| Microbial fuel cell(MFC)sensors can rapidly monitor analytes in the environment.However,at present,it was not clear whether MFC sensor can maintain good detection performance in complex wastewater conditions,and its correlation,repeatability,anti-interference and other properties need to be explored.Electrochemical and microbial mechanisms affecting sensor performance have not been reported.Therefore,this study constructed MFC sensors to explore the feasibility of detecting nickel-containing heavy metal wastewater by MFC sensor and the main electrochemical factors limiting the performance of the sensor.The effects of biochar as anode catalyst with high porosity,large surface area and beneficial REDOX efficiency on sensor correlation,repeatability and anti-interference performance were studied.Finally,Constructed Wetland(CW)was used to reveal the effects of CW on the performance of MFC sensors,as well as to explore the electrochemical and microbial mechanisms behind these sensors.The main research results are as follows:When detecting the complex wastewater containing Cd,Zn,Cu and Ni heavy metals,the MFC sensor can establish a good linear relationship between the concentration of heavy metals and the output voltage,R~2=0.880-0.973.This indicated that MFC sensors have the potential to detect complex wastewater components.But the results also showed that the internal resistance of the sensor under the action of a single heavy metal was much less than that of the combined heavy metal group,and the power density(19.849 W/m~3)was 4 times that of the combined heavy metal group(3.109,4.589 W/m~3).Rs of the sensor in the combined heavy metal group were 0.868Ωand 0.860Ω,both larger than 0.768Ωof the single heavy metal sensor.With the increase of heavy metal concentration in the influent,the increase of Rct in the compound group was more obvious,while the increase of Rs in the single group was mainly.This indicated that the MFC sensor has the possibility to detect the water polluted by a variety of heavy metals,but its detection performance was mainly limited by Rct.Biochar has high porosity and surface area.After adding biochar,the output power of MFC sensor(BC-300)was 0.432 W/m~3,much higher than the maximum power density of CG and BC-0 of 0.117 and 0.088 W/m~3.The correlation coefficient of BC-300(R~2=0.9892)was higher than that of the control group under the concentration of 0.1-1.0 M/L combined heavy metals,showed the best performance in the correlation coefficient and detection range.Biochar can improve the recovery and anti-interference performance of the MFC sensor,and the recovery time of the highest output voltage was 1/3 of that of the control group.The internal mechanism of biochar to improve the performance of MFC sensor was as follows:on the one hand,through physical adsorption of heavy metals,reduced biological toxicity and enriched functional bacteria.The abundance of Pseudomonas aeruginosa and Rhodopseudomonas palustris increased obviously,and the electrogenic bacteria enriched 1.53 times more than the control group.On the other hand,the composition or structure of biochar increased the gene abundance of cytochrome c,flavin and other related proteins.The energy metabolism and encoding of cytochrome c(Mtr ABC,Cym A,Cox,etc.)and flavin(rib BA,Rib B,gdh,ush A,IDH,etc.)were increased by1.03-3.20 times,facilitating the transfer of electrons from intracellular to extracellular receptors.In CW with biochar as filler,the ability of MFC sensor to monitor wastewater with high concentration of heavy metals was improved.At 1.0 M/L heavy metal,the output voltage of B-CW sensor was 0.69 V,which was 62.2%higher than that of CW sensor and100%higher than that of MFC sensor.However,in CW,the correlation coefficient of the MFC sensor was lower,which was related to the volume of the CW-MFC.A large number of fillers can absorb heavy metals before they come into contact with the bioanode,reduced the biotoxicity of electric-producing microorganisms and increasing the detection limit.However,large anode and cathode spacing was not conducive to the sensor to establish correlation between heavy metal concentration and output voltage,and the sensor correlation coefficient in CW was lower.Biochar can promoted the increase of sensor detection limit,which made B-CW have stronger heavy metal toxicity tolerance than CW.At 1.0 M/L heavy metal concentration,there was 0.69 V output voltage,and no sensor failure was observed.The results showed that B-CW had higher abundance of electrogenic bacteria than CW.The electric-producing microbe Shewanellaceae accounted for 6.2%of the microbial population of B-CW,but was not detected in CW.Proteobacteria contains a large number of electroactive microorganisms,and B-CW had a higher abundance.B-CW was 62%higher than CW in 2.7.13.3,which played a key role in TAC cycle.The key enzymes related to REDOX reaction and DNA replication,such as 2.7.7.7,5.6.2.4 and7.1.1.2,were also much higher in B-CW than in CW. |
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