Membrane Technology in the Water Treatment
The reverse osmosis (also known as hyperfiltration) process is the reverse of the osmosis process, driven by a pressure difference, i.e., by adding a pressure higher than the osmotic pressure on one side on the liquid to be separated, so that the solvent in the original liquid is pressed to the other side of the semi-permeable membrane. Reverse osmosis technology is characterized by no phase change, low energy consumption, high membrane selectivity, compact device structure, simple operation, easy maintenance and no environmental pollution.
Nanofiltration technology is an ultra-low pressure reverse osmosis technology with nanoscale pore size. Nanofiltration membrane technology has poor retention of monovalent ions or organic matter with relative molecular mass below 200, while it has high removal rate of divalent or multivalent ions and organic matter with relative molecular mass between 200 and 1000. Nanofiltration membranes are charged and have selective retention of different charged solutes, while they are porous and have high water permeability at low pressure.
