In the world, fresh water resources are becoming increasingly scarce, especially for the millions people who already lack access to clean water. Overuse of ground waters and their contamination are the main causes for a spread of arid environment in Middle East countries. In Oman, most of fresh water is made by desalination of seawater by desalination plants. Usually, a desalination plant uses reverse osmosis (RO) membranes that allow fresh water to pass through the membrane and reject sea salts that are released back to the sea. Fouling of membranes is the Achilles heel of desalination process.
Biofouling is referred to the unwanted growth and accumulation of organisms on submerged man-made surfaces, such as vessels, nets, pipers, and membranes of desalination plants. Biofouling organisms, ranging from size of tenth of millimeters to centimeters, cause numerous technical and economic problems. Biofouling of RO membranes seriously affect operation of desalination plants in terms of reduction of filtration process and the quality and cost of the produced water. Annually countries spend billions of US dollars to control and deal with the problems of biofouling.
In order to prevent biofouling, engineers employ different techniques, which are based on application of toxic substances. In the case of desalination plants, ultraviolet light and chlorination treatment are commonly used. These methods are harmful to humans and marine environment. Additionally, they affect performance of RO membranes. Thus, there is an urgent need for the development of a novel, effective and environmentally friendly antifouling protection.
The research team headed by Dr. Sergey Dobretsov, the Director of Centre of Excellence in Marine Biotechnology, Sultan Qaboos University (SQU) together with his colleagues from University of Western Cape (UWC), South Africa are developing photo-catalytic coatings on polymer supports for effective filtration of organic contaminants from water and antifouling applications. SQU and National Research Foundation, South Africa fund this investigation. The main objective of the project is to use the complementary skills, background knowledge of the South African and Oman teams, train students and young researchers from UWC and SQU in the field of nanotechnology and biotechnology.
Nanotechnology referred to the manipulation of materials at nanometer scale (or 10000 times less than width of a human hair). At this scale, materials gain new physical and chemical properties that can be used in different industrial applications. Nanotechnology opens a new way to prevent biofouling. Nanocoatings are less toxic than traditional antifouling coatings and provide protection via chemical and physical surface modifications at nano-scale. Dr. Dobretsov together with Dr. Mohammed Al-Abri, the Director of the Center of Nanotechnology, SQU and Prof. Leslie Petrik, UWC are investigating antifouling properties of doped transition metal oxides, such as titanium oxide (TiO) and zinc oxide (ZnO). When such nanomaterials are exposed to sunlight, an electron in the atom moves to a higher energy level. This process creates negatively charged electrons and positively charged holes, which can react with water molecules to form reactive oxygen species (ROS), such as oxygen ions and peroxides. ROS are quickly break down any attached organic matter and fouling organisms and do not accumulate in the environment.
In laboratory experiments, South African and Omani teams were able to demonstrate that upon solar irradiation, photocatalytic nanocoatings could prevent bacterial growth and bacterial fouling. About of 90% of tested bacteria were eliminated and no bacterial re-growth was observed. Additionally, such nanocoatings can degrade and remove water contaminants, such as dyes. This effect was observed under artificial light, as well as sunlight in an outdoor experiment. These nanocoatings can work for water purification and disinfection. Moreover, nanocoatings keep membranes clean from biofouling. While these photocatalytic nanocoatings are a significant step towards the production of an eco-friendly antifouling coating, potential risks to human health and environment need to be carefully studied. In the future, both teams would like optimize production of these nanocoatings and test them in relevant industrial applications.