Study On The Effect Of Cu²⁺ On Glucose Fermentation Pathways And Microbial Diversity Of Electroactive Biofilm

As a new technology of biodegradation of pollutants,bioelectrochemical system?BES?has attracted the attention of scholars because of its excellent degradation effect,impact resistance and resource-based ability.Electroactive biofilms is the core of BES.It ferments and oxidizes organics,and transfers part of the generated electrons to the anode through extracellular electron transfer?EET?.It is the basic principle of BES to degrade pollutants.Its performance directly affects the energy output and pollutant degradation efficiency of the system.BES has been widely used in the treatment of practical wastewater.Organic substances and toxic and harmful substances?e.g.,heavy metal ions?typically coexist in the wastewater.However,there are few studies on the influence of toxic and harmful substances in wastewater on the fermentation pathways of Electroactive biofilm.In this paper,Cu²⁺in municipal sewage is selected as the representative heavy metal,and glucose is selected as the representative organic matter.The effects of Cu²⁺on the glucose fermentation pathways and biodiversity of the electroactive biofilm are studied by establishing a dual chamber three electrode BES,supplemented by electrochemistry,chemistry and microbiology.After adding Cu²⁺Solution for 7 consecutive cycles?168h?,the maximum current density and catalytic current of BES decreased compared with the first cycle.Among them,in the BES with initial Cu²⁺concentration of 0.1 and 1 mg/L,the maximum current density decreased by 20%and 27%respectively;when the initial Cu²⁺concentration was 7 mg/L,the maximum current density decreased by 52%.In particular,with the increase of Cu²⁺concentration,the time to reach the maximum current density in single cycle BES increases,which may be caused by the inhibition of Cu²⁺toxicity on the activity of electroactive bacteria?EAB?in biofilm.Analysis of the glucose fermentation pathways showed that the mixed type and acetogenesis type were the main types of glucose fermentation in anode.Cu²⁺changed the type of glucose fermentation,making it toward the acetic acid type fermentation which produced more acetic acid,and inhibited acetoclastic electricigenesis.Interestingly,when the initial concentration of Cu²⁺is less than 1 mg/L,the methane production in BES increases continuously,which may be due to the increasing substrate?acetic acid or hydrogen?required for Methane production in the fermentation liquid.When Cu²⁺is 7 mg/L,the methane contents is lower than that of 1 mg/L,which probably due to the Cu²⁺begins to inhibit the activity of methanogens.The results of microbial analysis showed that with the increase of Cu²⁺concentration in the anode,the abundance of the main EAB?Geobacter?in the biofilm decreased from 43%to 9%,while the relative abundances of acetic acid producing bacteria?unclassified?o??Rhizobiales?Klebsiellaand norank?f??norank?o??Bacteroidales?increased,which was the main reason for the decrease of the electroactivity of the electroactive biofilm and the change of glucose fermentation type.The dominant methanogen in BES is Methaospirillum,their relative abundance doesn't decrease until the concentration of Cu²⁺reached 7 mg/L.These results implied that the tolerance of different groups of bacteria to Cu²⁺toxicity was in the order of fermenters>methanogens>EAB.The results of diversity analysis showed that the addition of Cu²⁺not only increased the abundance and biodiversity of electroactive biofilm,but also the microbial structure.With the increase of Cu²⁺,the differences between samples were also increasing.