Nitrification performance and its kinetic characteristic of biological aerated filter (BAF)

Biological aerated filter (BAF) is an attractive technology option for the decentralisated wastewater treatment and reuse. In order to get deep understanding of the nitrification characteristics, which are crucial in the design and operation of BAF to achieve effluent requirement, the performances of COD and ammonia removal in BAF were investigated and the inorganic nitrogen distributing profile along the reactor height was also analysed. Moreover, the kinetic models of ammonia removal in BAF were established and the kinetic characteristics were analyzed. The results showed that the performance of ammonia removal declined rapidly when influent COD loading increased from 3.0 kg(m(3).d)(-1) whereas nitrification rate was not affected when COD loading rate changed between 1-3 kg(m(3).d)(-1). It was also demonstrated that the levels of dissolved oxygen (DO) and/or organic matter concentration along the reactor height determined the variety of inorganic nitrogen distributing profile. The kinetic characteristics of ammonia removal in BAF illustrated that the ammonia removal rate changed with the dominant distributing of activated ammonia oxidizer. Because the ammonia and nitrite oxidizing bacteria are inferior to heterotrophic bacteria in the competition of DO in simultaneous organics and ammonia removal processes, and that the pH value and stratum (ammonia) concentration in the reactor space are changed along the water flow, the ammonia removal in a BAF with a existence of organics would be partitioned into three different kinetics regions in the reactor dimension, namely DO control, stratum and DO control, and stratum control.