| Microbial fuel cell(MFC) has gained a great attention attributable to its ability in treating wastewaters and generating electricity directly from the wastewater treatment. Based on the current research status in MFC, the goal of this research was to improve MFC performances on electricity generation and wastewater water treatment. Effects of reactor configuration, cathodic dissolved oxygen(DO), and magnetic field on electricity generation and wastewater treatment in MFCs have been investigated. Moreover, ammonia inhibition and electricity generation coupled to ammonium in MFCs were also investigated. Finally, the landfill leachate was treated by combining MFC with microwave technology. The main results are listed as follows:The single-chamber MFC and two-chamber MFC both have the ability to remove nitrogen and phosphorus, the efficiencies and mechanisms in them were vary considerably. In the single-chamber MFC: The removal rates of total phosphorus(TP) and total nitrogen(TN) were 43.9% and 53.8%, respectively. Needle shaped prismatic morphology typical of struvite formation on the surface of the cathode may be the main reason for phosphorus and nitrogen removal. In the two-chamber MFC: There was no struvite crystal on the surface of the cathode, and the removal efficiencies of TP and TN were not significant in the anode chamber. The removal rate of TP in the cathode chamber was 94%. Furthermore, TP in the two-chamber MFC was removed by the combined effect of chemical precipitation and microbial absorption, and the chemical precipitates formed in the cathode chamber were analyzed to be the mixture of phosphate, carbonate and hydroxyl compound. Removal rate of TN was not favorable, and a large proportion of ammonium was converted to nitrites in the cathode. The average COD removal efficiencies by single-chamber MFC and two-chamber MFC were about 66% and 79%, respectively. The maximum voltages, maximum power densities, internal resistances, and coulombic efficiencies of single-chamber MFC and two-chamber MFC were 443 and 524 m V, 560 and 528 m W/m2, 181 and 227 Ω, 35% and 51%, respectively.The cathodic DO was an important factor for electricity generation and wastewater treatment in MFC. The maximum voltage, coulombic efficiency and maximum power density of MFC were decreased from 521 m V to 303 m V, 52.48% to 23.09% and 530 m W/m2 to 178 m W/m2 with cathodic DO declined. TP removal rates were always >85% with cathodic DO change. Furthermore, about 80% of TP was removed owing to chemical precipitation and around 4%-17% owing to microbial absorption. More than 85% TN was removed when MFC reacted with cathodic DO at 2.5 and 2.0 mg/L. However, as MFC reacted with cathodic DO at 3.5 and 2.8 mg/L, a large proportion of NH4+-N was converted to NO2--N. TN decreased a little compared with the effluent from anode chamber. Effects of cathodic DO on COD removal turn out to be small, and COD was first removed in anode chamber(>70%) then in cathode chamber(<5%). Chemical precipitates formed in cathode chamber with four cathodic DOs were verified as the mixture of phosphate, carbonate and hydroxyl compound.MFC performances on electricity generation and wastewater treatment could be improved by the application of a low intensity static magnetic field(MF). When a MF of 50 m T was applied to MFCs, the maximum voltage, TP removal efficiency, and COD removal efficiency increased from 523±2 to 553±2 m V, ~93% to ~96%, and ~80% to >90%, while the startup time and coulombic efficiency decreased from 16 to 10 days, and ~50% to ~43%. The applied MF didn’t promote much for TN removal, but much for nitrogen conversion. Nitrogen compounds in magnetic MFCs were nitrified more thoroughly. The startup and voltage output were less affected by the MF direction. The MF effects were immediate, reversible and not long-lasting, and negative effects on electricity generation and COD removal seemed to occur after the MF was removed, but no negative effect on TP/TN removal and nitrogen conversion.Ammonium was involved in electricity generation indirectly, rather than directly, as the anodic fuel. None of which stimulated voltage output when use NH4 Cl, KNO2, KNO3, KNO2 and Na NO3, NH4 Cl and Na NO3 as the nitrogen source in a nutrient solution without organic carbon sources, the form and amount of nitrogen in MFCs have no significant change during the operating period. When use the mixture of NH4Cl(20 m M) and KNO2(10 m M) as the nitrogen source, a small voltage was produced. The maximum output voltage increased from 18.1 to 32.5 m V with the growth of KNO2 concentration, and residual concentrations of NH4+-N and NO2--N in the effluent decreased greatly, a certain amount of NO3--N was found in the effluent. Therefore, the occurrence of anaerobic ammonium oxidation(ANAMMOX) in MFC was comfirmed, and the voltage output from MFC was a consequence of ANAMMOX bacteria(An AOB) and some heterotrophic electricigens. NH4+-N was the indirect electron donor for electricity generation. The voltage output from MFC lags for some time after ANAMMOX, which again proves that NH4+-N was the indirect electron donor for electricity generation. NH4+-N diffusion and NH3 volatilization were two important ways for NH4+-N loss in MFC. Compared with MFC without voltage output, in MFC with voltage output more NH4+-N loss via NH4+-N diffusion and NH3 volatilization.In certain range of concentrations, increase the concentration of ammonium helped increase the voltage output, maximum power density, and COD removal in MFCs. When the concentration of ammonium was higher than 100 m M, the activity of microorganisms in MFC was seriously inhibited, MFC performances on electricity generation and wastewater treatment decreased greatly. When the concentration of ammonium was 50 m M, MFC performances on voltage output and COD removal were the best, and the maximum output voltage and COD removal rate were 555 m V and 82%, respectively. When the concentration of ammonium was 100 m M, MFC with the maximum power density(602 m W/m2).With microwave power increasing and irradiation time prolonging, values of p H, BOD5, BOD5/COD related to landfill leachate increased gradually, the biodegrability of landfill leachate became better and better, while values of conductivity, COD, NH4+-N decreased gradually. Microwave pretreated landfill leachate(BOD5/COD>0.3) fueled MFC with shorter startup time, greater output voltage, greater maximum power density, greater internal resistance, lower coulombic efficiency, and significantly higher performances on nitrogen and carbon removal. The microwave pretreated landfill leachate with higher BOD5/COD value in MFC did not necessarily with better performance on electricity production. The conductivity may have a great effect on electricity generation of MFC. TP removal efficiencies in MFCs almost keep the same before or after pretreated with microwave. The optimum conditions for microwave pretreated landfill leachate were with microwave power and duration time at 210 W and 15 min, or 350 W and 5 min. |
