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A novel composite conductive microfiltration membrane and its anti-fouling performance with an external electric field in membrane bioreactors.

Huang J, Wang Z, Zhang J, Zhang X, Ma J, Wu Z - Sci Rep (2015)

Bottom Line: The fouling rate in continuous-flow MBRs treating wastewater was also decreased by about 50% for this conductive membrane with 2 V/cm electric field compared to the control test during long-term operation.The enhanced electrostatic repulsive force between foulants and membrane, in-situ cleaning by H2O2 generated from oxygen reduction, and decreased production of soluble microbial products and extracellular polymeric substances contributed to fouling mitigation in this MBR.The results of this study shed light on the control strategy of membrane fouling for achieving a sustainable operation of MBRs.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory of Pollution Control and Resource Reuse, College of Environmental Science and Engineering, Tongji University, Siping Road 1239, Shanghai 200092, P.R. China.

ABSTRACT
Membrane fouling remains an obstacle to wide-spread applications of membrane bioreactors (MBRs) for wastewater treatment and reclamation. Herein, we report a simple method to prepare a composite conductive microfiltration (MF) membrane by introducing a stainless steel mesh into a polymeric MF membrane and to effectively control its fouling by applying an external electric field. Linear sweep voltammetry and electrochemical impedance spectroscopy analyses showed that this conductive membrane had very good electrochemical properties. Batch tests demonstrated its anti-fouling ability in filtration of bovine serum albumin, sodium alginate, humic acid and silicon dioxide particles as model foulants. The fouling rate in continuous-flow MBRs treating wastewater was also decreased by about 50% for this conductive membrane with 2 V/cm electric field compared to the control test during long-term operation. The enhanced electrostatic repulsive force between foulants and membrane, in-situ cleaning by H2O2 generated from oxygen reduction, and decreased production of soluble microbial products and extracellular polymeric substances contributed to fouling mitigation in this MBR. The results of this study shed light on the control strategy of membrane fouling for achieving a sustainable operation of MBRs.

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(A) CLSM images of used membranes in the control MBR (upper part) and the electrochemical MBR (lower part), and (B) schematic illustration of anti-fouling mechanisms. Symbols for figure 7A: Red for α-polysaccharides (α-mannopyranosyl, α-glucopyranosyl stained with ConA); blue for β-polysaccharides (β-D-glucopyranose stained with Calcofour white); Green for proteins (stained with FITC).
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f7: (A) CLSM images of used membranes in the control MBR (upper part) and the electrochemical MBR (lower part), and (B) schematic illustration of anti-fouling mechanisms. Symbols for figure 7A: Red for α-polysaccharides (α-mannopyranosyl, α-glucopyranosyl stained with ConA); blue for β-polysaccharides (β-D-glucopyranose stained with Calcofour white); Green for proteins (stained with FITC).

Mentions: For further elucidating the anti-fouling mechanisms, confocal laser scanning microscope (CLSM) was used to visualize the membranes at the end of operation (Fig. 7A). It is evident that the electrochemical MBR had a thinner fouling layer compared to the control MBR. Furthermore, it is very interesting to find that the foulant compositions were much different. In the control MBR, polysaccharides (e.g., α-mannopyranosyl, α-glucopyranosyl and β-D-glucopyranose) accounted for a larger proportion of the deposited foulants compared to the electrochemical MBR. This indicates that the electrochemical MBR was much effective in mitigating polysaccharides-related fouling. Polysaccharides have been reported to induce severer fouling than proteins by a group of researchers363738, and thus the removal of polysaccharides in this study enhanced the filtration performance of the conductive membrane in the electrochemical MBR. One reason in mitigating polysaccharide fouling is the slightly lower polysaccharide concentrations in both SMP and EPS for the electrochemical MBR (2.6 ± 0.9 mg/L for SMP and 63.5 ± 21.4 mg/L for EPS) than the control MBR (2.9 ± 1.4 mg/L for SMP and 71.3 ± 20.6 mg/L for EPS). However, the polysaccharide/protein ratios (poly/pro) in SMP and EPS of the electrochemical MBR were 1.15 and 0.26, which were higher than those in SMP and EPS of the control MBR (see Table S3). Therefore, another reason may be attributed to the fact that the electrostatic repulsive force between membrane and polysaccharides was enhanced in the presence of electrical field. However, the removal of proteins might be impacted by the charge heterogeneity of proteins since they contain negatively charged carboxyl groups and positively charged amine groups3940. The other important factor should be ascribed to the reaction between H2O2 and the foulants. Polysaccharides usually have abundant hydroxyl groups41, which can be oxidized to carboxyl groups in the presence of H2O2 (H2O2 concentration in the electrochemical MBR was about 0.95 ± 0.21 mg/L as documented earlier). This in turn increases the absolute value of zeta potential of polysaccharides, thus improving the repulsive force between polysaccharides and membranes. The above-mentioned two reasons might explain why the conductive membrane in the electrochemical MBR was effective in mitigating polysaccharides-related fouling. In combination with CLSM analysis, the major mechanism for fouling mitigation can be schematically illustrated in Fig. 7B. Overall, fouling mitigation in the continuous-flow electrochemical MBR should be attributed to the enhanced repulsive force, in-situ H2O2 cleaning (in particular efficient in removing polysaccharides under investigated conditions), and decreased SMP and EPS concentrations as mentioned earlier.


A novel composite conductive microfiltration membrane and its anti-fouling performance with an external electric field in membrane bioreactors.

Huang J, Wang Z, Zhang J, Zhang X, Ma J, Wu Z - Sci Rep (2015)

(A) CLSM images of used membranes in the control MBR (upper part) and the electrochemical MBR (lower part), and (B) schematic illustration of anti-fouling mechanisms. Symbols for figure 7A: Red for α-polysaccharides (α-mannopyranosyl, α-glucopyranosyl stained with ConA); blue for β-polysaccharides (β-D-glucopyranose stained with Calcofour white); Green for proteins (stained with FITC).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4363883&req=5

f7: (A) CLSM images of used membranes in the control MBR (upper part) and the electrochemical MBR (lower part), and (B) schematic illustration of anti-fouling mechanisms. Symbols for figure 7A: Red for α-polysaccharides (α-mannopyranosyl, α-glucopyranosyl stained with ConA); blue for β-polysaccharides (β-D-glucopyranose stained with Calcofour white); Green for proteins (stained with FITC).
Mentions: For further elucidating the anti-fouling mechanisms, confocal laser scanning microscope (CLSM) was used to visualize the membranes at the end of operation (Fig. 7A). It is evident that the electrochemical MBR had a thinner fouling layer compared to the control MBR. Furthermore, it is very interesting to find that the foulant compositions were much different. In the control MBR, polysaccharides (e.g., α-mannopyranosyl, α-glucopyranosyl and β-D-glucopyranose) accounted for a larger proportion of the deposited foulants compared to the electrochemical MBR. This indicates that the electrochemical MBR was much effective in mitigating polysaccharides-related fouling. Polysaccharides have been reported to induce severer fouling than proteins by a group of researchers363738, and thus the removal of polysaccharides in this study enhanced the filtration performance of the conductive membrane in the electrochemical MBR. One reason in mitigating polysaccharide fouling is the slightly lower polysaccharide concentrations in both SMP and EPS for the electrochemical MBR (2.6 ± 0.9 mg/L for SMP and 63.5 ± 21.4 mg/L for EPS) than the control MBR (2.9 ± 1.4 mg/L for SMP and 71.3 ± 20.6 mg/L for EPS). However, the polysaccharide/protein ratios (poly/pro) in SMP and EPS of the electrochemical MBR were 1.15 and 0.26, which were higher than those in SMP and EPS of the control MBR (see Table S3). Therefore, another reason may be attributed to the fact that the electrostatic repulsive force between membrane and polysaccharides was enhanced in the presence of electrical field. However, the removal of proteins might be impacted by the charge heterogeneity of proteins since they contain negatively charged carboxyl groups and positively charged amine groups3940. The other important factor should be ascribed to the reaction between H2O2 and the foulants. Polysaccharides usually have abundant hydroxyl groups41, which can be oxidized to carboxyl groups in the presence of H2O2 (H2O2 concentration in the electrochemical MBR was about 0.95 ± 0.21 mg/L as documented earlier). This in turn increases the absolute value of zeta potential of polysaccharides, thus improving the repulsive force between polysaccharides and membranes. The above-mentioned two reasons might explain why the conductive membrane in the electrochemical MBR was effective in mitigating polysaccharides-related fouling. In combination with CLSM analysis, the major mechanism for fouling mitigation can be schematically illustrated in Fig. 7B. Overall, fouling mitigation in the continuous-flow electrochemical MBR should be attributed to the enhanced repulsive force, in-situ H2O2 cleaning (in particular efficient in removing polysaccharides under investigated conditions), and decreased SMP and EPS concentrations as mentioned earlier.

Bottom Line: The fouling rate in continuous-flow MBRs treating wastewater was also decreased by about 50% for this conductive membrane with 2 V/cm electric field compared to the control test during long-term operation.The enhanced electrostatic repulsive force between foulants and membrane, in-situ cleaning by H2O2 generated from oxygen reduction, and decreased production of soluble microbial products and extracellular polymeric substances contributed to fouling mitigation in this MBR.The results of this study shed light on the control strategy of membrane fouling for achieving a sustainable operation of MBRs.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory of Pollution Control and Resource Reuse, College of Environmental Science and Engineering, Tongji University, Siping Road 1239, Shanghai 200092, P.R. China.

ABSTRACT
Membrane fouling remains an obstacle to wide-spread applications of membrane bioreactors (MBRs) for wastewater treatment and reclamation. Herein, we report a simple method to prepare a composite conductive microfiltration (MF) membrane by introducing a stainless steel mesh into a polymeric MF membrane and to effectively control its fouling by applying an external electric field. Linear sweep voltammetry and electrochemical impedance spectroscopy analyses showed that this conductive membrane had very good electrochemical properties. Batch tests demonstrated its anti-fouling ability in filtration of bovine serum albumin, sodium alginate, humic acid and silicon dioxide particles as model foulants. The fouling rate in continuous-flow MBRs treating wastewater was also decreased by about 50% for this conductive membrane with 2 V/cm electric field compared to the control test during long-term operation. The enhanced electrostatic repulsive force between foulants and membrane, in-situ cleaning by H2O2 generated from oxygen reduction, and decreased production of soluble microbial products and extracellular polymeric substances contributed to fouling mitigation in this MBR. The results of this study shed light on the control strategy of membrane fouling for achieving a sustainable operation of MBRs.

Show MeSH