Development of air-cathode reactor to electrochemically generate hydrogen peroxide (H2O2) anaerobically
Electrochemcal production of hydrogen peroxide
M. Phukan (TU Delft - Civil Engineering & Geosciences)
D. van Halem – Mentor (TU Delft - Sanitary Engineering)
M. Roy – Mentor
Merle K. Kreuk – Mentor (TU Delft - Sanitary Engineering)
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Abstract
Groundwater is a major source of drinking water containing various elements out of which arsenic(As) is one of the toxic elements present. It is present in the form of arsenite, Conventionally, As(III) can be effectively removed if it is pre-oxidized to arsenate, As(V), thereby not involving any chemical dosage. There are various techniques to remove arsenic from drinking water like membrane filtration, electro-coagulation, filtration, adsorption and ion exchange. Among these the iron electro-coagulation technique of arsenic removal is one such technique which can be done by electrochemically generating oxidizing compounds like
hydrogen peroxide, H2O2. Instead of dosing H2O2 anaerobically, it can be generated before the aeration step and can improve the As(III) oxidation with the groundwater native Fe(II).
The in-situ electrochemical generation of H2O2 was done by means of an air-cathode reactor setup, which reduces atmospheric oxygen O2 to H2O2, under anoxic water. This H2O2 then reacts with ferrous iron, Fe(II) to produce ferric iron Fe(III) and reactive oxidizing species(ROS)/intermediate products/fenton products. These ROS mainly form poorly ordered solids, which have higher adsorption capacities than the products of aeration. The oxidation of
As(III) is 4 times more by H2O2, than the oxidation by O2.
By varying the applied charge dosage (CD) and the rate of dosage (Charge Dosage Rate, CDR),the faradaic efficiencies of both Fe and H2O2 were analyzed. It was found that as the CDR increased, the overall faradaic efficiency of H2O2 generation also increased from 76.32% to 92.07%. However, there might have been discrepancies in the faradaic efficiencies of Fe due to acid & base dilutions, human errors or the difference in the operational values of the current. In theory, 1 mole of H2O2 oxidizes 2 moles of Fe(II), and in the absence of O2 the main Fe(II)-oxidant is the generated H2O2.