How biofilm and granular sludge cope with dissolved oxygen exposure in anammox process: Performance, bioaccumulation characteristics and bacterial evolution

Abstract

In order to study the resistance mechanisms of biofilm and granular sludge to various dissolved oxygen (DO) exposures in anaerobic ammonium oxidation (anammox) process, a biofilm - granular sludge anammox reactor was established and operated. Experimental results showed that DO levels of ≤0.41 mg L^-1 hardly affected the total nitrogen removal efficiency (TNRE). Higher DO levels of 1.96-2.08 mg L^-1 promoted biomass disintegration and decreased specific anammox activity and extracellular polymeric substance (EPS) levels in granular sludge, but did not decrease EPS significantly in biofilm. The relative abundance of anammox genus Candidatus Kuenenia in granular sludge and biofilm decreased to 13.93% and 1.93%, respectively. NO₃^--N was accumulated due to the increased NOB genus Nitrospira in granular sludge and biofilm. The inhibition effects of 1.96-2.08 mg L^-1 DO on anammox system were reversible, and the TNRE was quickly restored to (82.21 ± 2.39)% with AnAOB accumulation after removing aeration. This study provided theoretical support for the development of coupled biological nitrogen removal system based on anammox with other aerobic processes.

Keywords: Anammox; Bacterial community structure; Dissolved oxygen stress; Extracellular polymeric substance.