Impact of different inoculum sources on the performance of membrane bioreactors for municipal wastewater treatment: Dynamic membrane versus ultrafiltration membrane

In this study, impact of different inoculum on the performance of membrane bioreactors (MBRs) was investigated for municipal wastewater treatment. Waste sludges from a conventional activated sludge (CAS) system and a high-rate activated sludge (HRAS) system were used as inoculums at Stage-1 and Stage-2, respectively. A commercial ultrafiltration (UF) membrane was tested in parallel with a low-cost polyester hollow fiber support material (dynamic membrane, DM). UF and DM membranes were operated for 67 days at a flux of 8 L/m²·h at each stage. High chemical oxygen demand (COD) and soluble COD (sCOD) removal efficiencies (>86% and >74%, respectively), low mixed liquor suspended solids (MLSS) concentration (<10 mg/L), and low turbidity values were achieved in permeates at each stage. Extracellular polymeric substances (EPS) content was higher at Stage-1, which caused an increase in sludge resistance to filtration (SRF) and sludge volume index (SVI). Based on morphological analysis, compact dynamic cake layer was formed on the support material at Stage-1, while porous dynamic layer was formed at Stage-2. Thus, DM was operated at lower TMP at Stage-2. Based on the results obtained from the study, sludge from HRAS system showed better performance as inoculum compared to the sludge from CAS system for DM applications.