The Enhanced Mechanism Of Biotic Degradation Of Azo Dyes With Biogenic/Synthesized Nanoparticles

Azo dyes are widely used in the textile,paper,food,cosmetics and pharmaceutical industries due to their good performance.They are various,large in quantity,not easily degradable,and are relatively stubborn compounds.In addition,most azo dyes are toxic or mutagenic and carcinogenic,which is harmful to human health.At present,for the biological treatment of azo dyes,the anaerobic decolorization rate of dyes is low.Therefore,it is a research subject to improve the biodegradation efficiency of azo dyes.This paper mainly studied the bioreduction of azo dyes was enhanced by nanoparticles.In this paper,the quinone respiration ability of Bacillus sp.was studied.The growth of Bacillus sp.was founded in the medium with Lawsone,AQS and HA as electron acceptors under anaerobic conditions.In addition,take the AQS as an example,the electron recovery?ER?of azo dyes reduced by B-AH₂QS,which was the AQS reduced by Bacillus sp.was studied.The results showed that the acid blue 113 was reduced nearly completely with a highest electron recovery of96.08%,while the ER for the reduction of RB5,CR and MO were 68.61%,67.90%and 77.60%,respectively.These results suggested that the chemical reaction of azo dyes by the B-AH₂QS were instantaneous and can effectively reduce azo dyes.According to the quinone respiration characteristics of Bacillus sp.,the effects of nanoparticles containing quinoid structure,i.e.immobilized quinone compounds on the biodegradation of azo dyes were studied.In this study,magnetic humic acid?MHA?nanoparticles were prepared by co-precipitation method and used to evaluate the promotion of the azo dyes degradation by Bacillus sp.under high salt concentration.This in-situ alternately oxidation and reduction of MHA acts as redox mediator?RM?to catalyze the anaerobic reduction of azo dye-methyl orange in biotic system.The biodegradation rates of methyl orange in both batch experiments and sequenced batch reactor with MHA were improved about 1.5-2.5 times as compared to that of control without MHA.Moreover,the negligible leaching of HA under various environmental conditions suggests the strong stability of the MHA.Together,the results showed that the as-prepared MHA is stable and easy to be recycled.It would be used as RM to catalyze the reduction of azo dyes by accelerating the extracellular electron transfer,and of great environmental significance for the potential biotic removal of various hazardous compounds.The synthesized MHA in this paper could promote the decolorization of methyl orange,however,considering the synthesis of the materials and the disposal of the used materials in the later stage,we studied a kind of nanoparticles which relied on microorganisms to produce nanoparticles in-situ to promote the degradation of azo dyes.In this study,Pd?0?nanoparticles?Bio-Pd?were generated by Klebsiella oxytoca GS-4-08 in fermentative condition and in-situ improved the azo dyes reduction.The Bio-Pd was mainly located on cell membrane with a size range of 5-20 nm by TEM and XRD data analyses.Anthraquinone-2-disulfonate?AQS?greatly increased the reduction rate of Pd?II?with a reduction efficiency as high as 96.54±0.23%in 24hours.The batch and sequenced batch experiments showed that Bio-Pd could promote the reduction of azo dyes continuously and steadily.These results indicate that the in-situ generated Bio-Pd by Klebsiella oxytoca GS-4-08 is efficient for azo dyes reduction without complex preparation processes,which is of great significance for the removal and subsequent safe disposal of hazardous environmental compounds.