Various combined processes are reported. Such as: activated sludge combined with membrane filtration (MBR), ozone treatment combined with membrane filtration, ozone treatment combined with photocatalysts, photocatalysts combined with membrane filtration, etc.

Each technology has advantages and challenges to be solved. The optimum process may differ with the application as the conditions may be very different, such as components in the solution, their concentrations, volume, target of the treatment, the location of installation, etc. have a huge variety.