When chitosan was modi fi ed by CFAL, the molecular weight ( M v ) of CFAL-Chitosan decreased (Fig. The long chain structure of chitosan is largely responsible for the bridging-netting property which is positively related to the molecular weight (Li et al., 2013). In addition, the pH and metal residuals in algal solution before and after fl occulation were unaffected by the test conditions in this study (Table S3). At the optimized dosage of F-12, the concentration of cells remaining in the fl occulated algal solution was (7.5 ± 6.2) Â 10 4 cells mL À 1, which was lower compared to the starting concentration (4.15 e 4.23 Â 10 6 cells mL À 1 ), but higher than the WHO recom- mendations (2.0 Â 10 4 cells mL À 1 ) for safe recreational waters (2003). In this study, a moderate amount of CFAL (CFAL/Chitosan ratio 12:1) optimized the charge neutralization of chitosan and a wide dosage range for effective M.A. fl occulation was generally obtained at the dosage where the zeta potential of algal fl ocs was near zero. This indicated that excessively increasing CFAL/Chitosan ratio may result in faster reversal of algal charge and narrow the dosage range of effective algal removal. However, when the CFAL/Chitosan ratio increased to 40:1, a sharp decline of algal removal occurred again at 3.5 mg L À 1 due to reversed charge ( þ 2.6 mv). For F-12, when the dosage was higher than 3 mg L À 1, the electrostatic repulsion between M.A. The free Al/Fe in CFAL-Chitosan may also contribute to enhancing the charge neutralization of chitosan and it requires further studies to explore the functions of chitosan-Al and -Fe. It indicated that the OH and NH 2 of chitosan might chelate with Al and Fe in CFAL. A distinct band emerged at 1500 cm À 1 which could potentially be the characteristic of Al e NH 2 or Fe e NH 2 (Himmel et al., 2000 Wang et al., 2011). Compared with the FT-IR spectrum of chitosan without CFAL (CFAL/Chitosan ratio 1⁄4 0:1), the amide II and aliphatic OH groups disappeared when chitosan was modi fi ed by CFAL (F-12, F-20, F-40 in Fig. The component analysis con fi rmed the formation of chitosan-Al and -Fe in the prepared fl occulants (Fig. This indicated that CFAL-Chitosan can maintain a better algal removal rate over a wide dosage range due to improved charge neutralization. fast reversal of zeta potential at dosage beyond 3 mg L (5 e 6 mg L À 1, Fig. removal was not stable and declined signi fi cantly at 5 mg L À 1 due to reversal of the zeta potential ( þ 3.4 mv) and re-stabilization of algal fl ocs (F-0 in Fig. However, 18.6% of algal cells were not removed since the surface charge of algal fl ocs were not suf fi ciently neutralized with zeta potential far below zero ( À 15.4 mv) at the optimized dosage of chitosan without CFAL (3 mg L À 1 ) (Li et al., 2015). The fl ocs of large size were formed (560 m m) through electrostatic attraction and bridging-netting function by the long polymer chain of chitosan (F-0 in Fig. 2) and has a long polymer chain structure (Li et al., 2013). Chitosan is a linear biopolymer with high molecular weight (682 kDa, Fig. When chitosan without CFAL (CFAL/Chitosan ratio 1⁄4 0:1) was added at 3 mg L À 1, the removal rate reached a peak of 81.4 ± 1.9% and the zeta potential increased from À 34.8 to À 15.4 mv, indicating the electrostatic repulsion was reduced, which may be due to attraction between the amine groups of chitosan and algal cells (F-0 in Fig. fl ocs was À 34.8 mv when pre-treated CFA alone (100 mg L À 1 ) was added and the algal cells were not removed from suspension due to the electrostatic repulsion (Figs. However, when excessive CFAL was added (F40), the fl oc stability decreased compared to CFAL-Chitosan (F-12, Fig. When the CFAL/Chitosan ratio was 12, the g of fl ocs was 0.39, lower than chitosan without CFAL (0.49) indicating that the fl oc stability was improved (Fig. The stable fl oc exponent ( g ) is a quantitative mea- surement of fl oc stability. The stability of algal fl ocs at 3 mg L CFAL-Chitosan was tested by measuring the fl oc size changes after applying a shear force (Shi et al., 2015). When the CFAL/Chitosan was 40:1, the fl oc size (380 m m) decreased compared to F-0, F-12 and F-20 and a lower removal rate of 72.8% was achieved at 60 min (Figs. The removal ef fi ciency of F-12 reached 97.2% within 2 min and remained stable, while 87.5% of algal cells were removed for F-20 after sedimentation for 60 min (Fig. 5), but F-12 exhibited a faster growth rate. When the CFAL/Chitosan was 12:1 and 20:1, the fl oc size increased to 750 m m (F-12 & F-20 in Fig. proceeded for the F-0 treatment (F-0 in Fig.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |