| As a kind of refractory organic pollutants,synthetic dyes do great harm to the environment.Bioremediation is one of the green and cheap alternative strategies to eliminate organic pollutants.In order to construct a stable and efficient biological treatment system,this paper is based on cell immobilization technology,took a strain of Aspergillus flavus A5P1 screened by the laboratory as the decolorization bacteria,and anthraquinone dye RB4 as the model pollutant,focusing on improving the efficiency of biological treatment and the stability of the biological system.The main conclusions are as follows:(1)The construction and basic characteristics of biological treatment system.Polyurethane foam(PUF)was selected as the matrix to construct the immobilized cell system,and the decolorization mechanism of the biological system was studied with anthraquinone RB4 dye as the model.The results showed that 60 PPI open-pore PUF immobilized cells had the best decolorization effect,and 200 mg/L of RB4 could be completely removed in 28 h,while the free cells required 48 h.Langmuir equation and Freundlich equation were used to study the adsorption characteristics of PUF on RB4.The theoretical maximum adsorption capacity was 3.96 mg/g,which was close to the experimental value of 3.35 mg/g,indicating that the decolorization of the immobilized system was mainly due to biological action.The relationship between dye decolorization and biological metabolites was described by Logistic equation.It was found that the higher maximum specific growth rate and extracellular enzyme activity of immobilized cells were one of the reasons for the enhanced decolorization.Morphological characteristics observed by SEM showed that the cells were successfully immobilized in PUF,presenting an alternately entangled open network.(2)Stability of immobilized biological systems.PUF immobilized cells can remove 300 mg/L of RB4 dye at 25-40 ℃ and pH=4-10.Under the optimum conditions of 30 ℃ and pH 6,the maximum decolorization rate of the immobilized system is 100%,and that of free system is 85.0%.PUF immobilized cells can tolerate2000 mg/L of RB4 dye and 50 g/L of salt concentration,and maintain good degradation activity.In addition,the immobilized cells could be reused for 7 cycles and the decolorization ability of the immobilized cells was maintained at 90.0%,while the free cells decreased to 74.3%.The results show that the PUF immobilized cell system has good tolerance and stability,and it has certain advantages to treat wastewater containing high concentration of pollutants.Preliminary analysis shows that cell growth and PUF adsorption are not the main factors affecting the decolorization of the immobilization system.The immobilization system can improve the microenvironment of cells,and the catalytic performance of related decolorizing enzymes and the adsorption capacity of cells are enhanced,which may be the reason for the improvement of decolorization efficiency of the immobilization system.(3)Scale-up study in PBBR.In the intermittent mode,PUF immobilized cells showed good decolorization at 20-40 ℃.The decolorization rate of immobilized cells was 94.7% and that of free cells was only 70.6% at the optimum temperature of30 ℃.The consumption of sugars by immobilized cells is higher than that of free cells,reflecting the higher metabolic activity of immobilized cells,which may be the reason for the high decolorization rate.When the concentration of RB4 was 700 mg/L,the phenomenon of bacterial infection appeared.The decolorization rate of immobilized cells was 68.5%,and the decolorization rate of free cells was only24.9%,indicating that the immobilized system had certain resistance to bacterial infection.In continuous mode,the immobilized cell system can maintain a decolorization rate of 81.0% at a flow rate of 60 m L/h,and the decolorization rate of free cells at a flow rate of 45 m L/h drops to 67.9%.The porous structure of PUF improved the mass transfer and promotes biodegradation of RB4 by microorganisms.At a flow rate of 30 m L/h,the immobilized cell reactor could operate stably for 26 days with a decolorization rate of 86.1%,while the decolorization rate of free cells decreased to 46.8%,indicating that PUF immobilized cells in the biorereactor have well operation stability and practical application potential. |
