Preparation Of Modificed Yeast-based Bioadsorbents And Their Performance Evaluation For The Treatment Of Dye Effluents

With the rapid development of dyestuff industrial production and consumption, the dyeing wastewater discharge brings a serious threat to the natural environment and human health. Accordingly, a safe and efficient treatment method for dye wastewater is urgently needed. Therefore, this paper tried to prepare a series of yeast-based composite biological adsorbents by modified yeast with a variety of materials. Meanwhile, the obtained products were characterized and their performances of dye wastewater treatment were evaluated.(1) Yeasts adsorbents were used to adsorb direct blue 71 and safranine T from aqueous solutions. Factors affecting the adsorption process were investigated. The results show that acidic condition is advantageous to the adsorption of direct blue 71, and neutral condition is advantageous to the adsorption of safranine T. The equilibrium adsorption quantities are increased with increasing initial concentration. With the increased amount of yeasts, equilibrium adsorption quantities are increased first and then decreased. The adsorption processes were described well by pseudo-first-order kinetic equation and pseudo-second-order kinetic equation. The adsorption equilibrium data were found to be in good correlation with the Langmuir isotherm model and the Freundlich isotherm model. Thermodynamic parameters indicate that the adsorptions are spontaneous and endothermic processes.(2) PDA@yeast composite microspheres with a core-shell structure were prepared. SEM ascertains that the PDA@yeasts retain ellipsoid shape of yeasts, and yeast cells were wrapped by PDA evenly. Factors affecting the adsorption process of PDA@yeasts were investigated. The results show that acidic condition is advantageous to the adsorption of direct blue 71, and alkaline condition is advantageous to the adsorption of safranine T. The equilibrium adsorption quantities are increased with increasing initial concentration. With the increased amount of PDA@yeasts, equilibrium adsorption quantities are increased first and then decreased. The adsorption processes were described well by pseudo-first-order kinetic equation and pseudo-second-order kinetic equation. The adsorption equilibrium data were found to be in good correlation with the Langmuir isotherm model and the Freundlich isotherm model. Thermodynamic parameters indicate that the adsorptions are spontaneous and endothermic processes.(3) On the basis of single factor experiments, static adsorption experiments were optimized through the response surface method. The results show that p H is the most significant factor that influence on adsorption processes of both yeasts and PDA@yeasts, and the initial concentration is second significant. The predicted best condition of direct blue 71 adsorbed by yeasts is p H = 2,C0 = 50 mg/L,m = 0.5 g/L. The predicted best condition of safranine T adsorbed by yeasts is p H = 7.11,C0 = 50 mg/L,m = 0.72 g/L. The predicted best condition of direct blue 71 adsorbed by PDA@yeasts is p H = 4,C0 = 50 mg/L,m = 0.56 g/L. And the predicted best condition of safranine T adsorbed by yeasts is p H = 9.44,C0 = 50 mg/L,m = 0.56 g/L.(4) Cd S@yeast hybrid microspheres were prepared via a hydrothermal process. Characterization results confirm that Cd S nanoparticles were successfully anchored on the surface of yeast cells, and the resulting samples were fructus rubi-like. Cd S@yeast microspheres showed well suspension property in aqueous solution, and there are negative charges on the microspheres’ surface under neutral condition. The interaction between host core yeast and guests Cd S nanoparticles was investigated by Fourier transform infrared(FT-IR) spectroscopy and the possible mechanisms for the formation of Cd S@yeast hybrid microspheres were proposed. The model photocatalytic test showed that the fructus rubi-like Cd S@yeast microspheres could efficiently remove methylene blue(MB) dyes from aqueous solutions due to the combined functions from the bio-sorption of the yeast core and photocatalytic degradation driven by the attached Cd S nanoparticles.(5) Methylene blue from aqueous solution was investigated using fix-bed adsorption column by Cd S@yeast microspheres. The results show that lower solution concentration, lower flow rate, bigger bed height and bigger p H are conducive to the adsorption. The adsorption data were fitted to three well-established fixed-bed adsorption models, namely, BDST model, Thomas model and Yoon-Nelson model. The photocatalytic performance of Cd S nanoparticles endowed a good regenerate capacity to Cd S@yeast microspheres.