### ForwardOsmosisTech has just made it easier for you to estimate structural parameters (S-values) of FO membranes

From our article covering concentration polarization effects in forward osmosis membranes, it is clear that FO membrane performance – to a large extent – is determined by S-values.

Below we present an easy-to-use calculator for estimating structural parameters of forward osmosis membranes. The calculator is based on equations developed by McCutcheon et. al.

#### Here’s what you need to estimate FO membrane S-values

In order to estimate S-values using ForwardOsmosisTech’s calculator you will need to determine the following FO membrane performance parameters and intrinsic membrane properties:

- The pure water membrane permeability coefficient (A)
- The salt permeability coefficient (B)
- The water flux J
_{w}– IN FO MODE – at a given osmotic driving force

For more details, please refer to our guide on how to determine FO membrane performance.

#### A few notes and suggested guidelines

- The calculator is based on the following S-value equation for an FO membrane operating in FO mode:
- S = (D/J
_{w})*ln((B+A*∏_{D,B})/(B+J_{w}+A*∏_{F,m})). - D is the diffusion coefficient for the draw solute used for J
_{w}(our equation assumes NaCl is used as standard) - ∏
_{D,B}is the osmotic pressure of the bulk draw solution - ∏
_{F,m}is the osmotic pressure of the feed solution close to the membrane surface - Providing membrane water flux performance is determined according to our suggested standardized methods, ∏
_{F,m}is assumed to be negligible (i.e. ∏_{F,m}= 0)

- S = (D/J
- Due to our assumption of ∏
_{F,m}= 0 along with other assumptions made by McCutcheon et. al., ForwardOsmosisTech’s S-value calculator should be used for estimations only - For an improved estimation, we suggest researchers to measure J
_{w}– and calculate the corresponding S-value – at 4 different initial draw solution concentrations, namely 0.25M NaCl, 0.5M NaCl, 1M NaCl, and 2M NaCl. The final S-value estimation is to be reported as the average of the 4 independent measurements - For cutting-edge FO membrane performance, researchers should aim for S-values below 300µm