Modelling the cathodic reduction of 2,4-dichlorophenol in a microbial fuel cell

Abstract

This work presents a simplified mathematical model able to predict the performance of a microbial fuel cell (MFC) for the cathodic dechlorination of 2,4-dichlorophenol (2,4-DCP) operating at different cathode pH values (7.0 and 5.0). Experimental data from previous work were utilized for the fitting of the model. The MFC modelled consisted of two chambers (bioanode and abiotic cathode), wherein the catholyte contained 300 mg L−1 of 2,4-DCP and the anolyte 1000 mg L−1 of sodium acetate. The model considered two mixed microbial populations in the anode compartment using sodium acetate as the carbon source for growth and maintenance: electrogenic and non-electrogenic biomass. 2,4-DCP, its intermediates of the reductive process (2-chlorophenol, 2-CP and 4-chlorophenol, 4-CP) and protons were considered in the model as electron acceptors in the electrogenic mechanism. The global process rate was assumed to be controlled by the biological mechanisms and modelled using multiplicative Monod-type equations. The formulation of a set of differential equations allowed to describe the simultaneous evolution of every component: concentration of sodium acetate in the anodic compartment; and concentration of 2,4-DCP, 2-CP, 4-CP, phenol and chloride in the cathode chamber. Current production and coulombic efficiencies were also estimated from the fitting. It was observed that most of the organic substrate was used by non-electrogenic mechanism. The influence of the Monod parameters was more important than the influence of the biomass yield coefficients. Finally, the model was employed to simulate different scenarios under distinct experimental conditions.

Coupling the electrocatalytic dechlorination of 2,4‐D with electroactive microbial anodes

“…This stability in the anode potential can be attributed to the excess of sodium acetate, which indicates that it was not a limiting substrate in bioprocess. According to the biological Monod kinetic model, as the substrate concentration increases, there reaches a point where the specific biomass growth or substrate consumption rate plateaus (it is important to note that excessively high substrate concentrations could potentially lead to substrate inhibition, where the growth or consumption rate may be hindered) (Leon‐Fernandez et al, 2022). This explains the stable conditions at the anode as long as the substrate is present in excess and the rest of the operating conditions remain unchanged (e.g., pH , counter reaction, cell voltage).…”

“…Carbon-based materials have far lower associated costs compared to the conventional electrochemical processes here evaluated, which use Platinum group metals-based materials (e.g., Pt, IrO 2 , RuO 2 ) for the oxygen evolution reaction (OER) catalysis (otherwise, a higher energy input would be required to overcome the activation overpotential of the OER). Pt prices currently oscillate between 950 and 1000 $/troy oz (30,543-32,150 $/kg) (Johnson Matthey, 2023). Current industrial practices do not use Pt for OER, but generally Nickel, Cobalt or Iron based materials in alkaline electrolysers (Marini et al, 2012;Zeng & Zhang, 2010), or Iridium or Ruthenium based materials in PEM electrolysers (Carmo et al, 2013), which have similar economic implications (prize of Ir and Ru are around 4600 $/troy oz and 465 $/troy oz, respectively) (Johnson Matthey, 2023).…”

“…Pt prices currently oscillate between 950 and 1000 $/troy oz (30,543-32,150 $/kg) (Johnson Matthey, 2023). Current industrial practices do not use Pt for OER, but generally Nickel, Cobalt or Iron based materials in alkaline electrolysers (Marini et al, 2012;Zeng & Zhang, 2010), or Iridium or Ruthenium based materials in PEM electrolysers (Carmo et al, 2013), which have similar economic implications (prize of Ir and Ru are around 4600 $/troy oz and 465 $/troy oz, respectively) (Johnson Matthey, 2023). Another handicap of noble metalbased anodes (i.e., platinum group metals, PGMs) is their stability in long-term operation, as catalyst deactivation and/or dissolution along OER will occur (Schalenbach et al, 2018).…”