Thermal desorption:
- Breaks the bond between PAHs and soil particles
- Enhances contaminant mobility
- Accelerates removal rates dramatically
- Reduces remediation time from years to weeks
Depending on contaminant type and treatment temperature, removal efficiencies exceeding 95–99% are routinely achieved.
Thermal treatment targets are often set between 150 - 250°C for better removal efficiency.
However, higher molecular weight PAHs such as Benzo(a)pyrene generally require higher treatment temperatures to achieve complete removal.
🔥 1. Controlled Heating
Smart Burners™ circulate hot gases through a network of steel heating pipes installed within the contaminated soil.
The heat is transferred directly into the soil, ensuring homogeneous treatment and precise temperature control.
🌡️ 2. Explosives volatile or decompose
As soil temperature rises, PAHs desorb from soil particles and their vapor pressure increases significantly.
Even heavier PAHs that are strongly bound to soil organic matter can be effectively removed at elevated temperatures.
💨 3. Vapor Extraction Under Vacuum
The treatment area is maintained under controlled negative pressure.
This ensures that PAHs vapors are continuously extracted while preventing fugitive emissions and protecting workers and nearby communities.
🧪 4. Advanced Vapor Treatment
Extracted vapors are safely treated using technologies such as:
✅ Re-burn systems
✅ Condensation
✅ Activated carbon adsorption
✅ Catalytic oxidation
The selected treatment train is adapted to the site-specific contaminants.
Key Benefits
🎯 Permanent Contaminant Removal
PAHs are removed from the soil rather than contained or transferred.
📈 High Removal Efficiency
Thermal desorption routinely achieves remediation targets for both light and heavy PAHs.
⚡ Fast Remediation
Projects are completed within weeks rather than years of biological treatment or monitoring.
🛡️ Controlled and Safe Operations
Smart Burners™ technology combines precise heating, vacuum extraction and advanced vapor treatment.
🏭 Ideal for Industrial Brownfields
Particularly suitable for former gasworks, coking plants, steel industries, refineries and creosote-contaminated sites.
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