Apparatus and method for purification of a fluid by means of a filter bed

An apparatus for purification of a fluid, the apparatus comprising:

• a vessel (1) for receiving a filter bed (2) with granular filter material;
• a transport system (8) configured to, during operation, transport filter material from a walled cavity (5) underneath the filter bed (2) to a location (17) above the filter bed;
• a fluid inlet (14) for introducing fluid to be purified into the apparatus;
• a mixing section (3) adapted to, in operation, provide a mixture of fluid from the fluid inlet and granular filter material from the filter bed;
• and
• a plurality of gas lift injectors (4) within said walled cavity, wherein each gas lift injector (4) is configured to, in operation, transport the mixture of fluid from the fluid inlet (14) and granular filter material from the filter bed (2) to the walled cavity (5), wherein at least one gas lift injector (4) comprises a pipe which runs diagonally upwards from an off-center position towards a center axis of the walled cavity (5).