FAQs on Fenton oxidation technology

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1. Dosing sequence: First add ferrous sulfate, 15 minutes later add hydrogen peroxide, then enter the Fenton reaction tank, and 20-40 minutes later add alkali to adjust the pH value, which can achieve better treatment effect.
2. Equipment requirements: Dosing equipment (sulfuric acid dosing tank, ferrous dosing tank, hydrogen peroxide dosing tank, PAM dosing tank), reaction tank (including mixer), monitoring equipment (pH probe, ORP probe), flocculation tank (including mixer), sedimentation tank (inclined pipe sedimentation tank, sludge pump) are required.
3. Problem and challenge: The Fenton oxidation process may produce a large amount of iron sludge, making it difficult for suspended solids in wastewater to settle. This may be due to improper control of the ratio of ferrous sulfate to hydrogen peroxide, or excessive or incomplete hydrogen peroxide addition. After this situation occurs, flocculants (polyacrylamide) can be added for enhanced flocculation and precipitation, or lime powder can be added for pH adjustment and coagulation assistance to coagulate and precipitate suspended solids.
4. The disadvantages and problems of Fenton treatment include high labor intensity, high cost, excessive sludge, difficult control, high corrosiveness, and unstable treatment effect.
5. The order of adding Fenton reagent is: first add acid, then add hydrogen peroxide and ferrous sulfate, finally add alkali, and then add PAM. This sequence can enable iron salts to form precipitates with good flocculation after Fenton treatment, saving the dosage of flocculation and precipitation agents after Fenton treatment.
6. The reason for the red color appearing after Fenton method treatment of wastewater may be that after adjusting the pH value to around 2.5, ferrous sulfate was not added first, allowing the divalent iron ion water to resolve before adding hydrogen peroxide for oxidation to generate free radicals. This can lead to the waste of hydrogen peroxide, causing the wastewater to turn black, the sedimentation tank to produce bubbles, and the COD to increase instead of decreasing.
7. The reason for the appearance of black color after Fenton process treatment of wastewater may be that the pH condition of Fenton reaction must be at 2.5 or slightly higher, and the low should not be lower than 2.5. Once the pH value is less than 2.5, ferrous ions completely react to trivalent iron ions, which cannot be converted. This will cause a large amount of iron sludge to precipitate and turn the wastewater red. As the reaction time increases, the red color will become more and more concentrated with the increase of ferrous sulfate.
8. The reasons for foam formation after Fenton process treatment of wastewater may include: the composition of process wastewater is complex, and whether there are some surfactants in the wastewater to generate foam; During the addition process of Fenton reagent ferrous sulfate, the hydraulic stirring conditions were not well controlled, resulting in uneven hydrolysis; Excessive dosing time and acceleration of hydrogen peroxide can also lead to rapid decomposition of hydrogen peroxide; The concentration of organic matter in wastewater is too high.
9. For the influent water quality control of the Fenton process, it is required that pollutants that are prone to producing toxic and harmful gases under acidic conditions should not enter the Fenton oxidation process unit; The suspended solids content in the influent should be less than 200mg/L.

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