A packed column for the absorption of ozone from ozonated air to further purify chemically clarified, biologically treated sewage, gave excellent results after fitting gas redistributor plates. Ozone utilization exceeded 85 % and the total losses over the unit process amounted to less than 5 % when an injector recontacting system was also incorporated into the calculation. Ozonation prior to active carbon treatment prolonged the operational life of the material considerably, probably through improved biological activity. Ozone could not entirely replace chlorine as a disinfectant.