Formation of Filamentous Microorganisms Impedes Oxygen Transfer and Decreases Aeration Efficiency for Wastewater Treatment


A low operational dissolved oxygen (DO) concentration in activated sludge improves oxygen transfer efficiency. However, it also can promote the growth of filamentous microorganisms that adversely affect sludge settling. In this study, filamentous microorganisms were found to additionally impede oxygen transfer; a previously unrecognized problem. We found that, when the operational DO of the complete-mix activated sludge reactor was reduced from 2.0 to 0.5 mg/L, the improvement in the oxygen transfer efficiency (OTE) was less than expected. Further investigation revealed that the change in OTE was highly correlated to the abundance of filamentous microorganisms and the excessive growth of filamentous microorganisms could reduce the OTE by 50%, even under the same operational DO condition. It was hypothesized that filamentous microorganisms impeded oxygen transfer mainly by increasing the mixed liquor viscosity due to their long filaments and large hydrodynamic volume. The results of this study imply that the formation of filamentous microorganisms in activated sludge process must be controlled for improving aeration efficiency and more studies are needed to better understand the effect of microbe types in activated sludge on the oxygen transfer.


Civil, Architectural and Environmental Engineering


This research was supported by grants from the Chinese National Natural Science Foundation (51608230), the Water Resource Science and Technology Innovation Program of Guangdong Province (201628), Guangzhou Science and Technology program(201704020138), the Fundamental Research Funds for the Central Universities (21616335), and the Army Research Lab (ARL) through the Leonard Wood Institute and Frontier Environmental Technology, LLC.

Keywords and Phrases

Activated sludge process; Efficiency; Microorganisms; Wastewater treatment; Water aeration; Activated sludge; Aeration efficiencies; Filamentous microorganisms; Low dissolved oxygen; Oxygen transfer; Dissolved oxygen

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Article - Journal

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© 2018 Elsevier, All rights reserved.

Publication Date

01 Jul 2018