Bioelectricity Generation Performance Enhancement Of Buffer-free Microbial Fuel Cell

Microbial fuel cell(MFC),as one of the novel environmental biotechnologies,is capable of synchronously treating wastes and conversing energy.At present,phosphate buffer solution(PBS)or NaHCO3 solution is indispensable to maintain stable anolyte pH value and provide certain conductivity in lab-scale MFCs to guarantee their efficient and stable operation.However,applying buffer-free MFC systems in future practical waste water treatment is more realistic,owing to the high operation cost and the potential environment problems,like eutrophication,caused by the additional of buffers.In buffer-free MFCs,protons(H+)were generated through the anode reaction and accumulated around the anode causing “anode acidification”,which seriously restricted the proliferation and activity of the electrochemically active bacteria(EAB).Therefore,relieving or eliminating the “anode acidification” is the crux to further improve the electricity performance of buffer-free MFCs.The main research content and results in this thesis are as follows:(1)In order to relieve the negative influence of the “anode acidification” on the proliferation and activity of the EAB,promote the formation of the anode biofilm,and improve the electric power,alkali-treated anion exchange resin(AER)were placed in the air-cathode single-chamber MFC to release OH-and neutralize the H+ in the anolyte.The experiment results indicated that “anode acidification” phenomenon appeared in the KCl-MFC as the pH value of the pristine KCl anolyte decreased from 7.09 to 5.82.The OHions carried by the AER were released out in two running cycles in the KCl-AER-MFC.In the subsequent running,the pH value fast fluctuated at the beginning of each running cycle and then mainly kept 6.66 in most time of each running cycle.The proliferation of the electrochemical active Geobacter was promoted and the electrochemical activity of the anode was improved.Finally,the maximum power density(Pmax)of the KCl-AER-MFC significantly increased from 307.5 m W/m2 to 542.8 mW/m2.(2)Short-term initial alkaline anolyte pH adjustments have been applied in the buffer-free MFCs to relieve the negative effect of the “anode acidification” on the proliferation of the EAB and the formation of the anode biofilm and to improve the performance of the buffer-free MFCs.The optimum adjusting strategy was determined,namely adjusting the initial pH of the KCl anolyte to 9 in five running cycles.Experiment results suggested that the proliferation of Geobacter was promoted as its relative abundance increased from 59.01% to 75.12%.Therefore,after the short-term initial anolyte pH adjustment,the electrochemical activity of the anode biofilm and the electron generation rate were significantly elevated.And,more OH-ions were produced through the cathode oxygen reduction reaction under the condition of H+ diffusion limitation to the cathode area andelevated the anolyte pH value.The Pmax of the KCl-pH9-MFC increased from 321.04 mW/m2 to 536.38 mW/m2.Furthermore,the short-term adjustment established the new equilibrium between the anolyte pH and the electrochemical activity of the anode biofilm,which ensured the sustainability of the improved electric power of the buffer-free MFCs.(3)The buffer-free anolyte was recycled at a certain ratio to accelerate the accumulation of the natural buffers,HCO3-and H2CO3,to eliminate the “anode acidification” phenomenon.The anolyte pH rapidly increased in the first 3 running cycles and reached at 8.19 in the fourth running cycle.After that,the anolyte pH gradually increased as the running of the KCl-R-MFC.The inorganic carbon(IC)concentration in the recycled anolyte increased from15.85 mmol/L to 59.10 mmol/L in the first four running cycles.The Pmax of the KCl-R-MFC significantly increased form 322.91 mW/m2 to 527.22 mW/m2,which is comparable with that of the PBS-MFC(523.74 mW/m2).