CHARACTERISTICS OF NITRIFICATION AND DENITRIFICATION OF THE MEDIA-ANAEROBIC-ANOXIC-OXIC PROCESS

Widespread use of the anaerobic-anoxic-oxic process (AAO) has been exp ected because nutrients (nitrogen and phosphorus) can be removed simul taneously without any chemicals. The authors: have been studying the n utrient removal performance of the media-anaerobic-anoxic-oxic process (M-AAIO) using pilot plants, the media of which were suspending in an oxic tank (Mishima et al., 1995). The purpose of the M-AAO was to rem ove nutrients from sewage using a bioreactor half the size of the one used in the AAO process. The average water quality of the treated effl uent of the M-AAO was 8.3 mg/l of T-N and 0.6 mg/l of T-P after a rete ntion time of 8-9 hours in the bioreactor. According to the batch expe rimental results, 93% of nitrification at low water temperatures (belo w 15 degrees C) was performed by the biofilm on the media. The specifi c nitrification activity of the biofilm was high showing 5-10 mg-N/g-M LSS/hr at low water temperatures. Media nitrification largely depended on the dissolved oxygen (DO). The denitrification rate of the activat ed sludge increased almost in proportion to BOD-SS loading. It was sug gested that the phosphorus uptake in the anoxic tank was closely linke d to denitrification. Copyright (C) 1996 IAWQ.