We have studied the colloidal properties of stable highly disperse emulsions: fresh and waste lubricant/liquid coolant (LLC) and water-emulsified waste waters. The fresh LLC is monodisperse and the particle size of the disperse phase is equal to 0.086 mu m. The particle size for the disperse phase of the waste LLC is 0.05-0.15 mu m. We have identified the trends in the variation in colloidal properties of the waste LLC during treatment in different stages: coalescence treatment, sorption of petroleum products by a composite sorbent, ultrafiltration, nanofiltration, final purification on an ion-exchange membrane. After the membrane treatment methods, the average particle size increases and the absolute value of the zeta potential decreases due to breaking of the emulsion; the particles instantaneously become larger due to loss of charge while passing through the pores of the membranes.