Effect of sludge retention time (SRT) on micro-ecological niche competition kinetics between ammonia-oxidizing organisms (AOO) and nitrite-oxidizing organisms (NOO) in a single system

Abstract

As a method for controlling the nitrification process, sludge retention time (SRT) control is based on the micro-ecological niche competition between ammonia-oxidizing organisms (AOO) and nitrite-oxidizing organisms (NOO). In this study, AOO and NOO were domesticated and cultured under different SRT conditions (40 d, 20 d, 10 d, and 5 d) in four continuous stirred-tank reactors (CSTRs) to investigate the relationship between their ecological niche shift and the typical environmental conditions. As the SRT decreased, the proportion of AOO colonies gradually increased and achieved spatial ecological niche competition superiority, which may be related to their maximum growth rate and ecological niche width. Moreover, the ecological niche width of the typical environmental impact parameters of AOO and NOO changed significantly with the SRT, which may be related to the changes in their internal flora. In addition, a micro-ecological niche competition model and kinetic systems were established and simulated on the basis of existing microbial biochemical models. The established model could be used to simulate and predict the ecological niche shift process of AOO and NOO under different SRT conditions in the CSTRs. In summary, this study explains the mechanism and basic kinetic parameters of SRT control in two-step nitrification based on micro-ecological niche competition theory. And a niche competition model has been established, providing a new method for controlling the process.