Potentials of using a rotating biological contactor (RBC) for post-treatment of anaerobically pre-treated domestic wastewater

The nitrogen removal from the nitrified effluent was investigated using a biofilm system consisting of three stages, viz. an anoxic up-flow submerged bio-filter followed by a segmental two stage aerobic RBC. The nitrified effluent of the second stage RBC was recycled to the anoxic up-flow submerged bio-filter reactor. The results obtained reveal that the introduction of an anoxic reactor as a first stage combined with recirculation of the nitrified effluent of the second stage RBC is accompanied with a conversion of nitrate into ammonia, at least in case the content of CODbiod. in the UASB effluent is low. In such a situation the ammonia needs to be nitrified two times, which obviously should be avoided. Therefore in such situations of a too high quality anaerobic effluent in terms of biodegradable COD content, the introduction of a separate anoxic reactor for denitrification as final post-treatment step can not be recommended.