| Azo dyestuffs dominate the dyestuff market due to their stable dyeing properties,the simplicity of their synthesis and the wide range of styles available.They are widely used in the printing,paper,pharmaceutical,cosmetic and textile dyeing industries.Dye effluent is already 10% of the total industrial effluent and is one of the main sources of pollution.This paper combines experiments and related literature to treat azo dye wastewater with a rotating algal biofilm system(RAB)alone and a rotating algal biofilm system combined with a microbial fuel cell system(RAB-MFC),and to analyse the effects of the different systems on microbial decolourisation and the characteristics of the biological community.The RAB system was used in this experiment to study the Acid Orange II(AO-2)dye,and the degradation products and microbial community characteristics were examined.Microbial fuel cell systems(MFC)offer a possible route to energy resource extraction from wastewater.This project combines a rotating algal biofilm system with a microbial fuel cell system to achieve efficient removal of azo dyes from dye wastewater and bioenergy conversion of chemical energy from wastewater.The project also used cathodic microbial modification to form a membrane free double chamber microbial fuel cell system and successfully performed biological decolourisation and complete mineralisation of complex azo dyes.On the basis of this the following conclusions were drawn:(1)RAB can efficiently degrade AO-2 under aerobic conditions with a removal efficiency of 683.82 mg/L/d.The degradation products of AO-2 are mainly amines and olefins.The decolorization experiments demonstrated that the azo dyes were synergistically degraded by the combined action of extracellular and intracellular enzymes.(2)In the RAB system,the efficiency of microbial degradation of AO-2 under acidic and neutral p H conditions was better than that under alkaline p H conditions.The effect of sulfate concentration on the microbial degradation of AO-2 was small,while the difference in p H and pollutant concentration had a significant effect on the microbial degradation of AO-2(p < 0.001),as analyzed by SPSS software.(3)High-throughput sequencing showed that the biofilm in the RAB reactor contained cyanobacteria,bacteria,rotifers and other microbial communities,and the bacterial-algal symbiotic biofilm was closely attached to the carrier surface,and a unique anaerobic-anoxic-aerobic structure was formed on the surface of the RAB reactor,which made the microbial species more complex and diverse,thus improving the stability of the system.(4)RAB-MFC can efficiently degrade complex structure azo dyes with degradation efficiency up to 400 mg/d.The decolorization of azo dyes is mainly completed in the anodic anaerobic region,and the degradation of intermediate products is mainly carried out in the biological cathode.Acid Big Red GR degradation products are amines and organohalides;Congo Red degradation products are alcohols,alkanes and olefins;Direct Red 80 degradation products are aniline substances as well as alkanes and organohalides.(5)In RAB-MFC,the transfer of electrons will promote the breakage of azo bonds in azo dyes,thus completing the decolorization process and producing colorless aromatic amines that can be further degraded by microorganisms,while the biological cathode will further degrade the aromatic amines.The structure of the dye has an influence on the decolorization performance and power performance of MFC.Azo dyes have electronabsorbing groups on the azo bond pair substituents,which will absorb electrons from the azo bond;therefore,azo dyes become more electrophilic and more favorable for dye reduction.(6)The highest power density of RAB-MFC is 27.64 m V/m2.high power density will promote the degradation of pollutants,and the microorganisms need to consume more energy in the high power density case,thus the respiratory chain will produce more energy,which stimulates the respiration of microorganisms.The biocathode has a larger specific surface area,which facilitates the transfer of oxygen and electrons and reduces the internal resistance of the reactor.There is a complete process between decolorization of azo dyes and biopower generation,with limited electron transfer from co-metabolism to the azo dye rather than the biocathode due to the higher redox potential of the azo dye.(7)The dominant microbial communities in the RAB-MFC system were mainly Chlorophyta,Ascomycota,Proteobacteria,Bacteroidota,Acidobacteriota,Firmicutes.The formation of an ecological chain of primary producers,consumers,decomposers,parasites and saprophytes in the mature biofilm system and the construction and formation of aquatic food webs drive the chemical cycle in the RAB-MFC system. |
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