Study Of Combined Anaerobic/Aerobic Biofilm Process For Effective Treament Of Azo Dye Wasteawater And Its Transformation Mechanisms

The declorization and degradation are the main aims for treating the azo dye-containing wastewater. In this study, a combined anaerobic/aerobic biofilm processes has been designed and used for the treatment of the cationic Red X-GRL (X-GRL) wastewater.Anaerobic sludge has been demonstrated to be greater on the decolorization of X-GRL, and biofilm performed greater on degradation of the aromatic intermediates. Based on these results, the upflow anaerobic biological filter (UABF), which combines the anaerobic sludge and the biofilm in a reactor, has been designed and used for the X-GRL degradation. The biofilm ratio and HRT for the UABF were optimized at 50 v% and 60 h, respectively. The color was completely removed by the anaerobic sludge in this reactor with the X-GRL concentration below 200 mg/L, and more than 90% of aromatic amines were removed by the biofilm. The COD removal efficiency decreased with increasing the X-GRL concentration in the influent.A Moving Bed Bioreactor (MBBR) was employed to follow the UABF for further mineralizing the residue aromatic amines. The HRT of the combined UBF/MBBR process was optimized at 60/12h. All color and more than 95% of COD were removed by the combined process. Although the COD removal efficiency of the UBF decreased with increasing the X-GRL concentration, the residue COD can be degraded by the MBBR with-50 mg/L remained in the effluent. The effect of sucrose concentration added in the influent on the performance of the UBF/MBBR was investigated as well. When the sucrose concentration was decreased to 50 mg/L, all the color,70% COD and 90% aromatic amines were removed by the UBF, and almost all the aromatic amines can be degraded in the MBBR.The UBF has been demonstrated to be important in the X-GRL degradation. The X-GRL adsorption is the first step in its biotransformation process, which determines its degradation properties by the anaerobic sludge. The adsorption capacity increased with increasing the pH, while it decreased with increasing the salinity and temperature. The electrostatic attraction between the EPS and the X-GRL has been determined as the main mechanism. The soluble EPS layer has an adsorption capacity of 1050 mg/g, much higher than the LB-EPS and TB-EPS. The X-GRL diffusion in the anaerobic sludge was considered as the control step in the X-GRL adsorption process.The anaerobic biodegradation of X-GRL has been investigated with sufficient and insufficient sucrose in the wastewater. Proteobacteria bacteria accounted for 45% of the total bacteria in the sludge feeding with sufficient sucrose, which utilizes sucrose to generate the VFAs and H2, and Firmicutes bacteria accounted for 55%, which can degrade the aromatic amines. The archaeal group is composed of 69.8% of hydrogenotrophic methanogenes and 30.2% of acetoclastic methanogens. The sucrose is the main initial electron donor, which can reduce the -N=N- and generate the colorless aromatic amines. The aromatic amines were then degraded to NH3 and CH4 by the bacteria and aechaea. In the sludge feeding with insufficient sucrose, hydrogenotrophic methanogenes competed with the H to the reduction of -N=N-, leading to the inhibition of microorganism activity.45.6% of proteobacteria and 48.2% of Firmicutes were detected as the bacterial group, and the 50% of Methanomicrobiales and 50% of Methanosarcinales were determined as the dominant archaeal community in the anaerobic sludge. The sucrose was one of the main electron donors for the reduction of X-GRL, and the polysaccharides in EPS and aromatic amines can also donate electrons for the decolorization of X-GRL.The resistance property of the biofilm against the toxic wastewater was investigated. For the anaerobic biofilm, the detachment of biomass was observed from 97% to 72% when the aniline concentration increased form 10 to 80 mg/L. The EPS amount of biofilm increased with increasing amines concentration, forming a thicker protective layer. The proportion of Firmicutes bacteria and hydrogenotrophic methanogens archaea increased as well. For the aerobic biofilm with growing stages, the EPS content increased with increasing the amine concentration, while the biofilm growth was inhibited. The mature biofilm has a better resistance ability than the growing biofilm.25.4 mg/g protein and 31.78 mg/g polysaccharides was detected in EPS of biofilm feeding with 60 mg/L amine, which is much higher than theses detected in the biofilm feeding without amine. More EPS forms a thicker layer, protecting the microorganisms against the toxic pollutants in the wastewater.