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University of Sheffield (2007)

Biofouling studies on reverse osmosis desalination of hypersaline waters

Ashhuby, Bashir Ali

Titre : Biofouling studies on reverse osmosis desalination of hypersaline waters

Auteur : Ashhuby, Bashir Ali

Université de soutenance : University of Sheffield

Grade : Doctor of Philosophy (PhD) 2007

Biological fouling of reverse osmosis (RO) membranes is affected by many factors, and it is not clearly understood, especially with respect to hypersaline waters. Biofouling minimisation requires understanding of the fundamentals of the biofilm development. It is also necessary to monitor biofilm development at various stages and its relation to concentration polarisation phenomena. The two main goals were to explore the biological diversity of a hypersaline lake called "Qabar-Onn"t located in the Sahara ; and to better understand what biotic and abiotic factors govem biofouling of RO membranes treating hypersaline waters. Three halotolerant bacteria] strains (Euhalothece species, BAAOOl and BAA002, and Halomonas pantelleriensis species, BAA003) were isolated from the lake using conventional culturing methods, and were identified based on 16S rRNA sequencing. Two isolated species, Eukalothece species BAAOOI and Halomonas pantelleriensis species BAA003 were used as model microorganisms to evaluate the potential of biofilm development on RO membranes. Salinity and surface roughness, which affect biofilm initiation and growth, were investigated. A novel, in-situ monitoring device was used to detect initiation of biofilm formation, and its relation to solutes and concentrations near RO membrane surfaces. The results showed that Qabar-Onn Lake is inhabited by a wide range of microorganisms, which seem to have a strong potential to adapt to the rapid increase in the lake salinity. In addition to salinity, pH also is limiting factor on biodiversity and microorganisms’ dominance. Biofouling was strongly controlled by membrane characteristics and feed salinity. Lower surface roughness and low salinity contributed to less biofilm formation. Furthermore, the absence of monovalent anions (i. e. chloride) in the feed enhanced flux at low salinities ; however, its absence severely decreased flux at higher salinities. Similarly, microorganisms present in the feed extremely enhanced the permeate flux at low salinities, however, at high salinities the flux decreased in the presence of microorganisms

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