1. A. HOWELL School ofChemical Engineering, University ofBath, Claverton Down, Bath, UK, BA2 7AY 1.1 WHAT IS A MEMBRANE PROCESS? Every day over 20 million litres of brackish water are pumped out of the ground near Jeddah in Saudi Arabia and passed through thin sheets of cellulose acetate known as reverse osmosis membranes before being used as part of the city's water supply. In St Maurice les Chateauneuf, France three million litres a day of ground water are ultrafiltered to supply the city and on test sites in Australia settled sewage is being disinfected by being passed through...