Degradation of Azo Dye (Acid Orange 7) in a Microbial Fuel Cell: Comparison Between Anodic Microbial-Mediated Reduction and Cathodic Laccase-Mediated Oxidation

Abstract

More than 80% of wastewater from industries is discharged into receiving water bodies without any pollution control. Microbial fuel cells (MFCs) are a promising technology for the simultaneous treatment of wastewater and electricity production. With regard to azo-dye containing wastewater (e.g., from textile manufacturing), the dye may be fed via the anode chamber containing electrochemically active bacteria or via the cathode chamber containing laccase enzyme as catalyst for oxygen reduction. This study investigated which of the two approaches is the best with regard to rate of decolourization of the dye (Acid orange 7), COD reduction and electricity production. The power density was higher for the MFC Dye Cathode (50 ± 4 mW m −2 , COD reduction 80.4 ± 1.2%) compared with 42.5 ± 2.6 mW m −2 (COD reduction 69 ± 2%) for MFC Dye Anode. The time required for decolourization was longer in the MFC Dye Anode (Shewanella oneidensis) where only 20% decolourization was obtained after 24 h compared to 80% for the MFC Dye Cathode. The anodic dye degradation products were unstable when exposed to air resulting in regaining of color. In case of degradation by laccase in the cathode chamber, the decolourization products were stable and simpler in chemical structure as determined by GC-MS. This work suggests that feeding azo dyes in cathode chambers of MFCs containing laccase is a better way of treating the dyes compared to the commonly used approach of feeding the dye in the anode chamber provided enzyme activity can be sustained.

Laccase Immobilization Strategies for Application as a Cathode Catalyst in Microbial Fuel Cells for Azo Dye Decolourization

“…The initial rapid decolourization is due to the high enzyme activity initially; the rate of decolourization decreases gradually as the enzyme activity decreases as shown in the enzyme activity graphs ( Figure 7 ). The dye decolourization by laccase is probably due to asymmetric cleavage of the azo-bonds and subsequent ring cleavage to form simple aromatic compounds (Mani et al, 2019 ).…”

“…Laccase is a multi-copper containing oxidase enzyme which is capable of one electron oxidation of other substrates and four electron reduction of O 2 to H 2 O (Galhaup and Haltrich, 2001 ). Laccase has been employed in the cathode chamber of MFC for dye decolourization and catalysis of the oxygen reduction reaction (Savizi et al, 2012 ; Mani et al, 2019 ).…”

A Brief History of Colour, the Environmental Impact of Synthetic Dyes and Removal by Using Laccases

“…The azo dyes degradation with laccases begins with the asymmetric excision of the azo bond followed by oxidative excision, desulfonation, deamination, demethylation or dihydroxylation, depending on the structure of the dye [160]. Discolouration of azo class dyes such as Methyl Orange (MO) has reported using Aspergillus ochraceus laccase NCIM-1146 [289], Congo Red (CO), with Tplac laccase from Trametes pubescens [280], Acid Orange 7 (AO7) using a laccase (not specified), [290]. In the three works, it was identified that in azo dyes, the first step in the discolouration is the splitting of the bond -N=N-, which results in obtaining two asymmetric intermediate products (Figure 4), [289][290][291].…”

“…Discolouration of azo class dyes such as Methyl Orange (MO) has reported using Aspergillus ochraceus laccase NCIM-1146 [289], Congo Red (CO), with Tplac laccase from Trametes pubescens [280], Acid Orange 7 (AO7) using a laccase (not specified), [290]. In the three works, it was identified that in azo dyes, the first step in the discolouration is the splitting of the bond -N=N-, which results in obtaining two asymmetric intermediate products (Figure 4), [289][290][291]. The mechanism that the laccases carry out for the excision of azo dyes is through the formation of an electron-deficient reaction centre (carbocation).…”

3D Self-Supported Nitrogen-Doped Carbon Nanofiber Electrodes Incorporated Co/CoOx Nanoparticles: Application to Dyes Degradation by Electro-Fenton-Based Process

“…Therefore, eco-friendly technology is crucially needed to transform organic pollutants present in the water into less toxic molecules or to completely degrade them into CO 2 and H 2 O [5]. Traditional approaches, such as coagulation, adsorption, chemical oxidation, chemical reduction [6], photocatalytic oxidation [7], and enzymatic degradation [8], are widely exploited to eliminate organic pollutants from effluents. However, they display some limitations [9], such as the need for complementary treatments before their elimination at wastewater treatment plants.…”