Abstract
The photo-Fenton oxidation process was employed to degrade methylene blue (MB) using a hydroxide sludge/hydrochar-Fe composite as a catalyst prepared by physical activation of raw hydroxide sludge from a drinking water treatment plant and hydrochar-Fe prepared by hydrothermal carbonization from two-phase olive mill waste. The prepared composite was characterized by XRD, SEM, EDS, ICP, and FT-IR. The effect of major parameters, including pH, H2O2 concentration, and a dose of composite on the removal of MB has been studied. The results indicated that the MB decolorization rate increased with the increase of H2O2 concentration and catalyst addition; however, further increase in H2O2 concentration and catalyst dosage could not result in an increase of MB removal efficiency. A high degradation of 95% was achieved within 150 min under UV light irradiation at natural pH (pH = 5), a catalyst loading of 2.5 g/L, a H2O2 dosage of 14.68 mol/L, and MB concentration of 50 mg/L. Recycling studies show a MB decolorization of 92% after three cycles and the use of the composite for the degradation of another dye (methyl orange) shows a degradation of 99%, demonstrating that this composite is a promising heterogeneous photo-Fenton catalyst for long-term removal of dyes from industrial wastewater.
Highlights
Hydroxides sludge (HS) is a byproduct from the coagulationflocculation process using aluminum- or iron-based salts to precipitate clay, colloidal particles, algae, and humic substances from water resources [1]. e chemical composition of HS varies depending on the source of water under treatment as well as the type of coagulant used
HS/HC-Fe composites with different mass ratios were applied for the catalytic degradation of Methylene blue (MB) under UV light irradiation in the presence of H2O2 under natural pH. e effect of mass ratio between HS and HC-Fe on the catalytic activity of the prepared composites is shown in Figure 2. e removal percentages of MB after 150 min of photo-Fenton reaction and by using HS/HC-Fe with 1 : 0, 1 : 1, 2 : 1, and 3 : 1 mass ratios were, respectively, 21%, 80%, 85%, and 75%
Increasing the ratio will decrease the iron concentration because there is more iron in HC-Fe than in HS according to the ICP (Table 1). e high degradation efficiency of MB was obtained by using the composite with 2 : 1 HS/HC-Fe mass ratio. is composite was selected in the following experiments
Summary
Hydroxides sludge (HS) is a byproduct from the coagulationflocculation process using aluminum- or iron-based salts to precipitate clay, colloidal particles, algae, and humic substances from water resources [1]. e chemical composition of HS varies depending on the source of water under treatment as well as the type of coagulant used. Wastewater management, in particular colored waste water, is a major occupation for textile, paper pulp, plastic, and other industries. Methylene blue (MB) is a good representative of cationic azo dyes, which does not decompose under ambient conditions and is usually resistant to classical biological treatment. Conventional physicochemical techniques such as adsorption, coagulation, and reverse osmosis are the most frequently used to remove MB from aqueous solutions [15]. These methods can merely accumulate MB and cannot convert the dye into being harmless
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