Study On Biodegradation Of Azo Dye By The MABR Process

Membrane aeration bioreactor(MABR) is a new technology of treating wastewater which developed from membrane bioreactor(MBR). Because of mass transfer between different phases, the layered structure of film, etc, the MABR is usually used to treating wastewater of high oxygen consumption, that of volatile organic compounds and so on. Using AO7 as a model, Membrane aeration technology was introduced to the field of biological treatment of azo dye wastewater in this paper. Under the premise of avoiding the autoxidation of azo dye decolorization products, decolorization of simulated dye wastewater and efficient removal of COD were achieved.In the first place, using silicone rubber membrane as the oxygen-permeable membrane and organism carrier, the MABR with 942cm2 of effective membrane surface area and 1.5L of effective volume was built. After being inoculated with sludge, MABR was successfully hanged film by 72h of aeration and had the preliminary ability of biological degradation. Afterward, domestication of biofilm with dye wastewater and optimization of experimental conditions were carried out. The results demonstrated that the optimal gas pressure and influent glucose concentration were 0.03MPa and 100mg/L, respectively.During the stable operation, the decolorization rate of 100mg/L AO7 influent reached to above 98.5%, and the removal rate of COD was 83.9%. In addition, the effluent didn't have apparent color. These showed the treatment effect exceeded that of conventional activated sludge A/O process. By analyzing degradation process of azo dyes, it was found that in a reaction cycle aerobic degradation of glucose and anaerobic decolorization of dyes mainly occurred during the first 6 h, after that aerobic degradation of aromatic amines was initiated. Dissolved oxygen was maintained at below lmg/L in MABR. Experimental results showed biofilm possessed the capability of catechol degradation, which made the degradation of aromatic ring compounds possible. SEM observation indicated biofilm were dominated by rod bacteria, while anaerobic sludge mainly consisted of cocci. DGGE fingerprint analysis found the shewanella sp. XB for sludge enhancement existed in the biofilm and anaerobic sludge which became one of the dominant bacteria.It is found by HPLC-MS analysis of influent and effluent, sulfanilic acid which was a decolorization product, had a stable structure. Moreover, self-oxidation didn't occur. Its biodegradability had the relative difficulty. However, about 67% of sulfanilic acid was biodegraded through the treatment of MABR. Self-oxidation products with 184 of m/z were detected in the oxidation products of AO7 decolorization products, and for the material structure further analysis is needed.At last, degradation experiment of nitrobenzene wastewater was carried out in MABR. Results indicated MABR could effectively avoid volatile organic compounds volatilization caused by conventional bubble aeration and secondary pollution of the air. After 24 days of sludge acclimation, removal rate of 300mg/L nitrobenzene reached 94.53% via 24h of treatment. The impact test showed MABR had a strong tolerance for influent nitrobenzene concentration.This work is the first study to realize Efficient Decolorization and degradation azo dyes wastewater applying MABR, which provides a new method to treat azo dyes wastewater.