Abstract: A method of recycling the off gas from an ozone disinfection step used with an activated sludge waste water treatment system, and apparatus for carrying out the method. The moisture is removed from a substantial portion but not all of the ozonation off gas, while the nitrogen and carbon dioxide contaminants that are contained in the off gas are left in it. The dried off gas is mixed with oxygen enriched gas from the original source, and the resulting mixture is delivered to the ozone generator for the production of more ozone. Another portion of the ozonation off gas is diverted upstream for introduction into the oxygen treatment facility of the activated sludge treatment plant. The drying of the ozonation off gas is preferably carried out by use of a two cycle self-purging dryer, with the portion of the ozonation off gas that is not delivered as a recycle component to the ozone generator utilized as the purge gas for the dryer before it is recycled upstream.