Study On Treatment Of Azo Dye Wastewater By A Membrane Bioreactor(MBR)bioaugmented With A Fungus

Azo dyes are important chemical products,as well as typical environmental pollutants.They are complex in structures,recalcitrant to biodegradation and possess certain bio-toxicity.They will cause serious environmental pollution if without effectively treatment.Biological processes are efficient,low-cost and environmentally friendly wastewater treatment methods,and are widely used in a serious of regions.However,traditional biological processes cannot satisfy the thorough treatment of high-molecular and recalcitrant organics,therefore,novel techniques are necessarily expoited.A yeast strain TL-F1 which can aerobically degrade various azo dyes was isolated from the sea mud of a harbor industrial zone in Dalian.The strain TL-F1 was identified as Candida tropicalis(KC311148)on the basis of morphological observation and 28 S rDNA sequencing method.The conditions for growth and biodegradation by strain TL-F1 was optimized through single-factor investigation method.The results showed that strain TL-F1 was an aerobic and thermophilic fungus which preferred neutral and weak acid conditions,and utilized sucrose and urea as optimal carbon and nitrogen sources for growth as well as decolorization of various azo dyes,respectively.Additionally,the degradation pathways of three acidic azo dyes were speculated through UV-Vis and HPLC-MS methods.It was shown that the processes were all consistent with a “reductive cleavage of azo bonds followed by a desulfurization/denitrification and finally a TCA cycle” pathway.Aerobic ARB wastewater treatment by the activated sludge systems which were augmented by strain TL-F1 was simulated through the experiments in flasks.Effects of inoculation size of strain TL-F1 were also investigated.The results showed that the decolorization efficiencies of bio-augmented systems showed better performances in both of color/COD removal and concentration/settling of the sludge than the non-augmented system.Furthermore,the bioaugmented system also showed higher stability,however,there was little difference in performance between three bioaugmented systems with different inoculation size(2-6 g/L,wet weight)of strain TL-F1.The results of microbial community structure analysis showed that there were obvious difference between the microbial structures of bioaugmented and non-augmented systems.Furthermore,the strain TL-F1 survived in the bioaugmented system and became dominant species.Finally,a lab-scale MBR was assembled for investigating the performance of continuous treatment of simulated ARB containing wastewater.The whole process was divided into three stages: I(non-augmented),II(bioaugmented under low-loading conditions)and ?(bioaugmented under high-loading conditions).The results showed that decolorization and COD removal efficiencies in stage?was relatively low and unstable,accompanying by a decrease of MLSS.By contrast,the performance of stages ? and ? were unstable at the beginning of each step,however,recovered after the initial adaptive phase,which suggested that bioaugmentation with strain TL-F1 obviously improved the traditional activated sludge system.The dynamics of microbial community structures were analyzed by high-throughput sequencing method,and the results showed that the abundance and biodiversity of bacterial community significantly increased after bioaugmentation compared with that before.Though the biodiversity slightly decreased when the loading increased,it was still much higher than that of the non-augmented system.On the other hand,Candida tropicalis survived in the MBR and became the absolutely dominant fungal genus,suggesting that the bioaugmentation fungus TL-F1 colonized in the sludge system.