# Strategies for Enhancing Extracellular Electron Transfer in Environmental Biotechnology: A Review
## 3 Strategies for Enhancing EET in Environmental Biotechnology
### Enhancing EET by Magnetism  
The application of magnetism can serve to augment the effectiveness of EET. Magnetic nanoparticles, such as magnetite (Fe\({}_{3}\)O\({}_{4}\)) or maghemite (\(\gamma\)-Fe\({}_{2}\)O\({}_{3}\)), can function as electron mediators in EET processes. Numerous scholars have employed the implementation of a magnetic field to enhance the efficiency of EET between the EABbeing applied and the surface of the electron acceptor. The possibility of magnetic effects as a cost-effective technique for increasing the performance of MFCs using a magnetic field with an intensity of 100 mT was investigated by [PERSON] et al. [87]. The absence of air in the MFC system resulted in a more significant loss in potential. The use of a magnet may be advantageous in instances when air supply is not feasible or when there is a need to reduce costs associated with air supply. A magnetic field with 100 mT intensity was used by [PERSON] et al. [88] to reduce the startup time of a one-chamber MFC supplied with mixed wastewater from six days to two days. Likewise, an enhancement in the performance of MECs through the utilization of magnetite nanoparticles (Figure 4) was reported by [PERSON] et al. [89]. The observation suggests that magnetite nanoparticles possess the ability to function as electron conductors, allowing for the flow of electrons from the surface of the anode to facilitate reduction reactions over significant distances. The performance of three different configurations of MFCs inoculated with a pure culture of _Shewanella oneidensis_ was evaluated by [PERSON] et al. [91]. The findings of the study demonstrated that all three configurations exhibited a substantial voltage output when subjected to magnetic fields. The observed increase in efficiency can be attributed to an elevation in the mediator's discharge and the catalytic activity of _S. oneidensis_. This led to a more rapid transfer of electrons and a reduction in the loss of activation energy. It was also found that the utilization of a magnetic field has the potential to diminish the resistance encountered during electron transport to the anode [92]. Consequently, this reduces the internal resistance of MFCs, ultimately resulting in an improvement in their overall performance. Among the three different intensities of magnetic fields (MF) examined by [PERSON] et al. [92] only the 200 mT intensity demonstrated an  
Figure 4: Conceptual depiction of an electron transfer pathway established by magnetite nanoparticles, facilitating the ease of electron movement between microorganisms and electrodes [90]. outstanding ability to enhance electricity generation. As a result, insufficient or excessive levels of intensity can lead to outcomes that are inconsistent with the intended objectives. It was found that the application of an appropriate static magnetic field can augment the extracellular electron transfer mechanism in microorganisms, resulting in an elevation of the maximum voltage output [93]. Excessive field strength may impede microbial growth and result in unfavorable consequences. The optimal magnetic field strength range that promotes the proliferation of EAMs and consequently amplifies the power generation of MFCs remains undetermined and requires additional investigation. Therefore, it is imperative to conduct a multi-omic approach in investigating the molecular regulation of genes and proteins related to EET to comprehend the mechanism behind the stimulation of EET by the magnetic field [94]. The effects of different magnetic field intensities on both attractive and repulsive fields were investigated by [PERSON] and [PERSON] [95] and the findings demonstrated that the utilization of magnetic fields with intensities of 50 and 100 mT led to an augmentation in electricity generation and a faster initiation of the process, particularly when employing the 50-mT magnetic field intensity. Conversely, the overall performance was adversely affected when the magnetic field intensity was increased to 200 mT.