| To solve the increasingly serious energy and environmental crisis,it is urgently to develop clean and efficient renewable energy technologies.Microbial fuel cells follow the biological electrochemistry principle,through microbiological oxidation,it can transfer the chemical energy into electricity when degrading pollutants at the same time.This technology provides a new way for renewable energy and waste management.The constructed wetland is a kind of traditional ecological purification process and it has been widely used in domestic sewage,industrial waste water management and restoration.Its special structural features can meet the demand of microbial fuel cells construction,that is,you can take advantage of the layered redox zone as fuel cell anode chamber and the cathode chamber respectively to realize fuel cell start-up.Both artificial wastewater and wetland plant root secretion can serve as the substrate to product electricity,synchronously implement wastewater purification ecological and energy regeneration.Based on this,this paper developed a low cost,easy to start,provided with the function of pollutant removal and electricity generation at the same time,constructed wetland type microbial fuel cell,CW-MFC device.It consisted of constructed wetland,in and out of the water system,the anode electrode,the cathode electrode and the connection of external electrode.The anode electrode was placed in the bottom of the constructed wetland and the cathode electrode was placed vertically near the plants with half buried in the matrixes and half exposed to the air.This MFC consumed both organic matter in wastewater and plant root secretion which was synthesized by photosynthesis CO2 fixation,utilized the widespread electrogenesis microorganism in soil as catalyst,through the electrons transfered and released,and generated continuous steady electric current.This paper firstly probed the start of the CW-MFC.The subsurface flow constructed wetland was selected and used.Two common substrates,sediment and soil were picked as inoculation of the substrate,yellow flag was the plant,artificial wastewater was used to cultivate the configuration of artificial wastewater intermittently.After about 6 cycles the fuel cell was successfully launched.The highest output voltage was 0.588 ±0.01 V with 1000 ? resistance.It could maintain about 26 h.With the substrate depleted,it was stable at around 0.305 V.The highest power density was about 9.6 mW/m2,the COD removal rate was about 91%.On this basis,the effect of different impact parameters on the CW-MFC electricity production was researched,including plant,matrix,operation mode,temperature and the load of COD,respectively.The conclusions were as below:the electric power output for CW-MFC needed to consider both the factor of plants and the matrix;voltage output for batch flow operation mode was higher than that of continuous flow operation mode,their maximum output voltages were 0.588±0.01 V and 0.529V respectively.Temperature effect on the CW-MFC electricity production results showed that the maximum output voltage value and its ability to maintain duration was on a contrary way,that is,the higher the voltage,the faster the consumption,thus the shorter the cycle.The highest output voltage value 0.618 V was obtained at 27±1? and it lasted about 22 h.The minimum output voltage,0.578 V was obtained at 32±?,maintaining time was about 28 h.The COD load impact on electricity production results showed that the heavier the COD load was,the higher the voltage output value was and the longer duration was.In the final,the power density curves,polarization curves and redox potential profile curves of the different CW-MFC were measured to compare and analyze their power generation abilities.It was concluded that internal resistance was the main influence factors to its production capacity.Besides,the effect of different parameters such as plant,the matrix of the CW-MFC on pollutants removal rate was explored.Results showed that COD,nitrogen and phosphorus removal ability of CW-MFC with plant was better than that of group without plants.The TN removal rate of zeolite CW-MFC was slightly lower than that of quartz sand group.In terms of NH3-N removal,zeolite CW-MFC showed a quicker removal rate than quartz sand CW-MFC.Besides,zeolite group presented a higher TP removal efficiency than the quartz sand group.The TP,TN,NH3-N and DIP removal rates of these three devices reached more than 95%,thus it predicted the CW-MFC great application potential in wastewater treatment.In addition,this paper also carried on the field experimental study and the results showed that such technology could realize the CW-MFC application in field,but its electricity production capacity needed to be further improved.In this study the CW-MFC not only showed significant removal efficiency of artificial wastewater,especially for COD and nitrogen and phosphorus pollutants,but also can produce green current at the same time.It synchronous implements the wastewater purification,green renewable energy and environmental protection of multiple effect,has a certain guiding significance for practical engineering applications and amplification. |
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