Start-Up Performance Evaluation of Submerged Membrane Bioreactors Using Conventional Activated Sludge Process and Modified Luzack-Ettinger Process

The rising trend of converting conventional activated sludge processes to membrane bioreactor (MBR) processes for water reuse requires studying the start-up performance of bioreactors, during which mixed liquid suspended solids concentrations increase significantly. One conventional activated sludge MBR (CAS-MBR) and one modified Luzack-Ettinger (MLE) type MBR (MLE-MBR) with mixed liquor recirculation were evaluated for their performance on organic and nutrient removal, membrane fouling, biomass characteristics, and bacterial activities during the start-up period. The two bench-scale MBRs had identical reactor volume (7.2 L) and were operated under continuous flow conditions with no sludge wasting during the start-up operation. It took approximately 130 days for the MBR biomass concentrations to increase from initial 2,500 mg biomass chemical oxygen demand (COD)/L to a final concentration of 13; 000 mgCOD/L with net specific biomass growth rates of 0.0125 day(-1) and 0.0127 day(-1) for the CAS-MBR and MLE-MBR, respectively. The total nitrogen removal efficiency of the MLE-MBR was 73%, higher than that of the CAS-MBR (44%), whereas both MBRs had excellent organic removal (>99%) soon after the start-up operation. Because of sequencing anoxic and aerobic operations, the biomass of the MLE-MBR exhibited higher heterotrophic and autotrophic respiration activities and better sludge settling than that of the CAS-MBR. Furthermore, the MLE-MBR experienced less membrane fouling than the conventional MBR. Results of the start-up performance suggest alternating anoxic/aerobic MBR operations improve wastewater nutrient removal, increase bacterial activities, and reduce membrane fouling. DOI: 10.1061/(ASCE)EE.1943-7870.0000559. (C) 2012 American Society of Civil Engineers.