| Dye wastewater is characterized by fluctuating water quality,complex composition and difficult degradation.The co-metabolism of algal-bacterial symbiotic system can achieve efficient degradation of dye.Previous studies by the group also showed that this dye wastewater treatment technology has better results than the traditional activated sludge method.However,before practical application,further analysis of the specific mechanisms of algae and bacteria action on dyes in the symbiotic system is needed to guide the adjustment and optimization when facing different practical conditions.Since microbial metabolic processes and products in symbiotic systems are extremely complex.Therefore,A system,A1(Chlorella)-A2(activated sludge)in series and B system,B1(activated sludge)-B2(Chlorella)in series were constructed to investigate the co-metabolic mechanism of the algal-bacterial symbiotic system,respectively.The main conclusions obtained in this thesis are as follows.(1)A system showed higher decolorization(88%)and COD removal(83%)than B system,and higher microbial activity than B system.The analysis of the influencing factors of the systems showed that when the dye concentration was 50 mg/L,the HRT was 36 h,and the aeration rate was 0.3-0.4 L/min,the COD removal rate of A system(92%)was still higher than that of B system(83%).The decolorization rate of Disperse Red 3B in A1(31%)was higher than that of B2(11%),probably Chlorella mainly degraded the Disperse Red 3B macromolecule.It indicates that Chlorella degrades the dye first in the algal-bacteria symbiotic system,and the formed intermediate products can be better utilized by activated sludge,which in turn improves the degradation efficiency of A system.(2)The community changes of lignin-degrading enzyme activity and activated sludge population were investigated.The degradation pathways of disperse red 3B dye were inferred.The results showed that the degradation pathways of disperse red 3B were different in the two systems,in A system,Chlorella oxidized disperse red 3B to cyclic lactone compounds by degrading enzymes,further hydrolyzed,and finally metabolized by activated sludge;in B system,functional bacteria of activated sludge degraded the dye.The laccase activity of Chlorella was higher in A system,which could reach 103 U/L after 35 days,while the highest laccase activity in B system could only reach 31.8 U/L.The average relative abundance of Bacteroidetes in B system(38%)was higher than that in A system(28%),and the significance analysis of species differences between groups revealed that there were significant differences between Bacteroidetes in A and B systems.It was presumed that Bacteroidetes were mainly responsible for the degradation of dispersed red 3B in B system.The dominant bacteria of activated sludge in both systems were Proteobacteria,and this bacterium was beneficial to the removal of organic pollutants from wastewater.(3)The effects of different reflux ratios on the co-metabolism of the algae-bacterial tandem system were investigated.By analyzing the degradation performance,microbial activity and effluent products of the AL system(A system after the volume was expanded by 3 times),the results showed that the reflux could provide nutrients to Chlorella and improve the co-metabolism of the algae-bacterial tandem system.The highest degradation rate of dispersed red 3B was achieved when the reflux ratio was 13%,with 92% and 96%decolorization and COD removal,respectively.The activity of Chlorella and activated sludge was also optimal according to microbial activity measurements.In addition,different reflux ratios did not change the effluent product of the system,but the increase of reflux ratio could improve the mineralization rate of disperse red 3B dye.This study provides a theoretical basis for the practical application of the algae-bacterial symbiotic system for the degradation of dyes. |
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