Reverse osmosis plants and nanofiltration plant
This process doesn’t consist only of a physical obstacle (produced by the membrane pores dimensions) to the passage of the molecules, but it use the different chemical affinity of the solutions with the membrane, permitting the hydrophile molecules (or water-like) passage.
This method uses the tangential filtration principle, like other separation techniques by the use of membranes as the ultrafiltration, microfiltration and the MBR membrane bioreactor (see Membrane technology).
Nanofiltration plants are usually used for softening. The installed membrane type installed make the nanofiltration plants different from the reverse osmosis units.
The nanofiltartion membrane has bigger pores and it doesn’t stop all the salts but only the molecules with bigger dimensions. The nanofiltration is mostly use to remove organic solutions (colored substances, nitrates, etc.) and multivalent ions.
Reverse osmosis and nanofiltration plants work at high pressures.
Microfiltration plants are mostly used to remove solid particular present in the effluent. Microfiltration plants are often used as pretreatment for reverse osmosis, nanofiltration and ultrafiltration plants. Ultrafiltration and microfiltration plants work at low pressures.
MBR technology combined with reverse osmosis plants produce an high quality water.
MBR membranes can work submerged in bioreactor containing a lot of activated sludges, helping the BOD and nitrogen reducing process.
MBR membranes combine biological treatment with membrane technology.
MBR technology reduces the dimensions of the biological plant area.