Membrane technology offers promising potential for the treatment of (acidic) process water in the steel industry. Innovative tubular membranes were examined, in which tailor-made polyelectrolytes were applied to a ceramic membrane support by means of layer-by-layer deposition. Furthermore, membrane-supported capacitive deionization was considered for the treatment of cooling water streams, which separates ions at low voltage according to the principle of electrostatic sorption. The positive experiences from two industrial applications are reported.