Study On Dye-containing Wastewater Treatment By A Novel Photocatalyst-microorganism Composite

Dye-containing wastewaters pose substantial environmental hazards due to their strong colors,high COD and the complex chemical composition of the discharged effluent.Reactive dyes,especially those containing azo-groups,constitute a large proportion of dye contaminants and resistance to biodegradation and photodegradation.Advanced oxidation technology was applied to treatment the refractory organic wastewater due to its strong oxidizing property.However,existing advanced oxidation pre-treatment methods based on the generation of non-selective radicals cannot efficiently remove these dyes from wastewater streams,and post-treatment oxidative dye removal is problematic because it may leave many byproducts with unknown toxicity profiles in the outgoing water,or cause expensive complete mineralization.These problems could potentially be overcome by combining photocatalysis and biodegradation.A novel visible-light-responsive hybrid dye removal agent featuring both photocatalysts(g-C3N4-P25)and photosynthetic bacteria encapsulated in calcium alginate beads was prepared by self-assembly.g-C3N4-P25 hybrid photocatalyst was synthesized using melamine and P25.Photocatalysts were characterized by X-ray diffraction(XRD),scanning electron microscope(SEM),transmission electron microscopy(TEM),N2 sorption,Fourier transform infrared spectroscopy(FT-IR),and UV-Vis DRS.The photocatalytic performances were evaluated by degradation of reactive brilliant red X-3B.It was found that g-C3N4-P25 with amass ratio of 1.5:1 exhibited the best degradation performance due to the synergistic effect.The photocatalytic mechanism was found that the main active species was ·O2-and h+.Photocatalysts(g-C3N4-P25)and photosynthetic bacteria encapsulated in calcium alginate beads were prepared by self-assembly and characterized by SEM.In addition,to evaluate its ability to treat wastewater contaminated with azo dyes,the composite was incubated with solutions containing reactive brilliant red X-3B(50 mg/L)and controlled COD levels(established by adding glucose,about 1500 mg/L).It was found that composite achieved a removal efficiency of 94%for the dye reactive brilliant red X-3B and COD of synthetic wastewater samples by 84.7%;successfully decolorized synthetic dye-contaminated wastewater and reduced its COD,demonstrating the advantages of combining photocatalysis and biocatalysis for wastewater purification.Moreover,affecting factors(photocatalyst loading?photosynthetic bacteria loading?pH?concentration of X-3B)on pollutants removal by g-C3N4-P25/photosynthetic bacteria composite were explored?analyzing its stability and universality.Finally,the composite's mechanism of action was explored by monitoring the intermediates formed during the oxidation process by UV-visible spectrophotometry,FT-IR and gas chromatography-mass spectrometry(GC-MS).Degradation pathway was assumed as follows.Firstly,the combined photocatalytic and biocatalytic degradation of X-3B by composites was the conversion of the azo dye into aniline and phenol derivatives.The aromatic rings of these products were then presumably attacked by free radicals generated by the photocatalyst,leading to the formation of linear alkyl compounds,thereby preventing aromatic hydrocarbon inhibition of bacterial metabolism.Finally,the alkyl products could then be degraded by the photosynthetic bacteria.