TERTIARY NITRIFICATION IN PILOT-PLANT PLUG-FLOW FIXED-FILM REACTORS WITH LONG-TERM AMMONIUM DEFICIENCY

The objective of this study is to investigate to what extent the nitri fication capacity of a pilot-plant fixed-film reactor changes during e xtensive periods of nutrient supply deficiency. The examined pilot-pla nt was an upflow reactor filled with swelling clay of medium grain siz e (6 to 8 mm). The experiments revealed that the maximum nitrification rate remained practically constant during the first weeks after the o nset of unregulated ammonium supply. The capacity declined slowly, dro pping to approximately 66% of the initial capacity after about ten wee ks. Still ammonium peaks of up to 8 mg/l were readily nitrified throug hout the entire period of the experiment. The reduction in nitrificati on capacity during the observation period did not result from decay pr ocesses of biomass but from the reactor becoming blocked and thus hamp ering transfer processes. It could be observed that the detached organ isms attached again further up. This semi-industrial project demonstra ted that a plug-flow fixed-film reactor can be used as effective means of tertiary nitrification.