Removal of humic substances with different apparent molecular sizes using Fenton’s reagent

Abstract

Fenton’s reagent was used as a coagulating agent in the treatment of water samples with high true color caused by humic substances (HS) extracted from peat. The effects of the apparent molecular size of HS on coagulation, flocculation, and flotation were studied. Four distinct water samples having the same true colors were prepared using HS with different molecular sizes obtained through ultrafiltration fractioning. Through optimization of the coagulant dosage and coagulation pH and the construction of coagulation diagrams for each water sample, it was verified that the sample with the smallest apparent molecular size of HS was the most difficult to treat, requiring higher coagulant (Fenton’s reagent) dosages than samples prepared with larger HS molecular sizes. Furthermore, filtration experiments after dissolved air flotation were carried out to simulate conventional treatment. The most representative results in filtered water were: absorbance at 254 nm ⩽ 0.016 cm⁻¹; apparent color ⩽ 3 HU; and residual iron concentration < 0.005 mg L⁻¹. The total organic carbon values of filtered water samples were also very low, always < 1.0 mg L⁻¹.

Keywords:

• Coagulation
• DAF
• Drinking water
• Fenton’s reagent
• Humic substances
• Molecular size

Acknowledgements

The authors are grateful to FAPESP (Fundação de Amparo à Pesquisa do Estado de São Paulo) for supporting this research (Process No. 02/04,622-1) and for providing the doctorate scholarships for the first (Process No. 02/07,680-2) and the fourth author (Process No. 00/0,786-5). The authors are also very grateful to Professor Eduardo Fausto de Almeida Neves (in memorium).