A secret of high-rate mass transfer in anammox granular sludge: Lung-like breathing

The granulation of anaerobic ammonium oxidation (Anammox) biomass can play a key role in developing stable and high-rate working of anammox process. It is important to know the working mechanism of anammox granular sludge (AnGS) for the optimization of reactor performance. In this study, a lung-like breathing determinator was invented to investigate the working behavior of AnGS in the bioreactor. The results showed that the AnGS had a regular expansion and contraction phenomenon, which was called lung-like breathing. With the biological loading rate (BLR) at 0.114 kg-N/(kg-VSS.d), the expansion and contraction amplitude (ExCA) was 1.29 +/- 0.05%, and the expansion and contraction frequency (ExCF) was 39.3 +/- 1.6 times/h. The AnGS cultivated in a bioreactor with higher nitrogen removal rate (NRR) was found to have the higher ExCA and ExCF when determinated at the same BLR, and the lung-like breathing behavior of one type of AnGS was revealed to bear a significantly (p < 0.05) positive correlation with the specific anammox activity (SAA). The mass transfer flux from lung-like breathing was far greater than that from molecular diffusion, which was regarded as a vital mechanism for the AnGS to demonstrate its high activity. These findings provided theoretical basis and technical parameters for the optimization of anammox nitrogen removal process. (C) 2019 Elsevier Ltd. All rights reserved.