# Strategies for Enhancing Extracellular Electron Transfer in Environmental Biotechnology: A Review
## 3 Strategies for Enhancing EET in Environmental Biotechnology
### Enhancing EET by Photo  
The EET process in bioelectrochemical systems can be enhanced by the use of light, particularly photosynthesis and photovoltaic activities. Photosynthetic bacteria can transmit electrons directly to the electrode surface, enabling effective EET. Advancements in electron transfer phenomena have resulted in the development of photoelectrochemical systems with microbial characteristics and solar energy support. Nevertheless, the limited current density observed in photo-bioelectrochemical cells (PBEC) imposes constraints on their progress and real-world implementation. These studies [79; 80] have shown that the introduction of _OmcS_ from _Geobacter_ into genetically altered _Synechococcus elongatus_ PCC7942 led to an increased capacity for EET. This enhancement in EET capacity led to a substantial rise in photocurrent generation at the anode of the PBEC system, about nine-fold greater than the control group. This methodology did not merely enhance the generation of photocurrent in cyanobacteria but additionally, it expedited the advancement of photosynthetic MFC technology. Solar light has been demonstrated to stimulate non-phototrophic bacteria's metabolic and development activities through the photocatalytic activity of semiconducting minerals [81] and bacteria that do not rely on photosynthesis are capable of converting carbon dioxide into acetate by employing cadmium sulfide nanoparticles in the presence of light [82]. Hematite, a prevalent mineral found in natural environments, has been employed as a photoanode. Analysis of the methods by which semiconducting minerals and microorganisms transport electrons when exposed to solar radiation has advanced in current research. Photo generation is the process by which semiconductor minerals produce electron and hole pairs when exposed to light. The extracellular electron transport pathway of microorganisms may be impacted by this event. Crystalline Fe (III) oxide is known to be excited by light and is frequently used as an electron acceptor in the natural environment by extracellular electron transfer microbial systems. The potential of visible light excitation for outer membrane _c_-type cytochromes in dissimilatory metal-reducing bacteria was investigated by [PERSON] et al. [83] and the impact of excited _c_-type cytochromes on the EET process between bacteria and semi-conductive electron acceptors using a TiO\({}_{2}\)-coated electrode was demonstrated. According to the study, the EET rate to TiO\({}_{2}\) was observed to exhibit a significant increase of more than eight-fold upon exposure to visible light. Similarly, the interaction between a hematite photoelectrode and _P. aeruginosa_ PAO1 when subjected to visible light irradiation was studied by [PERSON] et al. [84] as depicted in Figure 3.  
According to this study, the photocurrent density at the hematite electrode was 240% higher in the presence of light. This showed that light enhanced the transfer of electrons from hematite to PAO1, and also suggests that the microorganism _Pseudomonas aeruginosa_ PAO1 also played a crucial role in this process. Likewise, the extent to which visible light affected electron transport between bimestite photoanodes and _Pseudomonas aeruginosa_ PAO1 was investigated by [PERSON] et al. [85]. The photocurrent density of the electrochemical system consisting of light, bimestite, and PAO1 was 279.57 \(\mu\)A/cm\({}^{2}\) under circumstances of light illumination and positive bias. This number was 322% and 170% higher than the photocurrent densities reported in the abiotic control and dead culture, respectively. These data suggest that bimestite and _Pseudomonas_ have a photo-enhanced electrochemical interaction and the study exhibited a rapid light-induced EET process between the bacterium _Pseudomonas aeruginosa_ PAO1 and the semiconducting material bimestite.