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. 2023 Mar 17:16:100267.
doi: 10.1016/j.ese.2023.100267. eCollection 2023 Oct.

In situ coagulation-electrochemical oxidation of leachate concentrate: A key role of cathodes

Huankai Li  1 , Qian Zeng  2 , Feixiang Zan  3 , Sen Lin  2 , Tianwei Hao  1
Affiliations

In situ coagulation-electrochemical oxidation of leachate concentrate: A key role of cathodes

Huankai Li et al. Environ Sci Ecotechnol. .

Abstract

To efficiently remove organic and inorganic pollutants from leachate concentrate, an in situ coagulation-electrochemical oxidation (CO-EO) system was proposed using Ti/Ti4O7 anode and Al cathode, coupling the "super-Faradaic" dissolution of Al. The system was evaluated in terms of the removal efficiencies of organics, nutrients, and metals, and the underlying cathodic mechanisms were investigated compared with the Ti/RuO2-IrO2 and graphite cathode systems. After a 3-h treatment, the Al-cathode system removed 89.0% of COD and 36.3% of total nitrogen (TN). The TN removal was primarily ascribed to the oxidation of both ammonia and organic-N to N2. In comparison, the Al-cathode system achieved 3-10-fold total phosphorus (TP) (62.6%) and metal removals (>80%) than Ti/RuO2-IrO2 and graphite systems. The increased removals of TP and metals were ascribed to the in situ coagulation of Al(OH)3, hydroxide precipitation, and electrodeposition. With the reduced scaling on the Al cathode surface, the formation of Al3+ and electrified Al(OH)3 lessened the requirement for cathode cleaning and increased the bulk conductivity, resulting in increased instantaneous current production (38.9%) and operating cost efficiencies (48.3 kWh kgCOD -1). The present study indicated that the in situ CO-EO process could be potentially used for treating persistent wastewater containing high levels of organic and inorganic ions.

Keywords: Cathode material; Electrochemical process; Leachate concentrate; Removal mechanism; in situ coagulation treatment.

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Conflict of interest statement

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Figures

Image 1
Graphical abstract
Fig. 1
Fig. 1
The color and COD removals of each electrochemical treatment system, with a different cathode, over the treatment period. a, [COD]0 = 760 ± 40 mg L−1; b, [color]0 = 1867 ± 48 PCU.
Fig. 2
Fig. 2
The 3D-EEM spectrums of the mixed LC before and after electrochemical treatment. a, raw mixed-LC; b, Al-cathode system; c, Ti/RuO2–IrO2-cathode system; d, graphite-cathode systems. All samples were diluted 20 folds.
Fig. 3
Fig. 3
The nutrient removal of each electrochemical process. a, [TP]0 = 6.6 ± 0.3 mg L−1; b, [TAN]0 = 31.0 ± 8.4 mg L−1; c, [Nitrite-N]0 = 17.6 ± 7.7 mg L−1; d, [TN]0 = 149.6 ± 2.3 mg L−1; e, [Nitrate-N]0 = 67.4 ± 3.3 mg L−1.
Fig. 4
Fig. 4
The evolution of the nitrogen species for the three cathode systems. a, Al-cathode system; b, Ti/RuO2–IrO2-cathode system; c, graphite-cathode system.
Fig. 5
Fig. 5
The pH-dependent metal removal for all three electrochemical systems.
Fig. 6
Fig. 6
The SEM-EDS analyses of the three cathode surfaces and aluminum precipitate after 3 h of treatment. a–d, For SEM: Al (a); Ti/RuO2–IrO2 (b); graphite (c); and aluminum precipitate (d). e–f, For EDS: Al (e); Ti/RuO2–IrO2 (f); graphite (g); and aluminum precipitate (h).
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