Holdup of sub-granules towards enhanced production of anammox sludge in a dual circulation sludge bed reactor

Abstract

The performance of anammox process largely depends on the anammox sludge as the functional core. Enhancing the production and retention of anammox sludge in the reaction system was a hot while pressing issue to be addressed for the application of the anammox process. In this study, a novel reactor named Ducan (Dual Circulation Anammox) was developed to achieve promoted production of anammox sludge, and the mechanism was revealed meanwhile. It was found that the Ducan reactor could improve the sludge production rate by 96.2 % compared with the control group. The enhanced formation of new-born anammox granular sludge (AnGS) by holding up the wash-out anammox sludge was believed to be the main factor contributing to this result. Furthermore, the typical structure of the new-born AnGS was characterized and the sub-granule (SG) on a 100 μm scale was revealed as its direct structural unit. Vulnerable disassembly of aged AnGS was the main source of SG due to the weak binding force of AnGS caused by the formation of large cavities inside. By setting a unique structure of dual-systolic tubes in the Ducan reactor, the SG was endowed with reduced surface roughness and increased EPS protein with hydrophobic amino acids and a looser structure. These properties made it easier for SG to contact each other and assembled into new-born AnGS with big size, which could then settle back to the reactor and result in enhanced production of anammox sludge. The results in this study were expected to offer a viable reactor towards enhanced production of AnGS, and shed light on addressing the issue of sludge shortage during the extensive application of anammox technology.