Influence of the apparent molecular size of humic substances on the efficiency of coagulation using Fenton's reagent

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, fl occulation and fl otation 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 ultrafi ltration fractioning. Through optimisation of coagulant dosage and coagulation pH, as well as posterior construction of coagulation diagrams for each water sample, it was verifi ed that the sample prepared with the smallest apparent molecular size of HS was the most diffi cult to treat, requiring higher coagulant (Fenton's reagent) dosages than samples prepared with larger HS molecular sizes. Furthermore, fi ltration experiments after dissolved air fl otation (DAF) were carried out in an attempt to simulate conventional treatment. The most representative results in fi ltered 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 fi ltered water samples were also very low, suggesting that the formation of disinfection by-products with chlorine would likely be insignifi cant.

Chemical Characteristics of Humic Substances in Nature

“…Moreover, they can form by-products during pre-oxidation and disinfection and can complex with metals and organic micropollutants. Such by-products, if originating from the reaction with chlorine, are potentially carcinogenic chlorinated organic compounds, known as trihalomethanes (THM) [26,27]. Therefore, accurate methods for establishing humic acid concentrations are essential for maintaining water supplies, especially from watersheds.…”

Remoção De Ácidos Húmicos De Águas Com Fins De Potabilidade Utilizando O Reagente De Fenton Como Pré-Oxidante Em Processos De Tratamento De Água

“…Além disso, podem formar subprodutos durante a pré-oxidação e desinfecção e complexar-se com metais e micropoluentes orgânicos. Tais subprodutos, se originados pela reação com cloro, são compostos orgânicos clorados potencialmente cancerígenos, os chamados Trihalometanos (THM) [7,12,14].…”