Study On The Coupling Treatment Technology Of Straw Waste And Azo Dye Wastewater

Azo dyes are widely used in various industries because of their wide chromaticity and stable structure.However,the azo dyes and the aromatic amines formed after reductive decolorization of azo dyes are strongly biologically toxic.Anaerobic-aerobic sequential treatment is often used to achieve its harmlessness.At present,the researches that using agricultural waste to adsorb azo dye wastewater mainly focuses on improving the adsorption capacity of the adsorbent.There are few reports on the post-treatment of the adsorbent loaded with pollutants.Adsorption treatment of azo dyes only transfers the pollutants from the liquid phase to the solid state,which doesn’t realize the degradation of azo dye.Therefore,further disposal of pollutant-laden adsorbent materials is required to eliminate their environmental impact.According to the principle of"treating waste with waste",combined with the practical characteristics that azo dyes need anaerobic decolorization and aerobic mineralization.In addition,agricultural wastes can be utilized through anaerobic digestion and aerobic composting of digestion by-products,etc.Therefore,the straw waste and the azo dye wastewater can be treated at the same time.The research contents and the main conclusions are as follows:1.Coupling treatment of straw and azo dyes by"Adsorption-methanation-composting"strategy.It was found that the equilibrium adsorption of MO by the raw corn stover and quaternary ammonium salt cation-modified straw could reach 7.97 and 11.24 mg/g,respectively.The raw corn straw can be used as electron donor for the decolorization of azo dyes.In the anaerobic digestion experiment,it was found that the cumulative methane production of the raw corn straw loaded with azo dye（CS-MO）was 11.71%lower than that of the raw corn straw group（CS）.This may be because azo dyes and their decolorization product inhibit the activity of microorganisms to a certain extent.High-throughput sequencing showed that the addition of azo dyes did not significantly change the main dominant microbial species in the anaerobic digestion microbial community.The dominant bacterial species in the CS-MO group was the same as the CS control group,but the addition of azo dyes decreased the relative abundance of Firmicutes.The digested by-products were aerobic composted,no aromatic amines were detected in the biogas slurry and the extract,and the seed germination rate was increased to more than 95%,and reduced the ecotoxicity of biogas slurry.2.“ECMO-like”biogas slurry external circulation digestion device for simultaneous processing of azo dyes and agricultural wastes.Microaerobic external circulation of biogas slurry did not inhibit the decolorization of azo dyes,and the intermediate product aromatic amine achieved 92.87%mineralization at 35d.At the same time,the biogas purification was realized by aeration decarbonization and removal of hydrogen sulfide.The methane concentration of the biogas slurry under the micro-aerobic condition was maintained at 65-70%.Compared with the digestion of corn straw in the complete anaerobic group,the maximum methane production rate was increased by 44.86%and the digestion period was shortened by 23.76%under the microaerobic condition of biogas slurry external circulation.The micro-aerobic condition maintains the stability of the microbial community structure,and anaerobic and aerobic microorganisms can synergistically act on azo dyes,so that the system can continuously degrade available substrates and stably produce methane during the whole process of harmless treatment of azo dyes.3.Research on decolorization of azo dyes by syngas.The syngas generated from the digestion product biochar is used as an electron donor to decolorize azo dyes.The study found that the mixed culture of anaerobic granular sludge has the ability to decolorize MO in the presence of glucose.Among the three different syngas components,H₂and CO can be used as electron donors to participate in the decolorization of MO and generate intermediate aromatic amines,while CO₂alone cannot be used as an electron donor.The microbial community structure of the glucose and syngas groups was analysed,and it was found that the microbial communities of the two groups had little difference at the phylum and class levels,but at the genus level,the relative abundance of Pseudomonas,Clostridium and Sporomusa in the syngas group was significantly higher than glucose group.