## 2 MBR Types and Configuration
### Aerobic Membrane bioreactors in OMPs Removal

Table 1: _Cont._such as atenol (58%), propranolol (50%) and diltiazem (57%) have been reported with lab-scale MBR than anaerobic/anoxic/oxic process which demonstrated lower removal for atenol (43%), propranolol (17%) and diltiazem (35%), respectively [69]. It was deduced that biosorption on sludge surface was potential removal mechanism for beta-blockers [69]. In an MBR study, [PERSON] et al. (2016) report that gemfibrozil and carbamazepine were refractory molecules and highly persistent to biotransformation [72]. In another study, [PERSON] et al. (2018) examined the removal of three most consumed anticancer drugs namely ifosfamide, fluorouracil and cyclophosphamide and a pain killer codeine and antibiotic sulfamethoxazole were studied in submerged MBR. Biodegradation was successful removal mechanism for sulfamethoxazole and codeine achieving 79% and 95% removal efficiencies, respectively while ifosfamide and cyclophosphamide showed moderate elimination of less than 40%. However, for all selected pharmaceuticals of this study more than 89% removal were achieved due to intense membrane fouling. Needless to mention that membrane fouling led to high bio sorption of OMPs thereby prolonged their retention in bioreactor [73]. [PERSON] et al. (2017) studied pilot-scale MBR and membrane bioreactor-nanofiltration (MBR-NF) system using real sewage. MBR-NF system with nanofiltration (NF270) membrane outperformed MBR achieving 84% of removal for OMPs except caffeine and hydrochlorothiazzide. The MBR process found incapable with persistent OMPs such as carbamazepine and diclofenac compounds [78]. [PERSON] et al. (2017) also report (Table 1) that biodegradation was the governing mechanism for naproxen, ibuprofen and hormones removal in MBRs with PAC addition [70]. Albeit, partial biodegradation and partial sorption onto powdered activated carbon surface were the removal mechanism observed for OMPs such as erythromycincin and roxithromycin. Actually, membrane type influenced the removal of diclofenac and roxithromycin. It was noted that biosorption/biodegradation occurred in the cake layer of the membrane hence OMP removal. [PERSON] et al. (2017) demonstrated that biodegradation played a significant role for compounds adsorbed to the sludge as well as for recalcitrant OMPs. Author report that bezafibrate, ketoprofen and atenol showed better removal [69]. In another study [PERSON] et al. (2011) report that in an MF-MBR process salicylic acid, metronidazolezole, ketoprofen, naproxen, primidone and ibuprofen six model OMPs showed more than 85% removal which was higher than conventional MBRs. The authors correlated this higher hydrophilic OMP removal with -NH\({}_{2}\)- and -OH-like EDGs in their structure. Further, they report that strong EDGs were easy to attack by aerobic consortia [79]. In another hybrid MBR-MBBR study high removal efficiencies more than 80% for OMPs like nonylphenol, 17\(\alpha\)-ethynylestradiol, 17\(\beta\)-estradiol, estrone, bisphenol A and triclosan were noted. It was further deduced that with those hydrophobic OMPs better removal were achieved than hydrophylic OMPs, such as diclofenac, ibuprofen and sulfamethoxazole. It is well established that hydrophobic OMPs possess natural tendency to adsorb to the sludge led to high removal. However, by pH adjustment (pH < pKa) and thus more acidic environment may have enhanced removal of hydrophilic compounds such as sulfamethoxazole in the same study [53; 68]. High MLSS concentrations in bioreactor can provide more surface area and can favor biodegradation by enhancing retention time for OMPs as reported for pharmaceutical compound [72]. As reported by [PERSON] et al. (2011), removal efficiencies of 85% for roxithromycin and 92% for clarithromycin were obtained in MBR process due to higher biomass concentration of 10 g/L [79]. When operated in activated sludge process with typical 2.3-2.5 g/L biomass concentration, lower removals of 65% for roxithromycin and 78% for clarithromycin are reported [69]. [PERSON] et al.