Comparison of a single-stage and two-stage anaerobic fluidized-bed membrane bioreactor (AFMBR)

Aerobic processes are commonly adopted in conventional water treatment processes for being a resilient system with an ability to produce high quality effluent. However, its costly requirements for aeration and biosolids post-treatment have been concerns over recent years. Therefore, much attention has been placed on anaerobic processes, for its lower cost requirements and reduced production of biosolids. Two-stage Anaerobic Fluidised Membrane Bioreactor (AFMBR) concept has been proposed and a pilot plant installed by Inha University, South Korea has proven its feasibility in treating domestic wastewater. To further reduce costs for construction and maintenance of AFMBRs and lessen reactor footprint, combining both reactors into a single reactor has been examined. The single-stage AFMBR achieved comparable organic removal efficiency and membrane performance as the two-stage AFMBR at the similar flux (6-9 L/m2h, LMH) using a mixture of acetate and propionate as feed. However, under a condition using real wastewater containing more refractory organic substances and biosolids, whether the comparable performances in both AFMBRs especially operated at improved fluxes could be achieved is not clear. In addition, further exploration of organic components transportation and membrane foulants characterization in both AFMBR systems have not been performed yet. In this study, we compared reactor and membrane performances of lab-scale single-stage AFMBR (R1) and two-stage AFMBR (R2) fed with settled municipal wastewater at membrane fluxes of 20 LMH and 30 LMH. Although the less contribution of GAC bioadsorption/biodegradation and more contribution of membrane rejection for soluble organic substances removal in the two-stage AFMBR than those in the single-stage AFMBR, both AFMBRs exhibited comparable organic removal efficiency and membrane performances. At both permeate fluxes, cake layer fouling was predominant. Furthermore, the fouled membranes were taken out from the reactors for physical and chemical cleaning and the respective foulants were characterized. In both AFMBRs, Excitation Emission Matrix (EEM) analysis revealed that microbial products like substances were dominant for physically cleaned foulants and humic substances were dominant for chemically cleaned foulants. Inductively coupled plasma optical emission spectrometry (ICP-OES) analysis illustrated silica elements was the dominant chemically cleaned inorganic foulants. Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) images show that the fouled membranes under fluxes of 20 LMH and 30 LMH had different morphologies due to different drag forces under the same scouring force provided by fluidized GAC particles.Bachelor of Engineering (Environmental Engineering