Effects of Surfactants on the Improvement of Sludge Dewaterability Using Cationic Flocculants
et al. (2014) Effects of Surfactants on the Improvement of Sludge Dewaterability Using Cationic Flocculants. PLoS
ONE 9(10): e111036. doi:10.1371/journal.pone.0111036
Effects of Surfactants on the Improvement of Sludge Dewaterability Using Cationic Flocculants
Yong Liao 0
Yongjun Sun 0
Huaili Zheng 0
Jun Zhai 0
Houkai Teng 0
Chun Zhao 0
Chuanliang Zhao 0
Vishal Shah, Dowling College, United States of America
0 1 Key laboratory of the Three Gorges Reservoir Region's Eco-Environment, State Ministry of Education, Chongqing University , Chongqing , China , 2 National Centre for International Research of Low-carbon and Green Buildings, Chongqing University , Chongqing , China , 3 CNOOC Tianjin Chemical Research and Design Institute , Tianjin , China
The effects of the cationic surfactant (cationic cetyl trimethyl ammonium bromide, CTAB) on the improvement of the sludge dewaterability using the cationic flocculant (cationic polyacrylamide, CPAM) were analyzed. Residual turbidity of supernatant, dry solid (DS) content, extracellular polymeric substances (EPS), specific resistance to filtration (SRF), zeta potential, floc size, and settling rate were investigated, respectively. The result showed that the CTAB positively affected the sludge conditioning and dewatering. Compared to not using surfactant, the DS and the settling rate increased by 8%-21.2% and 9.2%-15.1%, respectively, at 40 mg?L21 CPAM, 1061023 mg?L21 CTAB, and pH 3. The residual turbidities of the supernatant and SRF were reduced by 14.6%-31.1% and 6.9%-7.8% compared with turbidities and SRF without surfactant. Furthermore, the release of sludge EPS, the increases in size of the sludge flocs, and the sludge settling rate were found to be the main reasons for the CTAB improvement of sludge dewatering performance.
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Funding: This research was supported by the National Natural Science Foundation of China (Project No. 21177164), Major projects on control and rectification of
water body pollution (Project No. 2013ZX07312-001-03-03), and the 111 Project (Project No. B13041). The funders had no role in study design, data collection and
analysis, decision to publish, or preparation of the manuscript.
Competing Interests: The authors have declared that no competing interests exist.
. These authors contributed equally to this work.
About 3.1026109 tons of municipal wastewater are generated in
China in 2007, 49.1% of which need to be treated by some
biological processes. Large amount of sewage sludge have been
produced in sewage treatment facilities [1]. Raw wastewater
sludge contains huge amount of water along with organic solids,
which causes problems in transportation, treatment, and disposal
[2]. One important stage of sludge treatment prior to disposal is
the reduction of sludge volume by sludge dewatering; this process
reduces transportation and handling costs [3]. Nevertheless, sludge
dewatering remains expensive [4].
Chemicals, such as alum, polymeric ferric sulfate,
polyacrylamide, and chitosan, are typically incorporated in sludge to
improve the dewaterability [57]. Flocculants, given at the fixed
dosages, are commonly used in conditioning the physical and
chemical properties of sludge to improve sludge the dewatering
performance, while the polyacrylamide added to sludge is a widely
used pretreatment procedure in the wastewater treatment plants
(WWTP). The previous reports indicate that the surfactants and
polyacrylamide could be used as the dewatering reagents to
substantially decrease the moisture content in filter cakes [89].
Sludge conditioned by the surfactants has gained considerable
attention because of their excellent performance in improving
sludge dewatering. The surfactants alter the microorganism cell
structure by allowing the cell materials to leave the attached
surface and simultaneously dissolve this surface in aqueous
solutions to improve sludge dewaterability [10]. Huang et al.
[11] found that the presence of the surfactants in alum sludge
systems was able to improve the sludge quality by reducing SRF
and bound water content, as well as increasing settling rate,
dewatering rate, and the solid content of the sludge cakes as long
as the polyacrylamides were not used. Chu et al. [12] concluded
that cationic (CTAB) and anionic surfactants sodium dodecyl
sulfate (SDS) enhance the filtration efficiency; however, the former
and the latter respectively increase and decrease the consolidation
rate, respectively. CTAB and SDS mainly interact with the
aggregate surface and interior, respectively. Besra et al. [1314]
reported that the mechanism of the reduction of surface tension
was responsible for the enhancement of the dewatering kaolin
suspensions. The mechanism of the absorption of the complex
surfactants in the presence of flocculants exhibits an important
function in enhancing the dewatering of kaolin suspensions. In
some cases, the reduction in surface tension and the increase in
hydrophobicity or a combination of both are able to (...truncated)