Extensive nitrogen removal in a new type of airlift reactor

A new type of CIRCOX® airlift reactor was started-up treating anaerobically pre-treated potato-processing waste water. This type of airlift reactor with biofilms on carrier is an airlift reactor extended with an anoxic compartment to obtain total nitrogen removal. This type of reactor was designed in the early nineties and was tested successfully at pilot-scale on brewery and municipal waste water. The 3 m3 pilot reactor was scaled-up to a size of 130 m3. Both the hydraulics and the biological performance were studied. High liquid velocities and equal concentrations of sludge throughout the whole reactor, indicated that the system was well mixed. Up to 5 kg COD/m3/day was removed. Ammonia was almost completely removed (up to 1.0 kg NH4–N/ m3/day in the aerated compartment). The denitrification efficiency was over 90%. The NOX–N concentration in the effluent never exceeded 6 mg/l. The biofilm layers were extremely dense: 30 g/l of VSS with a sludge volume of 220 ml/l. Therefore the particles had high settling velocities and could easily be retained in the reactor. It can be concluded that this new technology has been scaled-up successfully. With this an aerobic technology is available in which extended treatment and nitrogen removal are accomplished in a very compact system.