Study On The Self-Forming Dynamic Membrane Bioreactor Treating Of Alkali Decrement Printing And Dyeing Wastewater With Aerobic Granular Sludge

With development of the technology and times, alkali decrement technology is used to give the characteristics of silk to polyester fabric, which greatly improves its performance. A large amount of wastewater is produced in alkali decrement process. It is one of the most difficult handled and the most polluted wastewater in printing and dyeing industry.Aerobic granulation is a promising technology that has great potential in the wastewater treatment due to the advantages of excellent biomass settleability, less to prone sludge bulking, highly organic loading rate, synchronized nitrogen and phosphorus removal. Compared with traditional MBR, self-forming dynamic membrane bioreactor (SFDMBR) has the superiorities of low cost, low energy consumption, high effluent flux and it is easy to deal with membrane fouling. In this study, aerobic granular sludge was obtained under suitable conditions by seeding a self-forming dynamic membrane bioreactor (SFDMBR) with anaerobic granular sludge. Then based on the results, aerobic granulation technology was combined with the self-forming dynamic membrane technology for treating alkali-decrement printing and dyeing wastewater which had been treated by ABR. The process parameters, treatment efficiencies, activities of microorganism and membrane fouling characteristics were investigated. This paper includes the following research works:(1)Seeded with anaerobic granular sludge, a self-forming dynamic membrane reactor was started to cultivate aerobic granular sludge. DO was maintained about1.3～1.6mg/L and HRT was kept in48h. The COD load rate was gradually increased in the reactor.80d later, the anaerobic granular sludge turned into aerobic granular sludge and the starting procedure was completed.(2)In the training stage, SVI of the granular sludge increased from6.22mL/g to17.93mL/g and the dehydrogenase activity also increased from original1.81mg/gVSS-h to4.63mg/gVSS·h. It meant the dehydrogenase activity of the active microorganism in granular sludge was growing. At the end of incubation, the removal efficiency of COD in wastewater increased from initial30.92%to about75%. The particle size and sedimentation rate of the granular sludge remained relatively stable and there were no significant fluctuations.(3) DO and HRT had little influence on the effluent turbidity when a stable dynamic membrane in aerobic granule self-forming dynamic membrane bioreactor was formed and the effluent turbidity was less than10NTU with more than90%removal rate. The removal rate of chromaticity increased proportionately with increasing DO and HRT while the efficiency was generally not more than40%. (4)MLSS in aerobic granule self-forming dynamic membrane bioreactor was manually upgraded from4500mg/L to8600mg/L under the stable operation conditions. The treatment effect and the dehydrogenase activity increased gradually. The quality of effluent water could reach the emission standards of existing enterprises in "Discharge standards of water pollutants for dyeing and finishing of textile industry"(GB4287-2012).(5)Compared with the quality of effluent water from self-forming dynamic membrane formed by two substrates with different aperture, the quality of effluent water from25μm self-forming dynamic membrane was a little better than that of50μm. A more compact dynamic membrane with a smaller aperture of membrane substrate was the main reason for this phenomenon. The sedimentation tank of the reactor in this study had the role of eliminating and sorting inert sludge.(6)MLSS had a great impact on dynamic membrane fouling. When MLSS was upgraded, the operation cycle was shortened with increasing membrane resistance and pollutants. The resistance of self-forming dynamic membrane fouling mainly came from the cake layer. It accounted for over90%of the total resistance. The recovery rate of membrane flux could be67.5%after rinsed. The pollutants in gel layer were difficult to be removed and it was the crux of self-forming dynamic membrane fouling.(7)The content of EPSB-protein on the surface of dynamic membrane was the highest and the correlation between EPSB-protein and total resistance was the most significant. It indicated that protein substances were the key factor of dynamic membrane fouling. The content of protein substances on the surface of dynamic membrane was apparently higher than that in the mixed liquid. It illustrated that the dynamic membrane with non-woven polypropylene might enrich the protein in the mixed liquid and then it caused membrane fouling. A spot of S、Cl、Al、Si、Ca and other inorganic elements were found on the surface of dynamic membrane through EDS spectrum. It inferred that a certain degree of inorganic contamination layer might exist in membrane fouling.(8)The difference among different ways of washing contaminated dynamic membrane was due to the removal of protein substances. The best way to wash contaminated membrane was soaking with0.1%NaOH for1h and then0.1mol/L HCl for another1h. The flux of dynamic membrane could be recovered to89.78%of the original.