Enrichment Of Photosynthetic Exoelectrogenic Bacteria From Wastewater On Electrode Surface And Community Structure Analysis

Phototrophic Microbial Fuel Cells（PMFCs）are a newly-developing device which is an innovative idea combined traditional microbial fuel cells with solar cells.Solar energy served as sole or part source providing energy to PMFCs and giving this technology a perspective future in many field like wastewater treatment and clean energy collection.Therefore,it is very important that how to choose high-efficiency photosynthetic exoelectrogenic bacteria appropriately in practical application.In this study,a phototrophic mixed-culture with extracellular electron transformation ability have been enriched and cultivated through a special medium and illumination and selecting by Fe（Ⅲ）specifically.A three electrodes system under potentiostat controlled has been constructed as a platform to research current generation ability and bioelectrochemical catalytic activity from enriched mixed-culture using several electrochemical methods.In addition,we studied the effect on current generation from electrochemical active biofilms formed on two electrode materials under different illumination conditions.Scanning electron microscope and laser scanning confocal microscope have been used to characterization the morphology of biofilms.PCR amplification techniques for 16S rRNA gene partial regions from phototrophic biofilms’microbial communities were used to build gene clone libraries.Microbial community analysis has been operated by Illumina HiSeq 2500 platform to detect the relationship between different composition of microbial communities and variation of community structure with biofilms electricity generation performance.This thesis also made an understanding to the effect for biofilm microbial communities’composition by some environmental factors and the preponderant bacteria in phototrophic electricity output circumstance.Besides,this research proved the phototrophic bacteria enriched from electrode can secrete soluble mediator to assist extracellular electron transfer.The electrochemical characteristic of this mediator also has been analyzed.The main conclusions are as follows:（1）The enrichment and isolation of mixture bacteria equipping electron transfer capability in ambient were investigated by the methods of increase light and different gradient ferric ions.It has a significant difference in catalytic characteristics of respiratory biofilm with or without suffering ferric ions in medium.（2）Under illumination,the average current density for carbon cloth working electrode is1215μA cm^-2,which shows a 25.1%higher value than that on graphite sheet working electrode(970μA cm^-2).However,the maximum current densities of 876μA cm^-2and 827μA cm^-2were detected by using carbon cloth and graphite sheet working electrode,respectively,without illumination,indicating that the current generation might due to the inner spatial structure in carbon cloth and biofilm formation on electrode.（3）The phototrophic EAB formation and power output are always seriously effect by illumination,especially for the condition with or without illumination.It demonstrate that the maximum current density output under illumination presents 72.1%higher value than without illumination by selecting carbon cloth as working electrode.（4）There is a huge differentiation between formed biofilms which enriched under illumination and in the dark condition for microbial communities.In different conditions,there is a main exoelectrogentic bacteria including Rhodopseudomonas sp.in light and Citrobacter sp.in the dark,respectively.（5）In the different stages of phototrophic mixed-culture for selecting,enrichment and power generation,different classes showed in the mixed-culture communities including:Alphaproteobacteria,Gammaproteobacteria,Deltaproteobacteria,Bacteroidia,Negativicutes,Bacilli and Clostridia.（6）Medium replacement experiment giving an evidence that phototrophic exoelectrogenic bacteria conduct extracellular electron transfer by secreting soluble redox mediator.Differential pulse voltammogram demonstrated a specific mediator existing in bioreactor under illumination and its peak potential located in-0.59V.