Effects of extracellular polymer substances on aerobic granulation in sequencing batch reactors

WANG Zhi-ping^1,2, LIU Li-li³, YAO Jie¹, SUN Li-xin¹, CAI Wei-min^1,2

1.School of Municipal and Environmental Engineering, Harbin Institute of Technology, Harbin 150090, China;2.School of Environmental Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China;3.State Environmental Protection Key Laboratory of Environmental Risk Assessment and Control on Chemical Process, School of Resources and Environmental Engineering, East China University of Science and Technology, Shanghai 200237, China



Abstract:

The effects of extracellular polymeric substances (EPS) on aerobic granulation in sequencing batch reactors (SBR) were investigated by evaluating the EPS content, and the relationship between EPS composition and surface properties of glucose-fed aerobic granules. The results show that aerobic granular sludge contains more EPS than seed sludge, and it is about 47 mg/gMLSS. Corresponding to the changes of EPS, the surface charge of microorganisms in granules increases from -0.732 to -0.845 meq/gMLSS, whereas the hydrophobicty changes significantly from 48.46% to 73.16%. It is obviously that changes of EPS in sludge alter the negative surface charge and hydrophobicity of microorganisms in granules, enhance the polymeric interaction and promote the aerobic granulation. Moreover, EPS can serve as carbon and energy reserves in granulation, thus the growth between the interior and exterior bacteria is balanced, and the integrality of granules is maintained. SEM observation of the granules exhibits that EPS in granules are ropy; by mixing with bacteria, compact matrix structure can be formed. The distribution of EPS in granules profiles the importance of EPS storage. It can be concluded that EPS play a crucial role in aerobic granulation.

Key words:  extracellular polymeric substances  aerobic granulation  hydrophobicity  surface charge

DOI£º10.11916/j.issn.1005-9113.2009.01.028

Clc Number:X703.1

Fund: