The invention relates to liquid purification and/or desalination systems, predominantly water from different sources, and is used in household and/or drinking water supply, in suburb and country houses. Liquid purification system, comprising of raw liquid line with the inlet valve, reverse osmosis membrane connected to drainage line and purified liquid line and purified liquid consumption line and purified liquid vessel, secondary purified liquid line, connected to purified liquid vessel and to raw liquid line and to console panel, characterized in that debris layer on the reverse osmosis membrane is near totally dissolved by intensive repeated flushing of the reverse osmosis membrane with purified liquid.

The present invention generally relates to a process for reducing formaldehyde content from cationic melamine-formaldehyde resin solution. Said process comprises the steps consisting of charging a starting solution to an ultrafiltration membrane system, separating said starting solution into a concentrate solution which mainly comprises cationic melamine-formaldehyde resin of high molecular weight, formaldehyde and water, and a permeate solution which mainly comprises cationic melamine-formaldehyde resin molecules of low molecular weight, formaldehyde, acid compounds and water and treating the permeate solution to reduce the free formaldehyde content of the permeate.

A device for micro-, ultra-, or nanofiltration that includes one or more flat filter modules having flat filter elements arranged in parallel and at a distance from each other and gas injectors of one or more gas lifting systems for producing a circulating cross flow directed tangentially to the surface of the flat filter elements and having at least one rising area, in which the cross flow flows substantially vertically upward, and at least one falling area, in which the cross flow flows substantially vertically downward, in which the rising area flows through 10 to 100% and the falling area flows through 10 to 100% of an inlet-flow volume of the at least one flat filter module.