Wastewater polishing using membrane technology: a review of existing installations

The use of membrane technology for municipal wastewater reuse is growing in importance worldwide as water becomes increasingly scarce. A review of nine membrane technology-based water reuse plants from across the world has been conducted to provide an insight into the trends in design and operation of these plants, and elucidate the impact of key water quality and other determinants. Data reveal a number of common elements, such as the design flux for the reverse osmosis membrane, as well as a number of other trends. The microfiltration/ultrafiltration (MF/UF) backwash interval appears to correlate better with feed water temperature than turbidity or total suspended solids, whereas chemical cleaning requirements are more dependent on plant operating parameters and water quality. There is some indication that the MF/UF pore size influences the filtrate turbidity (and silt density index) and so downstream reverse osmosis fouling and cleaning. Finally, specific energy demand (SED) values vary widely, from 0.8 to 2.3 kWh m(-3) permeate. Whilst the SED for the MF/UF process follows the flux, the overall energy demand shows no apparent dependence on the dissolved solids concentration or other feed water quality determinants. This range of energy demand amounts to 25-70% of the energy demand for seawater desalination.