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Fe~0 Enhanced Continuous Flow Chlorella Vulgaris Biocathode MFC On Livestock Wastewater And The Effect Of Resistance Gene Transfer

Posted on:2023-10-19Degree:MasterType:Thesis
Country:ChinaCandidate:Z ZhaoFull Text:PDF
GTID:2531307172959699Subject:Engineering
Abstract/Summary:PDF Full Text Request
Microbial fuel cell(MFC)has received a lot of attention as a kind of chemical energy conversion of wastewater organic matter into electricity by using electricity-producing microorganisms,however,researchers have continued to optimize the research in recent years to address the problems of low electricity production efficiency and degradation efficiency,secondary pollution,etc.As a kind of double-chamber MFC,algae cathode microbial fuel cell(AC-MFC)not only has the advantages of simple construction and convenient operation,but also can harvest biomass energy,which has great potential for application.However,AC-MFC can lead to anode acidification due to intermittent or semi-continuous mode operation,which can degrade the performance of MFC.In addition,there are many problems such as low removal rate of nitrogen and phosphorus pollutants,non-involvement of microalgae in the cathode chamber,lack of continuous degradation ability and anaerobic environment of the anode is easily damaged.To address these problems,this study constructs an anode-cathode continuous flow model to investigate the mechanisms of cathode type,HRT,antibiotic(CTC)concentration and Fe0 dosage on the performance of MFCs in terms of electricity production,water treatment performance and biology.The study focused on the effects of continuous pollutant removal and electrical production performance,and revealed the intrinsic mechanism of Fe0-enhanced AC-MFC performance.The main findings are as follows.Firstly,two control experimental groups CA-MFC(cathode mechanical aeration)and CC-MFC(cathode unaerated)were constructed,and the hydraulic retention time(HRT)in continuous flow mode was used for 24 h,48 h,72 h and 96 h.The results showed that with increasing HRT,the cell density and cell dry weight of AC-MFC on COD,NH3-N,TP,internal resistance and Chlorella vulgaris The maximum power density of 3.62 W/m3 was obtained at HRT=24h,and the highest voltage of 350 m V was obtained during the light period of HRT=24 and 48h,which was much higher than that of the control MFCs in the dark.The highest AC-MFC biomass output was obtained at HRT=24 h.The cell density and cell dry weight of Chlorella were 2.40×106 cells/m L and 0.043 g/L,respectively.The initial concentration of tunicamycin(CTC)had a significant effect on the performance of MFCs,and the results showed that AC-MFC had a higher loading on CTC and lower absolute abundance of ARGs in the effluent.the water treatment performance,electricity production performance,and internal resistance of MFCs were negatively correlated with CTC concentration,and had a greater effect on anaerobic ammonia oxidizing bacteria in the anode,and the denitrification efficiency was significantly reduced.The maximum functional density of AC-MFC decreased to a minimum of 2.14 W/m3 when CTC was exposed initially,but showed a gradual recovery of performance at lower CTC concentrations.The significant increase of Rct in the internal resistance may be due to the toxic effect on Chlorella after CTC exposure and the decrease of charge transfer rate due to the increase of EOMs.The removal of CTC by AC-MFC reached more than 70%at different concentration gradients,and up to 87.12%when the actual CTC concentration was 78.41μg/L.Although AC-MFC could slightly reduce the number and relative abundance of resistance genes in the effluent,the number and relative abundance of resistance genes in the effluent continued to increase when treating wastewater containing high concentrations of CTC.3D-EEM showed a positive correlation between the fluorescence intensity and CTC concentration in the water samples,and the fluorescence intensity was derived from humic acid species,and the water quality in the effluent of MFCs deteriorated due to the reduced activity of microorganisms and Chlorella.The amount of Fe0 in the MFC anode had a significant effect on the performance of the MFCs system.Fe0 effectively inhibited the growth of microalgae and enhanced microbial activity in the anode,which improved the water treatment performance and power production performance of AC-MFC.The highest COD,NH3-N and TP removal rates of84.62%,76.94%and 52.62%,respectively,were obtained by AC-MFC after adding Fe0,which increased by 9.72%,17.4%and 9.93%compared with that without Fe0 addition,in addition to effectively reducing the concentration of soluble organic matter(DOMs)in the effluent.The coupling mechanism between reaction and denitrification enhanced the nitrogen removal efficiency significantly,while the enhanced mechanism for phosphorus removal was adsorption and chemical precipitation.The highest removal of CTC(249.8μg/L)was 89.19%,and the main enhanced mechanisms were complexation reaction,photodegradation reaction of algae and photo-Fenton reaction of algae driven by iron ions.Although Fe0 increased the internal resistance of the MFCs,the AC-MFC power production nearly doubled,reaching a maximum power production of 420 m V(light stabilization period)and 290 m V(dark stabilization period)with a maximum power density of 15.255 W/m3.When Fe0 was excessive it led to a significant decrease in power production performance and output power.Fe0 had a significant effect on the elimination of ARGs(resistance genes)and MGEs(mobility factors)from the wastewater by MFCs.By comparative analysis,the relative and absolute abundance of resistance genes in the effluent samples of MFCs were significantly lower than that of the initial sludge,proving that the MFC system effectively reduced the output of resistance genes.Although Chlorella could not reduce the number of resistance genes in the water,the absolute abundance of ARGs in the effluent water was lower and possessed a stronger antibiotic load.After adding Fe0,the absolute abundance of ARGs in AC-MFC effluent decreased to less than half of the original sludge,with the relative abundance of tetracyclines decreasing from 0.14 copies/16Sr DNA to 0.05,a 2-3-fold decrease in both categories.the enhanced mechanism of ARGs elimination may be due to the photodegradation reaction of Fe3+with Chlorella.Sequencing analysis showed that Fe0 led to significant changes in the structure of the anodic microbial community,and the genus Anaeroarcus,which is highly homologous to the reported iron-reducing bacteria such as Shewanella,was identified.After the addition of Fe0,Anaeroarcus spp.became the dominant genus in AC-MFC.Since the Gammaproteobacteria,which is a well-known electrophile phylum,also increased nearly 1.5-fold,there is still uncertainty whether Anaeroarcus is an electrophile.Therefore,Fe0 is an effective material to enhance the performance of continuous flow AC-MFC livestock wastewater treatment with the performance of electricity production.
Keywords/Search Tags:Microbial fuel cell, Biocathode, Zero-valent iron, Antibiotic, Resistance gene
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