What is the difference between forward and reverse osmosis?

If you are a water professional or system integrator you are probably familiar with reverse osmosis. While both RO and FO are membrane-based water treatment technologies there are some significant differences between the two.

Both RO and FO are used to diffuse water from one side of a membrane to the other, filtering out dissolved solids, ions and other undesirable compounds in the process. The main difference between the two technologies is how water is driven through the membrane.

In RO, the water is forced through the membrane using hydraulic pressure to overcome the natural osmotic pressure. The higher the salinity of the feed solution, the more pressure is needed. This requires high-pressure pumps and vessels with significant quantities of energy as a result. RO also requires membranes that are suited for the specific task, such as brackish water, seawater, high-pressure or ultra-high-pressure membranes designed for an operating pressure ranging between 1,000 and 1,740 psi delivering a brine with a TDS of up to 75,000 ppm. At brine TDS levels exceeding 75,000 ppm, the pressure requirements begin to make RO unfeasible.

FO, on the other hand, uses natural osmotic pressure to induce the flow of water through the membrane by running a highly saline draw solution on the other side of the membrane. This means that the feed solution flows through the FO membrane at a relatively low pressure which eliminates the need for high-pressure hydraulics. It also solves the issue of declining productivity with increasing TDS, as the salinity of the draw solution can be adjusted to create the necessary osmotic pull.

Lower risk of scaling and fouling

A well-known issue with RO membranes is fouling and scaling, where organic and chemical residue, oxidants and scaling ions build up on the membrane surface. This reduces the effectiveness of the membrane and requires frequent maintenance and backwashing. Ideally, a RO membrane should only handle water and pure salt, but with the complex composition of industrial wastewater effluent, this is rarely the case.

With FO, the low pressure of the feed solution makes the FO membrane less sensitive to fouling and scaling issues. This reduces the need for cleaning of the membrane and extends the lifetime of the membrane.

Difference between Reverse Osmosis and Forward Osmosis

Quality is key

In FO processes, the quality of the membrane is key. Aquaporin Inside® FO membranes use aquaporin proteins to filter water. Aquaporins are 100 % selective to water molecules, which ensures our FO membranes are highly efficient at rejecting chemicals, minerals, color and other contaminants

Aquaporin Inside® Forward Osmosis enables the efficient extraction of water, leaving behind challenging contaminants and reducing effluent volume. The process uses natural energy in the form of osmotic pressure to transport water through a filtration membrane, which improves efficiency without increasing energy use.

With Forward Osmosis you can:

  • Minimize waste by effluent volume and sludge reduction to save costs related to disposal or evaporation/crystallization in Zero or Minimal Liquid Discharge systems
  • Reuse more water with better quality by treating streams with difficult contaminants and high BOD/COD/TOC – where other technologies fail
  • Simplify treatment through fewer and faster process steps by partly/fully replacing primary, secondary and tertiary treatment – including chemical and biological treatments – to lower CAPEX/OPEX
  • Optimize land use through simpler and more efficient treatment

To learn more, download our e-book, visit our industrial water page or contact us to discuss your water treatment needs and challenges.


Published on Oct, 2020 in