Abstract
This work used Fenton's reagent as a coagulating agent in the treatment of water samples with high true colour caused by humic substances (HS) extracted from peat. In addition, the effects of the apparent molecular size of HS on coagulation, flocculation and flotation were studied. To that end, four distinct water samples having the same true colour were prepared using HS with different molecular sizes, which were obtained by ultrafiltration fractioning. Through optimisation of coagulant dosage and coagulation pH, as well as posterior construction of coagulation diagrams for each water sample, it was verified that the sample prepared 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 (DAF) were carried out in an attempt to simulate conventional treatment. The most representative results in filtered water were: apparent colour ≤ 3 HU; turbidity < 0.5 NTU; and residual iron concentration < 0.005 mg/L. The absorbance and total organic carbon values of filtered water samples were also very low, suggesting that the formation of disinfection by-products with chlorine would likely be insignificant.
Highlights
Humic substances (HS) are heterogeneous mixture of dark-coloured organic macromolecules of complex composition; they are present in soil and aquatic ecosystems and function as effective carbon reservoirs that prevent carbon dioxide emission
Even knowing that Fenton reaction is a combination of oxidation and coagulation, these results suggest that coagulation using Fenton’s reagent produces behaviour similar to that observed in studies using other coagulants, such as ferric chloride and alum
The fulvic acids have smaller chains, with structures dominated by aliphatics, a higher number of functional carboxylic groups, and phenolic and alcoholic hydroxyls. These characteristics make the HS more hydrophilic and acidic (Stevenson 1994). These findings suggest that the apparent molecular size and the structural characteristics of HS fractions play a significant role in the coagulation process
Summary
Humic substances (HS) are heterogeneous mixture of dark-coloured organic macromolecules of complex composition; they are present in soil and aquatic ecosystems and function as effective carbon reservoirs that prevent carbon dioxide emission. Humic substances comprise 60-70% total soil carbon and 60-90% total carbon dissolved. DE JULIO and LUIZ DI BERNARDO from potable water supplies because they can adversely affect appearance and taste and they can react with chlorine to form potentially carcinogenic chlorinated organic compounds (Lin and Wang 2011, Selcuk et al 2011). The presence of macromolecular dissolved organic matter may reduce the effectiveness of water treatment processes that employ membranes or microporous adsorbents (Zularisam et al 2006, Zheng et al 2011). The removal of (or the reduction in concentration of) such organic matter is an important factor in water treatment
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