A method and apparatus for the removal of surface scum by using an apparatus in connection with a liquid tank, including a collecting arrangement for gathering surface scum and removing the same from the liquid tank with a surface scum discharge arrangement, and an overflow arrangement based on continuous flow for separating liquid to be treated from surface scum and for removing purified liquid from the liquid tank. The presently treated liquid is overflowed from the liquid tank into a escort water collecting space included therein by way of which it is removed from the immediate vicinity of the liquid tank. The surface scum is removed with a separating arrangement by which the surface scum is first of all separated from liquid to be treated in the liquid tank below its supernatant layer of surface scum while being flowed into the escort water collecting space and is conveyed at the same time into a collecting space of the collecting arrangement.