Denitrification in a closed rotating biological contactor: effect of disk submergence

Several studies have employed rotating biological contactors (RBCs) for nit rogen removal. However, partially submersed disks are used for nitrificatio n, while completely submersed disks are used for denitrification. The objec tive of this study was to investigate the effect of disk submergence in the performance of rotating biological contactors, in terms of the denitrifica tion process. Two RBCs, one with completely submersed disks (100% submergen ce) and the other with partially submersed disks (64.5%), were operated und er the same conditions. Their performance was evaluated in terms of denitri fication efficiency as well as biofilm characteristics, composition and act ivity. As far as the denitrification process is concerned, the RBC with a c ompletely submersed biofilm was more efficient than the other but had a lon ger delay in start-up. The biofilm of both reactors was very thick ( > 0.6 mm), but with different structures. Biofilm activity seems to be directly d ependent on the biofilm structure, namely on the degree of hydration. (C) 2 001 Elsevier Science Ltd. All rights reserved.