Simultaneous Nitrification And Denitrification In A Microbubble-aerated Biofilm Reactor

Simultaneous nitrification and denitrification (SND) is a new wastewater treatmentprocess for biological nitrogen removal, which shows some significant advantagescompared with conventional biological nitrogen removal processes. The SND process in afixed bed biofilm reactor with microbubble aeration was investigated in this study. Theremoval efficiencies of COD and nitrogen were determined under different operationalconditions and the functional bacterial populations for nitrogen removal in the biofilmwere detected. The results showed that the efficient SND process could be achieved in thebiofilm reactor with microbubble aeration. The SND could be improved at lower dissolvedoxygen (DO) concentration and larger porosity of packing bed when COD loading rateand C/N ratio were increased. The removal efficiencies of COD and total nitrogen (TN)were97.6%and70.2%, respectively, at COD loading rate of0.86kg·(m3·d)-1, TN loadingrate of0.10kg·(m3·d)-1, and the packing bed porosity of81%, indicating the simultaneousefficient removal of COD and TN. Under these conditions, the oxygen utilizationefficiency was achieved as high as91.8%due to the enhanced oxygen mass transfer bymicrobubble aeration. In addition, the biofilm activity and the abundance of nitrifiers anddenitrifiers were consistent with the removal capacity of COD, ammonia and TN underdifferent operational conditions.The operation of shortcut nitrification-denitrification and the operation of SNDimprovement phase1were compared because of their similar COD loading rate, C/N ratioand total nitrogen loading rate. The results indicated the removal efficiencies of COD andTN were89.5%and58.3%, respectively, at COD loading rate of0.56kg·(m3·d)-1and TNloading rate of0.101kg·(m3·d)-1when DO concentration was controlled as about1.2mg·L-1. The nitate accumulation was also observed. Therefore, the efficient shortcutnitrification and denitrification process could be achieved in the biofilm reactor withmicrobubble aeration. Both DO concentration and oxygen mass transfer in biofilm wereimportant factors for SND. The SND process could be significantly improved whennitrification and denitrification were improved simultaneously and balanced.