A review of pressure-driven membrane processes in wastewater treatment and drinking water production

In pressure-driven membrane processes (reverse osmosis, nanofiltration, ultrafiltration, and microfiltration) a pressure exerted on the solution at one side of the membrane serves as a driving force to separate it into a permeate and a retentate. ne permeate is usually pure water, whereas the retentate is a concentrated solution that must be disposed of or treated by other methods. Membranes may be polymeric, organo-mineral, ceramic, or metallic, and filtration techniques differ in pore size, from dense (no pores) to porous membranes. Depending on the type of technique, salts, small organic molecules, macromolecules, or particles can be retained, and the applied pressure will differ. This paper reviews the principles behind the different techniques, the types of membranes used, rejection mechanisms, and process modeling. Applications of pressure-driven membrane processes are also considered, including reverse osmosis and nanofiltration for the treatment of waste-water from landfills and composting plants, nanofiltration in the textile industry, and ultrafiltration and microfiltration in drinking water production and wastewater treatment. Lastly, the paper discusses recent developments, including techniques to prevent membrane fouling by modifications affecting surface roughness or hydrophilicity/hydrophobicity, or by cleaning the membranes, and methods for treating or disposing of the retentate.