the invention relates to the safe and effective biotreatment of circulating fluids . in one general aspect of the invention , an apparatus for circulating and bioprocessing a fluid includes a conduit for circulating the fluid , an oxygenator for supplying oxygen to the fluid , a pump adapted to circulate the fluid through the conduit , a bioreactor unit , connected within the conduit , adapted to process the fluid , and a container connected within the conduit for receiving and releasing a portion of the fluid .