Osmosis is the tendency of water to flow from a purer solution through a semi-permeable membrane into a more concentrated solution, equalising the solute concentration on either side of the membrane. Solute molecules do not naturally pass through the membrane. Pressure can be used to reverse the natural course of osmosis. As such, RO involves applying pressure to brackish water to make it pass through a membrane, removing solutes.
Depending on the quality of the water, which varies considerably across sites, pre-filtration by other technologies also may be used in CSG water desalination plants. This ensures that larger particles that could damage the RO membranes are filtered out.
Key issues in the installation of RO plants relate to water quality and variability. Water contaminants, which include silica, iron and hydrocarbons can all affect the performance of the system, as can extracted water temperatures. The changing nature of water volumes over the life of the project – increasing then decreasing – also needs to be considered.
The remote location of CSG fields can also pose a challenge. The use of modularised plants can help minimise onsite construction and commissioning activities, says Osmoflo.