Desalination capacity of reverse osmosis membranes

The desalination efficiency of reverse osmosis is very high, with a minimum level of over 95% (although there are requirements regarding the pH of the water). One issue is scaling, which can be mitigated by using appropriate scale inhibitors. The main negative effects include the fact that during the desalination process, reverse osmosis membranes allow almost 100% of carbon dioxide to pass through, while allowing only a very low amount of calcium ions to pass through. This leads to an increase in the pH and calcium ion concentration on the concentrated water side; the increased pH in turn causes an increase in the proportion of bicarbonate ions in the water, which facilitates the precipitation of calcium carbonate on the membrane. The reaction is as follows: Ca(HCO3)2 → CaCO3 (precipitate) + CO2 + H2O. However, this issue can be addressed by using scale inhibitors (or by adding acid)

The removal rate mainly depends on the design of the problem; as long as it meets the process requirements, that’s sufficient.

First, one needs to consider the salt content in the raw water; secondly, it is necessary to take into account the number and number of stages of membranes in the device used. Ultimately, conductivity can be used as a criterion for assessment.

Generally, the removal efficiency of reverse osmosis membranes for ions is higher for divalent ions than for monovalent ions; the removal rate for divalent cations is typically over 98%. However, the removal efficiency for carbonate ions is very low, while the removal rate for chloride ions is around 90%

Water flux and desalination efficiency are affected by factors such as operating pressure, concentration, temperature, flow rate, pH value, and recovery rate.