Study On The Degradation Mechanism Of Typical Printing And Dyeing Wastewater By Tightly Coupled Modified TiO₂ And S-type Heterojunction Photocatalyst With Rhodopseudomonas Palustri

With the development of industrialization,many dyes are not fully utilized and discharged into the ecological environment,causing serious disturbance to the ecological system.In previous studies,microorganisms have been shown to play an important role in the degradation of pollutants,but biodegradation is difficult to degrade the emerging high-concentration,complex structure of refractory pollutants.Therefore,how to maintain the advantages of biological treatment technology and combine it with new sewage treatment technology to achieve effective degradation of refractory pollutants has become a research hotspot at present.The intimately coupled photocatalysis and biodegradation system（ICPB）would improve the degradation efficiency of pollutants and reduce the operating cost.In this study,typical printing and dyeing wastewater were used as the research object to study the degradation mechanism of typical printing and dyeing wastewater by the improved ICPB system,namely Rhodopseudomonas palustris（R.palustris）intimately coupled modified TiO₂ and S-type heterojunction photocatalyst.Firstly,the adaptability and degradability of R.palustris to typical printing and dyeing wastewater were investigated.Secondly,the adaptability of R.palustris to photocatalyst and the biocompatibility of photocatalyst and carrier to R.palustris were studied.At the same time,meta-transcriptomic were used to analyze the molecular mechanism of dye degradation by R.palustris and its adaptability and synergistic effect to photocatalyst.Finally,the performance and mechanism of photocatalyst coordination with R.palustris to degrade dye wastewater were studied.The main research results were as follows:（1）R.palustris was in a delayed period within 24 h of inoculation,entered a logarithmic growth stage within 24-72 h,and tended to be stable within 72 h.The tolerance to alkalis was better,and the growth of R.palustris could be achieved in neutral and mild alkalis environment.The addition of dye and photocatalyst could inhibit the logarithmic growth stage to some extent,but did not affect the normal growth and metabolism of R.palustris.The strain showed a certain tolerance to dye and photocatalyst.The degradation rate of concentration and COD for 30 mg/L Congo red reached 89.9%and 92.4%,respectively.（2）A novel ICPB system R.palustris/CAT@SA was prepared by coupled R.palustris with porous carrier sodium alginate（SA）and carbon nanotubule-silver modified titanium dioxide photocatalytic composite material（CAT）.The successful preparation of R.palustris/CAT@SA system has been verified by its good morphological and structural characteristics.The main oxidation function in CAT photocatalysis was superoxide radical（·O₂^-）and hydroxyl radical（·OH）,while hole（h⁺）didn’t play a significant role.R.palustris/CAT@SA system showed the batter degradation effect on Congo red wastewater when CAT photocatalyst and R.palustris adding ratio（C/P）was 0.1.Compared with immobilized photocatalyst and R.palustris,the removal rates of concentration and COD for 100 mg/L Congo red by the new ICPB system were increased by 14.3%,42.1%and 76%,44.6%,respectively.（3）The ICPB system for degrading azo dyes was prepared by chitosan modified polyurethane sponge carrier（CPU）combined with graphite phase carbon nitride-molybdenum disulfide S-type heterojunction photocatalyst（RCM）and R.palustris composite material.The rod-like RCM and egg-like R.palustris in the CPU were observed,the 13.1°and 27.6°characteristic peaks of g-C₃N₄ and 33.4°and 57.6°characteristic peaks of MoS₂ and N-H,N=C,C-S-MO,N-MO bonds were detected,confirmed the successful preparation of R.palustris/RCM@CPU.As the electron transfer direction of RCM photocatalysis under visible light was S-type,e^-and h⁺with stronger redox activity were generated.Therefore,the main oxidation role of RCM photocatalysis was.O₂^-,·OH and h⁺.When the doping ratio of molybdenum disulfide was 6%,the dosage of photocatalyst was 0.2 g,and the doping ratio of chitosan was0.75%,the ICPB system showed a better degradation effect,and the removal rates of concentration for 100 mg/L of Congo red,50 mg/L of methyl orange and carmine were99.4%,97.5%and 99.5%,respectively.（4）Meta-transcriptomic analysis showed that R.palustris（80.42%）was the main degradation bacterium of dyes at the species level.Functional gene annotation showed that genes were mainly enriched in metabolic process,cell membrane and catalytic activity in the GO database,while carbohydrate metabolism,amino acid metabolism and energy metabolism were the most abundant metabolic pathways expressed in the KEGG database.Differential gene enrichment analysis showed that the addition of photocatalyst promoted the degradation of azo dyes by R.palustris,and formed electron transfer between them.R.palustris obtained electrons to promote its own growth and metabolism,while reducing the recombination of photogenerated electron hole pairs and improving the photocatalytic efficiency.GC-MS analysis showed that the photocatalyst was more focused on the oxidation of refractory aromatic hydrocarbon compounds,and R.palustris could remove part of biodegradable alkane compounds in time to achieve final mineralization.The clear division of labor and the synergistic action between the photocatalyst and microorganisms effectively improved the removal efficiency of azo dyes in the ICPB system.In this study,a novel intimately coupled TiO₂,S-type heterojunction photocatalysis and R.palustris system with good removal effect on typical azo dyes was successfully prepared,and the synergistic effect between photocatalyst and microorganism was clarified,which provided theoretical support and experimental basis for the improvement of this system and its application in the practical treatment of printing and dyeing wastewater.