| Microbial fuel cells?MFCs?are electrochemical devices that can extract chemical energy from organics and convert them into electrical energy.For sustainable consideration,MFCs as green devices for vioenergy extraction have been widely used and developed in the fields of bioelectricity generation and wastewater treatment.To maximize energy utilization of MFCs,current research was focused on the significantly improve efficiencies of dye decolorization and bioelectricity generation in MFCs.Electron shuttles?ESs?are intermediators that can reversibly transformed between the electron donor and electron acceptor.In this process,the electrons are continuously accepted and released to appropriable mediators,stimulating performance of electron transfer.For bioenergy extraction,the research objects of RMs were mainly emphasized on artificially synthetical chemical?s?for assessment.In terms of chemical structure,they were aromatic compounds with hydroxyl?-OH?and amino?-NH2?on the benzene ring,which may own disadvantage of biological toxicity leading to the poor biocompatibility or environmental friendly.Here,the research on RMs mainly focused on the extraction of natural bioresources due to their low biotoxicity potency?good biocompatibility?.As they are aboudant in nature,they are highly economically-reasible for applications.Based on the universality of natural extract as RMs,this model study also chose three different sources of RMs and herbal extracts obtained through different procedures of separation and extraction.The electron-shuttling capabilities of herbal extract were systematically analysed via cyclic voltammetry and MFCs to reveal different degress of correlation.The main contents of the study include:1.Anthocyanins,as one of the important sources of color-bearing plants in nature,are well known for their excellent antioxidant capabilities.In this study,three natural anthocyanin-rich substances?i.e.,Lycium ruthenicum Murr,Clitoria ternatea Linn and Vaccinium Spp?were selected as the models for research,and methanol/pure water/acetic acid?85:15:0.5?was used as the solvent of extraction for organic extraction.With the assistance of ultrasonication,the extraction efficiency was further improved.The upper extractant was centrifuged,freeze-dried and ground to obtain the extract powder.The results of cyclic voltammetry scanning,DPPH-scavenging capacity evaluation and total phenol content determination revealed that the extract of Lycium ruthenicum Murr own the most significant reductive and oxitative potentical peaks,the most significant antioxidant activity and the highest total phenol content.Next would be Clitoria ternatea Linn and Vaccinium Spp among these three anthocyanin-rich natural substances.Supplementation of such candidate ESs to MFCs could significantly enhance the bioelectricity-generating efficiency of MFCs,and such stimulating effect was positively correlated to the electron-shuttling capabilities.Using ATP synthesis as the metabolic reporter,the postulated mechanism of electron shuttling effect was also verified.The results very likely indicated that ESs functioning on the surface of microbial cell membrane could significantly stimulate electron transfer on the surface of cell membrane,promoting the transporting efficiency of cell membrane,and dealing with the process of electron transfer chain.2.Bacterial-algal symbiosis is a common symbiotic system in nature.It has been widely used in treatment of environmental pollutants,aquaculture and biorefining.Evidently,the interaction?s? between bacteria and algae significantly influence the nutrient uptake and bacterial and algal metabolism for combined symbiosis.In this study,Chlorella was also selected as model microalgal species for study and the redox capabilities of extracellular metabolites in different growth phases were determined.Moreover,the effects of self-secrefed metabolites of algae in the symbiotic system as electron shuttles to stimulate biological electricity generation were evaluated as well.The characteristics of extracellular metabolites associated to the growth phase were assessed through cyclic voltammetry and their antioxidant capabilities were determined.Evidently,extracellular metabolites of microalgal at the end of exponential growth phase?10-15 days?owned significant redox and antioxidant capabilities.The extracellular metabolites of Chlorella with remarkable redox ability were also supplemented to different mixed consortia-seeded MFCs,indicating selective stimulation in power density analysis and impedance measurement.By analyzing the bacterial community of different mixed consortia-seeded MFCs,the results indicated that the MFC system with richer diversity and stronger evenness more likely seemed to be stimulated by redox mediators.3.Tea is one of the traditional Chinese drinks,which can be divided into green tea,yellow tea,white tea and black tea according to the degree of fermentation.Tea drink is considered as a natural drink with health care effect in daily life owing to the rich content of antioxidant.Moreover,green tea is the one with the most abundant of polyphenols and alcohols for no fermentation.Extraction is the most common way to extract natural substances in nature.When the same natural substance was extracted with different solvents,different components and properties will appear in the obtained extract.In this study,natural green tea was selected as the research object,and pure water and 80%methanol were respectively selected as extraction solvents to extract green tea.The obtained extract was applied to the MFCs toexplore the electron-shuttling characteristics.The CV scanning results indicated that the extraction with water owned more significant redox peaks compared with the extraction with methanol.The two extracts were respectively applied to two different MFCS,and the results indicated that both of them showed significant inhibitory effects on the power density of MFCs.Also,the inhibitory degree of methanol extract was much higher than that of pure water extract.The results of HPLC analysis towards components of the two extracts showed that there was a significant difference in the content of components?e.g.,gallic acid and EGCG?due to different extraction solvents.The bacterial community analysis towards MFCs respectively before and after the supplymentation of methanol extract was carried out and the results suggested that both the diversity and evenness of bacterial flora were significantly decreased with the addition of extracts.The original bacterial phase changed dramatically. |
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