Mass Transfer Enhancement And Electricity Generation Performance Improvement In Sediment Microbial Fuel Cells

Sediment microbial fuel cell（SMFC）degrades pollutants in the environment with specific microorganisms,converts chemical energy directly into electric energy,and at the same time realizes the in-situ ecological restoration of sediments and the production of clean electric energy.It can be used in the field of in-situ restoration of sediments and energy supply of low-power environmental sensors in remote areas.In this study,freshwater sediments were used as the research object to construct a microbial fuel cell reactor in sediments.The cathode and anode were respectively enhanced by means of hydro-driven cathode rotation and material transport channel construction in sediments.The effects of the above two methods on the electrical performance and microbial community structure of SMFC were studied,which provided a theoretical basis for the mass transfer enhancement and performance improvement of SMFC,and provided a reference for the practical application of SMFC.By building rotating cathode,the use of hydraulic drive rotation strengthening the cathode qualitative study,and is equipped with the traditional immersion level compared to cathode battery（SMFC-C）,the construction of a rotating cathode battery（SMFC-R）under the condition of static power density increased by 70.2%,in overlying water flow and hydraulic drive cathode revolving conditions,The power density increased by 21.9%.The overlying water flow can promote the oxygen transfer rate and oxygen reduction reaction（ORR）rate of the traditional submerged horizontal cathode,but the effect on the rotating cathode is not obvious,the main reason is that ORR occurs in the exposed part of the rotating cathode.When the cathode is rotated by hydraulic drive,a CO₂/carbonate and CO₂/bicarbonate buffer system can be better established near the cathode to maintain a low p H level and promote the mass transfer rate of Dissolved oxygen（DO）,thus achieving the mass transfer enhancement effect,and finally realizing the improvement of performance.In addition,the diversity and richness of microbial community in the anode were increased slightly when the cathode was rotated by hydraulic drive.In the study,it was found that the greater the thickness of the sediments above the anode,the greater the internal resistance and the lower the output voltage of SMFC,but the better the stability of SMFC electricity generation performance under the condition that the anode/cathode spacing remained unchanged.By establishing material transfer channels,the internal resistance of SMFC can be effectively reduced.At the same time,the H+generated by anode unit can be timely channelized to enhance mass transfer,so that the electrogenic microorganisms are in a favorable p H environment and obtain a lower anode potential.Since the performance of the anode is closely related to the performance of the cathode,the lower anode potential has a positive effect on the cathode,and ultimately the performance is improved.The internal resistance of the 3 cm transmission channel cell（SMFC-3）was reduced by34.7%and the power density was increased by 66.7%.In addition,the establishment of material transport channels can improve the diversity of microbial community structure on the lower surface of the anode,which is conducive to the improvement and stability of SMFC performance.In practical application,the construction of a rotating cathode similar to a water wheel can not only directly use the hydraulic cathode to rotate,strengthen the mass transfer of the cathode,improve the performance,but also beautify the landscape.The material transport channel is established in the sediment to strengthen the mass transfer of anode and improve the performance.Both strategies for improving performance require materials that are cheap,readily available and reliable.