| Energy is an important issue in today's world.Increasing human activities are consuming the natural energy sources leading to depletion of fossil fuel and global warming.In the ever-increasing search for renewable and environmental friendly energy alternatives to fossil fuels,various approaches to derive energy from renewable sources especially from waste have been examined. MFC is a biochemical-catalyzed system,which generates electricity by oxidizing biodegradable organic matter in the presence of either catalytic activity of microorganisms or enzyme.Since the MFC can trap renewable energy by using a variety of substrates including carbohydrate,protein, food wastewaterand swine wastewater, the application of MFC were studied quite extensively.The excess sludge from wastewater treatment plant is rich in polysaccharides and proteins and thus it is regarded as a potential substrate for MFC.Recently, some studies have been focused on using sludge to produce electricity with MFC.However, the reported maximum power density is very low by using the excess sludge as MFC fuel.Due to the low electricity yield from raw sewage, the pretreatment technology and the MFC technology were first combined to improve the power density.After inoculating with the supernatant in the cell operating with surplus sludge,a single-chamber and membrane-less microbial fuel cell was successfully started up by using the supernatant fluid of pretreated sludge as substrate.The effect of microwave power and time on the maximum output power destinies were investigated.Moreover, the features of electricity production and the substrates of the cell during one cycle were investigated, and the difference influences of external resistance on the performance of MFC and the morphologies of the microorganisms forming on the anode surface were also analyzed.The results indicated that the sludge on the pretreatment condition of longer irradiation time and moderate higher microwave power(<900W) could effectively improve the performance of MFC.On the optimal treatment conditions of (300s,720W),the maximum output power destinies could reach up to 306.2mW·m-2.The larger anode area of the cell made the output power density smaller. When the distance between cathode and anode decreased from 5cm to 0.5cm,the output power density first increased and then decreased later, which mainly due to the diffuseness of oxygen from the air-cathode may affect active of the anaerobic bacteria on anode.The maximum output destiny was observed while the distance was 2cm.When using NaCl as an ionic additive, it had a corresponding decrease in internal resistance with the dosage increased resulting an increase in output power density, and the maximum was 362.6mW·m-2.The coulombic efficiency were decreased obviously with the increase of external resistance(30Ω,500Ω,2000Ω) as shown in the following sequence:83.3%,79.0%,33.6%.The SEM observation showed that the surface of the anodic electrode was covered by spherical bacteria at higher external resistance of 2000Ω.However, it was covered by server kinds of bacteria at a lower external resistance of 30Ω, such as filamentous bacteria, spherical bacteria and bacilliform bacteria. The external resistance had minimal impact on the removel efficiency of SCOD.Finally, the output power density of microbial fuel cell with excess sludge as fuel was successfully raised to 387.6 mW·m-2 under optimal experimental conditions.
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