Treatment Of Methyl Orange Wastewater And Simultaneous Electricity Generation And Application By Microbial Fuel Cell

Azo dyes have a long-term hazard potential and are a typical refractory pollutant.Great attention has been paid to their detoxification.Methyl orange is a typical azo dye in printing and dyeing wastewater;therefore,it has reference value for degradation performance research of other dyes.Microbial fuel cell?MFC?is a bioelectrochemical technology for wastewater treatment.Using MFC,chemical energy of organic matter in wastewater can be converted into electric energy.Thus its main functions are environment protection and clean energy production.Treatment of wastewater containing azo dyes with MFC is economical and efficient,so it has theoretical value and practical engineering significance.In this paper,Methyl orange-rich azo dye wastewater in southern Fujian is the research object.MFCs are built to efficiently decolorize Methyl orange using microbiology,molecular biology and biochemistry methods.In addition,in order to make full use of the electric energy generated by the MFCs during decolorization and degradation of Methyl orange,a series of energy harvesting circuit systems is designed and used to power a wireless sensor module.Two-chamber MFCs with carbon felt as electrode material are used in the experiment.Activated sludge collected from a wastewater treatment plant is inoculated into MFC anodes with different pH values?3,5,7 and 9?.Dominant electrogenic bacteria with tolerance to the four pH values are domesticated.Power generation characteristics such as start-up time,power generation cycle,internal resistance of cell,power density curve,COD removal rate and coulombic efficiency of MFCs are compared.Meanwhile,the microbial community and diversity in MFC anodes are analyzed under different pH conditions.According to the results,the MFC with pH 7 anode solution has the smallest internal resistance,the highest output power density and power generation performance,and the best microbial survival.Moreover,two strains which can efficiently decolorize azo dyes and Methyl orange under anaerobic conditions have been isolated from the MFC anode electrode carbon felt.Using different detection methods,physiological and biochemical characteristics and electrochemical activity of the two strains,their decolorization effect on Methyl orange and Methyl orange degradation pathway are studied under different environmental conditions?pH,salinity and dye concentration?.The two strains are identified as Sphingomonas paucimobilis SP.A and Citrobacter-B C.B by scanning electron microscopy and 16S rDNA sequence alignment analysis.Strains SP.A and C.B can not only decolorize Methyl orange effectively,but also have electrochemical activity,which can improve the power output of MFC.The decolorization principle of Methyl orange is biodegradation.The mechanism is breakage of the azo bond of the molecule chromogenic group;C₆H₆O₂S is the final product.The two strains and mixed bacteria are used to decolorize Methyl orange and produce electricity simultaneously.The results show that,under the same conditions,strain C.B has the highest Methyl orange decolorization rate,up to 96.32%,and the strongest power production;mixed bacteria have the second best results;and SP.A have the worst results.It indicates that strain C.B could be used as the dominant strain for decolorization of Methyl orange with high concentration and simultaneous power generation.In order to effectively utilize the electric energy produced by MFCs,a series of energy harvesting circuit systems are designed.Since output voltage and power density of a single MFC are low,an energy harvesting circuit which can operate normally under 0.3 V input voltage and 0.5 mA input current is designed.A circuit utilizing a charge pump to control switching is employed,it can periodically charge and discharge an energy storage supercapacitor,and drive sensor load intermittently.Additionally,we compares two schemes with and without negative feedback loop.The time to light the same LED is 3.76 min and 3.63 min,respectively.It is proved that the negative feedback loop system can utilize the MFC-produced energy more effectively.Regarding the polarity reversal problem caused by direct connection of a series of MFCs,a scheme to convert battery series into capacitor series is designed and the corresponding circuits and systems are built for test and verification.In addition,in order to adapt to the actual wastewater treatment environment and solve the complex wiring problem of a sequence control circuit system,an energy harvesting circuit based on the automatic control principle is designed.Test results show that energy management systems of the two MFC series can effectively harvest electric energy,while eliminating or reducing the destructive effect of output voltage and power inversion.Finally,the designed energy management system is used in a wireless sensor system as a power supply for smart sensors.A transceiver hardware circuit,a sensor data acquisition program and a data transmission program for wireless temperature and humidity sensors driven by the above energy management system are designed.Test results show that the system can be fully applied in the field of unmanned environmental monitoring.