A method of treating liquid waste with ozone by passing the liquid to be treated between complementary horizontal electrodes having therebetween electrically conductive particles so as to form an electrode bed, pulsing air simultaneously with said liquid, and maintaining between said electrodes an electrical potential so that as the air and liquid pass through said electrode bed, the bed expands to establish electrical contact between the electrodes thus to create localized arcing between particles in the bed and to form ozone.