An adsorption process is described in which water based liquids are contacted with a flocculated adsorbent powder. The liquid rises through the treatment zone, the lowr part of which is equipped with an agitator. The speed of rotation, frequency and duration of the agitation can be varied. To ensure that adequate and stable flocculation takes place, a chemical flocculant is pref. added to the fluid in the lower treating zone. The max. concn. of flocculant in the fluid is 0.05 mg/l. To minimise the vertical movement of the flocculated grains, the vertical treating zone is pref. divided into smaller zones by horizontal filter plates. The process is partic. suitable with the use of activated carbon powder. The carbon can either by periodically...