Bioreactor

A bioreactor is a controlled vessel in which microbes, animal or plant cells, or isolated enzymes carry out a biological process, usually to make a product or to break down waste. Sizes range from benchtop vessels of a few liters to steel tanks holding many thousands of liters. Sensors and controllers keep temperature, pH, dissolved oxygen and nutrient levels steady, while stirring or rising air bubbles keep the contents mixed and supplied with oxygen. Everything that goes in is sterilized to keep out contaminating microbes.

The most common design is the stirred-tank bioreactor, a cylinder with a motor-driven impeller and a sparger that bubbles in air. Others include airlift and bubble-column reactors, packed beds that hold immobilized cells, and single-use plastic bags. Bioreactors also run in different modes. In batch culture everything is added at the start and the product is harvested at the end; in fed-batch culture nutrients are added during the run to reach higher cell densities; and in continuous or perfusion culture fresh medium flows in while spent medium flows out.

Bioreactors are central to biotechnology, producing antibiotics, enzymes, vaccines, monoclonal antibodies from mammalian cells and chemicals from engineered microbes. Scaling a process up from the lab is a major challenge, because mixing and oxygen supply change in a large tank.