Electrochemical removal of nitrate from waste water

Efficient cathode electrode materials suitable for NN reductionThe products of the electrochemical reduction of nitrate (ERN) are critically dependent on the nature of the electrode material, pH of the media and applied potential as well as the nature of supporting electrolyte. Cu-Sn alloys are promising electrode materials that up to now have not been completely investigated. For this reason, Cu and Cu-Sn cathodic materials were prepared and tested for nitrate reduction. The cyclic voltammetry studies allow establishing the specific parameters concerning the electrodeposition of the individual metals and alloy respectively. SEM images taken for Cu, Sn and Cu-Sn alloy deposits indicate significant structural changes by changing the electrodeposition parameters. The obtained electrode materials are suitable for nitrate reduction.In situ electrochemical methods for the detection of products resulting from ERNIn this thesis, two simple and fast electrochemical methodologies for determination of electroactive products resulting from ERN at a Cu and Cu-Sn electrode are proposed. For the detection of the products, cyclic hydrodynamic voltammetry (CHV) and square wave voltammetry (SWV) with high scan rates, with hydrodynamic techniques (Rotating Ring Disk Electrode) are combined. It is demonstrated that, the electroactive products resulting from ERN (NO2-, NH2-OH and NH4+) can be electrochemically detected by the CHV and SWV technique. The results obtained with the CHV and SWV techniques allow as well a real-time evaluation of the electrocatalytic properties of the used electrode material. Pilot plant test for electrochemical reduction of synthetic nitrate solutionThe effects of electrode materials, cell configuration and cell operating parameters on the electrochemical reduction of NN in synthetic nitrate solutions have been investigated to develop a robust process capable of treating volumes of nitrate waste. Different operating conditions such as applied current, the initial concentration of nitrate and flow rate were investigated to determinate the optimum conditions. Rate constants, current efficiencies and energy consumption were evaluated. Tests concerning direct reduction in electrochemical flow cell led to obtain the maximum permissible concentration (50 mg/L) in 16h with 99% removal at Cu-Sn cathode, while in the case of Cu cathode this performance was achieved in 20h. The calculated energy consumption for ERN, in the experimental conditions developed in this thesis, shows superiority in comparison with literature data.


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