Abstract
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·L−1 CPAM, 10×10−3 mg·L−1 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.
Highlights
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
Considering keeping the surfactant costs as low as possible at a highest possible dry solid (DS) content, the optimal CPAM1 dosage was 40 mg?L21, while the surfactant dosage was selected at 1061023 mg?L21 (2 wt% CPAM1), and the CTAB content was kept constant at 2 wt% CPAM1 in the subsequent tests
The flocculation performance significantly improved upon addition of CTAB during this process; incorporation of CTAB decreased the turbidity of the supernatant and increased the DS content
Summary
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. 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]. 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). 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. Interfacial tension can be reduced in the sludge system by adding CTAB, a good dewatering performance is obtained [13]
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