Doctoral Dissertations

Keywords and Phrases

activated sludge; Aeration control; dissolved oxygen; Energy saving; Nitrification; Nitrifier community


"The combined effects of solids retention time (SRT) and dissolved oxygen (DO) concentration on nitrification, nitrifying bacterial communities, and aeration needs in the activated sludge process were studied. Nitrification was almost completed in the 10, 20, and 40-day SRT reactors with a minimum DO of 0.37, 0.25, and 0.16 mg/L, respectively. Under long-term low DO conditions, the endogenous decay of nitrifiers was slowed down and then nitirfier biomass concentration increased, thereby reducing the adverse effect of low DO on nitrification. Under long-term low DO conditions, the oxygen affinity of nitrite-oxidizing bacteria (NOB) increased significantly and as a result, NOB became a better competitor for oxygen than ammonia-oxidizing bacteria (AOB). Nitrosomonas europaea/eutropha-like AOB were dominant with all tested SRTs and DO levels. Nitrobacter-like NOB and Nitrospira-like NOB played the main role in the nitrite oxidation in the 5 and 40-day SRT reactors, respectively. In all reactors, Nitrospira increased considerably when the DO was reduced to ≤ 0.5 mg/L. Compared to a baseline condition (SRT = 10 days and DO = 2 mg/L), aeration need was reduced by about 20% under these two conditions (SRT = 10 days and DO = 0.37 mg/L; SRT = 40 days and DO = 0.16 mg/L). It was found that the boom of filamentous bacteria inhibited the oxygen transfer efficiency considerably in the 20-day SRT reactor.

In the activated sludge process, a combination of effluent ammonia and nitrite could effectively report insufficient or excessive DO, which was proposed as the indicator for aeration control. A simple control approach can be developed to reduce the aeration when both effluent ammonia and nitrite concentrations are [less than or equal to] 0.5 mg-N/L. When either is ≥ 2 mg-N/L, increase the aeration."--Abstract, page iv.


Wang, Jianmin

Committee Member(s)

Fitch, Mark W.
Mendoza, Cesar
Mormile, Melanie R
Burken, Joel G. (Joel Gerard)


Civil, Architectural and Environmental Engineering

Degree Name

Ph. D. in Civil Engineering


Missouri University of Science and Technology

Publication Date

Fall 2012


xiv, 173 pages

Note about bibliography

Includes bibliographical references.


© 2012 Guoqiang Liu, All rights reserved.

Document Type

Dissertation - Open Access

File Type




Subject Headings

Sewage -- Purification -- Activated sludge process

Thesis Number

T 10094

Electronic OCLC #