Engineering

Reverse Osmosis Plants

Reverse Osmosis (RO) is a water purification technology that uses a semi-permeable membrane to remove larger particles from drinking water. In reverse osmosis, an applied pressure is used to overcome osmotic pressure, a colligative property, which is driven by chemical potential, a thermodynamic parameter. Reverse osmosis can remove many types of molecules and ions from solutions, including bacteria, and is used in both industrial processes and production of potable water. The result is that the solute is retained on pressurized side of the membrane and pure solvent is allowed to pass to other side. To be “selective,” this membrane should not allow large molecules or ions through pores (holes), but should allow smaller components of solution (such as solvent) to pass freely.

In the normal osmosis process, solvent naturally moves from an area of low solute concentration (high water potential), through a membrane, to an area of high solute concentration (low water potential). The movement of a pure solvent is driven to reduce free energy of system by equalizing solute concentrations on each side of the membrane, generating osmotic pressure. Applying an external pressure to reverse natural flow of pure solvent, thus, is reverse osmosis. The process is similar to other membrane technology applications. However, key differences are found between reverse osmosis and filtration.

The predominant removal mechanism in membrane filtration is straining or size exclusion so the process can theoretically achieve perfect exclusion of particles regardless of operational parameters such as influent pressure and concentration. Moreover, reverse osmosis involves a diffusive mechanism so that separation efficiency is dependent on solute concentration, pressure and water flux rate. Reverse osmosis is most commonly known for its use in drinking water purification from seawater, removing the salt and other effluent materials from the water molecules.

Ultra Filtration Plants

Ultra Filtration (UF) is a type of membrane filtration. Industries such as chemical and pharmaceutical manufacturing, food and beverage processing and wastewater treatment employ ultrafiltration in order to recycle flow or add value to later products.

UF’s main attraction is its ability to purify, separate and concentrate target macromolecules in continuous systems. UF does this by pressurizing solution flow. The solvent and other dissolved components that pass through membrane are known as permeate. The components that do not pass through are known as retentate. Depending on the Molecular Weight Cut Off (MWCO) of the membrane used, macromolecules may be purified, separated or concentrated in either fraction.

Currently, the study of UF processing occurs mainly in laboratory setups because it is very prone to membrane fouling caused by increased solute concentration at the membrane surface (either by macromolecular adsorption to internal pore structure of membrane, or aggregation of protein deposit on surface of membrane), which leads to concentration polarization (CP)). CP is the major culprit in decreasing permeate flux. Ultra Filtration is used as a pre-treatment step in reverse osmosis processes in many Middle Eastern countries to potable drinking water as there is little fresh water available in those areas.