Design and Performance of a Pilot Submerged Membrane Electro-Bioreactor (SMEBR) for Wastewater Treatment
The quality of wastewater treatment plants effluents in Canada, and more specifically in Quebec is of a huge concern. Hence, several technologies have been widely used in order to protect water resources from the discharge of many undesirable components. The main objective of this study was to design/scale-up, install, and operate a new hybrid, compact wastewater treatment system (Submerged Membrane Electro-Bioreactor; SMEBR) that would yield an excellent quality effluent, reduce membrane fouling, and improve sludge properties. SMEBR combined three phenomena; membrane filtration, electrokinetics, and biological treatment. Three Phases were performed in this study. In Phase 1 (4 Stages), SMEBR laboratory scale system treating synthetic wastewater operated under different operating conditions to screen out and determine the operating ranges of the technological design parameters. These included the determination of the membrane critical flux and variation of aeration intensity (Stage 1), variation of current density (Stage 2), variation of the electrical zone volume with respect to the total volume of the effective liquid in SMEBR (Stage 3), and variation of hydraulic retention time (HRT) (Stage 4). Phase 2 focused on the scaled-up pilot SMEBR treating raw municipal wastewater. It was divided into 3 Stages where in Stage 1 the pilot SMEBR was designed (Stage 1a), installed (Stage 1b), and operated (Stage 2) in the municipal wastewater treatment plant in the City of l’Assomption (Quebec, Canada) for 7 weeks. A comparative study to the conventioanl MBR was also performed in Stage 2. Stage 3 investigated the relationship between the transmembrane pressure (TMP) and the sludge properties in SMEBR and MBR as well as the interaction among the sludge properties. In Phase 3, the scale-up process was verified using raw wastewater under steady state conditions; and conducted in conjunction to the pilot facility in Phase 2. The design scale-up protocol was also provided for full scale applications. At steady state operation, the removal efficiencies of COD, ammonia (as NH3+-N) and phosphorous (as PO43--P) in SMEBR were 92%, 99% and 99%, respectively. Furthermore, the monitored transmembrane pressure (TMP) had not shown any significant increase which could lead to the conclusion that the membrane fouling was marginal. In SMEBR system, sludge filterability and dewaterability were significantly enhanced by 78% when the mean particle size diameter of the sludge flocs decreased from 69 to 17.5 µm. Specific cake resistance was minimized to 0.15x1014 m/kg (82% reduction). Moreover, SMEBR enhanced sludge settleability by 30% while the sludge volume index (SVI) had decreased from 170 to 119 mL/g. SMEBR significantly improved sludge flocculation while zeta potential had changed from -26.2 to -14.2 mV. Electrodes were found to last for five months before replacement. SMEBR was a “self-purification” system as some of the generated aluminum and major metals were retained and adsorbed on the surface of the electrodes, and small amounts would leave with the effluent or present in the wasted sludge. SMEBR without any additional unit was able to remove undesirable metals from wastewater. High removal rates of Pb (100%), Ni (98.1%), Cu (100%), and Cd (94.6%) were reported. SMEBR energy requirements were less than 1 kWh/m3 with a total energy cost of CAD $0.052/m3. It could be concluded that SMEBR showed superiority in performance over MBR and can be successfully applied to small and large scale wastewater treatment plants.