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International Journal of Environment Science and Technology
Center for Environment and Energy Research and Studies (CEERS)
ISSN: 1735-1472 EISSN: 1735-1472
Vol. 13, No. 2, 2016, pp. 581-588
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Bioline Code: st16053
Full paper language: English
Document type: Research Article
Document available free of charge
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International Journal of Environment Science and Technology, Vol. 13, No. 2, 2016, pp. 581-588
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Characteristics of free cells and aggregated flocs for the flocculation and sedimentation of activated sludge
Li, A.J.; Li, X.Y. & Gu, J.D.
Abstract
Laboratory experiments were conducted to
investigate the correlation of the free cells/aggregated flocs
characteristics and the sludge flocculation and separation
behavior during the activated sludge process. Activated
sludge was cultured in three laboratory-scale batch reactors
with same carbon sources of glucose but different sludge
retention times (SRTs) of 5, 10 and 20 days. The variation
in the operation condition produced sludge with different
flocculation and separation characteristics. The reactor
performance in terms of bioflocculation as measured by the
amount of suspended solids in the effluent, sludge sedimentation
and compression as measured by the sludge
value index improved considerably as the SRT lengthened.
The higher SRT was related to less negatively charged
surface of free cells and more hydrophobic of aggregated
flocs. The negative zeta potential of aggregated flocs
(11–13 mV) was smaller than that of free cells
(15–23 mV), and free cells carrying lesser negative surface
charges resulted in effluent clarification. Hydrophobicity of
aggregated flocs (10–17 %) in each reactor was higher than
that of free cells (5–8 %). The increase in hydrophobicity
of aggregated flocs had positive effect on settleability. Floc
strength measured by breakage/erosion index was closely
related to hydrophobicity of aggregated flocs, but no correlation
could be established with zeta potential of aggregated
flocs. In addition, different bacterial species existed
in free cells and aggregated flocs. Microbial similarity
between free cells and aggregated flocs increased with
shorter SRT and was closely related to effluent
clarification.
Keywords
Free cells; Aggregated flocs; Hydrophobicity; Zeta potential; Microbial community
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