Physico chemical cleaning of oil refinery waste water consists of controlled coagulation and flocculation, with up to 0.5 per cent by volume of sludge

The physico­chemical cleaning of oil refinery waste water comprises coagulation and flocculation at pH 6.5­9 by addition of polyacrylamidebased cationic polyelectrolyte. The additive, of 40 % cationicity, is a 0.1 % solution, at 1 ­2 mg of active matter per litre. EMBODIMENT ­ The treatment takes one hour, with maximum 0.5 % by volume sludge formation. The sludge is then dehydrated by centrifugation.