Before landfill leachate is discharged, extensive removal of organic substances is required which cannot be achieved by biological treatment only. Chemical oxidation has the advantage of the substances being almost completely converted. Hydrogen peroxide/UV, ozone and ozone/fixed bed catalyst processes were used for the purification of three biologically pre-treated leachates. With all processes sufficient purification levels were achieved. However, the required energy consumption is largest with the hydrogen peroxide/UV process. If chemical oxidation is combined with biological purification, the discharge quality can be increased at decreased oxidant consumption.