Study On2,4-DNT Wastewater Removal Using Membrane Bioreactor Enhanced By Low Intensity Ultrasound

In this study, low intensity ultrasound is used to enhance the2,4-DNT removal in the membrane bioreactor (MBR). The optimum cycle, frequency, intensity, and irradiation time of ultrasound treatment were determined. The parameters of water (COD and2,4-DNT) are investigated to reveal the ultrasound effect on the2,4-DNT wastewater. On the basis of the above research, the water composition (COD:N:P) is changed to show the effect under continuous experiment. The denaturing gradient gel electrophoresis (DGGE) is performed to analyze microbial community structure and their variations during different periods of this study. The objective of this dissertation is to provide an academic basis for the treatment of practical2,4-DNT which under the promoting influence of low-intensity ultrasound. The contents of the job are listed as follows:①Ultrasound irradiation with different parameters combination has great influence on the2,4-DNT removal of wastewater treatment. The optimum parameters of ultrasound treatment on the2,4-DNT removal are35KHz,140w, and irradiation time of20min. Compared with MBR,the effluent COD removal of LIU-MBR are increased by39.57%and degradation rate of2,4-DNT are above90%in both reactors. Low intensity ultrasound decreases the settle ability of the sludge, which might be due to the breaking of the particle size of sludge by continuous irradiation. During the study, negligible negative effect of ultrasound irradiation on the MLSS is found.②The bound EPS is a major component of EPS. The concentration of bound EPS and soluble EPS in LIU-MBR is lower than that in MBR. It can be concluded that low intensity ultrasound reduce the membrane fouling.③The COD and2,4-DNT degradation were investigated under the normal water composition (COD:N:P=100:5:1). The results suggested that the supernatant COD, effluent COD, effluent2,4-DNT of LIU-MBR were less than those of MBR. The supernatant COD removal rate is increased by12.8%in LIU-MBR and the2,4-DNT degradation rate is increased by23.7%. The concentration of EPS is increased under lacking nitrogen (COD:N: P=100:1:1) or lacking phosphorus (COD:N:P=100:5:0.5). In addition, several particulate matter and slime layer at the stage of normal water composition on the surface of membrane in LIU-MBR were less than the others. ④With the changes of COD: N: P, the diversity of microbial community in the LIU-MBR decreased. At last, the microbial community is mainly composed of Uncultured Sphingomonas sp. and uncultured beta proteobacterium, and the quantity of the microbial almost keeps stable.