3.4 Fenton and photo-Fenton processes

Fenton and photo-Fenton processes are powerful tools for treating wastewater. They use iron and hydrogen peroxide to create hydroxyl radicals that break down tough pollutants. These methods work best in acidic conditions and can handle a wide range of contaminants.

While effective, these processes have some drawbacks. They need careful pH control and can produce iron sludge. However, they're still popular for treating industrial wastewater and landfill leachate. Combining them with other methods can boost their effectiveness in cleaning up our water.

Fenton and Photo-Fenton Processes

Principles of Fenton reactions

Top images from around the web for Principles of Fenton reactions

• 

  Frontiers | A Review Study on Sulfate-Radical-Based Advanced Oxidation Processes for Domestic ... View original

  Is this image relevant?

• 

  Fenton Technology for Wastewater Treatment: Dares and Trends View original

  Is this image relevant?

• 

  Fenton Technology for Wastewater Treatment: Dares and Trends View original

  Is this image relevant?

• 

  Frontiers | A Review Study on Sulfate-Radical-Based Advanced Oxidation Processes for Domestic ... View original

  Is this image relevant?

• 

  Fenton Technology for Wastewater Treatment: Dares and Trends View original

  Is this image relevant?

1 of 3

Top images from around the web for Principles of Fenton reactions

• 

  Frontiers | A Review Study on Sulfate-Radical-Based Advanced Oxidation Processes for Domestic ... View original

  Is this image relevant?

• 

  Fenton Technology for Wastewater Treatment: Dares and Trends View original

  Is this image relevant?

• 

  Fenton Technology for Wastewater Treatment: Dares and Trends View original

  Is this image relevant?

• 

  Frontiers | A Review Study on Sulfate-Radical-Based Advanced Oxidation Processes for Domestic ... View original

  Is this image relevant?

• 

  Fenton Technology for Wastewater Treatment: Dares and Trends View original

  Is this image relevant?

1 of 3

• Fenton process involves the reaction between ferrous iron (Fe^2+^) and hydrogen peroxide (H2O2) generates hydroxyl radicals (•OH) which are powerful oxidants capable of degrading organic pollutants (pesticides, pharmaceuticals)
• Overall Fenton reaction: $Fe^{2+} + H_2O_2 \rightarrow Fe^{3+} + OH^- + \bullet OH$ involves complex reaction mechanisms with multiple steps and intermediate species (hydrogen peroxide complexes, hydroperoxyl radicals)
• Photo-Fenton process combines the Fenton reaction with UV irradiation enhances the regeneration of ferrous iron from ferric iron (Fe^3+^) increasing the production of hydroxyl radicals
• Photo-Fenton reaction: $Fe^{3+} + H_2O + h\nu \rightarrow Fe^{2+} + H^+ + \bullet OH$ utilizes UV light to drive the regeneration of the iron catalyst and produce additional hydroxyl radicals

Iron catalysts and pH effects

• Ferrous iron (Fe^2+^) initiates the Fenton reaction by decomposing hydrogen peroxide to generate hydroxyl radicals while ferric iron (Fe^3+^) can also participate forming complexes with hydrogen peroxide and producing hydroperoxyl radicals (HO2•)
• Fenton and photo-Fenton processes are most efficient in acidic conditions (pH 2.8-3.5) as at higher pH ferric iron precipitates as Fe(OH)3 reducing the availability of iron catalysts
• Acidic conditions favor the formation of reactive oxidant species (hydroxyl radicals, hydroperoxyl radicals) and prevent the precipitation of iron hydroxides maintaining the solubility and reactivity of the iron catalysts

Fenton vs photo-Fenton processes

• Advantages of Fenton and photo-Fenton processes include:
  1. Effective in degrading a wide range of organic pollutants including recalcitrant compounds (dyes, phenols)
  2. Can be operated at ambient temperature and pressure
  3. Reagents (iron salts, hydrogen peroxide) are relatively inexpensive and non-toxic compared to other advanced oxidation processes (ozonation, photocatalysis)
  4. Photo-Fenton process can utilize solar light reducing energy costs
• Limitations of Fenton and photo-Fenton processes include:
  1. Requires strict pH control (acidic conditions) for optimal performance
  2. High iron and hydrogen peroxide dosages may be needed for complete mineralization of pollutants increasing operational costs
  3. Iron sludge generated during the process requires proper disposal to avoid environmental issues
  4. Presence of inorganic anions (phosphates, sulfates) can inhibit the process by scavenging hydroxyl radicals or forming complexes with iron

Case studies in wastewater treatment

• Industrial wastewater treatment using Fenton and photo-Fenton processes have been successfully applied to treat wastewater from various industries (textile, pharmaceutical, pesticide manufacturing) demonstrating high removal efficiencies for COD, color, and specific pollutants
• Landfill leachate treatment using Fenton-based AOPs can effectively degrade recalcitrant organic compounds and improve the biodegradability of landfill leachate with the combination of Fenton process and biological treatment showing promising results
• Integration with other treatment methods such as combining Fenton and photo-Fenton processes with other AOPs (ozonation, photocatalysis) or conventional treatment methods (coagulation, adsorption) can enhance pollutant removal efficiency
• Sequential or hybrid treatment systems can be designed based on the characteristics of the wastewater and target pollutants to optimize treatment performance and cost-effectiveness (pre-treatment, post-treatment, combined processes)