The term Tertiary Treatment - by now well established in wastewater treatment - describes the further treatment of the secondary effluent of a conventional treatment plant by means of membrane filtration e.g. for disinfection purposes.

 The process offers the following advantages:

• Without expensive modifications, the wastewater of an existing plant is disinfected and virtually free from germs. Therefore a discharge into bathing water areas, or use for irrigation in agriculture is possible.
• A substantially improved effluent quality is achieved. As particulate biomass flocks are rejected and an effluent virtually free from solids is achieved, a major reduction of the parameters COD, N, and P is effected.
• Extremely low P-values can be achieved with post-COD precipitation (between secondary clarification and TT).
• Due to the existing conventional mixed liquor separation a subsequent membrane filtration faces a considerably lower concentration of solids, therefore more cost-efficient membranes with a higher packing density can be used. 
• If necessary, it is easily possible to filter just a partial flow. 
• The effluent is also suitable for re-use, i.e. as washing water or for cooling tower applications. A further treatment of the MBR filtrate by Reverse Osmosis or activated carbon is increasingly cost-efficient for industrial applications. As the influent is free from solids, better reliability, increased recovery rates and substantially longer service life are achieved.