Two-stage Sequential Electrochemical Treatment of Nitrate Brine Wastes |
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Authors: | Jiefei Yu Margaret J Kupferle |
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Institution: | (1) Department of Civil and Environmental Engineering, University of Cincinnati, PO Box 210071, Cincinnati, OH 45221-0071, USA |
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Abstract: | Nitrates in concentrated brines can be electrochemically reduced in the cathodic chamber of a split-cell electrochemical reactor
with formation of ammonium (and small amounts of nitrite). Fortunately, ammonium may be electrochemically oxidized to nitrogen
gas in the anodic reaction chamber if a coupled sequential process is used. The presence of chloride in the brine waste is
an important consideration in oxidative electrochemical processes, however, because it cycles through oxidized and reduced
states at the electrode surfaces and in the bulk solution. Electrochemical oxidation converts chloride ions to “active chlorine”
species with additional oxidizing capability (chlorine, hypochlorous acid and hypochlorite – essentially bleach), as well
as to chlorates, depending on the reaction conditions. The production of these active species improves treatment performance
in the ammonium oxidation phase since oxidation is no longer limited to the electrode surface. However, the process must be
engineered to minimize loss of process efficiency due to parasitic side reactions (chloramines and chlorate). In this study,
two-stage batch electrolysis was conducted using a three-electrode (copper anode, platinum-coated titanium cathode, silver/silver
chloride reference) electrochemical cell, with the anodic and cathodic chambers separated by a Nafion 117 membrane. Treatment
of nitrate and ammonium was tested with and without the presence of chloride in the waste. No significant difference was observed
in cathodic nitrate reduction with chloride present or absent. However, the presence of chloride in the solution favored overall
soluble nitrogen elimination upon oxidation. Increasing applied current increased production of undesirable byproducts (especially
chlorate). |
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Keywords: | Brine Electrolysis Chloride Nitrate |
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