Date of Award


Degree Type


Degree Name

Doctor of Philosophy


Civil and Environmental Engineering


Dr. George Nakhla


This comparative study evaluated a novel membrane bioreactor (NMBR) for biological nutrient performance and membrane fouling with conventional BNR systems i.e. anaerobic/anoxic/aerobic (A O) process and University of Capetown (UCT) modified MBR process (UMBR). Comparison of the NMBR and A20 process, conducted at hydraulic retention time (HRT) of 8 hr and solids retention time (SRT) of 10 days using synthetic wastewater (SWW) and municipal wastewater (MWW), revealed that NMBR achieved lower effluent phosphorus than the A O with 0.2 vs 1.2 mg/L (SWW) and 0.8 vs 1 mg/L (MWW) as well as 20% lower sludge production. The study also substantiated that NMBR intermediate clarifier assisted chemical oxygen demand (COD), nitrogen, and P removals. Furthermore, the NMBR achieved 0.3 m/L lower effluent dissolved organic nitrogen (DON) than A20 and the DON reduction by membrane averaging 0.4 mg/L. The second comparative study with NMBR and UMBR process, tested at an HRT of 6 hr and SRT of 10 days using two different strength of MWW, indicated that effluent nitrate and P concentrations were lower in the NMBR than the UMBR by as much as 1 - 1.7 and 0.3 mg/L, respectively. Sludge P fractionation substantiated that poly-P content increased from 27-37% to 57-59% of the total phosphorus (TP) and P uptake by denitrifying phosphate accumulating organisms (DPAO) accounted for 37-40% of the total uptake in both systems. Both MBR systems showed similar membrane fouling trends with similar fouling rate of 4.4x1 O'2 LMH/kPa-h. A statistical analysis confirmed that soluble microbial product impacts membrane fouling more significantly than floe size, the bound protein/total protein ratio and bound extracellular polymeric substance (EPS). The iii biofilm layer deposited on the membrane caused denitrification of as much as 1.5 mg N/L, which was primarily impacted by dissolved oxygen and transmembrane pressure, triggering membrane fouling. Another study of the impact of denitrification on membrane fouling propensity, using three different sludges i.e. conventional activated sludge (CAS), ordinary heterotrophic organisms (OHO) and DPAO, indicated that DPAO denitrification decreased cake layer resistance by 53% compared to an increase of 220 and 150% in CAS and OHO denitrification. The reduction in cake layer resistance for DPAO denitrification was associated with the increase in hydrophobicity and decrease in carbohydrate/protein ratio in bound EPS of DPAO after denitrification, with the reverse trend observed with CAS and OHO. Therefore, the contributions of this study are summarized as followings: 1. Identification of the role of the intermediate clarifier in the NMBR 2. Confirmation of the advantages & disadvantages of the NMBR relative to conventional systems 3. Extensive characterization of membrane foulants in BNR systems 4. Delineation of the fact that contrary to common belief, DPAO reduces fouling



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