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This dissertation, A Membrane Bioreactor(MBR) for an Innovative Biological Nitrogen Removal Process by Wen, Chen, 陳雯, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstract of thesis entitled A MEMBRANE BIOREACTOR (MBR) FOR AN INNOVATIVE BIOLOGICAL NITROGEN REMOVAL PROCESS submitted by CHEN Wen for the degree of Master of Philosophy at the University of Hong Kong in December 2007 Membrane bioreactor (MBR) is an emerging and promising biological wastewater treatment process. However, it is difficult to sufficiently remove nitrogen with the use of conventional MBR due to its aerobic condition. As part of the present experimental study, a hybrid system was developed for nitrogen removal that used a submerged MBR (SMBR) connected to the activated sludge nitrification-denitrification reactors with an intermediate sludge settler. The laboratory system had a working volume of 6.5 L which received an influent of glucose-based synthetic wastewater. The results demonstrated that the new process was highly effective for simultaneous organic and nitrogen removal. During stationary operation, a sludge MLSS (mixed liquor suspended solids) concentration of 6 g/L or higher could be maintained in the reactors. The system had an organic loading rate in total organic carbon (TOC) of up to 710 mg/L-d and a total nitrogen loading rate of up to 175 mg N/L-d. With a total hydraulic retention time (HRT) of 15.6 hours and a recirculation ratio of 8, the nitrogen removal efficiency reached 97% as the total nitrogen concentration was reduced from 100 mg/L to about 2 mg/L. With a shorter HRT of 10.4 hours and a lower recirculation ratio of 4, nitrogen removal efficiencies of 90% could be maintained. A high quality effluent was produced by the hybrid MBR system with a TOC below 10 mg/L, a suspended solids (SS) content of + less than 1 mg/L and a NH -N concentration of lower than 0.1 mg/L. The SMBR membrane fouling problem was also investigated during the experimental study. The fouling rate was characterized for the sludge suspensions that had a SS concentration varying from 2.4 to 8.7 g/L and a supernatant TOC varying from 10 to 30 mg/L. The results showed that the sludge cake layer on the membrane was the main cause of membrane fouling during the SMBR operation. The organic content in the liquid phase of the sludge mixture had a crucial effect on the fouling rate. For instance, at the MLSS level of 4.0-4.7 g/L, an increase in the supernatant TOC from 12 to 30 mg/L dramatically increased the membrane fouling rate by a factor of 10 times. By contrast, a variation in biomass concentration had a much smaller impact on the fouling rate. Detailed analysis revealed that in addition to soluble microbial products (SMPs), the organic matter in the SMBR sludge supernatant consisted of large-sized organic materials known as biopolymer clusters (BPCs). It is argued that BPCs are a special form of organic substances that are formed by the adsorption and affinity clustering of mainly SMPs in the sludge cake that are deposited on the membrane surface. Used as model biopolymers, alginate and bovine albumin serum were found to form larger clusters, which facilitated the attachment of biomass solids on the membrane surface. The identification of BPCs as important foulants in the sludge suspension provides new insights into the fouling mechanism of the MBR. DOI: 10.5353/th_b3955795 Subjects: BioreactorsSewage - Purification - Nitrogen removalSewage - Purification - Biological treatment

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