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Chemosphere. 2017 Feb;169:586-595. doi: 10.1016/j.chemosphere.2016.10.137. Epub 2016 Nov 27.

Oxygen transfer dynamics and activated sludge floc structure under different sludge retention times at low dissolved oxygen concentrations.

Author information

1
Research Center for Low carbon technology of water environment, Renmin University of China, Beijing 100872, China.
2
Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China.
3
Research Center for Low carbon technology of water environment, Renmin University of China, Beijing 100872, China. Electronic address: qilu@ruc.edu.cn.
4
Research Center for Low carbon technology of water environment, Renmin University of China, Beijing 100872, China. Electronic address: whc@ruc.edu.cn.

Abstract

In activated sludge systems, the aeration process consumes the most energy. The energy cost can be dramatically reduced by decreasing the operating dissolved oxygen (DO) concentration. However, low DO may lead to incomplete nitrification and poor settling performance of activated sludge flocs (ASFs). This study investigates oxygen transfer dynamics and settling performances of activated sludge under different sludge retention times (SRTs) and DO conditions using microelectrodes and microscopic techniques. Our experimental results showed that with longer SRTs, treatment capacity and settling performances of activated sludge improved due to smaller floc size and less extracellular polymeric substances (EPS). Long-term low DO conditions produced larger flocs and more EPS per unit sludge, which produced a more extensive anoxic area and led to low oxygen diffusion performance in flocs. Long SRTs mitigated the adverse effects of low DO. According to the microelectrode analysis and fractal dimension determination, smaller floc size and less EPS in the long SRT system led to high oxygen diffusion property and more compact floc structure that caused a drop in the sludge volume index (SVI). In summary, our results suggested that long SRTs of activated sludge can improve the operating performance under low DO conditions.

KEYWORDS:

EPS; Floc structure; Low DO; SRT; Settling performance

[Indexed for MEDLINE]

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