Micro-filtration is a very fine filtering system. All particles (even large colloids) over 0.03 µm, bakteria and large viruses are rejected and washed out with the concentrate flow. The rejection is about 95% and higher, compared to 10-25% with reverse osmosis (without antiscalling substances). The concentrate is normally put back into the main aquarium system. So any water losses occure.
The spiral wound modules used for this plant cannot be backwashed, therefore it should always be operated in a cross-flow process, i.e. waste water is simultaneously produced with the filtrate, which removes the retained substances - similar to reverse osmosis technology, but with a considerably higher recovery.