## 4 Conclusions  
The research undertaken in this study has provided a comprehensive analysis of the parameters that govern the efficiency of succinic acid production in an ORP-controlled MEC system, particularly focusing on the role of neutral red as an electron mediator, the application of voltage, and the optimization of ORP and fed-batch culture conditions.  
The incorporation of NR into the MEC system has been a pivotal step in enhancing the production of succinic acid. NR, as an electron mediator, has improved the sensitivity of the system to ORP regulation. This heightened sensitivity allows for more precise control over the redox environment within the MEC, which is crucial for the metabolic processes of the microorganisms involved, particularly _A. succinogenes_ (130Z).  
This study found that the optimal approach to ORP level control was the use of a \(-\)400 mV high-voltage electric pulse-based strategy. This strategy not only provided the necessary extracellular electrons for the microbial metabolic processes but also seemed to stimulate enzyme activity related to succinic acid production. The result was an electronic utilization efficiency of 192.02%, an impressive figure that indicates the system's ability to exceed the theoretical electron transfer efficiency. This could suggest that the ORP-controlled MEC system is capable of redirecting electron flow to enhance enzymatic pathways that are beneficial for succinic acid synthesis.  
The efficiency over 100% indicates that the system may be capturing and utilizing electrons more effectively than anticipated, which could be due to several factors such as enhanced mediator performance, improved microbial metabolism, or more effective electron transfer mechanisms. This exceptional utilization efficiency also implies that the system can sustain a long-term fermentation process, providing a consistent and enhanced yield of succinic acid.  
This research validates ORP control as a method to enhance succinic acid production in MEC systems, offering a pathway to more efficient and economical industrial fermentation with potential for commercial scaling, contingent on maintaining system performance. Future work in this area may focus on further refining the electron mediator system, perhaps by identifying new compounds that can perform better than NR, or by engineering microorganisms to more effectively interact with the existing mediators. Additionally, exploring the integration of this technology with other renewable energy sources or waste-to-energy systems could further improve the sustainability and economic viability of the process.  
In summary, this research has not only provided insights into the effective management of the ORP in MEC systems but has also showcased the potential for these systems torevolutionize the production of valuable biochemicals like succinic acid, aligning with the principles of green chemistry and sustainable industrial processes.  
Methodology, J.P. and S.Z.; formal analysis, J.P., S.Z. and Y.L.; resources, Z.W.; writing--original draft preparation, J.P.; writing--review and editing, Z.W.; supervision, Z.W. and L.C. All authors have read and agreed to the published version of the manuscript.  
This research was supported by the the National Nature Science Foundation of China [grant no. 21576134, 21390200]; 863 program of China [grant no. 2014 AA021703]; Jiangsu Postdoctoral Research Funding [grant no. 2021K348C]; Liangvungang Postdoctoral Research Funding [grant no. LYG20210004] and Lianyungang \"521 High-level Talent Cultivation Project\" [grant no. LYG06521202342].  
Not applicable.  
All data are included in the manuscript.  
This work was supported by the Priority Academic Program Development of Jiangsu Higher Education Institutions.  
The authors declare no conflicts of interest.