Filtration resistance and efficient cleaning methods of the membrane with fixed nitrifiers

The authors have proposed a novel membrane process where nitrifying bacteria are fixed on the surface of the rotating membrane disks. With this proposed membrane process, the simultaneous performance of the strict solid–liquid separation and the oxidation of ammonia is enabled. In this study, three long-term experiments were carried out and the distribution of the filtration resistance and the efficient cleaning method of the proposed membrane process were investigated. The membrane flux was fixed at 0.8 m3/m2/d and the feed ammonia concentration was controlled within the range of 0.1–1.0 mg-N/l. In the proposed membrane process, the filtration resistance caused by the accumulated cake was dominant. The shear–stress induced by the increased disk’s rotational speed was found to be efficient for removing the accumulated cake. However, this cleaning method did not work well when feed water contained suspended particles at 10 of turbidity unit. In order to increase the cleaning efficiency, a small quantity of sponge particles were introduced into the membrane chamber and the disk’s rotational speed was increased. This membrane cleaning method using sponge particles proved so effective that the filtration resistance due to the accumulated cake was completely cancelled. Membrane filtration could be continued for more than 3000 h due to the implementation of this cleaning method utilizing sponge particles once every 1000–1500 h. For the maintenance of the ammonia oxidation rate, however, a part of the detached nitrifiers had to be returned to the membrane chamber after the membrane cleaning.