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

Abstract

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.