Study On Anode Acidification Adjustment And Electricity Generation Enhancement Of Buffer-less Microbial Fuel Cells

Microbial fuel cell?MFC?is a technology that uses electrochemical active bacteria?EAB?to degrade organic matter and generate electricity.During the operation of MFC,the anaerobic hydrolysis of organic substrates and the electricity generation produce protons?H⁺?,and the accumulation of H⁺in the anolyte will lead to anode acidification,which seriously limits the growth and electricity generation activity of EAB.At present,it is necessary to add phosphate buffer?PBS?or bicarbonate to adjustment the pH of the anolyte in neutral to weakly alkaline range during the operation of MFC.However,the addition of buffer not only greatly increase the operating cost,but also cause problems such as the total phosphorus and salinity of the effluent exceeds the discharge standard.Therefore,it is not suitable for large-scale practical application.However,anode acidification cannot be avoided during the operation of the buffer-less microbial fuel cell?BLMFC?,which seriously limits the electricity generation of the system.Thus,how to alleviate and eliminate the anode acidification of BLMFC is one of the important problems to be solved.Based on this,this paper investigated the situation of anode acidification and its impacts on electricity generation of the BLMFC running with different substrates.For the BLMFC with sodium acetate as substrate,anode acidification was alleviated by adding anaerobic sludge to enhance IC accumulation;For the BLMFC with glucose as substrate,anode acidification was alleviated by coupling anode denitrification.The main research contents and conclusions are as follows:?1?Six common carbon sources?formate,acetate,propionate,oxalate,butyrate and glucose?were respectively used as the substrates of BLMFC.The degree of anode acidification,the IC accumulated concentrations,and electricity generation of the BLMFC were investigated.Experimental results showed that there was no anode acidification during the running of the BLMFC with sodium formate and sodium oxalate as substrates.For the BLMFC with sodium butyrate as the substrate,the minimum anolyte pH decreased at the beginning of each running cycle,but the anolyte pH decline did not inhibit the electricity generation.For the BLMFC with sodium acetate and sodium propionate as substrates,anode acidification occurred and seriously restricted the electricity generation.The most serious anode acidification occurred in the BLMFC with glucose as the substrate.The anolyte pH rapidly decreased to?5.3 in the first 10hours of each running cycle although the initial pH was adjusted to 10.The IC accumulated concentrations in the BLMFCs using sodium formate,sodium acetate,sodium propionate,sodium oxalate,sodium butyrate,glucose as substrates were 14.60 mM,8.34 mM,5.98 mM,9.62 mM,10.07 mM and 1.2 mM,respectively.The maximum power density(P_max)of the corresponding systems were 190.2 mW/m²,340.1 mW/m²,108.0 mW/m²,3.8 mW/m²,315.1mW/m² and 41.9 mW/m²,respectively.Terefore,the BLMFC with sodium acetate as the substrate had the highest output power and the best electricity generation performance.?2?The exsitance of a certain amount of anaerobic sludge can eliminate the anode acidification of the BLMFC running with sodium acetate as the substrate.Experimental results showed that in the KCl-S-BLMFC,the IC concentration increased from 8.30 mM to 12.50 mM,the anolyte pH remained above 7.5 in each running cycle,the P_max increased significantly from332.2 mW/m² to 628.1 mW/m²,and the coulomb efficiency?CE?increased slightly from 16.37%to 19.45%.The results of high-throughput sequencing indicated that Geobacter was the main genera of EAB and it's relative abundance increased from 0.2%to 5.75%in the anode biofilm of KCl-S-BLMFC.?3?Coupling heterotrophic anode denitrification process eliminated the anode acidification of the glucose mediated BLMFC.Experimental results showed that,the anolyte pH was matained above 6.5 in each running cycle,and the P_max increased to 264.5 mW/m²,which was 5.4 times higher than that of the Control after adding 90 mg/L NO₃^--N.However,the substrate insufficiency caused by the introduction of excess NO₃^--N?120 mg/L?severely limited the power generation of the DNMFC-120.In the DNMFCs with the initial NO₃^--N concentration of 60 mg/L,90 mg/L and 120 mg/L,NO₃^--N was completely removed in the first15 hours of the running cycle.The TOC consumed by the denitrification process accounted for17.6%,26.1%and 35.8%of the total TOC removal.In the anode biofilms of the DNMFCs Dysgonomas and Petrimonas were the main EAB genera and denitrifying bacteria and their relative abundance increased with the increase of the initial NO₃^--N concentration.