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

Abstract

Enzymatic biocathodes have the potential to replace platinum as an expensive catalyst for the oxygen reduction reaction in microbial fuel cells (MFCs). However, enzymes are fragile and prone to loss of activity with time. This could be circumvented by using suitable immobilization techniques to maintain the activity and increase longevity of the enzyme. In the present study, laccase from Trametes versicolor was immobilized using three different approaches, i.e., crosslinking with electropolymerized polyaniline (PANI), entrapment in copper alginate beads (Cu-Alg), and encapsulation in Nafion micelles (Nafion), in the absence of redox mediators. These laccase systems were employed in cathode chambers of MFCs for decolourization of Acid orange 7 (AO7) dye. The biocatalyst in the anode chamber was Shewanella oneidensis MR-1 in each case. The enzyme in the immobilized states was compared with freely suspended enzyme with respect to dye decolourization at the cathode, enzyme activity retention, power production, and reusability. PANI laccase showed the highest stability and activity, producing a power density of 38 ± 1.7 mW m−2 compared to 25.6 ± 2.1 mW m−2 for Nafion laccase, 14.7 ± 1.04 mW m−2 for Cu-Alg laccase, and 28 ± 0.98 mW m−2 for the freely suspended enzyme. There was 81% enzyme activity retained after 1 cycle (5 days) for PANI laccase compared to 69% for Nafion and 61.5% activity for Cu-alginate laccase and 23.8% activity retention for the freely suspended laccase compared to initial activity. The dye decolourization was highest for freely suspended enzyme with over 85% decolourization whereas for PANI it was 75.6%, Nafion 73%, and 81% Cu-alginate systems, respectively. All the immobilized laccase systems were reusable for two more cycles. The current study explores the potential of laccase immobilized biocathode for dye decolourization in a microbial fuel cell.

Applications and immobilization strategies of the copper-centred laccase enzyme; a review

“…It is environmentally safe, can be cheaply manufactured, can act as a direct mediator for electron transfer in redox reactions, and exhibits high conductivity and thermal stability [ 330 ]. For instance, Mani et al [ 554 ], compared the catalytic oxygen reduction in microbial fuel cell of laccase immobilized by crosslinking with PANI, entrapment in Cu-alginate, and encapsulation in Nafion micelles. The PANI-laccase showed the highest stability, activity, and reusability.…”

Laccase Immobilization Using Polymeric Supports for Wastewater Treatment: A Critical Review

“…[123] It is essential to know the strength and weakness of various immobilization procedures that might affect the laccase performance. [124][125][126] The most well-known advantages and disadvantages of the immobilization techniques have been summarized and presented (Table 5). Adsorption, entrapment, and encapsulation are the most basic operation methods, indicating that the laccase enzyme's natural structure is neither degraded nor modified in the process.…”

“…[130,131] On the other hand, the covalent binding and cross-linking cause conformational changes in enzymatic structure and loss of activity, which can reduce the laccase activity. [74,87,129] Despite this weakness, covalent binding is the most often employed approach in wastewater treatment owing to the significant contacts between the laccase enzyme and the polymer support. [15,83,106,108,120]…”

“…[ 86 ] In another report, cross‐linking immobilization of laccase has been performed on electropolymerized polyaniline resulting in a more durable biocathode for dye removal in a microbial fuel cell. [ 87 ] Optimization of laccase cross‐linking immobilization on woven nylon (the schematic diagram of its preparation is presented in Figure ) has been carried out employing 24 full factorial designs with protein retention reaching 30%. [ 88 ] Other optimization strategy is by using response surface methodology to obtain optimum enzyme loading, pH, time, and cross‐linker concentration.…”

Engineered nanomaterials in microbial fuel cells – Recent developments, sustainability aspects, and future outlook

“…However, the basis of these technologies is to harvest the energy directly and transform and store it for further use. In this regard, microbial fuel cells have emerged as a sustainable technology for the simultaneous elimination of pollutants from (waste)water and generating electricity through redox reactions of organic substances [8,9]. There are also reports on bioelectricity generation from (waste)water in MFCs by reducing heavy metals such as hexavalent chromium [10].…”