Study On The Shortcut Nitrification Process And The Kinetics Of Shortcut Denitrification In Biological Aerated Filters

Conventional nitrogen removal process had some weakness, such as long reaction step, high energy consumption. To solve these problems, this paper studied shortcut nitrification-denitrification process, which shorted the reaction course, with lower energy consumption and high efficiency. A novel generation of biofilm reactor, biological aerated filters (BAF), was used in the experiments. The shortcut nitrification process and the kinetics of shortcut denitrification was discussed under high ammonia, by controlling dissolved oxygen and pH in BAF. The experiments results showed: (1) The nitrite accumulation was attained in the middle of the filter, and the maximal nitrite accumulation rate is 78%(0.8m, the third sampling port). The decreasing rate of nitrite concentration was smaller than those reported in references, because of controlling dissolved oxygen in the reactor under the most suitable conditions to ammonia oxidizer bacteria. It showed that dissolved oxygen is the most principal factor to effect on nitrite accumulation. (2) The transformation in the BAF of nitrogen happened in the below of the filter. The nitrogen removal via denitrification happened in the top of the filter, which resulted in the decrease of nitrite and nitrate. The removal rate of COD (chemical oxygen demanded) in BAF was only 70%, which showed the denitrification was not specially obvious in BAF. (3) The kinetics of shortcut denitrification was studied, supposing the shortcut denitrification obeying the Monod equation. The kinetics parameters of shortcut denitrification was attained, using the experiments data: the maximal denitrification rate of nitrite is 0.0167h-1, the half saturation parameter of nitrite is 1.40mg/L, the half saturation parameter of organism is 6.21 mg/L. (4) The period of backwashing cycle was determined for 40h, after considering the influence of backwash to BAF performance. Tap water was used in the test, the backwashing duration was 10min. The reactor didn't block under these conditions.