Contaminants are removed from a quantity of contaminated liquid in a treatment reservoir (2,28) containing a carbon based adsorbent material capable of electrochemical regeneration. The adsorbent material is in the form of a bed supported on a plate (6) at the base of the reservoir. The bed is agitated for a period to distribute the adsorbent material in the liquid and adsorb contaminant therefrom. At the end of the period the agitation ceases, and the bed of adsorbent material is allowed to settle. The adsorbent is then regenerated, during or after settlement, by passing an electric current through the bed to release from the adsorbent gaseous products derived from the contaminant, in bubbles rising through the decontaminated liquid in the reservoir. Various methods of regenerating the adsorbent material are disclosed, as are apparatus in which the method can be applied.