For waste water purification, industrial companies and public utilities use increasingly fixed-bed reactors. Whether on pumice, lava or sinter glass, the immobilized microorganisms degrade organic compounds in waste water fast and reliably. However, traditional fixed-bed reactors have one disadvantage: Their flow channels can easily be blocked by crystalization products and excessively grown fixed-bed particles. The Fraunhofer Institute for Interfacial Engineering and Biotechnology has developed a novel reactor, which does not block any more. The whole point: The fixed-bed particles are circulated from time to time thereby getting cleaned from the blocking matter.

The principle of operation of the new bioreactor: The waste water is led into the reactor from the bottom and streams through the fixed bed while the bacteria degrade the organic contaminations and thus purify the waste water. "To ensure that in case of large nutrient offer the excessively growing microorganisms do not stick to the particles, a pump periodically drives water from the top of the reactor into the inner conveying pipe", Dr. Werner Sternad explains the exceptional feature of the plant. The particles of the fixed bed are dragged along with the water stream and washed up to the top of the reactor. The resulting turbulences clean the particles and the reactor cannot block any more.

"Particle circulation allows a continuous and trouble-free operation of the reactor" the scientist points out the advantages. The first prototypes of the new reactor generation are already being tested for application in two industrial companies.