## 3 High Retention Membrane bioreactors (HRMBR)
### Membrane Distillation Bioreactor (MDBR) for OMPs Removal  
Membrane distillation incorporates hydrophobic microporous membranes that operate at low-temperature, involving solely transfer of water vapor from feed side to the distillate side through membrane pores. Due to gas-phase mass transfer, only volatiles could pass through the membrane and thus MD completely retains non-volatiles in feed solution [75; 105]. A novel MDBR process combines thermophilic activated sludge membrane bioreactor (MBR) with the membrane distillation (MD) process where usually direct contact membrane distillation module is immersed in a biologic reactor [49; 106]. Hydrophobic membrane modules in MDBR are usually made of polypropylene (PP), polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE) [106]. The advantages with MDBR consist of high organic removal in sewage reuse, less sludge production and least affected by salinity build up as in OMBR process, while complete rejection of salt can be achieved. MDBR offers advantages such as being less susceptible to membrane fouling, low installation cost and good performance under moderate thermophilic temperatures [82]. Compared to MBR and OMBR, in an industrial facility where both hot effluent and surplus heat is available MDBR could be an attractive emerging technology to be applied [107]. [PERSON] et al. (2014) noted that MDBR could achieve enhanced OMP removal compared to stand-alone MD process. Actually, in MD process OMP removal depends on the Henry's constant, H (vapor pressure) and the water partition coefficient (log D) of the OMPs to be removed. When MD process has a low (<2.5) 'pKH/log D' ratio poor OPMs removal is accomplished. But in MDBR even at low (<2.5) 'pKH/log D' ratio' higher OMP removal is possible due to the sorption of OMPs onto the sludge surface which prolongs OMPs retention followed by potential biodegradation [75; 108]. In MDBR process OMP removal mechanism involves hydrophobic membrane rejection, sorption onto the sludge particles and biotransformation in bioreactor in the presence of thermophilic bacteria [75]. Table 5 presents some of the MDBR reports on OMP removal. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Wastewater**} & \multirow{2}{*}{ \begin{tabular}{c} **Membrane with** \\ **Operating Conditions** \\ \end{tabular}  } & \multirow{2}{*}{ \begin{tabular}{c} **Temperature** \\ **Lead** \\ \end{tabular}  } & \multicolumn{2}{c}{ \begin{tabular}{c} **MD Flux** \\ **LMH** \\ \end{tabular}  } & \multirow{2}{*}{**OMPs Investigated**} & \multirow{2}{*}{ \begin{tabular}{c} **\%** \\ **Removal** \\ \end{tabular}  } & \multirow{2}{*}{**References**} \\ \cline{3-4} \cline{6-7}  & & & & & & & \\ \hline \multirow{8}{*}{ \begin{tabular}{c} **Synthetic** \\ wastewater \\ \end{tabular}  } & \multirow{8}{*}{ \begin{tabular}{c} **Top size 0.2 \(\mu\)m**, \\ 95-100 \(\mu\)M (DMP) **/min** \\ \end{tabular}  } & \multirow{8}{*}{ \begin{tabular}{c} 30 \\ **10** \\ \end{tabular}  } & \multirow{8}{*}{ \begin{tabular}{c} 10 \\ **(Study)** \\ \end{tabular}  } & \multirow{8}{*}{ \begin{tabular}{c} **(Steady \\ **(R)** \\ \end{tabular}  } & \multirow{8}{*}{\ \begin{tabular}{c} Proxur \\ **(R)** \\ \end{tabular}  } & \multirow{8}{*}{ \begin{tabular}{c} 99 \\ **(R)** \\ \end{tabular}  } \\