A process for conditioning an ozone gas recycle stream in an ozone pulp bleaching process, wherein the level of carbon dioxide in the recycle stream is controlled to allow full capacity operation of the ozone generator. Carbon dioxide concentration is identified over the relevant operational ranges and maximum concentration is identified for full capacity/optimum efficiency operation. Specific methods are described for controlling carbon dioxide concentration including purging a portion of the recycle stream, counter-current scrubbing of the recycle stream with an alkaline solution and passing the recycle stream through an adsorbent material. Contaminants entering the system also may be reduced by directing the purged recycle stream, which is relatively oxygen rich, into the dewatering press where pulp consistency is increased. In this manner nitrogen surrounding the pulp is displaced by oxygen and thus, does not enter the bleaching/ozone system with the pulp.