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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., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)

A combination of Fourier-transform infrared (FTIR) spectroscopy, multivariate analysis and conventional microbiological assays were utilized to characterize and differentiate membrane biofouling formed in the presence of antiscalants. Based on the FTIR spectra of biofouled reverse osmosis membranes obtained after incubating with antiscalants and H. aquamarina (as model microorganism), it was found that the biofouling intensity and composition was dependent on the type of antiscalants used. The growth of the bacterium was also highly affected by the type of antiscalants as shown by the colony forming unit (CFU) counts. By combining the techniques of principle component analysis (PCA) and FTIR, it was demonstrated that the biofouling was more intense and composed of proteins, polysaccharides and lipids, when polymer antiscalant was used. By applying PCA-FTIR with CFU counts, faster prediction of the effect of antiscalants on biofouling was made possible.

• 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]