Removal Of Endocrine Disrupting Chemicals In Wastewater By A Membrane Bioreactor And Enhanced Process With Nanofiltration Membrane

In order to increase the safety of the effluent of membrane bioreactor (MBR) and explore its utilization in the wastewater reclamation, the removals of endocrine disrupting chemicals (EDCs) by MBR were studied in this dissertation, and the nanofiltration (NF) membrane was used to filtrate the MBR effluent to enhance the EDCs removal, with the concentrated liquor feeding-back to the MBR. In addition, the NF membrane fouling mechanism and the cleaning methods were investigated, and then the cleaning mode was designed to make the NF system run continuously.The removal of bisphenol A (BPA) and nonylphenol ethoxylates (NPnEO, n=1~4) by a submerged MBR were studied, and the comparisons were made with a conventional activated sludge reactor (CASR) in the case of the same target contaminant-sludge loadings. It was found that the removal rates of BPA and NPnEO by MBR were both a little higher than those by CASR, but MBR could bear much higher volumetric loadings of the target contaminants. Through the studies on the transference of target contaminants in the reactors, it was found that the biodegradation were the dominate processes to BPA and NPnEO removal in both reactors, and the contributions of sludge adsorption to their removal were both quite low. Furthermore, the released EDCs from MBR system were much less than those from CASR in the running periods, which showed that the total security of MBR to EDCs removal was higher than that of CASR.Subsequently, the removals of 5 typical EDCs by MBR combined with NF system were studied, and the comparisons were made with the normal submerged MBR in the case of same running conditions. What could be found was that the NF rejection could enhance the removal of EDCs, but the contributions of NF rejection to the removal of EDCs were different with the substances. It was also found that the NF rejection could decrease the estrogenicity of the MBR effluent obviously. Furthermore, the anoxic tank, upstream of the MBR, supplied more than 80% of removal rates to the 5 EDCs in both systems. Furthermore, it could be found that the supernatant colloidal organic matters in the bioreactor increased caused by the feeding-back of the concentrated liquor of NF membrane rejection, which made the microfiltration membrane fouling occur earlier in MBR. It was also found that the settleability of the activated sludge declined with the feeding-back of the concentrated liquor, but the species and the quantities of the dominant bacteria in activated sludge were not influenced obviously.Additionally, the cleaning mode to the NF membrane fouling, including the online cleaning with 0.1% NaOH assisted with flushing by 2% critic acid and dipping with 1,2-propanediol, was determined through the cleaning experiments of NF membrane, with which the continuous running of NF system was achieved. With the help of some surface analytical methods, it was found that the foulants referring to NF membrane fouling included organic and inorganic matters, which contained the elements of phosphorous, magnesium, calcium and iron. The acidic cleaning could remove the inorganic foulants, leading to the exposure of the organic foulants to the subsequent alkali cleaning agent so as to improve the effect of alkali cleaning. According to the above results, the membrane fouling process could be conjectured as follows. The NF membrane was firstly fouled by the adsorption of the hydrophilic (or amphoteric) organic matters onto the membrane surface; and then the inorganic substances bound with the organic matters or covered them, which prevented the cleaning by alkali agent. As a result, the membrane fouling was accelerated.