The treatment of pharmaceutical wastewater using in a submerged membrane bioreactor under different sludge retention times

The performance of a lab-scale submerged membrane bioreactor system (SMBR) for treating a process wastewater containing the pharmaceutical active compound (PhAc) etodolac with four different microfiltration (MF) membranes (MP005, MV02, CA, and MCE) was investigated at three different sludge retention times (SRTs) under constant pressure. In the first phase of the study, the continuous bioreactor system was operated at SRTs of 15 and 30 days and without sludge wasting (WSW). After steady state conditions were reached, the SMBR process was started as the second phase. Short-term filtration (24 h) tests were conducted for each SRT. When the SRTs were increased, both permeate volumes and steady-state flux values increased. The best etodolac removals were obtained in case of WSW for both bioreactor system and SMBR. The etodolac removals achieved by the different membranes for the period WSW were observed in the following order: MV02=MP005>CA=MCE. In addition, the chemical oxygen demand (COD) removal efficiencies for bioreactor system and SMBR were approximately 80±2% and 86±2%, respectively, at all SRTs. The COD removals at each of the three SRTs were similar for all of the membranes. Extracellular polymeric substances (EPSs) and soluble microbial products (SMPs) were analyzed as fouling control factors. Increasing the SRT caused increases in sludge concentrations in the SMBR as well as in increased etodolac removal, while EPS and SMP protein and carbohydrate concentrations decreased. Fouling on the pores and surfaces of the membranes were characterized using a Scanning Electron Microscope (SEM), an Atomic Force Microscope (AFM), a Fourier transform infrared spectroscopy (FT-IR), and contact angle measurements. The resistance in series model was used to evaluate the flux decline caused by the gel layer, cake resistance, and internal pore blocking in the MF membranes at the three different SRTs.