Removing charged particles (such as ions) can be done, besides ion exchange, with elektrodialysis. This is a membrane process where separation happens under influence of an electric field. Positive ions are drawn towards the negative electrode and vice versa, through a selective membrane that only lets the right charges pass. Because of the electric field as motive force, no large pressures are needed.
Non-charged particles aren’t influenced by the electric field, so they can’t be removed with ED.
Such an electrodeionization (EDI) unit is usually positioned after a RO in order to further purify the demineralised water to produce water with a very low conductivity (< 1 µS).
The advantage of an EDI is that no chemicals are needed. It is also a continuous process.
PCA can help you with this technology, both in design and construction of the installation.