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Improvement of membrane surface antimicrobial properties to enhance resistance to fouling in the treatment of municipal wastewater
Author(s)
Nkombe, Aude Mailys Minang
Date Issued
2024
Type
Thesis
Publisher
Cape Peninsula University of Technology
Abstract
The increase in water scarcity has become a worldwide issue due to population growth and growing
pollution. Therefore, implementing wastewater management strategies and wastewater treatment
techniques has been on the rise to create environmental sustainability and reduce freshwater
consumption.
Municipal wastewater effluent is used for tertiary treatment to produce water quality suitable for various
reuse applications. Effective tertiary treatments such as reverse osmosis (RO) membranes are
additional to secondary treatments for further reduction of bacteria, organics, and inorganics in
municipal wastewater. However, fouling significantly hinders reverse osmosis membrane applications
as it lowers membrane performance by causing the permeate flux decline, reducing the permeate
quality and shortening the membrane life span. Microbial fouling is a significant contributor, accounting
for more than 45% of membrane fouling.
In this study, the surface modification of a thin film RO membrane was investigated by graft
polymerization of 3-allyl-5, 5-dimethylhydantoin (ADMH) to improve the membrane’s antimicrobial
properties.
The modifying agent ADMH was synthesized at four different concentrations and grafted onto a lowpressure
RO membrane, producing modified RO membranes with varying concentrations of ADMH.
The synthesis of ADMH was confirmed by Fourier Transform Infrared Spectroscopy (FTIR), Scanning
Electron Microscopy (SEM) and NMR (Nuclear Magnetic Resonance) were used to characterize the
surface of modified membranes. The anti-microbial tests used two types of bacteria, E. coli (Gramnegative)
and S. aureus (Gram-positive) contaminants. The membranes were further tested with humic
acid and sodium bicarbonate, depicting municipal wastewater organic and inorganic foulant models,
respectively.
The FTIR and NMR peaks characteristics confirmed the presence of ADMH bonds, such as the C=O
bond at 3107 𝑐𝑚−1 and (=CHCH2) bond at 42.17 ppm, respectively, on the surface of the membrane.
The appearance of a new layer on the membrane surface shown in the cross-sectional view of the
membrane.
The antimicrobial tests with E. coli and S. aureus bacteria revealed 45.23%, 58.93%, 48.48% and
33.76% enhanced mortality ratio compared to the unmodified membrane for the M0.2mol/L, M0.4mol/L,
M0.6mol/L and M0.8mol/L respectively. In contrast, the antimicrobial tests with S. aureus bacteria revealed
an improved mortality ratio of 6.71%, 37.42%, 22.89%, and 2.44% for the aforementioned membranes,
respectively. Additionally, it was found that membranes M0.4mol/L and M0.6mol/L exhibited a flux decline ratio (FDR) of
12.68% and 8.91% against E. coli, respectively, while the unmodified membrane FDR was and FRR
values of 94.27% and 96.88%, respectively. Also, the same membranes had FDR values of 30.21%
and 23.79% and FRR values of 59.70% and 70.15% against S. aureus.
Overall, this study demonstrated the significant impact of ADMH concentration against biofouling on
reverse osmosis membranes. The ADMH exhibited qualities that contributed to improving the
antimicrobial properties of reverse osmosis membranes while enhancing the membrane permeability
and salt rejection, and slightly maintaining its resistance to organic and inorganic fouling. This study is
an excellent step towards future studies in developing fouling mitigation methods to treat municipal
wastewater.
pollution. Therefore, implementing wastewater management strategies and wastewater treatment
techniques has been on the rise to create environmental sustainability and reduce freshwater
consumption.
Municipal wastewater effluent is used for tertiary treatment to produce water quality suitable for various
reuse applications. Effective tertiary treatments such as reverse osmosis (RO) membranes are
additional to secondary treatments for further reduction of bacteria, organics, and inorganics in
municipal wastewater. However, fouling significantly hinders reverse osmosis membrane applications
as it lowers membrane performance by causing the permeate flux decline, reducing the permeate
quality and shortening the membrane life span. Microbial fouling is a significant contributor, accounting
for more than 45% of membrane fouling.
In this study, the surface modification of a thin film RO membrane was investigated by graft
polymerization of 3-allyl-5, 5-dimethylhydantoin (ADMH) to improve the membrane’s antimicrobial
properties.
The modifying agent ADMH was synthesized at four different concentrations and grafted onto a lowpressure
RO membrane, producing modified RO membranes with varying concentrations of ADMH.
The synthesis of ADMH was confirmed by Fourier Transform Infrared Spectroscopy (FTIR), Scanning
Electron Microscopy (SEM) and NMR (Nuclear Magnetic Resonance) were used to characterize the
surface of modified membranes. The anti-microbial tests used two types of bacteria, E. coli (Gramnegative)
and S. aureus (Gram-positive) contaminants. The membranes were further tested with humic
acid and sodium bicarbonate, depicting municipal wastewater organic and inorganic foulant models,
respectively.
The FTIR and NMR peaks characteristics confirmed the presence of ADMH bonds, such as the C=O
bond at 3107 𝑐𝑚−1 and (=CHCH2) bond at 42.17 ppm, respectively, on the surface of the membrane.
The appearance of a new layer on the membrane surface shown in the cross-sectional view of the
membrane.
The antimicrobial tests with E. coli and S. aureus bacteria revealed 45.23%, 58.93%, 48.48% and
33.76% enhanced mortality ratio compared to the unmodified membrane for the M0.2mol/L, M0.4mol/L,
M0.6mol/L and M0.8mol/L respectively. In contrast, the antimicrobial tests with S. aureus bacteria revealed
an improved mortality ratio of 6.71%, 37.42%, 22.89%, and 2.44% for the aforementioned membranes,
respectively. Additionally, it was found that membranes M0.4mol/L and M0.6mol/L exhibited a flux decline ratio (FDR) of
12.68% and 8.91% against E. coli, respectively, while the unmodified membrane FDR was and FRR
values of 94.27% and 96.88%, respectively. Also, the same membranes had FDR values of 30.21%
and 23.79% and FRR values of 59.70% and 70.15% against S. aureus.
Overall, this study demonstrated the significant impact of ADMH concentration against biofouling on
reverse osmosis membranes. The ADMH exhibited qualities that contributed to improving the
antimicrobial properties of reverse osmosis membranes while enhancing the membrane permeability
and salt rejection, and slightly maintaining its resistance to organic and inorganic fouling. This study is
an excellent step towards future studies in developing fouling mitigation methods to treat municipal
wastewater.
Additional information
Thesis (MEng (Chemical Engineering))--Cape Peninsula University of Technology, 2024
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