## 4 Concluding Remarks and Future Perspectives  
This paper reviewed recent research (2015-till date) concerning the practical application of membrane bioreactors (MBRs) and high-retention membrane bioreactors (HRMBRs) towards the removal of OMPs from wastewater on both laboratory and pilot scale units. Challenges and apparent obstacles to the applications were discussed in the previous sections. Environmental legislation all over the world should be tightened to include a wide range of OMPs in sewage and industrial treatments. Nevertheless, sound knowledge of their fate and transport during wastewater treatment and detailed environmental risk information is still missing [17]. Furthermore, standard operating procedures (SOPs) for OMPs measurement using analytical techniques and validation protocols should be established to prevent limitations and uncertainties in prevailing sampling methods [17; 67]. [PERSON] et al. (2012) suggested that exposure of OMPs such as pharmaceuticals to the environment should be assessed not only on sales statistics data, but also data on degradation, removal by CAS and MBR treatment and bioconcentration should be taken into account [109]. In short, ranking of OMPs to be included in legislative guidelines should be based on its risk potential [110]. To answer the growing concerns with emerging micropollutant, stricter discharge limits would likely be imposed on industrial effluents soon. As noted by [PERSON] and [PERSON] (2015) recent R & D trends of MBR technology was shifted from process optimization and economic evaluation to the installation of new process architecture to enrich functional strains like nitrifiers and to applying MBR hybrid systems for achieving simultaneous removals of nutrients and OMPs [111]. Conventional MF/UF MBRs are already installed for wastewater treatment application. Therefore, scope exists to improve membrane morphologies and to integrate carefully with other established processes for better OMP removal [110]. Furthermore, low-pressure (MF and UF) membranes can be used in MBRs by addition of polymers or surfactants. While Polymer-enhanced and micellar-enhanced membrane processes can be efficiently used for the treatment of OMPs, little or no work has been reported, and scope exists to explore such techniques for OMP removal [110; 112]. Some challenges with AnMBR for sewage treatment include the dilute nature and temperature difference of municipal wastewater, salinity build-up when diluted wastewater is preconcentrated, membrane fouling and stability and inhibitory substances (e.g., free ammonia and sulfide). However, commercialization of AnMBR at industrial scale is still pending due to membrane fouling and membranes sensitivity to toxicity [82]. Thus, future studies are required for the development of effective strategies to address these challenges for further development of AnMBR [81]. Furthermore, future trends should focus on novel ideas such as electrically enhanced AnMBR and electrically enhanced OMBR to further reduce energy consumption and ensure energy efficiency [53]. Due to the fewer reports of MBR and HRMBR treating real wastewater, a complete understanding of the OMP removal mechanisms is still missing. Thus, it is difficult to comment precisely on OMP removal solely by considering results obtained from lab-scale data with simulated water matrices, meaning that a true representation of real water matrices is required [110]. Nevertheless, in real effluents, it is difficult to predict OMP removal accurately from a blend of OMPs with varying concentration due to their simultaneous interactions [67; 110]. A state-of-the-art HR-MBRs was successfully demonstrated from lab-scale experiments. Low flux, high salinity and membrane fouling and stability are critical issues for practical applicability of HRMBRs. Additionally, several technological challenges are associated with scaling-up of robustness and techno-economically feasible HRMBR at the pilot and commercial level to achieve high OMP removal and minimize toxic by-products [95].