| Dyes have been widely used in the textile, leather, paper, rubber, plastics, cosmetics, pharmaceutics and other industries. Large amounts of dye-containing effluents from these industries into the environment often pose serious pollution problems to nature water bodies. Among industrial wastewaters, dye-containing wastewaters are one of the most problematic wastewaters to be treated because dyes have a synthetic origin and complex aromatic molecular structures which make them inert and difficult to biodegrade. The biosorption of four water-soluble dyes, reactive brilliant red, acid red, neutral red and malachite green, from aqueous solution by Penicilium sp. was systemically investigated in this study.Firstly, the effect of cultivation conditions of Penicilium sp. including cultivation time, speed of shaker, inoculation quantity of spore and C/N ratio on biosorption of dyes was evaluated. To improve biosorption capacity of dyes on biomass preparations, pretreatment methods including acid, salt and alkali pretreatment were introduced in this study. Then, the effect of parameters such as initial pH value, adsorption time, adsorption temperature, salt concentration, heavy metal ion, etc, on biosorption of dyes onto pretreated fungal biosorbents was studied in batch systems. Desorption of dyes from dye-loaded biomass was carried on and the possibility of reusing fungal biosorbent was also investigated. Kinetics and thermodynamics of dye biosorption were analyzed, and the mechanism of biosorpton of dyes on Penicillium sp was revealed. Lastly, biosorption of reactive brilliant red on pretreated fungal biosorbent as well as dye desorption from dye-loaded biomass were performed in packed column.It was shown that the mycelia of Penicilium sp., growing in the shaked liquid medium was observed in form of spherical pellets. Biosorption of dyes on native fungal biomass and growth of Penicillium sp. were affected by the speed of shaker, inoculation quantity of spore and ratio of C/N. Cultivation conditions of Penicillium sp. in this study were speed of shaker of150r/min, spore inoculation quantity of1%(v/v), C/N ratio of5and cultivation time of3d at temperature of30℃. The pretreatment methods were found to have a significant effect on biosorption of four dyes. Of several studied pretreatment methods, nitric-pretreated biomass was optimal for biosorption of reactive brilliant red and acid red, and NaHCO3-pretreated biomass was optimal for biosporption of neutral red and malachite green. Both pretreated biosorbents increased more over40%uptakes of dyes comparison with that the native biosorbent. At initial pH of3.0, the maximum adsorption capacity of reactive brilliant red and acid red onto nitric-pretreated biomass was occurred. Adsorption of neutral red and malachite green onto NaHCO3-pretreated biomass gain the highest capacities at initial pH of5.0-6.0. At the present of any heavy metal ion of Pb2+, Cu2+or Zn2+of50mg/L in aqueous solution, the biosorption capacities of reactive brilliant red and acid red on nitric pretreated biomass were increased and those of neutral red and malachite green on NaHCO3-pretreated biomass were decreased. In batch elution experiments, reactive brilliant red and acid red were easily eluted by the0.01mol/L NaOH solution, while neutral red and malachite green were well eluted from dye-loaded fungal biomass by0.001mol/L HNO3. And desorption rates of those dyes were all above90%.The pseudo second order rate equations were applicable to biosorption of dyes. The results showed that adsorption kinetics of four dyes on pretreated preparations could be well described by pseudo second order model. And the rate-limiting step of adsorption process was external mass transfer. The biosorption of reactive brilliant red and acid red on nitric-pretreated biomass could be described by the Langmuir isotherm models in studied temperature ranges. At temperature of25and30℃, equilibrium biosorption data of neutral red on NaHCO3-pretreated biomass were found to better follow the Freundlich isotherm model, while the Langmuir isotherm model was better fitted at35and40℃. Biosorption of malachite green on NaHCO3-pretreated biomass could be described by the Freundlich isotherm model at temperature of25-40℃. The equilibrium adsorption capacity increased with increasing temperature from25to40℃. Thermodynamic parameters, such as△G,△H and△S were calculated. The results indicated that biosorption of dyes on pretreated Penicilium sp. was spontaneous and endothermic. Biosorption isotherm experiments, under the studied temperature conditions, revealed that increasing the temperature favored biosorption of dyes.Scanning electron microscopic examination of untreated and pretreated fungal mycelia revealed differences on the cell surface after various chemical treatments. The nitric treated biomass showed a rougher surface than that of any other chemical agent pretreated biomass. In order to confirm the existence and changes of amino, carboxylic, phosphate, etc. in before and after pretreated biomass of Penicilium sp., a FT-IR study was carried out. The FT-IR spectra of untreated and pretreated fungal biomass revealed the presence of different characters peaks of amino, carboxylic, phosphate group, etc. In the biosorption of anionic dyes, reactive brilliant red and acid red, on pretreated fungal biomass, it was indicated that the amino groups were the main binding sites, and carboxyl groups also played a role in biosorption. In the biosorption of cationic dyes, neutral red and malachite green, on pretreated fungal biomass, it was observed the carboxylic groups were important functional groups, and phosphate groups could be binding sites but not the main sites. The lipid fraction played a minor role in biosorption of two dyes.At initial pH of3, electrostatic interaction played main role in the biosorption of anionic dyes, reactive brilliant red and acid red, on nitric pretreated biomass from aqueous solution. Biosorption of cationic dyes, neutral red and malachite green, on NaHCO3-pretreated biomass existed electrostatic interaction at initial pH of5-6. The change of metal ion concentration after adsorption of dyes, neutral red and malachite green, on NaHCO3-pretreated biomass in aqueous solutions was investigated. It was found that large amount of metal ions released into solution after adsorption equilibrium and this indicated that ion exchange adsorption also played important role. Energy spectra of pretreated biosorbents also confirmed ion exchange adsorption occurred in biosorption of two dyes.Column experiment showed that the fungal mycelia immobilized with quartz sands possessed higher biosorption capacity for reactive brilliant red than that of fungal mycelia immobilized by calcium alginate in the form of beads. The breakthrough point and bed exhaustion time adsorbed reactive brilliant red on nitric pretreated biomass decreased with increasing flow rate, so did exhaustion capacity and dye removal rate. The breakthrough point time, bed exhaustion time, biosorption capacity and dye removal rate all increased with increasing biosorbent dose. The result also showed that with increasing inlet concentration of reactive brilliant red, the breakthrough point time and exhaustion time decreased, while biosorption capacity increased. The Thomas model was used to analyze the experimental data and described well. The relative coefficients could reach0.98above. |
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