Membrane manufacturers? It will depend if you want membranes themselves or membrane systems. It will also depend on the market/projected use.
Municipal water/wastewater: Pall Corp., US Filter, Zenon Environmental, Mitsubishi-Rayon, Kubota Hydronautics, Osmonics, Leopold, etc.
Ultrapure Water: GE Glegg, Asahi, Millipore, and a few others.
Gas Sep. mfrs. were listed in another post.
Several good reference materials available to help you in your search:
Journal of Membrane Science
The Membrane Handbook (W.S. Ho and K.K. Sirkar, eds.)
Water Treatment: Membrane Processes (AWWARF Publication, McGraw-Hill)
The Handbook of Membrane Science
Separation Technology (Journal)
Also you may try the WEF website (
For members of the organisation they have/are in the process of implementing an on-line tool for membrane bioreactors that will allow for project specific searches of a custom database. The database mainly covers the "big four" for bioreactors (US Filter, Zenon, Kubota and Mitsubishi-Rayon).
Good luck.
J