Carbon Nanotube Membrane Stack for Flow-through Sequential Regenerative Electro-Fenton

Electro-Fenton is a promising advanced oxidation process for water treatment consisting a series redox reactions. Here, we design and examine an electrochemical filter for sequential electro-Fenton reactions to optimize the treatment process. The carbon nanotube (CNT) membrane stack (thickness similar to 200 mu m) used here consisted of 1) a CNT network cathode for O-2 reduction to H2O2, 2) a CNT-COOFe2+ cathode to chemical reduction H2O2 to OH and HO and to regenerate Fe2+ in situ, 3) a porous PVDF or PTFE insulating separator, and 4) a CNT filter anode for remaining intermediate oxidation intermediates. The sequential electro-Fenton was compared to individual electrochemical and Fenton process using oxalate, a persistent organic, as a target molecule. Synergism is observed during the sequential electro-Fenton process. For example, when [DO](in) = 38 +/- 1 mg L-1, J = 1.6 mL min(-1), neutral pH, and E-cell = 2.89 V, the sequential electro-Fenton oxidation rate was 206.8 +/- 6.3 mgC m(-2) h(-1), which is 4-fold greater than the sum of the individual electrochemistry (16.4 +/- 3.2 mgC m(-2) h(-1)) and Fenton (33.3 +/- 1.3 mgC m(-2) h(-1)) reaction fluxes, and the energy consumption was 45.8 kWh kgTOC(-)1. The sequential electro-Fenton was also challenged with the refractory trifluoroacetic acid (TFA) and trichloroacetic acid (TCA), and they can be transferred at a removal rate of 11.3 +/- 1.2 and 21.8 +/- 1.9 mmol m(-2) h(-1), respectively, with different transformation mechanisms.