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In this paper, commercially available graphene oxide (GO) was used as nanomaterials to modify polyamide reverse osmosis (RO) membrane surface. After functionalization, the membrane surface properties were improved as the water contact angle was reduced from 41.7 ± 4.5⁰ to 26.9 ± 0.9⁰ demonstrating improvement in hydrophilic properties besides decreasing membrane surface roughness. Membrane scaling tests were done in the presence of CaSO 4 solution at 20 mM concentration as feedwater showed that the modified membranes (GO@RO) had superior anti-scaling properties. Results indicated that the permeate flux was reduced by only 15% at the end of the scaling experiment as opposed to the bared RO membrane which faced up to 22% decline in flux. The results of scanning electron microscopy, Fourier transform infrared, and X-ray diffraction confirmed that the bared RO membrane was extensively scaled by the CaSO 4 precipitates. The results of antibacterial tests showed that GO functionalization caused an inhibition of bacterial growth by 81.7% as compared to the unmodified RO membrane. Moreover, experiments were also performed to investigate microbially induced calcium sulfate precipitation on membranes. Overall, it was found that GO functionalization not only reduces biofouling but can also inhibit mineral scaling and microbially induced mineral formation. Image 1 [ABSTRACT FROM AUTHOR]

Abstract Seawater reverse osmosis (SWRO) is a commonly used desalination technique owing to its lesser environmental and economic impacts as compared to thermal desalination techniques. Antiscalants are used in SWRO to reduce membrane scaling caused by the supersaturation of salts present in feed water. However, to remain effective in reducing membrane scaling, antiscalants should be highly stable and resistant to biological degradation by seawater microorganisms. In this research, several bacteria from Qatar's seawater were isolated and screened for their ability to use antiscalants as a carbon and energy source. The biodiversity of antiscalant degrading seawater bacteria was demonstrated through combining the techniques of MALDI-TOF MS and principle component analysis. It was found that the bacteria isolated from Qatar's seawater such as H. aquamarina, H. elongata, P. fragi, P. stutzeri and others can degrade antiscalants and use them as a carbon and energy source. It was observed that the growth rates varied based on the type of antiscalant and the bacteria used. Among the tested strains, H. aquamarina, which is also known for its potential to cause biofouling, demonstrated the highest growth rates in antiscalants media. Thus, it was concluded that there is wide variety of bacteria in Qatar's seawater that can biodegrade the antiscalants; reducing their efficiency to combat membrane scaling. Since, these antiscalants will be used as a source of carbon and energy, microbial growth will increase resulting in enhanced membrane biofouling in SWRO. Graphical abstract Unlabelled Image Highlights • Antiscalants are commonly used to reduce scaling in seawater reverse osmosis. • The antiscalants are prone to enhance membrane biofouling. • There is a biodiversity of seawater bacteria that can biodegrade antiscalants. • Bacterial biodiversity can be explored through combining MALDI-TOF MS with PCA. • The specific growth rates vary with the type of bacteria and antiscalants. [ABSTRACT FROM AUTHOR]

The polyamide reverse osmosis (RO) membrane was modified with graphene oxide (GO), followed by polymerization of acrylic acid (used as an antiscalant) for the reduction of both biofouling and mineral scaling. After functionalization, the water contact angle reduced from 41.7 ± 4.5° for unmodified RO membrane to 24.4 ± 1.3° for the modified RO membranes, which showed that membrane hydrophilicity was significantly enhanced, in addition to the improvement in surface smoothness. The modified membranes were tested for their anti-scaling and anti-biofouling characteristics. When the mineral scaling test was performed using CaSO 4 solution as feedwater, the permeate flux was reduced by only 3% as compared to the unmodified RO membrane which encountered up to 22% decline in flux by the end of the experiment. After the scaling test, the membrane surface was characterized by Scanning electron microscopy – energy-dispersive X-ray spectroscopy, Fourier transform infrared, and X-ray diffraction techniques. The results showed that the unmodified RO membrane was fully covered with gypsum precipitates. Whereas, the precipitates were detected only at the highly saturated zones of the water channel i.e. towards the exit of water flow. Additionally, the anti-bacterial test was performed through bacteriostasis rate determination, which showed that the modified membranes inhibited the growth of nearly 95% of the bacterial cells. Further experiments were also performed to investigate the inhibition of both scaling and biofouling by modified RO membranes. Thus, it was found that the polymer-modified GO coated RO membranes were able to diminish both gypsum scaling and biofilm formation demonstrating their potential to control different types of membrane fouling. Unlabelled Image • The reverse osmosis membrane was modified with graphene oxide and polyacrylic acid. • The surface smoothness and hydrophilicity of the modified membranes were improved. • The permeate flux was reduced by only 3% as compared to unmodified RO membrane. • The modified membranes inhibited the growth of nearly 97% of the bacterial cells. • The modified membranes were able to diminish both gypsum scaling and biofouling. [ABSTRACT FROM AUTHOR]

• Microorganism-mineral interactions can affect the membrane fouling in SWRO. • Bacteria present in seawater can induce gypsum precipitation on RO membranes. • Crystals' morphology varies from needle like to floral structures under SEM-EDX. • The presence of divalent ions in a medium enhances microbial growth rates. Membrane fouling affects the performance of membrane technologies such as reverse osmosis (RO), in water treatments and desalination industries. The membrane fouling is a multifaceted phenomenon and various components of feedwater like organic and inorganic substances, and microorganisms interact with each other to further complicate and intensify the membrane fouling. In this research, the interaction between microorganisms and calcium sulfate (mineral chosen as a model scaling) was investigated. Using scanning electron microscopy – energy dispersive x-ray (SEM-EDX) technique, it was found that the variety of microorganisms present in seawater were able to form calcium sulfate crystals on the RO membrane, although no precipitation occurred under abiotic conditions (i.e. in control samples). The results of SEM-EDX were further confirmed by quantitative analysis of precipitation through ion chromatography (IC) technique, and it was found that the concentration of calcium ions remaining in the bacteria-containing medium was significantly lower than that of controls at 95 % confidence level. Furthermore, the kinetics of biomineralization and the effect of different concentrations of calcium and sulfate ions was investigated. It was found that the bacteria were able to form needle-like crystals even at the lowest concentration (Ca2+=20 mM) and at the lowest incubation times (i.e. 1 day) studied. On the other hand, the effect of calcium ions on bacterial growth was also investigated and it was noted that the presence of ions resulted in a statistically significant increase in growth rates of bacteria, showing their potential to enhance biofouling rates. [ABSTRACT FROM AUTHOR]

• Membrane fouling is major hurdle for the widespread use of membrane technology. • Increase in temperature can affect CaSO 4 scaling intensity, and morphology. • At higher temperature, crystal morphology changes from rod shape to rosette structures. • Using PCA, membrane's permeate flux can be differentiated at different conditions. • FTIR results showed the involvement of OH, COOH and NH 2 groups in membrane scaling. Membrane fouling is one of the major hurdles in widespread use of seawater reverse osmosis (SWRO) in desalination industry. There are various factors that affect the inorganic fouling or scaling of Reverse osmosis (RO) membranes. In this research, the effect of temperature on scaling of RO and Graphene oxide (GO) coated RO membrane by calcium sulfate was investigated. It was found that the increase in temperature enhanced the membrane scaling which was evident by the severe flux decline over time leading to increase in mass of crystals precipitated (M t) and thickness of the scale layer. There was strong positive correlation (R2 ≥ 0.97) noted between M t and the temperature. The results of SEM-EDX and XRD confirmed that the crystals formed under the experimental conditions are gypsum. Results of this research showed that there was no significant difference in terms of crystal morphology, scaling intensity and mechanism after modifying RO membrane with GO. It was noted that the morphology of the crystals varied from rod shaped to rosette structures under the influence of temperature. Furthermore, the results of FTIR helped to understand the mechanism of interaction between the membranes and the gypsum. The hydrophilicity of the scaled membrane was also measured to investigate the changes in the properties of the membrane after scaling. [ABSTRACT FROM AUTHOR]