# Strategies for Enhancing Extracellular Electron Transfer in Environmental Biotechnology: A Review
## 3 Strategies for Enhancing EET in Environmental Biotechnology
### Integrated Strategies for Enhancing EET
(**b**) Fused Deposition Modelling (FDM) technology operates by sequentially constructing parts in a layered manner (bottom-to-up approach), wherein a thermoplastic filament is heated and extruded. The thermoplastic material is subjected to heat within the 3D printer, causing it to transition into a partially liquid state. Subsequently, this semi-liquid material is deposited along the extrusion path in the form of ultra fine beads. (**c**) The bacteria is then sprayed using an Anest-Iwata spray gun. An airbrush connected to nitrogen gas is used to directly spray five milliliters of inoculum, or approximately 10% of the anodic solution, onto the 3D anode surface of the Al structure. The inoculum is then preserved at 4 °C in a liquid medium until the MFC assembly. (**d**) MFC assembly [97]. Additionally, the efficacy of EET can be augmented through the concurrent integration of mediator material reinforcement and light amplification. Research has demonstrated that _Shevanella xianenensis_ is capable of internalizing carbon dots at the nanoscale level [127]. Carbon dots have been found to not only augment the electrical conductivity of cells but also stimulate the secretion of a significant quantity of flavin-like ESs, thereby facilitating the process of EET [128]. In addition, internalized carbon dots can augment the process of EET under illumination by enabling light-enhancing mechanisms that promote electron transfer to cellular metabolism [129]. Certain investigations have combined the biological anode and photoanode to increase the power generation of the photocoupled system [130]. This has been achieved by creating a hybrid photoelectrochemical and microbial electrochemical system that harnesses both solar and biological energy. The cathode reaction barrier can be effectively reduced by the activation of the bioachode reaction through the amalgamation of visible light as an energy source. The bioachode can use the difference in voltage between the anode and the cathode to make it easier to separate photogenerated hole/electron pairs [131]. The study conducted by [132], involved the design and testing of an air-cathode MFC-adsorption hybrid system, which utilized an earthen pot. The purpose of the system was to achieve simultaneous wastewater treatment and energy recovery. The design exhibited notable attributes including a low internal resistance of 29.3 \(\Omega\), making it cost-effective andthus resulting in efficient wastewater treatment and power generation. It achieved a power output of 55 mW/m\({}^{3}\) while maintaining an average current of 2.13 \(\pm\) 0.4 mA. A comparison was made between the performance of the MFC-adsorption hybrid system and the standalone adsorption system. The results indicated that the integrated system exhibited significant removal of contaminants. The field of synthetic biology has also been seen to integrate biology with engineering to advance the efficient EET of electroactive cells. Recent advancements in synthetic biology techniques include expanding the range of feedstocks, enhancing intracellular electron generation, improving conductive cytochrome systems, stimulating the production and release of ESs, and creating conductive biofilms [61]. Numerous research endeavors have integrated synthetic biology with mediator material augmentation, light amplification, and other modalities to facilitate EET. Proteorhodopsin has been utilized to augment the efficacy of substrate absorption, specifically lactate, in _S. oneidensis_[133]. The study found that upon illumination, there was an acceleration in the consumption of lactate, and this led to a 250% increase in current production when compared to the wild strain of MR-1. In addition, the efficacy of Osmium-based polymers has been substantiated in promoting direct extracellular electron transfer (EET) in organisms that do not possess the intrinsic capability to engage in such processes. This accomplishment which has been documented by [PERSON] et al.